Metabolic Characterization Of Soil Microbial Community In Apple Orchards Based On Grass-Growing Technology

Grass-growing in apple orchards is an environmentally friendly soil management practice that is important for ensuring the sustainable use of modern apple orchard soils.Soil microorganisms play a central role in soil nutrient cycling and quality assessment,however,previous studies on the metabolic characteristics of soil microorganisms in apple orchards have mainly focused on short-term weeding,and studies to reveal how soil microorganisms respond to long-term weeding conditions are relatively weak.In this study,the functional metabolism of long-term grassed soil microbial communities was analysed on the basis of a long-term grassed positioning experiment in Weibei apple orchards,with clear-cutting as the control,and the evolution of the functional metabolism of soil microbial communities of white clover in different years with the number of years of grassing was investigated.The main results are as follows:(1)Long-term grassing increased the metabolic activity of soil microorganisms in the orchard.The metabolic activity of soil microorganisms in different soil layers was as follows: white clover > chickweed > chokecherry > clearcut.0-20 cm soil layer showed the highest metabolic activity,with the AWCD(Average Well Color Development)values of white clover,chickweed and chokecherry increasing by 53.7%,47.4% and 36.9%,respectively,compared to the clearcut treatment.Notably,the AWCD values of the white clover treatment were 29.0% and 38.7% higher in the 0-20 cm soil layer compared to the white clover treatment in the 20-40 cm soil layer and 40-60 cm soil layer,respectively.(2)Differences in microbial diversity indices between treatments.The microbial diversity indices were higher in the 0-20 cm soil layer than in the deeper layers.The order of the indices in the 0-20 cm soil layer was as follows: Shannon’s index,white clover>crown vetch>orchard grass>clear tillage;Mc Intosh’s index,Simpson index and Uniformity index were consistent,that was white clover>orchard grass>crown vetch>clear tillage.(3)The carbon source material that had a greater effect on soil microbial activity varied between treatments in different soil layers.The different herbaceous treatments showed the greatest variety and quantity of carbon sources utilised by soil microorganisms in the 0-20 cm,20-40 cm and 40-60 cm soil layers,and the effect was more pronounced in the 0-20 cm soil layer,where the carbon sources were mainly sugars(β-methyl-Dglucoside,N-acetyl-D-glucosamine,D-mannitol,D-cellobiose),amino acids(L-arginine,L aspartic acid,glycyl-L-glutamic acid),carboxylic acids(D-glucosaminic acid,Dgalacturonic acid),and polymers(Tween 40).(4)The results of the redundancy analysis showed that there were differences in the environmental drivers affecting the carbon source metabolism of the soil microbial community in the different soil layers between the treatments.Soil organic matter and Available phosphorus were the main factors affecting the variation of soil microbial carbon metabolism in the 0-20 cm soil layer of the different herbaceous treatments.Total soil nitrogen and organic matter were the main factors influencing the variation in soil microbial carbon metabolism in the 20-40 cm soil layer between the different herbaceous treatments.Organic matter and p H were the main factors influencing the variation in microbial carbon metabolism in the 40-60 cm soil layer of the different herbaceous treatments.(5)The metabolic activity of soil microorganisms in the orchard increased with the number of years of grass production,i.e.it showed that: white clover 15 years old > white clover 10 years old > white clover 6 years old.15 years old white clover treatment had the highest AWCD value,the largest microbial diversity index and the largest variety and number of carbon sources that had a greater influence on soil microbial activity.Compared to the 10-year-old white clover treatment,the 15-year-old treatment had 14.2% higher AWCD values and increased microbial metabolic activity for sugars(β-methyl D-glucoside,D-mannitol),amino acids(L-asparagine),and carboxylic acids(y-hydroxybutyric acid);compared to the 6-year-old white clover treatment,the 15-year-old treatment had 25.1%higher AWCD values and increased microbial metabolic activity for sugars(β-methyl Dglucoside,D-cellulose),amino acids(L-arginine),carboxylic acids(D-malic acid,yhydroxybutyric acid,D-galacturonic acid)and phenolic acids(methyl pyruvate)with increased metabolic activity compared to the 6-year-old white clover treatment.The results of the redundancy analysis indicated that soil fast-acting phosphorus and total nitrogen were the main drivers influencing the variation in the metabolism of soil microbial carbon sources in different years of white clover treatments.(6)The relative abundance of soil microbial flora changed with the number of years of herbaceous life.Spearman’s correlation analysis showed that at the bacterial phylum level,the main dominant bacteria were Actinobacteria and Firmicutes,both of which had the highest number of carbon source species significantly associated with microbial carbon use.Eleven carbon sources were significantly positively correlated with Actinobacteria and three with Firmicutes.At the bacterial genus level,the main dominant bacteria were Streptomyces,which had the largest number of carbon sources significantly and positively associated with microbial carbon use,with 16 species.