A study on the community characteristics of natural cover grasses in apple orchard in Luochuan county

Abstract:【Objective】As a widely used soil management in the world, grass-growing in orchards has many advantages, such as increasing soil organic matter, improving soil microbial community diversity,enhancing orchard ecosystem diversity, and improving fruit quality. According to the current situation of rural development, labor losses have caused orchards with poor management, where weeds are ram- pant. There is an urgent need to develop a set of management and protection methods for dryland natu- ral grass orchards, so as to reduce labor input in cutting while ensuring fruit quality. Therefore, it is nec-essary to clarify the growth habits of orchard weeds and screen out the dominant benign grass species suitable for apple orchards. This experiment explored the ecological adaptability of different dominant grass species in the process of community succession in dryland apple orchards with natural grass cov-er, and provided reference for screening available natural grass species in apple orchard (Fengqi town, Luochuan county as an example).【Methods】The species of grass was determined by photographing, sample collecting, consulting literature, and expert identification. Three quadrats of natural grass each of 1 m2 were randomly investigated in each orchard with the diagonal as the benchmark. Twenty or-chards were investigated, and a total of 60 quadrats were investigated. The growth (plant number, height) and community distribution of grass species per month were analyzed and recorded. In order to record conveniently, the underground part of grass species was recorded as the root length of grass. The ecological habits of the dominant grass species were mastered through literature review, and the domi-nant benign grass species suitable for natural cover in apple orchard were screened. The collected sam-ples were classified and identified based on species. With species as the statistical unit, Margalef rich-ness index, Simpson index, dominance and niche breadth were calculated.【Results】Through the inves-tigation of the annual succession of grass species in Luochuan apple orchard, it was found that there were 32 main grass species belonging to 15 families growing in the orchard in one year. Among them, the grass species of Gramineae and Compositae were the dominant, accounting for 19% of the total spe-cies. The species richness was highest in August and September, and relatively low in April, May and November. The species richness was mainly affected by weather changes. In April, May, August, Sep-tember and October, the Simpson index hardly changed; the coverage rate of grass was high; the density of grass was large; and the distribution of grass was uniform. In April and May, the species distribution of Capsella bursa-pastoris and Melica turczaninowiana Ohwi grass was concentrated and uniform. Ad- ditionally, the diversity index was the lowest in June because farmers were mowing. The temperature inapple orchard in July reached the highest value in the whole year with low rainfall, which affected the growth rate of grass cover, resulting in a relatively low coverage rate. Ixeris denticulata, Taraxacum mongolicum, Potentilla kleiniana and Solanum septemlobum Bunge plants were relatively large, the cover density was larger, and their ability to use different habitat resources was stronger, while that of Stellaria media, Setaria viridis and Chloris virgata was weal. Therefore, the grass species with larger niche breadth were not necessarily the dominant species of the community, and the niche breadth of the dominant species of the community was not necessarily the largest. According to the composition and frequency of herbaceous plants in the dryland apple orchards, 14 dominant species were screened, be-longing to 9 families. Among them, Setaria viridis, Chloris virgate and Stellaria media had obvious growth advantages. In spring, Stellaria media, Chenopodiaceae and cruciferous herbaceous plants were the main species. From summer, cruciferous herbaceous plants gradually subsided, Stellaria media, Gra-mineae and Compositae herbaceous plants dominated until November. Setaria viridis, showy chloris,Echinochloa crusgalli, Digitaria sanguinalis and Stellaria media have the longest covering time and the largest covering density in the orchards. Through the experimental data analysis, affected by weather(temperature and precipitation) in August and September, the richness index of herbaceous plants in ap-ple orchards is higher and the coverage density is the highest. Plants that are too tall can easily affect or-chard operations, and plants that are too large usually have taproots and the root system is deeply root-ed. However, the longer the grass root is, the more likely to compete for nutrition and water with the root of fruit trees, which is not conducive to the development of dryland orchards. Therefore, we should timely carry out artificial intervention to leave grass species with shallow roots or with no main root. This can not only promote the formation of aggregates on the soil surface, but also prioritize the avoid- ance of water competition. The comprehensive comparison showed that Setaria viridis, showy chloris,Echinochloa crusgalli, Digitaria sanguinalis and Stellariamedia, Taraxacum mongolicum, Ixeris dentic-ulate and Glechoma longituba cover the surface for a long time and have high density, drought toler-ance and shallow roots. Their water requirement is low with strong drought resistance. Therefore, they can be used as excellent species for natural grass cover in dryland apple orchard.【Conclusion】The nat-ural grass species in orchards change with seasons, but it is necessary to ensure that the left grass spe- cies have the basic characteristics of high coating density, strong resistance and shallow root system. In future studies, the influence of root exudates of grass species left under artificial intervention on grass species and soil will be analyzed. Many grass species have certain medicinal value. Under the basic screening rules, they can be cultivated in the orchard for medical purpose, which can not only optimize the microclimate environment of the orchard, but also increase the economic value of the orchard.