Integrated Effects of Co-Inoculation with Phosphate-Solubilizing Bacteria and N2-Fixing Bacteria on Microbial Population and Soil Amendment Under C Deficiency

Abstract

The inoculation of beneficial microorganisms to improve plant growth and soil properties is a promising strategy in the soil amendment. However, the effects of co-inoculation with phosphate-solubilizing bacteria (PSB) and N2-fixing bacteria (NFB) on the soil properties of typical C-deficient soil remain unclear. Based on a controlled experiment and a pot experiment, we examined the effects of PSB (M: Bacillus megaterium and F: Pseudomonas fluorescens), NFB (C: Azotobacter chroococcum and B: Azospirillum brasilence), and combined PSB and NFB treatments on C, N, P availability, and enzyme activities in sterilized soil, as well as the growth of Cyclocarya Paliurus seedlings grow in unsterilized soil. During a 60-day culture, prominent increases in soil inorganic N and available P contents were detected after bacteria additions. Three patterns were observed for different additions according to the dynamic bacterial growth. Synergistic effects between NFB and PSB were obvious, co-inoculations with NFB enhanced the accumulation of available P. However, decreases in soil available P and N were observed on the 60th day, which was induced by the decreases in bacterial quantities under C deficiency. Besides, co-inoculations with PSB and NFB resulted in greater performance in plant growth promotion. Aimed at amending soil with a C supply shortage, combined PSB and NFB treatments are more appropriate for practical fertilization at intervals of 30–45 days. The results demonstrate that co-inoculations could have synergistic interactions during culture and application, which may help with understanding the possible mechanism of soil amendment driven by microorganisms under C deficiency, thereby providing an alternative option for amending such soil.

Effects of Phosphate-Solubilizing Bacteria and N2-fixing Bacteria on Nutrient Uptake, Plant Growth, and Bioactive Compound Accumulation in Cyclocarya paliurus (Batal.) Iljinskaja

“…According to a previous study [23], the bacterial population hit a peak at days 30-45 of incubation. Available soil N and P contents and related enzyme activity were significantly increased in co-inoculations with PSB and NFB.…”

“…The present study found that co-inoculation with PSB and NFB resulted in higher SAP than the others, while treatment CB achieved the highest value of SAN. Based on our previous study, synergistic effects between PSB and NFB may contribute to higher availability of soil nutrients and stimulate plant growth [23]. Several studies reported that inoculating plants with both PSB and NFB could result in higher available N and P contents in soil and nutrient uptake in plants [18,54].…”

“…The medium for plant growth in pot-experiment was a mixture of soil, sand, organic fertilizer, and coconut residuum (7:2:0.8:0.2, v/v). The soil was collected from the plow layer of soil (0-20 cm) at C. Paliurus plantation in Nanjing, China (31 • 35 N, 119 • 10 E), more information was presented in our previous study [23]. The organic fertilizer added to the medium was used to improve the survival and multiplication of bacteria.…”

“…The basic physicochemical properties of medium were as follows: pH 5.98, total C of 18.9 g•kg −1 The bacterial strains used in this study were Bacillus megaterium W17 [18], Pseudomonas fluorescens W12 [24], and Azotobacter chroococcum HKN-5 [25] and Azospirillum brasilence CW903 [26]. These bacteria have been documented with the ability of improving soil nutrients such as N and P, and none of these bacterial strains showed any antagonistic effects against one another [23]. Prior to use, bacteria strains were incubated in lysogeny-broth medium (LB, pH 7.0, comprised of 10 g tryptone, 5 g yeast extract, and 10 g NaCl per liter) to the mid-exponential growth phase.…”

Succession of the Resident Soil Microbial Community in Response to Periodic Inoculations

“…The influences of different microbial inoculants on soil properties under controlled conditions and the practical effects on plant nutrient uptake under natural conditions have been thoroughly evaluated ( 31 – 33 ). In this study, we sought to investigate the dynamics of soil nutrients, plant growth, and the soil-resident bacterial community in response to successive microbial inoculations over the course of a growing season.…”