Abstract
Water availability is the most influential factor affecting plant carbon (δ 13C) and nitrogen (δ 15N) isotope composition in arid and semi-arid environments. However, there are potential differences among locations and/or species in the sensitivity of plant δ 13C and δ 15N to variation in precipitation, which are important for using stable isotope signatures to extract paleo-vegetation and paleo-climate information. We measured δ 13C and δ 15N of plant and soil organic matter (SOM) samples collected from 64 locations across a precipitation gradient with an isotherm in northern China. δ 13C and δ 15N for both C3 and C4 plants decreased significantly with increasing mean annual precipitation (MAP). The sensitivity of δ 13C to MAP in C3 plants (-0.6±0.07‰/100 mm) was twice as high as that in C4 plants (−0.3±0.08‰/100 mm). Species differences in the sensitivity of plant δ 13C and δ 15N to MAP were not observed among three main dominant plants. SOM became depleted in 13C with increasing MAP, while no significant correlations existed between δ 15N of SOM and MAP. We conclude that water availability is the primary environmental factor controlling the variability of plant δ 13C and δ 15N and soil δ 13C 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.
Highlights
In drought-prone ecosystems, water availability controls ecosystem structure and processes by affecting long-term balances between ecosystem inputs and outputs of elements and the cycling of carbon and nutrients within ecosystems [1]
Plant Carbon and Nitrogen Stable Isotope Composition The d13C values of all samples ranged from 231.1% to
No significant correlations existed between d15N values of soil organic matter and mean annual precipitation (Fig. 6b; R2 = 0.012, P = 0.45). Plants balance their needs between CO2 intake for photosynthesis and conservation of water by adjusting the conductance of their leaf stomata
Summary
In drought-prone ecosystems, water availability controls ecosystem structure and processes by affecting long-term balances between ecosystem inputs and outputs of elements and the cycling of carbon and nutrients within ecosystems [1]. Plant performance along environmental gradients offers one way to evaluate potential plant responses to climate change [3]. Plants discriminate against 13CO2 during photosynthetic CO2 fixation in ways that reflect plant metabolism and environmental conditions. In contrast to C3 plants, the d13C values of C4 plants are expected to be less sensitive to water stress [12]. No correlation between the d13C values of C4 plants and water availability (e.g. precipitation) is commonly observed [5,10,13]
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