Plant biodiversity is often correlated with ecosystem functioning in terrestrial ecosystems. However, we know little about the relative and combined effects of above- and belowground biodiversity on multiple ecosystem functions (for example, ecosystem multifunctionality, EMF) or how climate might mediate those relationships. Here we tease apart the effects of biotic and abiotic factors, both above- and belowground, on EMF on the Tibetan Plateau, China. We found that a suite of biotic and abiotic variables account for up to 86% of the variation in EMF, with the combined effects of above- and belowground biodiversity accounting for 45% of the variation in EMF. Our results have two important implications: first, including belowground biodiversity in models can improve the ability to explain and predict EMF. Second, regional-scale variation in climate, and perhaps climate change, can determine, or at least modify, the effects of biodiversity on EMF in natural ecosystems.

Biodiversity is crucial for the provision of ecosystem functions. However, ecosystems are now exposed to a rapidly growing number of anthropogenic pressures, and it remains unknown whether biodiversity can still promote ecosystem functions under multifaceted pressures. Here we investigated the effects of soil microbial diversity on soil functions and properties when faced with an increasing number of simultaneous global change factors in experimental microcosms. Higher soil microbial diversity had a positive effect on soil functions and properties when no or few (i.e., 1–4) global change factors were applied, but this positive effect was eliminated by the co-occurrence of numerous global change factors. This was attributable to the reduction of soil fungal abundance and the relative abundance of an ecological cluster of coexisting soil bacterial and fungal taxa. Our study indicates that reducing the number of anthropogenic pressures should be a goal in ecosystem management, in addition to biodiversity conservation.

The Tibetan alpine grasslands, sharing many features with arctic tundra ecosystems, have a unique non‐growing‐season climate that is usually dry and without persistent snow cover. Pronounced winter warming recently observed in this ecosystem may significantly alter the non‐growing‐season carbon cycle processes such as soil respiration (R_s), but detailed measurements to assess the patterns, drivers of, and potential feedbacks on R_s have not been made yet. We conducted a 4 year study on R_s using a unique R_s measuring system, composed of an automated soil CO₂ flux sampling system and a custom‐made container, to facilitate measurements in this extreme environment. We found that in the nongrowing season, (1) cumulative R_s was 82–89 g C m⁻², accounting for 11.8–13.2% of the annual total R_s; (2) surface soil freezing controlled the diurnal pattern of R_s and bulk soil freezing induced lower reference respiration rate (R₀) and temperature sensitivity (Q₁₀) than those in the growing season (0.40–0.53 versus 0.84–1.32 µmol CO₂ m⁻² s⁻¹ for R₀ and 2.5–2.9 versus 2.9–5.6 for Q₁₀); and (3) the intraannual variation in cumulative R_s was controlled by accumulated surface soil temperature. We found that in the summer monsoon‐dominated Tibetan alpine grassland, surface soil freezing, bulk soil freezing, and accumulated surface soil temperature are the day‐, season‐, and year‐scale drivers of the non‐growing‐season R_s, respectively. Our results suggest that warmer winters can trigger carbon loss from this ecosystem because of higher Q₁₀ of thawed than frozen soils.