Biochar built soil carbon over a decade by stabilizing rhizodeposits

Abstract

Biochar can increase the stable C content of soil. However, studies on the longer-term role of plant-soil-biochar interactions and the consequent changes to native soil organic carbon (SOC) are lacking. Periodic 13 CO 2 pulse labelling of ryegrass was used to monitor belowground C allocation, SOC priming, and stabilization of root-derived C for a 15-month period-commencing 8.2 years after biochar (Eucalyptus saligna, 550 • C) was amended into a subtropical ferralsol. We found that field-aged biochar enhanced the belowground recovery of new root-derived C ( 13 C) by 20%, and facilitated negative rhizosphere priming (it slowed SOC mineralization by 5.5%, that is, 46 g CO 2 -C m −2 yr −1 ). Retention of root-derived 13 C in the stable organo-mineral fraction (<53 µm) was also increased (6%, P < 0.05). Through synchrotron-based spectroscopic analysis of bulk soil, fieldaged biochar and microaggregates (<250 µm), we demonstrate that biochar accelerates the formation of microaggregates via organo-mineral interactions, resulting in the stabilization and accumulation of SOC in a rhodic ferralsol.

Biochar influences on soil CO2 and CH4 fluxes in response to wetting and drying cycles for a forest soil

“…reduced SOM decomposition and lower CO 2 effluxes), this period could be quite long. For our case, in which a positive priming was observed, which is consistent with expectations for a sandy soil 14 , the minimum period of climatic benefit could be less.…”

“…Further, our study did not consider the enhanced biomass growth commonly observed in response to biochar additions to forest soils 7 . In particular, it has been shown that biochar can stabilize root-derived carbon 14 , and even when biochar causes a short-term positive priming of native SOM, the biochar remains stable in soils over centuries 16 to millennial time scales 29 with a net positive impact on soil C stocks 16 .…”

“…Biochar also represents a global negative emission potential of 0.7 Pg C yr −1   12 , and has been shown to be effective for reducing soil fluxes of greenhouse gases in some contexts 13 . Research has shown that biochar additions can contribute to the stabilization of root-derived organic C, increasing the stable C content in soil 14 . Some studies have found that biochar additions can stimulate the decomposition of soil organic matter (SOM) in a process known as the “priming effect” 15 .…”

Functional differences in the microbial processing of recent assimilates under two contrasting perennial bioenergy plantations

“…Previous isotopic tracer studies have shown a strong coupling between recently fixed plant photosynthates and belowground C allocation to roots, soil microbes and respiratory fluxes (Bahn et al, 2013;Barthel et al, 2014;Epron et al, 2011;Hogberg et al, 2008;Jin and Evans, 2010;Sommer et al, 2016;Street et al, 2013;Subke et al, 2012;Tavi et al, 2013;Weng et al, 2017). The fate of this C is ultimately controlled by the composition and activity of soil biota, however our understanding of the below ground C flux and its partitioning amongst roots, mycorrhizae and free living soil microbes is still limited (De Deyn et al, 2008;Stuart Chapin et al, 2009).…”

Responses of soil carbon sequestration to climate‐smart agriculture practices: A meta‐analysis

“…Cover crops provide additional biomass inputs from above-and belowground (Blanco-Canqui, Mikha, Presley, & Claassen, 2011), increase carbon and nitrogen inputs, and enhance the biodiversity of agroecosystems (Lal, 2004). Biochar amendments affect SOC dynamics through two pathways: (a) improving soil aggregation and physical protection of aggregate-associated SOC against microbial attack; and (b) increasing the pool of recalcitrant organic substrates resulting in a low SOC decomposition rate and substantial negative priming (Du, Zhao, Wang, & Zhang, 2017;Weng et al, 2017;Zhang et al, 2012). Biochar amendments affect SOC dynamics through two pathways: (a) improving soil aggregation and physical protection of aggregate-associated SOC against microbial attack; and (b) increasing the pool of recalcitrant organic substrates resulting in a low SOC decomposition rate and substantial negative priming (Du, Zhao, Wang, & Zhang, 2017;Weng et al, 2017;Zhang et al, 2012).…”