Litter quality mediated the effect of nitrogen addition and precipitation reduction on the release and immobilization of plant litter nitrogen and phosphorus

A long-term field litterbag manipulation experiment was conducted to examine the effects of reduced precipitation (-30% of through-fall), nitrogen (N) addition (50 kg N.ha(-1).yr(-1)), and their combination (-30% of through-fall and 50 kg N.ha(-1).yr(-1)) on the release and immobilization of N and phosphorus (P) in four litter types (Pinus koraiensis (PK), Tilia amurensis (TA), Quercus mongolica (QM), and their mixture (MIX)). The results showed that N addition did not significantly stimulate litter decomposition, whereas precipitation reduction and the interaction significantly inhibited litter decomposition. N immobilization was significantly enhanced by N addition and reduced precipitation in the PK, QM, and MIX litters but was significantly inhibited in the TA litter. N addition, reduced precipitation, and their combination significantly increased the final P concentration of the litter in each sampling period. Furthermore, interestingly, there was a significant exponential correlation between the remaining N and final P concentration in the PK litter and a significant linear correlation for the QM and MIX litters, but no significant correlation for the TA litter, indicating that the dynamic relationship between the remaining N and final P concentration in the litter depended on the litter type. These results suggest that the forest litter layer may alleviate the effects of N deposition by increasing litter N immobilization and aggravating soil P limitation by inhibiting litter P release following N deposition. Reduced precipitation may further affect biogeochemical cycles by inhibiting the release of litter N and P.