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Nitrogen deposition contributes to soil acidification in tropical ecosystems
Author(s) -
Lu Xiankai,
Mao Qinggong,
Gilliam Frank S.,
Luo Yiqi,
Mo Jiangming
Publication year - 2014
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.12665
Subject(s) - soil acidification , soil ph , ecosystem , environmental chemistry , soil water , ocean acidification , cation exchange capacity , leaching (pedology) , environmental science , acid neutralizing capacity , terrestrial ecosystem , chemistry , ecology , soil science , acid deposition , biology , climate change
Elevated anthropogenic nitrogen (N) deposition has greatly altered terrestrial ecosystem functioning, threatening ecosystem health via acidification and eutrophication in temperate and boreal forests across the northern hemisphere. However, response of forest soil acidification to N deposition has been less studied in humid tropics compared to other forest types. This study was designed to explore impacts of long‐term N deposition on soil acidification processes in tropical forests. We have established a long‐term N‐deposition experiment in an N‐rich lowland tropical forest of Southern China since 2002 with N addition as NH 4 NO 3 of 0, 50, 100 and 150 kg N ha −1 yr −1 . We measured soil acidification status and element leaching in soil drainage solution after 6‐year N addition. Results showed that our study site has been experiencing serious soil acidification and was quite acid‐sensitive showing high acidification ( pH (H2O) <4.0), negative water‐extracted acid neutralizing capacity (ANC) and low base saturation (BS,< 8%) throughout soil profiles. Long‐term N addition significantly accelerated soil acidification, leading to depleted base cations and decreased BS, and further lowered ANC. However, N addition did not alter exchangeable Al 3+ , but increased cation exchange capacity (CEC). Nitrogen addition‐induced increase in SOC is suggested to contribute to both higher CEC and lower pH . We further found that increased N addition greatly decreased soil solution pH at 20 cm depth, but not at 40 cm. Furthermore, there was no evidence that Al 3+ was leaching out from the deeper soils. These unique responses in tropical climate likely resulted from: exchangeable H + dominating changes of soil cation pool, an exhausted base cation pool, N‐addition stimulating SOC production, and N saturation. Our results suggest that long‐term N addition can contribute measurably to soil acidification, and that shortage of Ca and Mg should receive more attention than soil exchangeable Al in tropical forests with elevated N deposition in the future.