Precipitation Variability Affects Aboveground Biomass Directly and Indirectly via Plant Functional Traits in the Desert Steppe of Inner Mongolia, Northern China

Plant Functional Traits, but Not Community Composition, Are Affected by Summer Precipitation and Herbivory in an Old-Field Ecosystem

Both precipitation and herbivores can independently control plant community composition and ecosystem function. However, few studies have experimentally examined the potential interactive effects of altered precipitation and herbivores on plant communities and plant traits. Here, we manipulated summer precipitation and insect presence in an old-field ecosystem and quantified their interactive effects on plant community structure and functional traits. Overall, the effect of an insect herbivore on the plant community was contingent on the precipitation treatment. There were no experimental effects on total plant biomass or plant species richness, but grass biomass was higher in the absence of insect herbivores only in reduced summer precipitation plots. Furthermore, plant functional diversity and the community-averaged trends of several plant functional traits related to resource use and herbivore resistance varied systematically with reduced precipitation and insect presence. We demonstrate that the effect of reduced precipitation on plant biomass, functional diversity, and the community-averaged trends of plant functional traits can be mediated by the presence of insects. Our findings further suggest that the functional traits of the common plant species in the community are the most affected by the combined manipulation of altered summer precipitation and insect presence.

Differential responses of plant and microbial respiration to extreme precipitation and drought during spring and summer in the Eurasian meadow steppe

Increasing extreme precipitation and drought events along changes in their seasonal patterns due to climate change are expected to have profound consequences for carbon cycling. However, how these climate extremes impact ecosystem respiration (Reco) and whether these impacts differ between seasons remain unclear. Here, we reveal the responses of Reco and its components to extreme precipitation and drought in spring and summer by conducting a five-year manipulative experiment in a temperate meadow steppe. Based on a 5-year average, the seasonal mean values (±SE) of Reco, Rh, Rroot, Rabg and Rplant significantly increased (p < 0.01) under both extreme precipitation treatments: wet spring (WSP) and wet summer (WSU), and significantly decreased (p < 0.01) under both extreme drought treatments: dry spring (DSP) and dry summer (DSU), except in Rabg under DSU, which remained comparable to the control. The sensitivity of Reco, Rh, Rroot and Rplant to extreme precipitation was significantly higher in spring than in summer. On average, Rplant was the primary contributor of Reco, accounting for 37.18% and 38.31% of the total across all its components under WSP and WSU, respectively during the growing season over the five study years. Moreover, linear models revealed Rplant explained 87% of the variance in Reco. Our findings indicate that future changes in precipitation events, particularly extreme precipitation may lead to increased carbon release from ecosystems, largely driven by enhanced plant respiration rather than microbial respiration. However, due to this study focused solely on respiration and did not measure photosynthesis, the findings represent only the carbon release processes and do not account for potential carbon uptake by plants during the same conditions. These emergent identified contribution to ecosystem respiration provide valuable insights for improving model benchmarks to better predict ecosystem respiration responses to extreme climate in specified season.

Precipitation in July maximizes total above-ground productivity of the desert steppe in Inner Mongolia, China

Precipitation distribution during the growing season and interannual precipitation variation may have significant impacts on grassland ecosystem productivity at the site level. To explore the effect of the distribution of precipitation on plant communities in the Inner Mongolian desert steppe dominated by Stipa breviflora, we analyzed monthly precipitation patterns during the growing season (May-October) over the past 60 years (1961-2020) and identified four major precipitation distribution patterns. These included the concentrated precipitation during July (TΛ7), August (TΛ8), and during the early and late growth stages. However, with precipitation being scarce during the boom (TM), the distribution resembled a normal distribution (T∩). Field experiments simulating the four distributions were conducted from May to October 2021. The results showed that the effects of the distribution of precipitation on plant species, diversity, and abundance were not significant; only the Pielou evenness showed a significant effect after July. The total above-ground net primary productivity (ANPP) of TΛ7 was 55.4% higher than those of the other three patterns, whereas the differences among the other three precipitation distributions were not significant. The annual forb Neopallasia pectinate was the primary contributor to the increased ANPP of TΛ7. These results suggest that the S. breviflora desert steppe achieved maximum productivity when the precipitation reached 41.6% of the annual average during July and satisfied the basic plant growth requirements during other months. This study emphasizes the implementation of management measures (irrigation or artificial precipitation) for maximizing forage yield and forecasting the plant composition in desert steppes.

Rainfall fluctuation causes the invasive plant Prosopis juliflora to adapt ecophysiologically and change phenotypically

Understanding the impact of rainfall variability on the ecophysiology of invasive plants in tropical grasslands is crucial for sustainable ecosystem management. Climate change alters rainfall patterns, which, in turn, may influence the functional traits and physiological responses of plants. Recent studies have explored how fluctuating precipitation affects plant growth and broader ecological dynamics. In this study, we examined these effects on Prosopis juliflora under three different rainfall treatments using rainout shelters: low rainfall (LR, 500 mm, 50% less than ambient), normal rainfall (NR, 1000 mm, representing average ambient rainfall), and high rainfall (HR, 1400 mm, 40% more than ambient). Each shelter was divided into three replicate plots (2 m x 2 m) in a randomized block design. P. juliflora seedlings (20 seedlings per subplot) were transplanted into each subplot within a 4m2 area, with a 0.5 m distance between each plant, and data were collected one year after plot establishment (2020). The physiological parameters measured included leaf traits, growth metrics such as biomass, height, diameter, photosynthetic rate, leaf area (LA), specific leaf area (SLA), leaf carbon (LC), the leaf carbon-to-nitrogen (C/N) ratio, and the root-to-shoot ratio. These parameters showed significant positive responses to changes in precipitation i.e. increase with the increase in rainfall. However, water use efficiency (WUE), leaf nitrogen (LN), leaf dry matter content (LDMC), and root length (RL) showed negative responses i.e. decrease with the increase in rainfall and were highest in the LR plots. Our findings suggest that the ecophysiology and functional traits of P. juliflora are strongly influenced by rainfall variability. The species exhibits considerable phenotypic plasticity, thriving in both drought and elevated precipitation conditions. This adaptability has important implications for its invasive potential and the overall functioning of ecosystems under shifting climatic conditions.

Precipitation-induced biomass enhancement and differential allocation in Inner Mongolia's herbaceous and shrub communities

Changes in precipitation patterns induced by global climate change have profound implications for the structure and function of grassland ecosystems. However, the relationship between plant diversity and ecosystem function across different grassland types, particularly those with varying plant compositions and dominant species, remains inadequately understood. To address this knowledge gap, a five-year experimental manipulation of precipitation was conducted within herbaceous and shrub communities in the desert grasslands of Inner Mongolia. We found that increased precipitation significantly enhances aboveground biomass (AGB), belowground biomass (BGB), and community total biomass (CTB) in both herbaceous and shrub communities. In herbaceous communities, increased precipitation led to a disproportionate increase in both aboveground and belowground biomass, supporting the optimal allocation hypothesis. Structural equation modeling (SEM) further elucidated that precipitation regulates AGB and CTB through species richness and functional traits in herbaceous communities. In shrub communities, precipitation influences AGB, BGB, and CTB by affecting species richness and soil water content. This study highlights the critical role of precipitation in shaping biomass dynamics and allocation strategies within herbaceous and shrub communities in desert steppe of Inner Mongolia. These findings provide essential insights into the potential responses of desert grassland ecosystems to ongoing climate change.

Plant size traits are key contributors in the spatial variation of net primary productivity across terrestrial biomes in China

Understanding the spatial variability of ecosystem functions is an important step forward in predicting changes in ecosystems under global transformations. Plant functional traits are important drivers of ecosystem functions such as net primary productivity (NPP). Although trait-based approaches have advanced rapidly, the extent to which specific plant functional traits are linked to the spatial diversity of NPP at a regional scale remains uncertain. Here, we used structural equation models (SEMs) to disentangle the relative effects of abiotic variables (i.e., climate, soil, nitrogen deposition, and human footprint) and biotic variables (i.e., plant functional traits and community structure) on the spatial variation of NPP across China and its eight biomes. Additionally, we investigated the indirect influence of climate and soil on the spatial variation of NPP by directly affecting plant functional traits. Abiotic and biotic variables collectively explained 62.6 % of the spatial differences of NPP within China, and 28.0 %-69.4 % across the eight distinct biomes. The most important abiotic factors, temperature and precipitation, had positive effects for NPP spatial variation. Interestingly, plant functional traits associated with the size of plant organs (i.e., plant height, leaf area, seed mass, and wood density) were the primary biotic drivers, and their positive effects were independent of biome type. Incorporating plant functional traits improved predictions of NPP by 6.7 %-50.2 %, except for the alpine tundra on the Qinghai-Tibet Plateau. Our study identifies the principal factors regulating NPP spatial variation and highlights the importance of plant size traits in predictions of NPP variation at a large scale. These results provide new insights for involving plant size traits in carbon process models.

Beach-cast seagrass wrack: A natural marine resource improving the establishment of dune plant communities under a changing climate

Seagrass wrack plays multiple ecological roles in coastal habitats but is often removed from beaches and used for economical processing, neglecting its potential role in sustaining dune plant establishment under changing climate scenarios. Rainwater shortage is a major stress for seedlings and reduced precipitations are expected in some coastal areas. We investigated in mesocosm how wrack influenced seedling performance of Cakile maritima, Thinopyrum junceum, and Calamagrostis arenaria under current and reduced precipitation. We also assessed wrack water holding capacity and leachate chemical/physical properties. Wrack stimulated seedling growth while reduced precipitation decreased root development. Wrack mitigated the effects of reduced precipitation on T. junceum and C. arenaria biomass. Wrack retained water up to five-fold its weight, increased water pH, conductivity, and nutrient content. Wrack promotes dune colonization by vegetation even under rainwater shortage. Thus, the maintenance of this natural resource on beaches is critical for improving dune resilience against climate changes.

The influence of precipitation timing and amount on soil microbial community in a temperate desert ecosystem

Introduction

Global climate change may lead to changes in precipitation patterns. This may have a significant impact on the microbial communities present in the soil. However, the way these communities respond to seasonal variations in precipitation, particularly in the context of increased precipitation amounts, is not yet well understood.

Methods

To explore this issue, a five-year (2012-2016) field study was conducted at the northeast boundary of the Ulan Buh Desert, examining the effects of increased precipitation during different periods of the growing season on both bacterial and fungal communities. The study included five precipitation pattern treatments: a control group (C), as well as groups receiving 50 and 100% of the local mean annual precipitation amount (145 mm) during either the early growing season (E50 and E100) or the late growing season (L50 and L100). The taxonomic composition of the soil bacterial and fungal communities was analyzed using Illumina sequencing.

Results

After 5 years, the bacterial community composition had significantly changed in all treatment groups, with soil bacteria proving to be more sensitive to changes in precipitation timing than to increased precipitation amounts within the desert ecosystem. Specifically, the alpha diversity of bacterial communities in the late growing season plots (L50 and L100) decreased significantly, while no significant changes were observed in the early growing season plots (E50 and E100). In contrast, fungal community composition remained relatively stable in response to changes in precipitation patterns. Predictions of bacterial community function suggested that the potential functional taxa in the bacterial community associated with the cycling of carbon and nitrogen were significantly altered in the late growing season (L50 and L100).

Discussion

These findings emphasize the importance of precipitation timing in regulating microbial communities and ecosystem functions in arid regions experiencing increased precipitation amounts.

Intraspecific trait variation and adaptability of Stipa krylovii: Insight from a common garden experiment with two soil moisture treatments

Understanding patterns of intraspecific trait variation can help us understand plant adaptability to environmental changes. To explore the underlying adaptation mechanisms of zonal plant species, we selected seven populations of Stipa krylovii, a dominant species in the Inner Mongolia Steppe of China, and evaluated the effects of phenotypic plasticity and genetic differentiation, the effects of climate variables on population trait differentiation, and traits coordinated patterns under each soil moisture treatment. We selected seeds from seven populations of S. krylovii in the Inner Mongolia Steppe, China, and carried out a soil moisture (2) × population origin (7) common garden experiment at Tianjin City, China, and measured ten plant traits of S. krylovii. General linear analyses were used to analyze how soil moisture and population origin affected each trait variation, Mantel tests were used to analyze population trait differentiation-geographic distance (or climatic difference) relationships, regression analyses were used to evaluate trait-climatic variable relationships, and plant trait networks (PTNs) were used to evaluate traits coordinated patterns. Both soil moisture and population origin showed significant effects on most of traits. Aboveground biomass, root-shoot ratio, leaf width, specific leaf area, and leaf nitrogen (N) content were significantly correlated with climate variables under the control condition. Specific leaf area and leaf N content were significantly correlated with climate variables under the drought condition. By PTNs, the hub trait(s) was plant height under the control condition and were aboveground biomass, root length, and specific leaf area under the drought condition. This study indicates that both phenotypic plasticity and genetic differentiation can significantly affect the adaptability of S. krylovii. In addition, soil moisture treatments show significant effects on trait-climate relationships and traits coordinated patterns. These findings provide new insights into the adaptive mechanisms of zonal species in the semiarid grassland region.

Precipitation and temperature regulate species diversity, plant coverage and aboveground biomass through opposing mechanisms in large-scale grasslands

INTRODUCTION

Although the relationships between species diversity and aboveground biomass (AGB) are highly debated in grassland ecosystems, it is not well understood how climatic factors influence AGB directly and indirectly via plant coverage and species diversity in large-scale grasslands along a topographic gradient. In doing so, we hypothesized that climatic factors would regulate plant coverage, species diversity and AGB due to maintaining plant metabolic and ecological processes, but the relationship of plant coverage with AGB would be stronger than species diversity due to covering physical niche space.

METHODS

To test the proposed hypothesis, we collected data for calculations of species richness, evenness, plant coverage and AGB across 123 grassland sites (i.e., the mean of 3 plots in each site) dominated by Leymus chinensis in northern China. We used a structural equation model for linking the direct and indirect effects of topographic slope, mean annual precipitation and temperature on AGB via plant coverage, species richness, and evenness through multiple complex pathways.

RESULTS

We found that plant coverage increased AGB, but species evenness declined AGB better than species richness. Topographic slope influenced AGB directly but not indirectly via plant coverage and species diversity, whereas temperature and precipitation increased with increasing topographic slope. Regarding opposing mechanisms, on the one hand, precipitation increased AGB directly and indirectly via plant coverage as compared to species richness and evenness. On the other hand, temperature declined AGB indirectly via plant coverage but increased via species evenness as compared to species richness, whereas the direct effect was negligible.

DISCUSSION

Our results show that niche complementarity and selection effects are jointly regulating AGB, but these processes are dependent on climatic factors. Plant coverage promoted the coexistence of species but depended greatly on precipitation and temperature. Our results highlight that precipitation and temperature are two key climatic drivers of species richness, evenness, plant coverage and AGB through complex direct and indirect pathways. Our study suggests that grasslands are sensitive to climate change, i.e., a decline in water availability and an increase in atmospheric heat. We argue that temperature and precipitation should be considered in grassland management for higher productivity in the context of both plant coverage and species diversity which underpin animals and human well-being.

Stand structure adjustment influences the biomass allocation in naturally generated Pinus massoniana seedlings through environmental factors

The natural regeneration of seedlings is a key factor for forest succession. Nevertheless, studies explaining the mechanism of growth and biomass allocation in regenerated seedlings after disturbance are lacking. Therefore, we measured the growth, biomass accumulation, and biomass allocation in current-age seedlings of Pinus massoniana after selective logging (logging of competitive trees, LCT; logging of inferior trees, LIT; and unlogged control, CK), and established structural equation models (SEMs) among the spatial structure characteristic indexes of the stand, environmental factors, and biomass allocation in different organs. As compared to the CK, the mingling index (M), uniform angle index (W), opening degree (O), soil organic carbon (SOC), available nitrogen (SAN), available phosphorus (SAP), available potassium (SAK), and bulk density (SBD) significantly increased (p < 0.05), while the competition index (CI) and neighborhood comparison (U) significantly decreased after logging (p < 0.05). After the LCT, seedling branch biomass improved, with an increase in the ground-diameter, crown-root ratio, and seedling quality index. More biomass was allocated to foliage and roots by an increase in the height and height-diameter ratio under the LIT. In the CK, increasing stem biomass helped the seedlings absorb and utilize more light. The Pearson correlation coefficient showed that biomass allocation to organs was independent, and seedlings adopted the strategies of heterogeneous adaptation and growth, thereby resulting in the separation of the allocation patterns among the organs. As per the redundancy analysis (RDA), CI was the main factor in biomass allocation. Environmental factors had direct effects on biomass allocation to organs, while the stand spatial structure characteristic indexes had indirect effects on biomass allocation based on SEMs. In summary, the LCT had significant, albeit indirect, effects on SOC, SAN, and SBD by reducing the CI for the regeneration and growth of seedlings in the stand, which was of great significance to the sustainable development of the forest stand of P. massoniana.

Intra-annual growing season climate variability drives the community intra-annual stability of a temperate grassland by altering intra-annual species asynchrony and richness in Inner Mongolia, China

Understanding the factors that regulate the functioning of our ecosystems in response to environmental changes can help to maintain the stable provisioning of ecosystem services to mankind. This is especially relevant given the increased variability of environmental conditions due to human activities. In particular, maintaining a stable production and plant biomass during the growing season (intra-annual stability) despite pervasive and directional changes in temperature and precipitation through time can help to secure food supply to wild animals, livestock, and humans. Here, we conducted a 29-year field observational study in a temperate grassland to explore how the intra-annual stability of primary productivity is influenced by biotic and abiotic variables through time. We found that intra-annual precipitation variability in the growing season indirectly influenced the community intra-annual biomass stability by its negative effect on intra-annual species asynchrony. While the intra-annual temperature variability in the growing season indirectly altered community intra-annual biomass stability through affecting the intra-annual species richness. At the same time, although the intra-annual biomass stability of the dominant species and the dominant functional group were insensitive to climate variability, they also promoted the stable community biomass to a certain extent. Our results indicate that ongoing intra-annual climate variability affects community intra-annual biomass stability in the temperate grassland, which has important theoretical significance for us to take active measures to deal with climate change.

Climatic Factors Determine the Distribution Patterns of Leaf Nutrient Traits at Large Scales

Leaf nutrient content and its stoichiometric relationships (N/P ratio) are essential for photosynthesis and plant growth and development. Previous studies on leaf nutrient-related functional traits have mainly focused on the species level and regional scale, but fewer studies have investigated the distribution patterns of the leaf N and P contents (LN, LP) and N/P ratios (N/P) in communities and their controlling factors at a large scale; therefore, we used LN, LP, and N/P data at 69 sites from 818 forests in China. The results showed significant differences (p < 0.05) in the LN, LP, and N/P at different life forms (tree, shrub, and herb). Neither LN, LP, nor N/P ratios showed significant patterns of latitudinal variation. With the increase in temperature and rainfall, the LN, LP, and leaf nutrient contents increased significantly (p < 0.001). Across life forms, LN at different life forms varied significantly and was positively correlated with soil P content (p < 0.001). The explanatory degree of climatic factors in shaping the spatial variation patterns of LN and N/P was higher than that of the soil nutrient factors, and the spatial variation patterns of the leaf nutrient traits of different life forms were shaped by the synergistic effects of climatic factors and soil nutrient factors.

Species richness and asynchrony maintain the stability of primary productivity against seasonal climatic variability

The stability of grassland communities informs us about the ability of grasslands to provide reliable services despite environmental fluctuations. There is large evidence that higher plant diversity and asynchrony among species stabilizes grassland primary productivity against interannual climate variability. Whether biodiversity and asynchrony among species and functional groups stabilize grassland productivity against seasonal climate variability remains unknown. Here, using 29-year monitoring of a temperate grassland, we found lower community temporal stability with higher seasonal climate variability (temperature and precipitation). This was due to a combination of processes including related species richness, species asynchrony, functional group asynchrony and dominant species stability. Among those processes, functional group asynchrony had the strongest contribution to community compensatory dynamics and community stability. Based on a long-term study spanning 29 years, our results indicate that biodiversity and compensatory dynamics a key for the stable provision of grassland function against increasing seasonal climate variability.