Relationship Between Soil Microbial And Three-dimensional Fluorescence Characteristics Of Water-soluble Organic Matter In Apple Orchards On The Loess Plateau

The Loess Plateau is a major producing area of high-quality apples in China.The improvement of apple yield and quality and the sustainable development of orchard are inseparable from the healthy suitable soil environment for the growth of fruit trees.In the past,the evaluation of orchard soil quality was mainly about basic physical and chemical properties,but there has been no systematic evaluation of orchard soil aggregates,three-dimensional fluorescence of water-soluble matter and soil microorganisms.In this experiment,a large number of apple orchard soil samples were collected on the Loess Plateau,and the basic physical and chemical properties and aggregates of high-quality and non-high-quality orchards were analyzed,as well as the relationship between soil soluble organic matter(DOM)components and microbial communities,in order to provide data and theoretical support for the improvement of soil quality in orchards.The following main results are obtained:1.The contents of soil organic matter,available phosphorus,available potassium,nitrate nitrogen and ammonium nitrogen in 0-20,20-40 and 40-60 cm soil layers of high quality orchards were all higher than those of non-high quality orchards.2.The dominant soil aggregates in both high quality orchards and non-high quality orchards were > 0.25 mm aggregates,but the proportion of high quality orchards > 0.25 mm aggregates was 88.2%,while the proportion of non-high quality orchards > 0.25 mm soil aggregates was only 68.03%,significantly lower than that of high quality orchards.3.In high-quality orchards and non-high-quality orchards,DOM components identified included two humic acid components(C1,C2)and one protein-like component(C3).The total fluorescence intensity of high quality orchards was higher than that of non-high quality orchards,which was the same with the trend of total DOC content.UVC humus(C1)was dominant in both high and non-high quality orchards,followed by UVA humus(C2),and tyrosine(C3)was the lowest.C1,C2 and C3 accounted for 40.91%,34.33% and 24.76% of high-quality orchards,respectively.The proportion of C1,C2 and C3 in non-quality orchards was 45.5%,35.89% and 18.61%,respectively.The total fluorescence intensity of high quality orchards was 129.52% higher than that of non-high quality orchards.4.The diversity and abundance of bacteria in high-quality orchards were higher than those in non-high-quality orchards.For example,the abundance of dominant bacteria Proteobacteria,Acidobacteria,Gemmatimonadota,Actinobacteriota and Chloroflexi was higher than that of non-quality orchards.The relationship between the diversity and abundance of fungi and different types of orchards was complex.5.Different management measures and nutrient inputs in different types of orchards changed soil DOM components and microbial community structure.The close coordination between these communities had an impact on soil nutrient cycling and orchard health.