不同母质发育土壤团聚体分布对外源输入秸秆的响应及其与有机碳矿化的关系

土壤团聚体的形成和稳定对于有机碳的转化和积累具有重要意义,然而不同母质发育土壤团聚体对有机碳的物理保护作用及其与有机碳矿化之间的关系仍不清楚.本文以石灰岩、第四纪红土、花岗岩、玄武岩和红砂岩母质发育的典型土壤为对象,研究添加玉米秸秆7 d和184 d时土壤团聚体和各组分有机碳的变化规律,分析不同母质土壤有机碳矿化的主要影响因素.结果表明,不添加秸秆时,所有母质土壤以1.0～0.5、 0.5～0.25和0.25 mm粒级团聚体为主,添加玉米秸秆有效促进了2 mm和2～1 mm粒级团聚体的形成.石灰岩、第四纪红土和玄武岩土壤形成水稳性大团聚体并且保持其稳定的能力高于花岗岩和红砂岩土壤.添加玉米秸秆培养184 d,石灰岩、第四纪红土和玄武岩土壤有机碳的累积矿化率显著(P0.05)低于花岗岩和红砂岩土壤.相关性分析表明,土壤有机碳的累积矿化率与游离态有机碳的比例极显著(P0.01)正相关,而与0.25 mm团聚体有机碳的比例极显著(P0.01)负相关.利用~(13)C核磁共振(~(13)C-NMR)技术对土壤有机碳进行结构表征,结果显示团聚体内轻组有机碳的分解程度低于游离态轻组有机碳,且石灰岩、第四纪红土和玄武岩土壤这两个组分有机碳的分解程度都低于其他母质土壤,直接证实了团聚体对于有机碳的物理保护作用.成土母质通过控制土壤胶体的数量和性质致使团聚体及有机碳分布对输入外源有机物质的响应存在较大差异,进而影响有机碳的矿化.石灰岩、第四纪红土和玄武岩土壤中团聚体稳定性高且对有机碳的保护容量大,有利于有机碳的积累和稳定.

Response of Aggregate Distribution to Input Straw and Their Linkages to Organic Carbon Mineralization in Soils Developed from Five Different Parent Materials

Development and the dynamics of stable aggregates in many soils are known to be closely related to the cycling as well as accumulation of soil organic carbon (SOC). This study explored the aggregation processes and distributions of soil organic carbon in soils developed from limestone (L), quaternary red earth (Q), granite (G), basalt (B), and tertiary red sandstone (T) subtropical China related to the addition of maize residues during 7 days and 184 days of incubation. The soils were sieved to<0.25 mm before incubation. We aimed to clarify the mechanisms underlying SOC mineralization across soils from the perspective of soil aggregate protection. Fractionation of the water stable aggregates showed that addition of maize straw promoted the formation of>2 mm and 2-1 mm aggregates, while only 1.0-0.5, 0.5-0.25 and <0.25 mm aggregates were detected in the absence maize straw. The proportion of macroaggregates as well as their stability was always higher in L, Q, and B developed soils than those in G and T developed soils. In amended soils, the accumulation of total SOC was much obvious in L, Q, and B developed soils than those in G and T developed soils, and these increases were mainly contributed by the >0.25 mm macroaggregate-associated SOC. This result indicated that>0.25 mm macroaggregates were important spots for SOC sequestration. Furthermore, the proportions of>0.25 mm macroaggregate-associated SOC were also significantly (P<0.05) higher in L, Q, and B developed soils than those in G and T developed soils, and the free light organic carbon (fLOC) followed an inverse parent material pattern as>0.25 mm macroaggregate-associated SOC. Results also demonstrated that ratios of accumulative mineralized CO₂-C to total soil organic carbon in L, Q, and B soils were significantly (P<0.05) lower than those in G and T soils. The correlation analysis further suggested that ratios of cumulative respired CO₂-C to total soil organic carbon were significantly and positively correlated (P<0.01) with the proportion of fLOC, but inversely correlated (P<0.01) with the proportion of>0.25 mm macroaggregate-associated SOC. By applying ¹³C-NMR to characterize the inherent chemical composition of soil organic carbon fractions, we noted that fLOC was more deeply decomposed than intra-aggregate light organic carbon (intra-aggregate LOC), and both the fractions were advanced decomposed in G and T developed soils, verifying enhanced protection of added maize residues inside soil aggregates. The findings of the research suggested that the parent material exerts a significant influence on SOC mineralization by controlling the formation of aggregates and location of SOC in the hierarchical structure of the soil aggregate system. We demonstrated that enhanced physical protection of SOC by forming more stable macroaggregates contributes to carbon accumulation in limestone, quaternary red earth, and basalt developed soils treated with organic amendments.