生态恢复对石漠化地区土壤有机碳累积特征及其机制的影响

Effects of soil organic carbon fractions on aggregates under ecological restoration in rocky desertification region

为从土壤碳组分对团聚体及其结合有机碳的影响的角度去解析生态恢复下土壤有机碳积累特征及其机制,以典型干热河谷石漠化地区生态恢复措施(次生林,15—20a;花椒林,15—20a)和对照耕地(>50 a)为研究对象,测定0—10 cm和10—20 cm土层土壤有机碳(SOC)、颗粒有机碳(POC)、易氧化有机碳(EOC)、矿物结合有机碳(MOC)、非活性有机碳(NLOC)、团聚体、团聚体有机碳含量,研究了生态恢复对SOC及组分、团聚体以及团聚体有机碳的影响。结果表明:(1)与耕地相比,生态恢复显著增加0—20 cm土层SOC及组分的含量与储量(MOC除外),含量与储量的增幅范围为10.4%—151.7%和6.3%—134.5%,其中POC、EOC含量和储量增幅最大,且POC、EOC与SOC相关性较强;(2)生态恢复显著提高>2 mm团聚体数量、MWD和MGD,其中以次生林0—10 cm土层的增幅最大(379.3%、172.0%、265.2%);(3)生态恢复显著增加各粒径团聚体有机碳含量,团聚体有机碳含量增幅随团聚体粒径增大而减小,然而生态恢复后>2 mm团聚体有机碳贡献率显著上升,<2 mm团聚体有机碳贡献率显著减小,土壤团聚体对有机碳的贡献率转为以>2 mm团聚体贡献为主,且>2 mm团聚体数量的显著增加是>2 mm团聚体有机碳贡献率高的主要原因;(4)土壤SOC、POC、EOC、NLOC与>2 mm团聚体数量、MWD、MGD、>2 mm团聚体有机碳贡献率显著正相关(P<0.05),其中POC、EOC与这些指标的相关性较强(P<0.01)。此外,从土壤有机碳及组分、团聚体数量及稳定性、>2 mm团聚体有机碳贡献率的增幅来看,自然恢复措施(次生林)较人工种植恢复措施(花椒林)增幅较大。

Ecological restoration is vital to improve soil structure and promote the accumulation of soil organic carbon(SOC).The effects of ecological restoration on SOC and its labile fractions,aggregate-associated organic carbon have been widely studied,but the relation of SOC fractions(especially POC and MOC)and aggregate in natural restoration measures(secondary forests)and the planted restoration measures(Chinese prickly ash planting)are still unclear.To analyze the accumulation characteristics and mechanisms of SOC under ecological restoration based on the influence of soil carbon fractions on aggregates and aggregate-associated organic carbon,we chose ecological restoration measures(secondary forest,15—20 a;Chinese prickly ash planting,15—20 a)and control cropland(>50 a)in a typical dry-heat valley rocky desertification region as the study subjects.The contents were measured in soil layers(0—10 cm and 10—20 cm),including soil organic carbon(SOC),particulate organic carbon(POC),easily oxidizable organic carbon(EOC),mineral associated organic carbon(MOC),non-liable organic carbon(NLOC),aggregates and aggregate-associated organic carbon.We studied the effect of ecological restoration on SOC and its fractions,aggregates and aggregate-associated organic carbon.The results shows that:(1)Compared with the cropland,ecological restoration significantly increased the content and storage of SOC and its fractions(except MOC)in the 0—20 cm soil layer,with increments ranging from 10.4%to 151.7%and 6.3%to 134.5%,respectively.The content and storage of POC and EOC increased largely in the SOC fractions,which showed the stronger relationship with SOC.(2)Ecological restoration significantly increased>2 mm aggregates content,mean weight diameter(MWD)and mean geometric diameter(MGD),which increased greatly with 379.3%,172.0%and 265.2%among the 0—10 cm soil layer of the secondary forest.(3)Ecological restoration significantly increased the aggregate-associated organic carbon content of various particle sizes.The degree of improvements in aggregate-associated organic carbon content decreased with aggregates size increasing.However,after ecological restoration,carbon contribution in>2 mm aggregates increased significantly and carbon contribution in<2 mm aggregates decreased significantly.Carbon contribution in soil aggregates shifted to the chief contribution in>2 mm aggregates.The increase of>2 mm aggregates content was the main causes for carbon contribution in>2 mm aggregates increasing.(4)More than 2 mm aggregates content,MWD,MGD,and carbon contribution in>2 mm aggregates were positively correlated with SOC,POC,EOC and NLOC(P<0.05).And they had stronger correlation for POC and EOC(P<0.01).In addition,from SOC and its fractions,the number and stability of aggregates,and carbon contribution in>2 mm aggregates,natural restoration measures increased greater than the planted restoration measures.The study suggests that SOC fractions(especially POC and EOC),aggregates and aggregate-associated organic carbon became more abundant in secondary forest and Chinese prickly ash planting than in cropland,which highlighted that ecological restoration plays a crucial role in soil carbon sequestration in rocky desertification region.