| In recent years,the citrus industry has developed rapidly and has become the first fruit in China in terms of production and cultivation area.In order to obtain high yield,the application of chemical fertilizers in production is generally excessive,but the utilization rate is much lower than that of developed countries and regions such as the United States and the European Union.Excessive application of chemical fertilizers has caused problems such as soil structure damage and environmental pollution,which in turn has led to many adverse effects such as yield decline and soil degradation.Organic fertilizer is an effective way to promote chemical fertilizer efficiency and reduction,and to achieve green and sustainable production of citrus,which can change the bulk and rhizosphere soil microbial community structure,improve soil fertility and crop yield and quality.Bulk and rhizosphere soil microorganisms play an extremely important role in the growth and development of plants,while there are few studies on the changes in citrus soil and microbial microorganisms after organic fertilizer application,and the studies in alkaline purple soils,which are widely distributed in the southwest,have not been reported.Therefore,in order to reduce chemical fertilizer application,improve fruit yield and quality,and improve soil environment,it is important to investigate how organic fertilizer application changes soil microbial community structure and function and its relationship with soil-tree nutrient status and fruit quality.Through two consecutive years（2021-2022）of field trials,we investigated the effects of common plant-derived organic fertilizer rapeseed cake（CZB）and animal-derived organic fertilizer cow manure（NF）on yield,fruit quality,leaf nutrients,and soil physicochemical properties of‘Orah mandarin’grown in alkaline purple soil by using 16s r RNA amplicons and metagenome sequencing.The changes in the soil microbial community were analyzed using 16s r RNA amplicons and metagenome sequencing to find the association between environmental factors and soil microbial community in combination with yield,fruit quality,leaf nutrients,and soil physicochemical properties,so as to identify candidate functional strains and explore their intrinsic connections,and the main findings were as follows:1.Analysis of fruit yield,quality,and leaf nutrients after organic fertilizer treatment revealed that NF treatment significantly increased the yield per plant,with an increase of66.22%in 2021.Both organic fertilizers improved fruit quality by increasing the appearance quality such as single fruit weight and fruit skin redness,enhancing the intrinsic quality such as vitamin C content and reducing titratable acid content,and better fruit flavor and merchantability.CZB treatment increased the content of phosphorus,calcium,magnesium,iron,manganese,and zinc in the leaves,and NF treatment increased the content of magnesium and iron in the leaves.Both organic fertilizers significantly increased the relative chlorophyll content of leaves and improved tree nutrition,and the effect was more obvious in 2022 after two consecutive years of application,with 54.69%and 35.80%increase in CZB and NF treatments,respectively,compared with the control.2.The analysis of soil bulk structure,nutrient content,and phosphatase activity of organic fertilizer from two sources showed that organic fertilizer could effectively improve the problem of high p H of alkaline soil,increase the effectiveness of phosphorus,calcium,and iron,increase phosphatase activity and improve soil bulk structure.Organic fertilizer application significantly reduced soil p H and increased organic matter content,with increases of 53.97%and 147.05%in CZB and NF organic matter in 2022,respectively.There was no significant difference in the effect of organic fertilizer application on the effective phosphorus in the bulk soil of‘Orah mandarin’Orchard in the first year of application,and the NF treatment significantly increased the effectiveness of phosphorus in the bulk soil of‘Orah mandarin’Orchard after two consecutive years of application by 114.79%to 60.70 mg·kg-1.Both CZB and NF treatments significantly increased the effectiveness of phosphorus in the rhizosphere soil of‘Orah mandarin’Orchard by 61.30%and 101.34%to 49.26 mg·kg-1 and 61.49 mg·kg-1,respectively.The effective calcium and iron contents in NF were also significantly increased to 31.98%and120.22%,respectively,and collectively,the NF treatment was more effective than the CZB treatment in improving soil fertility.Soil alkaline phosphatase activity was significantly higher in the bulk and rhizosphere soils,and the correlation analysis results indicated that p H was significantly negatively correlated with effective phosphorus content and alkaline phosphatase activity was significantly positively correlated with effective phosphorus content,reflecting the increase in phosphorus solubilization capacity caused by the decrease in p H and the increase in alkaline phosphatase activity.The application of organic fertilizer also significantly increased the percentage content of water-stable agglomerates with particle size>0.25 mm,with CZB and NF increasing by26.66%and 98.76%,respectively,in 2022,and the mean weight diameter（MWD）and geometric mean diameter（GMD）were also improved,with better agglomerate stability,and the soil agglomerate improvement effect was ranked as NF>CZB.3.Sequencing of bacterial amplicons from bulk and rhizosphere soils showed that there was no significant difference inα-diversity among treatments under organic fertilizer application,but significantly reduced rhizosphere soil bacterial richness and diversity and changedβ-diversity,indicating that microbial community composition differed among organic fertilizer treatments and different sampling sites.The relative abundance of bacterial composition changed under different treatments,with Actinobacteriota,Proteobacteria,Acidobacteriota,and Crenarchaeota as the top 4bacterial taxa in terms of abundance.The results of the difference analysis showed that there were differentially dominant bacteria,such as Cupriavidus and Dongia,in both CZB and NF treatments.4.The results of correlation analysis between environmental factors and microbial communities showed that fruit yield,quality,and leaf nutrient uptake were mainly influenced by rhizosphere soil microbial communities,among which,rhizosphere soil microbial communities mainly had significant effects on titratable acid content in intrinsic quality,and on magnesium,iron and relative chlorophyll content of leaf nutrients,and soil p H,organic matter,alkaline dissolved nitrogen,effective calcium,effective magnesium,effective iron,effective manganese,effective zinc,and effective copper content were correlated with the rhizosphere soil microbial community,while the effective phosphorus content was correlated with the corresponding microbial community.Microorganisms related to soil physicochemical properties,leaf nutrients,fruit yield,and quality exist in the bulk and rhizosphere soil microorganisms.Integrating the whole ecosystem,it is hypothesized that Dongia,Cupriavidus,and Streptomyces may be the citrus rhizosphere-promoting bacteria that increase soil nutrient effectiveness,promote leaf nutrient uptake and improve fruit quality.5.Microbial metagenome analysis showed that the abundance of both small molecule organic acids and metabolic pathways related to phosphorus metabolism increased after organic fertilizer application.The differential metabolic pathways were related to organic acid secretion and organic phosphorus mineralization,and it was hypothesized that the activation of soil microorganisms by organic fertilizer application caused an increase in microbial organic acid secretion,which lowered soil p H and increased the solubility of insoluble phosphorus on the one hand,and secreted various enzymes such as phospholipase on the other hand,which promoted the mineralization of organic phosphorus and increased the effectiveness of phosphorus,and the differential dominant strains Cupriavidus and Streptomyces played a key role in this study.In conclusion,this study analyzed the changes in soil,tree nutrient elements,and fruit quality as well as soil microorganisms through the application of organic fertilizers in citrus orchards,elaborated the mutual influence between environmental factors and microorganisms,identified differentially dominant microorganisms,and initially explored their intrinsic connections,which provided a theoretical basis for further screening of beneficial microorganisms and exploration of plant-microbial influence mechanisms in citrus orchards in the future. |
PDF Full Text Request