Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, University of Kassel, Steinstr. 19, 37123, Witzenhausen, Germany.
Soil Biology and Plant Nutrition, University of Kassel, Nordbahnhofstr. 1a, 37213, Witzenhausen, Germany.
Sci Rep. 2021 Jan 18;11(1):1653. doi: 10.1038/s41598-021-81120-y.
Long-term provision of ecosystem services by grasslands is threatened by increasing stocking densities. The functions of grassland ecosystems depend on a mutual relationship between aboveground and belowground biota. While the effects of increasing stocking density on plant biomass are well studied, little is known about its impact on soil microbial properties. To fill this knowledge gap a grazing experiment was conducted on a summer pasture in the Chinese Altai Mountains during the summers of 2014 and 2015 using a randomized block design with stocking densities of 0, 8, 16, and 24 sheep ha replicated four times. After two summer grazing periods (each 56 days), topsoil samples (1-7 cm) were taken in September 2015 and analyzed for major physical, chemical, and microbial soil properties. Except for the metabolic quotient (qCO; p < 0.05), the examined soil properties remained unaffected by the increasing stocking densities, likely due to high spatial variability. The qCO declined from 13.5 mg CO-C g microbial biomass C d at zero grazing to 12.2 mg CO-C g microbial biomass C d at a stocking density of 24 sheep ha. Low values of qCO indicate an aged and dormant microbial community that diverts less soil organic carbon (SOC) to catabolic processes within their cells, characteristic for C limiting conditions. The aboveground biomass affected by grazing intensity correlated positively with SOC (r = 0.60, p = 0.015) and ergosterol (r = 0.76, p = 0.001) pointing indirectly to the effect of stocking density. Additionally to the relatively high values of qCO, highest values of SOC (39.2 mg g soil), ergosterol (6.01 µg g soil), and basal respiration (10.7 µg g soil d) were observed at a stocking density of 8 sheep ha indicating that a low grazing intensity is recommendable to avoid soil degradation.
草原生态系统服务的长期提供受到放牧密度增加的威胁。草原生态系统的功能取决于地上和地下生物区系之间的相互关系。虽然增加放牧密度对植物生物量的影响已得到充分研究，但对其对土壤微生物特性的影响知之甚少。为了填补这一知识空白，我们在中国阿尔泰山脉的夏季牧场进行了一项放牧实验，该实验在 2014 年和 2015 年的夏季使用随机区组设计，放牧密度分别为 0、8、16 和 24 只羊/公顷，重复 4 次。经过两个夏季放牧期（每个 56 天），于 2015 年 9 月采集表层土壤（1-7 cm）样本，并分析主要的物理、化学和微生物土壤特性。除代谢商（qCO；p<0.05）外，随着放牧密度的增加，检查的土壤特性不受影响，这可能是由于空间变异性高。qCO 从零放牧时的 13.5 mg CO-C g 微生物生物量 C d 下降到 24 只羊/公顷时的 12.2 mg CO-C g 微生物生物量 C d。qCO 的低值表明微生物群落老化和休眠，其将较少的土壤有机碳（SOC）转移到细胞内的分解代谢过程中，这是 C 限制条件的特征。受放牧强度影响的地上生物量与 SOC（r=0.60，p=0.015）和麦角固醇（r=0.76，p=0.001）呈正相关，这间接指向放牧密度的影响。除了相对较高的 qCO 值外，在 8 只羊/公顷的放牧密度下，SOC（39.2 mg g 土壤）、麦角固醇（6.01 µg g 土壤）和基础呼吸（10.7 µg g 土壤 d）的最高值表明，低放牧强度可避免土壤退化。
