Distribution characteristics of soil nematode communities and trophicgroup in the rhizosphere of Citrus reticulata Blanco‘Tankan’with different planting years

Abstract:【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 developmentof fruit trees as well. Soil nematode is an indicator organism of soil environment, which can be used toevaluate 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 communities in rhizospheric soil of Jiaogan (Citrus reticulata Blanco‘Tankan’) with different planting years wereinvestigated. In order to ascertain the causes of the distribution differences of the nematode nutrientgroups, the effects of planting years on diversity of nematode community were studied by analyzing itscomposition and structure characteristics.【Methods】Four Jiaogan planting fields with different plantingyears were chosen as sample fields in Jiaogan planting base of Hongyang town, Jieyang city. Sample fieldsW1 and S2, with 6 and 7 planting years were set as short time planting fields. Sample fields N1 and 85-2,with 13 and 16 planting years were set as long time planting fields with same field management. In eachsample field, three 4 m×4 m lands were set as sample points. Soil samples were taken from the 40 cmdepth soil within 1 m range of main roots using 100 cm3 ring samplers. The soils from different layers weremixed evenly before two hundred grams fresh soils were taken from each sample point. Nematodes wereisolated from these samples by shallow plate method. Data analysis was performed using the combinationof 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 (W1 and S3) belonged to 29and 28 genera, with relative abundance of 31.49% and 29.05%, respectively. On the contrary, the nema⁃todes from the fields with long planting years (N1 and 85-2) belonged to 24 and 23 genera, with relativeabundance 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 (W1 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 com⁃munity, 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 S3) and long planting years (N1 and 85-2), suggest⁃ing that the composition of the soil nematode community in the rhizosphere of Jiaogan distinctly variedwith the fields with different planting years. The results also showed difference in nutrient group composi⁃tion and distribution of the nematodes among the soils from the four sample fields. Fungal nematodes andmost 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 correla⁃tion analysis indicated that there were significant negative correlations between planting years and theplant biomass, pH, soil organic matter, soil moisture content, soil porosity and soil density and other soilenvironmental 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 signifi⁃cant 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 plantingyears were significantly higher than those with short planting years (P＜0.05). The planting-feeding nema⁃todes tended to live in the rhizosphere of Jiaogan with long planting years. The NCR index showed that thedecomposition pathway of soil organic matter was mainly functionally related to bacteria in the field withshort planting years.【Conclusion】Extension of planting years would result in degeneration of the quality ofsoil environmental factors, decreasing the density, richness and diversity of soil nematode in the rhizosphere 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 plantingfeedingnematodes.