Research on the community structure and diversity of soil nematodes in the orchards of Shanxi province

Abstract：【Objective】It is crucial to study the community structure and diversity of nematodes in the rhizosphere of orchards for preventing soil degradation. This research aims to investigate the community structure and species diversity of nematodes in the rhizospheric soil of fruit trees in the orchards of Shanxi province. The study was conducted at three different locations, including seven species of fruit crops and six rhizosphere depths.【Methods】The test samples for this study were selected from the orchard of Shanxi Academy of Agricultural Sciences, Polomogy Istitute, Shanxi Agricultural University and Hancun village orchards. Nematodes were collected from the rhizosphere of seven different fruit crops, namely apricot (Armeniaca vulgaris), grape (Vitis vinifera), jujube (Ziziphus jujuba), apple (Malus pumila), pear (Pyrus sp.), peach (Prunus perisica) and walnut (Juglans regia). Soil samples were collected using the five-point sampling method with a cylinder driller. The rhizosphere of the fruit trees was sampled at a depth of 5-30 cm. For each tree, 100 g of soil was taken in four directions. These soil samples were mixed, and 500 g of soil was selected as the final sample. The sampling site, data, and host plant were marked. The specimens were then brought back to the lab for further treatment. In each sample plot, three samples were taken, resulting in a total of 189 soil samples collected in three replicates. The Shanxi Fruit Research Institute conducted vertical distribution plots of soil nematodesin the rhizosphere of fruit trees. The soil depth was divided into six levels: 0-10 cm, ＞10-20 cm, ＞20- 30 cm, ＞30-40 cm, ＞40-50 cm and ＞50-60 cm. The five-point sampling method was used to select soil samples from the same layer and fruit tree. A sample of 500 g of mixed soil was taken and three samples were collected from each sample plot. In total, 126 soil samples were collected in three replicates, resulting in a total of 315 soil samples for the experiment. The collected samples were promptly stored in a 4 ℃ refrigerator upon arrival at the laboratory. Nematode populations in a 100 g soil sample were extracted using the Whitehead tray method. The abundance of nematodes was determined by counting the quantity of nematodes per 100 g of dry soil. The nematodes were then authenticated and counted under a microscope. The soil nematode communities were classified into four trophic groups based on their feeding habits and esophageal characteristics: plant-parasitic nematodes, fungivore, bacterivore and omnivore-predator feeders. They were further classified into three groups based on the number of individuals in each genus. The genus with more than 10% of the total of individuals was considered dominant, those with 1% to 10% were considered common, and those with less than 1% were considered rare.【Results】The study identified a total of 26 genera of nematodes belonging to two classes, four orders and 15 families. Among these, 15 genera were identified as plant-parasitic nematodes, 6 genera as bacterivores, 3 genera as fungivores and 2 genera as omnivore-predator feeders. In the soil surrounding various fruit trees, the dominant genera were Filenchus and Mesorhabditis, which accounted for 36.32% of the total population. Filenchus was classified as a plant-parasitic trophic nematode, while Mesorhabditis was classified as a bacterivore. Common genera included Aphelenchoides, Aphelenchus, Rhabditis, Cephalobus, Ditylenchus, Mesodorylaimus, Dorylaimus, Protorhabditis, Eucephalobus, Alaimus, Tylenchus, Paratylenchus, Pratylenchus, Tylenchorhynchus, Criconemella, Xiphinema, Longidorus, Doryllium, Eudorylaimus and Aporcelaimus, accounting for 61.58% of the total population. Rare genera including Psilenchus, Helicotylenchus and Rotylenchus accounted for 2.1% of the total population. The investigation and analysis conducted at Shanxi Agricultural University orchard focused on the total number of soil nematodes present in the rhizosphere soil of fruit trees. The findings revealed that the range of nematodes varied from 530 to 940 per 100 g of dry soil, with an average of 684 nematodes per 100 g of dry soil. However, the number differed in the other two sites. The study also observed variations in the total number of soil nematodes among different host species and geographical environments. The dominant trophic group was bacterivore, followed by plant-parasitic nematodes, while fungivores and omnivore-predators were present in lower quantities. Nematodes were distributed throughout the 0-60 cm soil layer, with the highest number observed at a depth of ＞20-30 cm. Among the fruit species, apple and pear exhibited the highest number of nematodes in each soil layer, followed by grape vines. Jujube and peach trees had a lower number of soil nematodes.【Conclusion】The study revealed that the highest abundance of nematodes was primarily concentrated in the ＞20-30 cm soil layer within the rhizosphere soil of fruit trees. Additionally, the study conducted has identified 26 genera of soil nematodes belonging to two classes, four orders, and 15 families. The dominant trophic group observed was bacterivore or bacteria-feeding nematodes, which indicated that the soil was in a healthy state. The study is of great significance for monitoring soil environment and improving management of orchards in Shanxi province. At present, the soil environment in orchards of Shanxi province is healthy, but it is advisable to regularly monitor plant-parasitic nematodes in orchards to ensure timely detection.