Effects of forest decline on uptake and leaching of deposited nitrate determined from 15 N and 18 O measurements

摘要: ATTEMPTS to understand how atmospheric nitrogen deposition affects forest ecosystems1'2 have been hampered by the lack of a direct method trace fate deposited nitrogen. Nitrate originating in atmosphere has natural abundances and oxygen isotopes that differ measurably from those soil nitrate3. Here we present an analysis isotope ratios nitrate spring waters eight forested watersheds, ranging apparently healthy spruce plantations decline owing acidification. We find for healthy, slightly declining limed sites, only 16–30% water originates directly without being processed soil, whereas more severely damaged sites almost all atmos-pheric finds its way into water. This suggests acid-induced significantly inhibits consumption microorganisms trees, liming ameliorate acidification restores nitrate. Nevertheless, ecosystems total output remains high because internal production ecosystem.