Effect of N and P addition on soil organic C potential mineralization in forest soils in South China

摘要

Atmospheric nitrogen deposition is at a high level in some forests of South China. The effects of addition of exogenous N and P on soil organic carbon mineralization were studied to address: (1) if the atmospheric N deposition promotes soil C storage through decreasing mineralization; (2) if the soil available P is a limitation to organic carbon mineralization. Soils (0-10 cm) was sampled from monsoon evergreen broad-leaved forest (MEBF), coniferous and broad-leaved mixed forest (CBMF), and Pinus massoniana forest (PMF) in Dinghushan Biosphere Reserve (located in Guangdong Province, China). The soils were incubated at 25℃ for 45 weeks, with addition of N (NH{sub}4NO{sub}3 solution) or P (KH{sub}2PO{sub}4 solution). CO{sub}2-C emission and the inorganic N ((NH{sub}4){sup}+-N and (NO{sub}3){sup}--N) of the soils were determined during the incubation. The results showed that CO{sub}2-C emission decreased with the N addition. The addition of P led to a short-term sharp increase in CO{sub}2 emission after P application, and the responses of CO{sub}2-C evolution to P addition in the later period of incubation related to forest types. Strong P inhibition to CO{sub}2 emission occurred in both PMF and CBMF soils in the later incubation. The two-pool kinetic model was fitted well to the data for C turnover in this experiment. The model analysis demonstrated that the addition of N and P changed the distribution of soil organic C between the labile and recalcitrant pool, as well as their mineralization rates. In our experiment, soil pH can not completely explain the negative effect of N addition on CO{sub}2-C emission. The changes of soil inorganic N during incubation seemed to support the hypothesis that the polymerization of added nitrogen with soil organic compound by abiotic reactions during incubation made the added nitrogen retard the soil organic carbon mineralization. We conclude that atmospheric N deposition contributes to soil C accretion in the three subtropical forest ecosystems, however, the shortage of soil available P in CBMF and PMF may also retard soil organic C mineralization.