Responses of hydraulics at the whole-plant level to simulated nitrogen deposition of different levels in Fraxinus mandshurica.
Nitrogen (N) deposition is expected to have great impact on forest ecosystems by affecting many aspects of plant-environmental interactions, one of which involves its influences on plant water relations through modifications of plant hydraulic architecture. However, there is a surprising lack of integrative study on tree hydraulic architecture responses to N deposition, especially at the whole-plant level. In the present study, we used a 5-year N addition experiment to simulate the effects of six different levels of N deposition (20-120 kg ha(-1) year(-1)) on growth and whole-plant hydraulic conductance of a dominant tree species (Fraxinus mandshurica Rupr.) from the typical temperate forest of NE China. The results showed that alleviation of N limitation by moderate concentrations of fertilization (20-80 kg ha(-1) year(-1)) promoted plant growth, but further N additions on top of the threshold level showed negative effects on plant growth. Growth responses of F. mandshurica seedlings to N addition of different concentrations were accompanied by corresponding changes in whole-plant hydraulic conductance; higher growth rate was accompanied by reduced whole-plant hydraulic conductance (Kplant) and higher leaf water-use efficiency. A detailed analysis on hydraulic conductance of different components of the whole-plant water transport pathway revealed that changes in root and leaf hydraulic conductance, rather than that of the stem, were responsible for Kplant responses to N fertilization. Both plant growth and hydraulic architecture responses to increasing levels of N addition were not linear, i.e., the correlation between measured parameters and N availability exhibited bell-shaped curves with peak values observed at medium levels of N fertilization. Changes in hydraulic architecture in response to fertilization found in the present study may represent an important underlying mechanism for the commonly observed changes in water-related tree performances in response to N deposition.
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Ai-Ying
AY
Wang
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.
Miao
M
Wang
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Da
D
Yang
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Jia
J
Song
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.
Wei-Wei
WW
Zhang
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China.
Shi-Jie
SJ
Han
Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110010, China haogy@iae.ac.cn.
Guang-You
GY
Hao
D031661:Fraxinus / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D018526:Plant Transpiration / Q000502:physiology; D014867:Water / Q000378:metabolism; D052584:Xylem / Q000378:metabolism
D014867:Water; D009584:Nitrogen
high-pressure flow meter; hydraulic architecture; long-distance water transport; xylem