Changes in water extractable organic matter (WEOM) in a calcareous soil under field conditions with time and soil depth.
Changes in water extractable organic matter (WEOM) in a calcareous soil under field conditions with time and soil depth.
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DOI：
10.1016/j.geoderma.2009.11.026
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发表时间：
2010-01-01
期刊：
影响因子：
6.1
通讯作者：
Theraulaz, F.
中科院分区：
文献类型：
--
作者：
Hassouna, M.;Massiani, C.;Theraulaz, F.
水可提取有机质(WEOM)在土壤的主要生物地球化学过程中起着关键作用。然而，关于其在土壤剖面内和在不受控制的田间条件下的动态的信息很少，特别是在农业土壤中。在这里，我们介绍了一项为期七个月的100厘米土壤剖面上的WEOM动态研究。土壤样本是从法国地中海地区的一块田里采集的。在取样之前，玉米残留物被混合到土壤中，深至20厘米左右。WEOM在串联的XAD-8/4树脂上进行分级，并用UV/Vis吸收光谱和荧光光谱进行分析。采用主成分分析(PCA)对总体数据进行进一步分析。大量WEOM的平均浓度随着土壤深度的增加而显著下降，这是由于随后的所有疏水(HPOA)、转亲水(TPIA)和亲水(HPIA)酸组分的枯竭。在深层土壤中，WEOM在HPOA中的消耗最严重，导致其芳香性显著降低，用254 nm处的紫外比吸光度(UVSA254)估计。典型的WEOM三维荧光光谱显示出两个类似腐殖质的峰A和C，在整个土壤剖面上持续存在。在土壤表层的WEOM中也可观察到由木质素氧化降解副产物引起的低强度肩部H。缺乏可归因于不稳定和类蛋白质结构的荧光信号表明，无论土壤深度如何，WEOM的状态都发生了很大的变化。这很可能与钙离子偏好与微生物降解副产物形成联系，导致不稳定结构的密集降解有关。WEOM的进一步变化表现为其类腐殖质峰的蓝移和发射强度之比IA/IC的增大。这表明WEOM在更简单、更少共轭和更古老的结构中具有深度的富集性。WEOM在土壤剖面上的变化可能是植物残留物垂直输出较少以及本地SOM在其生产中的更大贡献的结果。主成分分析显示，大量WEOM及其随后的分级浓度与变量负荷中的第一个因素有关，这表明在采样期间存在显着差异。这些变化主要与土壤表层的降水和土壤水分有关。这些变量对总方差的解释作用随深度的增加而逐渐减小，与水体WEOM的分布相关性较弱。温度与三个土层中变量负荷的第二和第三因子相关，表明对WEOM动态的控制有限。与UVSA254相比，主成分分析显示IA/IC对气候变化的敏感性更高，这表明它作为时间WEOM动态的示踪剂具有更高的潜力。
Water extractable organic matter (WEOM) is attributed a key role in soil major biogeochemical processes. Yet, information concerning its dynamics within the soil profile and under uncontrolled field conditions is scarce, particularly in agricultural soils. Here, we present a study of WEOM dynamics across a soil profile of 100 cm over a period of seven months. Soil samples were collected from a field in the French Mediterranean region. Prior to sampling, maize residues were incorporated into soil down to around 20 cm. WEOM was fractionated on XAD-8/4 resins connected in tandem and analysed using UV/Vis absorbance and fluorescence spectroscopy. The overall data were further investigated by principal components analysis (PCA). The average concentrations of bulk WEOM decreased significantly with increasing soil depth as a result of the depletion of all its subsequent hydrophobic (HPOA), transphilic (TPIA), and hydrophilic (HPIA) acids fractions. In deeper soil layers, WEOM was most severely depleted in HPOA leading to significant decrease in its aromaticity estimated by UV specific absorbance at 254 nm (UVSA254). Typical three-dimensional fluorescence spectra of WEOM exhibited two humic-like peaks, A and C, persistent across the entire soil profile. A low-intensity shoulder, H, attributed to lignin oxidative degradation by-products was also perceptible in WEOM from the soil surface layer. The absence of fluorescence signals attributed to labile and protein-like structures suggested highly altered status of WEOM regardless of soil depth. This is most probably related to Ca++ preference to form links with microbial degradation by-products leading to intensive degradation of labile structures. Further alteration of WEOM is revealed by its humic-like peaks' blue-shifting and increasing the ratio between their emission intensities, IA/IC. This indicated WEOM's enrichment in simpler, less conjugated, and older structures with depth. WEOM's alteration across the soil profile may be a consequence of low vertical export of plant residues and more significant contribution of native SOM in its production. PCA revealed the association of bulk WEOM and its subsequent fractions concentrations to the 1st factor in variables' loads suggesting significant variations over the sampling period. These variations were mainly associated to rainfall and soil moisture in the upper soil layer. The contribution of these variables in explaining the overall variance decreased gradually with depth and showed weak correlation with the distribution of bulk WEOM. Temperature was associated to the 2nd and 3rd factors in variables' loads in the three soil layers indicating limited control on WEOM dynamics. PCA revealed higher sensitivity of IA/IC to climatic variations compared to UVSA254 suggesting its higher potential as a tracer of temporal WEOM dynamics.