土壤矿物质-可溶态生物炭的交互作用及其对碳稳定性的影响

将生物质转化为生物炭并输入土壤被认为是一种很有前景的碳封存技术.生物炭颗粒在土壤中会不断释放出可溶态生物炭,这部分生物炭不稳定,易被微生物分解.探明土壤组分矿物质对可溶态生物炭稳定性的影响对评估生物炭的碳封存作用具有重要意义.因此,本文以核桃壳生物炭为研究对象,通过批次吸附实验及微生物降解实验研究了2种代表性土壤矿物质高岭土和针铁矿与核桃壳生物炭可溶有机组分的结合机理,以及这种结合作用对可溶态生物炭稳定性的影响.结果表明:低浓度(如20 mg·L-1)可溶态生物炭条件下,高岭土与可溶态生物炭之间以Ca2+架桥作用为主,约占吸附总量的65%;高浓度(如80 mg·L-1)条件下,以范德华力为主,约占吸附总量的76%.随着可溶态生物炭初始浓度的升高,针铁矿对其吸附量先升高后下降,且以范德华力为主,Ca2+会抑制针铁矿对可溶态生物炭的吸附.被矿物质吸附后的可溶态生物炭,其微生物降解性显著下降,可降解的碳下降了47.9%~85.3%,土壤矿物质能够吸附保护可溶态生物炭,提高其在土壤中的稳定性.

Interactions between soil minerals and dissolvable biochar and its influence on carbon stability

Converting biomass into biochar and then inputting it into soil has been considered as a potential way for carbon sequestration. However, the dissolvable fraction of biochar could be unstable and readily degradable compared to the bulk biochar. In order to fully assess the long-term ability of biochar for carbon sequestration, it is important to elucidate the effect of soil mineral on the stability of dissolvable biochar. This study focused on the bonding mechanisms between dissolvable walnuts biochar and two typical soil minerals (kaolinite and goethite) and then the stability of dissolvable biochar associated with the minerals. The results showed that the sorption of dissolvable biochar by kaolinite increased with the initial increasing biochar concentrations. Ca²⁺ bridging was the main process for the sorption at low concentration (e.g. 20 mg·L^-1), accounting for about 65% of the total sorption. About 76% of dissolvable biochar was sorbed via the van der Waals force at high concentration (e.g. 80 mg·L^-1). For the goethite mineral, the sorption increased as the initial biochar concentrations increased until 80 mg·L^-1, and then decreased. Ca²⁺ inhibited the sorption of dissolvable biochar by goethite. The existence of minerals could reduce the biodegradation of dissolvable biochar, with the reduction of biodegradation by 47.9%~85.3%. In conclusion, minerals can reduce the degradation of dissolvable biochar and thus improve the long-term carbon stability of biochar.