汛期前后老鹳河干流人类干扰下浮游细菌多样性及功能预测

老鹳河是丹江口水库距离调水口最近的入库支流，水质好坏直接影响调水安全.为探究老鹳河干流汛期前后浮游细菌的群落组成和功能变化规律，分别于2018年和2019年汛期前（5月）与汛期后（10月）对老鹳河干流4个典型生态位点进行水质分析和浮游细菌高通量测序，杨河位点（YH）属轻度干扰；西峡北位点（XX）属中度干扰；垱子岭位点（DZL）属重度干扰；张营位点（ZY）属中度干扰.结果表明，老鹳河干流浮游细菌由40门599属组成，汛期前浮游细菌多样性高于汛期后，中度干扰有利于Shannon-Wiener指数的提高.LEfSe分析显示，汛期前优势门中杨河的装甲菌门，西峡北的Epsilonbacteraeota和厚壁菌门，垱子岭的蓝藻门与其他样点有显著性差异；汛期后仅垱子岭的厚壁菌门和蓝藻门与其他样点有显著性差异.浮游细菌群落PCoA分析显示，汛期前后各个样点区分明显，汛期前各样点间群落差异大于汛期后；RDA和CCA分析表明，流经县城后引起浮游细菌多样性下降的主要环境因子为总氮和氨氮.PICRUSt浮游细菌功能基因预测发现，COG基因10大类功能家族为优势类群.与氮代谢相关的30个KO功能基因呈现出汛期前样点间差异大于汛期后，汛期前杨河碳酸酐酶基因（cynT和can）与其他样点差异显著的特征.氮和磷是老鹳河调控浮游细菌群落结构和水体富营养化的主要因子，氮输入的变化会造成河流不同区域氮代谢功能的改变.

Diversity and Function Prediction of Bacterioplankton Under Human Disturbance in the Main Stream of the Laoguan River Before and After the Flood Season

The Laoguan River is the tributary of Danjiangkou Reservoir located nearest to the water diversion outlet, and water quality here directly affects the safety of the diverted water. To explore the community composition and functional change of bacterioplankton in the Laoguan River before and after the flood season, four representative sites were sampled in the main stream before (May) and after (October) the 2018 and 2019 flood seasons. Water quality was assessed and high-throughput sequencing of bacterioplankton was performed. Yanghe (YH) was slightly disturbed, Xixiabei (XX) was moderately disturbed, Dangziling (DZL) was heavily disturbed, and Zhangying (ZY) was moderately disturbed. In total, 599 genera from 40 phyla were collected. The diversity of bacterioplankton before the flood season was higher than afterwards, and moderate levels of disturbance increased the Shannon-Wiener diversity index. LEfSe analysis indicated that significant differences existed in some dominant phyla; Armatimonadete in Yanghe, Epsilonbacteraeota and Firmicutes in Xixiabei, and Cyanophyta in Dangziling dominated before flood season, while significant differences only occurred in Firmicutes and Cyanophyta in Dangziling after the flood season. The PCoA of the bacterioplankton community showed that the sampling points were distinct before and after the flood season, and that differences among samples were greater before the flood season. The RDA and CCA indicated that total nitrogen and ammonia nitrogen were the main environmental factors causing declines in bacterioplankton diversity. PICRUSt showed a total of ten dominant categories of COG function genes. A total of 30 KO function genes related to nitrogen metabolism group also different between the two periods, with greater differences before flood season. The genes cynt and can in Yanghe were significant different from the other three sampling points before the flood season. Overall, nitrogen and phosphorus were the main factors regulating the bacterioplankton community structure and eutrophication in the Laoguan River. Changes in nitrogen inputs will result in changes in microbial nitrogen metabolic function in different regions of the river.