Effects of Nitrogen Deposition on CH_4 Uptake and CO_2 Emission from temperate forests in Northeastern China

摘要

Little is known about how N deposition affects greenhouse gas balances in different temporal patterns (daytime and nighttime), and few studies have been conducted to quantify the effects of N deposition on soil CH_4 uptake and CO_2 emission in a typical temperate forests. To investigate the effects of N deposition on soil CH_4 uptake and CO_2 emission, simulated N deposition experiment was initiated in temperate forests in Northeastern China in May 2011. In this study, NH_4NO_3 fertilizer was applied throughout the growing season at four N treatment levels (three replicates): control (CK), no added N; low-N (T_L), 5 g N m~(-2)·yr~(-1); medium-N (T_M), 10 g N m~(-2)·yr~(-1); and high-N (T_H), 15 g N m~(-2)·yr~(-1). Diurnal soil CH_4 uptake and CO_2 emission rates were observed in August 2014 using Greenhouse Gas Analyzers. Our results showed that N deposition tended to restrict CH_4 uptake and significantly increased soil CO_2 emission (except in the T_H treatment). In addition, the CO_2 and CH_4 fluxes in daytime and nighttime were significantly different. These results indicate that N deposition controls the CH_4 uptake and suggest that alterations of the N cycle due to N deposition may convert sequestered C in forest soils into a C source. However, this paper is also to promote a better understanding of the impact of N deposition on soil C fluxes under the different temporal patterns.