Nitrogen Deposition Enhances Interactions Between Litter Types During the Early Stage of Decomposition

Nitrogen deposition can alter the interactions between litter types during their decomposition, and thus affect material cycling and ecosystem stability. However, it is unclear how the differences in the initial chemical properties of litter mixtures affect their response to nitrogen deposition. In this study, we investigated three litter mixtures: high quality–high quality (Robinia pseudoacacia–Stipa grandis, Rp‐Sg, mixed form F1), high quality–low quality (Rp–Setaria viridis, Rp‐Sv, F2), and low quality–low quality (Artemisia gmelinii–Sv, Ag‐Sv, F3). Each of the litter types can be found in Rp plantations in the Loess Hilly Region, China. We subjected the litter mixtures to nitrogen deposition treatments (0 and 4–12 g·m−2·a−1) in a 326‐day indoor decomposition experiment. Decomposition parameters of each litter type in monospecific and mixed decomposition were compared to investigate the interactions between litter types under nitrogen deposition. The results indicated that, in the early stage of mixed decomposition, litter types of similar substrate quality did not affect the decomposition of each other (i.e., in the F1 and F3 mixtures). In contrast, the decomposition of low‐quality litter (Sv) was accelerated by that of high‐quality litter (Rp) when there was no nitrogen deposition. The overall degree of the mutual effects (Rinter,t) for the litter decomposition rate in F1, which has an overall higher quality, increased and then decreased with increasing nitrogen deposition; whereas the Rinter,t for the litter decomposition rate in F2 and F3, which have an overall poor quality (p < 0.05), increased continuously. In general, nitrogen deposition increased the interactions between litter types during the early stage of mixed decomposition. Given that most interactions were synergistic, this effect of nitrogen deposition may alleviate its inhibitory effects on litter decomposition in the study region.