Effect of nitrogen addition on the variations in the natural abundance of nitrogen isotopes of plant and soil components

Abstract

Anthropogenic nitrogen (N) addition has dramatically increased and significantly affected global nitrogen cycling. The natural abundance of stable N isotope ratios (δ15N) has been used as an indicator of the N status of an ecosystem. However, how plant and soil δ15N signatures would respond to N addition is still unclear. Herein, we synthesized the data of 951 observations from 48 individual studies associated with responses of plant and soil δ15N values to N addition and conducted a meta-analysis to explore a general pattern of N addition effects on δ15N values of plant and soil. Our results showed that δ15N values of plant, soil total N, and soil NO3 − were significantly increased by N addition, while δ15N value of soil N2O was significantly decreased and δ15N value of soil NH4 + was not significantly changed. The δ15N value of soil total N of different ecosystems showed similar responses to N addition, whereas δ15N values of different plant types showed different responses. Increasing treatment duration significantly increased the effects of inorganic N addition on δ15N values of shrubs and soil NH4 + but did not affect the responses of δ15N values of soil total N and NO3 −. With increasing inorganic N addition rate, only δ15N value of plant was significantly increased, but no significant relationship was found between the effect of N addition on other components and N addition rate because of the input of isotopically depleted sources. Our study revealed a comprehensive picture of the effects of N addition on δ15N signatures in terrestrial ecosystems and could help us understand how plant and soil δ15N signatures change with N addition and how these signatures can be used as an indicator of ecosystem N status under increasing N deposition or fertilization.