Responses of growing‐season soil respiration to water and nitrogen addition as affected by grazing intensity

1. Most grasslands in the world, including the semi-arid steppe in China, are threatened by nitrogen deposition, precipitation change, and livestock grazing, which greatly affect soil carbon processes (e. g., soil respiration). Although the individual effects of nitrogen deposition and precipitation change on soil respiration are well understood, how their effects on soil respiration are altered by different grazing intensities is unclear. 2. To determine how the effects of nitrogen deposition and precipitation change on soil respiration are affected by grazing intensity, we conducted an experiment in a semi-arid steppe involving areas that experienced 10 years of no, light, moderate, or heavy grazing. These areas were treated with water addition (110 mm, 30% of the mean annual precipitation) and nitrogen addition (10.5 g m-2 yr-1). 3. Our results showed that relative to no grazing, grazing decreased growing-season soil respiration by 10-19%. The decline in soil respiration was mainly v...1. 全球多数草原，包括中国的半干旱干草原（semi-arid steppe），正遭受氮沉降（nitrogen deposition）、降水变化（precipitation change）与家畜放牧（livestock grazing）的胁迫，上述因素会显著干扰土壤碳循环过程（soil carbon processes，例如土壤呼吸（soil respiration））。尽管学界已明晰氮沉降与降水变化对土壤呼吸的单一作用效应，但不同放牧强度如何调控二者对土壤呼吸的影响效果，目前仍不明确。 2. 为明确放牧强度如何调控氮沉降与降水变化对土壤呼吸的影响，我们在一处已开展10年梯度放牧处理（无放牧、轻度放牧、中度放牧与重度放牧）的半干旱干草原样地中开展了野外控制实验。实验设置了水分添加处理（施加量为110毫米，约占样地年均降水量的30%）与氮添加处理（施加量为10.5 g·m⁻²·yr⁻¹）。 3. 本研究结果显示，相较于无放牧对照样地，放牧处理使生长季土壤呼吸降低了10%~19%。土壤呼吸的下降主要……