烟草青枯病危害对烟田中小型土壤动物群落的影响

为了掌握重庆植烟区烟草青枯病危害对烟田中小型土壤动物群落结构及多样性特征的影响,分别于2015年3月烟田休耕期、6月烟株旺长期和9月烟叶成熟期在重庆市彭水县进行了定点实验,调查了烟草青枯病连续成灾烟田及其对照无青枯病危害烟田中的中小型土壤动物群落。共捕获中小型土壤动物50112只,隶属于33个类群。其中,线虫、螨类和弹尾虫构成了烟田中小型土壤动物的主体,对烟田土壤动物群落特征起决定性作用。不同季节青枯病田及其对照田土壤动物整体数量表现为3月6月9月。两类烟田不同季节的土壤动物及其主要类群相对多度和密度,以及群落Margalef丰富度指数、Shannon-Wiener多样性指数、Pielou均匀度指数和Simpson优势集中性指数均表现出了明显的动态变化,且出现了显著性差异(P0.05)。群落相似性分析显示,两类烟田土壤动物群落组成相似度高,但烟草青枯病危害加剧会使相似度降低。群落稳定性结果表明,6月和9月对照田稳定性均要明显大于青枯病田。螨类与弹尾虫个体数的A/C比值均为对照田大于青枯病田,且3月和6月差异显著(P0.05)。主成分分析(PCA)表明,青枯病危害对土壤动物个体数、土壤动物密度、中气门亚目、甲螨亚目、线虫、啮虫目和棘跳虫科以及螨类与弹尾虫个体数的A/C比值影响较大;而这些对青枯病危害反应敏感的土壤动物指标,可作为青枯病发生和危害程度评价的特征指标;另外,基于PCA得分的土壤样品采集点排序结果进一步指出,两类烟田土壤动物群落组成的异质性随着青枯病危害程度的加剧而加大。上述结果说明土壤动物群落组成和多样性特征与青枯病的发生和危害密切相关;在农业生产上要开展可持续和有效的烟草青枯病生物防治,应不断加强该病原菌与土壤中小型动物生态关系的基础研究。

Effects of tobacco bacterial wilt on meso-micro soil fauna in tobacco fields of Chongqing

Tobacco bacterial wilt (TBW), an important tobacco disease caused by the soil borne gram-negative bacterium Ralstonia solanacearum, occurs universally in the main tobacco planting area of China and is one of the main reasons for the decline of Chinese tobacco yield and quality. To date, there are no effective measures from agricultural cultivation, breeding for disease resistance, chemicals, or biological agents to adequately control the wilt disease. The occurrence of and damage due to TBW are closely related to rhizosphere soil fauna. However, only few studies have reported the effects of TBW on meso-micro soil fauna in tobacco fields in tobacco-producing countries. Therefore, it is necessary to understand the relationship between soil fauna and soil microorganisms related to TBW for effective control of TBW. In this study, field experiments were carried out from March to September, 2015, in Runxi town, Pengshui County, Municipality of Chongqing. Two treatments were designed in Baiguoping and Yingtaojing villages, which respectively represent the tobacco field in hazard fields of tobacco wilt (HFTW) that have been affected by TBW for more than 10 consecutive years and control fields without this hazard (CK). The modified Tullgren and Bearmann''s methods were used to extract a total of 50,112 individuals of meso-micro soil animals, belonging to 33 groups. Among them, Nematoda, Acari, and Collembola were the dominant groups. The individual numbers of soil animal communities as well as dominant groups of Nematoda, Acari, and Collembola showed a decreasing trend from March to September. The relative abundance and density of soil animals as well as dominant groups varied widely between the two treatments during different periods of investigation. For example, abundance and density of Nematoda were significantly higher in CK than in HFTW in March (P < 0.05); the density of Acari was significantly higher in HFTW than in CK in June (P < 0.05); the density of Collembola was significantly higher in HFTW than in CK during all investigation periods; and the abundance of Isotomidae in CK was significantly higher in March and lower in September, compared to those in HFTW. The density of rare groups was significantly different between the two treatments in June and September as well. The dynamics of several community diversity indices of soil fauna varied between HFTW and CK during different periods of investigation. Although the richness index of Margalef was significantly greater in CK than in HFTW in March and June, it was significantly higher in HFTW than in CK in September. The Shannon-Weiner index of diversity was significantly higher in HFTW than in CK in March and September, but it was lower in June. The evenness index of Pielou was significantly higher in CK than in HFTW in June. In March, the Simpson index was significantly higher in CK than in HFTW in the presence of Nematoda, but it was significantly lower in the absence of Nematoda. However, in the absence of Nematoda, the Simpson index was significantly higher in CK than in HFTW in June and September. Similarity analysis using the Sørensen index showed that the composition and structure of soil animal community between HFTW and CK were highly similar, but the similarity declined markedly under effects of TBW with increased severity of damage level from March to September. Stability analysis showed that the structure of soil animal community in CK had higher stability than that in HFTW in June and September. The ratio of individual number between Acari and Collembola (A/C value) was higher in CK than in HFTW, and was significantly different in March and June. The results of the principal component analysis (PCA) indicated that the occurrence and damage of TBW had a considerable effect on individual numbers and density of soil fauna, individual numbers of Oribatida, Mesostigmata, Nematoda, Corrodentia, and Onychiuridae, and values of A/C, which could be used as an indicator to monitor the environmental impacts on the disease. In addition, PCA ordination diagrams of soil collection points in tobacco fields suggested that the differences in soil animal community composition were considerably influenced by the damage and its severity of TBW from March to September. On the basis of these results, we can conclude that abundance and diversity of meso-micro soil fauna is closely related to the occurrence and severity of TBW in tobacco fields.