Non-Additive Effects of Water and Nitrogen Addition on Ecosystem Carbon Exchange in a Temperate Steppe |
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Authors: | Shuli Niu Haijun Yang Zhe Zhang Mingyu Wu Qi Lu Linghao Li Xingguo Han Shiqiang Wan |
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Institution: | (1) State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing, 100093, China;(2) The Research Institute of Forestry, Chinese Academy of Forestry, Beijing, 100091, China |
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Abstract: | Changes in precipitation and nitrogen (N) deposition can influence ecosystem carbon (C) cycling and budget in terrestrial
biomes, with consequent feedbacks to climate change. However, little is known about the main and interactive effects of water
and N additions on net ecosystem C exchange (NEE). In a temperate steppe of northern China, a field-manipulated experiment
was conducted to evaluate the responses of NEE and its components to improve N and water availability from 2005 to 2008. The
results showed that both water and N additions stimulated gross ecosystem productivity (GEP), ecosystem respiration (ER),
and NEE. Water addition increased GEP by 17%, ER by 24%, and NEE by 11% during the experimental period, whereas N addition
increased GEP by 17%, ER by 16%, and NEE by 19%. The main effects of both water and N additions changed with time, with the
strongest water stimulation in the dry year and a diminishing N stimulation over time. When water and N were added in combination,
there were non-additive effects of water and N on ecosystem C fluxes, which could be explained by the changes in species composition
and the shifts of limiting resources from belowground (water or N) to aboveground (light). The positive water and N additions
effects indicate that increasing precipitation and N deposition in the future will favor C sequestration in the temperate
steppe. The non-additive effects of water and N on ecosystem C fluxes suggest that multifactor experiments are better able
to capture complex interactive processes, thus improving model simulations and projections. |
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