Biochar stimulates the decomposition of simple organic matter and suppresses the decomposition of complex organic matter in a sandy loam soil

Abstract

Incorporating crop residues and biochar has received increasing attention as tools to mitigate atmospheric carbon dioxide (CO 2 ) emissions and promote soil carbon (C) sequestration. However, direct comparisons between biochar, torrefied biomass, and straw on both labile and recalcitrant soil organic matter (SOM) remain poorly understood. In this study, we explored the impact of biochars produced at different temperatures and torrefied biomass on the simple C substrates (glucose, amino acids), plant residues (Lolium perenne L.), and native SOM breakdown in soil using a 14 C labeling approach. Torrefied biomass and biochars produced from wheat straw at four contrasting pyrolysis temperatures (250, 350, 450, and 550°C) were incorporated into a sandy loam soil and their impact on C turnover compared to an unamended soil or one amended with unprocessed straw. Biochar, torrefied biomass, and straw application induced a shift in the soil microbial community size, activity, and structure with the greatest effects in the straw-amended soil. In addition, they also resulted in changes in microbial carbon use efficiency (CUE) leading to more substrate C being partitioned into catabolic processes. While overall the biochar, torrefied biomass, and straw addition increased soil respiration, it reduced the turnover rate of the simple C substrates, plant residues, and native SOM and had no appreciable effect on the turnover rate of the microbial biomass. The negative SOM priming was positively correlated with biochar production temperature. We therefore ascribe the increase in soil CO 2 efflux to biochar-derived C rather than that originating from SOM. In conclusion, the SOM priming magnitude is strongly influenced by both the soil organic C quality and the biochar properties. In comparison with straw, biochar has the greatest potential to promote soil C storage. However, straw and torrefied biomass may have other cobenefits which may make them more suitable as a CO 2 abatement strategy.

Impact of Biochar Organic and Inorganic Carbon on Soil CO2and N2O Emissions

“…Specifically, biochar has been shown to cause selective positive priming of simple soil organic matter molecules and fresh plant residues (Arif et al, 2016; Cui et al, 2017; Farrell et al, 2015). Our findings of an apparent positive priming in response to bicarbonate‐soluble biochar OC amendment are in agreement with assertions that biochar LOC is largely responsible for observed positive priming effects of biochar (Cheng et al, 2016; Cross and Sohi, 2011). For the biochars studied here, positive priming with untreated biochar amendment was likely prevented by sorption of the biochar LOC pool to the solid biochar matrix that occurred when acid‐ or base‐extracted biochar LOC was added to soils separately.…”

Historical charcoal additions alter water extractable, particulate and bulk soil C composition and stabilization

“…Considering longevity of charcoal in soils and its capability to sorb non‐pyrolyzed organic matter, several authors ( Borchard et al, ; Cheng et al, ; Hardy et al, ; Kerré et al., ) concluded that the presence of charcoal in soils most likely affects quantity and quality of dissolvable organic matter. In the present study, the presence of charcoal in soils of abandoned kiln sites reduced the total amount of WEOC relative to the corresponding reference soils, as also reported by Kerré et al ().…”

“…Lignin‐like compounds found in all samples indicate the ubiquitous presence of transitional forms of plant biomass and lignin‐like compounds released from charcoal that are enriched and formed during SOM stabilization processes ( Blume et al, ; Ohno et al, ; Lu et al, ). However, the less‐evident presence of condensed hydrocarbon signals in the water extracts of charcoal enriched soils may indicate a sorption of highly aromatic humified fragments onto charcoal particles (both are poorly water‐soluble) and thus stabilization of complex organic molecules by charcoal ( Cheng et al, ). However, varying abundances of condensed hydrocarbons with less abundance in topsoil than in subsoil may indicate their decomposition in topsoil or their translocation into subsoil.…”

“…Thus, the topsoil from the Eifel site, in particular, received substantial amounts of plant biomass as indicated by the presence of carbohydrates and aliphatic structures. Cheng et al, 2016;Hardy et al, 2017;Kerré et al, 2017) concluded that the presence of charcoal in soils most likely affects quantity and quality of dissolvable organic matter. In the present study, the presence of charcoal in soils of abandoned kiln sites reduced the total amount of WEOC relative to the corresponding reference soils, as also reported by Kerré et al (2017).…”

“…Stabilization and sequestration of non-charred organic C in charcoal enriched soils is presumably controlled by physical (e.g., aggregation) and chemical (e.g., sorption) processes (von Lü tzow et al, 2006;Borchard et al, 2014;Lu et al, 2014;Hagemann et al, 2017;Kerré et al, 2017). However, the sorption of non-charred organic C might be less effective on long-term perspective as Lehmann et al (2011) stated that non-charred organic C sorbed onto charred biomass remains partially accessible to microorganisms (De Laat et al, 1985;Cheng et al, 2016). Consequently, any net gain of noncharred C in charcoal enriched soils may explain the charcoal-induced capability to stabilize natural organic matter (Borchard et al, 2014;Hardy et al, 2017;Kerré et al, 2017).…”