Grazing disrupts the trade‐off between silica‐ and phenol‐based plant defences along an aridity gradient in grasslands

Abstract Silicon (Si) and phenolics are vital players in the plant kingdom, enabling plants to combat both biotic stresses, like herbivory and abiotic challenges, such as drought. Yet, the interplay between community‐level silica and phenolic defences in response to livestock grazing and climatic factors across large spatial scales remains underexplored. We analysed the Si and phenolic concentrations of plant communities from 15 widely distributed sites, strategically selected along a 1700‐km aridity gradient in the temperate grasslands of northern China, with livestock grazing manipulated (grazed vs. ungrazed) at each location. Our findings revealed that grazing significantly enhanced community‐level silica‐based defences in less arid grasslands, mainly due to increased intraspecific Si concentration, while its impact on phenol‐based defences was minimal. Notably, as aridity increased, Si concentration surged while phenolic concentration dwindled, indicating a shift from phenol‐ to silica‐based defences in drier environments. In ungrazed grasslands, silica and phenolic defenses were negatively correlated, a relationship that vanished in grazed treatment. Further analysis revealed that Si concentration was primarily influenced by grazing management, while phenolic concentration was mainly associated with aridity. Our study provides the community‐level and regional scale assessment of how grazing management impacts plant silica‐ and phenol‐based defences along an aridity gradient in the temperate grasslands. Together, our results showed that plants accumulated Si but not phenolics as a defence mechanism in response to decades of livestock grazing. Importantly, our findings suggested that grazing disrupted the trade‐off between the two plant defence strategies along the aridity gradient. These insights emphasize the critical role of grazing management and aridity in shaping silica and phenolic defences, revealing a complex interplay between environmental conditions and plant defence strategies in grassland ecosystems. Read the free Plain Language Summary for this article on the Journal blog.