Effects of long-term nitrogen addition and precipitation reduction on glomalin-related soil protein and soil aggregate stability in a temperate forest

As a microbial-derived carbon (C) compound, the glomalin-related soil protein (GRSP) is not only a considerable amount of soil active organic C, but also an effective aggregate binder. At present, due to various global change factors, the forest ecosystem C stock and soil stability are facing unprecedented challenges. As the two of important global change factors, the effects of increased nitrogen (N) deposition, precipitation pattern change and their interaction on the soil organic C (SOC) stock, aggregate stability and GRSP and their correlations are not clear. Based on this, we conducted a long-term field experiment in a temperate forest to simulate N addition and precipitation reduction (n = 3). The experimental design included a control, decreased precipitation (DP), N addition (+N) and their interaction (+NxDP). Compared with the control, the negative effect of N addition on the total GRSP (T-GRSP) was not significant, but it significantly reduced the easily extractable GRSP (EE-GRSP) and mean weight diameter (MWD) (P < 0.05). The T-GRSP, EE-GRSP and MWD all showed significant negative responses to the DP treatment (P < 0.05). Compared with the single treatment, the +NxDP treatment further strengthened the negative effects on the EE-GRSP and MWD (P < 0.05). In addition, we found that the MWD was mainly controlled by large aggregates (> 2 mm), and the DP and +NxDP treatments destroyed the seasonal stability of aggregate. The correlation analysis showed that the T-GRSP had a strong correlation with the SOC, while the EE-GRSP had a more significant correlation with the MWD (P < 0.001). Through this study, we emphasized the profound impact of global change factors on temperate forest, clarified the ecological functions of the T-GRSP and EE-GRSP, and confirmed the reciprocal mechanism of the GRSP, SOC and MWD. Collectively, our results will be helpful to evaluate the impact of climate change on forest ecosystems from the perspective of microbial derivatives.