Effects of microbial agents on nutrient and bacterial community diversity in rhizosphere soil of eggplant cultivated in facilities

Abstract:

[Background] Continuous cropping and excessive application of chemical fertilizers of eggplant in greenhouse cause a series of soil quality problems such as imbalance of soil nutrients, decrease of microbial diversity and serious soil-borne diseases. The application of microbial agents can improve soil environmental quality. [Objective] To investigate the effect of microbial agents application on the soil nutrients and bacterial community diversity of eggplant planting soil. [Methods] In the Dahe Experimental Station of Hebei Academy of Agricultural and Forestry Sciences, the microbial agents containing Trichoderma harzianum and Bacillus megaterium were used as fertilizers for eggplant planting in greenhouse. The soil nutrient were detected by traditional chemical methods. The number of culturable microorganisms in soil was measured by dilution plate method and the bacterial diversity and community distribution in rhizosphere were determined by high-throughput sequencing on PCR-amplified 16S rRNA gene V3?V4 fragments. [Results] Compared with control group, microbial agents treatment increased the nutrients of rhizosphere soil in eggplant flowering and seedling-pulling stages. The total nitrogen, alkali-hydrolyzed nitrogen, available phosphorus and available potassium in the soil of microbial agents treatment at seedling-pulling stage increased by 13.85%, 21.07%, 31.51% and 55.94% respectively compared with that of control. Application of microbial agents changed the quantity and composition of culturable microorganisms in soil. Microbial agents increased the number of bacteria, fungi, actinomycetes and the proportion of bacteria and actinomycetes in the total microbial number. The Shannon index was higher and the Simpson index was lower in microbial agents treatment than that in control group. However, ACE index and Chao1 index had no significant difference between microbial agents treatment and control. The results indicated that microbial agents can increase the diversity of soil microbial communities, and have no significant impact on microbial community richness. Analysis of microbial communities of soil treated with microbial agents or not showed that microbial agents treatment increased the content of Xanthomonadales, Rhodospirillales, Sphingobacteriales, Bacillales, Cytophagales, Pseudomonadale and decreased the content of Burholderiales and Flavobacteriales in soil. The application of microbial agents could promote the vegetative growth of eggplant and increase the yield of eggplant by 18.52%. [Conclusion] As a new type of environmental protection fertilizer, microbial agents can improve soil nutrition, increase the number of culturable microorganisms and improve soil microbial diversity. The results provided a scientific basis for the rational application of microbial agents.