BETA-FOR_SP4_Soil microbial activity and biomass_2023

We took four soil cores per patch (5cm diameter, 10 cm depth), pooled these per patch and sieved them at 2mm. We used an automated O2 microcompensation system (Scheu, 1992) to assess basal respiration and microbial biomass. Basal respiration represents the mean oxygen consumption per hour (µl O2 h-1 g soil dw-1) without any substrate addition. This indicates the active portion of the soil microbial community at the time and soil condition of sampling. For this, the mean oxygen consumption between the hours 10-20 was taken. Microbial biomass carbon was determined through substrate-induced respiration, which measures the respiratory response of microorganisms to added glucose and water. An aqueous solution containing 8 mg of glucose per gram of dry soil was added. The lowest substrate-induced respiration observed over three consecutive hours within the first 10 hours was taken as the maximum initial respiratory response (MIRR), taking place before microbial growth started. Microbial biomass (µg C g-1 soil dw) was calculated as 38 x MIRR (Beck et al., 1997). This method measures the full potential of the living microbes that can use glucose. The respiratory quotient is calculated by dividing the basal respiration by the microbial biomass. It determines the ratio of built up carbon to investment in respiration. If the respiratory quotient is low, carbon use is efficient, as more microbial biomass can be built up with less respiration. Soil water content was determined by weighing the fresh sample, drying it at 75°C for three days, and reweighing it. The percentage of water in the fresh sample was calculated and used as the measure of soil water content. It is recommended to use device as a random effect in models when analyzing the data because the different devices might measures slightly different.每个土壤样斑采集4个直径5cm、深度10cm的土壤柱样，将同一样斑的柱样混合后过2mm孔径筛。本研究采用自动化氧气微量补偿系统（automated O2 microcompensation system，Scheu, 1992）测定土壤基础呼吸速率与微生物生物量。基础呼吸速率指未添加任何底物时的单位小时耗氧量（µl O₂·h⁻¹·g⁻¹干土重），其反映采样时刻与土壤当前条件下，土壤微生物群落的活性组分。本研究选取10至20小时区间内的平均耗氧量作为基础呼吸速率。微生物生物量碳通过底物诱导呼吸法测定，该方法通过检测微生物对添加的葡萄糖与水分的呼吸响应来表征生物量。实验中添加的葡萄糖水溶液浓度为每克干土对应8mg葡萄糖。在采样后前10小时内，选取连续3小时测得的最低底物诱导呼吸值作为最大初始呼吸响应（maximum initial respiratory response, MIRR），该值对应微生物生长启动前的呼吸水平。微生物生物量（µg C·g⁻¹干土重）通过公式38×MIRR计算得到（Beck等, 1997）。该方法可表征能够利用葡萄糖的活体微生物的总代谢潜力。呼吸商通过基础呼吸速率除以微生物生物量计算得到，其表征微生物碳积累量与呼吸碳投入的比值。呼吸商越低，碳利用效率越高，即仅需更少的呼吸消耗即可合成更多微生物生物量。土壤含水量通过以下方法测定：称取新鲜土样重量后，将其置于75℃烘箱中烘干3天，再次称重。通过计算新鲜土样的水分占比，得到土壤含水量。数据分析时建议将仪器设为随机效应，因为不同仪器的测定结果可能存在细微差异。