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Nitrogen saturation, soil acidification, and ecological effects in a subtropical pine forest on acid soil in southwest China
Author(s) -
Huang Yongmei,
Kang Ronghua,
Mulder Jan,
Zhang Ting,
Duan Lei
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg003048
Subject(s) - soil acidification , soil water , environmental science , saturation (graph theory) , subtropics , nitrate , soil ph , temperate forest , pinus massoniana , temperate climate , environmental chemistry , tropical and subtropical moist broadleaf forests , leaching (pedology) , chemistry , soil science , ecology , botany , biology , mathematics , combinatorics
Abstract Elevated anthropogenic nitrogen (N) deposition has caused nitrate (NO 3 − ) leaching, an indication of N saturation, in several temperate and boreal forests across the Northern Hemisphere. So far, the occurrence of N saturation in subtropical forests and its effects on the chemistry of the typically highly weathered soils, forest growth, and biodiversity have received little attention. Here we investigated N saturation and the effects of chronically high N inputs on soil and vegetation in a typical, subtropical Masson pine ( Pinus massoniana ) forest at Tieshanping, southwest China. Seven years of N flux data obtained in ambient conditions and in response to field manipulation, including a doubling of N input either as ammonium nitrate (NH 4 NO 3 ) or as sodium nitrate (NaNO 3 ) solution, resulted in a unique set of N balance data. Our data showed extreme N saturation with near‐quantitative leaching of NO 3 − , by far the dominant form of dissolved inorganic N in soil water. Even after 7 years, NH 4 + , added as NH 4 NO 3 , was nearly fully converted to NO 3 − , thus giving rise to a major acid input into the soil. Despite the large acid input, the decrease in soil pH was insignificant, due to pH buffering caused by Al 3+ mobilization and enhanced SO 4 2− adsorption. In response to the NH 4 NO 3 ‐induced increase in soil acidification and N availability, ground vegetation showed significant reduction of abundance and diversity, while Masson pine growth further declined. By contrast, addition of NaNO 3 did not cause soil acidification. The comparison of NH 4 NO 3 treatment and NaNO 3 treatment indicated that pine growth decline was mainly attributed to acidification‐induced nutrient imbalance, while the loss in abundance of major ground species was the combining effect of N saturation and acidification. Therefore, N emission control is of primary importance to curb further acidification and eutrophication of forest soils in much of subtropical south China.