Biodiversity-function relationships in ecosystems are known to be driven by environmental conditions, including climate change. Plant functional groups (PFGs), specifically their evolutionary history, nitrogen-fixation capacity or photosynthetic-pathway likely play a critical role in shaping microbial communities and their impact on ecosystem functions, but experimental evidence is limited. Here, we simultaneously manipulated plant and microbial diversity in a microcosm study to investigate their interactions and impact on soil functions during drought. Our results highlight the dominant role of PFGs in explaining the effects of biodiversity loss on soil functions. Microbial diversity loss significantly influenced microbially-driven soil N and P pools and processes, with PFGs moderating these effects, especially under drought. Our findings offer crucial mechanistic insights for ecosystem management in the face of climate change, emphasizing the significance of PFGs in shaping soil functions and their resilience. This study underscores the importance of considering above- and belowground biodiversity, for preserving belowground functions in changing environments.

Isolating significant signals from temporal variations in autotrophic and heterotrophic components of ecosystem respiration (Reco) is required to better quantify the temperature sensitivity of the land carbon cycle processes. Here we present diurnal and seasonal patterns in field and model-based components of respiration and investigate their responses to environmental conditions at a dry eucalypt forest, the Cumberland Plain SuperSite of the Australian Terrestrial Ecosystem Research Network. We conducted measurement campaigns of total CO2 flux from the soil surface (Rsoil), soil microbial respiration (Rmicrobe), root respiration (Rroot), litter respiration (Rlitter), and stem respiration (Rstem) in 2018. In total, six infrared gas analyzers with closed, dynamic auto-chambers and six forced diffusion auto-chambers were used for periodic campaigns. Further, Reco and its components were simulated using the Community Atmosphere-Biosphere Land Exchange model (CABLE), constrained by eddy covariance measurements and chamber measurements of Rsoil. A new version of CABLE was implemented with the Dual Arrhenius Michaelis Menten (DAMM) formulation to assess the importance of substrate availability for simulating Rmicrobe. We found that respiration rates showed similar diurnal patterns among the components, showing diurnal hysteresis between respiration components and temperature. In this dry ecosystem, the respiratory components were more responsive to seasonally increasing temperature in wet than in dry periods, and the responses were dependent on atmospheric relative humidity affecting the litter layer moisture content. The temperature sensitivity was significantly higher in Rstem than in other components. Based on observed fluxes of Rmicrobe in trenched plots and Rsoil in intact soil plots, the mean contribution of Rroot to Rsoil was less than 20 % for the dry seasons, while mean Rstem was two times greater than mean Rsoil suggesting that Rstem should be not overlooked in ecosystem flux estimations. This study highlights that partitioning the respiratory components and accounting for their different temperature-responses will be necessary to reduce uncertainty in modelling carbon-climate feedbacks.