How soil carbon is stabilized durin

How soil carbon is stabilized during centuries of cultivation and how this would be influenced by land use
largely remain unclear. Here the relative role of physical and chemical stabilization mechanisms in
agricultural soil organic carbon (SOC)accumulationwere studied by fractionation of paddy/upland cropland
soils along a 500-year soil chronosequence created by intermittent reclamation of estuarine wetlands. In
unreclaimed wetlands, about 50% of SOC was chemically-stabilized by binding to Fe/Al oxyhydrates (mainly
amorphous Fe) and 30% by unknown forms of chemical association with silt/clay particles. Physical
stabilizationofSOC bysoil aggregationwasnegligibleinwetlands.Afterconversionofwetlandstocroplands,
SOC rapidly declined within the
first 16 years and then recovered slowly with cultivation time. Chemical
mechanismsstilldominatedSOC stabilizationprocessesduring500yearsofcultivation,butthecontribution
of Fe/Al-bound and Ca-bound carbon to total SOC decreased with time. The contribution of physically
stabilized carbon (i.e. microaggregate-occluded particulate organic carbon,iPOM) to SOCkept around 16% in
croplands even when microaggregate contents increased from 8.83% to 30.52% between 16 and 500 years.
The iPOM fractionwas not closely related to microaggregate formation but to free coarse particulate organic
matter, a carbon fraction indicative of inputs of plant materials. Consistently higher SOC density in paddy
soils than in upland soils was observed along the chronosequence, which could be accounted for by higher
contents of physical andchemical carbon fractions inpaddy
fields.The higher physically-stabilized carbon of
paddy soils probably resulted from larger stubble return rather than from stronger soil aggregation given
similar contents of microaggregates between the two cropland types. Notably, in both paddy and upland
soils, carbon concentrations of intra-microaggregate silt/clay particles were consistently higher than those
of free silt/clay particles. An implication was that despite the small proportion (

Results (Chinese) 1:

如何在几个世纪的栽培和如何，这会受到土地使用过程中稳定土壤碳很大程度上仍不清楚。这里的相对作用的物理和化学稳定机制在进行分馏的水稻/旱耕地的农业土壤有机碳 (SOC) accumulationwere沿着由间歇填海的河口湿地产生 500 年土壤上的土壤。在待复垦的湿地，约 50%的 SOC 是绑定到铁/铝 oxyhydrates 化学稳定 （主要无定形铁） 和 30%的未知形式的化学协会与淤泥的粘土。物理stabilizationofSOC bysoil aggregationwasnegligibleinwetlands。Afterconversionofwetlandstocroplands，SOC 迅速下降内第 16 个年头，随着培养时间的推移慢慢地恢复。化工mechanismsstilldominatedSOC stabilizationprocessesduring500yearsofcultivation butthecontributionFe/Al-绑定及 Ca 绑定总 SOC 的碳含量降低随着时间的推移。所作的贡献身体稳定的碳 （即有机质闭塞的颗粒有机碳、 iPOM） SOCkept 在 16%左右甚至当有机质含量由 8.83%增至 16 和 500 年之间的价值 3 052%的农田。不密切相关有机质形成但免费粗颗粒有机 iPOM fractionwas指示性的植物材料投入碳分数，事关重大。稻田的一贯高 SOC 密度。土壤比旱地土壤中被观测到沿上，可以占由更高理化碳组分稻田的内容字段。更高的身体稳定碳的水稻土可能导致较大茬返回而不是从给出的较强土壤聚合微团聚体两种退耕还林类型之间的类似内容。值得注意的是，在水田和旱地土壤碳内有机质淤泥黏土颗粒浓度始终高于免费的淤泥/粘土颗粒。言下之意，尽管比例很小 (< 20%在这里) 的物理-对农田的总 SOC 的稳定的碳，土壤聚合可以促进化学 SOC 稳定的创建闭塞的碳与土壤矿物集料内的亲密互动。总括来说，期间五个世纪的土壤培肥、 化学碳稳定是占主导地位的机制通过聚合控制水稻/旱地农田的有机碳的积累，但物理闭塞的碳可能有促进化学稳定化的 soc。

Results (Chinese) 3:

土壤碳是如何稳定在几个世纪的种植，这将如何影响土地利用在很大程度上仍然不清楚。这里的物理和化学稳定机制的相对作用农业土壤有机碳（SOC）积累均进行分馏水陆田在500年的土壤序列通过河口湿地土壤开垦了间歇。在荒地湿地，约50%的SOC是化学稳定结合铁/铝oxyhydrates（主要无定形铁）和30%的未知形式的化学与淤泥/粘土颗粒。物理stabilizationofsoc aggregationwasnegligibleinwetlands afterconversionofwetlandstocroplands土壤，迅速下降的系统内前16年，然后慢慢恢复与培养时间。化学mechanismsstilldominatedsoc stabilizationprocessesduring500yearsofcultivation，butthecontribution随着时间的推移，铁/铝结合态和钙结合碳对总有机碳含量的降低。物理贡献稳定碳（即微栓颗粒有机碳、IPOM）来sockept 16%左右农田即使微团聚体含量从8.83%增加到30.52%，16和500岁之间。该法利用密切相关的微团聚体的形成而无粗颗粒有机物质，一种表示植物材料输入的碳分数。不断提高水稻的土壤有机碳密度土高于旱地土壤观察沿时间，可以用较高的占物理和化学碳组分方式内容字段，较高的物理稳定碳水稻土可能是由较大的茬回报，而不是从更强的土壤聚集这两种农田类型之间的相似内容的影响。值得注意的是，在水田和旱地土壤微团聚体内淤泥/粘土颗粒的碳浓度始终高于游离的淤泥/粘土颗粒。一个含义是，尽管在身体上的比例很小（< 20%）—稳定的碳在农田土壤总有机碳含量，可以促进土壤有机碳的稳定的化学聚合在聚集内建立闭塞的碳和土壤矿物之间的亲密相互作用。结论，在期间五个世纪的土壤耕作，化学碳稳定是主导机制控制水稻旱作农田土壤有机碳的积累，但聚合碳物理遮挡可能促进了化学稳定的片上系统。