Plant community responses to experimental warming across the tundra biome

Hexabromocyclododecanes in soils, plants, and sediments from Svalbard, Arctic: Levels, isomer profiles, chiral signatures, and potential sources

This study investigated the occurrence, stereoisomeric behavior, and potential sources of hexabromocyclododecanes (HBCDs) in topsoil and terrestrial vegetation from Svalbard and ocean sediment samples from Kongsfjorden, an open fjord on the west coast of Spitsbergen. The mean levels of total concentrations (Σ3HBCDs) were comparable to those in other remote regions and were lower than those in source regions. Elevated proportions of α-HBCD with an average of 41% in the terrestrial samples and 25% in ocean sediments compared to those in commercial products (10-13% for α-HBCD) were observed, implying isomerization from γ- to α-HBCD in the Arctic environment. In addition, the extensive deviations of enantiomeric fractions (EFs) from the racemic values reflected the effect of biotransformation on HBCD accumulation. Linear correlation analysis, redundancy analysis, and back-trajectory were combined to infer possible HBCD sources, and the results showed the important role of global production and long-range environmental transport (LRET) for the entry of HBCDs into the Arctic at an early stage. To the best of our knowledge, this study represents the first report on the diastereoisomer- and enantiomer-specific profiles of HBCDs in the Arctic terrestrial environment and sheds light on the transport pathways and environmental fate for more effective risk management related to HBCDs in remote regions.

Plant height as an indicator for alpine carbon sequestration and ecosystem response to warming

Growing evidence indicates that plant community structure and traits have changed under climate warming, especially in cold or high-elevation regions. However, the impact of these warming-induced changes on ecosystem carbon sequestration remains unclear. Using a warming experiment on the high-elevation Qinghai-Tibetan Plateau, we found that warming not only increased plant species height but also altered species composition, collectively resulting in a taller plant community associated with increased net ecosystem productivity (NEP). Along a 1,500 km transect on the Plateau, taller plant community promoted NEP and soil carbon through associated chlorophyll content and other photosynthetic traits at the community level. Overall, plant community height as a dominant trait is associated with species composition and regulates ecosystem C sequestration in the high-elevation biome. This trait-based association provides new insights into predicting the direction, magnitude and sensitivity of ecosystem C fluxes in response to climate warming.

Interactive effects of grassland utilization and climatic factors govern the plant diversity-soil C relationship in steppe of North China

The relationship between plant diversity and the ecosystem carbon pool is important for understanding the role of biodiversity in regulating ecosystem functions. However, it is not clear how the relationship between plant diversity and soil carbon content changes under different grassland use patterns. In a 3-year study from 2013 to 2015, we investigated plant diversity and soil total carbon (TC) content of grasslands in northern China under different grassland utilization methods (grazing, mowing, and enclosure) and climatic conditions. Shannon-Wiener and Species richness index of grassland were significantly decreased by grazing and mowing. Plant diversity was positively correlated with annual precipitation (AP) and negatively correlated with annual mean temperature (AMT). AP was the primary regulator of plant diversity. Grazing and mowing decreased TC levels in grasslands compared with enclosures, especially in topsoil (0-20 cm). The average TC content was decreased by 58 % and 36 % in the 0-10 cm soil layer, while it was decreased by 68 % and 39 % in 10-20 cm soil layer. TC was positively correlated with AP and negatively correlated with AMT. Principal component analysis (PCA) showed that plant diversity was positively correlated with soil TC, and the correlation decreased with an increase in the soil depth. Overall, this study provides a theoretical basis for predicting soil carbon storage in grasslands under human disturbances and climate change impacts.

Acclimation of subarctic vegetation to warming and increased cloudiness

Subarctic ecosystems are exposed to elevated temperatures and increased cloudiness in a changing climate with potentially important effects on vegetation structure, composition, and ecosystem functioning. We investigated the individual and combined effects of warming and increased cloudiness on vegetation greenness and cover in mesocosms from two tundra and one palsa mire ecosystems kept under strict environmental control in climate chambers. We also investigated leaf anatomical and biochemical traits of four dominant vascular plant species (Empetrum hermaphroditum, Vaccinium myrtillus, Vaccinium vitis-idaea, and Rubus chamaemorus). Vegetation greenness increased in response to warming in all sites and in response to increased cloudiness in the tundra sites but without associated increases in vegetation cover or biomass, except that E. hermaphroditum biomass increased under warming. The combined warming and increased cloudiness treatment had an additive effect on vegetation greenness in all sites. It also increased the cover of graminoids and forbs in one of the tundra sites. Warming increased leaf dry mass per area of V. myrtillus and R. chamaemorus, and glandular trichome density of V. myrtillus and decreased spongy intercellular space of E. hermaphroditum and V. vitis-idaea. Increased cloudiness decreased leaf dry mass per area of V. myrtillus, palisade thickness of E. hermaphroditum, and stomata density of E. hermaphroditum and V. vitis-idaea, and increased leaf area and epidermis thickness of V. myrtillus, leaf shape index and nitrogen of E. hermaphroditum, and palisade intercellular space of V. vitis-idaea. The combined treatment caused thinner leaves and decreased leaf carbon for V. myrtillus, and increased leaf chlorophyll of E. hermaphroditum. We show that under future warmer increased cloudiness conditions in the Subarctic (as simulated in our experiment), vegetation composition and distribution will change, mostly dominated by graminoids and forbs. These changes will depend on the responses of leaf anatomical and biochemical traits and will likely impact carbon gain and primary productivity and abiotic and biotic stress tolerance.

Limiting resources for soil microbial growth in climate change simulation treatments in the subarctic

The microbial use of resources to sustain life and reproduce influences for example, decomposition and plant nutrient provisioning. The study of "limiting factors" has shed light on the interaction between plants and their environment. Here, we investigated whether carbon (C), nitrogen (N), or phosphorus (P) was limiting for soil microorganisms in a subarctic tundra heath, and how changes in resource availability associated with climate change affected this. We studied samples in which changes in resource availability due to climate warming were simulated by the addition of birch litter and/or inorganic N. To these soils, we supplied factorial C (as glucose), N (as NH4 NO3 ), and P (as KH2 PO4 /K2 HPO4 ) additions ("limiting factor assays," LFA), to determine the limiting factors. The combination of C and P induced large growth responses in all soils and, combined with a systematic tendency for growth increases by C, this suggested that total microbial growth was primarily limited by C and secondarily by P. The C limitation was alleviated by the field litter treatment and strengthened by N fertilization. The microbial growth response to the LFA-C and LFA-P addition was strongest in the field-treatment that combined litter and N addition. We also found that bacteria were closer to P limitation than fungi. Our results suggest that, under a climate change scenario, increased C availability resulting from Arctic greening, treeline advance, and shrubification will reduce the microbial C limitation, while increased N availability resulting from warming will intensify the microbial C limitation. Our results also suggest that the synchronous increase of both C and N availability might lead to a progressive P limitation of microbial growth, primarily driven by bacteria being closer to P limitation. These shifts in microbial resource limitation might lead to a microbial targeting of the limiting element from organic matter, and also trigger competition for nutrients between plants and microorganisms, thus modulating the productivity of the ecosystem.

Warming positively promoted community appearance restoration of the degraded alpine meadow although accompanied by topsoil drying

On-going climate warming is threatening the ecological function of grassland ecosystems. However, whether warming has positive effects on community microhabitats and appearance, especially in degraded grasslands, remains elusive. To address this issue, we conducted a 2-year field experiment on the severely degraded alpine meadow and undegraded alpine meadow with no warming and warming treatments. Community coverage and height in degraded meadow significantly increased under warming, while these changes were not significant in undegraded meadow. Two-year warming increased the community height of degraded meadow and undegraded meadow by 56.55% and 10.99%, respectively. Warming also increased community coverage by 41.88% in degraded meadow and decreased community coverage by 3.01% in undegraded meadow. Moreover, the response of topsoil temperature to warming was stronger in degraded meadow (6.89%) than in undegraded meadow (- 0.26%), while the negative response of topsoil moisture to warming was weaker in degraded meadow (- 13.95%) than in undegraded meadow (- 20.00%). The SEMs further demonstrated that warming had positive effects on topsoil temperature and community height, while had negative effects on topsoil moisture both in degraded and undegraded meadows. Our results confirm that warming-induced soil drying is an important pathway affecting the community appearance in alpine meadows. These findings highlight that warming has positive effects on community height and coverage and is particularly effective in improving community coverage appearance in severely degraded alpine meadow with topsoil drying.

Higher sensitivity of gross primary productivity than ecosystem respiration to experimental drought and warming across six European shrubland ecosystems

Shrubland ecosystems across Europe face a range of threats including the potential impacts of climate change. Within the INCREASE project, six shrubland ecosystems along a European climatic gradient were exposed to ecosystem-level year-round experimental nighttime warming and long-term, repeated growing season droughts. We quantified the ecosystem level CO2 fluxes, i.e. gross primary productivity (GPP), ecosystem respiration (Reco) and net ecosystem exchange (NEE), in control and treatment plots and compared the treatment effects along the Gaussen aridity index. In general, GPP exhibited higher sensitivity to drought and warming than Reco and was found to be the dominant contributor to changes in overall NEE. Across the climate gradient, northern sites were more likely to have neutral to positive responses of NEE, i.e. increased CO2 uptake, to drought and warming partly due to seasonal rewetting. While an earlier investigation across the same sites showed a good cross-site relationship between soil respiration responses to climate over the Gaussen aridity index, the responses of GPP, Reco and NEE showed a more complex response pattern suggesting that site-specific ecosystem traits, such as different growing season periods and plant species composition, affected the overall response pattern of the ecosystem-level CO2 fluxes. We found that the observed response patterns of GPP and Reco rates at the six sites could be explained well by the hypothesized position of each site on site-specific soil moisture response curves of GPP/Reco fluxes. Such relatively simple, site-specific analyses could help improve our ability to explain observed CO2 flux patterns in larger meta-analyses as well as in larger-scale model upscaling exercises and thereby help improve our ability to project changes in ecosystem CO2 fluxes in response to future climate change.

Using photogrammetry to create virtual permanent plots in rare and threatened plant communities

Premise

Many plant communities across the world are undergoing changes due to climate change, human disturbance, and other threats. These community-level changes are often tracked with the use of permanent vegetative plots, but this approach is not always feasible. As an alternative, we propose using photogrammetry, specifically photograph-based digital surface models (DSMs) developed using structure-from-motion, to establish virtual permanent plots in plant communities where the use of permanent structures may not be possible.

Methods

In 2021 and 2022, we took iPhone photographs to record species presence in 1-m2 plots distributed across alpine communities in the northeastern United States. We then compared field estimates of percent coverage with coverage estimated using DSMs.

Results

Digital surface models can provide effective, minimally invasive, and permanent records of plant species presence and percent coverage, while also allowing managers to mark survey locations virtually for long-term monitoring. We found that percent coverage estimated from DSMs did not differ from field estimates for most species and substrates.

Discussion

In order to continue surveying efforts in areas where permanent structures or other surveying methods are not feasible, photogrammetry and structure-from-motion methods can provide a low-cost approach that allows agencies to accurately survey and record sensitive plant communities through time.

Response of Aboveground Net Primary Production, Species and Phylogenetic Diversity to Warming and Increased Precipitation in an Alpine Meadow

The uncertain responses of aboveground net primary productivity (ANPP) and plant diversity to climate warming and increased precipitation will limit our ability to predict changes in vegetation productivity and plant diversity under future climate change and further constrain our ability to protect biodiversity and ecosystems. A long-term experiment was conducted to explore the responses of ANPP, plant species, phylogenetic α-diversity, and community composition to warming and increased precipitation in an alpine meadow of the Northern Tibet from 2014 to 2019. Coverage, height, and species name were obtained by conventional community investigation methods, and ANPP was obtained using observed height and coverage. Open-top chambers with two different heights were used to simulate low- and high-level climate warming. The low- and high-level increased precipitation treatments were achieved by using two kinds of surface area funnel devices. The high-level warming reduced sedge ANPP (ANPPsedge) by 62.81%, species richness (SR) by 21.05%, Shannon by 13.06%, and phylogenetic diversity (PD) by 14.48%, but increased forb ANPP (ANPPforb) by 56.65% and mean nearest taxon distance (MNTD) by 33.88%. Species richness, Shannon, and PD of the high-level warming were 19.64%, 9.67%, and 14.66% lower than those of the low-level warming, respectively. The high-level warming-induced dissimilarity magnitudes of species and phylogenetic composition were greater than those caused by low-level warming. The low- rather than high-level increased precipitation altered species and phylogenetic composition. There were significant inter-annual variations of ANPP, plant species, phylogenetic α-diversity and community composition. Therefore, climate warming and increased precipitation had non-linear effects on ANPP and plant diversity, which were due to non-linear changes in temperature, water availability, and/or soil nutrition caused by warming and increased precipitation. The inter-annual variations of ANPP and plant diversity were stronger than the effects of warming and especially increased precipitation on ANPP and plant diversity. In terms of plant diversity conservation and related policy formulation, we should pay more attention to regions with greater warming, at least for the northern Tibet grasslands. Besides paying attention to the responses of ANPP and plant diversity to climate change, the large inter-annual changes of ANPP and plant diversity should be given great attention because the large inter-annual variation indicates the low temporal stability of ANPP and plant diversity and thus produces great uncertainty for the development of animal husbandry.

Plant traits poorly predict winner and loser shrub species in a warming tundra biome

Climate change is leading to species redistributions. In the tundra biome, shrubs are generally expanding, but not all tundra shrub species will benefit from warming. Winner and loser species, and the characteristics that may determine success or failure, have not yet been fully identified. Here, we investigate whether past abundance changes, current range sizes and projected range shifts derived from species distribution models are related to plant trait values and intraspecific trait variation. We combined 17,921 trait records with observed past and modelled future distributions from 62 tundra shrub species across three continents. We found that species with greater variation in seed mass and specific leaf area had larger projected range shifts, and projected winner species had greater seed mass values. However, trait values and variation were not consistently related to current and projected ranges, nor to past abundance change. Overall, our findings indicate that abundance change and range shifts will not lead to directional modifications in shrub trait composition, since winner and loser species share relatively similar trait spaces.

Climate drivers alter nitrogen availability in surface peat and decouple N2 fixation from CH4 oxidation in the Sphagnum moss microbiome

Peat mosses (Sphagnum spp.) are keystone species in boreal peatlands, where they dominate net primary productivity and facilitate the accumulation of carbon in thick peat deposits. Sphagnum mosses harbor a diverse assemblage of microbial partners, including N₂ -fixing (diazotrophic) and CH₄ -oxidizing (methanotrophic) taxa that support ecosystem function by regulating transformations of carbon and nitrogen. Here, we investigate the response of the Sphagnum phytobiome (plant + constituent microbiome + environment) to a gradient of experimental warming (+0°C to +9°C) and elevated CO₂ (+500 ppm) in an ombrotrophic peatland in northern Minnesota (USA). By tracking changes in carbon (CH₄ , CO₂ ) and nitrogen (NH₄ -N) cycling from the belowground environment up to Sphagnum and its associated microbiome, we identified a series of cascading impacts to the Sphagnum phytobiome triggered by warming and elevated CO₂ . Under ambient CO₂ , warming increased plant-available NH₄ -N in surface peat, excess N accumulated in Sphagnum tissue, and N₂ fixation activity decreased. Elevated CO₂ offset the effects of warming, disrupting the accumulation of N in peat and Sphagnum tissue. Methane concentrations in porewater increased with warming irrespective of CO₂ treatment, resulting in a ~10× rise in methanotrophic activity within Sphagnum from the +9°C enclosures. Warming's divergent impacts on diazotrophy and methanotrophy caused these processes to become decoupled at warmer temperatures, as evidenced by declining rates of methane-induced N₂ fixation and significant losses of keystone microbial taxa. In addition to changes in the Sphagnum microbiome, we observed ~94% mortality of Sphagnum between the +0°C and +9°C treatments, possibly due to the interactive effects of warming on N-availability and competition from vascular plant species. Collectively, these results highlight the vulnerability of the Sphagnum phytobiome to rising temperatures and atmospheric CO₂ concentrations, with significant implications for carbon and nitrogen cycling in boreal peatlands.

Simulated climate warming decreases fruit number but increases seed mass

Climate warming is changing plant sexual reproduction, having consequences for species distribution and community dynamics. However, the magnitude and direction of plant reproductive efforts (e.g., number of flowers) and success (e.g., number and mass of fruits or seeds) in response to warming have not been well-characterized. Here, we generated a global dataset of simulated warming experiments, consisting of 477 pairwise comparisons for 164 terrestrial species. We found evidence that warming overall decreased fruit number and increased seed mass, but little evidence that warming influenced flower number, fruit mass, or seed number. The warming effects on seed mass were regulated by the pollination type, and insect-pollinated plants exhibited a stronger response to warming than wind-pollinated plants. We found strong evidence that warming increased the mass of seeds for the nondominant species but no evidence of this for the dominant species. There was no evidence that phylogenetic relatedness explained the effects of warming on plant reproductive effort and success. In addition, the effects of warming on flowering onset negatively related to the responses in terms of the number of fruits and seeds to warming, revealing a cascading effect of plant reproductive development. These findings provide the first quantification of the response of terrestrial plant sexual reproduction to warming and suggest that plants may increase their fitness by producing heavier seeds under a warming climate.

Increasing precipitation weakened the negative effects of simulated warming on soil microbial community composition in a semi-arid sandy grassland

Soil microbial diversity, composition, and function are sensitive to global change factors. It has been predicted that the temperature and precipitation will increase in northern China. Although many studies have been carried out to reveal how global change factors affect soil microbial biomass and composition in terrestrial ecosystems, it is still unexplored how soil microbial diversity and composition, especially in microbial functional genes, respond to increasing precipitation and warming in a semiarid grassland of northern China. A field experiment was established to simulate warming and increasing precipitation in a temperate semiarid grassland of the Horqin region. Soil bacterial (16S) and fungal (ITS1) diversity, composition, and functional genes were analyzed after two growing seasons. The result showed that warming exerted negative effects on soil microbial diversity, composition, and predicted functional genes associated with carbon and nitrogen cycles. Increasing precipitation did not change soil microbial diversity, but it weakened the negative effects of simulated warming on soil microbial diversity. Bacterial and fungal diversities respond consistently to the global change scenario in semiarid sandy grassland, but the reasons were different for bacteria and fungi. The co-occurrence of warming and increasing precipitation will alleviate the negative effects of global change on biodiversity loss and ecosystem degradation under a predicted climate change scenario in a semiarid grassland. Our results provide evidence that soil microbial diversity, composition, and function changed under climate change conditions, and it will improve the predictive models of the ecological changes of temperate grassland in future climate change scenarios.

Cryptogam plant community stability: Warming weakens influences of species richness but enhances effects of evenness

Community stability is a fundamental factor sustaining ecosystem functioning and is affected by species richness and species evenness. The Arctic is warming more rapidly than other biomes, and cryptogam plant species (specifically lichens and bryophytes in this study) are major contributors to tundra biodiversity and productivity. However, to our knowledge, the impacts of warming on cryptogam community stability and the underlying mechanisms have not been investigated. We conducted a 13-year summer warming experiment in mesic birch hummock tundra vegetation near Daring Lake in the continental interior of low Arctic Canada and recorded patterns of cryptogam species abundance in several different growing seasons. Warming decreased the stability of total community abundance, had no effects on species richness, but increased species evenness and species synchrony. Structural equation model analyses indicated that higher species richness was the principal factor associated with the stronger community abundance stability in the control plots and that this effect was driven primarily by a negative correlation with species synchrony. By contrast, higher species evenness was the principal factor associated with the weakened community abundance stability in the warming plots, and this effect was driven primarily by a positive correlation with species synchrony. Our study suggests that climate warming could reduce cryptogam plant community stability in low Arctic tundra and, therefore, decrease important ecosystem services, including carbon storage and food availability to caribou in northern regions.

Soil Microbial Communities Associated with Three Arctic Plants in Different Local Environments in Ny-Ålesund, Svalbard

Understanding soil microbial community structure in the Arctic is essential for predicting the impact of climate change on interactions between organisms living in polar environments. The hypothesis of the present study was that soil microbial communities and soil chemical characteristics would vary depending on their associated plant species and local environments in Arctic mature soils. We analyzed soil bacterial communities and soil chemical characteristics from soil without vegetation (bare soil) and rhizosphere soil of three Arctic plants (Cassiope tetragona [L.] D. Don, Dryas octopetala L. and Silene acaulis [L.] Jacq.) in different local environments (coal-mined site and seashore-adjacent site). We did not observe any clear differences in microbial community structure in samples belonging to different plant rhizospheres; however, samples from different environmental sites had distinct microbial community structure. The samples from coal-mined site had a relatively higher abundance of Bacteroidetes and Firmicutes. On the other hand, Acidobacteria was more prevalent in seashore-adjacent samples. The relative abundance of Proteobacteria and Acidobacteria decreased toward higher soil pH, whereas that of Bacteroidetes and Firmicutes was positively correlated with soil pH. Our results suggest that soil bacterial community dissimilarity can be driven by spatial heterogeneity in deglaciated mature soil. Furthermore, these results indicate that soil microbial composition and relative abundance are more affected by soil pH, an abiotic factor, than plant species, a biotic factor.

Antarctic Lichens under Long-Term Passive Warming: Species-Specific Photochemical Responses to Desiccation and Heat Shock Treatments

Climate warming in the Antarctic tundra will affect locally dominant cryptogams. Being adapted to low temperatures and freezing, little is known about the response of the polar lichens’ primary photochemistry to warming and desiccation. Since 2008, we have monitored the ecophysiological responses of lichens to the future warming scenario during a long-term warming experiment through open top chambers (OTCs) on Fildes Peninsula. We studied the primary photochemical response (potential Fv/Fm and effective efficiency of photosystem II YPSII) of different lichen taxa and morphotypes under desiccation kinetics and heat shock experiments. As lichens grow slowly, to observe changes during warming we methodologically focused on carbon and nitrogen content as well as on the stable isotope ratios. Endemic Himantormia lugubris showed the strongest effect of long-term warming on primary photochemistry, where PSII activity occurred at a lower %RWC inside the OTCs, in addition to higher Fv/Fm values at 30 °C in the heat shock kinetic treatment. In contrast, Usnea aurantiaco-atra did not show any effect of long-term warming but was active at a thallus RWC lower than 10%. Both Cladonia species were most affected by water stress, with Cladonia aff. gracilis showing no significant differences in primary photochemical responses between the warming and the control but a high sensibility to water deficiency, where, at 60% thallus RWC, the photochemical parameters began to decrease. We detected species-specific responses not only to long-term warming, but also to desiccation. On the other hand, the carbon content did not vary significantly among the species or because of the passive warming treatment. Similarly, the nitrogen content showed non-significant variation; however, the C/N ratio was affected, with the strongest C/N decrease in Cladonia borealis. Our results suggest that Antarctic lichens can tolerate warming and high temperature better than desiccation and that climate change may affect these species if it is associated with a decrease in water availability.

Dominance by non-native grasses suppresses long-term shifts in plant species composition and productivity in response to global change

Climate warming and increased atmospheric nitrogen deposition are both predicted to alter the primary productivity of grass-dominated systems in the coming decades. In field experiments, while both factors can have substantial effects on productivity in the initial years, further changes can be delayed by lags in plant species composition responses. However, the effects of experiment age can be confounded by annual variability in environmental conditions, and a replicate experiment established at a later time is therefore needed to separate these effects. We added new warming and nitrogen plots to an ongoing (14 year-old) field experiment in a grass-dominated temperate old field to compare the short-term vs. long-term treatment effects on plant productivity and species composition, while controlling for interannual environmental variability. We predicted treatment effects on relative species abundances would be most pronounced in the old plots. Although treatment responses of productivity (specifically to N addition) were highest in the old plots in the first year, by the second year there were no interactions between treatment and plot age. Moreover, there were no plot age effects on plant species composition, which was associated with continued dominance of non-native grasses. Our results therefore suggest that despite initial increases in productivity in response to global change, dominance by non-native grasses can suppress the emergence of further long-term treatment effects on productivity by inhibiting the responses of other species.

Different temporal trends in vascular plant and bryophyte communities along elevational gradients over four decades

Despite many studies showing biodiversity responses to warming, the generality of such responses across taxonomic groups remains unclear. Very few studies have tested for evidence of bryophyte community responses to warming, even though bryophytes are major contributors to diversity and functioning in many ecosystems. Here, we report an empirical study comparing long‐term change in bryophyte and vascular plant communities in two sites with contrasting long‐term warming trends, using “legacy” botanical records as a baseline for comparison with contemporary resurveys. We hypothesized that ecological changes would be greater in sites with a stronger warming trend and that vascular plant communities, with narrower climatic niches, would be more sensitive than bryophyte communities to climate warming. For each taxonomic group in each site, we quantified the magnitude of changes in species' distributions along the elevation gradient, species richness, and community composition. We found contrasted temporal changes in bryophyte vs. vascular plant communities, which only partially supported the warming hypothesis. In the area with a stronger warming trend, we found a significant increase in local diversity and dissimilarity (β‐diversity) for vascular plants, but not for bryophytes. Presence–absence data did not provide sufficient power to detect elevational shifts in species distributions. The patterns observed for bryophytes are in accordance with recent literature showing that local diversity can remain unchanged despite strong changes in composition. Regardless of whether one taxon is systematically more or less sensitive to environmental change than another, our results suggest that vascular plants cannot be used as a surrogate for bryophytes in terms of predicting the nature and magnitude of responses to warming. Thus, to assess overall biodiversity responses to global change, abundance data from different taxonomic groups and different community properties need to be synthesized.

Three years of warming and rainfall reduction alter leaf physiology but not relative abundance of an annual species in a Mediterranean savanna

Increasing air temperatures and decreasing rainfall can alter Mediterranean ecosystems, where summer heat and drought already limit plant regeneration. Manipulative field studies can help to understand and anticipate community responses to climate changes. In a Mediterranean oak wooded pasture, we have investigated the effects of warming (W, via open-top chambers increasing 1.4 °C mean air temperature), reduced rainfall (D, via gutters removing 33% of rainfall) and the combination of both factors (WD) on the winter-annual Geranium dissectum L. We measured reproductive phenology and output, leaf physiology during the reproductive phase, and plant relative abundance. Warming had a positive effect on plant height and little effects on leaf physiology. Rainfall reduction enhanced leaf water use efficiency. However, the most noticeable effects occurred in WD plants, which exhibited lower leaf predawn water potential and earlier flowering phenology in the first year of treatment, and a higher ratio of leaf dark respiration (R) to net CO₂ assimilation (P_n) at comparable temperatures in the third year, compared to control plants. Leaf R at ambient temperature was similar across climatic treatments. The relative abundance of G. dissectum decreased by 23% over three years, but similarly across treatments. A short life cycle helps G. dissectum to escape severe late-spring heat and drought stress. Moreover, stomata closure and thermal acclimation of R can attenuate plant stress impact on reproduction. Adaptability of the short-lived annual G. dissectum could mitigate climate change impact on community composition over short periods (e.g. three years); however, a reduction in net carbon gain could eventually affect its reproductive success and persistence in the community.

Warming enhances dominance of vascular plants over cryptogams across northern wetlands

Climate warming causes profound effects on structure and function of wetland ecosystem, thus affecting regional and global hydrological cycles and carbon budgets. However, how wetland plants respond to warming is still poorly understood. Here, we synthesized observations from 273 independent sites to explore responses of northern wetland plants to warming. Our results show that warming enhances biomass accumulation for vascular plants including shrubs and graminoids, whereas it reduces biomass accumulation for cryptogams including moss and lichen. This divergent response of vascular plants and cryptogams is particularly pronounced in the high latitudes where permafrost prevails. As warming continues, this divergent response is amplified, however, the reduction in cryptogams is more drastic. Warming leads to declined surface soil moisture and lowered water table, thereby shifting wetlands from a wet system dominated by cryptogams to a drier system with increased cover of vascular plants. Under a high-emission scenario of Shared Socioeconomic Pathways (SSP5), a 4.7-5.1°C mean global temperature rise will cause more than fivefold loss of cryptogams compared with current climate. As cryptogams are largely concentrated at northern high latitudes, where warming will likely be greater than the projected global mean, modification in wetland plant composition and major reduction in cryptogams are expected to occur even much earlier than 2100.

Climate warming, but not Spartina alterniflora invasion, enhances wetland soil HONO and NOx emissions

Climate warming and invasive plant growth (plant invasion) may aggravate air pollution by affecting soil nitrogen (N) cycling and the emissions of reactive N gases, such as nitrous acid (HONO) and nitrogen oxides (NO_x). However, little is known about the response of soil NO_y (HONO + NO_x) emissions and microbial functional genes to the interaction of climate warming and plant invasion. Here, we found that experimental warming (approximately 1.5 °C), but not Spartina alterniflora invasion, increased NO_y emissions (0-140 ng N m^-2 s^-1) of treated wetland soils by 4-10 fold. Warming also decreased soil archaeal and fungal richness and diversity, shifted their community structure (e.g., decreased the archaeal classes Thermoplasmata and Iainarchaeia, and increased the archaeal genus Candidatus Nitrosoarchaeum, and the fungal classes Saccharomycetes and Tritirachiomycetes), and decreased the overall abundance of soil N cycling genes. Structural equation modeling revealed that warming-associated changes in edaphic factors and the microbial N cycling potential are responsible for the observed increase in soil NO_y emissions. Collectively, the results showed that climate warming accelerates soil N cycling by stimulating large soil HONO and NO_x emissions, and influences air quality by contributing to atmospheric reactive N and ozone cycling.

Evaluating tropical drought risk by combining open access gridded vulnerability and hazard data products

Droughts are causing severe damages to tropical countries worldwide. Although water abundant, their resilience to water shortages during dry periods is often low. As there is little knowledge about tropical drought characteristics, reliable methodologies to evaluate drought risk in data scarce tropical regions are needed. We combined drought hazard and vulnerability related data to assess drought risk in four rural tropical study regions, the Muriaé basin, Southeast Brazil, the Tempisque-Bebedero basin in Costa Rica, the upper part of the Magdalena basin, Colombia and the Srepok, shared by Cambodia and Vietnam. Drought hazard was analyzed using the variables daily river discharge, precipitation and vegetation condition. Drought vulnerability was assessed based on regionally available socioeconomic data. Besides illustrating the relative severity of each indicator value, we developed drought risk maps combining hazard and vulnerability for each grid-cell. While for the Muriaé, our results identified the downstream area as being exposed to severe drought risk, the Tempisque showed highest risk along the major streams and related irrigation systems. Risk hotspots in the Upper Magdalena were found in the central valley and the dryer Southeast and in the Srepok in the agricultural areas of Vietnam and downstream Cambodia. Local scientists and stakeholders have validated our results and we believe that our drought risk assessment methodology for data scarce and rural tropical regions offers a holistic, science based and innovative framework to generate relevant drought related information. Being applied to other tropical catchments, the approaches described in this article will enable the selection of data sets, indices and their classification - depending on basin size, spatial resolution and seasonality. At its current stage, the outcomes of this study provide relevant information for regional planners and water managers dealing with the control of future drought disasters in tropical regions.

Reduced methane emissions in former permafrost soils driven by vegetation and microbial changes following drainage

In Arctic regions, thawing permafrost soils are projected to release 50 to 250 Gt of carbon by 2100. This data is mostly derived from carbon-rich wetlands, although 71% of this carbon pool is stored in faster-thawing mineral soils, where ecosystems close to the outer boundaries of permafrost regions are especially vulnerable. Although extensive data exists from currently thawing sites and short-term thawing experiments, investigations of the long-term changes following final thaw and co-occurring drainage are scarce. Here we show ecosystem changes at two comparable tussock tundra sites with distinct permafrost thaw histories, representing 15 and 25 years of natural drainage, that resulted in a 10-fold decrease in CH₄ emissions (3.2 ± 2.2 vs. 0.3 ± 0.4 mg C-CH₄  m^-2  day^-1 ), while CO₂ emissions were comparable. These data extend the time perspective from earlier studies based on short-term experimental drainage. The overall microbial community structures did not differ significantly between sites, although the drier top soils at the most advanced site led to a loss of methanogens and their syntrophic partners in surface layers while the abundance of methanotrophs remained unchanged. The resulting deeper aeration zones likely increased CH₄ oxidation due to the longer residence time of CH₄ in the oxidation zone, while the observed loss of aerenchyma plants reduced CH₄ diffusion from deeper soil layers directly to the atmosphere. Our findings highlight the importance of including hydrological, vegetation and microbial specific responses when studying long-term effects of climate change on CH₄ emissions and underscores the need for data from different soil types and thaw histories.

N/P Addition Is More Likely Than N Addition Alone to Promote a Transition from Moss-Dominated to Graminoid-Dominated Tundra in the High-Arctic

Nutrient availability for tundra vegetation could change drastically due to increasing temperatures and frequency of nitrogen deposition in the Arctic. Few studies have simultaneously examined the response of plant communities to these two pressures over a long period. This study aims to assess which driver between increasing nitrogen (N) and phosphorus (P) availability through global warming and increasing N availability alone via N deposition is more likely to transform arctic wetland vegetation and whether there is a time lag in this response. An annual fertilization experiment simulating these nutrient inputs was conducted for 17 years in the Canadian High-Arctic to assess the impact on aboveground net primary productivity, floristic composition, and plant nutrient concentration. While the primary productivity of mosses remains unchanged by fertilization after 17 years, productivity of graminoids was increased slightly by N addition (36% increase at the highest dose). In contrast, the primary productivity of graminoids increased strongly with N/P addition (over 227% increase). We noted no difference in graminoid productivity between the 2nd and 5th year of the experiment, but we observed a 203% increase between the 5th and 17th year in the N/P addition treatments. We also noted a 49% decrease in the total moss cover and an 155% increase in the total graminoid cover between the 2nd and 17th year of N/P addition. These results indicate that the impact of warming through increased N/P availability was greater than those of N deposition alone (N addition) and promoted the transition from a moss-dominated tundra to a graminoid-dominated tundra. However, this transition was subject to a time lag of up to 17 years, suggesting that increased productivity of graminoids resulted from a release of nutrients via the decomposition of lower parts of the moss mat.

Transient Effects of Snow Cover Duration on Primary Growth and Leaf Traits in a Tundra Shrub

With the recent climate warming, tundra ecotones are facing a progressive acceleration of spring snowpack melting and extension of the growing season, with evident consequences to vegetation. Along with summer temperature, winter precipitation has been recently recognised as a crucial factor for tundra shrub growth and physiology. However, gaps of knowledge still exist on long-living plant responses to different snowpack duration, especially on how intra-specific and year-to-year variability together with multiple functional trait adjustments could influence the long-term responses. To fill this gap, we conducted a 3 years snow manipulation experiment above the Alpine treeline on the typical tundra species Juniperus communis, the conifer with the widest distributional range in the north emisphere. We tested shoot elongation, leaf area, stomatal density, leaf dry weight and leaf non-structural carbohydrate content of plants subjected to anticipated, natural and postponed snowpack duration. Anticipated snowpack melting enhanced new shoot elongation and increased stomatal density. However, plants under prolonged snow cover seemed to compensate for the shorter growing period, likely increasing carbon allocation to growth. In fact, these latter showed larger needles and low starch content at the beginning of the growing season. Variability between treatments slightly decreased over time, suggesting a progressive acclimation of juniper to new conditions. In the context of future warming scenarios, our results support the hypothesis of shrub biomass increase within the tundra biome. Yet, the picture is still far from being complete and further research should focus on transient and fading effects of changing conditions in the long term.

The need to understand the stability of arctic vegetation during rapid climate change: An assessment of imbalance in the literature

In early studies, northern vegetation response to global warming recognised both increases in biomass/cover and shrinking of species' distributional ranges. Subsequent field measurements focussed on vegetation cover and biomass increases ("greening"), and more recently decreases ("browning"). However, satellite observations show that more than 50% of arctic vegetation has not changed significantly despite rapid warming. While absence of change in remote sensing data does not necessarily mean no ecological change on the ground, the significant proportion of the Arctic that appears to be stable in the face of considerable climate change points to a greater need to understand Arctic ecosystem stability. In this paper, we performed an extensive review of the available literature to seek balances or imbalances between research focussing on "greening", "browning" and "stability/no change". We find that greening studies dominate the literature though two relatively small areas of the Arctic are disproportionately represented for this main change process. Critically, there are too few studies anywhere investigating stability. We highlight the need to understand the mechanisms driving Arctic ecosystem stability, and the potential longer-term consequences of remaining stable in a rapidly changing climate.

Environmental variables drive plant species composition and distribution in the moist temperate forests of Northwestern Himalaya, Pakistan

By assessing plant species composition and distribution in biodiversity hotspots influenced by environmental gradients, we greatly advance our understanding of the local plant community and how environmental factors are affecting these communities. This is a proxy for determining how climate change influences plant communities in mountainous regions ("space-for-time" substitution). We evaluated plant species composition and distribution, and how and which environmental variables drive the plant communities in moist temperate zone of Manoor valley of Northwestern Himalaya, Pakistan. During four consecutive years (2015-2018), we sampled 30 sampling sites, measuring 21 environmental variables, and recording all plant species present in an altitudinal variable range of 1932-3168 m.a.s.l. We used different multivariate analyses to identify potential plant communities, and to evaluate the relative importance of each environmental variable in the species composition and distribution. Finally, we also evaluated diversity patterns, by comparing diversity indices and beta diversity processes. We found that (i) the moist temperate zone in this region can be divided in four different major plant communities; (ii) each plant community has a specific set of environmental drivers; (iii) there is a significant variation in plant species composition between communities, in which six species contributed most to the plant composition dissimilarity; (iv) there is a significant difference of the four diversity indices between communities; and (v) community structure is twice more influenced by the spatial turnover of species than by the species loss. Overall, we showed that altitudinal gradients offer an important range of different environmental variables, highlighting the existence of micro-climates that drive the structure and composition of plant species in each micro-region. Each plant community along the altitudinal gradient is influenced by a set of environmental variables, which lead to the presence of indicator species in each micro-region.

Pastures and Climate Extremes: Impacts of Cool Season Warming and Drought on the Productivity of Key Pasture Species in a Field Experiment

Shifts in the timing, intensity and/or frequency of climate extremes, such as severe drought and heatwaves, can generate sustained shifts in ecosystem function with important ecological and economic impacts for rangelands and managed pastures. The Pastures and Climate Extremes experiment (PACE) in Southeast Australia was designed to investigate the impacts of a severe winter/spring drought (60% rainfall reduction) and, for a subset of species, a factorial combination of drought and elevated temperature (ambient +3°C) on pasture productivity. The experiment included nine common pasture and Australian rangeland species from three plant functional groups (C3 grasses, C4 grasses and legumes) planted in monoculture. Winter/spring drought resulted in productivity declines of 45% on average and up to 74% for the most affected species (Digitaria eriantha) during the 6-month treatment period, with eight of the nine species exhibiting significant yield reductions. Despite considerable variation in species' sensitivity to drought, C4 grasses were more strongly affected by this treatment than C3 grasses or legumes. Warming also had negative effects on cool-season productivity, associated at least partially with exceedance of optimum growth temperatures in spring and indirect effects on soil water content. The combination of winter/spring drought and year-round warming resulted in the greatest yield reductions. We identified responses that were either additive (Festuca), or less-than-additive (Medicago), where warming reduced the magnitude of drought effects. Results from this study highlight the sensitivity of diverse pasture species to increases in winter and spring drought severity similar to those predicted for this region, and that anticipated benefits of cool-season warming are unlikely to be realized. Overall, the substantial negative impacts on productivity suggest that future, warmer, drier climates will result in shortfalls in cool-season forage availability, with profound implications for the livestock industry and natural grazer communities.

The danger and indeterminacy of forfeiting perching space of bryophytes from climate shift: a case study for 115 species in China

Identifying the danger and expressing the indeterminacy of forfeiting perching space of species induced by rapid climate warming is crucial for biodiversity risk management under future changes in climate conditions. The scenarios of climate shift named the representative concentration pathways, the categorizing technique with regard to fuzzy-set, and Monte Carlo scheme was employed to survey the indeterminacy and the danger of forfeiting perching space caused by climate warming for 115 bryophytes in China. For the deterministic scenarios of climate shift, the richness of 115 bryophytes improved in several areas in north-eastern China, while it dropped in some areas in southern, eastern, south-eastern, and central China. In addition, for the deterministic scheme of altering climatic state, the count for bryophytes with the proportion of contracting the present areal range as less than 20%, 20-40%, 40-60%, 60-80%, and over 80% was belike 34-38, 19-38, 24-35, 9-19, and 4-9, separately; the count of bryophytes with the ratio of the occupying entire areal range as over 80%, 60-80%, and less than 20% was roughly 97-109, 4-14, and 2-8, separately. For the scenarios of randomly change in climate state, the number of bryophytes with a various proportion of forfeiting the present perching space dropped with enhancing the possibility; with the likelihood beyond 0.6, the count of bryophytes with forfeiting present perching space as less than 20%, 20-40%, 40-60%, 60-80% and high than 80% of the present areal range was approximately 7-14, 2-10, 0-7, 2-9, and 13-20, separately; the number of bryophytes with the ratio of occupying the whole areal range as less than 20%, 20-40%, 40-60%, 60-80%, and over 80% was more or less 1-3, 0-3, 1-5, 1-3, and 38-44, separately. Roughly 48 bryophytes would face the risk of extinction from climate warming, including endemic and non-endemic species. Forfeiting perching space induced by climate warming would cause variations in species composition and the disappearance of some ecological functions associated with these bryophytes. The inconstancy of forfeiting areal range caused by climate warming should be incorporated into the policy-making of conservation bryophytes for adaptation of climate warming.

Experimental Climate Warming Reduces Floral Resources and Alters Insect Visitation and Wildflower Seed Set in a Cereal Agro-Ecosystem

Declines in pollinating insects and wildflowers have been well documented in recent years. Climate change is an emerging threat to insect pollinators and their food plants, but little is known about how whole communities of interacting species will be affected or what impacts there may be on ecosystem services such as pollination. Using a novel open-air field experiment, we simulated an increase in temperature of 1.5°C and rainwater of 40% for two growing seasons to investigate how climate change may impact several within-field features of temperate arable agro-ecosystems: (1) wildflower floral resources; (2) insect visitation; (3) flower-visitor network structure; and (4) wildflower seed set. Experimental warming reduced total floral abundance by nearly 40%, and nectar volumes by over 60% for two species. The species richness of the visiting insects and flowering plants (dominated by annuals) were unaffected by warming, and while a negative impact on visitor abundance was observed, this effect appears to have been mediated by different community compositions between years. Warming increased the frequency of visits to flowers and the complexity of the flower-visitor interaction networks. Wildflower seed set was reduced in terms of seed number and/or weight in four of the five species examined. Increased rainwater did not ameliorate any of these effects. These findings demonstrate the adverse impacts that climate warming might have on annual wildflowers in arable systems and the pollinating insects that feed on them, highlighting several mechanisms that could drive changes in community composition over time. The results also reveal how cascading impacts within communities can accumulate to affect ecosystem functioning.

Influences of summer warming and nutrient availability on Salix glauca L. growth in Greenland along an ice to sea gradient

The combined effects of climate change and nutrient availability on Arctic vegetation growth are poorly understood. Archaeological sites in the Arctic could represent unique nutrient hotspots for studying the long-term effect of nutrient enrichment. In this study, we analysed a time-series of ring widths of Salix glauca L. collected at nine archaeological sites and in their natural surroundings along a climate gradient in the Nuuk fjord region, Southwest Greenland, stretching from the edge of the Greenlandic Ice Sheet in the east to the open sea in the west. We assessed the temperature-growth relationship for the last four decades distinguishing between soils with past anthropogenic nutrient enrichment (PANE) and without (controls). Along the East-West gradient, the inner fjord sites showed a stronger temperature signal compared to the outermost ones. Individuals growing in PANE soils had wider ring widths than individuals growing in the control soils and a stronger climate-growth relation, especially in the inner fjord sites. Thereby, the individuals growing on the archaeological sites seem to have benefited more from the climate warming in recent decades. Our results suggest that higher nutrient availability due to past human activities plays a role in Arctic vegetation growth and should be considered when assessing both the future impact of plants on archaeological sites and the general greening in landscapes with contrasting nutrient availability.

The influence of climate change on the suitable habitats of Allium species endemic to Iran

Identifying the consequences of global warming on the potential distribution of plant taxa with high species diversity or a high proportion of endemic species is one of the critical steps in conservation biology. Here, present and future spatial distribution patterns of 20 Allium endemic species were predicted in Iran. In this regard, the maximum entropy model (MaxEnt) and seven environmental factors were applied. In addition, optimistic (RCP2.6) and pessimistic (RCP8.5) scenarios of 2050 and 2080 were also considered to predict the future spatial distributions. The results showed that annual mean temperature (BIO1), temperature annual range (P5-P6) (BIO7), soil organic carbon content, annual precipitation (BIO12), and depth of soil were the most important environmental variables affecting the distributions of the studied taxa. In total, the model predictions under the future scenarios represented that the suitable habitats for all Allium species endemic to Zagros except for A. saralicum and A. esfahanicum are most probably increased. In contrast, the suitable habitats for all species in Azerbaijan Plateau, Kopet Dagh-Khorassan region, and Alborz except for A. derderianum are most likely decreased under the future climate conditions. The present study indicates that the habitats of Alborz, Azarbaijan, and Kopet Dagh-Khorassan will be probably very fragile and vulnerable to climate change and most species will respond strongly negatively under applied scenarios, while Zagros species occupy new habitats by expanding their distributions. Therefore, determining conservation strategies for the species in these regions seems to be very important and high priority for decision makers.

Plant community responses to experimental climate manipulation in a Welsh ombrotrophic peatland and their palaeoenvironmental context

We test whether vegetation community composition from a 10-year climate manipulation experiment on a Welsh peat bog resembles vegetation communities during periods of climate change inferred from a peat core. Experimentally warmed and combined warmed and droughted treatments drove significant increases in ericaceous shrubs but Sphagnum was unaffected. Similarly, Calluna vulgaris seeds increase during inferred warmer periods in the palaeoecological record. Experimental short-term episodic drought (four 4-week drought treatments) did not affect vegetation. Plant community composition has undergone several abrupt changes throughout the past c. 1500 years, often in response to human disturbance. Only slight changes occurred during the Medieval Climate Anomaly (c. 950-1250 Common Era [CE]) in vegetation and hydrology, while abrupt changes occurred during the Little Ice Age (c. 1300-1850 CE) when water tables were highest, suggesting that these shifts were driven by changes in water table, modulated by climate. A period of water table drawdown c. 1800, synchronous with historical records of increased drainage, corresponds with the development of the present-day vegetation community. Modern analogues for fossil material, characterized by abundant Rhynchospora alba and Sphagnum pulchrum, are more common after this event. Vegetation changes due to climate inferred from the palaeo record differ from those observed in the experiments, possibly relating to differences in the importance of drivers of vegetation change over varying timescales. Whereas temperature is frequently identified as the dominant driver of plant community change in experiments, sustained changes in water table appear to be more important in the long-term record. We find evidence that recent climate change and other anthropogenic stressors (e.g. drainage, heavy metal and nitrogen pollution) may promote the development of novel plant communities without analogues in the fossil record. These communities may be poorer at sequestering carbon and may respond differently to future climate change.

Warming has a minor effect on surface soil organic carbon in alpine meadow ecosystems on the Qinghai-Tibetan Plateau

The alpine meadow ecosystem on the Qinghai-Tibetan Plateau (QTP) is very sensitive to warming and plays a key role in regulating global carbon (C) cycling. However, how warming affects the soil organic carbon (SOC) pool and related C inputs and outputs in alpine meadow ecosystems on the QTP remains unclear. Here, we combined two field experiments and a meta-analysis on field experiments to synthesize the responses of the SOC pool and related C cycling processes to warming in alpine meadow ecosystems on the QTP. We found that the SOC content of surface soil (0-10 cm) showed a minor response to warming, but plant respiration was accelerated by warming. In addition, the warming effect on SOC was not correlated with experimental and environmental variables, such as the method, magnitude and duration of warming, initial SOC content, mean annual temperature, and mean annual precipitation. We conclude that the surface SOC content is resistant to climate warming in alpine meadow ecosystems on the QTP.

Thermal Acclimation of Foliar Carbon Metabolism in Pinus taiwanensis Along an Elevational Gradient

Climate change could negatively alter plant ecosystems if rising temperatures exceed optimal conditions for obtaining carbon. The acclimation of plants to higher temperatures could mitigate this effect, but the potential of subtropical forests to acclimate still requires elucidation. We used space-for-time substitution to determine the photosynthetic and respiratory-temperature response curves, optimal temperature of photosynthesis (T opt), photosynthetic rate at T opt, temperature sensitivity (Q 10), and the rate of respiration at a standard temperature of 25°C (R 25) for Pinus taiwanensis at five elevations (1200, 1400, 1600, 1800, and 2000 m) in two seasons (summer and winter) in the Wuyi Mountains in China. The response of photosynthesis in P. taiwanensis leaves to temperature at the five elevations followed parabolic curves, and the response of respiration to temperature increased with temperature. T opt was higher in summer than winter at each elevation and decreased significantly with increasing elevation. Q 10 decreased significantly with increasing elevation in summer but not winter. These results showed a strong thermal acclimation of foliar photosynthesis and respiration to current temperatures across elevations and seasons, and that R 25 increased significantly with elevation and were higher in winter than summer at each elevation indicating that the global warming can decrease R 25. These results strongly suggest that this thermal acclimation will likely occur in the coming decades under climate change, so the increase in respiration rates of P. taiwanensis in response to climatic warming may be smaller than predicted and thus may not increase atmospheric CO2 concentrations.

Biophysical Determinants of Shifting Tundra Vegetation Productivity in the Beaufort Delta Region of Canada

Temperature increases across the circumpolar north have driven rapid increases in vegetation productivity, often described as ‘greening’. These changes have been widespread, but spatial variation in their pattern and magnitude suggests that biophysical factors also influence the response of tundra vegetation to climate warming. In this study, we used field sampling of soils and vegetation and random forests modeling to identify the determinants of trends in Landsat-derived Enhanced Vegetation Index, a surrogate for productivity, in the Beaufort Delta region of Canada between 1984 and 2016. This region has experienced notable change, with over 71% of the Tuktoyaktuk Coastlands and over 66% of the Yukon North Slope exhibiting statistically significant greening. Using both classification and regression random forests analyses, we show that increases in productivity have been more widespread and rapid at low-to-moderate elevations and in areas dominated by till blanket and glaciofluvial deposits, suggesting that nutrient and moisture availability mediate the impact of climate warming on tundra vegetation. Rapid greening in shrub-dominated vegetation types and observed increases in the cover of low and tall shrub cover (4.8% and 6.0%) also indicate that regional changes have been driven by shifts in the abundance of these functional groups. Our findings demonstrate the utility of random forests models for identifying regional drivers of tundra vegetation change. To obtain additional fine-grained insights on drivers of increased tundra productivity, we recommend future research combine spatially comprehensive time series satellite data (as used herein) with samples of high spatial resolution imagery and integrated field investigations.

Simulating climate change in situ in a tropical rainforest understorey using active air warming and CO2 addition

Future climate-change effects on plant growth are most effectively studied using microclimate-manipulation experiments, the design of which has seen much advance in recent years. For tropical forests, however, such experiments are particularly hard to install and have hence not been widely used. We present a system of active heating and CO2 fertilization for use in tropical forest understoreys, where passive heating is not possible. The system was run for 2 years to study climate-change effects on epiphytic bryophytes, but is also deemed suitable to study other understorey plants. Warm air and CO2 addition were applied in 1.6-m-tall, 1.2-m-diameter hexagonal open-top chambers and the microclimate in the chambers compared to outside air. Warming was regulated with a feedback system while CO2 addition was fixed. The setup successfully heated the air by 2.8 K and increased CO2 by 250 ppm on average, with +3 K and +300 ppm as the targets. Variation was high, especially due to technical breakdowns, but not biased to times of the day or year. In the warming treatment, absolute humidity slightly increased but relative humidity dropped by between 6% and 15% (and the vapor pressure deficit increased) compared to ambient, depending on the level of warming achieved in each chamber. Compared to other heating systems, the chambers provide a realistic warming and CO2 treatment, but moistening the incoming air would be needed to avoid drying as a confounding factor. The method is preferable over infrared heating in the radiation-poor forest understorey, particularly when combined with CO2 fertilization. It is suitable for plant-level studies, but ecosystem-level studies in forests may require chamber-less approaches like infrared heating and free-air CO2 enrichment. By presenting the advantages and limitations of our approach, we aim to facilitate further climate-change experiments in tropical forests, which are urgently needed to understand the processes determining future element fluxes and biodiversity changes in these ecosystems.

Low-Altitude Boundary of Abies faxoniana Is More Susceptible to Long-Term Open-Top Chamber Warming in the Eastern Tibetan Plateau

With global climate change, for evaluating warming effect on subalpine forest distribution, the substantial effects of long-term warming on tree growth and soil nutrients need to be explored. In this study, we focused on different responses in the boundaries of trees and soils to warming. Using the open-top chamber (OTC), a 10-year artificial warming experiment was conducted to evaluate the impacts of warming on Abies faxoniana at three different altitudes. We determined metabolites and nutrient concentrations in needles of A. faxoniana and characterized the soil chemistries. Many kinds of sugars, amino acids, and organic acids showed higher contents at high altitude (3,500 m) compared with low altitude (2,600 m), which could have been due to the temperature differences. Warming significantly decreased needle sugar and amino acid concentrations at high altitude but increased them at low altitude. These results indicated contrasting physiological and metabolic responses of A. faxoniana to long-term warming at different altitudes. Furthermore, we found that OTC warming significantly increased the concentrations of soil extractable sodium, aluminum (Al), and manganese (Mn), while decreased potassium (K) and phosphorus (P) concentrations and pH values at low altitude rather than at middle (3,000 m) or high altitude. The soil carbon and nitrogen contents were increased only at the middle altitude. In A. faxoniana at low altitudes, more mineral nutrients iron, K, and P were demand, and a mass of Al, Mn, and zinc was accumulated under warming. Soil P limitation and heavy metals accumulation are disadvantageous for trees at low altitudes with warming. Therefore, compared with high altitudes, A. faxoniana growing at low boundary in alpine regions is expected to be more susceptible to warming.

Plant Sedimentary Ancient DNA From Far East Russia Covering the Last 28,000 Years Reveals Different Assembly Rules in Cold and Warm Climates

Woody plants are expanding into the Arctic in response to the warming climate. The impact on arctic plant communities is not well understood due to the limited knowledge about plant assembly rules. Records of past plant diversity over long time series are rare. Here, we applied sedimentary ancient DNA metabarcoding targeting the P6 loop of the chloroplast trnL gene to a sediment record from Lake Ilirney (central Chukotka, Far Eastern Russia) covering the last 28 thousand years. Our results show that forb-rich steppe-tundra and dwarf-shrub tundra dominated during the cold climate before 14 ka, while deciduous erect-shrub tundra was abundant during the warm period since 14 ka. Larix invasion during the late Holocene substantially lagged behind the likely warmest period between 10 and 6 ka, where the vegetation biomass could be highest. We reveal highest richness during 28–23 ka and a second richness peak during 13–9 ka, with both periods being accompanied by low relative abundance of shrubs. During the cold period before 14 ka, rich plant assemblages were phylogenetically clustered, suggesting low genetic divergence in the assemblages despite the great number of species. This probably originates from environmental filtering along with niche differentiation due to limited resources under harsh environmental conditions. In contrast, during the warmer period after 14 ka, rich plant assemblages were phylogenetically overdispersed. This results from a high number of species which were found to harbor high genetic divergence, likely originating from an erratic recruitment process in the course of warming. Some of our evidence may be of relevance for inferring future arctic plant assembly rules and diversity changes. By analogy to the past, we expect a lagged response of tree invasion. Plant richness might overshoot in the short term; in the long-term, however, the ongoing expansion of deciduous shrubs will eventually result in a phylogenetically more diverse community.

Critical summer foraging tradeoffs in a subarctic ungulate

Summer diets are crucial for large herbivores in the subarctic and are affected by weather, harassment from insects and a variety of environmental changes linked to climate. Yet, understanding foraging behavior and diet of large herbivores is challenging in the subarctic because of their remote ranges. We used GPS video-camera collars to observe behaviors and summer diets of the migratory Fortymile Caribou Herd (Rangifer tarandus granti) across Alaska, USA and the Yukon, Canada. First, we characterized caribou behavior. Second, we tested if videos could be used to quantify changes in the probability of eating events. Third, we estimated summer diets at the finest taxonomic resolution possible through videos. Finally, we compared summer diet estimates from video collars to microhistological analysis of fecal pellets. We classified 18,134 videos from 30 female caribou over two summers (2018 and 2019). Caribou behaviors included eating (mean = 43.5%), ruminating (25.6%), travelling (14.0%), stationary awake (11.3%) and napping (5.1%). Eating was restricted by insect harassment. We classified forage(s) consumed in 5,549 videos where diet composition (monthly) highlighted a strong tradeoff between lichens and shrubs; shrubs dominated diets in June and July when lichen use declined. We identified 63 species, 70 genus and 33 family groups of summer forages from videos. After adjusting for digestibility, monthly estimates of diet composition were strongly correlated at the scale of the forage functional type (i.e., forage groups composed of forbs, graminoids, mosses, shrubs and lichens; r = 0.79, p < .01). Using video collars, we identified (1) a pronounced tradeoff in summer foraging between lichens and shrubs and (2) the costs of insect harassment on eating. Understanding caribou foraging ecology is needed to plan for their long-term conservation across the circumpolar north, and video collars can provide a powerful approach across remote regions.

How does a wetland plant respond to increasing temperature along a latitudinal gradient?

Global warming affects plant fitness through changes in functional traits and thereby ecosystem function. Wetlands are declining worldwide, and hence, ecosystem functions linked to wetlands are threatened. We use Caltha palustris "a common wetland plant" to study whether warming affects growth and reproduction differently depending on origin of source population, potentially affecting phenotypic response to local climate. We conducted a 2-year in situ temperature manipulation experiment using clone pairs of C. palustris in four regions, along a 1300-km latitudinal gradient of Sweden. Open-top chambers were used to passively increase temperature, paired with controls. Growth and reproductive traits were measured from 320 plants (four regions × five sites × two treatments × eight plants) over two consecutive seasons to assess the effect of warming over time. We found that warming increased plant height, leaf area, number of leaves, and roots. High-latitude populations responded more strongly to warming than low-latitude populations, especially by increasing leaf area. Warming increased number of flowers in general, but only in the second year, while number of fruits increased in low-latitude populations the first year. Prolonged warming leads to an increase in both number of leaves and flowers over time. While reproduction shows varying and regional responses to warming, impacts on plant growth, especially in high-latitude populations, have more profound effects. Such effects could lead to changes in plant community composition with increased abundance of fast-growing plants with larger leaves and more clones, affecting plant competition and ecological functions such as decomposition and nutrient retention. Effects of warming were highly context dependent; thus, we encourage further use of warming experiments to predict changes in growth, reproduction, and community composition across wetland types and climate gradients targeting different plant forms.

Do plant-soil interactions influence how the microbial community responds to environmental change?

Global change alters ecosystems and their functioning, and biotic interactions can either buffer or amplify such changes. We utilized a long-term nitrogen (N) addition and species removal experiment in the Front Range of Colorado, USA to determine whether a codominant forb and a codominant grass, with different effects on nutrient cycling and plant community structure, would buffer or amplify the effects of simulated N deposition on soil bacterial and fungal communities. While the plant community was strongly shaped by both the presence of dominant species and N addition, we did not find a mediating effect of the plant community on soil microbial response to N. In contrast to our hypothesis, we found a decoupling of the plant and microbial communities such that the soil microbial community shifted under N independently of directional shifts in the plant community. These findings suggest there are not strong cascading effects of N deposition across the plant-soil interface in our system.

Functionally explicit partitioning of plant β-diversity reveal soil fungal assembly in the subarctic tundra

Metabarcoding technologies for soil fungal DNA pools have enabled to capture the diversity of fungal community and the agreement of their β-diversity with plant β-diversity. However, processes underlying the synchrony of the aboveground-belowground biodiversity is still unclear. By using partitioning methods for plant β-diversity, this study explored the process driving synchrony in tundra ecosystems, in which drastic vegetation shifts are observed with climate warming. Our methods based on Baselga's partitioning enabled the division of plant β-diversity into two phenomena and three functional components. Correlation of fungal β-diversity with the components of plant β-diversity showed that the spatial replacement of fungi was promoted by plant species turnover, in particular, plant species turnover with functional exchange. In addition, spatial variety of graminoid or forbs species, rather than shrubs, enhanced fungal β-diversity. These results suggest the importance of small-scale factors such as plant-fungal interactions or local environments modified by plants for the fungal community assemblage. The process-based understanding of community dynamics of plants and fungi allows us to predict the ongoing shrub encroachment in the Arctic region, which could weaken the aboveground-belowground synchrony.

Response of the peatland carbon dioxide sink function to future climate change scenarios and water level management

Stress factors such as climate change and drought may switch the role of temperate peatlands from carbon dioxide (CO₂ ) sinks to sources, leading to positive feedback to global climate change. Water level management has been regarded as an important climate change mitigation strategy as it can sustain the natural net CO₂ sink function of a peatland. Little is known about how resilient peatlands are in the face of future climate change scenarios, as well as how effectively water level management can sustain the CO₂ sink function to mitigate global warming. The authors assess the effect of climate change on CO₂ exchange of south Swedish temperate peatlands, which were either unmanaged or subject to water level regulation. Climate chamber simulations were conducted using experimental peatland mesocosms exposed to current and future representative concentration pathway (RCP) climate scenarios (RCP 2.6, 4.5 and 8.5). The results showed that all managed and unmanaged systems under future climate scenarios could serve as CO₂ sinks throughout the experimental period. However, the 2018 extreme drought caused the unmanaged mesocosms under the RCP 4.5 and RCP 8.5 switch from a net CO₂ sink to a source during summer. Surprisingly, the unmanaged mesocosms under RCP 2.6 benefited from the warmer climate, and served as the best sink among the other unmanaged systems. Water level management had the greatest effect on the CO₂ sink function under RCP 8.5 and RCP 4.5, which improved their CO₂ sink capability up to six and two times, respectively. Under the current climate scenario, water level management had a negative effect on the CO₂ sink function, and it had almost no effect under RCP 2.6. Therefore, the researchers conclude that water level management is necessary for RCP 8.5, beneficial for RCP 4.5 and unimportant for RCP 2.6 and the current climate.

Microclimatic Warming Leads to a Decrease in Species and Growth Form Diversity: Insights From a Tropical Alpine Grassland

Due to warming, changes in microclimatic temperatures have shifted plant community structure and dynamics in tundra and alpine regions. The directionality and magnitude of these changes are less known for tropical alpine ecosystems. To understand the likely trajectory of these shifts in the Andes, we conducted a warming experiment in the northern Andes—using open-top chambers (OTC). In this study, we ask (1) how do OTCs affect air and soil temperatures in microclimates of tropical alpine regions, year-round and during the dry season? (2) What are the effects of 7 years of warming on (a) the aboveground biomass (AGB) and (b) the plant taxonomic and growth form diversity? We installed five monitoring blocks in 2012 at ca. 4,200 m asl with 20 OTCs and 50 control plots randomly distributed within each block. We measured AGB, plant community diversity, and growth form diversity between 2014 and 2019. After 7 years of warming, we found significant increases in mean monthly (+0.24°C), daily (+0.16°C), and night air temperatures (+0.33°C) inside the OTCs, and the OTCs intensified microclimatic conditions during the dry season. Additionally, OTCs attenuated extreme temperatures—particularly in the soil—and the number of freezing events. AGB significantly increased in OTCs, and by 2019, it was 27% higher in OTCs than in control. These changes were driven mainly by a progressive increment of tussock grasses such as Calamagrostis intermedia, typical of lower elevations. The increase of tussocks led to a significant decrease in species diversity and evenness inside OTCs, but not in species richness after accounting by sampling time. Furthermore, cushions and herbs decreased inside OTCs. Our results show that experimental warming using OTCs in equatorial regions leads to decreased daily thermal amplitude and night temperatures rather than the level of increase in mean temperatures observed in temperate regions. The increase of tussocks and decrease in diversity of species and growth forms due to prolonged modifications in microclimatic temperature might be a step toward shrub-dominated ecosystems. Further research on this topic would help understand shifts in growth form dominance and the direction and rate of change of the system.

Identification and Isolation Pattern of Globisporangium spp. from a Sanionia Moss Colony in Ny-Ålesund, Spitsbergen Is., Norway from 2006 to 2018

Globisporangium spp. are soil-inhabiting oomycetes distributed worldwide, including in polar regions. Some species of the genus are known as important plant pathogens. This study aimed to clarify the species construction of Globisporangium spp. and their long-term isolation pattern in Sanionia moss in Ny-Ålesund, Spitsbergen Is., Norway. Globisporangium spp. were isolated at two-year intervals between 2006 and 2018 at a Sanionia moss colony, Ny-Ålesund, Spitsbergen Is., Norway. The isolates were obtained by using three agar media and were identified based on sequences of the rDNA-ITS region and cultural characteristics. Most of the Globisporangium isolates obtained during the survey were identified into six species. All six species were grown at 0 °C on an agar plate and used to infect Sanionia moss at 4 and/or 10 °C under an in vitro inoculation test. The total isolation frequency of Globisporangium gradually decreased throughout the survey period. The isolation frequency varied among the six species, and four of the species that showed a high frequency in 2006 were rarely isolated after 2016. The results suggested that Globisporangium inhabiting Sanionia moss in Ny-Ålesund has a unique composition of species and that most of the species reduced their population over the recent decade.