, Volume 28, Issue 5, pp 735-748

Patterns of foliar δ15N and their control in Eastern Asian forests

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Abstract

Foliar δ15N has been used increasingly in research on ecosystem nitrogen (N) cycling, because it can serve as an integrator of ecosystem N cycling and thus has a potential to reveal temporal and spatial patterns of N cycling as well as how the N cycle is altered by disturbances. However, the current understanding on controls of foliar δ15N is based principally on studies from America, Europe, Australia and Africa. Here we compiled data from 65 forests at 33 sites across East Asia to explore regional patterns and what controls foliar δ15N by linking it to climate, species composition, soil depth, slope position, N deposition, and soil N availability. In East Asia, foliar δ15N ranged from −7.1 to +2.7‰. Mean foliar δ15N values for tropical, subtropical and temperate forests were all −3.1‰, which was unexpected. The patterns of foliar δ15N with precipitation, temperature and altitude were not clear. The variation in foliar δ15N among species and between different slope positions appeared to be small within a given forest. The δ15N for both bulk soil N and extractable inorganic N generally increased with soil depth as expected, strengthening the idea that deep-rooted trees may have access to 15N-enriched N. Different from the positive correlations reported across America and Europe, in East Asia we found that foliar δ15N decreased with increasing N deposition and did not relate to soil N availability. These discrepancies deserve more research to elucidate the mechanisms by which foliar δ15N is affected by ecosystem N availability at a regional scale.