Nitrogen deposition contributes to soil acidification in tropical ecosystems

Xiankai Lu, Qinggong Mao, Frank S. Gilliam, Yiqi Luo, Jiangming Mo

Research output: Contribution to journalArticlepeer-review

436 Scopus citations


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 NH4NO3 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 Al3+, 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 Al3+ 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.

Original languageEnglish (US)
Pages (from-to)3790-3801
Number of pages12
JournalGlobal change biology
Issue number12
StatePublished - Dec 1 2014
Externally publishedYes


  • Acid neutralizing capacity
  • Acidification
  • Aluminum
  • Calcium
  • Cation exchange capacity
  • Nitrogen addition
  • Nitrogen deposition
  • Nitrogen saturation
  • Soil buffering capacity
  • Tropical forest

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Ecology
  • General Environmental Science


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