Effects Of Alteration In Microbiome On Brassica And Maize Growth

A number of reports showed that soil microbes could impact plant growth, development, and immunity through nutrient competition, excreation of phytohormone and alelochemicals. However, previous studies majorly focused on the interaction of plant with specific isolated strain. Recently, some found close relationship between plant growth and microbial diversity and structure in different soils or under different managements, and claimed the important role of microbiome in plant growth. However, the effects of soil conditions could not be excluded in these studies. In the present study, we sterilized soil and inoculated entire soil microbial population to investigate the effects of altering entire microbiome(loss of the microbial diversity and microbial communities affected by long-term fertilization) on crop healthy and growth. Our results showed that:1. Compared with unsterilized soil, sterilized soil inoculated with 1-, 10-2-, 10-4- and10-6-fold dilution of a soil suspension reduced bacterial richness on average by 16.4%, 24.0%, 34.2% and 35.8%. In no insecticide control, Brassica growth in original unsterilized soil was slower than those in soils inoculated with different microbial dilutions. In the insecticide treatment, Brassica growth was again lowest in original unsterilized soil and was the highest in soil inoculated with 1-fold suspension. Soil available nitrogen was significant affected by microbial dilutions. Olsen P and available K did not change as dramatically as what observed in soil available nitrogen. The accumulations of the insecticides Acetamiprid and imidacloprid in Brassica tissues increased when microbes in soil were diluted, likely due to decreased degradation of the insecticides. Potential active insecticide-degrading bacteria were identified based with higher relative abundance compared with no insecticide control. These bacteria were clustered into three groups. The dominant group reached highest abundance in soils inoculated with 1-, 10-2-or 10-4-fold microbial dilutions, but abundance declined in soil inoculated with a 10-6-fold dilution. The second dominant group decreased steadily with decreasing biodiversity in soil. The third dominant group increased steadily with decreasing biodiversity in soil. The results showed that undesirable impact by the loss of soil biodiversity at an intermediate level could be alleviated by functional redundancy in the microbial community, likely through increase in growth of a dominant functional microbial group, but severe loss of soil biodiversity threatens environmental and food safety.2. In the present study, shoot and root biomass of maize grown in unsterilized soil were significantly higher than in sterilized soil inoculated with microbes from long-term fertilization treatment. In addition, soil microbial communities shaped by long-term fertilization could affect the growth of maize. Compared with no fertilization treatment, the shoot biomass of maize grown in soils inoculated with microbes from long-term manure and phosphorus and potassium treaments was increased by 34% and 26%. Soil microbial community shaped by different long-term fertilization significantly changed inorganic nitrogen concentration, but had little effects on soil available phosphorus. The concentration of ammonium nitrogen in unsterilized treatment was higher than other treatments. Maize biomass did not correlate with soil available nutrient and soil enzyme activity.Taken together, our results suggest that alteration in microbiome can affect crop growth in agricultural ecosystems. Hower, the mechanism underlying the microbial influence on plant growth seems to be much complex. The differences in plant growth could not be well explained by the distinctions in nutrient transformation and soil enzyme activities. In agroecosystem, strong disturbance by human activity has substantially changed diversity and structure of soil microbial community. Thus exploring the mechanism of how these changes affect on crop growth is neccessary and will provide theoretical basis for engineering soil microbiome in agricultural ecosystem in future.