Abstract
Litter is an important hinge connecting plants and soil, and its decomposition is a crucial process of nutrient cycling. However, the litter mixing effects (ME) on main functions related to soil carbon (C), nitrogen (N), and phosphorus (P) cycling, particularly in alpine ecosystems, remain unclear. Here, we incubated four single litters and six mixtures formed by pairwise combinations of single litter in the field for 630 days in an alpine grassland on the Tibetan Plateau, to determine ME (additive, synergistic or antagonistic effect) on soil functional indicators, including total and dissolved soil nutrients, microbial biomass, and enzyme activities. The results showed that: (1) Mixed litter decomposition produced mostly non-additive effects on soil indicators, of which synergistic effects were more prevalent than antagonistic effects. Specifically, soil dissolved organic carbon (SDOC), soil dissolved organic nitrogen (SDON), soil microbial biomass nitrogen (SMBN), soil β-1,4-glucosidase (BG) activity, and soil acid phosphatase (AP) activity exhibited mostly synergistic effects, accounting for 66.7%, 50.0%, 60.0%, 53.3%, and 40.0% of all cases, respectively. In contrast, only three indicators were dominated by additive effects, with 83.3% for soil organic carbon (SOC), 60.0% for soil total phosphorus (STP), and 56.7% for soil urease (URE) activity. (2) Strength of ME on soil functional indicators exhibited variability, with an average of 17.10% for SDOC, 18.65% for SDON, 28.74% for SMBN, 8.64% for BG activity, and 5.26% for AP activity due to synergistic effects. In contrast, there was an average decrease of 16.57% for STP due to antagonistic effects. (3) Strength of ME on SDOC, SDON, SMBN, and activities of BG and AP was correlated with cellulose (CE), P, and C/N ratio of litter. Our findings highlight litter mixtures enhance the accumulation of soil active C, N, and promote hydrolase activities in a synergistic way, and strengths of these effects were regulated by litter chemical traits. These findings suggest that the coexistence of plant species with contrasting litter chemical traits can accelerate the recovery of soil fertility through synergistic litter mixing effects in degraded alpine grasslands, thereby contributing to the functional maintenance of alpine grassland ecosystems.