Effects of Experimental Nitrogen Deposition and Litter Manipulation on Soil Organic Components and Enzyme Activity of Latosol in Tropical Rubber Plantations

Abstract

It is of great scientific significance in regulating plantation ecosystem restoration to investigate the effects of the nitrogen (N) deposition and litter manipulation on soil organic carbon components and enzyme activities. A micro-plot experiment was conducted with four nitrogen additions[CK (0 kg·hm-2·a-1, calculated by N), LN (50 kg·hm-2·a-1), MN (100 kg·hm-2·a-1), and HN (200 kg·hm-2·a-1)] and two litter treatments[LR (litter removal) and L (litter retained)] for tropical rubber plantations in western Hainan Island. The soil physico-chemical properties, soil organic carbon components, and enzyme activities in 0-10 cm and 10-20 cm depths were analyzed. The results showed that soil pH significantly decreased with elevated N addition and litter removal. The contents of NO3--N and NH4+-N significantly increased with elevated N addition. Moreover, there was a significant interaction between N addition and litter treatment on the contents of NO3--N and NH4+-N (P < 0.05). Compared to that with L, LR reduced SOC and its component contents; particularly, the largest decrease was in LFOC by 29.0%-81.4% in the 0-10 cm depth and 23.5%-58.4% in 10-20 cm, respectively. The contents of SOC and its components presented a trend of increasing first and then decreasing with elevated N addition irrespective of litter treatment, and those contents were significantly higher at LN than those at HN. There was a significant interaction between N addition and litter treatment on SOC, LFOC (0-10 cm), and HFOC contents. Compared with that under L, PPO activity was significantly reduced at LR under CK and LN but was significantly increased at LR under MN and HN, respectively. Variance analysis showed significant interactive effects between N addition and litter treatment on PPO and CBH (0-10 cm) activities, and the soil enzyme activity (BG, PPO, and CBH) responding to N addition was greater than that to the litter treatment. Pearson correlation analysis showed that SOC content was extremely positively correlated with MBC, POC, LFOC, and HFOC contents. To summarize, litter retained combined with low N deposition played an important synergistic role of improving SOC pool and soil enzyme activities for tropical rubber plantation systems.