种植模式和坡位对茶园土壤细菌群落结构及功能类群的影响

茶树（Camellia sinensis L.）种植是亚热带丘陵山区主要的土地利用类型，茶园种植模式是影响土壤细菌群落结构的主要人为因素。为揭示种植模式和坡位对土壤细菌群落结构和功能的影响，选取两种不同种植模式（常规和有机种植模式）和3个坡位（上、中、下坡位）表层土壤（0-20cm）为对象，采用野外调查、Illumina Miseq高通量测序和PICRUSt2功能预测相结合的研究方法，研究不同种植模式和坡位下土壤细菌群落结构和功能特征，阐明土壤理化性质对土壤细菌群落结构的影响，预测土壤细菌功能特征。研究结果表明：（1）与常规种植模式相比，有机种植模式茶园土壤细菌Alpha多样性有所降低，其中中坡位常规茶园土壤细菌Sobs和Simpson指数显著高于有机茶园（P<0.05）；从坡面尺度看，两种种植模式下土壤细菌Alpha多样性指标均以中坡位最高，其中常规茶园中坡位土壤细菌Ace和Simpson指数均显著高于下坡位（P<0.05）。（2）各样地茶园土壤细菌共获得29个门82个纲190个目316个科517个属929个种，主要细菌优势门为绿弯菌门（Chloroflexi）、放线菌门（Actinobacterita）、变形菌门（Proteobacteria）、酸杆菌门（Acidobacteria）。土壤细菌群落优势属以AD3、热酸菌属（Acidothermus）、norank_f__norank_o__Elsterales和norank_f__Xanthobacteraceae为主。（3）主坐标分析（PCoA）显示，不同种植模式的茶园土壤细菌群落结构存在明显差异，常规种植模式下不同坡位之间的土壤细菌群落结构有显著差异（P<0.05），有机种植下不同坡位之间的土壤细菌群落结构无显著差异。置换多元方差分析（PERMANOVA）结果表明不同种植模式的土壤细菌群落结构差异显著（P<0.05），而不同坡位土壤细菌群落结构无显著差异（P>0.05），说明种植模式对茶园土壤细菌群落结构的影响更大。组间群落差异分析（LEfSe）表明，57个差异物种对种植模式非常敏感，不同种植模式富集了不同的细菌类群。（4） PICRUSt2功能预测共获得6个一级功能层和46个二级功能层，表现出功能上的丰富性，土壤细菌群落在代谢、遗传信息处理和环境信息方面功能活跃。有机种植模式提高了土壤细菌碳水化合物代谢、氨基酸代谢、膜运输、信号转导、脂质代谢及外源生物降解与代谢功能。（5）相关分析和冗余分析结果表明，土壤碱解氮、速效磷、全磷、全钾和pH是影响土壤细菌群落丰度和多样性的主要影响因子。总体而言，有机种植模式改变了茶园土壤细菌群落结构和代谢功能，增加土壤有益细菌的数量，有利于保持茶园土壤可持续的生态环境。

Effects of planting patterns and slope positions on soil bacterial community structure and functional groups in tea gardens

Tea (Camellia sinensis L.) is one of the most important and traditional economic crops widely cultivated in acid red soils in the subtropical zones in China, and the planting pattern constitutes the major artificial factor affecting the soil bacterial community structure. However, the effect of the planting patterns on soil bacterial community structures and functions in the tea garden remains unclear. To study the characteristics of soil bacterial community compositions and functional groups under different planting patterns and slope positions, soil samples derived from topsoil (0-20cm) were collected from the upper, middle, and lower slope positions of conventional (CT) and organic (OT) tea gardens. Illumina MiSeq sequencing and PICRUSt2 predictions were performed to investigate the bacterial community structures and functional groups, respectively. Further, the Spearman correlation analysis and redundancy analysis (RDA) were also used to examine the soil property factors that drived the community structure. The results showed that:(1) compared with the conventional planting pattern, the soil bacterial diversity under organic planting pattern decreased remarkably, and the Sobs and Simpson indices significantly decreased in the middle slope position (P<0.05). Regardless of the planting patterns, the soil bacterial diversities were the highest in the middle slope position. Ace and Simpson indices of the bacterial community in this slope position were significantly higher than the respective values of the lower slope position under the conventional planting pattern (P<0.05). (2) A total of 29 phyla, 82 classes, 190 orders, 316 families, 517 genera and 929 species were detected in soil bacteria of tea gardens. The dominant bacterial phyla were Chloroflexi, Actinobacterita, Proteobacteria and Acidobacteria. The dominant bacterial genera were AD3, Acidothermus, norank_f__norank_o__Elsterales, and norank_f__Xanthobacteraceae. (3) The results of principal coordinates analysis (PCoA) showed that the soil bacterial community structures could be distinctly separated in different planting patterns. The community structures of soil bacteria in different slope positions were significantly different under the conventional planting pattern (P<0.05), whereas they were similar under the organic planting pattern. The permutational multivariate analysis of variance (PERMANOVA) indicated that the bacterial community structures under different planting patterns showed significant differences (P<0.05), whereas those in different slope positions did not (P>0.05). The linear discriminant analysis effect size (LEfSe) analysis showed that 57 biomarkers were very sensitive to the planting patterns, with different planting patterns enriching different bacterial populations. (4) PICRUSts2 platform predicted 6 biological metabolic pathways and 46 subfunctions in the soil bacteria of tea gardens, suggesting of abundant soil bacterial functions. These pathways mainly involved metabolic processes, genetic information processing, and environmental information processing. The organic planting pattern increased carbohydrate metabolism, amino acid metabolism, membrane transport, signal transduction, and lipid metabolism of cofactors and vitamins functional genes. (5) The results of the Spearman correlation analysis and RDA showed that soil alkaline nitrogen, available phosphorus, total phosphorus, total potassium and pH were the main factors affecting the abundance and diversity of the soil bacterial community. In conclusion, the organic planting changes the community structure and the metabolic functions of soil bacteria, promotes soil bacteria carbon and nitrogen metabolism and enriches beneficial bacteria, and thus is beneficial to maintain the sustainable ecosystem in tea garden soil.