Grassland Ecosystem Function Research Articles

Detecting and attributing the impact of human activities on grassland aboveground biomass in China's Loess Plateau

Human activities significantly influence grassland ecosystem functions, particularly plant biomass. However, the direction and magnitude of these effects remain insufficiently explored. Herein, we quantitively assessed both the positive and negative effects of various human activities on grassland aboveground biomass (AGB) in China's Loess Plateau from 2000 to 2022. The results indicated that the magnitudes of positive effects increased by 0.29 g m−2 per year, whereas the negative effects decreased by 0.31 g m−2 per year. Spatially, 32 % of the grasslands experienced significant positive effects, whereas the rest grasslands faced negative effects. Notably, only 20 % of the areas with negative effects showed worsening trends mainly due to ecological restoration, sustainable agriculture, and population migration. Agricultural production activities and population changes emerged as dominant factors, with some activities, like livestock farming, exhibiting dual effects (i.e., positive and negative effects) on AGB. These findings underscore the complexity of human activities in affecting the grassland production function and highlight the necessity for balanced management strategies to sustain grassland productivity and resilience.

Past, Present, and Future of Forbs in Old-Growth Tropical and Subtropical Grasslands

Forbs are important contributors to species diversity and ecosystem functions in low-latitude grasslands, where they support diverse herbivore communities and millions of people. Native forb assemblages tolerate disturbances and physiological stressors (fire, herbivory, drought, and frost) that together have shaped their exceptional functional diversity. Yet, compared to trees and grasses, forbs have received much less attention in grassland studies until recently. Here, we review forb-centric literature to illustrate that land conversion and responsible management of fire and herbivory are crucial to maintaining forb diversity. Management practices promoting forb diversity offer (a) high-quality food items and medicinal resources that support rural livelihoods and animal diversity (from wild ungulates and livestock to fossorial rodents and insects), including their adaptive foraging patterns, and (b) carbon and nutrient inputs that regulate belowground processes. Improved understanding of the above- and belowground regeneration strategies of forbs is critical for restoration and conservation to secure their services in future old-growth tropical and subtropical grasslands.

Behavioural responses to mammalian grazing expose insect herbivores to elevated risk of avian predation.

Large mammalian herbivores (LMH) are important functional components and drivers of biodiversity and ecosystem functioning in grasslands. Yet their role in regulating food-web dynamics and trophic cascades remains poorly understood. In the temperate grasslands of northern China, we explored whether and how grazing domestic cattle (Bos taurus) alter the predator-prey interactions between a dominant grasshopper (Euchorthippus unicolor) and its avian predator the barn swallow (Hirundo rustica). Using two large manipulative field experiments, we found that in the presence of cattle, grasshoppers increased their jumping frequency threefold, swallows increased foraging visits to these fields sixfold, and grasshopper density was reduced by about 50%. By manipulatively controlling the grasshoppers' ability to jump, we showed that jumping enables grasshoppers to avoid being incidentally consumed or trampled by cattle. However, jumping behaviour increased their consumption rates by swallows 37-fold compared with grasshoppers that were unable to jump. Our findings illustrate how LMH can indirectly alter predator-prey interactions by affecting behaviour of avian predators and herbivorous insects. These non-plant-mediated effects of LMH may influence trophic interactions in other grazing ecosystems and shape community structure and dynamics. We highlight that convoluted multispecies interactions may better explain how LMH control food-web dynamics in grasslands.

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.

Impact of naphthalene on soil fauna diversity: Consequences for ecosystem functioning and carbon cycling in grasslands

Soil fauna, key indicators of grassland ecosystem health, face significant threats from the vast amounts of chemical pollutants released by human activities. These organisms are crucial for fundamental processes such as litter decomposition and carbon cycling. However, the response of soil animal communities and their functional dynamics to environmental chemical stress remains poorly understood. To investigate this, we conducted a naphthalene addition and litterbag experiment in the Bashang Grassland, located on the southern Inner Mongolia Plateau, to analyze its effects on soil fauna and litter decomposition. The investigated soil fauna groups included Arachnida (Arachnids), Insecta (Insects), Collembola (Springtails), Enoplea (enopleans), and Chromadorea (chromadoreans). The litter composition included Leymus chinensis, Stipa krylovii, Artemisia, Saussurea amara, and Artemisia giraldii. The findings indicated that a high diversity of soil fauna enhanced the decomposition of litter and the release of organic carbon from the litter. While the addition of naphthalene decreased both the abundance of soil fauna and the rate of litter decomposition, it specifically increased the relative proportion of Collembola (Springtails). Microfauna and mesofauna (0.1–2.0 mm) contributed more to the loss of litter mass and the release of organic carbon from the litter than macrofauna (2.0–4.0 mm). The effects of diverse soil fauna on litter decomposition and soil organic carbon accumulation were diminished by naphthalene exposure. This study further reveals the relationship between composite soil fauna diversity, litter decomposition, and soil organic carbon under chemical stress, highlighting the threat of environmental pollution to ecosystem health. It also enriches our understanding of the complexity of grassland ecosystems, especially in response mechanisms under chemical pollution stress.

Non-linear response of plant caloric value to N addition and mowing treatments in a meadow steppe

BackgroundCaloric value is an important indicator of grassland ecosystem function, but the response of caloric value to nitrogen (N) addition and mowing is still unclear. We explored the adaptive changes of plant caloric value and energy standing crop along a N addition gradient after six-year NH4NO3 addition and mowing treatments in an Inner Mongolian temperate meadow steppe in northern China.ResultsWe found that the response of plant caloric value to N addition at different organizational levels was diverse. The caloric value of legumes increased linearly with N addition rates. The caloric value of grasses exhibited a non-linear response trend, initially increasing followed by saturation or decrease, with a N response threshold present. Due to the dominance of grass species, the caloric value at the community level followed a similar pattern to that of the grasses along the N addition gradient. Under mowing, the caloric value of plants at each organizational level increased and usually mowing enhanced the N response threshold. Amongst these, the N response threshold of Leymus chinensis increased from 3.302 to 5.443 g N m−2 yr−1, grasses increased from 4.414 to 5.746 g N m−2 yr−1, and community increased from 5.373 to 9.216 g N m−2 yr−1. Under non-mowing treatment, the N response thresholds of the most dominant species, Leymus chinensis, and community energy standing crop were 10.001 and 15.119 g N m−2 yr−1, respectively. Under mowing, the energy standing crops showed a linear increasing trend.ConclusionsN response thresholds of plant caloric value and energy standing crop vary at different organizational levels (community > functional group > species). The results reveal varying regulatory capabilities of plants on the ecological environment at different organizational levels. These findings enhance our understanding of plant-environment interactions in grassland ecosystems under N deposition from an energy perspective, which is of great significance to clarify the response mechanism of grassland ecosystem structure and function to N deposition.

Strengthened plant-microorganism interaction after topsoil removal cause more deterministic microbial assembly processes and increased soil nitrogen mineralization

Topsoil removal, among other restoration measures, has been recognized as one of the most successful methods to restore biodiversity and ecosystem functioning in European grasslands. However, knowledge about how removal as well as other restoration methods influence interactions between plant and microbial communities is very limited. The aims of the current study were to understand the impact of topsoil removal on plant-microorganism interactions and on soil nitrogen (N) mineralization, as one example of ecosystem functioning. We examined how three different grassland restoration methods, namely ‘Harvest only’, ‘Topsoil removal’ and ‘Topsoil removal + Propagules (plant seed addition)’, affected i) the interactions between plants and soil microorganisms, ii) soil microbial community assembly processes, and iii) soil N mineralization. We compared the outcome of these three restoration methods to initial degraded and target semi-natural grasslands in the Canton of Zurich, Switzerland. We were able to show that ‘Topsoil removal’ and ‘Topsoil removal + Propagules’, but not ‘Harvest only’, reduced the soil total N pool and available N concentration, but increased soil N mineralization and strengthened the plant-microorganism interactions. Microbial community assembly processes shifted towards more deterministic after both topsoil removal treatments. These shifts could be attributed to an increase in dispersal limitation and selection due to stronger interactions between plants and soil microorganisms. The negative relationship between soil N mineralization and microbial community stochasticity indicated that microbial assembly processes, to some extent, can be incorporated into model predictions of soil functions. Overall, the results suggest that topsoil removal may change the microbial assembly processes and thus the functioning of grassland ecosystems by enhancing the interaction between plants and soil microorganisms.

Land use modulates resistance of grasslands against future climate and inter-annual climate variability in a large field experiment.

Climate and land-use change are key drivers of global change. Full-factorial field experiments in which both drivers are manipulated are essential to understand and predict their potentially interactive effects on the structure and functioning of grassland ecosystems. Here, we present 8 years of data on grassland dynamics from the Global Change Experimental Facility in Central Germany. On large experimental plots, temperature and seasonal patterns of precipitation are manipulated by superimposing regional climate model projections onto background climate variability. Climate manipulation is factorially crossed with agricultural land-use scenarios, including intensively used meadows and extensively used (i.e., low-intensity) meadows and pastures. Inter-annual variation of background climate during our study years was high, including three of the driest years on record for our region. The effects of this temporal variability far exceeded the effects of the experimentally imposed climate change on plant species diversity and productivity, especially in the intensively used grasslands sown with only a few grass cultivars. These changes in productivity and diversity in response to alterations in climate were due to immigrant species replacing the target forage cultivars. This shift from forage cultivars to immigrant species may impose additional economic costs in terms of a decreasing forage value and the need for more frequent management measures. In contrast, the extensively used grasslands showed weaker responses to both experimentally manipulated future climate and inter-annual climate variability, suggesting that these diverse grasslands are more resistant to climate change than intensively used, species-poor grasslands. We therefore conclude that a lower management intensity of agricultural grasslands, associated with a higher plant diversity, can stabilize primary productivity under climate change.

Species richness and dominant functional groups enhance aboveground biomass, with no effect on belowground biomass in Qinghai-Tibet Plateau's grasslands

Understanding the role of plant diversity in maintaining grassland ecosystem functioning is of great importance in ecological research. Despite decades of research, ecologists have struggled to understand the biodiversity-ecosystem functioning relationships and how the dominance of plant functional groups impacts ecosystem function. In attempting to understand (i) the temporal patterns of above- and below-ground biomass (AGB and BGB) and species richness, (ii) whether species richness is consistently associated with AGB and BGB, and (iii) the relative contributions of plant functional groups (forb, grass, legume, and sedge) in stabilizing ecosystem function, we used biomass productivity data of meadow steppe and alpine meadow in the Qinghai-Tibet Plateau (QTP) for the period 2015–2019. Our results show that AGB for both grasslands increased, but BGB stayed steady over 5 years. The rising tendency of AGB was caused by the upward trend of AGB in forbs and grasses, which are the dominant functional groups in QTP, stressing the importance of dominant functional groups to ecosystem functioning. The biodiversity-ecosystem functioning relationships were significantly positive for AGB, stable for BGB, and negative for the BGB:AGB ratio, which highlights the crucial role of higher species richness in ecosystem functioning. Significant differences in mean species richness among sites (9–19 species in meadow steppe and 8–22 species in alpine meadow) highlight the varying levels of species diversity across sites in the QTP. While 42% of the sites showed stable species richness, the reported increasing trends in species richness at 58% of the sites indicate the potential for ecological changes or processes in these areas. AGB in both grasslands increased, while BGB remained stable with increasing precipitation. The top soil layer (0–10 cm) dominated the observed BGB in both grasslands, as abundant nutrients in the top layer provide favorable conditions for root proliferation. In meadow steppe, AGB formed an isometric relationship with BGB, indicating that AGB increased with BGB. This study concludes that species richness influenced ecosystem functioning, and forbs and grasses dominated biomass productivity, of which the topsoil layer contributed three-quarters of BGB. Our study (i) provides empirical evidence of stable to increasing species richness in both grasslands over 5 years, and (ii) highlights the role of greater species richness in enhancing ecosystem functioning. These findings serve as a scientific reference for policymaking regarding ecosystem stability.

Defoliation modifies the impact of drought on the transfer of recent plant-assimilated carbon to soil and arbuscular mycorrhizal fungi

Abstract Aims The allocation of recent plant photosynthates to soil via arbuscular mycorrhizal (AM) fungi is a critical process driving multiple ecosystem functions in grasslands. Yet, our understanding of how defoliation modifies below-ground allocation of recent plant photosynthate and its response to drought, which is becoming more intense and frequent, remains unresolved. Methods Here we undertook a 13C pulse-labelling experiment in a mesotrophic temperate grassland to evaluate in situ how defoliation intensity modifies the transfer of recently assimilated 13C from plant shoots to roots, extraradical AM fungal hyphae, soil, and 13C-CO2 efflux (soil respiration) in response to simulated drought. Results We found that, individually, both defoliation and drought reduced initial plant 13C uptake, but when defoliation and drought were combined, we detected a significant reduction in below-ground 13C allocation to soil. Furthermore, while defoliation stimulated 13C transfer to plant roots and soil, high intensity defoliation amplified 13C-CO2 efflux relative to the amount of 13C taken up by plants. Drought stimulated 13C transfer to fungal hyphae relative to initial plant uptake. High intensity defoliation, however, suppressed both 13C enrichment of extraradical AM fungal hyphae and 13C transfer to fungal hyphae relative to initial uptake. Conclusions Our findings suggest that defoliation can reduce the transfer of recent photosynthate below-ground under simulated drought and provide new insights into how defoliation may influence grassland C allocation dynamics and cycling between plants and AM fungi in grasslands facing drought.

Root exudation is involved in regulation of nitrogen transformation under mowing in a temperate steppe

Nitrogen (N) transformation in soil is an important process involved in regulation of functioning of grassland ecosystems by affecting soil N availability and nitrous oxide (N2O) emission from soil. As a common grassland management practice worldwide, mowing has impacts on nutrient status in soil and nutrient cycling in grassland ecosystems. Root exudates including the organic carbon (C) and N substances are stimulated by mowing and involved in regulation of microbial community in the rhizosphere. Despite reports of mowing effects on soil nitrogen transformation and root exudation in the literature, few studies have specifically evaluated whether and how the mowing-induced root exudates are involved in mowing-induced soil N transformation in grassland ecosystems. Here, we investigated the effects of mowing on root exudation and the role of root exudates in soil N transformation by both field experiments in a temperate steppe and greenhouse experiments. We found that mowing enhanced soil net N mineralization rate (NNMR) by 3.2-fold and N2O flux by 75.0% in field experiment. We further demonstrated that mowing stimulated exudation of organic acids, amino acids, sugars, and phenolics in both field and greenhouse experiments. To explore the function of the root exudates, microcosm experiments were conducted to evaluate the roles of exuded amino acids, organic acids, sugars, and phenolics in regulating NNMR, N2O flux, enzyme activity, and functional genes related to soil N transformation by adding these chemicals to soil. We discovered that the addition of glycine enhanced NNMR mainly by enhancing the abundance of ureC, gdh, and amoA related to soil N mineralization. The addition of oxalic acid and glucose increased N2O flux mainly by increasing the abundance of nirS related to denitrification. Our findings reveal that root exuded organic acids, amino acids and sugars play an important role in the mowing-induced increases in soil N transformation. These novel findings would contribute to development of mowing-based grassland management.

Mowing increased community stability in semiarid grasslands more than either fencing or grazing.

A substantial body of empirical evidence suggests that anthropogenic disturbance can affect the structure and function of grassland ecosystems. Despite this, few studies have elucidated the mechanisms through which grazing and mowing, the two most widespread land management practices, affect the stability of natural grassland communities. In this study, we draw upon 9 years of field data from natural grasslands in northern China to investigate the effects of gazing and mowing on community stability, specifically focusing on community aboveground net primary productivity (ANPP) and dominance, which are two major biodiversity mechanisms known to characterize community fluctuations. We found that both grazing and mowing reduced ANPP in comparison to areas enclosed by fencing. Grazing reduced community stability by increasing the likelihood of single-species dominance and decreasing the relative proportion of nondominant species. In contrast, mowing reduced the productivity of the dominant species but increased the productivity of nondominant species. As a consequence, mowing improved the overall community stability by increasing the stability of nondominant species. Our study provides novel insight into understanding of the relationship between community species fluctuation-stability, with implications for ecological research and ecosystem management in natural grasslands.

Below‐ground root nutrient‐acquisition strategies are more sensitive to long‐term grazing than above‐ground leaf traits across a soil nutrient gradient

Abstract Understanding how plant nutrient acquisition strategies respond to grazing at the community level is critical understanding ecosystem structure and functioning in grasslands. However, few studies have simultaneously compared the difference in above‐ground (leaf) and below‐ground (root) nutrient‐acquisition strategies in response to long‐term grazing, especially at the regional scale. Here, we measured a set of leaf and fine‐root traits that correspond to the fast‐slow economic spectrum at the community level in 10 experimental sites from paired grazed and ungrazed grasslands across a soil nutrient gradient covering three major types of grasslands in northern China. We found that patterns of variations of leaf and fine‐root traits were consistent with both a leaf and root economic spectrum at the community level for both grazed and non‐grazed plots. Grazing had minor effect on community‐level leaf nutrient‐acquisition strategies but strongly influenced community‐level root nutrient‐acquisition strategies. Specifically, root nutrient‐acquisition strategies were shifted to more exploitative resource use in grazed communities. Moreover, soil nutrient contributed to the changes in both leaf and root nutrient‐acquisition strategies, which tended towards a more resource acquisition strategy with increasing soil nutrient levels. Grazing significantly interacted with soil nutrient to affect root nutrient‐acquisition strategies, and grazing contributed more to root nutrient‐acquisition strategies than soil nutrient. Synthesis. Our results demonstrated completely inconsistent responses of community‐level above‐ and below‐ground resource acquisition strategies to long‐term grazing, and below‐ground acquisition strategies were more sensitive to long‐term grazing. Our findings also suggest that high intensity anthropogenic activities such as grazing may strongly modify below‐ground resource acquisition strategies. Read the free Plain Language Summary for this article on the Journal blog.

Multidimensional response of China’s grassland stability to drought

Drought usually affects the normal functioning of grassland ecosystems. Due to sustained global warming, the frequency and intensity of drought have significantly increased, leading to greater impacts on many aspects of grassland ecosystem functions, such as soil moisture, vegetation physiological structure and ecosystem community structure. Ecosystem stability dimension can help us better understand the changes induced by drought occurred within ecosystems. Using the Normalized Vegetation Index (NDVI), climate and biodiversity data, we quantified resistance, resilience and temporal stability of grassland ecosystems under long term drought in northern China and calculated the ecosystem stability dimension based on the correlation between the three stability indicators. The results indicated that Qinghai Tibet Plateau and Inner Mongolian Plateau showed strong resistance to drought, while Loess Plateau region presented rapid recovery after drought. The resistance, compared to resilience and temporal stability, exhibited stronger sensitivity to drought in space. Drought promoted the transformation of grassland ecosystems into multidimensional structures. The reduction of aboveground biomass caused by frequent droughts accelerated the transformation in grassland ecosystems. Our findings provide the new insights for guiding the response mechanism of drought on grassland ecosystems.

The Effects of Infectious Diseases on the Consequences of Interspecific Competition in Grassland Communities

As infectious diseases have a severe impact on the individual survival and competitive ability of host species in grassland communities, competition between relevant species may have different consequences, potentially influencing the species composition of grassland communities and the functioning of grassland ecosystems. Understanding the impact of infectious diseases on competition is thus crucial for the health management of grassland ecosystems. How do infectious diseases affect the competitive coexistence of grassland plant species? In this study, by drawing on Tilman’s multispecies competition model and incorporating the spread characteristics of grassland plant diseases, we built three spatial competition models of two grass species subject to infectious diseases, and we analyzed the invasion conditions of infectious diseases and how they impact the population dynamics and competitive consequences of the species. Our model revealed the following: (1) Diseases with high transmission rates and low virulence are more likely to invade populations, while the presence of non-host species is detrimental to disease invasion. (2) Disease promotes the coexistence of competing species, breaking down the original competition–compromise trade-off mechanism for species coexistence and greatly expanding the range of parameters within which the two species can coexist. (3) Pathogen infections indirectly weaken the suppression of inferior species by dominant species, which is similar to the cascade effect seen in trophic interactions. Our findings highlight the importance of disease in species coexistence and grassland biodiversity maintenance.

Increased frequency of extreme climatic events weakens the community stability of natural grassland under directional climate changes by reducing resilience

AbstractAimChronic directional climate changes in temperature and precipitation are predicted to increase the frequency of extreme climatic events (ECEs); however, their co‐occurring effects on the temporal stability of community productivity (i.e. ANPP stability) are still unclear. Here, we evaluate whether the increased frequency of ECEs reduces ANPP stability, and how it modulates the effects of chronic directional climate factors on ANPP stability in natural grassland.LocationTwenty‐two sites in Asia and 14 sites in North America.Time period1980s–2010s.Major taxa studiedHerbaceous plant.MethodsWe collected 36 long‐term observational and consecutive ANPP data (at least 10 years) and resampled yearly ANPP via a consecutive resampling method of nested time windows for each field. We used linear mixed‐effect models, partial regression analysis and structure equation models to explore the interactive effects of three climatic factors on ANPP stability and their associated intermediate processes of sensitivity, asymmetry, resistance and resilience.ResultsThe increased frequency of ECEs was observed within the long‐term rising temperature and elevating precipitation trend across sites in the past several decades. Elevating precipitation rather than rising temperature was the primary driver influencing ANPP stability. Elevating precipitation increased ANPP stability through increasing mean ANPP and decreasing the standard deviation (i.e. SD) of ANPP due to a decrease in sensitivity of ANPP to precipitation. The increased frequency of ECEs decreased ANPP stability mainly by increasing the SD of ANPP, and it reduced the positive effect of elevated precipitation on ANPP stability via a decrease in resilience.Main conclusionOur results demonstrated that recurrent and discrete ECEs had cumulatively negative effects on ANPP stability, and the decreased resilience was identified as the primary factor reducing the grassland community stability under long‐term climate change. This highlighted the potential risks of increased frequency of ECEs for grassland ecosystem functions.

Water isotopic composition traces source and dynamics of water supply in a semi‐arid agricultural landscape

AbstractChanges in seasonality and form of precipitation alter the structure and function of grassland and steppe ecosystems and pose challenges for land management and crop production in regions like the Northern Great Plains, North America. This research uses isotopic composition of water (δ18O and δ2H) to explore the sources and fate of soil water in lower‐elevation agricultural areas of the Judith River watershed, in the headwaters of the Missouri River, USA. Extensive non‐irrigated cereal crop production in this area occurs on well‐drained soils and depends on careful water management. Our observations indicate that colder precipitation contributes isotopically distinct water to cultivated terrace soils relative to downgradient groundwaters and streams. Riparian waters also exhibit a higher fraction of contributions from colder precipitation relative to terrace groundwaters and streams. Apparent contributions from colder precipitation in terrace and riparian soil waters suggest that snowmelt is a key component of the water supply to these systems. Riparian waters also show evidence of evaporation suggesting that water spends sufficient time in some ponds and open channels in the riparian corridor to reflect fractionation by evaporation. The evolution of water isotopic composition from soils to shallow aquifers to stream corridors indicates source water partitioning as precipitation moves through this semi‐arid agricultural landscape. The apparent mixing processes evident in this evolution reveal source water dynamics that are necessary to understand plant transpiration, solute processing, and contaminant leaching processes.

Reverse diversity–biomass patterns in grasslands are constrained by climates and stoichiometry along an elevational gradient

Diversity and biomass play an important role in grassland ecosystem functions. However, diversity and biomass are variable because of their high sensitivity to environmental change in natural ecosystems. How plant diversity, biomass, and driving factors (climates, soils, and plants) in grasslands vary with environmental change remains unclear. We conducted intensive fieldwork (≈1000 km transect) on plant diversity, biomass, and associated drivers (i.e., climates, soils, and plants) to identify the patterns of diversity and biomass along an elevational gradient (50–4000 m) in grasslands of southwest China. Grassland biomass decreased significantly, but grassland diversity increased with increasing elevation. Consequently, a significant reverse pattern between biomass and diversity was detected along an elevational gradient. We also observed that the reverse pattern was primarily driven by the shifts in climates (i.e., temperature and precipitation), leaf stoichiometric traits (i.e., leaf N:P ratio), and soil properties (i.e., soil N content) along the elevational gradient. Our results contradicted previous studies on the positive diversity-biomass relationships, suggesting that previous studies might weaken the effects of climatic factors and plant stoichiometry under environmental change. These findings revealed that the reverse pattern between diversity and biomass in grasslands was shaped by the combined effects (climates, plants, soils) in grasslands, thus providing new insights into the debates and predictions on the diversity and biomass in grasslands under climate change.

Functional Groups Dominate Aboveground Net Primary Production under Long-Term Nutrient Additions in a Tibetan Alpine Meadow

Anthropogenic nutrient additions are influencing the structure and function of alpine grassland ecosystems. However, the underlying mechanisms of the direct and indirect effects of nutrient additions on aboveground net primary productivity (ANPP) are not well understood. In this study, we conducted an eight-year field experiment to explore the ecological consequences of nitrogen (N) and/or phosphorous (P) additions on the northern Tibetan Plateau. ANPP, species diversity, functional diversity, and functional groups were used to assess species’ responses to increasing nutrients. Our results showed that nutrient additions significantly increased ANPP due to the release in nutrient limitations. Although N addition had a significant effect on species richness and functional richness, and P and N + P additions altered functional diversity, it was functional groups rather than biodiversity that drove changes in ANPP in the indirect pathways. We identified the important roles of N and P additions in begetting the dominance of grasses and forbs, respectively. The study highlights that the shift of functional groups should be taken into consideration to better predict the structure, function, and biodiversity–ANPP relationship in grasslands, particularly under future multifaceted global change.

Connecting competitor, stress-tolerator and ruderal (CSR) theory and Lund Potsdam Jena managed Land 5 (LPJmL 5) to assess the role of environmental conditions, management and functional diversity for grassland ecosystem functions

Abstract. Forage offtake, leaf biomass and soil organic carbon storage are important ecosystem services of permanent grasslands, which are determined by climatic conditions, management and functional diversity. However, functional diversity is not independent of climate and management, and it is important to understand the role of functional diversity and these dependencies for ecosystem services of permanent grasslands, since functional diversity may play a key role in mediating impacts of changing conditions. Large-scale ecosystem models are used to assess ecosystem functions within a consistent framework for multiple climate and management scenarios. However, large-scale models of permanent grasslands rarely consider functional diversity. We implemented a representation of functional diversity based on the competitor, stress-tolerator and ruderal (CSR) theory and the global spectrum of plant form and function into the Lund Potsdam Jena managed Land (LPJmL) dynamic global vegetation model (DGVM) forming LPJmL-CSR. Using a Bayesian calibration method, we parameterised new plant functional types (PFTs) and used these to assess forage offtake, leaf biomass, soil organic carbon storage and community composition of three permanent grassland sites. These are a temperate grassland and a hot and a cold steppe for which we simulated several management scenarios with different defoliation intensities and resource limitations. LPJmL-CSR captured the grassland dynamics well under observed conditions and showed improved results for forage offtake, leaf biomass and/or soil organic carbon (SOC) compared to the original LPJmL 5 version at the three grassland sites. Furthermore, LPJmL-CSR was able to reproduce the trade-offs associated with the global spectrum of plant form and function, and similar strategies emerged independent of the site-specific conditions (e.g. the C and R PFTs were more resource exploitative than the S PFT). Under different resource limitations, we observed a shift in the community composition. At the hot steppe, for example, irrigation led to a more balanced community composition with similar C, S and R PFT shares of aboveground biomass. Our results show that LPJmL-CSR allows for explicit analysis of the adaptation of grassland vegetation to changing conditions while explicitly considering functional diversity. The implemented mechanisms and trade-offs are universally applicable, paving the way for large-scale application. Applying LPJmL-CSR for different climate change and functional diversity scenarios may generate a range of future grassland productivities.