World-wide impacts of climate change and nitrogen deposition on vegetation structure, composition, and functioning of shrublands.

Environmental changes and their effects are among the most pressing topics of today's ecological research. Shrublands, although widespread across the globe, remain understudied in this respect. We conducted a global meta-analysis of 81 shrubland sites subjected to experimental warming, shifts in precipitation (e.g. increased precipitation and drought), and nitrogen addition to quantify seven types of vegetation responses, including density and cover, species diversity, shrub proportion, and ecosystem functions. Our results indicated that the magnitude of responses varied depending on the vegetation metrics and treatment conditions. Specifically, aboveground biomass (AGB) was most sensitive to warming, increased precipitation, and nitrogen addition, while density was most responsive to drought treatment. Short-term treatments (1-5 yr) generally elicited stronger responses than long-term ones (> 5 yr), particularly under drought. High sensitivity to changes in climate and nitrogen addition was observed at extremely arid sites (aridity index < 0.2), and water availability strongly mediated sensitivity variation. Surprisingly, many vegetation metrics revealed no association between sensitivity variability and site water availability. Our research offers a global perspective on shrubland vegetation responses to environmental changes, highlighting the importance of water availability in sustaining shrubland biodiversity and functioning under future conditions.