Abstract
Soil amendment with biochar can modify soil microbial abundance, activity and community structure. Nevertheless, the long-term evolution of these effects is unknown and of critical importance because biochar persists in soil for centuries. We selected nine charcoal kiln sites (CKS) from forest (4 sites) and cropland (5 sites) and determined microbial properties of their topsoil, largely enriched with charcoal for > 150 years. Adjacent soils were used as references unaffected by charcoal production. Soils were incubated in controlled conditions and emissions of CO2 were measured during 138 days. At day 68, an aliquot was sampled from each soil to determine microbial abundance and community structure by phospholipid fatty acid (PLFA) analysis. Before the extraction, one standard PLFA (C21:0 PC) was added to soil to test the influence of charcoal on PLFAs recovery. The content of uncharred SOC and pH explained a main part of the variance of soil CO2 emissions, which supports the view that charcoal had a limited effect on soil respiration. The recovery of C21:0 PC was increased in presence of aged charcoal, which contrasts with the decreased recovery recorded shortly after biochar application. This underlines that properties of charcoal evolve dramatically over time, and that a long-term vision is critical in the perspective of amending soils with biochar. Land-use had an overriding control on microbial community structure, surpassing the effect of a vast amount of charcoal present in the soil. In forest, 10 PLFAs from gram positive and general bacteria were significantly different between CKS and adjacent reference soils, whereas in cropland only four PLFAs from fungi, gram negative bacteria and actinomycetes were significantly affected. These results suggest that the long-term effect of charcoal on soil microbiota is overwritten by management practices. Biochar properties must therefore be regarded altogether with soil conditions to correctly design a successful soil amendment with biochar. Additionally, the absence of relationship between individual PLFAs and charcoal-C supports the idea that the long-term effect of charcoal is related to a modification of soil ecological niche (e.g. nutrient availability, pH) rather than to an alteration of the source of organic C available to biota.
Highlights
Biochar application to soil is a carbon negative technology used to tackle climate change while sustainably improving soil fertility (Lehmann et al, 2006)
phospholipid fatty acid (PLFA) were extracted at the Department of Soil Management of Ghent University, according to the procedure described in detail by Sleutel et al (2012), with the exception that we introduced a known amount of 1,2-dihenarachidoyl-sn-glycero-3-phosphocholine (C21:0 PC; Avanti Polar Lipids Inc.), a PLFA standard absent from soil, to test whether the presence of charcoal decreases the PLFA extraction efficiency, as it was observed for fresh biochars (Gomez et al, 2014)
Preindustrial charcoal kiln sites were used as a natural field experiment to investigate the long-term (>150 years) effect of charcoal on microbial properties of forest and cropland soils, which is an original approach to unravel the long-term fate of biochar in soil
Summary
Biochar application to soil is a carbon negative technology used to tackle climate change while sustainably improving soil fertility (Lehmann et al, 2006). The main source of the increase in CO2 emissions from a biochar amended soil seems to be the microbially mediated decomposition of labile biochar constituents (e.g., Cross and Sohi, 2011; Hilscher and Knicker, 2011). In a meta-analysis of 46 studies, Sagrilo et al (2014) showed that large additions of biochar to soil considerably increased CO2 emissions, whereas a low input of biochar relative to native soil organic carbon (SOC) content did not significantly affect emissions. Biochars produced at a higher temperature resulted in lower CO2 emissions (Fabbri et al, 2012), probably related to an increasing degree of aromaticity and aromatic condensation (Keiluweit et al, 2010; Wiedemeier et al, 2015) and the relative decrease of the labile fraction of biochar. Biochar application has contrasting effects on soil biology depending on its amount and quality as well as initial soil properties (Lehmann et al, 2011)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
