Soil Respiration Dynamics And Soil Microbial Community Structure Characteristics In Rainfed Apple Orchard Under Grass-planting Patterns

The practice of grass cultivation in rainfed apple orchards can increase soil nutrients,promote microbial activities,and improve fruit quality while improving soil environment.In order to clarify soil respiration dynamics and soil microbial community characteristics under the grass-planting patterns in dry apple orchard.In this study,a 13-year-old apple orchard was used to analyze the dynamics of soil respiration rate and its relationship with temperature and soil water content in 0-5 soil layer under grass-planting patterns including orchard grass?Dactylis glomerata?and white clover?Trifolium repens?.And high-throughput sequencing technology was use to study the soil microbial community structure in 0-10 soil layer.The main results are as follows:1?During the growth season,soil respiration rate increased first and then decreased under grass-planting patterns in apple orchard.The average soil respiration rate under clean tillage,orchard grass and white clover treatments was 3.33,6.58,and8.83?mol·m^-2·s^-1 in 2017,respectively,and 1.34,5.01 and 6.83?mol·m^-2·s^-1 in 2018.During the dry-wet cycle of growth season,soil respiration rate increased significantly with the increase of soil water content.Soil respiration of apple orchard in non-growth under clean tillage,orchard grass and white clover accounted for 22.2%-27.7%of the total annual soil respiration.The average soil respiration rate under clean tillage,orchard grass and white clover treatments was 0.46,0.82 and 0.93?mol·m^-2·s^-1,respectively.There were significant differences among three treatments.During the freeze-thaw cycle in non-growing season,soil respiration rate of the three treatments were significantly different.2?The average soil temperature in 2017 was 16.17,17.65 and 17.21?,under clean tillage,orchard grass and white clover treatments,and 14.68,15.26 and 15.96?in 2018,respectively.Soil respiration rate was positively correlated with soil temperature in both growth and non-growing seasons.The explanatory rates of soil temperature on soil respiration rate were 64.6%-75.7%in the three treatments in the growth season,and 63.7%-77.3%in the non-growing season.The Q₁₀ values of soil temperature sensitivity were 1.92?2.39 and 2.18 in the growing season of 2017,2.29,2.59 and 3.10 in 2018,and 2.61,4.48 and 3.78 in the non-growing season,respectively.The average soil water content in 2017 was 21.5,25.29 and 25.33 m³·m^-3under clean tillage,orchard grass and white clover treatments,and 23.17,28.39 and27.55 m³·m^-3,respectively.There was also a significant correlation between soil moisture content and soil respiration rate.In the dry period,soil respiration rate increased significantly with the increase of soil water content.When the water was sufficient,the soil respiration rate was not sensitive to soil water content.During the growth season in 2017 and 2018,soil water content explained the range of soil respiration rate from 4.1%to 43%,and the non-growth season was 38.9%-60.4%.When analyzing the relationship between soil respiration rate,soil temperature and soil water content,the two-factor model is superior to the single-factor model.The explanatory rate was 38.8%-79.8%in the growing season and 65.7%-86.1%in the non-growing season.3?High throughput sequencing?Illumina Hiseq PE250?was used to detect soil microbial communities at apple orchards.Alpha diversity of soil bacteria was the highest under the treatment of orchard grass,and that of soil fungi was the highest under the treatment of white clover.The dominant phylum of soil bacteria was Proteobacteria,Bacteroidetes and Acidobacteria,while the dominant phylum of soil fungi was Ascomycota and Zygomycota.At the genus level,Kaistobacter,Pseudomonas and Flavobacterium were dominant genus in soil bacterial community,while Gloeotinia,Fusarium and Mortierella were dominant in soil fungal community.The specific genuses were found in the soil under apple orchard grass-planting patterents.Clostridium and Thermomyces appeared in orchard grass treatment,the former could promote soil nitrogen accumulation,and the latter was closely related to protein and sugar degradation.The specific genuses in white clover treatment are Bacillus,Nannocystis,Stachybotrys and Actinomucor.Bacillus is related to nitrogen fixation of plants,while the Stachybotrys and Actinomucor can affect the growth of microorganisms.The community structure of soil bacteria and fungi was similar under clean tillage,orchard grass and white clover treatments,but the relative abundance of beneficial specific genuses increased under grass-planting treatments,and grass-planting was beneficial to the production of soil beneficial specific genuses.