Maize Inoculation with Microbial Consortia: Contrasting Effects on Rhizosphere Activities, Nutrient Acquisition and Early Growth in Different Soils

Abstract

The benefit of plant growth-promoting microorganisms (PGPMs) as plant inoculants is influenced by a wide range of environmental factors. Therefore, microbial consortia products (MCPs) based on multiple PGPM strains with complementary functions, have been proposed as superior, particularly under challenging environmental conditions and for restoration of beneficial microbial communities in disturbed soil environments. To test this hypothesis, the performance of a commercial MCP inoculant based on 22 PGPM strains was investigated in greenhouse experiments with maize on three soils with contrasting pH, organic matter content and microbial activity, under different P and N fertilization regimes. Interestingly, the MCP inoculant stimulated root and shoot growth and improved the acquisition of macronutrients only on a freshly collected field soil with high organic matter content, exclusively in combination with stabilized ammonium fertilization. This was associated with transiently increased expression of AuxIAA5 in the root tissue, a gene responsive to exogenous auxin supply, suggesting root growth promotion by microbial auxin production as a major mode of action of the MCP inoculant. High microbial activity was indicated by intense expression of soil enzyme activities involved in C, N and P cycling in the rhizosphere (cellulase, leucine peptidase, alkaline and acid phosphatases) but without MCP effects. By contrast, the MCP inoculation did not affect maize biomass production or nutrient acquisition on soils with very little Corg and low microbial activity, although moderate stimulation of rhizosphere enzymes involved in N and P cycling was recorded. There was also no indication for MCP-induced solubilization of Ca-phosphates on a calcareous sub-soil fertilized with rock-phosphate. The results demonstrate that the combination of multiple PGPM strains with complementary properties as MCP inoculants does not necessarily translate into plant benefits in challenging environments. Thus, a better understanding of the conditions determining successful MCP application is mandatory.

Microbial consortia inoculants stimulate early growth of maize depending on nitrogen and phosphorus supply

“…This is in line with recent follow-experiments, which showed significant stimulatory effects on the respective enzymatic activities in the maize rhizosphere only in a soil substrate with extremely low background activities of the respective enzymes, reflecting a low microbial activity due to long-term dry storage of the respective soil for more than 20 years. By contrast, on a freshly collected field soil, as similarly used in the present study, the inoculant effects were completely superimposed by high background activities of the rhizosphere marker enzymes exceeding the recorded MCP-induced changes by two orders of magnitude (Bradáčová et al 2019b). This point to beneficial MCP effects on nutrient cycling and mineralisation preferentially expressed in heavily disturbed soil environments with limited microbial activities but not in fertile agricultural soils.…”

Fertilizer Potential of Struvite as Affected by Nitrogen Form in the Rhizosphere

“…+ absorption [21,22]. The range of the pH drop following NH 4 -N supply was similar [25,41] or higher [42] than that reported for ryegrass by other authors, which is likely due to the differences of pH buffering capacity between the studied soils [31,43,44]. 2.…”

“…The lower root biomass under NH 4 -N supply ( Table 5; Table 6) is consistent with the well-reported inhibition effect of aluminum toxicity on root growth [52] and may in turn impair P uptake by plants. For instance, in the rhizosphere of NH 4 -N fed maize, Bradáčová et al [43] found that the pH decrease from 6.1 to 4.6 resulted in a 60% reduction in root growth, which in turn limited P uptake by plants. Table 4.…”

Developmental plasticity of Brachypodium distachyon in response to P deficiency: Modulation by inoculation with phosphate‐solubilizing bacteria

“…(2012) in in vitro gnotobiotic conditions and Bradácová et al. (2019) in soils with low organic matter content. On the other hand, some studies have revealed a deleterious impact of inoculation with bacterial strains on plant growth under gnotobiotic conditions due to the accumulation of bacterial toxic metabolites (Rybakova et al., 2016; Timmusk et al., 2015).…”