Synergisms of Microbial Consortia, N Forms, and Micronutrients Alleviate Oxidative Damage and Stimulate Hormonal Cold Stress Adaptations in Maize.

Narges Moradtalab,Birgit Höglinger,Frank Walker,Uwe Ludewig,Joerg Geistlinger,Aneesh Ahmed,Günter Neumann

doi:10.3389/fpls.2020.00396

Abstract

AimsLow soil temperature in spring is a major constraint for the cultivation of tropical crops in temperate climates. This study aims at the exploitation of synergistic interactions of micronutrients, consortia of plant growth-promoting microorganisms and N forms as cold-stress protectants.MethodsMaize seedlings were exposed for two weeks to low root zone temperatures at 8–14°C under controlled conditions on a silty clay-loam soil (pH 6.9) collected from a maize field cultivation site. A pre-selection trial with fungal and bacterial PGPM strains revealed superior cold-protective performance for a microbial consortium of Trichoderma harzianum OMG16 and Bacillus spp. with Zn/Mn supplementation (CombiA+), particularly in combination with N-ammonium as a starting point for the characterization of the underlying physiological and molecular mechanisms.ResultsIn nitrate-treated plants, the cold stress treatment increased oxidative leaf damage by 133% and reduced the shoot biomass by 25%, related with reduced acquisition of phosphate (P), zinc (Zn) and manganese (Mn). The supplying of N as ammonium improved the Zn and Mn nutritional status and increased the ABA shoot concentration by 33%, as well as moderately increased detoxification of reactive oxygen species (ROS). Moreover, use of N as ammonium also increased the root auxin (IAA) concentration (+76%), with increased expression of auxin-responsive genes, involved in IAA synthesis (ZmTSA), transport (ZmPIN1a), and perception (ZmARF12). Additional inoculation with the microbial consortium promoted root colonization with the inoculant strain T. harzianum OMG16 in combination with ammonium fertilization (+140%). An increased ABA/cytokinin ratio and increased concentrations of jasmonic (JA) and salicylic acids (SA) were related to a further increase in enzymatic and non-enzymatic ROS detoxification. Additional supplementation with Zn and Mn further increased shoot IAA, root length and total antioxidants, resulting in the highest shoot biomass production and the lowest leaf damage by oxidative chemical species.ConclusionOur results suggest the mitigation of cold stress and reduction of stress priming effects on maize plants due to improved ROS detoxification and induction of hormonal stress adaptations relying on the strategic combination of stress-protective nutrients with selected microbial inoculants.

Highlights

The cultivation of tropical and subtropical crops in agricultural production systems under temperate climates continuously increases and is further promoted by global warming
Due to the importance of micronutrients as co-factors for enzymatic and non-enzymatic detoxification of reactive oxygen species (ROS), oxidative stress appears in consequence of ROS overproduction, which causes a severe damage to membranes, organelles, and cell functions (Cakmak, 2000; Gong et al, 2005)
The first experiment addressed the impact of ammonium fertilization versus nitrate supply on the cold-protective performance of the CombiA+ consortium

Summary

Introduction

The cultivation of tropical and subtropical crops in agricultural production systems under temperate climates continuously increases and is further promoted by global warming Under these conditions, short vegetation periods due to low temperatures in early spring remain a major challenge for crops, such as maize, tolerating soil temperatures not much lower than 15◦C for normal germination and early growth (Cutforth et al, 1986; Kaspar and Bland, 1992). Short vegetation periods due to low temperatures in early spring remain a major challenge for crops, such as maize, tolerating soil temperatures not much lower than 15◦C for normal germination and early growth (Cutforth et al, 1986; Kaspar and Bland, 1992) This is further complicated by the more widespread adoption of no-tillage or conservation tillage, leading to a slower seedbed warming in spring (Hayhoe et al, 1996). Impairment of photosynthesis due to oxidative leaf damage and impaired auxin production related to zinc limitation are factors further contributing to inhibition of root growth, impaired nutrient acquisition and limited plant regrowth (Moradtalab et al, 2018)

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