Zhang Jing, Duan Qianwen, Ma Jie, Hou Fujiang
State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, Key Laboratory of Grassland Livestock Industry Innovation, Ministry of Agriculture and Rural Affairs, Lanzhou University, Lanzhou, 730020, China; College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, 730020, China.
State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, Key Laboratory of Grassland Livestock Industry Innovation, Ministry of Agriculture and Rural Affairs, Lanzhou University, Lanzhou, 730020, China; College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, 730020, China.
J Environ Manage. 2023 Jun 15;336:117647. doi: 10.1016/j.jenvman.2023.117647. Epub 2023 Mar 9.
Biological soil crust (BSC) exists widely in many kinds of grassland, its effect on soil mineralization in grazing systems has well been studied, but the impacts and threshold of grazing intensity on BSC have rarely been reported. This study focused on the dynamics of nitrogen mineralization rate in biocrust subsoils affected by grazing intensity. We studied the changes in BSC subsoil physicochemical properties and nitrogen mineralization rates under four sheep grazing intensities (i.e., 0, 2.67, 5.33, and 8.67 sheep ha) in seasons of spring (May-early July), summer (July-early September), and autumn (September-November). Although this moderate grazing intensity contributes to the growth and recovery of BSCs, we found that moss was more vulnerable to trampling than lichen, which means the physicochemical properties of the moss subsoil are more intense. Changes in soil physicochemical properties and nitrogen mineralization rates were significantly higher under 2.67-5.33 sheep ha than other grazing intensities (Saturation phase). In addition, the structural equation model (SEM) showed that the main response path was grazing, which affected subsoil physicochemical properties through the joint mediation of BSC (25%) and vegetation (14%). Then, the further positive effect on nitrogen mineralization rate and the influence of seasonal fluctuations on the system was fully considered. We found that solar radiation and precipitation all had significant promoting effects on soil nitrogen mineralization rates, the overall seasonal fluctuation has a direct effect of 18% on the rate of nitrogen mineralization. This study revealed the effects of grazing on BSC and the results may enable a better statistical quantification of BSC functions and provide a theoretical basis to formulate grazing strategies in the grazing system of sheep in Loess Plateau even worldwide (BSC symbiosis).
生物土壤结皮（BSC）广泛存在于多种草原中，其对放牧系统土壤矿化的影响已得到充分研究，但放牧强度对生物土壤结皮的影响及阈值鲜有报道。本研究聚焦于受放牧强度影响的生物结皮下层土壤氮矿化速率的动态变化。我们研究了在春季（5月至7月初）、夏季（7月至9月初）和秋季（9月至11月）四个绵羊放牧强度（即0、2.67、5.33和8.67只羊/公顷）下生物结皮下层土壤理化性质和氮矿化速率的变化。尽管这种适度的放牧强度有助于生物土壤结皮的生长和恢复，但我们发现苔藓比地衣更容易受到践踏，这意味着苔藓下层土壤的理化性质变化更为剧烈。在2.67 - 5.33只羊/公顷的放牧强度下，土壤理化性质和氮矿化速率的变化显著高于其他放牧强度（饱和阶段）。此外，结构方程模型（SEM）表明，主要响应路径是放牧，它通过生物土壤结皮（25%）和植被（14%）的联合介导影响下层土壤理化性质。然后，充分考虑了对氮矿化速率的进一步积极影响以及季节波动对该系统的影响。我们发现太阳辐射和降水对土壤氮矿化速率均有显著促进作用，总体季节波动对氮矿化速率有18%的直接影响。本研究揭示了放牧对生物土壤结皮的影响，研究结果可能有助于更好地统计量化生物土壤结皮的功能，并为制定黄土高原乃至全球绵羊放牧系统中的放牧策略提供理论依据（生物土壤结皮共生）。
