松散土样和填装土柱及紧实程度对土壤有机碳矿化的影响
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1.中国科学院南京土壤研究所;2.河海大学农业科学与工程学院;3.中国农业大学土地科学与技术学院

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国家自然科学基金委员会-中国科学院大科学装置科学研究联合基金


Effects of loose soil samples, repacked soil columns and compactness on soil organic carbon mineralization
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1.Institute of Soil Science, Chinese Academy of Sciences;2.College of agricultural science and engineering, Hohai University;3.College of Land Science and Technology, China Agricultural University

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the NSFC-CAS Joint Fund Utilizing Large-scale Scientific Facilities

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    摘要:

    土壤有机碳(SOC)矿化一般通过培养松散土样来测定,但是松散土样与原状土的结构存在很大差异,二者之间SOC矿化的关系尚不明确;通过填装土柱可以获得接近田间状态的土壤样品,但填装的紧实程度会改变土壤孔隙结构,因此可能影响SOC矿化。本研究首先以施用不同量有机肥的红壤为研究对象,设置松散土样和填装土柱两个处理,采用室内培养法比较二者之间SOC矿化的差异;然后选择其中一种土壤填装土柱,设置四个紧实程度处理,分别为1.1(BD1.1)、1.3(BD1.3)、1.5(BD1.5)和1.7 g?cm-3(BD1.7),利用X射线显微CT(Computed Tomography, CT)成像技术分析土壤孔隙结构,分析紧实程度对土壤孔隙结构及SOC矿化的影响。结果表明,松散土样与填装土柱的SOC矿化量有显著差异,培养结束时(第57天),松散土样的有机碳累积矿化量约是填装土柱的4倍。紧实程度增加较大程度地降低了土壤的总孔隙度和大孔隙度,降低比例分别为12.9% ~ 17.4%和18.7% ~ 88.5%;并且使充气孔隙度从63.6%下降到了8.2%,而充水孔隙度从36.4%增加到了91.8%。填装土柱的SOC矿化量随紧实程度增加呈先增加后降低的趋势,培养结束时(第28天),BD1.5的SOC矿化量最高。回归分析的结果表明,SOC矿化量与总孔隙度、大孔隙度(>16 μm)、充水孔隙度(Water-filled pore space, WFPS)或充气孔隙度(Air-filled pore space, AFPS)之间存在显著的非线性关系。当总孔隙度或大孔隙度低于46%或3.7%时,SOC矿化量随孔隙度增加而增加;反之,SOC矿化量随孔隙度增加而降低。SOC矿化量与WFPS或APFS之间的关系呈现出类似的规律,当WFPS为66%或AFPS为34%时,SOC矿化量最高。以上结果说明,通过培养松散土样测定SOC矿化将会高估田间SOC的矿化潜力;紧实程度的变化会改变土壤的孔隙结构进而影响填装土柱的SOC矿化;SOC矿化量与孔隙度之间存在显著的非线性关系。

    Abstract:

    【Objective】Soil organic carbon (SOC) mineralization is generally measured by laboratory incubation of loose soil samples. However, the structure of loose soil samples is of great difference from that of bulk soil samples. The relationship between SOC mineralization of loose soil samples and bulk soil samples is not clear. Soil samples close to field conditions can be obtained by repacking soil columns. Nevertheless, compactness can affect soil pore structure and may influence SOC mineralization. Therefore, this study aimed to evaluate whether it is accurate to represent SOC mineralization in the field by incubating loose soil samples and how compactness influences soil pore structure or SOC mineralization in repacked soil columns. 【Method】Soil samples were collected from a long-term field experimental site with treatments receiving different amount of pig manure. In our first incubation experiment, all of these soils were selected and two treatments were set up in each soil: loose soil samples and repacked soil columns. In the second incubation experiment, only one soil was used, and the soil was repacked into columns with four bulk densities, which were 1.1 (BD1.1), 1.3 (BD1.3), 1.5 (BD1.5) and 1.7 (BD1.7) g?cm-3. The samples of these two experiments were incubated for 57 d and 28 d, respectively. SOC mineralization was measured during incubation, and soil pore structure was quantified using X-Ray micro-computed tomography (μ CT) imaging. 【Result】At the end of incubation (57 d), the cumulative amount of SOC mineralization was significantly different between loose soil samples and repacked soil columns. The cumulative amount of SOC mineralization in the loose soil samples was about 4 times that of the repacked soil columns. In the second experiment, the total porosity decreased by 12.9%, 14.8% and 17.4%, respectively under BD1.3, BD1.5 and BD1.7 compared with BD1.1. In relative to BD1.1, the increase of compactness decreased macro-porosity by 19.0%, 65.5% and 88.5%, respectively under BD1.3, BD1.5 and BD1.7. In addition, the water-filled pore space (WFPS) increased from 36.4% to 91.8% and air-filled pore space (AFPS) decreased from 63.6% to 8.2%. At the end of incubation (28 d), the cumulative amount of SOC mineralization generally increased as bulk density increased up to 1.5 g?cm-3, after which there was a decrease. The regression analysis showed that there was a significant nonlinear relationship between the cumulative amount of SOC mineralization and total porosity, macro-porosity, WFPS and AFPS. The cumulative amount of SOC mineralization increased with increasing total porosity and macro-porosity until a level of 46% and 3.7% was respectively reached, afterwards it began to decline. Also, the relationship between the cumulative amount of SOC mineralization and WFPS and AFPS showed the same trend. The cumulative amount of SOC mineralization was the highest when WFPS was 66% or AFPS was 34%. 【Conclusion】Laboratory incubation using loose soil samples will overestimate the potential of SOC mineralization in the field, while a change of compactness will modify soil pore structure and subsequently affect SOC mineralization. There is a significant nonlinear relationship between the cumulative amount of SOC mineralization and porosity.

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荣慧,房焕,蒋瑀霁,赵旭,彭新华,孙波,周虎.松散土样和填装土柱及紧实程度对土壤有机碳矿化的影响[J].土壤学报,,[待发表]
Rong Hui, Fang Huan, Jiang Yuji, Zhao Xu, Peng Xinhua, Sun Bo, Zhou Hu. Effects of loose soil samples, repacked soil columns and compactness on soil organic carbon mineralization[J]. Acta Pedologica Sinica,,[In Press]

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