Effects of simulated nitrogen deposition on litterfall carbon and nitrogen fractions in a monsoon evergreen broad-leaved forest

Objective  To investigate responses of litterfall carbon (C) and nitrogen (N) fractions to atmospheric N deposition in a monsoon evergreen broad-leaved forest.

Method  Three levels of N addition, including low N (LN, 35 kg·hm^–2), medium N (MN, 70 kg·hm^–2) and high N (HN, 105 kg·hm^–2), were conducted for two years, with a control without extra N addition (CK). Fresh litterfall samples were collected in the dry and wet seasons, respectively. C and N fraction contents were analyzed.

Result  N additions significantly increased the contents of total organic carbon (TOC) and water-soluble organic carbon (WSOC) in the wet season, with the WSOC/TOC ratio presenting a rising trend. N additions did not significantly alter acid-insoluble fraction carbon (AIFC) content and its proportion to TOC, although a decreasing trend was observed compared with the control. Different N addition treatments did not significantly change the contents of litterfall total nitrogen (TN), water-soluble nitrogen (WSN) and acid-insoluble fraction nitrogen (AIFN). The proportions of WSN and AIFN to TN were not altered significantly either. The short-term N additions did not significantly affect litterfall C/N ratio and AIFC/AIFN ratio, but significantly increased WSOC/WSN ratio in the dry season.

Conclusion  The atmospheric N deposition promotes labile C accumulation and therefore is beneficial for litterfall decomposition to transfer nutrients into soil, which will further affect nutrient cycling in the tropical forest.