Effects of climate warming on Sphagnum photosynthesis in peatlands depend on peat moisture and species-specific anatomical traits

Host Species-Microbiome Interactions Contribute to Sphagnum Moss Growth Acclimation to Warming

Sphagnum moss is the dominant plant genus in northern peatlands responsible for long-term carbon accumulation. Sphagnum hosts diverse microbial communities (microbiomes), and its phytobiome (plant host + constituent microbiome + environment) plays a key role in nutrient acquisition along with carbon cycling. Climate change can modify the Sphagnum-associated microbiome, resulting in enhanced host growth and thermal acclimation as previously shown in warming experiments. However, the extent of microbiome benefits to the host and the influence of host-microbe specificity on Sphagnum thermal acclimation remain unclear. Here, we extracted Sphagnum microbiomes from five donor species of four peatland warming experiments across a latitudinal gradient and applied those microbiomes to three germ-free Sphagnum species grown across a range of temperatures in the laboratory. Using this experimental system, we test if Sphagnum's growth response to warming depends on the donor and/or recipient host species, and we determine how the microbiome's growth conditions in the field affect Sphagnum host growth across a range of temperatures in the laboratory. After 4 weeks, we found that the highest growth rate of recipient Sphagnum was observed in treatments of matched host-microbiome pairs, with rates approximately 50% and 250% higher in comparison to maximum growth rates of non-matched host-microbiome pairs and germ-free Sphagnum, respectively. We also found that the maximum growth rate of host-microbiome pairs was reached when treatment temperatures were close to the microbiome's native temperatures. Our study shows that Sphagnum's growth acclimation to temperature is partially controlled by its constituent microbiome. Strong Sphagnum host-microbiome species specificity indicates the existence of underlying, unknown physiological mechanisms that may drive Sphagnum's ability to acclimatize to elevated temperatures. Together with rapid acclimation of the microbiome to warming, these specific microbiome-plant associations have the potential to enhance peatland resilience in the face of climate change.

Dual controls of vapour pressure deficit and soil moisture on photosynthesis in a restored temperate bog

Despite only covering ~3 % of the land mass, peatlands store more carbon (C) per unit area than any other ecosystem. This is due to the discrepancy between C fixed by the plants (Gross primary productivity (GPP)) and decomposition. However, this C is vulnerable to frequent, severe droughts and changes in the peatland microclimate. Plants play a vital role in ecosystem C dynamics under drought by mediating water loss to the atmosphere (surface water vapour conductance) and GPP by the presence/absence of stomatal regulation. This is dependent on soil moisture, air temperature, and vapour pressure deficit (VPD). Although there is ample evidence of the role of VPD on stomatal regulation and GPP, the impact of soil moisture is still debated. We addressed this knowledge gap by investigating the role of bulk surface conductance of water vapour in shifts between climatic (Air temperature (Tair), incoming shortwave radiation (SWR) and VPD) and water limitation of GPP in a peat bog in Canada. A causal analysis process was used to investigate how environmental factors influenced GPP. The results suggested that stomatal regulation in response to increased VPD caused the reduction in GPP in 2016 (~2.5 gC m-2 day-1 as opposed to ~3 gC m-2 day-1 in 2018). In contrast, GPP was limited again in 2019 due to the dry surface. This was driven by the relaxed stomatal regulation adopted by the ecosystem following the initial drought to maximise C assimilation. We found the threshold at which surface water decline limited GPP was at about -8 cm water table depth (82.5 % soil moisture). The causal inference corroborated our findings. The temporal variations of water and energy limitation seen in this study could increasingly restrict GPP due to the projected climate warming.

Metallic protection of soil carbon: divergent drainage effects in Sphagnum vs. non-Sphagnum wetlands

The established paradigm assumes that drainage may decrease the vast soil organic carbon (SOC) reservoir in global wetlands. Yet drainage can also promote SOC stabilization by fostering the accrual of metal-bound organic carbon (bound OC) upon oxygen exposure. Here, this emergent mechanism is tested for the first time at a regional scale, using literature data and a nationwide, pairwise survey of drained wetlands across China. We show that long-term (15-55 years) drainage largely increased metallic protection of SOC (bound OC%) in non-Sphagnum wetlands, but consistently decreased bound OC% in Sphagnum wetlands following replacement of the 'rust engineer' Sphagnum by herbaceous plants. Improved SOC stock estimates based on 66 soil profiles reveal that bound OC increases can compensate for the loss of unbound SOC components in non-Sphagnum wetlands with substantial accrual of reactive metals. Metallic stabilization of wetland SOC is hence a widespread but overlooked mechanism that is heavily influenced by vegetational shifts. Incorporating this novel mechanism into models will improve prediction of wetland SOC dynamics under shifting hydrological regimes.

Impact of changing climate on bryophyte contributions to terrestrial water, carbon, and nitrogen cycles

Bryophytes, including the lineages of mosses, liverworts, and hornworts, are the second-largest photoautotroph group on Earth. Recent work across terrestrial ecosystems has highlighted how bryophytes retain and control water, fix substantial amounts of carbon (C), and contribute to nitrogen (N) cycles in forests (boreal, temperate, and tropical), tundra, peatlands, grasslands, and deserts. Understanding how changing climate affects bryophyte contributions to global cycles in different ecosystems is of primary importance. However, because of their small physical size, bryophytes have been largely ignored in research on water, C, and N cycles at global scales. Here, we review the literature on how bryophytes influence global biogeochemical cycles, and we highlight that while some aspects of global change represent critical tipping points for survival, bryophytes may also buffer many ecosystems from change due to their capacity for water, C, and N uptake and storage. However, as the thresholds of resistance of bryophytes to temperature and precipitation regime changes are mostly unknown, it is challenging to predict how long this buffering capacity will remain functional. Furthermore, as ecosystems shift their global distribution in response to changing climate, the size of different bryophyte-influenced biomes will change, resulting in shifts in the magnitude of bryophyte impacts on global ecosystem functions.

Warming affects leaf light use efficiency and functional traits in alpine plants: evidence from a 4-year in-situ field experiment

Introduction

Light use efficiency (LUE) is a crucial determinant of plant productivity, while leaf functional traits directly affect ecosystem functions. However, it remains unclear how climate warming affects LUE and leaf functional traits of dominant species in alpine meadows.

Methods

We conducted a 4-year in-situ field warming experiment to investigate the eco-physiological characteristics for a dominant species (Elymus nutans) and a common species (Potentilla anserina) on the Tibetan Plateau. The leaf traits, photosynthesis and fluorescence characteristics were measured, along with the soil physical-chemical properties associated with the two species.

Results and discussions

Experimental warming increased the leaf LUE, maximum photochemical efficiency, non-photochemical quenching, relative water content and specific leaf area for both species. However, there was a decrease in leaf and soil element content. Different species exhibit varying adaptability to warming. Increasing temperature significantly increased the photosynthetic rate, stomatal conductance, transpiration rate, total water content, and specific leaf volume of E. nutans; however, all these traits exhibited an opposite trend in P. anserina. Warming has a direct negative impact on leaf LUE and an indirectly enhances LUE through its effects on leaf traits. The impact of warming on plant photosynthetic capacity is primarily mediated by soil nutrients and leaf traits. These results indicate that the two different species employ distinct adaptive strategies in response to climate change, which are related to their species-specific variations. Such changes can confer an adaptive advantage for plant to cope with environmental change and potentially lead to alterations to ecosystem structure and functioning.

Temperature and CO2 interactively drive shifts in the compositional and functional structure of peatland protist communities

Microbes affect the global carbon cycle that influences climate change and are in turn influenced by environmental change. Here, we use data from a long-term whole-ecosystem warming experiment at a boreal peatland to answer how temperature and CO2 jointly influence communities of abundant, diverse, yet poorly understood, non-fungi microbial Eukaryotes (protists). These microbes influence ecosystem function directly through photosynthesis and respiration, and indirectly, through predation on decomposers (bacteria and fungi). Using a combination of high-throughput fluid imaging and 18S amplicon sequencing, we report large climate-induced, community-wide shifts in the community functional composition of these microbes (size, shape, and metabolism) that could alter overall function in peatlands. Importantly, we demonstrate a taxonomic convergence but a functional divergence in response to warming and elevated CO2 with most environmental responses being contingent on organismal size: warming effects on functional composition are reversed by elevated CO2 and amplified in larger microbes but not smaller ones. These findings show how the interactive effects of warming and rising CO2 levels could alter the structure and function of peatland microbial food webs-a fragile ecosystem that stores upwards of 25% of all terrestrial carbon and is increasingly threatened by human exploitation.

More is not always better: peat moss mixtures slightly enhance peatland stability

Terrestrial wetland ecosystems challenge biodiversity-ecosystem function theory, which generally links high species diversity to stable ecosystem functions. An open question in ecosystem ecology is whether assemblages of co-occurring peat mosses contribute to the stability of peatland ecosystem processes. We conducted a two-species (Sphagnum cuspidatum, Sphagnum medium) replacement series mesocosm experiment to evaluate the resistance, resilience, and recovery rates of net ecosystem CO2 exchange (NEE) under mild and deep water table drawdown. Our results show a positive effect of mild water table drawdown on NEE with no apparent role for peat moss mixture. Our study indicates that the carbon uptake capacity by peat moss mixtures is rather resilient to mild water table drawdown, but seriously affected by deeper drought conditions. Co-occurring peat moss species seem to enhance the resilience of the carbon uptake function (i.e. ability of NEE to return to pre-perturbation levels) of peat moss mixtures only slightly. These findings suggest that assemblages of co-occurring Sphagnum mosses do only marginally contribute to the stability of ecosystem functions in peatlands under drought conditions. Above all, our results highlight that predicted severe droughts can gravely affect the sink capacity of peatlands, with only a small extenuating role for peat moss mixtures.

Sphagnum mosses, the impact of disturbances and anthropogenic management actions on their ecological role in CO2 fluxes generated in peatland ecosystems

Mosses of the genus Sphagnum are the dominant vegetation in most pristine peatlands in temperate and high-latitude regions. They play a crucial role in carbon sequestration, being responsible for ca. 50% of carbon accumulation through their active participation in peat formation. They have a significant influence on the dynamics of CO2 emissions due to an efficient maximum potential photosynthetic rate, lower respiration rates, and the production of a recalcitrant litter whose decomposition is gradual. However, various anthropogenic disturbances and land use management actions that favor its reestablishment have the potential to modify the dynamics of these CO2 emissions. Therefore, the objective of this review is to discuss the role of Sphagnum in CO2 emissions generated in peatland ecosystems, and to understand the impacts of anthropogenic practices favorable and detrimental to Sphagnum on these emissions. Based on our review, increased Sphagnum cover reduces CO2 emissions and fosters C sequestration, but drainage transforms peatlands dominated by Sphagnum into a persistent source of CO2 due to lower gross primary productivity of the moss and increased respiration rates. Sites with moss removal used as donor material for peatland restoration emit twice as much CO2 as adjacent undisturbed natural sites, and those with commercial Sphagnum extraction generate almost neutral CO2 emissions, yet both can recover their sink status in the short term. The reintroduction of fragments and natural recolonization of Sphagnum in transitional peatlands, can reduce emissions, recover, or increase the CO2 sink function in the short and medium term. Furthermore, Sphagnum paludiculture is seen as a sustainable alternative for the use of transitional peatlands, allowing moss production strips to become CO2 sink, however, it is necessary to quantify the emissions of all the components of the field of production (ditches, causeway), and the biomass harvested from the moss to establish a final closing balance of C.

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.

Will climate change cause the global peatland to expand or contract? Evidence from the habitat shift pattern of Sphagnum mosses

Peatlands play a crucial role in the global carbon cycle. Sphagnum mosses (peat mosses) are considered to be the peatland ecosystem engineers and contribute to the carbon accumulation in the peatland ecosystems. As cold-adapted species, the dominance of Sphagnum mosses in peatlands will be threatened by climate warming. The response of Sphagnum mosses to climate change is closely related to the future trajectory of carbon fluxes in peatlands. However, the impact of climate change on the habitat suitability of Sphagnum mosses on a global scale is poorly understood. To predict the potential impact of climate change on the global distribution of Sphagnum mosses, we used the MaxEnt model to predict the potential geographic distribution of six Sphagnum species that dominate peatlands in the future (2050 and 2070) under two greenhouse gas emission scenarios (SSP1-2.6 and SSP5-8.5). The results show that the mean temperature of the coldest quarter, precipitation of the driest month, and topsoil calcium carbonate are the main factors affecting the habitat availability of Sphagnum mosses. As the climate warms, Sphagnum mosses tend to migrate northward. The suitable habitat and abundance of Sphagnum mosses increase extensively in the high-latitude boreal peatland (north of 50°N) and decrease on a large scale beyond the high-latitude boreal peatland. The southern edge of boreal peatlands would experience the greatest decline in the suitable habitat and richness of Sphagnum mosses with the temperature rising and would be a risk area for the transition from carbon sink to carbon source. The spatial-temporal pattern changes of Sphagnum mosses simulated in this study provide a reference for the development of management and conservation strategies for Sphagnum bogs.

Seasonal climate drivers of peak NDVI in a series of Arctic peatlands

Changes in plant cover and productivity are important in driving Arctic soil carbon dynamics and sequestration, especially in peatlands. Warming trends in the Arctic are known to have resulted in changes in plant productivity, extent and community composition, but more data are still needed to improve understanding of the complex controls and processes involved. Here we assess plant productivity response to climate variability between 1985 and 2020 by comparing peak growing season NDVI (Normalised Difference Vegetation Index data from Landsat 5 and 7), to seasonal-average weather data (temperature, precipitation and snow-melt timing) in nine locations containing peatlands in high- and low-Arctic regions in Europe and Canada. We find that spring (correlation 0.36 for peat dominant and 0.39 for mosaic; MLR coefficient 0.20 for peat, 0.29 for mosaic), summer (0.47, 0.42; 0.18, 0.17) and preceding-autumn (0.35, 0.25; 0.33, 0.27) temperature are linked to peak growing season NDVI at our sites between 1985 and 2020, whilst spring snow melt timing (0.42, 0.45; 0.25, 0.32) is also important, and growing season water availability is likely site-specific. According to regression trees, a warm preceding autumn (September-October-November) is more important than a warm summer (June-July-August) in predicting the highest peak season productivity in the peat-dominated areas. Mechanisms linked to soil processes may explain the importance of previous-Autumn conditions on productivity. We further find that peak productivity increases in these Arctic peatlands are comparable to those in the surrounding non-peatland-dominant vegetation. Increased productivity in and around Arctic peatlands suggests a potential to increased soil carbon sequestration with future warming, but further work is needed to test whether this is evident in observations of recent peat accumulation and extent.

Draft Metagenome Sequences of the Sphagnum (Peat Moss) Microbiome from Ambient and Warmed Environments across Europe

We present 49 metagenome assemblies of the microbiome associated with Sphagnum (peat moss) collected from ambient, artificially warmed, and geothermally warmed conditions across Europe. These data will enable further research regarding the impact of climate change on plant-microbe symbiosis, ecology, and ecosystem functioning of northern peatland ecosystems.

Impact of climate change-induced alterations in peatland vegetation phenology and composition on carbon balance

Global climate is changing faster than humankind has ever experienced. Model-based predictions of future climate are becoming more complex and precise, but they still lack crucial information about the reaction of some important ecosystems, such as peatlands. Peatlands belong to one of the largest carbon stores on the Earth. They are mostly distributed in high latitudes, where the temperature rises faster than in the other parts of the planet. Warmer climate and changes in precipitation patterns cause changes in the composition and phenology of peatland vegetation. Peat mosses are becoming less abundant, vascular plants cover is increasing, and the vegetation season and phenophases of vascular plants start sooner. The alterations in vegetation cause changes in the carbon assimilation and release of greenhouse gases. Therefore, this article reviews the impact of climate change-induced alterations in peatland vegetation phenology and composition on future climate and the uncertainties that need to be addressed for more accurate climate prediction.

Assessing leached TOC, nutrients and phenols from peatland soils after lab-simulated wildfires: Implications to source water protection

Pollutant leaching from wildfire-impacted peatland soils (peat) is well-known, but often underestimated when considering boreal ecosystem source water protection and when treating source waters to provide clean drinking water. Burning peat impacts its physical properties and chemical composition, yet the consequences of these transformations to source water quality through pollutant leaching has not been studied in detail. We combusted near-surface boreal peat under simulated peat smoldering conditions at two temperatures (250 °C and 300 °C) and quantified the concentrations of the leached carbon, nutrients and phenols from 5 g peat L^-1 reverse osmosis (RO) water suspensions over a 2-day leaching period. For the conditions studied, measured water quality parameters exceeded US surface water guidelines and even exceeded EU and Canadian wastewater/sewer discharge limits including chemical oxygen demand (COD) (125 mg/L), total nitrogen (TN) (15 mg/L), and total phosphorus (TP) (2 mg/L). Phenols were close to or higher than the suggested water supply standard established by US EPA (1 mg/L). Leached carbon, nitrogen and phosphorus mainly came from the organic fraction of peats. Heating peats to 250 °C promoted the leaching of carbon-related pollutants, whereas heating to 300 °C enhanced the leaching of nutrients. Post-heated peats leached higher loads of pollutants in water than pre-heated peats, suggesting that fire-damaged boreal peats may be a critical but underappreciated source of water pollution. A simplified Partial Least Squares (PLS) model based on other easily measured parameters provided a simple method for determining the extent of COD and phenolic pollution in bulk water, relevant for water and wastewater treatment plants. Conclusions from this lab study indicate the need for field measurements of aquatic pollutants downstream of peatland watersheds post-fire as well as increased monitoring and treatment of potable water sources for leachable micropollutants in fire-dominated forested peatlands.

Two Mechanisms Drive Changes in Boreal Peatland Photosynthesis Following Long-Term Water Level Drawdown: Species Turnover and Altered Photosynthetic Capacity

Climate change and the related increases in evapotranspiration threaten to make northern peatlands drier. The carbon sink function in peatlands is based on the delicate balance between the photosynthesis and decomposition. However, little is known about how existing and invading plant species will photosynthesize under drier conditions. The aim of this study is to quantify the long-term consequences of climate change-induced drying for peatland photosynthesis in the level of individual species and vegetation community. We measured the species-level photosynthesis of vascular plants and mosses characteristic for the three peatland types (rich fen, poor fen, bog) within a 16-year water level drawdown (WLD) experiment. Measurements were made in the laboratory from mesocosms collected from the field within the same day. We applied nonlinear mixed-effects models to test the impact of WLD on hyperbolic photosynthetic light response curve parameters. The model was then used to upscale photosynthesis to site-level. WLD impacted site-level photosynthesis through two mechanisms: species turnover and changes in species-level photosynthesis rate. The rich fen was the most sensitive and underwent major changes through both mechanisms; the vascular plant community shifted to woody plant dominance with higher rate of photosynthesis than the pre-treatment vegetation, and the rate of species-level photosynthesis increased significantly. The bog had a stable plant community with little change in photosynthesis, while the poor fen was an intermediate of the three peatland types. Our results suggest that vascular plants are the main drivers of site-level productivity changes, while mosses are more resistant to change. The change seems proportional to the availability of mineral nutrients, with higher nutrient status supporting vascular plant expansion.

Physiological and Shoot Growth Responses of Abies holophylla and Abies koreana Seedlings to Open-Field Experimental Warming and Increased Precipitation

Projected changes in temperature and precipitation in mid-latitude wet regions are expected to significantly affect forest ecosystems. We studied the physiological and shoot growth responses of Abies holophylla and Abies koreana seedlings to warming (3 °C above ambient temperature) and increased precipitation (irrigation with 40% of rainfall) treatments under open-field conditions. The physiological parameters, quantified by the net photosynthetic rate, transpiration rate, stomatal conductance, and total chlorophyll content, were monitored from July to October 2018. Shoot growth (i.e., root collar diameter and height) was assessed in August and December 2018. Irrespective of the treatments, the physiological parameters of both species decreased from July to August under warming treatment due to heat stress before recovering in September and October. Warming alone (W) and warming along with increased precipitation (W*P) decreased the physiological activities of both species in July, August, and September, with more pronounced effects on A. koreana compared with A. holophylla. Increased precipitation resulted in the increased chlorophyll content of both species in October. Shoot growth was not generally affected by the treatments, except for a subtle reduction in height under W*P for A. koreana. A. holophylla had consistently higher values for the physiological parameters and shoot growth than A. koreana. Our results indicate that the physiological activities of the Abies species could be seriously reduced under climate change, with a more severe impact on A. koreana. Among the two species, A. holophylla appears to be a more robust candidate for future forest planting.

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.

Impact of warming and reduced precipitation on morphology and chlorophyll concentration in peat mosses (Sphagnum angustifolium and S. fallax)

Peatlands are one of the most important ecosystems due to their biodiversity and abundant organic compounds; therefore, it is important to observe how different plant species in peatlands react to changing environmental conditions. Sphagnum spp. are the main component of peatlands and are considered as the creator of conditions favorable for carbon storage in the form of peat. Sphagnum angustifolium and Sphagnum fallax are taxonomically very close species. To examine their adaptability to climate change, we studied the morphology and pigment content of these two species from environmental manipulation sites in Poland, where the environment was continuously manipulated for temperature and precipitation. The warming of peat was induced by using infrared heaters, whereas total precipitation was reduced by a curtain that cuts the nighttime precipitation. Morphology of S. angustifolium stayed under climate manipulation relatively stable. However, the main morphological parameters of S. fallax were significantly affected by precipitation reduction. Thus, this study indicates S. angustifolium is better adapted in comparison to S. fallax for drier and warmer conditions.

Testate amoebae taxonomy and trait diversity are coupled along an openness and wetness gradient in pine-dominated Baltic bogs

Sphagnum peatlands host a high abundance of protists, especially testate amoebae. Here, we designed a study to investigate the functional diversity of testate amoebae in relation to wetness and forest cover in Baltic bogs. We provided new data on the influence of openness/wetness gradient on testate amoebae communities, showing significant differences in selected testate amoebae (TA) traits. Three key messages emerged from our investigations: 1) we recorded an effect of peatland surface openness on testate amoebae functional traits that led us to accept the hypothesis that TA traits differ according to light intensity and hydrology. Mixotrophic species were recorded in high relative abundance in open plots, whereas they were nearly absent in forested sites; 2) we revealed a hydrological threshold for the occurrence of mixotrophic testate amoebae that might be very important in terms of peatland functioning and carbon sink vs. source context; and 3) mixotrophic species with organic tests were nearly absent in forested sites that were dominated by heterotrophic species with agglutinated or idiosomic tests. An important message from this study is that taxonomy of TA rather indicates the hydrological gradient whereas traits of mixotrophs the openness gradient.