2022, Vol. 43
2. 河南农业大学农学院, 省部共建小麦玉米作物学国家重点实验室, 郑州 450002
, YUE Jun-qin1 , YAN Ya-qian2 , ZHANG De-qi1 , YANG Cheng1 , ZHANG Su-yu1 , LI Xiang-dong1
, SHAO Yun-hui1 , FANG Bao-ting1 , WANG Han-fang1 , QIN Feng1
2. Co-construction State Key Laboratory of Wheat and Maize Crop Science, College of Agronomy, Henan Agricultural University, Zhengzhou 450002, China
土壤微生物群落是生态系统生物化学循环过程的关键参与者[1], 是植物生产力的重要驱动者[2].在农业生态系统中, 土壤微生物群落多样性和活性会受到作物种植的影响[3, 4], 同时, 微生物活动直接或间接影响作物生产过程的植物营养、生长调节和生物防治等关键环节[5, 6], 作物-土壤微生物相互作用与反馈对土壤健康和作物生产至关重要[7].真菌是土壤微生物群落的主要成员之一, 在作物生产上可分为有害真菌和有益真菌, 有害真菌可侵染作物引起植物病害, 有益真菌能够抑制病原菌、促进植物生长和分解植物残体等[8].充分了解农业管理实践对土壤真菌群落的影响, 对发展生态可持续农业生产具有重要意义.
随着集约化种植强度的增加, 现代农业生产的一个突出特点是种植制度的简化[3, 4], 作物多样性的降低可能导致农业生态系统功能和服务减少.有研究表明, 在连作条件下, 玉米的生物量和产量会由于土壤微生物的负反馈而降低[9]; 连续单一栽培花生会显著增加土壤病原真菌的相对丰度, 减少潜在有益真菌, 造成土壤真菌群落生态失衡和花生产量降低[10]; 连作大豆减弱了根际土壤真菌群落网络结构, 加强了潜在病原真菌之间的正向互作, 导致土壤功能退化和大豆产量下降[11, 12].作物种植多样化被认为是提高农业生态系统生物多样性[13]和增加气候变化条件下粮食生产稳定性[14, 15]的有力措施之一.通过轮作增加时间上的作物多样性可恢复地上-地下的正相互作用[16], 充分利用水分和养分等自然资源, 最大限度地利用生态位和土壤生物多样性[17], 具有增强土壤生态系统功能的潜力, 对维持农业系统中土壤服务功能至关重要[18, 19].有研究表明, 作物轮作显著改变了土壤细菌和真菌群落多样性、组成和网络[20]; 随着轮作作物从1种增加到5种, 土壤团聚体、有机碳和全氮增加[16]; 与简单轮作相比, 更多样化的轮作增加了土壤微生物群落代谢多样性和活性[4, 16], 增加了作物生物量和产量[21].通过Meta分析, 与连作相比, 轮作作物产量平均增加20%, 且豆科作物的轮作效益更高[22]; 调查结果表明, 与连作小麦相比, 小麦与豆科作物轮作具有明显的经济优势[23].
受光温水资源的影响, 不同作物种类和轮作顺序的选择具有地域性.在华北平原, 冬小麦-夏玉米、冬小麦-夏花生和冬小麦-夏大豆等一年两熟制是主要种植制度, 其中, 以连续冬小麦-夏玉米周年轮作为主导.有研究表明, 与冬小麦-夏玉米一年两熟制相比, 冬小麦-夏花生种植模式具有较高的净收益和较低的单位净产值碳排放[24], 花生茬口的土壤含水量显著高于玉米茬口, 可提高后茬冬小麦的净光合速率, 显著提高小麦籽粒产量[25]; 与玉米茬口相比, 大豆茬口和玉米大豆间作茬口显著增加后茬小麦的穗数和穗粒数, 增加小麦籽粒产量, 提高氮肥利用率[26]; 与玉米相比, 花生或大豆作为前茬作物可增加土壤速效养分含量, 增加小麦产量9.57% ~10.32%[27]; 与玉米-小麦种植体系相比, 花生-小麦和大豆-小麦具有更高的当量产量和收益, 具有较高的土地利用效率和生产效率[28].鉴于多样化轮作的诸多优势, 在华北平原有必要探索发展冬小麦与不同作物(夏玉米、夏花生和夏大豆)多样化轮作的种植模式, 不同作物轮作下土壤真菌群落的差异及其影响因子值得深入地研究.基于此, 本研究以常年冬小麦-夏玉米周年轮作为基础, 加入夏花生或夏大豆替代夏玉米进行不同周期轮作, 利用多年定位试验, 分析了小麦与不同作物多样化轮作对土壤真菌群落的影响, 以期为生态可持续种植制度的构建和优化提供理论依据.
1 材料与方法 1.1 研究地点本研究地点位于河南现代农业研究开发基地(河南省新乡市平原新区, 35°00′ N, 113°41′ E).该区域累年年平均气温14.4℃, 累年月平均气温0℃(1月)至26.9℃(7月); 累年年平均降水量566.2 mm, 约三分之二的降水量集中于6~9月.土壤为黄河冲积物发育的砂壤质潮土, 其0~20 cm土壤中ω(有机碳)为4.29 g·kg-1, ω(全氮)0.31 g·kg-1, ω(全磷)0.87 g·kg-1, ω(全钾)19.65 g·kg-1, pH值8.52.研究基地处于华北平原, 该区域传统以冬小麦-夏玉米一年两熟为主要种植制度.
1.2 试验设置以常年冬小麦-夏玉米周年轮作为基础, 加入夏花生或夏大豆替代夏玉米进行不同周期轮作, 设置1个冬小麦-夏玉米处理(M)、3个冬小麦-夏花生(夏玉米)处理(PM1、PM2和PM3)和3个冬小麦-夏大豆(夏玉米)处理(SM1、SM2和SM3), 共计7个轮作处理, 作物种植顺序如表 1所示.田间试验处理始于2015年6月, 每个处理设3个重复, 共21个小区, 小区长宽6 m×5 m, 四周以深2 m的混凝土隔开.冬小麦10月播种, 次年6月初收获; 随后播种夏玉米、夏花生或夏大豆, 9月底收获.除轮作处理外, 各小区田间管理措施一致.
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表 1 不同轮作处理的作物种植顺序 Table 1 Cropping sequences of different rotations |
1.3 测定项目与方法 1.3.1 土壤样本采集与微生物总DNA提取
于2020年9月30日, 使用土钻(内径3 cm)采集作物收获后的行间土壤样品, 取样深度0~20 cm, 每个小区随机取5个样点混合作为该小区的土壤样本.冷藏箱带回实验室后, 除去石块和植物残体, 过2 mm筛混匀, 保存于-80℃.
称取0.5 g冷冻土壤, 使用FastDNA Spin Kit for Soil和FastPrep Instrument(MP Biomedicals, USA)提取土壤微生物基因组DNA, 采用NanoDrop 2000(Thermo Scientific, USA)进行DNA纯度和浓度检测, 1%琼脂糖凝胶电泳进行DNA完整性检测.
1.3.2 实时荧光定量PCR以土壤微生物基因组DNA为模板, 采用引物ITS3F(5′- GCATCGATGAAGAACGCAGC -3′)和ITS4R(5′- TCCTCCGCTTATTGATATGC -3′)[29, 30]进行实时荧光定量PCR(qPCR), 测定土壤真菌ITS序列拷贝数.qPCR反应中的DNA Polymerase、SYBR Green I和dNTPs等使用ChamQ SYBR Color qPCR Master Mix(Cat. No. Q411-02, 南京诺唯赞生物科技股份有限公司, 中国), qPCR仪使用Applied Biosystems 7300 Real-Time PCR System(Applied Biosystems, USA).qPCR反应体系包含: 10 μL 2× ChamQ SYBR Color qPCR Master Mix、0.8 μL Forward Primer(5 μmol·L-1)、0.8 μL Reverse Primer(5 μmol·L-1)、0.4 μL 50× ROX Reference Dye 1、2 μL Template DNA和6 μL ddH2 O.qPCR反应条件为: 95℃预变性3 min; 95℃变性5 s, 58℃退火30 s, 72℃延伸1 min, 40个循环.将已知浓度含有目的序列的质粒DNA进行10倍梯度稀释, 随样品同时进行qPCR, 制作标准曲线.每个样本和标准曲线各3个复孔, 根据标准曲线计算样本的真菌ITS序列拷贝数.
1.3.3 土壤真菌ITS序列扩增与高通量测序以土壤微生物基因组DNA为模板, 采用引物ITS3F(5′- GCATCGATGAAGAACGCAGC -3′)和ITS4R(5′- TCCTCCGCTTATTGATATGC -3′)[29, 30]进行真菌ITS序列的PCR扩增, PCR反应中的DNA Polymerase、Buffer和dNTPs等使用TransStart FastPfu DNA Polymerase(Cat. No. AP221-02, 北京全式金生物技术有限公司, 中国), PCR仪使用GeneAmp PCR System 9700(Applied Biosystems, USA). PCR反应体系包含: 4 μL 5×TransStart FastPfu Buffer、2 μL 2.5 mmol·L-1 dNTPs、0.8 μL Forward Primer(5 μmol·L-1)、0.8 μL Reverse Primer(5 μmol·L-1)、0.4 μL TransStart FastPfu DNA Polymerase、0.2 μL BSA、10 ng Template DNA和ddH2 O补充至20 μL. PCR反应条件为: 95℃预变性3 min; 95℃变性30 s, 55℃退火30 s, 72℃延伸45 s, 35个循环; 72℃最后延伸10 min.每个样本3个重复, PCR反应后将同一样本的产物混合, 2%琼脂糖凝胶电泳检测, 使用AxyPrep DNA Gel Extraction Kit(Cat. No. AP-GX-250, Axygen, USA)切胶回收目的DNA片段, Tris-HCl洗脱DNA, 2%琼脂糖电泳检测.使用QuantiFluor-ST Handheld Fluorometer(Promega, USA)采用PicoGreen荧光染料法进行DNA定量, 按相应体积比例混合, Illumina MiSeq测序平台进行PE300高通量测序.
1.3.4 数据统计分析Illumina MiSeq下机数据使用FLASH[31]对两端测序序列进行拼接(overlap≥10 bp), 采用Fastp对原始数据进行质量控制和数据过滤[32], 根据barcode区分样本数据, 得到优化数据.使用USEARCH[33]以97%相似性进行OTU聚类(UPARSE)[33, 34]和嵌合体检查去除(UCHIME)[35].使用RDP Classifier[36]对OTU进行分类注释, 采用UNITE[37]数据库.按最小样本序列数进行抽平, 以抽平后的有效数据进行后续微生物群落多样性和组成分析.
使用Mothur进行α多样性分析[38, 39]. β多样性分析采用基于Binary Jaccard距离算法的非度量多维尺度分析(non-metric multidimensional scaling, NMDS), 通过置换多元方差分析(permutational multivariate analysis of variance, PERMANOVA)和相似性分析(analysis of similarities, ANOSIM)评估不同处理对真菌群落结构的影响.采用Circos对不同处理群落组成数据进行可视化[40].采用线性判别分析工具LEfSe(linear discriminant analysis effect size)分析不同轮作茬口的差异物种[41], LDA阈值设置为3.5.采用FUNGuild对土壤真菌营养方式在OTU水平进行分类注释[42].
采用单因素方差分析(one-way ANOVA)比较不同处理间的土壤真菌ITS序列拷贝数和真菌群落α多样性指数, 多重比较采用LSD法(P＜0.05).采用Pearson相关性分析研究ITS序列拷贝数和真菌群落α多样性指数与土壤性质的相关关系; 通过Mantel test检验群落结构与土壤性质的相关关系.
2 结果与分析 2.1 不同作物轮作对土壤真菌群落丰度的影响采用实时荧光定量PCR(qPCR)测定不同轮作茬口土壤真菌ITS序列拷贝数的结果如图 1所示, 与连续冬小麦-夏玉米处理相比, 冬小麦-夏花生(夏玉米)PM2处理和冬小麦-夏大豆(夏玉米)SM2处理的土壤真菌ITS序列拷贝数显著降低(P＜0.05).冬小麦-夏花生(夏玉米)PM1、PM3处理和冬小麦-夏大豆(夏玉米)SM1、SM3处理的土壤真菌ITS序列拷贝数与对照相比差异未达显著水平(P＞0.05).
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误差线表示标准差, 不同字母表示差异达显著水平(P＜0.05) 图 1 不同轮作茬口的土壤真菌群落丰度 Fig. 1 Abundance of soil fungal community in different crop rotations |
Illumina MiSeq测序数据经过拼接质控后, 21个样本共得到1 400 274条优化序列, 每个样本33 961~74 991条, 平均序列长度312 bp.以97%相似性对非重复序列进行OTU聚类, 按最小样本序列数进行抽平, 每个样本30 765条有效序列, 共对应1 658个OTU.注释后这些OTU归属于432个属(Genus)、224个科(Family)、113个目(Order)、54个纲(Class)和17个门(Phylum).根据稀释曲线(图 2), 随着序列数量的增加, 各个样本的群落覆盖度和群落多样性(Shannon指数)均趋于平缓, 表明抽平后的序列数据量趋近饱和, 能够覆盖样本中真菌群落的绝大部分物种, 足够进行后续的真菌群落分析.
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图 2 基于群落覆盖度和Shannon指数的真菌群落稀释曲线 Fig. 2 Rarefaction curves of fungal community based Good's coverage and Shannon index |
土壤真菌群落α多样性分析结果表明, 与连续冬小麦-夏玉米处理相比, 轮作花生或大豆处理显著增加了土壤真菌群落丰富度(Chao1指数和ACE指数, P＜0.05, 表 2).冬小麦-夏花生(夏玉米)和冬小麦-夏大豆(夏玉米)处理的土壤真菌群落多样性(Shannon指数和InvSimpson指数)与对照相比有所增加, 其中SM1和SM2处理与对照相比差异达显著水平(P＜0.05).轮作花生或大豆的不同种植顺序处理间土壤真菌群落丰富度和多样性差异未达显著水平(P＞0.05).
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表 2 不同轮作茬口的土壤真菌群落α多样性1) Table 2 The α diversity of soil fungal community in different crop rotations |
2.4 不同作物轮作对土壤真菌群落结构的影响
土壤真菌群落β多样性非度量多维尺度分析(NMDS)结果如图 3所示, 不同作物轮作处理分别聚集在一起, 在第一坐标轴或第二坐标轴具有明显分离, 而同种作物的不同种植顺序轮作处理之间没有明显分离, 表明不同作物轮作处理之间土壤真菌群落结构存在明显差异.置换多元方差分析(PERMANOVA)和相似性分析(ANOSIM)结果均表明, 不同轮作作物对土壤真菌群落结构的影响达显著水平(PERMANOVA: r2=0.350, P=0.001; ANOSIM: r=0.478, P=0.001).
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图 3 不同轮作茬口土壤真菌群落结构的非度量多维尺度分析 Fig. 3 Non-metric multidimensional scaling (NMDS) analysis of soil fungal community structure in different crop rotations |
在门水平, 不同作物轮作处理的土壤真菌群落均以Ascomycota为优势类群, 相对丰度高达73.67% ~85.48%(图 4).其次为Mucoromycota(3.91% ~6.97%)、Zoopagomycota(1.20% ~6.84%)、Basidiomycota(0.61% ~5.56%)和Mortierellomycota(0.59% ~2.99%).unclassified Fungi占真菌群落的2.57% ~10.22%.
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1. M, 2. PM1, 3. PM2, 4. PM3, 5. SM1, 6. SM2, 7. SM3, 8. Ascomycota, 9. unclassified Fungi, 10. Mucoromycota, 11. Zoopagomycota, 12. Basidiomycota, 13. Mortierellomycota, 14. others 图 4 不同轮作茬口的门水平土壤真菌群落组成 Fig. 4 Soil fungal community compositions in different crop rotations at phylum level |
在纲水平, 不同作物轮作处理的土壤真菌群落均以Sordariomycetes和Eurotiomycetes为优势类群, 相对丰度分别为30.53% ~48.19%和11.12% ~31.19%(图 5).另外, 还鉴定出相对丰度大于1%的真菌纲10个, 其中相对丰度在各处理土壤中均大于1%的类群有: Dothideomycetes(7.58% ~14.35%)、Mucoromycetes(3.91% ~6.97%)和unclassified Zoopagomycota(1.20% ~6.84%).
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1. M, 2. PM1, 3. PM2, 4. PM3, 5. SM1, 6. SM2, 7. SM3, 8. Sordariomycetes, 9. Eurotiomycetes, 10. Dothideomycetes, 11. unclassified Fungi, 12. Mucoromycetes, 13. unclassified Zoopagomycota, 14. Agaricomycetes, 15. Leotiomycetes, 16. Pezizomycetes, 17. unclassified Ascomycota, 18. ohers, 19. Mortierellomycetes, 20. Pezizomycotina cls Incertae sedis, 21. Saccharomycetes 图 5 不同轮作茬口的纲水平土壤真菌群落组成 Fig. 5 Soil fungal community compositions in different crop rotations at class level |
以LDA 3.5为阈值, 对不同作物轮作处理土壤真菌群落组成进行线性判别分析, 结果如图 6所示, 共识别出21个差异类群.在属水平, Striaticonidium、Preussia、Meyerozyma和Chrysosporium在连续冬小麦-夏玉米处理中显著富集; Neocosmospora、Trichocladium、Plectosphaerella、Podospora、Gibellulopsis和unclassified Bionectriaceae在冬小麦-夏花生(夏玉米)轮作处理中显著富集; Penicillium和Zopfiella在冬小麦-夏大豆(夏玉米)轮作处理中显著富集.
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a. f_Sporormiaceae, b. g_Preussia, c. g_Trichocladium, d. g_Zopfiella, e. g_Podospora, f. f_Bionectriaceae, g. g_unclassified_f_Bionectriaceae, h. f_Stachybotryaceae, i. g_Striaticonidium, j. f_Nectriaceae, k. g_Neocosmospora, l: o_Glomerellales, m. f_Plectosphaerellaceae, n. g_Plectosphaerella, o. g_Gibellulopsis, p. o_Onygenales, q. f_Onygenales_fam_Incertae_sedis, r. g_Chrysosporium, s. g_Penicillium, t. f_Debaryomycetaceae, u. g_Meyerozyma 图 6 不同轮作茬口的土壤真菌群落差异物种分析 Fig. 6 Differential taxa analysis of soil fungal communities in different crop rotations |
通过FUNGuild注释分析, 不同轮作茬口的土壤真菌营养方式划分为病理营养型(pathotroph)、共生营养型(symbiotroph)和腐生营养型(saprotroph), 以及病理-共生营养型(pathotroph-symbiotroph)、病理-腐生营养型(pathotroph-saprotroph)、腐生-共生营养型(saprotroph-symbiotroph)和病理-腐生-共生营养型(pathotroph-saprotroph-symbiotroph)等兼性营养方式(图 7).腐生营养型真菌的相对丰度较高, 占土壤真菌群落的36.80% ~59.33%.与连续冬小麦-夏玉米处理相比, 轮作花生或大豆处理增加了病理营养型、病理-共生营养型和腐生-共生营养型土壤真菌的相对丰度, 而腐生营养型土壤真菌相对丰度有所降低.
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图 7 不同轮作茬口的土壤真菌营养方式相对丰度 Fig. 7 Relative abundance of soil fungal trophic mode in different crop rotations |
Pearson相关性分析结果显示, 不同作物轮作处理的土壤真菌群落丰度和多样性InvSimpson指数与土壤有机碳和速效氮磷钾含量相关性未达显著水平(P＞0.05, 表 3).土壤真菌群落丰富度与土壤有机碳、无机氮和速效钾含量显著负相关, 而与土壤有效磷含量显著正相关(P＜0.05).土壤真菌群落多样性Shannon指数与土壤无机氮含量显著负相关, 而与土壤有效磷含量显著正相关(P＜0.05).
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表 3 土壤真菌群落丰度和α多样性指数与土壤有机碳和速效养分的Pearson相关系数1) Table 3 Pearson correlation coefficients between abundance, α diversity indices of soil fungal community, soil organic carbon, and available nutrients |
Mantel test分析结果显示, 不同作物轮作处理的土壤真菌群落结构与土壤有机碳、无机氮、有效磷和速效钾含量显著相关(P＜0.05, 表 4).
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表 4 土壤真菌群落结构与土壤有机碳和速效养分的Mantel test相关性 Table 4 Mantel test correlations between soil fungal community structure, soil organic carbon, and available nutrients |
3 讨论
群落丰富度代表生态系统中的物种数量, 是群落α多样性基本的衡量指标, 而群落多样性是群落丰富度和均匀度的综合反映.为排除不同指标计算方法的干扰, 本研究同时采用Chao1指数和ACE指数表征群落丰富度, 采用Shannon指数和InvSimpson指数表征群落多样性, 不同指标计算方法的结果一致.与连续冬小麦-夏玉米处理相比, 轮作花生或大豆处理增加了土壤真菌群落丰富度和多样性(表 2), 这与前人在其他作物上的研究结果相一致.有研究表明, 随马铃薯连作时间的延长, 土壤真菌群落丰富度和多样性显著降低[43]; 与谷子连作相比, 谷子轮作大豆、籽粒苋或藜麦有利于提高土壤真菌群落丰富度和多样性[44]; 与玉米连作相比, 玉米-大豆轮作提高了土壤真菌群落Shannon指数[45].Venter等[3]的研究通过Meta分析表明, 地上和地下生物多样性之间具有相关性, 轮作作物多样性的提高可增加土壤微生物群落丰富度(15.11%, n=26)和多样性(3.36%, n=43), 且轮作时间越长, 对微生物群落丰富度的正效应越强.植物通过根系分泌物和植物残体为土壤微生物提供营养[46], 通过多样化轮作增加时间上的作物多样性, 能够在一定程度上增加土壤有机输入的数量、质量和化学多样性[47], 更多样化的碳源可支持多样化微生物类群的繁殖和生长[3], 因此作物多样化对土壤真菌多样性的增加效应可能归因于多样化的根系分泌物和植物残体.由于更广泛的微生物能够同时支持多种生态系统功能[48], 土壤微生物多样性被认为是维持土壤质量和健康的关键[49], 土壤真菌多样性的增加可能会对农业生态系统功能和可持续性产生有益影响[50].同时, 轮作对土壤真菌群落多样性的影响因作物而不尽相同.有研究显示, 与黄瓜单作相比, 番茄-芹菜-黄瓜-大白菜轮作可降低土壤真菌群落丰富度和多样性[51]; 与连作处理相比, 轮作大豆处理显著提高了土壤真菌群落的Shannon指数, 而轮作小麦、玉米处理与连作处理相比差异未达显著水平[52].不同作物轮作对土壤真菌群落多样性影响差异的原因还需进一步深入研究.
本研究中, 在连续冬小麦-夏玉米周年轮作的基础上, 加入夏花生或夏大豆替代夏玉米进行不同周期轮作, 显著改变了土壤真菌群落结构(图 3).作为重要的营养物质和信号化学物质, 植物可通过根系分泌物改变土壤微生物群落[17].不同植物的根系分泌物存在差异, 因此每种植物会选择特定的微生物类群[46].首先, 多样化轮作为地下生物提供了多样化的碳源, 不同的碳源刺激了特定微生物类群的繁殖和生长, 进而影响土壤微生物群落结构.其次, 某些作物的根系分泌物中含有独特的代谢成分, 对特定类群的微生物存在抑制或刺激作用, 例如, 花生根系分泌物中的酚酸[53]、大豆根系分泌物中的异黄酮[54, 55]和小麦玉米根系分泌物中的苯并唑嗪酮[56, 57]等均可以促进土壤微生物群落的变化.另一方面, 在秸秆全量还田条件下, 不同作物轮作处理土壤具有不同种类的秸秆输入, 不同生物化学性质的有机物质能够刺激特定的真菌分解者[45], 例如, 玉米秸秆有利于生长相对缓慢的真菌分解者, 而大豆秸秆促进生长快速的真菌分解者[58].因此, 多样化轮作处理在一定时间内增加了作物秸秆的种类, 利于更广泛的真菌物种存在[45].
本研究中, 华北平原砂壤质潮土中土壤真菌群落以Ascomycota为优势菌门, 这与前人在华北平原的研究结果一致[59, 60].另外, 在宁夏中部干旱带[44]、黄土高原半干旱区[61]、长江中下游平原水旱轮作区[62]和台州湾滨海滩涂地[63], 土壤真菌群落在纲水平的优势类群有所差别, 而门水平均以Ascomycota为优势类群.通过LEfSe分析结果显示, Neocosmospora、Plectosphaerella和Gibellulopsis等在冬小麦-夏花生(夏玉米)轮作处理中显著富集(图 6).有研究表明, Neocosmospora可侵染花生[64, 65]、大豆[66]、柑橘[67]和火龙果[68]等作物引起茎基腐病; Plectosphaerella可引发卷心菜[69]和莴苣[70]等园艺作物的根茎腐病[71]; Gibellulopsis可引发甜菜萎蔫病[72]和茼蒿苗腐病[73]等真菌性病害.由此, 在连续冬小麦-夏玉米轮作中加入夏花生进行不同周期轮作, 可增加病原真菌的相对丰度, 在生产上要更加注重病害的防治.另外, 在冬小麦-夏大豆(夏玉米)轮作处理中显著富集了Penicillium和Zopfiella(图 6).有研究表明, Penicillium是一种植物促生菌, 具有溶磷活性[74], 还可以通过激活多种防御信号诱导作物对病原菌的抗性[75]; 从猕猴桃植株中分离得到的内生真菌Zopfiella能够抑制引起猕猴桃溃疡病病原菌Pseudomonas syringae的生长[76].以上分析表明, 在连续冬小麦-夏玉米轮作中加入夏大豆进行不同周期轮作, 可增加潜在有益真菌的相对丰度, 具有一定的优势.
有研究表明, 前茬作物的种植对后茬作物根际微生物群落具有显著影响[77, 78], Meta分析结果显示, 轮作对后续作物产量的遗留效益可持续2~3 a[22].由此, 不同轮作茬口对土壤真菌群落的影响差异在下茬冬小麦生长期内的遗留效应值得进一步深入研究.
4 结论(1) 在华北平原常年冬小麦-夏玉米周年轮作的基础上, 加入夏花生或夏大豆替代夏玉米进行不同周期轮作, 可增加土壤真菌群落丰富度和多样性, 显著影响土壤真菌群落结构.
(2) 不同轮作茬口土壤真菌群落组成存在差异显著的类群, Neocosmospora、Plectosphaerella和Gibellulopsis等潜在病原菌在冬小麦-夏花生(夏玉米)轮作处理中显著富集, 而Penicillium和Zopfiella等潜在有益真菌在冬小麦-夏大豆(夏玉米)轮作处理中显著富集.
(3) 与连续冬小麦-夏玉米周年轮作相比, 轮作花生或大豆可增加病理营养型、病理-共生营养型和腐生-共生营养型土壤真菌的相对丰度.
(4) 不同作物轮作处理的土壤真菌群落丰富度和群落结构与土壤有机碳、无机氮、有效磷和速效钾含量显著相关.
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