Aims <p>Functional trait assembly along environmental stress gradients is a cornerstone for predicting community responses to global change, yet leaf anatomical traits remain under-represented in community ecology, especially regarding the balance between species turnover and intraspecific trait variation (ITV).</p> Methods <p>We quantify community-level leaf anatomical trait assembly across three major: the Mongolian Plateau (MP), the Loess Plateau (LP), and the Qinghai-Tibet Plateau (TP). These regions span convergent stress gradients of declining precipitation, temperature and soil fertility but increasing solar and UV radiation. We measured six traits (epidermal thickness, mesophyll thickness, leaf thickness, palisade thickness, spongy thickness and palisade-to-spongy ratio) for 30 grassland communities, and decomposed trait variation into ITV and species turnover components (occurrence vs. abundance).</p> Results <p>Communities on TP exhibited the most conservative anatomical syndromes, with markedly thicker epidermis and palisade tissues, reflecting strong abiotic filtering under extreme cold and radiation. Across all plateaus, most community-weighted traits displayed unimodal responses to stress, consistent with a transition from competition-driven acquisitive strategies under low stress to stress-tolerant conservative strategies under high stress. Variance partitioning revealed that species turnover, especially through shifts in species occurrence, explained substantially more trait variation than ITV. The weak trait-environment coupling on TP suggests a saturation of anatomical conservatism under long-term extreme stress.</p> Conclusions <p>Our findings demonstrate that grassland communities adapt to intensifying environmental stress predominantly through species turnover, which is a relatively low-cost process, rather than through costly anatomical plasticity. This provides a mechanistic basis for predicting shifts in functional composition under global change.</p>