Decreased glomalin-related soil protein with nitrogen deposition in a 3-year-old Cunninghamia lanceolata plantation

Purpose Glomalin-related soil protein (GRSP) is an essential component of soil organic C for maintaining soil quality and structure and plays a critical role in soil carbon (C) sequestration. However, how GRSP changes under nitrogen (N) deposition remains poorly understood. Materials and methods We assessed total GRSP (T-GRSP) and easily extractable GRSP (EE-GRSP) under a control (no N input), low N addition (LN, 40 kg N ha −1 year −1 ), and high N addition (HN, 80 kg N ha −1 year −1 ) treatments in 2015 and 2016 in a Chinese fir ( Cunninghamia lanceolata ) plantation in the subtropical China. We also analyzed soil properties contents and explored the stoichiometric ratios of soil organic C (SOC), total N (TN), and total phosphorus (TP) with GRSPs. Results Compared to the control, both T-GRSP and EE-GRSP were significantly reduced under the HN treatment, but had no significant difference under the LN treatment. The ratio of T-GRSP and EE-GRSP was reduced by the N addition. Soil organic C (SOC) and dissolved organic C (DOC) were significantly affected by N addition treatments. The ratios of GRSP-C to SOC and of EEGRSP-C to SOC ranged from 6.29 to 16.07% and 1.34 to 3.52%, respectively. T-GRSP and EE-GRSP were positively correlated with SOC/TN ratio, but negatively correlated with soil TN/TP and SOC/TP ratios. Conclusion Our results indicated that the GRSP reductions under N deposition in soil are mediated by soil C, N, and P stoichiometry, and particularly, the reduction of EE-GRSP by DOC. This study improved our mechanistic understanding of dynamics of GRSPs under increasing N enrichment in subtropical plantation ecosystems.