There is an increasing concern over how elevated nitrogen (N) can affect ecosystem processes in tropical and subtropical forests. To better understand the risks and consequences of N deposition in the subtropical forests in southern China, a N addition experiment has been conducted in three forests in Dinghushan Biosphere Reserve, Guangdong province since July 2003.

Recently, the responses of dissolved inorganic and organic N leaching in these studied forests to N additions have been reported in internationally prestigious journals (Forest Ecology and Management, and Ecosystems, respectively), by Dr. FANG Yunting, Prof. MO Jiangming, and Prof. ZHOU Guoyi at South China Botanical Garden, CAS (China), Prof. Per Gundersen at University of Copenhagen (Denmark), Prof ZHU Weixing at State University of New York - Binghamton (USA), and Prof. Muneoki Yoh at Tokyo University of Agriculture and Technology (Japan). 

They found that experimental N additions immediately increased inorganic N leaching in all three forests. The increased N leaching accounted for 25~66% of added N leached over the 3-year experiment. These N leaching rates were substantially higher than the reported values for typical temperate forests in Europe and USA, indicating that the forests in southern China may be more sensitive to N deposition. N leaching may result in soil acidification, nutrient imbalance, and consequently forest health (Forest Ecology and Management, 2009, 257: 332-342).

In addition, the results that dissolved organic N (DON) leaching made up a considerable fraction of total N leaching (23~38％) in these forests were also shown by the authors. DON leaching further increased after N additions; the increase in DON leaching induced by N additions comprised 4~17% of the added N. These results above highlighted that DON could be a significant pathway of N loss from forests moving toward N saturation and were reported in Ecosystems (2009, 12: 33-45). In that paper, the mechanisms were also proposed to explain why DON leaching increased in N saturated forest soils.

The study was funded by the National Natural Science Foundation of China (No. 40703030; 30670392), Provincial Natural Science Foundation of Guangdong (No. 7006915), and Key Project of Chinese Academy of Sciences Knowledge Innovation Program (KZCX2-YW-432-2, KSCX2-SW-133).