采煤塌陷区复垦土壤有机碳固持及酶活性对长期施肥的响应

Responses of soil organic carbon sequestration and enzyme activities of reclaimed soil in a coal-mining subsidence area to long-term fertilization regimes

研究复垦后连续11年施肥对土壤团聚体及粉黏粒组分中有机碳(OC)含量和酶活性的影响,以期深入理解复垦土壤中有机碳(SOC)的固存机制.采集不施肥(CK)、施氮磷钾肥(NPK)、单施有机肥(M)和有机无机肥配施(MNPK)4个处理0-20 cm土层土壤样品,另取未复垦生土和周边未破坏多年种植的农田土壤作为参照.利用湿筛法分离水稳性团聚体(>2 mm、0.25-2 mm和0.053-0.25 mm)和粉黏粒组分(<0.053 mm),并测定其中OC含量,分析土壤脲酶、蛋白酶、蔗糖酶和β-葡萄糖苷酶活性,探究团聚体及粉黏粒组分中OC含量与SOC之间的关系,以及它们与累积碳投入量之间的关系,量化各酶活性对大团聚体中有机碳固存的贡献.结果表明,长期不同施肥显著提高了SOC储量和固碳速率,尤其是MNPK处理.同CK相比,NPK处理对各粒径团聚体中OC含量无显著影响,而M和MNPK处理均显著提高了>2 mm团聚体中OC含量,增幅达25.01-27.44%.所有施肥处理亦均显著增强了土壤各酶活性(除NPK处理下蛋白酶活性),增幅达14.98%-192.00%,且以MNPK效果最佳.通过分析团聚体及粉黏粒组分中OC含量和土壤酶活性的指标发现,连续复垦11年土壤肥力显著高于未复垦的生土,但仍低于当地农田土壤肥力状况的相当水平.SOC含量与大团聚体中OC含量呈显著的线性相关(P<0.05),尤其是>2 mm团聚体对SOC的贡献最大.累积碳投入量与SOC和大团聚体中OC含量呈显著的线性相关(P<0.05).4种酶对>2 mm粒径团聚体中有机碳含量变化的总体解释率为89.20%,尤其是蔗糖酶,它对>2 mm粒径团聚体中有机碳含量的解释率高达87.90%.因此,采煤塌陷区复垦土壤有机碳库仍未饱和,即使在碳投入为零的条件下土壤有机碳仍会增加.>2 mm团聚体在蔗糖酶的驱动下,作为土壤有机碳固存的主要载体,对土壤有机碳的固存发挥着主要作用.有机无机肥配施措施对于增加本区域复垦土壤碳汇、促进农业可持续发展具有良好的效果.

To understand the mechanism of soil organic carbon(SOC)sequestration under various fertilization regimes,the organic carbon(OC)content within the aggregate,silt,and clay fractions,and enzyme activities were investigated for reclaimed soil in a coal-mining subsistence area.Based on a long-term fertilization experiment in reclaimed soil in Xiangyuan City,Shanxi Province,topsoil samples from the 0–20 cm horizon were collected from four different fertilization treatments(CK,NPK,M,and MNPK).Simultaneously,nonreclaimed raw soil and surrounding farmland soil that had not been destroyed for many years were used as references to evaluate the fertilization effects.Soil particle size was fractionated using the wet-sieving method,which included large macroaggregates(>2 mm),small macroaggregates(0.25–2 mm),microaggregates(0.053–0.25 mm),water-stable aggregates,and silt and clay fractions(<0.053 mm).OC content within aggregates and silt and clay fractions was measured and the activities of urease,protease,sucrase,andβ-glucosidase analyzed.Further,the relationships between OC content within aggregates,silt,and clay fractions,and SOC content and their relationships with the cumulative carbon input were investigated,and the contributions of all soil enzyme activities to macroaggregate-associated OC content were quantified.The results showed that various long-term fertilization regimes significantly increased SOC stock and sequestration rates,particularly for the MNPK treatment.Compared with CK,NPK had no significant effect on the OC content within the aggregates and silt and clay fractions.M and MNPK treatments significantly increased the OC content in large aggregates by 25.01%–27.44%.Long-term fertilization significantly increased soil enzyme activities(except protease under NPK treatment)by 14.98%–192.00%,and MNPK treatment had the highest effect.Analysis of OC contents within aggregates,silt and clay fractions,and enzyme activities revealed that although the soil fertility after 11 years of continuous reclamation was significantly higher than that of the non-reclaimed raw soil,it was still difficult to restore it to a level equivalent to the soil fertility of farmland.The organic carbon content in macroaggregates was significantly and positively correlated with SOC content(P<0.05),and aggregates>2 mm made the largest contribution to SOC content.Cumulative carbon input was significantly and linearly correlated with SOC and OC contents within the macroaggregates(P<0.05).The total explanation of the four enzymes for the change in OC content in large aggregates was 89.20%,with sucrase accounting for 87.90%.Therefore,the reclaimed SOC pool in the coal mining subsidence area is still not saturated and the SOC content still increases,even under the condition of zero carbon input.Driven by sucrase,large aggregates act as the main carrier of SOC sequestration and play a major role in SOC sequestration.The combined application of NPK fertilizers and organic manure(MNPK)had a positive effect on increasing the carbon stock of the reclaimed soil in the study area and the promoting of sustainable agricultural development.