State Key Laboratory of Sustainable Dryland Agriculture (in preparation), College of Resources and Environment, Shanxi Agricultural University, Taiyuan 030031, China.
State Key Laboratory of Sustainable Dryland Agriculture (in preparation), College of Resources and Environment, Shanxi Agricultural University, Taiyuan 030031, China; Jiangsu Provincial Key Lab for Organic Solid Waste Utilization, National Engineering Research Center for Organic-based Fertilizers, Jiangsu Collaborative Innovation Center for Solid Organic Waster Resource Utilization, Nanjing Agricultural University, Nanjing 210095, China.
Sci Total Environ. 2022 Sep 15;839:156209. doi: 10.1016/j.scitotenv.2022.156209. Epub 2022 May 27.
The 'enzyme latch' theory believes that oxygen constraints on phenol oxidase can restrain the activity of hydrolytic enzymes responsible for decomposition, while the 'iron (Fe) gate' theory suggests that Fe oxidation can decrease phenol oxidase activity and enhance Fe-lignin complexation under oxygen exposure. The objective of this study was to explore the roles of the 'enzyme latch' and 'Fe gate' mechanisms in regulating soil organic carbon (SOC) sequestration in a rice-wheat cropping system subjected to six fertilization treatments: control (CT), chemical fertilizer (CF), CF plus manure (CFM), CF plus straw (CFS), CF plus manure and straw (CFMS), and CF plus organic-inorganic compound fertilizer (OICF). Soil samples were collected after the rice and wheat harvests and wet sieved into large macroaggregates, small macroaggregates, microaggregates, and silt and clay particles. Variations in amorphous and free Fe oxides, Fe-bound organic carbon and phenol oxidase activity were examined. After nine years, compared with the initial soil, the activation degree of free Fe oxides increased by 1.3- to 1.6-fold and the topsoil SOC stock increased by 13-61% across all treatments. Amorphous Fe oxide content, phenol oxidase activity and aggregate mean-weight diameter were higher after the wheat harvest than after the rice harvest. Amorphous Fe oxide content was positively correlated with Fe-bound organic carbon content (P < 0.001) but negatively correlated with phenol oxidase activity (P < 0.001). Therefore, seasonal alternation of wetting and drying can progressively drive the rejuvenation of Fe oxides and simultaneously affect the activity of phenol oxidase. Oxidative precipitation of amorphous Fe oxides promoted the formation of organo-Fe complexes and macroaggregates, while flooding of the paddies decreased the activity of phenol oxidase, thereby resulting in year-round hindered decomposition. Organic fertilization strengthened the roles of the 'Fe gate' and 'enzyme latch' mechanisms, and thus accelerated SOC sequestration in the rice-wheat cropping system.
“酶锁”理论认为，氧对多酚氧化酶的限制可以抑制负责分解的水解酶的活性，而“铁（Fe）门”理论则表明，在有氧暴露下，Fe 氧化可以降低多酚氧化酶的活性，并增强 Fe-木质素络合物的形成。本研究的目的是探讨“酶锁”和“Fe 门”机制在调节水稻-小麦轮作系统中土壤有机碳（SOC）固存中的作用，该系统接受了六种施肥处理：对照（CT）、化肥（CF）、化肥+有机肥（CFM）、化肥+秸秆（CFS）、化肥+有机肥和秸秆（CFMS）和化肥-有机-无机复混肥（OICF）。在水稻和小麦收获后采集土壤样品，并通过湿筛分成大团聚体、小团聚体、微团聚体和粉粒和粘粒。检测了无定形和游离 Fe 氧化物、Fe 结合有机碳和多酚氧化酶活性的变化。经过九年的时间，与初始土壤相比，所有处理的游离 Fe 氧化物的活化程度增加了 1.3-1.6 倍，表层土壤 SOC 储量增加了 13-61%。在小麦收获后，无定形 Fe 氧化物含量、多酚氧化酶活性和团聚体平均重量直径均高于水稻收获后。无定形 Fe 氧化物含量与 Fe 结合有机碳含量呈正相关（P < 0.001），与多酚氧化酶活性呈负相关（P < 0.001）。因此，干湿交替的季节性变化可以逐渐促进 Fe 氧化物的更新，并同时影响多酚氧化酶的活性。无定形 Fe 氧化物的氧化沉淀促进了有机-Fe 配合物和大团聚体的形成，而稻田的淹没降低了多酚氧化酶的活性，从而导致全年的分解受阻。有机施肥增强了“Fe 门”和“酶锁”机制的作用，从而加速了水稻-小麦轮作系统中 SOC 的固存。
