Abstract—

The microbial population of soil is diverse and is regulated by different soil properties. This study aimed to determine the impact of climate and grazing on soil community composition in two semiarid areas, Kerman province, Iran. Soil samples were taken from four zones which were either cold or warm and either grazed by cattle or not grazed. Soil chemical analyses were determined by standard methods and the bacterial community by DNA extraction from soil followed by next generation sequencing of the 16S rRNA gene. Soil at cold areas had higher moisture, organic carbon, total nitrogen, available phosphorous and exchangeable potassium concentrations than warm sites. The abundance of Proteobacteria (28.3% ± 1.0) and Actinobacteria (44.6% ± 1.1) was highest at the cold-grazed and warm-grazed zones, respectively, which account for ~70% of all OTUs. Greater richness and evenness of bacteria at the cold areas, compared to the warm areas, was also observed and is attributed to more vegetation cover and soil organic matter, nutrient availability and moisture. There was no significant difference of chemical soil properties between the grazed and not grazed sites. However, significant differences were observed in bacterial diversity between the grazed and not grazed sites, suggesting that bacteria respond much more rapidly to grazing than to soil chemical properties. According to the Chao1 and J values, the least richness and the highest evenness belonged to the warm-grazed zone, indicating grazing had a greater effect at the warm areas, compared to the cold areas. In conclusion, change in community composition at managed (i.e. grazed versus not grazed) semiarid sites, estimated by next generation sequencing, precede detectable changes in soil chemical properties, thereby providing an early sign of change in soil quality.

中文翻译：

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伊朗半干旱地区放牧和气候对土壤化学性质和细菌群落的影响

摘要—

土壤的微生物种群是多种多样的，并受不同土壤性质的调节。这项研究旨在确定气候和放牧对伊朗克尔曼省两个半干旱地区土壤群落组成的影响。从四个寒冷或温暖的地区采集土壤样品，这些地区要么被牛放牧，要么未被放牧。土壤化学分析通过标准方法确定，细菌群落通过从土壤中提取DNA，然后对16S rRNA基因进行下一代测序来确定。与温暖地区相比，在寒冷地区的土壤具有更高的水分，有机碳，总氮，有效磷和可交换的钾浓度。在冷磨和热磨区分别有最高的变形杆菌（28.3％±1.0）和放线菌（44.6％±1.1）的丰度，约占所有OTU的70％。与温暖地区相比，在寒冷地区细菌的丰富度和均匀性也更高，这归因于更多的植被覆盖和土壤有机质，养分利用率和水分。放牧与未放牧之间的化学土壤性质没有显着差异。然而，在放牧和未放牧的地点之间观察到细菌多样性的显着差异，这表明细菌对放牧的反应比对土壤化学性质的反应要快得多。根据Chao1和J值，最富裕度和最高均匀度属于温暖磨砂区，这表明与寒冷地区相比，放牧对温暖地区的影响更大。总之，管理（即放牧与未放牧）半干旱地点的社区组成发生了变化，个性。