东南湿润区典型丹霞地貌土壤有机碳组分及其敏感性研究

Soil Organic Carbon Fractions and Their Sensitivities to Land Use in the Typical Danxia landform Area in the Humid Region of Southeast China

“中国丹霞”是中国东南部湿润地带脆弱的生态系统之一。研究其土壤有机碳组分、碳库的敏感性和碳库管理的变化特征,对脆弱生态区土壤固碳和生态环境的可持续性发展具有重要意义。在广东仁化丹霞山典型地貌区,选取4种土地利用方式土壤(自然林地NL、灌丛SL、撂荒草地AG和农田CL)为研究对象,测定土壤总有机碳(TOC)、溶解性有机碳(DOC)、易氧化有机碳(EOC)、颗粒态有机碳(POC)和微生物量碳(MBC)含量,旨在探明东南湿润区典型丹霞地貌不同土地利用方式下土壤有机碳组分及其敏感性特征。结果表明,(1)TOC、DOC和POC质量分数在NL土壤表现最高,分别为24.32 g·kg^(−1)、291.10 mg·kg^(−1)和6.49 g·kg^(−1)。与其他利用方式相比,AG土壤EOC和微生物熵显著增加,分别提高了21.04%—43.19%和36.16%—171.43%,而CL表层土壤MBC含量显著降低,降幅达258.40%—347.89%。(2)4种土地利用方式土壤有机碳组分均以POC最敏感,DOC差异性较小。(3)表层土壤的碳库管理指数以AG最高,而亚表层土壤以NL最高,MBC是土壤碳库管理指数变化的重要影响因素。(4)线性拟合分析表明,土壤TOC变化量与DOC变化无明显相关,与EOC呈显著负相关,与POC、非活性有机碳、矿物结合态有机碳呈极显著正相关。POC是土壤有机碳组分敏感性指标,而MBC是土壤碳库管理指数变化的有效性表征指标,这揭示了丹霞地貌不同土地利用方式是通过土壤团粒结构和土壤微生物代谢活动影响土壤有机碳库变化。此外,该区域林地有机碳组分含量较高,退耕还林有助于土壤固碳和土壤质量提升。

The Danxia landform area is one of the typical ecologically fragile zones in southeast China.Knowledge of the soil organic carbon fractions,the sensitivities of carbon pools and the variation characteristics of carbon pool management in this area is of importance for the carbon sequestration and sustainable development of ecosystems in ecologically fragile zones.In this study,four land-use types,i.e.,natural forest(NL),shrubland(SL),abandoned grassland(AG),and cropland(CL),were selected in the Danxia Mountain area,Renhua,Guangdong.Soil organic carbon fractions,including total organic carbon(TOC),dissolved organic carbon(DOC),easily oxidizable organic carbon(EOC),particulate organic carbon(POC),and microbial biomass carbon(MBC),were quantified with the aim to investigate the changes and sensitivities of soil organic carbon fractions under different land-use types on the typical Danxia landform in southeastern humid zone.The results showed that the NL soil had significantly higher TOC,DOC,and POC contents with 24.32 g·kg^(−1),291.10 mg·kg^(−1) and 6.49 g·kg^(−1),respectively.Compared with other three land-use types,EOC and microbial entropy in AG soil increased by 21.04%‒43.19%and 36.16%‒171.43%,respectively,whereas the MBC content in CL surface soil was significantly reduced by 258.40%‒347.89%.Of the soil organic carbon fractions,POC was the most sensitive to land-use type,whereas DOC showed fewer differences among the four land-use types.The highest values of carbon pool management index for surface and subsurface soils were obtained in AG and NL,respectively,and MBC was an important influencing factor of soil carbon pool management index.Linear regression analysis showed that TOC variation was not significantly(P>0.05)correlated with DOC variation,but was significantly(P<0.05)negatively correlated with EOC and significantly(P<0.01)positively correlated with POC,inactive organic carbon,and mineral-associated organic carbon.POC was a sensitive indicator of the soil organic carbon fractions,whereas MBC was an effective indicator of changes in soil carbon pool management index,which revealed that different land-use types in the Danxia landform area affected the soil organic carbon pool by influencing the soil aggregate structure and soil microbial metabolic activities.In addition,the NL soil showed high contents of all organic carbon fractions,so returning farmland to forest would be conducive to soil carbon sequestration and soil quality improvement.