Effects of complex bacterium inoculants on rhizosphere soil nutrients and yield of Angelica sinensis in continuous croppin

Abstract:

[Background] Continuous cropping causes imbalance in microbial community structure, deterioration of soil environment, poor nutrient cycling, and thus the yield reduction of Angelica sinensis (Oliv.) Diels. Therefore, it is imperative to improve soil by modern microbial technology and reduce continuous cropping obstacles. [Objective] To explore the effects of complex bacterium inoculants on rhizosphere soil enzyme activities, available nutrients, and yield of A. sinensis, clarify the yield-improving mechanism, and improve the measures for increasing yield. [Methods] The phosphorus-solubilizing activity of different strains was detected based on the halo zone, nitrogen-fixing activity by acetylene reduction assay, and peroxidase activity and nitrifying ability with kits. Complex bacterium inoculants T1 (Pseudomonas fluorescens CBS5, P. alcaligenes CBS7, P. extremaustralis CBSB, Zoogloea ramigera CBS4), T2 (P. fluorescens CBS5, P. alcaligenes CBS7, P. extremaustralis CBSB), and CK (sterile potato dextrose broth) were used to treat A. sinensis. The activities of enzymes related to nutrient cycling and transformation, and the content of available nutrients such as nitrogen, phosphorus and potassium in rhizosphere soil were determined by spectrophotometry. The yield was measured with conventional method. Statistical software was employed for variance analysis and principal component analysis of data. [Results] CBS7 had poor phosphorus-solubilizing ability. All the strains had nitrogen-fixing ability, peroxidase activity, and nitrifying ability, which were particularly prominent in CBS4. Compared with the CK, T1 and T2 significantly increased the activities of enzymes related to soil carbon and nitrogen metabolism and decreased the activity of soil alkaline phosphatase at the vigorous growth stage and late growth stage of A. sinensis root. They improved the content of available potassium, nitrate nitrogen, ammonium nitrogen, and available nitrogen in soil, content of ammonium nitrogen and nitrate nitrogen in root, and the nitrate reductase activity in root. Moreover, they promoted the root growth of A. sinensis and increased the yield. Compared with T2, T1 significantly enhanced the activities of sucrase and urease in soil, and raised the content of ammonium nitrogen and available nitrogen in soil and the content of ammonium nitrogen in root during the vigorous growth stage of root, and T1 improved the content of nitrate nitrogen and available nitrogen in soil, content of ammonium nitrogen and nitrate nitrogen in root, and nitrate reductase activity in root at the late growth stage of root. [Conclusion] T1 and T2 activated potassium in rhizosphere soil and improved the proportion of nitrate nitrogen in rhizosphere soil by nitrification to alleviate the toxicity of the high-concentration ammonium salt to root. The ratio of nitrate nitrogen to ammonia nitrogen in root was increased by active transport of nitrate nitrogen in A. sinensis. Then the nitrate reductase activity in root was improved, promoting the transformation of nitrate nitrogen to ammonium nitrogen and nitrogen utilization. In a word, T1 and T2 promoted the absorption and utilization of nutrients, particularly T1.