Theory predicts that consumers may stabilise or destabilise plant production depending on model assumptions, and tests in aquatic food webs suggest that trophic interactions are stabilising. We quantified the effects of trophic interactions on temporal variability (standard deviation) and temporal stability (mean/standard deviation) of grassland biomass production and the plant diversity–stability relationship by experimentally removing heterotrophs (large vertebrates, arthropods, foliar and soil fungi) from naturally and experimentally assembled grasslands of varying diversity. In both grassland types, trophic interactions proportionately decreased plant community biomass mean and variability over the course of 6 years, leading to no net change in temporal stability or the plant diversity–stability relationship. Heterotrophs also mediated plant coexistence; their removal reduced diversity in naturally assembled grasslands. Thus, herbivores and fungi reduce biomass production, concurrently reducing the temporal variability of energy and material fluxes. Because of this coupling, grassland stability is robust to large food web perturbations.

Plant diversity and plant–consumer/pathogen interactions likely interact to influence ecosystem carbon fluxes but experimental evidence is scarce. We examined how experimental removal of foliar fungi, soil fungi and arthropods from experimental prairies planted with 1, 4 or 16 plant species affected instantaneous rates of carbon uptake (GPP), ecosystem respiration (Re) and net ecosystem exchange (NEE). Increasing plant diversity increased plant biomass, GPP and Re, but NEE remained unchanged. Removing foliar fungi increased GPP and NEE, with the greatest effects at low plant diversity. After accounting for plant biomass, we found that removing foliar fungi increased mass‐specific flux rates in the low‐diversity plant communities by altering plant species composition and community‐wide foliar nitrogen content. However, this effect disappeared when soil fungi and arthropods were also removed, demonstrating that both plant diversity and interactions among consumer groups determine the ecosystem‐scale effects of plant–fungal interactions.

Climate over Asian montane rangelands is changing faster than the global average, posing serious threats to the future of the region's livestock‐based economies and cultures. Effects of climate change on rangeland vegetation likely depend on grazing by herbivores but the potential responses of vegetation to such changes in climate and grazing regimes remain unclear. We examined vegetation responses to experimentally simulated climate change (warming, drought and increased rainfall) and grazing (clipping vegetation) between 2015 and 2018 at two mountain rangeland sites: Spiti valley, in the Indian Trans‐Himalaya and Tost, in the Gobi‐Altai Mountains in Mongolia. Clipping and climate change manipulations interactively reduced vegetation cover and biomass but did not affect species richness. Treatment effects and their interactions varied between sites. In ungrazed plots, vegetation cover and biomass declined sharply in response to warming (18%–35%) and drought (20%–50%) at the two sites, and, surprisingly also declined slightly in response to increased rainfall (20%) at Tost. While the effects of climate treatments were largely similar in the grazed and ungrazed plots in Tost, they were larger in the ungrazed plots in Spiti. The decline in vegetation cover was driven by a decline in the cover of both forbs and grasses. In combination, grazing and warming (Tost) or drought (Spiti) had sub‐additive effects, that is, the decrease in vegetation cover in response to grazing and warming/drought was less than the sum of their independent effects but greater than the effect of either manipulation alone. Of the two, warming had a greater effect than drought at the more arid site (Tost), whereas drought had a larger effect at the more mesic site (Spiti). Synthesis and applications. Our findings show that future changes in climate, including just over 1°C of warming, could undermine the sustainability of pastoral economies and the persistence of wildlife across Asian montane rangelands. Furthermore, grazing by herbivores will play an important role in mediating rangeland responses to climate change; thus, pasture management in concert with local pastoralists will be crucial in mitigating the adverse effects of climate change on rangelands, pastoral livelihoods and wildlife populations.

No abstract

1. Foliar fungal pathogens can substantially reduce plant biomass. This effect can be modulated by environment conditions, such as soil nitrogen availability and air temperature. The ongoing global changes are altering these variables and thus interact with pathogens to influence plant biomass, but experimental test of their interactions is scarce.2. We conducted a 4-year field experiment in a Tibetan alpine meadow to examine the interactive effects of nitrogen addition, warming and foliar pathogens (via fungicide application) on plant biomass. We also measured plant functional traits, species richness and abundance to test the possible mechanisms underlying these interactions.3. Our results showed that foliar fungal pathogens reduced plant community biomass under nitrogen addition, which in turn weakened the positive nitrogen effect on community biomass. Mechanistically, nitrogen addition shifted the plant communities towards fast-growing traits; this happened predominantly because of changes in within-species trait values, including an increase in specific leaf