Semi-arid Grassland Research Articles

Litter accumulation suppresses grass production but facilitates shrub expansion in a long‐term fenced grassland

AbstractShrub expansion is increasing in grasslands worldwide and has profound effects on biodiversity and ecosystem functions. Shrub expansion has primarily been explained by extrinsic factors such as climate change and human activities, yet the roles of intrinsic shrub demographic population dynamic and shrub–grass interaction remain poorly understood. With a paired mown and exclosure comparison experiment and baseline levels of shrub abundance in a semiarid grassland, we confirmed that long‐term livestock exclusion promotes expansion of two native shrubs, Artemisia sacrorum and Caragana brachypoda. Shrub abundance increased during the livestock exclusion period. Shrub biomass in fenced plots was about 5‐ to 10‐fold greater than in mown plots. Both increase in population density and individual size (especially height) contributed to shrub increase. The mechanism behind this was the divergent effects of litter accumulation on shrubs and grasses. Litter accumulation suppressed grass production, while facilitating shrub recruitment and growth. Our findings highlight the potential role of litter accumulation‐mediated shifts in shrub–grass interactions, which should be incorporated into grazing top‐down control to better predict the restoration outcomes of grassland management changes. The identified internal biotic mechanism raises the possibility that removal of accumulated litter by grazing or mowing may be an alternative way to maintain or restore a grass‐dominated state in shrub expansion areas.

Nutrients addition decreases soil fungal diversity and alters fungal guilds and co-occurrence networks in a semi-arid grassland in northern China

Anthropogenic eutrophication is known to impair the diversity and stability of aboveground community, but its effects on the diversity, composition and stability of belowground ecosystems are not yet fully understood. In this study, we conducted a 9-year nitrogen (N) and phosphorus (P) addition experiment in a semi-arid grassland of Northern China to elucidate the impacts of nutrients addition on soil fungal diversity, functional guilds, and co-occurrence networks. The results showed that N addition significantly decreased soil fungal diversity and altered fungal community composition, whereas P addition had no impact on them. The relative abundance of arbuscular mycorrhizal fungi and leaf_saprotroph were reduced by N and P addition, but P addition enhanced the abundance of saprotrophic fungi. Co-occurrence network analysis revealed that N addition destabilized fungal network complexity and stability, while P addition slightly increased the network complexity. Additionally, the network analysis of N × P interaction revealed that P addition mitigated negative effects of N addition on network complexity and stability. Structural equation modeling (SEM) results suggested that nutrients addition directly or indirectly influenced the fungal community structure through the loss of plant richness and the increase of perennial grass biomass. These findings indicate that in comparison to P addition, N addition exhibits a pronounced negative effect on soil fungal communities. Our findings also suggest that changes in plant functional groups under nutrients deposition are pivotal in shaping soil fungal community structure in semi-arid grassland and highlight the need for a better understanding of the belowground ecosystem dynamics.

Urea fertilization increased CO2 and CH4 emissions by enhancing C-cycling genes in semi-arid grasslands

Global climate change is predicted to increase exogenous N input into terrestrial ecosystems, leading to significant changes in soil C-cycling. However, it remains largely unknown how these changes affect soil C-cycling, especially in semi-arid grasslands, which are one of the most vulnerable ecosystems. Here, based on a 3-year field study involving N additions (0, 25, 50, and 100 kg ha−1 yr−1 of urea) in a semi-arid grassland on the Loess Plateau, we investigated the impact of urea fertilization on plant characteristics, soil properties, CO2 and CH4 emissions, and microbial C cycling genes. The compositions of genes involved in C cycling, including C fixation, degradation, methanogenesis, and methane oxidation, were determined using metagenomics analysis. We found that N enrichment increased both above- and belowground biomasses and soil organic C content, but this positive effect was weakened when excessive N was input (N100). N enrichment also altered the C-cycling processes by modifying C-cycle-related genes, specifically stimulating the Calvin cycle C-fixation process, which led to an increase in the relative abundance of cbbS, prkB, and cbbL genes. However, it had no significant effect on the Reductive citrate cycle and 3-hydroxypropionate bi-cycle. N enrichment led to higher soil CO2 and CH4 emissions compared to treatments without added N. This increase showed significant correlations with C degradation genes (bglA, per, and lpo), methanogenesis genes (mch, ftr, and mcr), methane oxidation genes (pmoA, pmoB, and pmoC), and the abundance of microbial taxa harboring these genes. Microbial C-cycling genes were primarily influenced by N-induced changes in soil properties. Specifically, reduced soil pH largely explained the alterations in methane metabolism, while elevated available N levels were mainly responsible for the shift in C fixation and C degradation genes. Our results suggest that soil N enrichment enhances microbial C-cycling processes and soil CO2 and CH4 emissions in semi-arid ecosystems, which contributes to more accurate predictions of ecosystem C-cycling under future climate change.

Slope aspect of a mountainous grassland landscape shapes the structure of an encroaching shrub (Euryops floribundus N.E. Br): insights from communal grazing sites located at varying distances from rural homesteads

Mountainous grassland landscapes are severely threatened by the proliferation of shrub encroachment. So far, it remains unclear though how slope aspect coupled with land disturbances linked to the proximity of homesteads to communal grazing sites affects the distribution, density and structure of the encroaching shrubs in these grassland ecosystems. In this study, we investigated the role that slope aspect plays in determining the density and structure of an encroaching shrub species Euryops floribundus N.E. Br in three communal grazing sites located at varying distances from rural homesteads in a semi-arid mountainous grassland in the Eastern Cape Province of South Africa. Three sites were strategically chosen in Cala communal grazing lands in an encroached mountainous grassland landscape that depicted north and south-facing slope aspects. The selected sites were Tsengiwe; a site located in close proximity to homesteads at a distance of less than 100 m, Upper Mnxe situated at an intermediate distance ranging from 200 to 800 m away from homesteads and Manzimdaka, which was located furthest from homesteads at a distance greater than 1600 m. In each site and corresponding slope aspect, the density and structure of the shrub E. floribundus were evaluated on 36 randomly distributed plots, yielding a total of 108 plots across all sites. We found that shrub density was significantly higher (50%) on the north-facing slope compared to the south-facing slope in Tsengiwe, the site located near homesteads. Shrub height was significantly higher (53 and 17%) on the north-facing slope compared to the south-facing slope at Upper Mnxe and Manzimdaka, which were located at intermediate and furthest distances from the homesteads. Notably, shrub height was significantly lower (37%) in the north-facing slope compared to the south-facing slope in Tsengiwe. Following a similar pattern to shrub height, total stem number was significantly higher (20 and 85%) in the north-facing slope compared to the south-facing slope at Upper Mnxe and Tsengiwe, respectively. Shrub crown area was higher (33 and 11%) in the north-facing slope compared to the south-facing slope at Upper Mnxe and Manzimdaka, respectively. A strong positive relationship was established between the height of shrubs and their longest crown diameter, shortest crown diameter and shrub crown area across all sites, suggesting that the investigated shrub species E. floribundus employs its structural characteristics to survive, and thrive and this was more evident in the north-facing slope. The results highlight the importance of considering the proximity of homesteads into account in ecological studies, and puts emphasis on improved understanding of the vegetation patterns shaped by shrub encroachment in mountainous grasslands, which is crucial in the development of effective land management strategies.

Testing prescribed burning to shift an agronomic grass community to a diverse native plant community

Prescribed burning can be an effective land management tool. Here, we study changes in plant diversity and composition following experimental fire disturbance in microcosm units extracted from a twenty-five-year-old historically reclaimed grassland located at Highland Valley Copper mine in British Columbia (B.C.), Canada. Experimental microcosm units were dominated by agronomic grass species Elymus lanceolatus, Thinopyrum intermedium and Bromus inermis. The disturbance treatment was fire intensity, represented by three levels (light, moderate, and heavy), replicated six times per treatment. Fire intensity was controlled by modifying the weight of dried litter applied to each microcosm unit (50 g,150 g, 200g), along with the time each grass turf was burned (10 s, 15 s, 20 s). One day after the fire treatment was applied, microcosm units were seeded with a native species mix consisting of six grassland species common to southern B.C. to examine effectiveness of plant establishment postburn. Disturbance treatments resulted in higher overall alpha diversity, richness, evenness, and beta diversity. Plant community changes included colonization of seeded native forbs, grasses, and legumes in response to disturbance. Aboveground net primary productivity (ANPP) was net neutral within the light and moderate burning disturbance treatments but resulted in increased ANPP with heavy disturbance. Litter mass reduced plant diversity and ANPP, indicating that litter was a major factor in plant community dynamics. These results suggest disturbance by burning leads to short term positive plant community response towards increasing diversity of semi-arid grasslands, and aids in shifting plant communities to higher diversity composed of an increase in native plant species. Our results also suggest that without active management the gains observed in native species establishment might quickly be out shadowed and restricted by the previously dominant agronomic plant community.

Forb stability, dwarf shrub stability and species asynchrony regulate ecosystem stability along an experimental precipitation gradient in a semi-arid desert grassland.

Precipitation pattern changes may affect plant biodiversity, which could impact ecosystem stability. However, the effects of changes in precipitation regime on ecosystem stability and their potential mechanisms are still unclear. We conducted a 3-year field manipulation experiment with five precipitation treatments (-40%, -20%, 0% (CK), +20% and +40% of ambient growing season precipitation) in a semi-arid desert grassland to examine the effects of precipitation alterations on functional group stability, species asynchrony, and diversity, and the underlying mchanisms of ecosystem stability using structural equation modelling. Alterations in precipitation had different effects on community biomass and functional group biomass. Moreover, ecosystem stability was mainly driven by forb stability (path coefficient = 0.79). Changes in precipitation had significant effects on soil dissolved inorganic N (P < 0.01) further affecting ecosystem stability through species asynchrony (path coefficient = 0.25). Dwarf shrubs had a stabilizing effect on ecosystem stability (path coefficient = 0.32), mainly via deep roots. Ecosystem stability tended to be lower in the -40% (4.72) and +40% (2.74) precipitation treatments. The common reduction in species asynchrony and stability of forb and dwarf shrub functional groups resulted in lower ecosystem stability under the -40% treatment. The lower stability under the +40% treatment might be ascribed to unimproved dwarf shrub stability. Higher dwarf shrub and forb stability contributed to higher ecosystem stability under normal precipitation changes (±20% treatments) and CK. Species diversity was not a crucial driver of ecosystem stability. Our results indicate that precipitation alteration can regulate ecosystem stability via functional group stability (e.g. forb stability, dwarf shrub stability) and species asynchrony in a semiarid desert grassland.

Drought shifts soil nematode trophic groups and mediates the heterotrophic respiration

Abstract As the most diverse metazoan taxa, soil nematodes serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode–microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are hardly explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant–soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid (PLFA) and heterotrophic soil respiration. Overall, in the field and the microcosm experiments, we found that nematode abundance, carbon footprint and diversity, microbial PLFA and heterotrophic respiration were reduced under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. The soil decomposition channel shifted from a bacterial to a fungal pathway in response to drought, indicating decelerated heterotrophic respiration under drought. These results highlight the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our findings underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.

A more effective approach for species-level classifications using multi-source remote sensing data: Validation and application to an arid and semi-arid grassland

The distribution of grassland communities significantly influences biodiversity conservation and resource management. Remote sensing datasets, such as Sentinel land cover images with high spatial and temporal resolution, have been commonly employed to simulate the distribution and community structure of plant species in grasslands. Nevertheless, the precision of grassland and community classification requires further enhancement for more effective grassland management. In response, our study presents a dynamic workflow for simulating the distribution of grassland plant species under different hydroclimatic conditions. Leveraging a random forest classifier with multi-source remote sensing features, we mapped the distribution of nine plant communities and six types of land cover in the upstream grasslands of the Xilingol River Basin, Inner Mongolia from 2017 to 2022. Utilizing the Google Earth Engine platform, our findings reveal a remarkable consistency in the overall spatiotemporal accuracy and classification precision of grassland communities across different years, even under varying hydroclimatic conditions. When critical features were carefully selected, the integration of Sentinel-1 (C-band synthetic aperture radar), Sentinel-2 (surface reflectance), SRTM DEM 30 m (Digital Elevation Model data), and MOD16A2.006 (evapotranspiration/latent heat flux product) data yielded a high overall accuracy ranging from 87.0 % to 89.5 % over multiple years. Our study not only determined the spatial patterns of various grassland plant communities but also explored the mechanism of their responses to different hydroclimatic conditions. The proposed approach holds practical implications for fine-scale grassland classification, providing valuable support for landscape classification and monitoring efforts. Furthermore, the insights derived from our findings offer valuable guidance for land managers and policymakers, aiding them in making informed decisions related to grassland conservation and sustainable land use planning.

Driving mechanisms of community biomass allocation along environmental gradients in different grasslands in China

A variable future climate would lead to changes in the biomass allocation pattern of plant communities, but its divergent changes under different environments have not been clearly explored, greatly limiting a better understanding of the responsess of grassland ecosystems to environmental changes. Herein, we conducted field samplings at 215 grassland sites in the Qinghai-Tibetan and Inner Mongolian Plateaus to analyze community biomass allocation patterns (specifically, the ratio of root to shoot, R/S) in various grasslands along environmental gradients. We found a gradual increase in R/S from humid to semi-arid and arid environments across both plateaus. In humid environment, soil factor had a significant effect on the R/S of alpine humid grassland, while climate factor had a significant effect on the R/S of humid grassland. In semi-arid environment, both climate and plant factors had significant effects on R/S in semi-arid grassland. In arid environments, climate and plant factors had significant effects on R/S in arid grassland. These findings emphasize the multifaceted role of environmental factors in shaping biomass allocations across diverse ecosystems, enriching our understanding of ecological dynamics. The current results are timely in advancing the fundamental understanding of the mechanisms of biomass allocation in grasslands and are useful for global research on grasslands in different environments.

Precipitation variation: a key factor regulating plant diversity in semi-arid livestock grazing lands.

Livestock presence impacts plant biodiversity (species richness) in grassland ecosystems, yet extent and direction of grazing impacts on biodiversity vary greatly across inter-annual periods. In this study, an 8-year (2014-2021) grazing gradient experiment with sheep was conducted in a semi-arid grassland to investigate the impact of grazing under different precipitation variability on biodiversity. The results suggest no direct impact of grazing on species richness in semi-arid Stipa grassland. However, increased grazing indirectly enhanced species richness by elevating community dominance (increasing the sheltering effect of Stipa grass). Importantly, intensified grazing also regulates excessive community biomass resulting from increased inter-annual wetness (SPEI), amplifying the positive influence of annual humidity index on species richness. Lastly, we emphasize that, in water-constrained grassland ecosystems, intra-annual precipitation variability (PCI) was the most crucial factor driving species richness. Therefore, the water-heat synchrony during the growing season may alleviate physiological constraints on plants, significantly enhancing species richness as a result of multifactorial interactions. Our study provides strong evidence for how to regulate grazing intensity to increase biodiversity under future variable climate patterns. We suggest adapting grazing intensity according to local climate variability to achieve grassland biodiversity conservation.

Nitrogen addition does not alter symmetric responses of soil respiration to changing precipitation in a semi-arid grassland

Concurrent changing precipitation regimes and atmospheric nitrogen (N) deposition can have profound influences on soil carbon (C) cycling. However, how N enrichment regulates the responses of soil C fluxes to increasing variability of precipitation remains elusive. As part of a field precipitation gradient experiment with nine levels of precipitation amounts (−60 %, −45 %, −30 %, −15 %, ambient precipitation, +15 %, +30 %, +45 %, and +60 %) and two levels of N addition (0 and 10 g N m−2 yr−1) in a semi-arid temperate steppe on the Mongolian Plateau, this work was conducted to investigate the responses of soil respiration to decreased and increased precipitation (DP and IP), N addition, and their possible interactions. Averaged over the three years from 2019 to 2021, DP suppressed soil respiration by 16.1 %, whereas IP stimulated it by 27.4 %. Nitrogen addition decreased soil respiration by 7.1 % primarily via reducing microbial biomass C. Soil respiration showed symmetric responses to DP and IP within all the four precipitation variabilities (i.e., 15 %, 30 %, 45 %, and 60 %) under ambient N. Nevertheless, N addition did not alter the symmetric responses of soil respiration to changing precipitation due to the comparable sensitivities of microbial biomass and root growth to DP and IP under the N addition treatment. These findings indicate that intensified precipitation variability does not change but N addition could alleviate soil C releases. The unchanged symmetric responses of soil respiration to precipitation variability under N addition imply that N deposition may not change the response pattern of soil C releases to predicted increases in precipitation variability in grasslands, facilitating the robust projections of ecosystem C cycling under future global change scenarios.

Seasonal variation of net ecosystem carbon exchange and gross primary production over a Loess Plateau semi-arid grassland of northwest China

Grassland ecosystems store approximately one-third of the global terrestrial carbon stocks, which play a crucial role in regulating the carbon cycle on regional and global scales, but the current scientific understanding of the variation in net carbon dioxide exchange (NEE) on grassland ecosystems is still limited. Based on the eddy covariance technique, this study investigated the seasonal variation of ecosystem respiration (Reco) and gross primary production (GPP) from 2018 to 2020 in a semi-arid grassland on the Loess Plateau in northwest China. The results indicated that the annual cumulative average NEE value was − 0.778 kg C/m2, the growing season cumulative value accounted for approximately 83.81%, which suggested that the semiarid grassland showed a notable soil carbon sink. The correlation analysis revealed that soil temperature (Ts) (RReco = 0.71, RGPP = 0.61) and soil water content (SWC) (RReco = 0.47, RGPP = 0.44) were the two main driving factors in modulating the variation of daily average GPP and Reco (P < 0.01). Therefore, the monthly average of GPP and Reco increased with the increase in Ts (RGPP = 0.716, P < 0.01; RReco = 0.586, P < 0.05), resulting in an increase in the carbon sequestration capacity of the grass ecosystem. This study also showed that soil moisture has a promoting effect on the response of Reco and GPP to Ts, and the correlation among GPP, Reco, and Ts was much stronger under wet conditions. For instance, the coefficient of determination of Reco and GPP with Ts under wet conditions in 2018 increased by 0.248 and 0.286, respectively, compared to those under droughty conditions. Additionally, the temperature sensitivity of Reco (Q10) increased by 46.13% compared to dry conditions. In addition, carbon exchange models should consider the synergistic effect of Ts and SWC as one of the main driving factors for theoretical interpretation or modeling. Under the potential scenario of future global warming and the frequent extreme weather events, our findings have important implications for predicting future CO2 exchange and establishing an optimal ecological model of carbon flux exchange.

Both evenness and dominant species identity have effects on litter decomposition.

Exploring how interactions between species evenness and dominant species identity affect litter decomposition processes is vital to understanding the relationship between biodiversity and ecosystem functioning in the context of global changes. We carried out a 127-day litter decomposition experiment under controlled conditions, with interactions of four species evenness types (high, medium, low and single species) and three dominant species identity (Leymus chinensis, Serratula centauroides, Artemisia capillaris). After collecting the remaining litter, we estimated how evenness and dominant species identity affected litter mass loss rate, carbon (C) loss rate, nitrogen (N) loss rate and remaining litter C/N directly or indirectly, and assessed relative mixture effects (RMEs) on litter mass loss. The main results are shown as follows. (1) By generalized linear models, litter mass loss rate was significantly affected by evenness after 69-day decomposition; N loss rate was affected by dominant species identity after 69-day decomposition, with treatment dominated by Serratula centauroides being at least 9.26% higher than that dominated by any of other species; and remaining litter C/N was affected by the interactions between evenness and dominant species identity after 30-, 69- and 127-day decomposition. (2) Twenty-three out of 27 RMEs were additive, and dominant species identity showed a significant effect on RMEs after 127-day decomposition. (3) By confirmatory path analyses, litter mass loss rate was affected by dominant species identity directly after 127-day decomposition, and by both species evenness and dominant species identity indirectly which was mediated by initial litter functional dispersion (FDis) after 30- and 69-day decomposition; remaining litter C/N was affected by evenness indirectly which was mediated by initial litter FDis after 127-day decomposition. These findings highlight the importance of evenness and dominant species identity on litter decomposition. The study provides insights into communities during retrogressive successions in semi-arid grasslands in the context of global changes.

Persistent greening against drying in northeast Asian semiarid grasslands: Asymmetrical responses of direct and legacy effects to intensified drought

Despite experiencing a decadal shift towards drought conditions at the end of the 20th century, semiarid grasslands in northeast Asia (NEA) exhibited an evident greening trend from 1982 to 2020. However, the mechanism behind this phenomenon remains unclear. Hence, we analysed the interdecadal changes in vegetation response to drought on the basis of the standardised precipitation evapotranspiration index (SPEI) and Global Inventory Modelling and Mapping Studies LAI4g datasets, with an emphasis on the differences between direct and legacy effects (as measured by resilience), to explore the mechanism of persistent grassland greening. Results revealed that during the post-drought shift period (2000–2020), the sudden decrease in the water content of the intermediate soil layer triggered an intensified vegetation response to drought. Specifically, although direct effects and resilience were amplified, they exhibited asymmetric changes. Resilience was stronger than direct effects, and this difference increased with increasing drought (drought recovery) levels. These combined effects may account for persistent greening against intensified drying in the semiarid grasslands in NEA. Given the projected exacerbation of future droughts, this study holds notable importance for comprehending the long-term change dynamics of dryland ecosystems.

Methane uptake responses to extreme droughts regulated by seasonal timing and plant composition

Increasingly frequent and severe droughts are occurring in multiple seasons of a year in many dryland ecosystems, with unknown impacts on the role of drylands in cycling of methane (CH4), a potent greenhouse gas. In particular, there is limited understanding of how drought occurring at different times within the growing season regulates biological CH4 uptake, and how these responses are mediated by plant community composition. Here, we quantify how drought timing and plant community composition regulate CH4 uptake in a semiarid grassland. We employ a field experiment in which droughts were imposed in early, middle, or late growing season in three different communities (two graminoids, two shrubs and their mixture), respectively. All three droughts increased CH4 uptake, but the effect size and pathway varied with seasonal timing. Early and middle drought increased CH4 uptake through increasing both soil pomA abundance and diffusivity resulting from reduced soil water content (SWC), while late drought increased CH4 uptake only by reducing SWC. Overall, early drought had the least positive effects on CH4 uptake because it excluded the least precipitation and therefore had smaller impacts on SWC. Besides, plant composition did not affect CH4 uptake under normal environment but regulated CH4 uptake in response to droughts due to different response of plant composition to droughts. Early and middle drought had larger positive effects on CH4 uptake in shrub communities than the other two communities, consistent with larger reductions in SWC and larger increases in pomA abundance, respectively. In contrast, late drought had consistent effects on CH4 uptake across three communities. Our results suggest that the magnitude and pathways of extreme drought effects on CH4 uptake are strongly co-regulated by seasonal timing and plant composition.

Coordination of leaf, root, and seed traits shows the importance of whole plant economics in two semiarid grasslands.

Uncertainty persists within trait-based ecology, partly because few studies assess multiple axes of functional variation and their effect on plant performance. For 55 species from two semiarid grasslands, we quantified: (1) covariation between economic traits of leaves and absorptive roots, (2) covariation among economic traits, plant height, leaf size, and seed mass, and (3) relationships between these traits and species' abundance. Pairs of analogous leaf and root traits were at least weakly positively correlated (e.g. specific leaf area (SLA) and specific root length (SRL)). Two pairs of such traits, N content and DMC of leaves and roots, were at least moderately correlated (r > 0.5) whether species were grouped by site, taxonomic group and growth form, or life history. Root diameter was positively correlated with seed mass for all groups of species except annuals and monocots. Species with higher leaf dry matter content (LDMC) tended to be more abundant (r = 0.63). Annuals with larger seeds were more abundant (r = 0.69). Compared with global-scale syntheses with many observations from mesic ecosystems, we observed stronger correlations between analogous leaf and root traits, weaker correlations between SLA and leaf N, and stronger correlations between SRL and root N. In dry grasslands, plant persistence may require coordination of above- and belowground traits, and dense tissues may facilitate dominance.

Warming differentially affects above- and belowground ecosystem functioning of the semi-arid alpine grasslands

Rapid climate warming is altering multiple ecosystem functions of alpine grasslands. However, the responses of the above- and belowground ecosystem multifunctionality (EMF) to climate warming might exhibit difference in semi-arid alpine grasslands. Based on manipulative field experiments at an alpine meadow and an alpine steppe, we explored warming effects on the functioning of alpine grassland ecosystems on the Tibetan Plateau. Warming significantly decreased plant diversity and aboveground biomass, but tended to increase belowground biomass, soil carbon, and soil nutrient contents. Experimental warming generally had neutral effects on the EMF of both alpine grasslands. Nevertheless, warming differentially affects the above- and belowground ecosystem functioning of Tibetan semi-arid alpine grasslands, with the aboveground EMF (AEMF) deceased but the belowground EMF (BEMF) increased under warmer conditions. Our results further showed that the negative effect of experimental warming on AEMF was mainly regulated by the changes of plant and soil biodiversity. However, plant productivity had a pivotal role in propelling the positive effect of warming on BEMF. Our results emphasized the potential impacts of plant and soil biodiversity, productivity, and soil nutrients in maintaining the EMF of alpine grasslands, which could offer novel views for sustainable management of Tibetan semi-arid alpine ecosystems.

Nitrogen deposition mediates more stochastic processes in structuring plant community than soil microbial community in the Eurasian steppe.

Anthropogenic environmental changes may affect community assembly through mediating both deterministic (e.g., competitive exclusion and environmental filtering) and stochastic processes (e.g., birth/death and dispersal/colonization). It is traditionally thought that environmental changes have a larger mediation effect on stochastic processes in structuring soil microbial community than aboveground plant community; however, this hypothesis remains largely untested. Here we report an unexpected pattern that nitrogen (N) deposition has a larger mediation effect on stochastic processes in structuring plant community than soil microbial community (those <2 mm in diameter, including archaea, bacteria, fungi, and protists) in the Eurasian steppe. We performed a ten-year nitrogen deposition experiment in a semiarid grassland ecosystem in Inner Mongolia, manipulating nine rates (0-50 g N m-2 per year) at two frequencies (nitrogen added twice or 12 times per year) under two grassland management strategies (fencing or mowing). We separated the compositional variation of plant and soil microbial communities caused by each treatment into the deterministic and stochastic components with a recently-developed method. As nitrogen addition rate increased, the relative importance of stochastic component of plant community first increased and then decreased, while that of soil microbial community first decreased and then increased. On the whole, the relative importance of stochastic component was significantly larger in plant community (0.552±0.035; mean±standard error) than in microbial community (0.427±0.035). Consistently, the proportion of compositional variation explained by the deterministic soil and community indices was smaller for plant community (0.172-0.186) than microbial community (0.240-0.767). Meanwhile, as nitrogen addition rate increased, the linkage between plant and microbial community composition first became weaker and then became stronger. The larger stochasticity in plant community relative to microbial community assembly suggested that more stochastic strategies (e.g., seeds addition) should be adopted to maintain above- than below-ground biodiversity under the pressure of nitrogen deposition.

Rehabilitation of Semi-Arid Grasslands through the Perennialization of Lots by Implementing Perennial Forage Exotic Grass

Rehabilitation of Semi-Arid Grasslands through the Perennialization of Lots by Implementing Perennial Forage Exotic Grass

The impact of climate change on plant distribution and niche dynamics over the past 250 years in Switzerland

Herbarium specimens provide an irreplaceable source of historical plant distribution data, enabling analysis of changes in plant distribution spanning centuries. Most studies on plant distribution shifts focus on recent decades and rare species, especially along elevational gradients. We examined about 2000 historical herbarium specimens from the Botanical Garden of the University of Bern, representing 30 plant species from five Swiss lowland habitats (six species per habitat) dating back to 1768 and covering all Swiss cantons. All historical data were transcribed, georeferenced and then combined with current data resulting in about 170 000 plant records over 250 years. Combined with climatic data from the same period, we found that all habitats increased their potential distribution area with a significant gain in the semi-arid grasslands (+8.15 %, p-value = 0.031). On species level, 75 % of the selected species expanded their distribution, while 25 % of the species retracted. Despite these shifts, 90–99.6 % niche stability was observed between historical and current climatic niches across all species. Shifts in co-occurring species were specific to the species, not to the habitat. The consistent overlap in historical and current climatic niches suggest that distribution expansion is due to the growth of areas with suitable climates, pointing to climate change as a driving factor for plant distribution changes over the past 250 years.