Forage quality in tundra grasslands under herbivory: Silicon‐based defences, nutrients and their ratios in grasses

Herbivore-induced changes in both leaf silicon-based defence and nutrient levels are potential mechanisms through which grazers alter the quality of their own grass supply. In tundra grasslands, herbivores have been shown to increase contents grasses; yet, it is an open question whether they also levels. Here, we asked if, what extent, affect silicon content silicon:nutrient ratios grasses found grasslands. We performed herbivore-interaction field-experiment spanning four tundra-grassland sites. At each site, established reindeer-open reindeer-exclusion plots tundra-patches that had disturbed or not by small rodents during previous winter, for a total 96 plots. randomly collected over 1,150 samples inherently silicon-rich silicon-poor species throughout growing season analysed silicon, nitrogen phosphorus leaf. Small-rodent winter disturbance did content, but increased (i.e. lowered ratios) enhancing (+20%–22%) (+26%–34%) grasses. Reindeer summer herbivory decreasing (−7%). However, two together offset these increments grasses, thus reducing towards level those absence further (+13%–22%) relative Synthesis. provide first community-level, field-based assessment how herbivory-driven grass-forage Herbivores promote net accumulation rather enhanced overall quality. Yet, magnitude varied depending on herbivore(s) involved differed between Such differential herbivory-induced within may mediate plant–herbivore interactions altering herbivore forage patterns food choices. utilised herbivores, was decreased This could advantage against herbivory, potentially being one pathways vegetation states dominated maintained herbivores.