Forest soil respiration response to increasing nitrogen deposition along an urban–rural gradient

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Forest soil respiration is an important part of the terrestrial ecosystem carbon (C) cycle and controlled by multiple factors, especially atmospheric nitrogen (N) deposition and environmental change. However, it remains unclear how soil respiration responds to N deposition in forests along an urban–rural gradient, as most studies have only been conducted in single environmental areas, especially in natural forests. Here, in order to explore how N deposition influences soil respiration, a field experiment with different levels of N deposition (50 and 100 kg N·ha−1·yr−1) was conducted in forests along an urban–rural gradient of Hefei (31°52′N, 117°17′ E). Soil temperature (T), soil water content (SW), soil physiochemical properties, and soil microbes were simultaneously measured to investigate the underlying mechanisms of N deposition effects on soil respiration. The results showed that the soil respiration and cumulative emission flux of CO2 (RCUM) were increased by N deposition in all forests. Nitrogen addition treatments significantly enhanced the mean RCUM by approximately 6.04%, 11.02%, and 3.62%, respectively, in urban, suburban, and rural forests. The positive effects of N deposition on soil respiration had different temporal variations in different forests, and the strongest positive effects occurred with the shortest time was found in the urban forest. Temperature sensitivities of soil (Q10) were significantly different in the three forests, showing higher Q10 values in forests more near to the urban. In all forests, the total interpretation rates of climate factors, soil physicochemical properties and soil microbes to soil respiration were over 80%. Climate factors were the primary factor for explaining the variation of soil respiration under N deposition. The interpretations of the climate factors, soil physiochemical properties, and soil microbes to soil respiration were changed by N deposition, and the combined effects of these factors were much higher than those of the individual factors. Our findings provide novel insights for studying the response of soil respiration to N deposition under different environmental factors.