Positive association regulates divergent diversity patterns of co‐occurring growth forms

Abstract Plant diversity patterns across broad spatial extents are shaped by regional climatic factors, local edaphic conditions, and biotic interactions. These patterns can diverge among different growth forms (e.g. woody versus herbaceous species) due to varying responses to environmental conditions and interspecific associations. However, biodiversity inventories across large spatial extents rarely collect data on multiple growth forms at the same sites. We evaluated macroecological multifacet diversity patterns of woody shrubs and understorey herbs in 1341 inventory plots along steep climatic and edaphic gradients from China's shrublands. We further examined the role of growth‐form association and its potential influence on diversity patterns along environmental gradients. We found that temperature and precipitation were the primary drivers of biodiversity. However, temperature had contrasting effects: shrub diversity increased with temperature, while herb diversity decreased. Soil properties had less influence than climate but still played a role, with soil organic carbon positively correlated with shrub diversity. Patterns of taxonomic and phylogenetic diversity were generally similar, but the effects of precipitation were more pronounced for phylogenetic diversity. Notably, shrub diversity was positively associated with herb diversity, a pattern consistent with a potential role of biotic associations in modulating responses to abiotic stress. However, this did not fully offset the negative impacts of temperature on herb diversity. In addition, the relationships between shrub and herb diversity differed between annual and perennial herbs, with perennial herb diversity showing consistently positive associations with shrubs, whereas annual herbs exhibited more variable relationships with shrubs and environmental gradients. Synthesis . Biodiversity responses to environmental gradients diverge across co‐occurring growth forms and between taxonomic and phylogenetic dimensions. By integrating these patterns within the same communities, this study offers a broader framework for understanding how environmental filtering and cross‐growth‐form associations jointly shape local assemblages. This perspective advances community assembly theory and improves predictions of plant community responses to environmental change.