不同种植年限蕉柑根际土壤线虫群落及营养类群结构特征

Distribution characteristics of soil nematode communities and trophic group in the rhizosphere of Citrus reticulata Blanco 'Tankan' with different planting years

【目的】分析种植年限对蕉柑根际土壤线虫群落组成与结构特征的影响,探明不同种植年限的蕉柑根际土壤线虫群落多样性与营养类群分布差异的成因。【方法】五点采样法采取土样,浅盘法分离提取线虫,运用生态学指数和主分量分析的PCA排序相结合的方法处理数据。【结果】(1)小树龄蕉柑根际土壤线虫群落的个体密度、属数、多样性指数和丰富度指数均显著高于大树龄蕉柑样地(P<0.05)。(2)PCA排序分析表明,食真菌线虫和大多数食细菌、捕食性/杂食性线虫主要分布在小树龄蕉柑样地,植食性线虫主要分布在大树龄蕉柑样地。(3)相关性分析表明,蕉柑种植年限与土壤环境因子、线虫总密度、线虫属数、生态学指数及食细菌和食真菌线虫、捕食/杂食性线虫密度呈极显著或者显著负相关,与植食性线虫密度呈显著正相关。(4)大树龄蕉柑根际土壤线虫的PPI值和PPI/MI指数显著高于小树龄蕉柑样地(P<0.05)。WI和NCR指数表明,小树龄蕉柑样地土壤健康程度优于种植年限长的大树龄蕉柑样地,小树龄蕉柑样地土壤有机质的分解途径以细菌为主。【结论】果树种植年限的延长会改变土壤的养分与结构,从而降低蕉柑根际土壤线虫密度和群落的多样性,对蕉柑根际土壤线虫各营养类群的结构及分布产生趋向性影响。

[ Objective ] Planting age plays an important role in the yield and quality of fruits. Environmental factors of soil also are closely related to the yield and quality of fruit, and the growth and development of fruit trees as well. Soil nematode is an indicator organism of soil environment, which can be used to evaluate the quality of soil environment with composition and characteristics of soil nematode community, and the distribution and tendency of nematode nutrient groups. In the present study, nematode communi- ties in rhizospheric soil of Jiaogan （Citrus reticulata Blaneo ＇ Tankan＇） with different planting years were investigated. In order to ascertain the causes of the distribution differences of the nematode nutrient groups, the effects of planting years on diversity of nematode community were studied by analyzing its composition and structure characteristics. [Methods] Four Jiaogan planting fields with different planting years were chosen as sample fields in Jiaogan planting base of Hongyang town, Jieyang city. Sample fields W1 and $2, with 6 and 7 planting years were set as short time planting fields. Sample fields N1 and 85-2, with 13 and i6 planting years were set as long time planting fields with same field management. In each sample field, three 4 m ×4 m lands were set as sample points. Soil samples were taken from the 40 cm depth soil within 1 m range of main roots using 100 cm3 ring samplers. The soils from different layers were mixed evenly before two hundred grams fresh soils were taken from each sample point. Nematodes were isolated from these samples by shallow plate method. Data analysis was performed using the combination of diversity index, evenness index and richness index and PCA ordering of principal component analysis. [ Results ] （1） The nematodes isolated from the fields with short planting years （W 1 and S3） belonged to 29 and 28 genera, with relative abundance of 31.49% and 29.05%, respectively. On the contrary, the nematodes from the fields with long planting years （N1 and 85-2） belonged to 24 and 23 genera, with relative abundance of 18.95% and 20.51%, respectively. The individual densities, genera number, diversity indi- ces and richness indices of the nematodes isolated from the fields with short planting years （W 1 and S3） were significantly higher than that from the fields with long planting years （N1 and 85-2） （P 〈 0.05）. （2） The results of PCA ordination showed that the first two axes explained the 93.8% change of nematode community, and four axes explained the 97.8% changes of the nematode community. Axis 1 and axis 2 obviously separated the sample field with short （W1 and $3） and long planting years （N1 and 85-2）, suggesting that the composition of the soil nematode community in the rhizosphere of Jiaogan distinctly varied with the fields with different planting years. The results also showed difference in nutrient group composition and distribution of the nematodes among the soils from the four sample fields. Fungal nematodes and most eating bacteria, predators/omnivorous nematodes were mainly distributed in the soil with short planting years, whereas planting-feeding nematodes mainly in the soil with long planting years. （3） The correlation analysis indicated that there were significant negative correlations between planting years and the plant biomass, pH, soil organic matter, soil moisture content, soil porosity and soil density and other soil environmental factors, such as total density of nematodes, number of nematode genera, diversity index, richness index and edible bacterial and fungal nematode, predator-prey/omnivorous nematode. A significant positive correlation was found between planting-feeding nematode density and planting years. （4） The PPI value and PPI/MI index of the soil nematodes in the rhizosphere of Jiaogan with long planting year were significantly higher than those with short planting years （P 〈 0.05）. The planting-feeding nematodes tended to live in the rhizosphere of Jiaogan with long planting years. The NCR index showed that the decomposition pathway of soil organic matter was mainly functionally related to bacteria in the field with short planting years. [Conclusion]Extension of planting years would result in degeneration of the quality of soil environmental factors, decreasing the density, richness and diversity of soil nematode in the rhizo- sphere of Jiaogan soil. The change of composition and structure of the nematode nutrient groups in the rhizospheric soil would lead to tendency selection of distribution of eating bacterial nematodes and plantingfeeding nematodes.