环境科学  2025, Vol. 46 Issue (8): 5360-5368   PDF    
干旱区不同植被类型土壤细菌群落结构及代谢功能特征
安芳娇1, 牛子儒2, 刘婷娜3, 苏永中3     
1. 兰州理工大学土木工程学院,兰州 730050;
2. 陕西省土地工程建设集团有限责任公司,西安 710075;
3. 中国科学院西北生态环境资源研究院,兰州 730000
摘要: 通过探究荒漠绿洲过渡带不同植被类型对土壤细菌群落结构及代谢功能的影响,为荒漠生态脆弱区植被重建的物种配置和管理提供科学理论依据. 中国西北荒漠-绿洲过渡带以泡泡刺(Ns)和沙拐枣(Cm)为天然植被,梭梭(Ha)和花棒(Hs)为人工植被,Ha-Cm为混合群落. 了解典型植被类型下土壤微生物群落结构和功能,对荒漠植被精准管理和可持续利用具有重要意义. 采用高通量测序,探究不同植被类型对土壤细菌结构、多样性和代谢途径的影响,考察驱动细菌群落结构变化的关键因子. 人工植被和天然植被生长显著提高土壤细菌群落丰富度和多样性,但无显著差异;宏基因组分析显示,各植被中均存在相同优势细菌门但比例不同,放线菌门、变形菌门和绿弯菌门为优势菌门,占细菌总数的65.12%~78.68%;主坐标分析(PCoA)显示,人工植被的土壤细菌结构差异显著,而天然植被的相似;不同植被群落土壤细菌代谢途径相似;土壤有机碳(SOC)、速效磷(AP)和pH是影响细菌功能结构的重要因子. 研究结果有助于深入理解干旱荒漠生态脆弱区植物-土壤相互作用.
关键词: 干旱区      荒漠-绿洲过渡带      植被类型      土壤细菌结构      代谢功能     
Structure and Metabolic Function Characteristics of Soil Bacterial Communities under Different Vegetation Types in Arid Region
AN Fang-jiao1 , NIU Zi-ru2 , LIU Ting-na3 , SU Yong-zhong3     
1. School of Civil Engineering, Lanzhou University of Technology, Lanzhou 730050, China;
2. Shaanxi Provincial Land Engineering Construction Group, Xi'an 710075, China;
3. Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
Abstract: The aim of this study was to explore the effects of different vegetation types on soil bacterial community structure and metabolic function in an oasis-desert ecotone and provide scientific theoretical basis for species allocation and management of vegetation reconstruction in arid desert ecosystem. Nitraria sphaerocarpa Maxim and Calligonum mongolicum Turcz are the main natural vegetation, Haloxylon ammodendron Bunge, and Hedysarum scoparium Fisch are the primary artificial vegetation, and Ha-Cm are the main mixed community in an oasis-desert ecotone in northwest China. Understanding soil microbial community structure and function under typical vegetation types is crucial for accurate management and sustainable use of desert vegetation. We used high-throughput sequencing technology to explore the effects of different vegetation types on the structure, diversity, and metabolic pathways of soil bacteria and to investigate the key factors driving the change of soil bacterial community structure. The results showed that the growth of artificial vegetation and natural vegetation significantly increased the richness and diversity of the soil bacterial community, but no significant difference was observed. Metagenomic analysis showed that the same dominant bacterial phyla existed in all soils, but the proportions were different. Actinobacteriota, Proteobacteria, and Chloroflexi were the absolute dominant bacterial phyla, accounting for 65.12%-78.68% of the total bacteria. Principal co-ordinates analysis showed significant differences in soil bacterial community structure in the planted forest but similarities in the natural forest. The metabolic pathways of soil bacteria in different vegetation communities were similar. Soil organic carbon (SOC), available phosphorus (AP), and pH were important abiotic factors affecting the functional structure of bacteria. The findings are helpful for furthering the understanding of plant-soil interaction in ecologically fragile deserts.
Key words: arid region      oasis-desert ecotone      vegetation type      soil bacterial structure      metabolic function     

荒漠-绿洲过渡带植被作为西北干旱区主要生态屏障,对抑制荒漠化进程起积极作用. 生态保育,一是最大程度保护天然植被,二是在进行人工固沙植被建设时进行不同物种多样性配置. 天然植被与人工植被融合配置对维持植被系统长期稳定至关重要. 2000年以来,临泽绿洲边缘进行人工固沙植被建设时,在流动沙地配置了梭梭(Haloxylon ammodendron Bunge,Ha)和花棒(Hedysarum scoparium Fisch,Hs),形成单一的Ha和Hs群落;并保存生长较好的天然植被沙拐枣(Calligonum mongolicum Turcz,Cm)和泡泡刺群落(Nitraria sphaerocarpa Maxim,Ns),在沙拐枣密度较低区域补充梭梭以增强防护效应,形成梭梭-沙拐枣混合群落(Ha-Cm). 近年来,由于水资源匮乏和生态平衡受人为干扰,导致植被退化成为主要的生态问题. 针对荒漠-绿洲过渡带植被,较多研究集中于植被生态与地下水文过程互馈机制[12]、土壤养分空间分布特征[34]和土壤线虫演变[5]等方面. 然而,针对干旱区荒漠-绿洲过渡带不同植被生长过程中土壤细菌群落结构功能特性还需深入研究.

土壤微生物在有机质降解和腐殖质形成及土壤结构改善方面发挥重要作用[67],并通过调控土壤养分有效性影响植物生长[89]. 细菌是土壤微生物中最活跃的部分,其结构和多样性是土壤生态功能的关键指标,代谢功能是土壤生态过程的主控因素[1011]. 不同植被类型显著影响土壤性状和细菌群落组成及多样性[12~14]. 人工杨树林土壤有机质和TN高于天然油蒿和人工沙柳[15],黄土高原中天然植被土壤碳储量和细菌多样性显著高于人工林[16]. 也有研究表明植被不仅影响土壤细菌群落多样性,对其功能组成也有重要作用[17]. 然而,针对干旱区荒漠绿洲过渡带不同植被群落土壤细菌代谢功能研究甚少. 探究荒漠绿洲过渡带不同植被土壤细菌群落结构和代谢功能及其影响因素,是深入理解干旱区植被与土壤微生物相互作用及植被适应干旱环境机制的重要方面,也是评价植被土壤系统恢复的重要内容.

基于此,本研究以荒漠-绿洲过渡带人工林(Ha,Hs)和天然林(Cm,Ns)及混合林(Ha-Cm)为研究对象,取表层(0~10 cm)土样探究不同荒漠植被对土壤性状、细菌群落结构、多样性和潜在代谢功能的影响,分析驱动土壤细菌群落结构变化的关键因子. 本研究通过揭示荒漠生态系统中不同植被类型土壤细菌结构及其生态功能,以期为干旱荒漠生态脆弱区植被重建的物种配置和管理提供科学理论依据.

1 材料与方法 1.1 研究区概况

研究区位于河西走廊中段临泽平川荒漠-绿洲过渡带(39°09′~39°19′N,100°02′~100°21′E,海拔1 350~1 393 m). 本区域为典型温带荒漠气候,冬季寒冷,夏季干燥炎热. 年均气温7.6℃,降雨量117 mm,蒸发量2 390 mm. 风沙活动集中在3~5月,年均风速3.2 m·s-1,地下水位3~8 m[1819]. 土壤为风沙土,结构松散,易受风蚀[20]. 主要天然植被有Ns和Cm,人工植被有Ha和Hs. 一年生草本植物包括碱蓬(Suaeda przewalskii)、白茎盐生草(Halogeton arachnoideus)、雾冰藜(Bassia dasyphylla)、沙蓬(Agriophyllum squarrosum)和画眉草(Eragrostis pilosa).

1.2 调查取样

选择流动沙地(对照,Ms)、人工植被Ha和Hs、天然植被Cm和Ns及Ha-Cm混合群落作为6个处理. 每个处理设3个样方(20 m×20 m),共18个,间距大于100 m. 每个样方中选择5棵灌木,调查其生长状况. 每个样地设5个(1 m×1 m)草本样方,共90个,间距大于5 m,调查草本植物生长状况. 土壤取样:每棵灌木下随机选两个取样点,去除凋落物,取0~10 cm土样,将每个样方中10个(5×2)样品混合,得复合样. 用75%酒精对铁铲灭菌,保证土壤微生物样品采集在无菌条件进行. 样品运回实验室,部分鲜土转入-80℃冰箱,用于微生物分析,部分土样风干后用于养分分析.

1.3 土样理化性质分析

碱扩散法测定碱解氮(AN),碳酸氢钠浸提-钼锑抗比色法测定速效磷(AP),乙酸铵浸提-火焰光度法测定速效钾(AK),外加热-重铬酸钾法测定土壤有机碳(SOC),H2SO4-H2O2消煮-钼锑抗比色法测定总磷(TP). 元素分析仪(Vario Macro Cube elementar,德国)测定总氮(TN)和总碳(TC). Multiline F/SET-3(WTW,德国)在土水比分别为1∶1和1∶5下测定土壤pH和EC[21].

1.4 扩增子测序

取0.5 g鲜土,Fast DNA®SPIN试剂盒提取土样总DNA,NanoDrop2000紫外可见分光光度计检测DNA浓度. 引物338F(5'-ACTCCTACGGGAGGCAGCAG-3')和806R(5'-GGACTACHVGGGTWTCTAAT-3')对16S rRNA基因V3-V4可变区进行PCR扩增. 采用NEXTFLEX® Rapid DNA-Seq Kit建库,MiSeq PE300平台进行高通量测序. FASTP软件对原始16S rRNA基因测序数据质控,FLASH软件拼接,UPARSE软件在97%相似度水平下进行OTU聚类. 相同条形码序列分类至同一样本,UCHIME算法识别并剔除嵌合体,RDP分类器对每条序列进行物种分类注释,比对SILVA 16S rRNA数据库,设置比对阈值为70%.

1.5 数据分析

OTUs分类水平按照样本最少序列数进行均一化. 采用SPSS进行单因素方差分析(ANOVA)和最小显著性差异(LSD)多重比较,对不同植被群落土壤理化性质和细菌群落α多样性进行检测,在P < 0.05水平判断显著差异. 热图在细菌门和属水平展示优势群落组成. 主坐标分析(PCoA)细菌属水平下不同植被群落间土壤细菌结构差异. 冗余分析(RDA)在细菌纲水平检测土壤理化性质对细菌群落结构的影响. 使用R语言工具统计和作图.

2 结果与分析 2.1 不同植被形态及草本植物特征

不同植被特征差异显著(P < 0.01,表 1). 天然植被Ns和Cm株高、冠幅面积、死亡率和枯枝率差异显著,人工植被Ha和Hs基茎、死亡率和枯枝率差异显著. Ns株高最低,冠幅面积最大,无死亡;Ha株高、基茎、死亡率和枯枝率最高;Hs枯枝率最低. Ms以沙蓬为主,Ha和Cm出现耐盐雾冰藜和白茎盐生草,Hs、Ns和Ha-Cm群落出现画眉草(表 2).

表 1 不同植被群落生长特征1) Table 1 Growth characteristics of different vegetation communities

表 2 不同植被群落草本植物特征1) Table 2 Characteristics of herbaceous plants of different vegetation communities

2.2 不同植被群落土壤理化性质

不同植被间土壤理化性质差异显著(P < 0.05,表 3). Ha人工林和Ha-Cm混合林土壤pH显著高于其它植被群落,Ns和Cm天然林土壤pH显著低于Ms. Ha土壤EC显著高于Ms和Hs,但与其它植被群落无显著差异. 除AN和AK,SOC、TC、TN、TP和AP在Ha、Hs、Ns和Cm间均无显著差异,但均显著高于Ms. Ha-Cm土壤养分含量低于Ha和Cm.

表 3 不同植被群落土壤理化性质1) Table 3 Characteristics of soil physicochemical properties in different vegetation communities

2.3 不同植被群落土壤细菌群落组成

细菌门水平相对丰度 > 1%有11个:放线菌门(Actinobacteriota)、变形菌门(Proteobacteria)、绿弯菌门(Chloroflexi)、拟杆菌门(Bacteroidota)、浮霉菌门(Planctomycetota)和髌骨菌门(Patescibacteria)相对丰度在不同植被间差异显著[P < 0.05,图 1(a)]. 放线菌门、变形菌门和绿弯菌门是绝对优势菌门,占总细菌65.12%~78.68%.

图 1 细菌群落在门水平和属水平上相对丰度 Fig. 1 Relative abundance of bacterial communities at phylum level and genus level

根据物种相对丰度和相似性,不同植被前20属形成4个Bray-Curtis聚类[图 1(b)]. Ns和Cm天然林土壤细菌属分布趋于相似,Ha与Hs人工林土壤细菌属分布不同,Ms细菌属分布与其它植被群落不同. 分类属分为两个主要分支:RubellimicrobiumGeodermatophilusKocuriaBlastococcus. 除Ha人工林,在其它植被群落观察到较高丰度的细菌属群:MicrovirgaBlastococcus.

2.4 不同植被群落土壤细菌群落多样性

不同植被生长显著影响土壤细菌群落丰富度和多样性(P < 0.001,表 4). 各植被中细菌Shannon指数均显著高于Ms,Simpson指数均显著低于Ms,植被间无显著差异. 土壤细菌Chao指数在各植被群落中显著高于Ms,而在Ha中显著低于Hs、Ns、Cm和Ha-Cm. 样本细菌覆盖度指数高于97%,表明所获细菌序列很好地代表了细菌群落.

表 4 不同植被群落土壤细菌群落丰富度和多样性1) Table 4 Richness and diversity of soil bacterial community under different vegetation communities

PCoA显示不同植被土壤细菌结构差异显著[P < 0.01,图 2(a)]. 同组内细菌群落聚集,不同植被群落则分离;Ms和Ha细菌群落与其它植被明显分离,人工林Ha和Hs细菌群落明显分离,而天然林Ns和Cm几乎分布同一象限,前两轴共解释细菌结构变异量的67.25%. β多样性组间差异验证了组内样品差异离散程度及不同组间的距离差异[图 2(b)].

图 2 细菌群落结构主坐标和β 多样性组间差异分析 Fig. 2 Principal coordinates analysis and β diversity difference analysis of bacterial community structure

2.5 不同植被群落土壤细菌与理化性质关系

RDA前4轴对细菌群落结构变异累计解释率68.62%,前两轴分别解释28.90%和26.60%(表 5图 3). 土壤理化性质对细菌结构总变异解释率78.40%,SOC、pH和AP显著影响细菌结构(P < 0.05,表 6),SOC对细菌结构变异解释最大,其次是pH和AP. SOC、pH和AP对细菌结构变化解释的相对贡献分别为28.6%、27.9%和11.7%.

表 5 土壤细菌群落结构与土壤因子的RDA排序综述1) Table 5 RDA ordination summary for bacterial community structure and soil factors

-1、-2和-3表示不同植被群落下的3个平行样 图 3 土壤理化性质与细菌群落结构的冗余分析 Fig. 3 Redundancy analysis of bacterial community structure in relation to soil physicochemical properties

表 6 环境因子所解释总变异和解释变异比例 Table 6 Proportions of total variation and total explained variation explained by individual environmental factors

2.6 不同植被群落土壤细菌代谢功能

细菌代谢途径和功能潜力预测显示代谢功能相对丰度较高,其次是环境信息处理、遗传信息处理和未分类功能,其余丰度较低(图 4). 二级代谢水平上能量(5.6%~5.8%)、碳水化合物(10.7%~11.1%)和氨基酸代谢(11.4%~11.5%)是主要部分,但相对丰度在各植被间差异较小(图 5). 三级代谢水平上与酶、氨基酸、碳水化合物、能量和核苷酸代谢相关的功能,如肽酶、精氨酸和脯氨酸、丁酸、氧化磷酸化和嘌呤代谢是主要功能. 与酶、能量和核苷酸代谢相关的功能特征除氮和嘌呤代谢,其余在Ha中更普遍(图 6).

图 4 功能基因KEGG统计 Fig. 4 KEGG statistics of functional genes

1. 外源生物降解与代谢,2. 核苷酸代谢,3. 萜类和聚酮化合物代谢,4. 其他氨基酸代谢,5. 辅因子和维生素代谢,6. 脂质代谢,7. 多糖生物合成与代谢,8. 酶家族,9. 能量代谢,10. 碳水化合物代谢,11. 其他次生代谢物的生物合成,12. 氨基酸代谢 图 5 根据KEGG数据库分析二级代谢功能性状及分类 Fig. 5 Second-level metabolic functional traits and categories according to the KEGG pathway database

1. 精氨酸和脯氨酸代谢,2. 甘氨酸、丝氨酸和苏氨酸代谢,3. 丙氨酸、天冬氨酸和谷氨酸代谢,4. 丁酸代谢,5. 丙酸代谢,6. 丙酮酸代谢,7. 氨基糖和核苷酸糖代谢,8. 柠檬酸循环(TCA循环),9. 糖酵解/糖异生,10. 氮代谢,11. 原核生物中的碳固定途径,12. 甲烷代谢,13. 氧化磷酸化,14. 嘧啶代谢,15. 嘌呤代谢,16. 氨基酸相关酶,17. 肽酶 图 6 根据KEGG数据库分析三级代谢功能性状及分类 Fig. 6 Third-level metabolic functional traits and categories according to the KEGG pathway database

3 讨论

在天然林(Ns、Cm)和人工林(Ha、Hs)土壤中发现丰度显著差异的相同优势菌门. 土壤细菌群落主要以Actinobacteriota、Proteobacteria和Chloroflexi为主,这与沙特沙漠和科尔沁沙地的观察结果相似[2223],Actinobacteriota和Proteobacteria高比例表明对干旱环境的普遍适应,Actinobacteriota属革兰氏阳性菌,有助于分解复杂有机化合物[2425]. Wan等[26]发现在营养水平较高的天然林中土壤Proteobacteria丰度更高,但本研究发现营养水平较低的流动沙地中Proteobacteria丰度高于其它植被群落,表明Proteobacteria在土壤有机质较低的土壤中具有较强的生存竞争力.

有研究表明天然林土壤微生物多样性显著高于人工林[1627],也有研究发现天然林土壤细菌群落多样性显著低于人工林[26]. 然而,本研究发现天然林(Ns、Cm)和人工林(Ha、Hs)土壤细菌群落多样性和丰富度并无显著差异,这可能是由于干旱区荒漠绿洲过渡带天然植被恢复过程中物种单一,无法为土壤细菌群落提供更丰富的有机质[28]. 本研究结果表明与流动沙地相比,天然植被和人工植被的生长显著提高了土壤细菌群落多样性和丰富度. 植被可通过多种机制影响土壤微生物群落结构[29],植被作为生产者,为土壤微生物群落提供有机碳和氮源[30],土壤微生物群落构成大部分分解系统. 植物种类可能通过决定返回土壤凋落物基质质量和数量以及通过改变土壤理化环境对微生物群落组成和功能产生重要影响[31]. 本研究发现,天然植被(Ns、Cm)中土壤细菌群落结构差异较小,可能是由于泡泡刺和沙拐枣的生长对土壤的反馈作用相似;而人工植被(Ha、Hs)土壤细菌群落结构差异较大,主要是由于梭梭生长导致土壤盐分大量积累并驱动土壤细菌群落变化[8]. 因此,植被群落能够通过改变土壤养分和盐分状况间接影响细菌群落分布.

植被通过凋落物和根系分泌物输入调节生境小气候并影响土壤理化性质,土壤理化性质显著影响微生物群落结构. 本研究发现,土壤SOC、pH和AP是影响细菌群落结构的主要非生物因素. Andrew等[32]在索诺兰沙漠中发现土壤碳含量与微生物多样性显著相关,也有研究表明土壤SOC含量是中国北方荒漠化草地生态系统微生物群落组成和结构的关键驱动因素[3334],支持了本研究结果. 各种土壤研究中记录了pH是决定土壤细菌群落组成和多样性的主要因素. 例如,pH已被证明会影响中国东北黑土[35]、酸性带状土壤[36]和碱性沉积物[37]中的细菌群落. 同样,大量研究表明pH也是黄土高原土壤细菌群落组成的良好预测指标[1638]. 本研究结果显示,pH是另一个显著影响干旱区荒漠生态系统土壤细菌群落结构的因素,这可能与细菌群落最佳生长pH范围较窄有关[36],由于本研究土壤呈碱性,高pH通过限制土壤养分有效性在一定程度上抑制细菌群落多样性和丰富度[39]. 综上所述,pH是土壤细菌群落分布的普遍影响因子. Wan等[26]研究表明土壤磷是细菌群落结构的重要影响因子,与本研究结果相似.

本研究结果表明,在不同植被群落中土壤细菌代谢途径总体模式相似. 能量、碳水化合物和氨基酸代谢是重要的代谢途径,腾格里沙漠研究支持了本研究结果[40]. 氨基酸是蛋白质的组成部分,被认为是次级代谢物的前体[41]. 蛋白质不仅为微生物提供营养,也是氨基酸代谢表达的基础. 在三级代谢水平上,肽酶、精氨酸和脯氨酸、丁酸、氧化磷酸化和嘌呤代谢比例较高,表明细菌群落在土壤养分较低荒漠环境中的生存策略. 本研究发现与酶、能量和核苷酸代谢相关的功能特征除氮和嘌呤代谢,其余在梭梭人工林中更为普遍,表明在梭梭人工林中表达更为活跃. 这可能是由于梭梭人工林特定的生态环境和其对根际微生物的影响,为细菌提供了适宜的生长和活动环境,从而促进了细菌功能的表达[42].

4 结论

人工植被和天然植被生长显著改变了土壤细菌群落结构,天然植被土壤细菌群落结构相似,人工植被土壤细菌群落结构差异显著,并显著提高土壤细菌群落多样性和丰富度,但不同植被群落间无显著差异. 土壤SOC、pH和AP对细菌功能结构变化有显著贡献,并解释细菌群落变化的53.4%. 二级代谢水平上各代谢功能丰度在植被群落间变化较小,说明不同植被生长对土壤细菌群落代谢无显著影响. 三级代谢水平上,与酶、能量和核苷酸代谢相关的功能特征除氮和嘌呤代谢外,其余在梭梭人工林中表达更活跃. 本研究有助于深入认识荒漠-绿洲过渡带天然植被和人工植被与土壤微生物互作及生物学过程.

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