Abstract
The natural abundance of stable nitrogen (N) isotope (δ15N) in plants and soils can reflect N cycling processes in ecosystems. However, we still do not fully understand patterns of plant and soil δ15N at alpine treelines and shrublines in different climate zones. We measured δ15N and N concentration in leaves of trees and shrubs and also in soils along elevational gradients from lower altitudes to the upper limits of treelines and shrublines in subtropical, dry- and wet-temperate regions in China. The patterns of leaf δ15N in trees and shrubs in response to altitude changes were consistent, with lower values occurring at higher altitude in all three climate zones, but such patterns did not exist for leaf Δδ15N and soil δ15N. Average δ15N values of leaves (−1.2‰) and soils (5.6‰) in the subtropical region were significantly higher than those in the two temperate regions (−3.4‰ and 3.2‰, respectively). Significant higher δ15N values in subtro4pical forest compared with temperate forests prove that N cycles are more open in warm regions. The different responses of leaf and soil δ15N to altitude indicate complex mechanisms of soil biogeochemical process and N sources uptake with environmental variations.
Highlights
Variation in natural abundance of the stable isotope 15 N (δ15 N) in plants and soils can reflect N cycling in ecosystems [1] because it is related to the isotope compositions of N inputs and outputs and the internal N transformations [2]
We address the following questions: (1) Do leaf and soil δ15 N patterns change with climatic zones? We hypothesized that leaf and soil δ15 N values are higher in subtropical zones than in temperate zones as temperature is higher and available N is richer in subtropical forests than in temperate forests
Our results showed that leaf δ15 N and soil δ15 N were higher in subtropical forest than in dryand wet-temperate forests
Summary
Variation in natural abundance of the stable isotope 15 N (δ15 N) in plants and soils can reflect N cycling in ecosystems [1] because it is related to the isotope compositions of N inputs and outputs and the internal N transformations [2]. Many studies have examined the variations of spatial patterns of δ15 N in plants and soils [6,7,8,9]. Elevation appears to be a major influence on leaf and soil δ15 N due to its natural environmental variations, such as soil water and temperature. At lower elevations where temperature tends to be higher, δ15 N values are likely to be higher [10,11]
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