Local Alterations to the Nitrogen Cycle As Indicated By Soil, Foliage, and Tree-Ring Total N and δ15N: Shaanxi Province, China.

Monitoring of nitrogen (N) inputs to forested ecosystems in China has historically been limited despite known negative effects that high N additions can have on environmental and human health. To better understand terrestrial patterns of foliar, soil, and wood δ¹⁵N relative to soil N concentrations (%N) in a heavily polluted region, two Chinese parasol tree (Firmiana simplex) groves were examined on the Loess Plateau, approximately 80km east of the city of Xi’an, Shaanxi Province, China. Results suggest greater foliar uptake of N in the tree canopies bordering the industrialized basin compared to trees located at the forest interior. N concentrations and δ¹⁵N of soil and plant tissue were inversely correlated along this transect and indicate higher inputs of N from δ¹⁵N depleted sources in the basin. Tree ring δ¹⁵N values decline between 2003 and 2014 during a time of rapid development and expansion of the industry in the basin.