Defoliation and neighbouring legume plants accelerate leaf and root litter decomposition of Leymus chinensis dominating grasslands

Abstract Dominant plant species coexist with other species from the same or other trophic levels (e.g. neighbouring plants and herbivores), which may give rise to neighbourhood and defoliation effects on litter decomposition. Yet, little information exists on if and how neighbouring plant species and herbivore defoliation interactively affect the decomposition of dominant species, and further whether decomposition of leaves and roots has similar responses. Here, we simultaneously examined both the leaf and fine root litter decomposition of the dominant grass species, Leymus chinensis, in the presence and absence of a neighbouring plant species, Lathyrus quinquenervius (a functionally dissimilar legume species), and simulated herbivore defoliation by mowing. We found that both neighbouring legume plants and defoliation significantly accelerated both leaf and root litter decomposition of L. chinensis, and that neighbouring legume plants exerted stronger effects on litter decomposition than defoliation. The positive effects of neighbouring legume plants occurred across all study periods, whereas defoliation only had a positive effect during the first 15 days of litter decomposition. Neighbouring legume plants and defoliation exerted strong additive effects on root litter decomposition, and interactive effects on leaf litter decomposition. These findings highlight the significance of functionally dissimilar species coexistence to facilitate nutrient cycling in grasses - dominated grasslands.