Nitrogen (N) saturation hypothesis suggest that when an ecosystem reaches N-saturation, continued N input will cause increased N leaching, nitrous oxide (N2O) emission, and N mineralization and nitrification rates. It also suggests that a different element will become the main limiting factor when N saturation has been reached. Although this hypothesis has been tested in temperate forests, whether they can be directly applied to N-saturated tropical forests remains poorly addressed.

Recently, Dr. Hao Chen and Prof. Mo Jiangming of South China Botanical Garden, CAS used an 6 years of N and P addition experiment in Dinghushan(Guangdong) to test above hypothesis. They found that N addition caused significant increases in soil inorganic N concentration, N2O emission, and nitrate (NO3-) leaching but significant decreases in net N mineralization and nitrification rates. In addition, they also found that P addition significantly decreased soil inorganic N concentration, N2O emission, and NO3- leaching.

These results provide a new understanding of the N-saturation hypotheses, suggesting that the effects of long-term N deposition on net N mineralization and nitrification rates in N-saturated tropical forests can be negative, and that P addition can alleviate N-saturation in such tropical systems.

Above study has been published online in Functional Ecology (IF=4.857). DOI: 10.1111/1365-2435.12475.

Link：http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12475/abstract