Variation in the Stable Carbon and Nitrogen Isotope Composition of Plants and Soil along a Precipitation Gradient in Northern China

Water availability is the most influential factor affecting plant carbon ( δ 13 C) and nitrogen ( δ 15 N) isotope composition in arid and semi-arid environments. However, there are potential differences among locations and/or species in the sensitivity of plant δ 13 C and δ 15 N to variation in precipitation, which are important for using stable isotope signatures to extract paleo-vegetation and paleo-climate information. We measured δ 13 C and δ 15 N of plant and soil organic matter (SOM) samples collected from 64 locations across a precipitation gradient with an isotherm in northern China. δ 13 C and δ 15 N for both C 3 and C 4 plants decreased significantly with increasing mean annual precipitation (MAP). The sensitivity of δ 13 C to MAP in C 3 plants (-0.6±0.07‰/100 mm) was twice as high as that in C 4 plants (−0.3±0.08‰/100 mm). Species differences in the sensitivity of plant δ 13 C and δ 15 N to MAP were not observed among three main dominant plants. SOM became depleted in 13 C with increasing MAP, while no significant correlations existed between δ 15 N of SOM and MAP. We conclude that water availability is the primary environmental factor controlling the variability of plant δ 13 C and δ 15 N and soil δ 13 C in the studied arid and semi-arid regions. Carbon isotope composition is useful for tracing environmental precipitation changes. Plant nitrogen isotope composition can reflect relative openness of ecosystem nitrogen cycling.