High retention of15N-labeled nitrogen deposition in a nitrogen saturated old-growth tropical forest.
The effects of increased reactive nitrogen (N) deposition in forests depend largely on its fate in the ecosystems. However, our knowledge on the fates of deposited N in tropical forest ecosystems and its retention mechanisms is limited. Here, we report the results from the first whole ecosystem15N labeling experiment performed in a N-rich old-growth tropical forest in southern China. We added15N tracer monthly as15NH415NO3for 1 year to control plots and to N-fertilized plots (N-plots, receiving additions of 50 kg N ha-1yr-1for 10 years). Tracer recoveries in major ecosystem compartments were quantified 4 months after the last addition. Tracer recoveries in soil solution were monitored monthly to quantify leaching losses. Total tracer recovery in plant and soil (N retention) in the control plots was 72% and similar to those observed in temperate forests. The retention decreased to 52% in the N-plots. Soil was the dominant sink, retaining 37% and 28% of the labeled N input in the control and N-plots, respectively. Leaching below 20 cm was 50 kg N ha-1yr-1in the control plots and was close to the N input (51 kg N ha-1yr-1), indicating N saturation of the top soil. Nitrogen addition increased N leaching to 73 kg N ha-1yr-1. However, of these only 7 and 23 kg N ha-1yr-1in the control and N-plots, respectively, originated from the labeled N input. Our findings indicate that deposited N, like in temperate forests, is largely incorporated into plant and soil pools in the short term, although the forest is N-saturated, but high cycling rates may later release the N for leaching and/or gaseous loss. Thus, N cycling rates rather than short-term N retention represent the main difference between temperate forests and the studied tropical forest.
Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.|Department of Geosciences and Natural Resource Management, University of Copenhagen, 1958 Frederiksberg C, Denmark.|Sino-Danish Center for Education and Research, DK-8000, Aarhus C, Denmark.
Geshere Abdisa
GA
Gurmesa
Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.
Xiankai
X
Lu
Department of Geosciences and Natural Resource Management, University of Copenhagen, 1958 Frederiksberg C, Denmark.
Per
P
Gundersen
Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.|University of Chinese Academy of Sciences, Beijing, 100039, China.
Qinggong
Q
Mao
Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.|University of Chinese Academy of Sciences, Beijing, 100039, China.
Kaijun
K
Zhou
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110164, China.|Qingyuan Forest CERN, Chinese Academy of Sciences, Shenyang, 110016, China.
Yunting
Y
Fang
Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China. mojm@scib.ac.cn.
Jiangming
J
Mo
D002681:China; D017753:Ecosystem; D065928:Forests; D009584:Nitrogen; D012987:Soil
D012987:Soil; D009584:Nitrogen
15N tracer; N saturation; fate of deposited N; nitrogen addition; tropical forest