A Sharp Decline in Nitrogen Input in a N-Saturated Subtropical Forest Causes an Instantaneous Reduction in Nitrogen Leaching
Abstract
In China, as in other parts of the world, the emission and deposition of reactive nitrogen (N) have been reduced in recent years. Several decades of elevated N deposition in southwest China (40 to 60 kg ha-1 year-1) have resulted in extreme cases of N saturation, where N outputs are nearly equal to N inputs. Doubling N inputs using either NH4NO3 or NaNO3 fertilizer in a subtropical forest in Tieshanping, near Chongqing city in southwest China, caused an immediate doubling of N leaching (as NO3-). Reducing N inputs to ambient atmospheric deposition levels after 10 years of fertilization led to a rapid decrease in soil water NO3- concentration to levels similar to those in the reference plots that had not receive N fertilizer application. NO3- leaching via the soil water in the NH4NO3 plots was even lower than that in the NaNO3 plots or the reference plots, confirming the finding of a previous N-fertilizing experiment that found that NH4+ deposition, in contrast to NO3- deposition, increased N retention in the forest ecosystem. The N sink remained for at least 2 years after the cessation of N addition. Even with reduced N inputs, ambient atmospheric N deposition caused significant acidification, buffered partly by SO42- sorption. Therefore, further abatement of reactive N emissions is necessary in the future.
- Publication:
-
Journal of Geophysical Research (Biogeosciences)
- Pub Date:
- October 2018
- DOI:
- 10.1029/2017JG004322
- Bibcode:
- 2018JGRG..123.3320X
- Keywords:
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- leaching;
- N saturation;
- acidification;
- recovery