High Nitrogen and Biochar Additions Mitigate Soil Respiration When Soil Temperature Rises in a Subtropical Plantation

Abstract

Central China is an area of high nitrogen (N) deposition. The mechanisms of changes in forest soil respiration (Rs) and the direction of Rs in response to changes in soil temperature (Ts) after the addition of biochar to plantations under the influence of N deposition are not well understood. Nine N and biochar addition treatments were tested in a typical subtropical coniferous plantation forest. From 2019 to 2023, continuous measurements of Rs were conducted to study the effects on soil properties and the mechanisms of Rs changes, including the soil chemical and physical properties (aggregate indicators), microbial properties (enzyme activities and microbial biomass), and microbial communities. Results suggest that biochar addition increased soil organic carbon (C) stocks and microbial biomass and decreased soil aggregate stability. N addition affected Rs mainly by altering the fungal community and soil total phosphorus content, which significantly affected Rs in years 1 to 2 and diminished to insignificant in years 3 to 5. Biochar addition had a positive priming effect on Rs in the short term, and this effect increased with the amount of addition. Biochar addition increased the soil temperature sensitivity of Rs (Qs), while high N addition and the interaction of N and biochar decreased Qs. However, the stability of Rs progressively decreased in response to Ts changes with increasing N addition or with simultaneous increases in both N and biochar in the interactive treatments. This study provides a reference for managing soil and C emissions in the face of N deposition and potential temperature increase.

Keywords: soil respiration, biochar addition, nitrogen, soil temperature, subtropical plantation