Xiahong Feng - Current Research Interests in Stable Isotope Geochemistry

• Effect of Sea Ice on Arctic Precipitation
• Hydrogen and oxygen isotope studies of tree rings
• Oxygen and hydrogen isotopic compositions in leaf water
• Study of plants’ water used efficiency using C isotopes of tree rings
• Carbon and nitrogen cycles in plant-soil systems
• Isotope hydrology and hydrochemistry

Carbon and nitrogen cycles in plant-soil systems:

In collaboration with a number of ecologists both inside and outside Dartmouth College, I have been studying carbon and nitrogen isotopic variations of plants, litter and soil organic matter. The central focus of these projects is to understand C and N cycles in plant-soil ecosystems, and to use this understanding to predict future changes of carbon pools of terrestrial ecosystems as one of the carbon source or sink of the atmospheric CO 2 in response to climate and environmental changes. The following are two on-going projects under this theme.

1) C and N Isotopic Variations During Organic Matter Decomposition: We have been studying C and N isotopic variation during organic matter decomposition in partially decomposed litter materials. We are using the isotopic signature to infer decomposition rates and mechanisms of various components of organic matter. One specific project, in collaboration with Ross Virginia at Dartmouth and Diana Wall at Colorado State University, involves analyzing litter samples that has been partially decayed at over 20 locations of the world with wide distributions of temperature and precipitation.

2) C and N dynamics and Isotopic Systematics in Plant-Soil Systems Along Climate Gradients: In order to predict ecosystem responses to future climate change and its feedbacks to climate systems, it is important that we study C and N dynamics along climate gradients. Understanding from these studies helps us answer questions such as how water use and nutrient use efficiency of various ecosystems change when climate becomes warmer. Both water use and nutrient use efficiency are important variables for assessing changes of the terrestrial carbon pool and have strong implications to the atmospheric CO 2 budget. In collaboration with Weiguo Liu, Guoan Wang and Liping Zhuo, we are studying soils along several climate gradients in China, including the Northeast forests, the Loess Plateau and the Gangga Mountains in the Tibetan Plateau.