Abstract
A high level of antioxidants in organic-produced vegetables has been attributed to soil conditions; however, little is known about the relationships between antioxidants and rhizobacteria under different fertilization treatments. A pot trial for pakchoi (Brassica campestris ssp. chinensis L.) was conducted under greenhouse conditions with: (1) control; (2) chemical fertilizer; and (3) organic fertilizer. The responses of the plant, soil properties, and rhizobacterial community were measured after 45 days of cultivation. Fertilization increased soil nutrient levels and pakchoi productivity and the reshaped rhizobacterial community structure, while no differences in rhizobacterial abundance and total diversity were observed. Generally, most plant antioxidants were negatively correlated with inorganic nitrogen (N) and positively correlated to organic N in soil. The genera of Arthrospira and Acutodesmus contained differential rhizobacteria under chemical fertilizer treatment, which are known as copiotrophs. In addition, the addition of a chemical fertilizer may stimulate organic substance turnover by the enrichment of organic compound degraders (e.g., Microbacterium and Chitinophaga) and the promotion of predicted functional pathways involved in energy metabolism. Several beneficial rhizobacteria were associated with organic fertilizer amended rhizosphere including the genera Bacillus, Mycobacterium, Actinomycetospora, and Frankia. Furthermore, Bacillus spp. were positively correlated with plant biomass and phenolic acid. Moreover, predictive functional profiles of the rhizobacterial community involved in amino acid metabolism and lipid metabolism were significantly increased under organic fertilization, which were positively correlated with plant antioxidant activity. Overall, our study suggests that the short-term application of chemical and organic fertilizers reshapes the rhizobacterial community structure, and such changes might contribute to the plant’s performance.
Highlights
Organic farming is regarded as an environmentally friendly cultivation method with the application of organic fertilizers, the biocontrol of pests and disease, crop rotation, and residue mulch in comparison to conventional farming
Both chemical and organic fertilizers led to substantial increases in the yields of pakchoi compared to the control (53% and 67% dry weight, p < 0.05, Table 1)
The distinct responses of plant performance were primarily caused by the incorporation of chemical and organic fertilizers, respectively, we propose that the shift in rhizobacterial community composition might play important roles in mediating plant growth and health
Summary
Organic farming is regarded as an environmentally friendly cultivation method with the application of organic fertilizers, the biocontrol of pests and disease, crop rotation, and residue mulch in comparison to conventional farming. A previous study demonstrates that the main difference in the protein profiles between plants under organic and conventional farming is attributed to the fertilization regime, rather than pest control treatments and rotation practices [2]. We recently further demonstrated that the use of organic N (e.g., glycine) increased the levels of various antioxidants in lettuce when compared with the nitrate application [7]. These results suggest that the antioxidant level in plants might be influenced by the form and concentration of N in soil. Most available studies focus on the effects of fertilizers on the physicochemical characteristics of plant and soil, and little is known about how the soil microbial properties respond to different fertilizations
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