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

Klára Bradáčová,Katharina Tietz,Günter Neumann,Ellen Kandeler,Uwe Ludewig,Nils Berger,Maximilian Sittinger,Benjamin Neuhäuser

doi:10.3390/microorganisms7090329

Klára Bradáčová, Katharina Tietz + Show 6 more

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https://doi.org/10.3390/microorganisms7090329

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Journal: Microorganisms	Publication Date: Sep 7, 2019
Citations: 22	License type: CC BY 4.0

Affiliation: University of Hohenheim, Julius Kühn-Institut

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.

Highlights

The adoption of biostimulants (BS) based on bacterial and fungal inoculants or non-microbial bioactive compounds, has been discussed as a strategy to reduce the input of agrochemicals in crop production systems and related detrimental side effects on the environment [1,2]
Based on the results of the present study, the beneficial effects of the selected microbial consortia products (MCPs) inoculant on plant growth and nutrient acquisition were strongly dependent on the form of nitrogen fertilization, soil properties and the plant developmental stage, as has been previously shown for various single-strain inoculants [17,20,24]
Contrary to the initial hypothesis, compensating functions and preferential performance of the MCP inoculants in terms of plant growth promotion were not recorded on disturbed soils with limited nutrient availability, low microbial activity and low Corg

Summary

Introduction

The adoption of biostimulants (BS) based on bacterial and fungal inoculants or non-microbial bioactive compounds (e.g., humic acids, amino acids and peptides, chitosan, plant-, seaweed-, and compost-extracts), has been discussed as a strategy to reduce the input of agrochemicals in crop production systems and related detrimental side effects on the environment [1,2]. High variability and frequently limited reproducibility of the expected effects under real production conditions [5,6] suggests a strong impact of external factors, such as timing, dosage and mode of application, soil properties, fertilization management, environmental stress factors, interactions with the native soil microbiome, genotypic differences in responsiveness etc To address this problem, the concept of consortia products based on different microbial strains and non-microbial BS with complementary properties was discussed as a strategy to increase the efficiency and the flexibility of BS-based production strategies under variable environmental conditions. The composition of microbial consortia and non-microbial BS aims at the restoration of plant-beneficial, soil biological processes disturbed by soil degradation, intensive use of mineral fertilizers and chemical crop protection This may apply for processes of nutrient cycling and mineralization, biological nitrogen fixation, nutrient mobilization and the pathogen suppressive potential in agricultural soils [4,7,8]

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