Robust leaf trait relationships underpin plant adaptation to severe drought in grasslands

1. Leaf trait–trait relationships are central to plant adaptation and ecosystem functioning, yet their responses to extreme environmental conditions remain poorly understood. 2. To address this, we conducted an extreme drought experiment across six grasslands in Inner Mongolia, including desert steppe, typical steppe, and meadow steppe, with two treatments: ambient precipitation and extreme drought reducing growing-season rainfall by 66%. For 32 herbaceous species, we measured specific leaf area (SLA), leaf nitrogen (Nmass), and leaf phosphorus (Pmass) under both treatments and examined shifts in their correlations. We also evaluated intraspecific trait plasticity to uncover mechanisms underlying any changes. 3. Allometric relationships among SLA-Nmass, SLA-Pmass, and Nmass-Pmass persisted under both treatments. While extreme drought did not alter the slopes of these relationships, it significantly lowered the elevations of SLA-Pmass and Nmass-Pmass. The stability of slopes across species reflected interspecific variation in the plasticity of trait pairs, whereas the downward shifts in elevation were largely driven by reduced species-level phosphorus concentrations across most sites. 4. Synthesis. These results demonstrate that interspecific leaf trait relationships are robust under extreme drought, providing novel insights into the trait-based mechanisms that allow plants to adapt to severe environmental stress.