Wang Zhen, Tang Kai, Struik Paul C, Ashraf Muhammad Nadeem, Zhang Tongrui, Zhao Yanning, Wu Riliga, Jin Ke, Li Yuanheng
Grassland Research Institute, Chinese Academy of Agricultural Sciences, Hohhot, 010010, China; Key Laboratory of Grassland Ecology and Restoration of Ministry of Agriculture, Hohhot, 010010, China.
Institute for Applied and Environmental Microbiology, College of Life Science, Inner Mongolia Agricultural University, Hohhot, 010018, China.
J Environ Manage. 2023 Dec 1;347:119078. doi: 10.1016/j.jenvman.2023.119078. Epub 2023 Sep 25.
Grazing causes changes in microbiome metabolic pathways affecting plant growth and soil physicochemical properties. However, how grazing intensity affects microbial processes is poorly understood. In semiarid steppe grassland in northern China, shotgun metagenome sequencing was used to investigate variations in soil carbon (C) and nitrogen (N) cycling-related genes after six years of the following grazing intensities: G0, control, no grazing; G1, 170 sheep days ha year; G2, 340 sheep days ha year; and G3, 510 sheep days ha year. Taxa and functions of the soil microbiome associated with the C cycle decreased with increasing grazing intensity. Abundances of genes involved in C fixation and organic matter decomposition were altered in grazed sites, which could effects on vegetation decomposition and soil dissolved organic carbon (DOC) content. Compared with the control, the abundances of nitrification genes were higher in G1, but the abundances of N reduction and denitrification genes were lower, suggesting that light grazing promoted nitrification, inhibited denitrification, and increased soil NO content. Q-PCR further revealed that the copies of genes responsible for carbon fixation (cbbL) and denitrification (norB) decreased with increasing grazing intensity. The highest copy numbers of the nitrification genes AOA and AOB were in G1, whereas copy numbers of the denitrification gene nirK were the lowest. A multivariate regression tree indicated that changes in C fixation genes were linked to changes in soil DOC content, whereas soil NO content was linked with nitrification and denitrification under grazing. Thus, genes associated with C fixation and the N cycle affected how C fixation and N storage influenced soil physicochemical properties under grazing. The findings indicate that grazing intensity affected C and N metabolism. Proper grassland management regimes (e.g., G1) are beneficial to the balances between ecological protection of grasslands and plant production in the semiarid steppe.
放牧会导致微生物群落代谢途径发生变化，进而影响植物生长和土壤理化性质。然而，人们对放牧强度如何影响微生物过程却知之甚少。在中国北方的半干旱草原，采用鸟枪法宏基因组测序技术，研究了在以下放牧强度持续六年之后，土壤碳（C）和氮（N）循环相关基因的变化情况：G0，对照，不放牧；G1，每年每公顷170羊单位；G2，每年每公顷340羊单位；G3，每年每公顷510羊单位。与碳循环相关的土壤微生物群落的分类群和功能随着放牧强度的增加而减少。在放牧区域，参与碳固定和有机质分解的基因丰度发生了改变，这可能会影响植被分解和土壤溶解有机碳（DOC）含量。与对照相比，G1中硝化基因的丰度较高，但氮还原和反硝化基因的丰度较低，这表明轻度放牧促进了硝化作用，抑制了反硝化作用，并增加了土壤中NO含量。定量聚合酶链反应（Q-PCR）进一步表明，负责碳固定（cbbL）和反硝化（norB）的基因拷贝数随着放牧强度的增加而减少。硝化基因AOA和AOB的最高拷贝数出现在G1中，而反硝化基因nirK的拷贝数最低。多元回归树分析表明，碳固定基因的变化与土壤DOC含量的变化相关，而在放牧条件下，土壤NO含量与硝化作用和反硝化作用相关。因此，与碳固定和氮循环相关的基因影响了放牧条件下碳固定和氮储存对土壤理化性质的影响。研究结果表明，放牧强度影响了碳和氮的代谢。适当的草地管理制度（如G1）有利于半干旱草原在生态保护和植物生产之间实现平衡。
