Divergence in leaf versus root decomposition in three Stipa species along a grassland grazing exclusion gradient

Litter decomposition is a critical driver of carbon and nutrient cycling in terrestrial ecosystems. Numerous studies have demonstrated that plant litter typically decomposes faster in its native habitat (‘home’) than in foreign environments (‘away’), known as the home-field advantage (HFA). Much of our understanding of the HFA effect arises from leaf litter decomposition in forest ecosystems, how HFA regulates the decomposition of leaf and root litters in grasslands remains unclear. We performed a reciprocal litter transplant experiment using leaf and root materials from three Stipa species (Stipa bungeana, Stipa grandis, and Stipa przewalskyi) that dominate semi-arid grassland sites with different grazing exclusion durations (5, 15, and 32 years). Generally, we found no HFA effect for either leaf or root decomposition across the three Stipa species. Litter type and plant identity interactively affected the decomposition rate: roots decomposed slower than leaves in S. bungeana and S. grandis, while decomposition rates of roots and leaves were similar in S. przewalskyi. Notably, compared with the other two species, S. przewalskyi exhibited faster root decomposition and slower leaf decomposition. Our results demonstrated that, in terms of litter decomposition traits of dominant species, leaf decomposition decreased with longer grazing exclusion duration, while root decomposition rates increased. In addition, litter carbon and nitrogen losses exhibited stronger stoichiometric coupling in leaves compared to roots. Our findings provide little evidence for HFA effects in enclosed grasslands. Instead, shifts in dominant species lead to distinct temporal patterns in leaf versus root decomposition along the grazing exclusion chronosequence, providing new insights into above- and belowground C and N dynamics during grassland restoration.