亚热带典型地貌下旱地和水田可溶性有机物化学组成特征

Chemical Constituents of DOM in Upland and Paddy Soils Under Typical Landforms in Subtropical Region

阐明亚热带典型地貌下旱地与水田土壤可溶性有机物(DOM)化学组成差异可为农田土壤DOM稳定性评价提供理论依据。研究采用XAD-8树脂分组和热裂解气质联用仪(Py-GCMS)技术,分析比较休闲期、耕作期亚热带喀斯特山区、丘陵区及平原湖区旱地和水田土壤DOM化学组成特征。结果表明:休闲期,亲、疏水性可溶性有机碳(DOC)含量以水田(10.2、33.4 mg/kg)显著高于旱地(4.15、12.8 mg/kg),耕作期无显著性差异。与休闲期相比,耕作期水田亲、疏水性DOC含量均显著降低,而旱地亲、疏水性组分DOC含量在两个时期间保持相对稳定。休闲期旱地和水田土壤DOM中有机酸相对比例分别为31.9%、35.6%,耕作期显著降至17.9%、20.0%(P<0.05)。脂类相对比例趋势与有机酸相反,旱地和水田土壤DOM中脂类相对比例在休闲期分别为55.0%、49.5%,耕作期显著增至70.1%、62.9%(P<0.05)。Adonis分析表明,亲、疏水性DOC含量在旱地和水田、休闲期和耕作期差异显著(P<0.05);DOM化学组成在不同时期(休闲期和耕作期)及地貌(喀斯特山区和丘陵区、丘陵区和平原湖区)差异显著(P<0.05)。Random Forest分析表明,有机酸和脂类参与微生物代谢过程,在休闲期和耕作期差异显著(P<0.05);芳香化合物作为DOM稳定性组分,在不同地貌区差异较大(P<0.05)。总体上,田间条件下水田DOC比旱地DOC对时期响应更敏感,且土壤DOM中微生物代谢相关组分(有机酸、脂类)和稳定性组分(芳香族化合物)在不同时期及地貌区的差异性不同,这对评价旱地和水田土壤DOM稳定性及土壤有机碳积累具有一定的参考意义。

In this study, the chemical constituents of dissolved organic carbon(DOM) in upland and paddy soils under typical landforms in subtropical region were investigated in order to provide theoretical basis for evaluating its stability. The chemical constituents of DOM in upland and paddy soils from karst, hilly and plain-lake areas in southern China at fallow and ploughing periods were analyzed using an XAD-8 resin-based fractionation method and pyrolysis-gas chromatography-mass spectrometry analysis. Results showed that higher contents of hydrophilic DOC(Hi-DOC) and hydrophobic DOC(Ho-DOC) were found in paddy soils(10.2 and 33.4 mg/kg) than in upland soils(4.15 and12.8 mg/kg) at fallow period(P<0.05), whereas no significant difference of these components was found at ploughing period. As compared with fallow period, the contents of Hi-DOC and Ho-DOC in paddy soil were significantly decreased at ploughing period(P<0.05). However, those in upland soils were not greatly changed between fallow and ploughing periods. The relative proportions of organic acids in total DOM in upland and paddy soils were 31.9% and 35.6% at fallow period, but were decreased to 17.9% and 20.0% at ploughing period, respectively(P<0.05). Contrary to organic acids, the relative proportions of lipids in DOM from upland and paddy soils were 55.0% and 49.5% at fallow period, but increased up to 70.1% and 62.9% at ploughing period, respectively(P<0.05). The adonis test showed that the contents of Hi-DOC and Ho-DOC were significantly different between upland and paddy soils and between fallow and ploughing stages(P<0.05), whereas the DOM constituents were significantly different between different periods(fallow and plough) and between different landforms(karst mountain region vs hill region, hill region vs plain-lake region)(P<0.05). The random forest test showed that the organic acids and lipids involved in microbial metabolic processes, were significantly different between fallow and ploughing periods(P<0.05). However, the aromatics as a stable component of DOM was significantly different between different landforms(P<0.05). In brief, this study indicates that the DOC in paddy soil was more sensitive to periods than in upland soil, and reveals that the significant differences in microbial metabolic-related components(organic acids and lipids) and a stable component(aromatics) in soil DOM were various with different periods and landforms, which could provide a reference for DOM stability as well as SOC accumulation in upland and paddy soils.