模拟干旱条件对重度石漠化土壤易提取态腐殖质光化学行为的影响

Effect of Simulated Drought Conditions on Photochemical Behavior of Easily Extratable Humus in Soils with Severe Rocky Desertification

为探讨光照对土壤腐殖质直接光反应的影响,采集重度石漠化土壤模拟干旱条件,探讨不同波段紫外线(长波黑斑效应紫外线(UVA)、中波红斑效应紫外线(UVB)、短波灭菌紫外线(UVC))照射对重度石漠化土壤腐殖质易提取态光化学行为的影响。结果表明:(1)土壤有机碳质量分数无明显变化,UVA和UVB组全氮质量分数随照射时间逐渐增加,而UVC组逐渐减小,碳氮质量分数比与全氮质量分数变化相反;(2)由于氮损失造成含氮水溶性的芳香类物质减少,导致UVC组水提液整体呈现疏水组分减少的状态,而脂肪链类的疏水官能团整体均呈增加趋势,A_(250)/A_(365)值同样支持上述结论;(3)以甲醇为提取剂时,UVA、UVB、UVC组的芳香性及相对分子质量均减小,且变化程度明显大于水提液的变化,均以腐殖酸为主且有向富里酸转化的趋势,S_(254)、S_(260)、A_(253)/A_(203)值均表明不溶于水的极性物质的芳香性和疏水组分均减少;(4)以正己烷为提取剂时,S_(254)、S_(260)、A_(253)/A_(203)值均表明不溶于水的非极性物质的芳香性和疏水组分均减少。故增加甲醇和正己烷的提取能够印证结论(2),并补充水提液无法提取非水溶性物质的不足,同时拓展了紫外光谱技术在腐殖质表征技术方面的应用。综上所述,不同波段紫外线光照能对重度石漠化地区土壤腐殖质组成及相关性质产生不同程度改变,并且可以通过改变氮素的固定与释放,影响石漠化土壤生态的碳氮循环过程。

To explore the impact of light on the direct photoreaction of soil humus,severely rocky desertification soil was collected to simulate arid conditions.The effects of different wavelengths of ultraviolet light(long-wave black spot effect ultraviolet light(UVA),medium-wave red spot effect ultraviolet light(UVB),and short-wave sterilizing ultraviolet light(UVC))on the light chemical behavior of easily extractable humus in severely rocky desertification soil were investigated.The results showed that:(1)The mass fraction of soil organic carbon did not change significantly.However,the mass fraction of total nitrogen increased with the irradiation time in the UVA and UVB groups,while it decreased in the UVC group.The mass fraction ratio of carbon and nitrogen showed an opposite trend to the change in total nitrogen mass fraction.(2)Due to nitrogen loss,the nitrogen-containing water-soluble aromatic substances decreased,resulting in a decrease in the overall hydrophobic components of the water extract in the UVC group,while the hydrophobic functional groups of the fatty chain increased overall,and the A_(253)/A_(203)value also supported the above conclusion.(3)When methanol was used as the extraction agent,the aromaticity and relative molecular mass of the UVA,UVB,and UVC groups decreased.The degree of change was significantly greater than that of the water extract.The main components consisted of humus acid,which tended to transform into fulvic acid.This was indicated by the S_(254),S_(260),and A_(253)/A_(203)values,which all indicated a decrease in the aromaticity and hydrophobic components of the polar substances insoluble in water.(4)When n-hexane was used as the extraction agent,the S_(254),S_(260),and A_(253)/A_(203) values all indicated a decrease in the aromaticity and hydrophobic components of the non-polar substances insoluble in water.Therefore,increasing the extraction of methanol and n-hexane can confirm conclusion(2),and supplement the deficiency of water extracting solution’s inability to extract non-water-soluble substances.This also expands the application of ultraviolet spectroscopy in humus characterization techniques.In conclusion,different wavelengths of ultraviolet light can cause varying degrees of changes in the composition of soil humus and related properties in severely rocky desertification areas,and can affect the carbon and nitrogen cycling process of rocky desertification soil ecology by altering nitrogen fixation and release.