免耕条件下不同秸秆覆盖量对土壤木质素含量的影响

Effects of Different Stalk Mulching on Soil Lignin Content

【目的】研究不同秸秆覆盖量免耕对土壤木质素(VSC)含量的影响,探讨免耕作对土壤有机碳截获和平衡的影响过程和机制。【方法】以吉林省梨树县黑土免耕作长期定位试验田的表层土壤为研究对象,对比分析无秸秆覆盖、33%秸秆覆盖、67%秸秆覆盖、100%秸秆覆盖4种处理土壤中木质素的变化特征。【结果】与无覆盖相比,经过4年连续秸秆覆盖后,木质素在土壤表层聚集,随着土壤深度的增加,木质素含量逐渐减少;随着覆盖量的增多,0—2 cm土层中VSC含量逐步增大,100%覆盖是无覆盖处理的5.06倍;5—20 cm土层中各处理间VSC含量差异并不显著;木质素来源碳在有机碳中的相对比例随着深度的增加而减少;与无覆盖相比,秸秆覆盖增加了木质素来源碳在有机碳中的相对比例;秸秆覆盖后,木质素丁香基单体(S)与香草基单体(V)比值(S/V)以及肉桂基单体(C)与S单体比值(C/V)减少,S类和V类单体的酸醛比(Ac/Al)s和(Ac/Al)v增大,表明秸秆还田不同程度降低了土壤有机质的氧化程度。【结论】秸秆覆盖免耕条件下,植物来源木质素在土壤表层选择性积累,延缓了木质素的氧化,增加了土壤有机碳的截获量和稳定性。

[Objective] The effects of different amounts of residue incorporation on the contents of no-tillage soil lignin （VSC） was examined to investigate the impact of the processes and mechanisms of conservation tillage on soil organic carbon sequestration and balance. [Method] Soil samples were collected from four treatments （no stalk mulching, 33% stalk mulching, 67% stalk mulching and 100% stalk mulching） for assessing lignin and its degree of structural alteration in a long-term field experiment with conservation tillage in Lishu. [Result] Compared with no stalk mulching, lignin was accumulated on the soil surface layer with stalk mulching for four years, and lignin contents decreased with soil depth. VSC gradually increased along with the increasing residue incorporation in 0-2 cm layer, and the contents of VSC in 100% straw mulching was 5.06 times that of no stalk mulching. Compared with no stalk mulching, lignin contents was found among the treatments in 5-20 cm layer. The relative accumulation of lignin-derived carbon in SOM was reduced with depth, but increased with straw mulching. The ratios of syringyl-to-vanillyl phenols（S/V） and cinnamyl-to-vanillyl phenols （C/V） declined while the acid-aldehyde ratios of the S （Ac/A1）s and V （Ac/A1）v units increased, suggesting a lower state of lignin degradation with stalk mulching. [Conclusion] The results suggest that the lignin derived from plants was a selective accumulation, and lignin degradation was evidently retarded in no-tillage with straw mulching treatments. No-tillage has benefit effect on enhancing the sequestration and stabilization of carbon.