State Key Laboratory of Soil and Sustainable Agriculture, Changshu National Agro-Ecosystem Observation and Research Station, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Department of Soil Science of Temperate Ecosystems, Department of Agricultural Soil Science, University of Göttingen, Germany; Agro-Technological Institute, RUDN University, 117198 Moscow, Russia.
Sci Total Environ. 2021 Apr 10;764:144300. doi: 10.1016/j.scitotenv.2020.144300. Epub 2020 Dec 24.
Soil acidity is one of the vital factors that influence organic matter transformation and accumulation. Long-term studies on the mechanisms of biochar's effects on soil organic matter (SOM) accumulation dependent on pH values are lacking. A four-year column experiment was conducted without and with biochar application (11.3 Mg ha crop) in acid (pH = 5.24) and alkaline (pH = 8.22) soils under paddy rice/wheat annual rotation. To explore organic matter accumulation mechanisms, SOM pools were extracted (physical-chemical fractionation) and their chemical structures were analyzed using advanced solid-state C nuclear magnetic resonance (C NMR) techniques. Biochar increased the proportion of aromatic carbon (C) in all SOM pools, which led to an increased C content in two soils. The elevated pH after biochar application (∆pH = 1.03) increased Fe (III) oxidation and precipitation, and therefore, stimulated amorphous Fe content in 53-μm pool in the acid soil. This change increased the interaction between organic compounds and Fe (hydr)oxide, which impeded bacteria access to substrates, and in turn, promoted SOM accumulation in the acid soil. Conversely, low Fe (hydr)oxide availability resulted in the decomposition of the labile substrates (di-O-alkyl C, NCH, and OCH) in mobile humic acids via microbial respiration, thereby lowering the effect of SOM sequestration in the alkaline soil. Our study revealed that organic matter accumulation after biochar amendment is not solely dependent on the chemical recalcitrance of biochar, but also is controlled by the transformation of Fe (hydr)oxide in SOM pools.
土壤酸度是影响有机质转化和积累的重要因素之一。关于生物炭对土壤有机质（SOM）积累的影响机制依赖于 pH 值的长期研究还很缺乏。在水稻/小麦轮作下，在酸性（pH = 5.24）和碱性（pH = 8.22）土壤中进行了为期四年的不添加和添加生物炭（11.3 Mg ha-1 作物）的柱状实验。为了探究有机质积累机制，采用先进的固态 C 核磁共振（C NMR）技术对 SOM 库进行了提取（物理化学分级）和化学结构分析。生物炭增加了所有 SOM 库中芳香碳（C）的比例，导致两种土壤中的 C 含量增加。生物炭施用后 pH 值升高（∆pH = 1.03），促进了 Fe（III）的氧化和沉淀，从而增加了酸性土壤中 53-μm 级团聚体中非晶质 Fe 的含量。这种变化增加了有机化合物与 Fe（氢）氧化物之间的相互作用，阻止了细菌对底物的利用，从而促进了酸性土壤中 SOM 的积累。相反，低 Fe（氢）氧化物的可用性导致可移动腐殖酸中易分解的底物（二-O-烷基 C、NCH 和 OCH）通过微生物呼吸分解，从而降低碱性土壤中 SOM 固定的效果。本研究表明，生物炭添加后有机质的积累不仅依赖于生物炭的化学稳定性，还受 SOM 库中 Fe（氢）氧化物的转化控制。
