The Impact of Soil-Applied Biochars From Different Vegetal Feedstocks on Durum Wheat Plant Performance and Rhizospheric Bacterial Microbiota in Low Metal-Contaminated Soil.

Arianna Latini,Annamaria Bevivino,Giovanni Bacci,Manuel Teodoro,Daniele Mirabile Gattia,Lukáš Trakal

doi:10.3389/fmicb.2019.02694

Abstract

Biochar shapes the soil environment and plant growth. Nevertheless, the mechanisms associated with an improved plant biomass and soil microbiome in low metal-contaminated soils are still unclear. In this study, the influence of biochar on soil physico-chemical properties, plant performance, and rhizosphere microbiota in durum wheat was investigated at the above- and belowground levels. Two kinds of biochar from different feedstocks (wood chips and wheat straw pellets) and two Italian durum wheat varieties, Duilio and Marco Aurelio, were analyzed in a greenhouse using a low-nutrient gleyic fluvisol containing a very small amount of Pb and Zn. Four different treatments were performed: soil-only control (C), soil amended with woody biochar equilibrated with nutrient solution (B1+) and non-activated (B1−), and soil amended with non-activated (B2−) wheat straw biochar. Seven weeks after seed germination, (1) the physico-chemical properties of soil, biochars, and mixtures were assessed; (2) the fresh and dry weight of aboveground plant tissues and roots and other morphometric traits were measured; and (3) metabarcoding of the 16S rRNA bacterial gene was performed on rhizosphere soil samples. The results showed that the biochar from wheat straw had stronger impact on both durum varieties, with higher electrical conductivity, higher levels of available K and Na, and a substantial increase of dissolved Na+, K+, and Cl− ions in pore water. Generally, biochar amendment decreased Zn availability for the plants. In addition, biochar improved plant growth in the early growth stage, and the more positive effect was achieved by combining wheat straw biochar with Marco Aurelio. Rhizosphere bacterial microbiota showed variation in alpha diversity only due to treatment; on the other hand, the differential analysis showed consistent variation among samples with significant effects on amplicon sequence variant (ASV) abundance due to the specific biochar treatment as well as the genotype. The pure B1−, due to its scarce nutrient content with respect to the richer types (B1+ and B2−), had a negative impact on microbiota richness. Our study highlights that an appropriate combination of biochar feedstock and crop species may lead to superior yield.

Highlights

In the last decade, biochar has been focused upon due to its great potential for climate change mitigation, and its application to soil has emerged as an attractive strategy for sequestering carbon, reducing greenhouse gas (GHG) emissions, and improving soil quality (Lehmann, 2007; Atkinson et al, 2010; Agegnehu et al, 2016)
To assess the possible changes caused by biochar incorporation and/or the durum genotype to the soil microbiome, we focused on the rhizosphere, which is the interface between plant roots and soil, since the microorganisms colonizing the rhizosphere may contribute to plant growth and health (Richter-Heitmann et al, 2016); different studies have already established that the rhizosphere corresponds to the plant-soil compartment harboring a higher richness (Qian et al, 2019)
Wheat straw biochar better adapted the soil for durum wheat plant growth than woody biochar, strongly increasing soil Electric Conductivity (EC) and the concentrations of important ions (Na+, K+, and Cl−) available to plants

Summary

Introduction

Biochar has been focused upon due to its great potential for climate change mitigation, and its application to soil has emerged as an attractive strategy for sequestering carbon, reducing greenhouse gas (GHG) emissions, and improving soil quality (Lehmann, 2007; Atkinson et al, 2010; Agegnehu et al, 2016). Several studies have reported that soil microorganisms are affected following biochar application, with it increasing or decreasing (Han et al, 2017; Kolton et al, 2017; Li et al, 2018) their biomass, while others have found that amendment with biochar had no significant effect (Lehmann et al, 2011). These variable microbial responses are controlled by multiple environmental factors like types and rates of biochar amendment, the initial edaphic conditions, land use and management regimes, and vegetation types. Very little is known about the mechanisms through which different types of biochar in the same soil environment affect the microbial abundance and community composition, and this has recently been reviewed by Abbreviations: ASV, amplicon sequence variant; B1−, untreated wood chip biochar; B1+, wood chip biochar activated by incubation with nutrient-rich solution; B2−, untreated wheat straw biochar; C/N, carbon to nitrogen ration; CEC, cation exchange capacity; DW, dry weight; EC, electrical conductivity; FLL, flag leaf length; FW, fresh weight; mFLW, maximum flag leaf width; PH, plant height; SOM, soil organic matter; tAGFW and tAGDW, total aboveground fresh and dry weight; tBGFW and tBGDW, total belowground fresh and dry weight; TC, total carbon; TN, total nitrogen; TOC, total organic carbon; V1, Duilio durum wheat variety; V2, Marco Aurelio durum wheat variety; WHC, water holding capacity

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Discussion

Conclusion