1. Key Lab. of Terrestrial Ecological Process; Institute of Applied Ecology, Chinese Academy of Sciences; Shenyang 110016 China
2. Graduate School of the Chinese Academy of Sciences; Beijing 100049 China
3. State Key Lab. of Urban and Regional Ecology Research Centre for Eco-Environmental Sciences; Chinese Academy of Sciences; Beijing 100085 China
4. Key Lab. of Pollution Processes and Environmental Criteria (Ministry of Education); College of Environmental Science and Engineering Nankai University; Tianjin 300071 China