关键词: 氮沉降, 土壤呼吸, 土壤特性, 滇中高原

Abstract:

【Objective】The study explored effects of changes in soil characteristics in zonal forests on soil respiration under nitrogen deposition in the central Yunnan Plateau. The study aimed to elucidate the mechanism underlying the response of soil respiration to nitrogen deposition in zonal forests, and provide a theoretical basis for the accurate assessment of the carbon budget and material cycle of subtropical forest ecosystems. 【Method】This study focused on two types of zonal forest soils, namely, evergreen broad-leaved forests and Quercus aquifolioides forests, in the central Yunnan Plateau. The soils were treated with different gradients of nitrogen, control [0 g/(m²·a) nitrogen, CK], low nitrogen [10 g/(m²·a) nitrogen, LN], medium nitrogen [20 g/(m²·a) nitrogen, MN], and high nitrogen [25 g/(m²·a) nitrogen, HN]. The variations in the characteristics of soil respiration (RS), temperature (T), humidity (W), organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), nitrate nitrogen ($\mathrm{NO}_{3}^{-}-\mathrm{N}$), ammonium nitrogen ($\mathrm{NH}_{4}^{+}-\mathrm{N}$) content, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) were determined under nitrogen deposition. Additionally, the correlation between soil respiration and soil characteristics were determined to elucidate the mechanism underlying the effect of nitrogen deposition on soil respiration. 【Result】Compared to the CK group, soil respiration increased in the LN treatment group and decreased in the MN and HN treatment groups in the evergreen broad-leaf forests. Compared with the CK group, soil respiration increased with an increase in nitrogen application for all the treatment groups in the Q. aquifolioides forests. Soil respiration was lower in the dry season than that in the rainy season in both stands, and increased by 155.15% and 181.78% in the Q. aquifolioides and evergreen broad-leaf forests, respectively, in the rainy season compared to those in the dry season. The TOC, TN, $\mathrm{NO}_{3}^{-}-\mathrm{N}$, and $\mathrm{NH}_{4}^{+}-\mathrm{N}$ contents in the soil increased with the gradient of applied nitrogen in different seasons in both stands. Additionally, the contents of soil MBC in both stands were lower than that of the CK group in the rainy season at the different concentrations of nitrogen. The soil respiration of the evergreen broad-leaved forests exhibited a non-significant positive correlation with the pH, TP content and MBN (P > 0.05) in the dry and rainy seasons. Soil respiration in the Q. aquifolioides forests exhibited a non-significant positive correlation with the TOC, TN, $\mathrm{NO}_{3}^{-}-\mathrm{N}$, and $\mathrm{NH}_{4}^{+}-\mathrm{N}$ content, non-significant negative correlation with the TP content, MBC and MBN, and a significant negative correlation with the pH (P < 0.05) during the dry and rainy seasons. 【Conclusion】Nitrogen deposition can alter soil respiration by affecting the soil chemical indicators, including the TOC, TN, TP, $\mathrm{NO}_{3}^{-}-\mathrm{N}$, $\mathrm{NH}_{4}^{+}-\mathrm{N}$ content, MBC, and MBN. The findings revealed that moderate nitrogen deposition can promote soil respiration, while excessive nitrogen addition can inhibit soil respiration.

Key words: nitrogen deposition, soil respiration, soil charcteristics, the central Yunnan Plateau