Abstract
ABSTRACT Leaf nitrogen (N) status and stable isotope ratios of carbon (δ 13C) and nitrogen (δ 15N) were used to study environmental factors that control mountain individuals of Picea neoveitchii trees, a coniferous species endemic and endangered in China. From May to September 2016, we carried out observations at four different altitude locations extending southeast of Daba Mountain in western Hubei Province. Needle-shaped leaf δ 13C was positively correlated with needle N and C content calculated from the needle area (Narea and Carea content), needle δ 15N, needle mass, and leaf mass per area (LMA), respectively. Needle δ 15N was also positively correlated with monthly temperature and precipitation for the current month and last month. The seasonal normalised difference vegetation index (NDVI) was highest in June at the lowest altitude and August at the highest altitude. We found that N availability as an important driving factor for tree growth is controlled by surface soil temperature, while in summer, air temperatures above 23 °C exceed the physiological threshold of trees and limit the growth of trees. We concluded that the negative effect of higher temperature on tree growth is greater than the positive effect of higher nitrogen.
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