环境科学  2023, Vol. 44 Issue (9): 5164-5175   PDF    
华北平原典型城市土壤微生物群落时空变化规律及其驱动因子
赵鑫宇, 陈慧, 常帅, 宋圆梦, 赵波, 卢梦淇, 崔建升, 张璐璐     
河北科技大学环境科学与工程学院, 河北省污染防治生物技术实验室, 石家庄 050000
摘要: 微生物群落结构和功能受多种环境因素的共同影响,为阐明典型城市土壤中微生物群落的时空变化规律及其主要影响因素,亟需开展典型城市土壤中微生物群落时空动态变化特征研究.鉴于此,选取华北平原典型城市——石家庄市为研究区,共设置12个采样点,分别于2021年6月(夏季)和9月(秋季)采集表层土壤,并利用16S rRNA高通量测序技术对土壤中微生物群落结构及功能进行研究,探究其时空变化规律;同时运用Pearson相关性分析建立微生物群落与环境因子间的相关性,识别微生物群落时空变化的主要驱动因子.结果表明:①石家庄市表层土壤中主要优势菌门为放线菌(Actinobacteriota)和变形菌(Proteobacteria);就季节变化而言,在门水平上,Actinobacteriota和Proteobacteria相对丰度均呈降低趋势;在属水平上,夏季主要优势菌属为节杆菌属(Arthrobacter)和未知分类菌属,秋季主要优势菌属为ArthrobacterCandidatus_Nitrocosmicus,且优势菌属呈显著季节差异(P < 0.05);②就季节变化而言,Simpson、Ace和Chao指数均值呈升高趋势,而OTU均值呈降低趋势;就空间差异而言,Shannon指数和Simpson指数呈显著空间差异(P < 0.01和P < 0.05);③各类功能基因无显著季节和空间差异;其中能源生产和转换类功能基因相对丰度最高,在夏季和秋季的相对丰度分别为24.06%~24.84%和24.63%~25.98%;④微生物群落结构组成、多样性指数和功能基因与喹诺酮类抗生素(QNs)、总磷(TP)和硝氮(NO3--N)呈显著相关,且与QNs显著相关性最强(|r| >0.900);这表明在石家庄市表层土壤中抗生素成为影响微生物群落变化的主要驱动因素.因此,为保障城市土壤中微生物群落结构和功能稳定,应进一步加强土壤中抗生素污染的综合管控.
关键词: 土壤      微生物群落      多样性指数      功能基因      时空分布      驱动因素     
Spatial-temporal Changes and Driving Factors of Soil Microbial Communities in a Typical City of North China Plain
ZHAO Xin-yu , CHEN Hui , CHANG Shuai , SONG Yuan-meng , ZHAO Bo , LU Meng-qi , CUI Jian-sheng , ZHANG Lu-lu     
Biotechnology Laboratory for Pollution Prevention in Hebei Province, School of Environmental Science and Engineering, Hebei University of Science and Technology, Shijiazhuang 050000, China
Abstract: The structure and function of microbial communities are affected by several environmental factors. To clarify the spatial-temporal changes and main influencing factors of soil microbial communities in a typical pharmaceutical city, it is urgent to study the spatial-temporal changes in microbial communities in soils for typical cities. Shijiazhuang City was selected as the study area, and 12 sampling sites were selected. The topsoil was collected in June (summer) and September (autumn) of 2021. The 16S rRNA high-throughput sequencing technology was used to study the structure and function of microbial communities in the soil and explore their spatial-temporal changes. Concurrently, Pearson correlation analysis was applied to establish the correlation between the microbial community and environmental factors, and identify the main driving factors of temporal and spatial changes in the microbial community. The results showed that: ① Actinobaciota and Proteobateria were the main dominant bacteria in the surface soil of Shijiazhuang City; at the phylum level, the relative abundance of Actinobacteria and Proteobateria decreased from summer to autumn; at the genus level, the dominant genera were Arthrobacter and unknown genera in summer and Arthrobacter and Candidatus_Nitrocosmicus in autumn, which showed significant seasonal differences (P < 0.05). ② For seasonal variation, the mean values of the Simpson, Ace, and Chao indices increased, whereas the mean values of OTU decreased; for spatial variation, the Shannon and Simpson indices showed significant spatial difference (P < 0.01 and P < 0.05). ③ There were no significant spatial-temporal differences in various functional genes; thereinto, the relative abundances of energy production and transformation functional genes were the highest (24.06%-24.84% in summer and 24.63%-25.98% in autumn, respectively). ④ The compositions of microbial community, diversity index, and functional genes were significantly correlated with quinolone antibiotics (QNs), total phosphorus (TP), and nitrate nitrogen (NO3--N), most significantly correlated with QNs (|r|>0.900), which indicated that antibiotics were the main driving factor of soil microbial communities. Therefore, to ensure the stability of microbial community structure and function in urban soil, the comprehensive management and control of antibiotic pollution in soil should be further strengthened.
Key words: soil      microbial community      diversity index      functional genes      temporal and spatial distribution      driving factors     

微生物群落(包括细菌、古菌和真菌)作为驱动生物地球化学循环和维持生态系统功能的基础[1, 2], 在土壤生态系统中发挥着重要作用.土壤微生物群落易受环境变化的影响, 其结构组成、多样性和功能在不同环境条件下存在显著差异[3~5].季节变化作为微生物群落变化的重要驱动因素, 其可通过影响植被类型、生物量、水分和温度进而改变微生物群落的结构和功能[6~10].其中温度变化可改变土壤中微生物群落的生物活性和结构组成[11].而土壤水分是影响微生物群落多样性和功能时空变化的关键因素[12].当土壤被雨水淹没时, 会加剧土壤中微生物群落的生物转化机制[13]; 洪涝变化会显著改变湿地土壤中微生物群落多样性和组成, 进而影响土壤生物地球化学循环[14]; 降水量的增加会显著增加高寒草地土壤中真菌群落的α多样性[15].此外, 降雨量的变化可导致表层土壤理化性质(如氮和磷等营养元素含量)发生改变[16], 而土壤理化性质与土壤微生物群落结构密切相关[17].华北平原的雨季集中在7~8月[18], 研究雨季前后(6月和9月)土壤微生物群落的空间分布特征, 对于了解不同水文时期土壤微生物群落的时空变化规律具有重要意义.

整体而言, 微生物群落的结构和功能受多种环境因子的共同影响, 且不同季节的主要环境影响因素存在差异[19], 如:pH和总氮(TN)与中亚热带毛竹林土壤中微生物群落结构显著相关(P<0.05)[20]; TN和总碳(TC)是驱动尾矿坝面土壤中微生物群落结构动态变化的主要环境因子[21]; pH、TC和多酚氧化酶是戴云山夏季土壤微生物群落变化的主要驱动因子, 而有效磷、全钾和TC是戴云山冬季土壤微生物群落变化的主要驱动因子[10].然而, 此前研究多集中于土壤pH、电导率(EC)、TN、TC、可溶性有机碳含量和有效磷含量等理化因子对土壤微生物群落的影响, 而较少关注土壤中各形态氮和土壤粒径的影响.Li等[22]研究表明, 亚硝氮(NO2--N)是解释湿地土壤中门水平微生物群落结构变化和组成的主要因素之一; 赵河[23]和王华林[24]研究发现, 微生物群落结构和多样性与氨氮(NH4+-N)、硝氮(NO3--N)和总磷(TP)显著相关, 土壤粒径也会影响微生物群落分布.因此, 本研究拟选择NH4+-N、NO3--N、NO2--N、土壤粒径和TP作为环境影响因子.此外, 由于微生物群落对环境变化敏感, 抗生素等污染物也会影响微生物群落的结构和功能[25], 如:低含量四环素和土霉素能显著降低土壤中细菌和真菌数量[26]; 恩诺沙星能降低微生物群落的活性[27]等.有研究表明, 喹诺酮类(QNs)抗生素在京津冀地区土壤中的污染最为严重[28].由于QNs吸附能力较强, 在土壤中不断蓄积, 最终会影响土壤微生物群落的多样性及功能.因此, 为保障土壤生态系统的稳定, 亟需进一步探究QNs污染土壤中微生物群落结构及功能变化的主要驱动因素.

石家庄市作为华北平原的典型城市, 制药企业发达.其中华北制药集团的抗生素原料药总产量占全国总产量的15%左右.石家庄市表层土壤中存在抗生素污染, 且已证实会对土壤微生物群落的多样性及功能产生影响[29].但目前对石家庄市土壤中微生物群落的时空变化特征及其驱动因子的研究仍未见报道.因此, 本研究分别于2021年6月和9月采集了12个代表性表层土壤样品, 利用16S rRNA高通量测序技术对土壤中微生物群落组成、功能和多样性进行研究, 明晰其季节动态变化特征, 同时建立微生物群落与多种环境因子(QNs和土壤理化性质)的相关性, 识别长期抗生素污染土壤中微生物群落时空变化的主要环境驱动因子, 以期为土壤生态系统的恢复与稳定提供理论支撑.

1 材料与方法 1.1 研究区域概况与样品采集

石家庄市有“华北药都”之称, 位于河北省中南部(东经113°30′~115°20′, 北纬37°27′~38°47′之间), 属温带季风气候, 季节性变化显著.按地貌类型和土地利用可分为西部山区、中部山麓平原建设用地和东部平原农业用地.其中中部建设用地制药企业发达, 分布有三大产业园区[30].2021年《经济日报》称, 截至2020年底, 石家庄市医药工业规模位居全市主导产业前列, 创造了占全市工业36.5%的利润.

根据石家庄市地形, 并结合其空间方位, 分别在其东部(S1)、北部(S2)、中部(S3)和南部(S4)各均匀布设3个采样点, 共12个采样点, 依次为S1(木邱、木连城、寺头)、S2(协神、正莫、连家庄)、S3(方台、宋营、固营)和S4(南清河、北王里、高邑城关), 采样点分布见图 1.其中S1、S2和S4区域主要为农业用地, 而S3区域主要为建设用地.用干净的铁铲采集0~25 cm的表层土壤, 使用聚乙烯袋进行密封装袋标记, 放入恒温箱低温保存, 运送回实验室后放入-20℃冰箱进行冷冻保存直至分析.

图 1 采样点分布示意 Fig. 1 Distribution of sampling sites

1.2 DNA提取与高通量测序

将新鲜土壤样品过40目筛, 取适量过筛后的土壤转移至聚乙烯离心管内, 标记后进行密封低温保存, 并送至测序公司进行高通量测序.使用A.E.Z.N.A.TM土壤DNA试剂盒进行土壤样品DNA提取.采用引物341F(5′-CCTACGGGNGGCWGCAG-3′)和806R(5′-GGACTACHVGGGTWTCTAAT-3′) 进行PCR扩增.扩增产物经切胶回收后, 建立基因文库并进行定量和DNA序列质控, 然后利用Illumina MiSeq平台进行16S rRNA高通量测序.在95%相似水平下进行OTU聚类分析.本研究的高通量测序由上海美吉生物有限公司完成.

1.3 环境因子分析

称取40 g土壤样品, 风干粉碎后过40目筛, 混合均匀, 使用LE400-05(USA)粒径分析仪测定土壤粒径.将剩余土壤样品分为两份, 一份用于TP测定, 另一份用于NH4+-N、NO2--N和NO3--N含量的测定.将测定TP所需土壤进行自然风干、粉碎和混匀, 混匀后的样品分为两份, 一份根据HJ 613-2011标准测定土壤样品(风干土壤)的干物质含量, 另一份过100目筛, 然后根据HJ 632-2011标准测定TP含量.将测定氮含量所需土样去除杂物、混匀并过100目筛, 将过筛后的样品分为两份, 其中一份根据HJ 613-2011标准测定土壤样品(新鲜土壤)的干物质含量, 另一份称取40 g土壤样品, 根据HJ 634-2011标准测定土壤中NH4+-N、NO2--N和NO3--N含量.土壤中QNs的测定方法参照文献[31].

1.4 数据统计与分析

采用SPSS 25.0和Excel软件进行土壤理化因子的数据处理与统计, 采用单因素方差分析进行差异显著性检验, 采用Pearson法进行相关性分析.利用Origin 2018软件绘制理化因子、α多样性指数和COG功能基因柱状分布.通过美吉生信云分析平台进行微生物群落物种组成分析、α多样性分析、PICRUSt功能预测、VIF方差膨胀因子筛选、相关性分析和Kruskal-Wallis秩和检验.使用ArcGIS软件绘制QNs含量空间分布.

2 结果与分析 2.1 微生物群落时空分异特征

就微生物群落物种组成而言, 6月检测出39门1 028属, 共计2 171种; 9月共检出51门961属, 共计1 953种.从6~9月, 土壤中主要菌门种类并无显著变化, 放线菌(Actinobacteriota)和变形菌(Proteobacteria)为主要优势菌门, 相对丰度均呈降低趋势.在属水平上, 5种相对丰度较高的菌属由某未知分类菌属、节杆菌属(Arthrobacter)、鞘氨醇单胞菌属(Sphingomonas)、norank_ f_ _JG30-KF-CM45和类诺卡氏菌属(Nocardioides)变为节杆菌属、Candidatus_NitrocosmicusNitrososphaeraceae、芽孢杆菌属(Bacillus)和鞘氨醇单胞菌属[图 2(e)图 2(g)].其中, 夏季(6月)土壤中的主要优势菌属为未知分类菌属和节杆菌属, 相对丰度分别为3.66%(S2)~6.01%(S4)和2.45%(S1)~7.65%(S3); 而秋季(9月)土壤中主要优势菌属为节杆菌属和Candidatus_Nitrocosmicus, 相对丰度分别为3.71%(S2)~7.41%(S3)和2.85%(S3)~7.99%(S4).根据Venn图和Kruskal-Wallis秩和检验, 属水平微生物群落组成空间差异显著(P<0.05), 而门水平微生物群落组成并无显著空间差异.

(a)和(c)分别为6月和9月土壤中门水平微生物群落组成; (b)和(d)分别为6月和9月土壤中门水平物种组成Venn图; (e)和(g)分别为6月和9月土壤中属水平微生物群落组成; (f)和(h)分别为6月和9月土壤中属水平物种组成Venn图 图 2 土壤中微生物群落时空分布 Fig. 2 Temporal and spatial distribution of microbial communities in soil

2.2 多样性指数和OTU的时空分异特征

6月和9月的Coverage指数平均值均高于0.98, 表明测序结果能够较为真实地反映样本中的微生物情况.OTU聚类和α多样性分析结果表明(图 3), 从6~9月, Simpson、Ace和Chao指数平均值分别由0.008、3 227和3 236升高为0.011、3 331和3 332, 而OTU平均值由2 720降低为2 589, 表明土壤中微生物群落多样性呈降低趋势, 而丰度呈升高趋势.单因素方差分析结果表明, 6月Shannon、Simpson、Ace和Chao指数空间差异显著(P<0.05), 9月Shannon指数和Simpson指数空间差异显著(P<0.01和P<0.05).

图 3 多样性指数和OTU数量的时空分布 Fig. 3 Spatial and temporal distribution of diversity index and OTU number

2.3 COG功能基因时空分异特征

COG功能基因相对丰度如图 4所示.从6~9月, 8种COG功能基因相对丰度并无显著变化.其中能源生产和转换类功能基因相对丰度最高, 其次为翻译、核糖体结构和生物发生类、无机离子转运和代谢类以及信号转导机制类功能基因, 相对丰度分别由: 24.06% ~24.84%、17.14% ~17.64%、18.26% ~19.53%和18.46% ~19.72%变为24.63% ~25.98%、17.80% ~20.18%、17.88% ~18.45%和16.79% ~18.84%. 且单因素方差分析结果表明, 6月和9月各类COG功能基因丰度并无显著空间差异.

图 4 COG功能基因相对丰度 Fig. 4 Relative abundance of COG functional genes

2.4 土壤理化因子时空分异特征

土壤理化因子分析结果表明(图 5), 从6~9月, 土壤中黏粒的占比平均值显著降低(9.94%和4.45%), 而砂粒的占比平均值显著升高(8.31%和16.82%); ω(TP)、ω(NH4+-N)、ω(NO3--N)和ω(NO2--N)平均值分别由836.4、16.79、13.26和0.632 7 mg·kg-1升高为964.5、24.45、78.57和1.113 mg·kg-1, 其中NO3--N含量平均值显著升高.且单因素方差分析结果表明, 各理化因子并无显著空间差异.

(a)6月土壤粒径组成; (b)9月土壤粒径组成; (c)6月理化因子空间分布; (d)9月理化因子空间分布 图 5 土壤理化因子时空分布 Fig. 5 Spatial and temporal distribution of soil physical and chemical factors

2.5 土壤中QNs时空分异特征

对土壤中QNs分析结果表明(图 6), 从6~9月, ω(总QNs)平均值由41.53 μg·kg-1升高为92.39 μg·kg-1, 整体呈S3>S4>S1>S2的空间分布特征.其中OFL、ENO、NOR、CIP、ENR、OXO和FLU的检出率均高于50%. 除ENO外, ω(OFL)、ω(NOR)、ω(CIP)、ω(ENR)、ω(OXO)和ω(FLU)平均值均呈升高趋势, 分别由1.36、15.86、13.72、5.11、0.06和0.35 μg·kg-1升高为3.45、72.49、31.94、6.15、0.38和6.48 μg·kg-1.且单因素方差分析结果表明, NOR含量和总QNs含量呈显著空间差异(P<0.05).

图 6 土壤中总QNs含量的时空分布 Fig. 6 Spatial and temporal distribution of total QNs content in soil

2.6 微生物群落与环境因子的相关性

将6月和9月各QNs和理化因子分别进行VIF方差膨胀系数筛选, 以去除共线性较高的环境因子, 筛选后的环境因子与多样性指数和COG功能基因进行Pearson相关性分析(图 7).结果表明, QNs与多样性指数和功能基因存在广泛显著相关性[图 7(a)图 7(b)], 而理化因子与多样性指数和功能基因相关性并不显著[图 7(c)图 7(d)].从6~9月, 理化因子与多样性指数和功能基因相关性显著增强.夏季(6月)微生物群落多样性和COG功能基因的主要驱动因子为NOR、CIP、ENR和总QNs, 而秋季(9月)微生物群落多样性和COG功能基因的主要驱动因子为ENO、NOR、CIP、OXO、FLU、总QNs、TP和NO2--N.

(a)和(b)分别为6月和9月QNs与多样性指数、OTU和功能基因相关性; (c)和(d)分别为6月和9月理化因子与多样性指数、OTU和功能基因相关性; B、C、D、F、J、P、Q和T分别为染色质结构和动力学类、能源生产和转换类、细胞周期控制、细胞分裂和染色体分割类、核苷酸转运和代谢类、翻译、核糖体结构和生物发生类、无机离子转运和代谢类、次级代谢产物生物合成、运输和分解代谢类及信号转导机制类功能基因; 1、2、3、4、5和6分别为OTU、Coverage指数、Chao指数、Ace指数、Simpson指数和Shannon指数; *表示P<0.05, **表示P<0.01 图 7 环境因子与多样性指数、OTU和功能基因相关性 Fig. 7 Correlation between environmental factors and diversity index, OTU, and functional genes

将进行VIF方差膨胀系数筛选后的环境因子与微生物群落进行Pearson相关性分析, 结果表明(图 8), QNs和土壤理化因子与门水平和属水平微生物群落存在显著相关性.其中ENR和CIP与GaiellaGemmatimonadaceae、Myxococcota和Nitrospirota显著正相关(P<0.05), NOR和总QNs与Arthrobacter显著正相关(P<0.01); TP和NO3--N与Streptomyces显著正相关(P<0.01), 与Bacillus显著负相关(P<0.05和P<0.01); NO2--N与Candidatus_Nitrocosmicus显著正相关(P<0.05).总体上, TP、NO3--N、CIP和ENR是驱动夏季(6月)微生物群落组成变化的主要环境因子, CIP、ENR和NOR是驱动秋季(9月)微生物群落组成变化的主要环境因子.

(a)6月环境因子与门水平微生物群落相关性; (b)9月环境因子与门水平微生物群落相关性; (c)6月环境因子与属水平微生物群落相关性; (d)9月环境因子与属水平微生物群落相关性; a1.TP, a2.NO3--N, a3.OXO, a4.黏粒, a5.粉粒, a6.NO2--N, a7.ENO, a8.FLU, a9.NOR, a10.OFL, a11.ENR, a12.CIP, a13.QNs; b1.OXO, b2.FLU, b3.ENO, b4.ENR, b5.粉粒, b6.黏粒, b7.NOR, b8.NO2--N, b9.NO3--N, b10.CIP, b11.TP, b12OFL; c1.TP, c2.NO3--N, c3.CIP, c4.ENR, c5.OFL, c6.NOR, c7.QNs, c8.粉粒, c9.OXO, c10.FLU, c11.NO2--N, c12.黏粒, c13.ENO; d1.ENR, d2.ENO, d3.OXO, d4.FLU, d5.粉粒, d6.黏粒, d7.NOR, d8.OFL, d9.NO3--N, d10.CIP, d11.TP, d12NO2--N; *表示P<0.05, **表示P<0.01, ***表示P<0.001; 色柱对应数值为Pearson相关性系数, 蓝色对应相关性系数为负值, 表示为负相关, 红色对应相关性系数为正值, 表示为正相关 图 8 土壤环境因子与微生物群落组成相关性 Fig. 8 Correlation between soil physical and chemical factors and microbial community composition

3 讨论 3.1 土壤中微生物群落的时空变化规律

因不同地区土壤的土地利用类型、气候及地形条件存在差异, 导致微生物群落的组成和多样性呈现空间差异[32~35].在本研究中, 石家庄市不同区域优势菌属的空间差异显著, 而优势菌门组成并无显著空间差异, 这与此前研究的结果一致[29].本研究土壤中优势菌门主要包括变形菌、放线菌、酸杆菌、绿弯菌和厚壁菌等, 与我国(西)北部草原、西部高原草甸、东部城市农田和南部林地土壤中优势菌门组成高度相似(见表 1)[36~41], 因此土壤中优势菌门组成受环境条件的影响较小.其中变形菌门为丰度最高的优势菌门, 其次为放线菌门, 这与高雪峰等[42]和刘洋等[43]研究的结果一致.优势种对外界环境条件(如污染物)具有一定适应性, 可利用特定的降解酶经多种代谢途径满足自身生长和发展需求[44].其中放线菌大量存在于土壤表层, 可利用水解酶实现对植物细胞壁的降解[45]; 厚壁菌作为石家庄表层土壤中优势菌门之一, 包括杆菌和梭菌等, 其中杆菌可有效分解土壤中的碳基污染物[46, 47].

表 1 我国不同地区土壤中优势菌门组成 Table 1 Composition of dominant bacteria in soils of different regions in China

就季节变化而言, 从6~9月, 本研究土壤中的厚壁菌相对丰度和QNs含量显著升高, 表明厚壁菌的相对丰度变化可能与表层土壤中QNs等碳基污染物含量有关.此外, 从6~9月, 微生物群落的α多样性和优势物种丰度整体呈降低趋势, 且主要优势菌属组成发生显著变化, 这与Chen等[48]研究的结果一致, 这可能与汛期前后降雨量和气温的变化有关.温度升高和降水量的增加, 有助于提高微生物群落的活性和生产力[49, 50].9月汛期结束, 降水量和土壤表层温度较6月显著降低, 改变了土壤中微生物群落组成和酶活性[50, 51], 抑制了微生物群落的生长, 导致微生物群落α多样性和丰度降低.

3.2 土壤中微生物群落的主要环境驱动因子

就微生物群落组成而言, 在夏季, 微生物群落组成变化的主要驱动因子为TP、NO3--N、CIP和ENR; 而在秋季, 微生物群落组成变化的主要驱动因子为CIP、ENR和NOR.其中TP和NO3--N对微生物群落主要表现为抑制作用, 这与之前研究的结果不同[10, 52], 这可能是由于石家庄市土壤中氮、磷含量处于饱和状态, TP和NO3--N含量的升高导致土壤pH降低, 从而降低微生物的碳利用效率, 抑制微生物群落的生长[53].Bloem等[54]和Riaz等[55]研究也证实, 抗生素会影响微生物群落结构.秋季降雨量和温度降低, 导致抗生素等污染物的垂向迁移减弱和吸附能力增强, 不断在表层土壤中吸附蓄积, 最终导致抗生素含量升高[56~58].本研究土壤中CIP和ENR对微生物群落主要表现为促进作用, 这表明在特定含量范围内, 随着抗生素含量的升高, 会刺激具有相应抗性(耐受性)的优势种丰度的增加, 如:Li等[59]研究发现, 亚硝基螺旋菌群某一分支菌属丰度随着磺胺嘧啶含量的升高(0~20 mg·kg-1)逐渐增加.由夏季进入秋季后, 土壤中TP和NO3--N含量升高, 但与微生物群落的相关性减弱, 可能是氮、磷含量的升高使得土壤中优势种转变为对养分需求低的微生物类群[60].

就微生物群落多样性及功能而言, 在夏季, 微生物群落多样性及功能变化的主要驱动因子为NOR、CIP和ENR; 而在秋季, 微生物群落多样性及功能变化的主要驱动因子为NOR、CIP、ENO、OXO、FLU、TP和NO2--N.其中QNs与微生物群落多样性指数呈显著负相关, 表明QNs会降低土壤中微生物群落多样性, 这与已有研究的结果一致[61~63], 如:NOR处理28d后可显著降低微生物群落的Shannon指数[64]; 高浓度的QNs残留能显著降低土壤微生物群落多样性[65].此外, 微生物群落的功能也被证实与抗生素等污染物显著相关, 如:OFL等抗生素能增加沉积物中微生物群落的反硝化功能基因的丰度[66], 同时OFL可降低微生物群落的固氮能力、光合能力和代谢能力[67].在本研究中, QNs对微生物群落功能基因的影响呈现季节性动态变化, 可能与功能基因对抗生素等污染胁迫的降解反应及毒性响应差异有关[68].NOR和CIP作为石家庄市表层土壤中检出含量最高的QNs, 在夏季, 其与各类代谢类和信号转导机制类功能基因正相关, 说明其可作为信号分子刺激微生物群落进行繁殖代谢活动; 而在秋季, 与信号转导机制类功能基因负相关, 这可能是由于秋季表层土壤中抗生素含量升高, 抑制了微生物群落信号转导功能, 降低了微生物群落的抗干扰能力[69, 70].总而言之, 相较于TP、NO3--N、NO2--N、NH4+-N和土壤粒径等理化因子而言, QNs是驱动石家庄市表层土壤中微生物群落结构及功能变化的主要环境因子.

不同地区土壤中微生物群落的环境驱动因子不同.在自然环境条件下, 除季节更替导致的温度和水分变化产生的影响外, 土壤微生物群落主要受土壤理化因子的影响.如:Wang等[71]对高原湖岸土壤的研究表明, OTU水平微生物群落组成的差异主要由盐度、TOC和TN决定; Li等[22]对黄河三角洲湿地土壤的研究表明, TK、Mn4+、NO2--N和Na是土壤中微生物群落结构和组成变化的主要驱动因子.而石家庄市作为典型制药城市, 在本研究中表层土壤中的微生物群落主要受QNs等抗生素的影响; Zhang等[17]研究发现, 在重金属污染土壤中, Cr和Cd是驱动微生物群落结构变化的环境因子. 这表明当土壤环境受到污染时, 污染物可能成为土壤微生物群落变化的主要驱动因子.

4 结论

(1) 就微生物群落组成季节变化而言, 土壤中优势菌属种类发生改变; 就空间分异而言, 优势菌属存在显著空间差异.

(2) 就多样性指数和功能基因季节变化而言, 微生物群落多样性呈降低趋势, 而丰度呈升高趋势; 就空间分异而言, 多样性指数呈显著空间差异.

(3) 就环境因子季节变化而言, 表层土壤中黏粒占比呈降低趋势, 而砂粒占比、NO3--N含量和QNs含量呈升高趋势; 就空间分异而言, QNs呈显著空间差异.

(4) 就微生物群落结构变化的驱动因子而言, 夏季为TP、NO3--N、CIP和ENR, 而秋季为CIP、ENR和NOR; 就微生物群落多样性及功能变化的驱动因子而言, 夏季为NOR、CIP和ENR, 而秋季为NOR、CIP、ENO、OXO、FLU、TP和NO2--N.

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