Responses of Low-Cost Input Combinations on the Microbial Structure of the Maize Rhizosphere for Greenhouse Gas Mitigation and Plant Biomass Production.

Caio Augusto Yoshiura,Maria Do Carmo Catanho Pereira De Lyra Lyra,Andressa Monteiro Venturini,Jorge Luiz Mazza Rodrigues,Siu Mui Tsai,Lucas Palma Perez Braga,Aline Giovana Da França

doi:10.3389/fpls.2021.683658

Abstract

The microbial composition of the rhizosphere and greenhouse gas (GHG) emissions under the most common input combinations in maize (Zea mays L.) cultivated in Brazil have not been characterized yet. In this study, we evaluated the influence of maize stover coverage (S), urea-topdressing fertilization (F), and the microbial inoculant Azospirillum brasilense (I) on soil GHG emissions and rhizosphere microbial communities during maize development. We conducted a greenhouse experiment and measured methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) fluxes from soil cultivated with maize plants under factorial combinations of the inputs and a control treatment (F, I, S, FI, FS, IS, FIS, and control). Plant biomass was evaluated, and rhizosphere soil samples were collected at V5 and V15 stages and DNA was extracted. The abundance of functional genes (mcrA, pmoA, nifH, and nosZ) was determined by quantitative PCR (qPCR) and the structure of the microbial community was assessed through 16S rRNA amplicon sequencing. Our results corroborate with previous studies which used fewer input combinations and revealed different responses for the following three inputs: F increased N2O emissions around 1 week after application; I tended to reduce CH4 and CO2 emissions, acting as a plant growth stimulator through phytohormones; S showed an increment for CO2 emissions by increasing carbon-use efficiency. IS and FIS treatments presented significant gains in biomass that could be related to Actinobacteria (19.0%) and Bacilli (10.0%) in IS, and Bacilli (9.7%) in FIS, which are the microbial taxa commonly associated with lignocellulose degradation. Comparing all factors, the IS (inoculant + maize stover) treatment was considered the best option for plant biomass production and GHG mitigation since FIS provides small gains toward the management effort of F application.

Highlights

Several inputs have been studied and documented to improve crop development and production, increasing soil health and plant resistance to pathogens and seasonal variations (Thangarajan et al, 2013; Wang et al, 2016; Abbott et al, 2018; Sharma and Bali, 2018)
Considering the total sum of greenhouse gas (GHG) emissions (Figure 2A), treatments containing A. brasilense (I/F + I (FI)/I + S (IS)/F + I + S (FIS)) presented, respectively, with a reduction of 11.9, 8.4, 16.2, and 1.6% in emissions compared to its “control treatment” without the inoculant (C, F, S, and F + S (FS), respectively), with the IS treatment demonstrating the most pronounced effect of GHG mitigation (p < 0.05)
Our results showed a high baseline effect promoted by the initial NPK fertilization in the furrow before seed sowing, which restricted our findings to each input effect

Summary

Introduction

Several inputs have been studied and documented to improve crop development and production, increasing soil health and plant resistance to pathogens and seasonal variations (Thangarajan et al, 2013; Wang et al, 2016; Abbott et al, 2018; Sharma and Bali, 2018). The excessive and indiscriminate use of synthetic nitrogen fertilizers can cause an imbalance in the nitrogen cycle at huge economic costs These are associated with human health problems due to drinking water contamination by high nitrate concentrations and environmental problems, such as freshwater eutrophication and climate change by the increase of nitrous oxide (N2O) and carbon dioxide (CO2) emissions (Galloway et al, 2008; Ward, 2009; Zamanian et al, 2018), enforcing the continuous search for alternatives to improve food production. Three inputs – synthetic nitrogen fertilizers, commercial microbial inoculants, and plant residues coverage from the adoption of no-tillage practices – have been commonly used in agricultural practices to increase crop yield and production. No-tillage areas in Brazil, the United States, and China are implemented in more than 50% of their total crop areas (He et al, 2010; USDA, 2010; Freitas and Landers, 2014)

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