放牧模式对内蒙古典型草原生长季土壤呼吸速率的影响

【目的】放牧改变了典型草原生产力和土壤养分循环，影响了植被和土壤微生物的生长状况，进而使草原土壤碳排放量发生变化。本研究通过分析不同放牧措施下内蒙古典型草原生长季土壤呼吸速率 (Rs) 的差异，了解不同放牧管理模式影响草原碳交换和碳平衡的主要途径。【方法】基于内蒙古典型草原全年放牧、休牧及禁牧三种放牧措施，于2014和2015年的7月和9月对Rs进行原位测定，并分析了不同放牧措施下Rs及其影响因子的差异。【结果】1) 三种放牧措施下，Rs表现为休牧样地 [CO₂ 2.00 μmol/(m2·s)] > 禁牧样地 [CO₂ 1.94 μmol/(m2·s)]> 全年放牧样地 [CO₂ 1.56 μmol/(m2·s)]。放牧对Rs的影响还存在季节效应，7月份放牧降低了Rs，而9月份放牧则提高了Rs。2) 与禁牧措施相比，放牧和休牧管理均降低了地上生物量(70.6%和47.3%)、土壤总碳含量(34.5%和32.0%)、土壤总氮含量(37.0%和34.5%)，但休牧显著提高了根系生物量(37.2%)。全年放牧样地中土壤可溶性有机碳提高，但微生物磷脂脂肪酸含量下降。3) 7月份Rs主要与土壤湿度和地上生物量显著正相关，而9月份则与土壤温度和土壤PLFAs含量显著正相关。结构方程模型 (SEM) 结果显示，土壤温度 (0.905) 和湿度 (0.188) 通过影响微生物和根系的代谢环境对生长季Rs起主导作用，放牧通过降低土壤湿度和地上生物量对Rs有抑制作用 (–0.137)。【结论】全年放牧通过抑制微生物的生长降低了土壤呼吸速率，休牧通过提高根系生物量增加了土壤呼吸速率，说明放牧对内蒙古典型草原生长季土壤呼吸速率的影响途径因放牧模式的不同而不同。

Effects of grazing on soil respiration in typical steppe during growing season in Inner Mongolia

【Objectives】Grazing changes the productivity and soil nutrient cycling of typical steppe, affecting the growth of vegetation and soil microbes, and thus changes the carbon emissions of grassland soils. This study analyzed the difference of soil respiration (Rs) rate in the growing season of typical steppe under different grazing measures, to understand the relationship between grassland carbon exchange and carbon balance for grazing. It has great theoretical significance for exploring and clarifying the rational utilization of grassland ecological resources and the trend of carbon emission.【Methods】On three types of grazing plots (yearlong grazing, rest rotation grazing and grazing exclusion) in Inner Mongolia typical grassland, Rs was measured in situ in July and September of 2014 and 2015. The vegetation, soil nutrient contents and microbiological indicators under three grazing system were also analyzed.【Results】1) The Rs in rest rotation grazing, grazing exclusion and yearlong grazing systems were CO₂ 1.94, 2.00 and 1.56 μmol/(m2·s), respectively, and showed an order of grazing exclusion > rest rotation grazing > yearlong grazing system. Grazing impacted Rs differently during the growing season, inhibiting Rs in July and increasing Rs in September. 2) Compared with grazing exclusion plots, the aboveground biomass of yearlong grazing and rest rotation grazing were reduced by 70.6% and 47.3%, the root biomass increased by 18.6% and 37.2%, the total soil carbon decreased by 34.5% and 32.0%, and the total soil nitrogen decreased by 37.0% and 34.5%. And compared with grazing exclusion, the root biomass of rest rotation grazing increased by 37.2% (P<0.05). Grazing had different effects on soil dissolved organic carbon (DOC) and soil phospholipid fatty acid (PLFAs). Compared with grazing exclusion control, yearlong grazing increased DOC but decreased PLFAs. 3) Soil respiration was positively correlated with soil moisture and aboveground biomass in July, and positively correlated with soil temperature and soil PLFAs in September. The Structure Equation Model showed that soil temperature (0.905) and moisture (0.188) dominated the variations of Rs through effecting the environment of soil microbial and root development during the growing season; Grazing inhibited Rs (–0.137) by decreasing soil moisture and aboveground biomass.【Conclusions】The main path affecting soil respiration is different with grazing modes. Yearlong grazing inhibits soil respiration by reducing microbial biomass in the growing season, while rest rotation grazing increases soil respiration by enhancing the underground biomass.