Biochar is colonized by select arbuscular mycorrhizal fungi in agricultural soils

Abstract

Arbuscular mycorrhizal fungi (AMF) colonize biochar in soils, yet the processes governing their colonization and growth in biochar are not well characterized. Biochar amendment improves soil health by increasing soil carbon, decreasing bulk density, and improving soil water retention, all of which can increase yield and alleviate environmental stress on crops. Biochar is often applied with nutrient addition, impacting mycorrhizal communities. To understand how mycorrhizas explore soils containing biochar, we buried packets of non-activated biochar in root exclusion mesh bags in contrasting agricultural soils. In this greenhouse experiment, with quinoa (Chenopodium quinoa) as the host plant, we tested impacts of mineral nutrient (as manure and fertilizer) and biochar addition on mycorrhizal colonization of biochar. Paraglomus appeared to dominate the biochar packets, and the community of AMF found in the biochar was a subset (12 of 18) of the virtual taxa detected in soil communities. We saw differences in AMF community composition between soils with different edaphic properties, and while nutrient addition shifted those communities, the shifts were inconsistent between soil types and did not significantly influence the observation that Paraglomus appeared to selectively colonize biochar. This observation may reflect differences in AMF traits, with Paraglomus previously identified only in soils (not in roots) pointing to predominately soil exploratory traits. Conversely, the absence of some AMF from the biochar implies either a reduced tendency to explore soils or an ability to avoid recalcitrant nutrient sources. Our results point to a selective colonization of biochar in agricultural soils.

Keywords: Amplicon sequencing; Manure; Paraglomus; Quinoa; Soil microbiomes; Soil-derived AMF.

Fig. 1

Relative abundances of AMF virtual taxa from bulk greenhouse soils and biochar packets combined across class level between (a) treatment, (b) soil type, and (c) sample type. Treatment groups include soils treated with biochar, fertilizer, biochar with fertilizer, and an untreated control. Soil types describe the geographic source of the soil used in the greenhouse study, including Beaverlodge, Cranford, Olds, and Vauxhall, all of which are found in Alberta, Canada. The sample type refers to the soil and biochar compartments within each pot. NA indicates unassigned species level ASVs. Only main effects are illustrated

Fig. 2

Ordinations of (a) soil samples and (b) soil samples compared to biochar samples. (a) Distance based redundancy analysis (dbRDA) of significant environmental parameters and microbial communities. Standard error ellipses represent Beaverlodge (red), Cranford (blue), Olds (green), and Vauxhall (purple). Environmental parameters which significantly improved the model are visualized as vectors with black arrows: TC (Total Carbon), pH, Biomass (Total Plant Biomass). Soil amendments are visualized as C (Control; coral), B (Biochar; yellow), B + M (Biochar and Manure; cyan), B + F (Biochar and Fertilizer; grey). An ANOVA showed that the model was significant (F = 3.9967, P = 0.001) and both axes dbRDA 1 (F = 11.2125, P = 0.001) and dbRDA 2 (F = 2.4002, P = 0.006) were significant. Ellipses represent the standard deviation of variation within each group, centered at the group centroid. (b) Non-metric multidimensional scaling plot (NMDS) of AMF community composition between biochar packet and bulk soil sample types. Community composition changes significantly between biochar and soils (PERMANOVA, p < 0.05). Ellipses represent the standard deviation of variation within each group, centered at the group centroid