Joint effects of shrub encroachment and aridity on herbaceous elemental traits and biogeochemical coordination in northern grasslands

Aims Shrub encroachment is projected to intensify under increasing drought in arid and semi-arid grasslands, potentially altering species interactions and ecosystem processes. Although leguminous shrubs are known to redistribute soil resources, their influence on the foliar elementomes and biogeochemical niches of coexisting herbs remains poorly understood. Methods Here, we conducted a large-scale transect survey across the Inner Mongolian steppe, measuring leaf macro- and micro-elements of Caragana shrubs and associated herbaceous species, alongside key soil properties. We developed a multidimensional framework that integrates biogeochemical niches with foliar elemental networks to evaluate shrub-herbaceous interactions. Results We found that Caragana generally reduced elemental accumulation in understory herbs, but this inhibition weakened with increasing aridity, supporting the stress-gradient hypothesis. Shrub presence and aridity jointly influenced herbaceous elemental traits, with grasses and forbs showing contrasting responses. The biogeochemical niche distance between forbs and grasses increased with aridity, indicating that shrubs may promote their resource-use partitioning. Meanwhile, we found that shrub encroachment increased nodes and edges while reducing clustering and edge density in foliar elemental networks of understory plants, suggesting that the herbs may form less integrated networks as a trade-off to lower their construction costs. Structural equation models further revealed that shrub height and soil fertility indirectly affected herbaceous productivity by weakening network connectivity, implying reliance on specific elemental phenotypes under stress. Conclusions Our findings highlight the utility of multidimensional elemental frameworks for understanding grassland responses to climate change and woody encroachment, providing novel mechanistic insights into biogeochemical cycling in degraded northern grasslands.