Nitrogen saturation in humid tropical forests after 6 years of nitrogen and phosphorus addition: Hypothesis testing

TY - JOUR

T1 - Nitrogen saturation in humid tropical forests after 6 years of nitrogen and phosphorus addition

T2 - Hypothesis testing

AU - Chen, Hao

AU - Gurmesa, Geshere A.

AU - Zhang, Wei

AU - Zhu, Xiaomin

AU - Zheng, Mianhai

AU - Mao, Qinggong

AU - Zhang, Tao

AU - Mo, Jiangming

PY - 2016/2/1

Y1 - 2016/2/1

N2 - Nitrogen (N) saturation hypothesis suggests 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 remain poorly addressed. To test this hypothesis, soil inorganic N, soil N mineralization and nitrification rate, soil N2O emission rate and nitrate () leaching rate were measured in an N-saturated old-growth tropical forest in southern China, after 6 years of N and P addition. We hypothesized that N addition would stimulate further N saturation, but P addition might alleviate N saturation. As expected, our results showed that six continuous years of experimental N addition did cause further N saturation, which was indicated by significant increases in soil inorganic N concentration, N2O emission and nitrate () leaching. However, in contrast to our expectations, N addition significantly decreased in situ rates of net N mineralization and nitrification, which could be related to associated changes in enzyme activity and microbial community composition. On the other hand, P addition mitigated N saturation, as expected. Soil inorganic N concentration, N2O emission and leaching decreased significantly after P addition, but the net rates of N mineralization and nitrification were significantly increased. Our results provide a new understanding of the N saturation hypothesis, 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.

AB - Nitrogen (N) saturation hypothesis suggests 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 remain poorly addressed. To test this hypothesis, soil inorganic N, soil N mineralization and nitrification rate, soil N2O emission rate and nitrate () leaching rate were measured in an N-saturated old-growth tropical forest in southern China, after 6 years of N and P addition. We hypothesized that N addition would stimulate further N saturation, but P addition might alleviate N saturation. As expected, our results showed that six continuous years of experimental N addition did cause further N saturation, which was indicated by significant increases in soil inorganic N concentration, N2O emission and nitrate () leaching. However, in contrast to our expectations, N addition significantly decreased in situ rates of net N mineralization and nitrification, which could be related to associated changes in enzyme activity and microbial community composition. On the other hand, P addition mitigated N saturation, as expected. Soil inorganic N concentration, N2O emission and leaching decreased significantly after P addition, but the net rates of N mineralization and nitrification were significantly increased. Our results provide a new understanding of the N saturation hypothesis, 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.

KW - China

KW - N<inf>2</inf>O emission

KW - Nitrogen deposition

KW - Nitrogen mineralization and nitrification

KW - Nitrogen saturation

KW - Phosphorus addition

KW - Tropical forest

UR - http://www.scopus.com/inward/record.url?scp=84930608215&partnerID=8YFLogxK

U2 - 10.1111/1365-2435.12475

DO - 10.1111/1365-2435.12475

M3 - Journal article

SN - 0269-8463

VL - 30

SP - 305

EP - 313

JO - Functional Ecology

JF - Functional Ecology

ER -