土壤线虫群落在贡嘎山东坡不同垂直气候带间的分布格局

Distribution pattern of soil nematode communities along the vertical climate zones on the eastern slope of Gongga Mountain

贡嘎山东坡自下而上分布着从亚热带到寒带的连续气候带及从常绿阔叶林到针叶林的连续植被类型,其地下土壤线虫群落的分布格局尚不清楚,为研究其不同气候带间的土壤线虫群落特征及其在垂直气候带间的变化趋势,2014年9月和12月对贡嘎山东坡5个气候带土壤线虫进行了2次调查.研究结果为:共捕获土壤线虫193 921条,隶属于2纲9目68科172属,平均密度2 155条/100 g干土,食细菌线虫为优势营养类群.不同气候带间土壤线虫群落结构差异性各异,并受季节变化影响;影响群落结构的主要类群是色矛目(Chromadorida)、窄咽目(Araeolaimida)、小杆目(Rhabditida)和单齿目(Mononchida).线虫群落密度及多样性指数在不同气候带间均无显著差异,但12月的密度显著高于9月,而多样性指数则显著低于9月.除食细菌线虫外,食真菌、捕食-杂食和植物寄生线虫的密度在不同气候带间(随海拔升高)呈先增加后下降趋势(P<0.05),且有显著季节差异(P<0.05).从亚热带到寒温带,土壤线虫的基础指数(BI)逐渐下降(P<0.05),成熟度指数(MI)逐渐增加(P<0.05),表明生态系统的抵抗力逐渐降低而成熟度逐渐增加;通道指数(CI)呈波动性下降(P<0.05),且均小于50,表明碎屑食物网以细菌分解途径为主;植物寄生成熟度指数(PPI)无明显变化趋势(P>0.05),但9月份显著高于12月份,表明9月份土壤生态系统比12月份更成熟.线虫群落密度、生态指数(BI、MI)、营养类群(PO、Pl)分别与土壤有效氮、全钾和土壤温度呈显著相关(P<0.05).综上表明气候带类型变化对土壤线虫群落密度和多样性影响较弱,对土壤线虫群落结构及生态指数影响较大,土壤有效氮、全钾及温度是主要影响因子.

The characteristic of stereoscopic climate is fairly clear on the eastern slope of Gongga Mountain, distributing from subtropical to frigid zones along the altitude. Accordingly, vegetation types changed from evergreen broad leaved forest to coniferous forest. The aim of this study was to elucidate the characteristics of soil nematode communities under different climate zones on the eastern slope of Gongga Mountain. In September and December 2014, soil samples from 0-5 cm, 5-10 cm and 10-15 cm layers were collected from five types of forest, including subtropical evergreen broad-leaved forest （SEB, 1 600 m）, subtropical evergreen and deciduous broad-leaved mixed forest （SEDB, 2 000 m）, warm temperate deciduous broadleaved forest （WTDB, 2 400 m）, mid-temperate coniferous-broadleaved mixed forest （MTC, 2 800 m） and cold temperate coniferous forest （CTC, 3 200 m） along the vertical climate zones on the eastern slope of Gongga Mountain. A total of 193 921 soil nematodes were collected, belonging to 2 classes, 9 orders, 68 families and 172 genera. The mean density was 2 155 ind. 100 g-1 dry soil： All nematode individuals were classified into the four trophic groups of bacterivores, fungivores, plant-Parasites and predators-omnivores, among which the bacterivores were the dominant. The structure of soil nematode community varied among different climate zones as well as seasons. The community structure was mainly affected by the changes in abundances of Chromadorida, Araeolaimida, Rhabditida and Mononchida. Individual density, taxonomic richness, Shannon-Weiner index and Pielou index varied with no significant difference among the vertical climate zones. However, the individual density in December was significantly higher than that in September, while an opposite pattern was observed for Shannon-Weiner index. The densities of fungivores, predators-omnivores and plant-parasitic fluctuated from SEB to CTC （P 〈 0.05）, and differed significantly between the two sampling months （P 〈 0.05）. As a whole, the densities of the four trophic groups were higher in September than in December. The basic index and channel index decreased significantly （P 〈 0.05）, while the maturity index increased significantly （P 〈 0.05） from SEB to CTC. The channel index of the nematodes for all climatic zones was smaller than 50, indicating that the detrital food webs on the eastern slope of the Gongga Mountain were dominated by bacterial decomposition channels. The plant-parasite index changed with no obvious tendency among the climatic zones （P 〉 0.05）, while it was significantly higher in September than in December （P 〈 0.05）, suggesting a more mature ecosystem in September than in December. The regression analysis showed that the densities of community, predators-omnivores and plant parasitic, basic index and maturity index significantly correlated With soil available nitrogen, total potassium and soil temperature. The results of this research indicated that climatic type change exerts greater effects on soil nematode community structure and ecological index than on the individual density and diversity index. Soil available nitrogen, total potassium and soil temperature are the main influencing factors.