Structural diversity surpasses species diversity in regulating the spatial variation of grassland productivity

Abstract Understanding the influence of biodiversity on ecosystem productivity remains crucial in ecology. Recent evidence indicates that structural diversity plays a critical role in regulating plant productivity. However, empirical studies on the relationship between community structure and plant productivity across different environments in grassland ecosystems remain limited. This limitation is in part due to the perceived simplicity of the grassland structure and the inherent methodological challenges in conducting detailed structural surveys. In this study, we investigated the contributions of structural and species diversity to grassland productivity and their associated interactions along a precipitation gradient on the Mongolian Plateau. We collected precise coordinate and height data for 55,311 individual plants across distinct grassland types, enabling a systematic assessment of vertical and horizontal structural dimensions. We hypothesized that structural diversity, encompassing both axes, would be a primary determinant of grassland productivity, with dominant structural dimensions shifting across the moisture gradient. We revealed that the relative contribution of structural diversity to productivity (77%) was significantly higher than that of species diversity (23%) in the grassland ecosystems of the Mongolian Plateau. However, the relative importance of species diversity, vertical structure and horizontal structure varied across the grassland types. Specifically, the key factors influencing productivity changed from species diversity in the desert steppe to vertical structure in the typical steppe and ultimately to horizontal structure in the meadow steppe. Synthesis : These findings underscore the important yet often‐overlooked role of structural diversity in predicting grassland productivity, while confirming the hypothesized shift in dominant structural dimensions along environmental gradients. Although detailed structural assessments in grassland ecosystems remain labour intensive and time‐consuming, future advances in remote sensing, particularly Light Detection and Ranging (LiDAR), hold great promise for overcoming these challenges by enabling large‐scale, high‐resolution structural measurements. These tools may substantially enhance our understanding of grassland ecosystem dynamics and inform effective management and conservation strategies.