Primary study on the effects of natural grass on nematode communities in the soil of red pear orchard in Yunnan province

Abstract: 【Objective】The ground-covering plant plays an important role in the orchard ecological environment. Yet there are still some reasons why the technique has not widely been applied. Subjectively,it is influenced by the thought of "uprooting weeds ensures the health of fruit trees and less competing for fertilizer with fruit trees". Objectively, grass species selection, orchard management and orchard climate will also have an impact. Ecological environment will be out of balance after long-tine clean tillage, resulting in the occurrence of pests and diseases. And the soil environment is deteriorated gradually at the same time. Soil nematode is a main group of soil animals, with large quantities, abundant species,short life history and high sensitivity to the environment. Nematodes of different nutrition groups have different effects on the virtuous circle of food webs in the soil, which are regarded as important indicator organisms in the soil environment by many scholars, and thus become an important indicator for evaluating the health of soil ecological environment. There are few reports on utilizing nematode communities to evaluate the impact of natural grass on the soil ecological environment and monitor soil health and soil sustainability at present. The aim of the trial is to study the effects of natural grass on nematode communities in a red pear orchard, to provide the basis for scientific management of pear orchards as well as to provide references for monitoring orchard soil health.【Methods】The study was conducted in a 4-year-old red pear orchard with a clean tillage pear orchard as the control. The areas of the two experimental orchards were both 0.667 hm2. In natural grass areas, the grass was mowed three times a year, and the mowed grass was covered under the pear trees. The clean tillage area was plowed three times a year. Rhizospheric soil samples were collected respectively from natural grass and clean tillage pear orchards in Anning City, Yunnan in mid-June and mid-October, 2018. When soil samples were collected, 9 pear trees were randomly selected in each area and 3 sampling points were selected at1 meter away from each tree trunk. The soil and debris on the surface were removed. Soil samples were collected from 0-20 cm deep and those of 3 trees(9 sampling points) were evenly mixed as a repeat.Each area was in triplicate and 1 kg of soil samples were taken back to the laboratory for isolation and identification of nematodes. Soil nematodes were trapped using a modified shallow dish method and then identified and counted under a light microscope. The community composition and nutrition community structure of soil nematodes were analyzed. Moreover, the diversity index and ecological function index of soil nematodes were calculated. The diversity index of nematodes included ShannonWeaver Index(focus on reflecting the diversity of rare nematodes), Genus Dominance Index(focus on reflecting the dominance of common nematodes), Trophic Diversity Index(reflect the balance degree of nematodes in different trophic groups) and Plant Parasites Index(describe the dominance of plant parasitic nematodes). The ecological function index included Nematode Channel Ratio(reflect the metabolic pathway of soil food web.), Wasilewska Index(indicate the healthy level of soil, the higher the value,the healthier the soil), Basal Index(describe the anti-interference ability of soil food web.), Enrichment Index(reflect the degree of soil nutrient enrichment.) and Structure Index(reflect the disturbance degree of soil food web).【Results】The proportion of bacterial-feeding nematodes increased significantly in the rhizospheric soil after the growth of natural grass in red pear orchards, especially the dominance of Eucephalobus, Acrobeles and Acrobeloides nematodes, while the proportion of plant parasitic nematodes decreased significantly in the rhizospheric soil, especially Ditylenchus, Tylenchus, Paratylenchus and Rotylenchus nematodes. Nevertheless, there was no significant effect on the percentages of fungifeeding and Omnivores/Predators nematodes. The Wasilewska Index(WI), Basal Index(BI) and Trophic diversity index(TD) of nematodes increased significantly. Meanwhile the Enrichment Index(EI)decreased significantly, but there were no significant effects on Shannon-Weaver Index(H′), Genus Dominance Index(Ig), Plant Parasites Index(PPI), Nematode Channel Ratio(NCR) and Structure Index(SI).【Conclusion】Natural grass in pear orchards can optimize the structure of soil nematode community, which is beneficial to the benign development of soil ecological environment. Therefore, the natural grass can improve the soil health in the red pear orchard in Anning, Yunnan.