喀斯特关键带不同干扰梯度下土壤-岩石界面对土壤有机质水解酶活性的影响

土壤酶在土壤生态系统的物质循环和能量流动中具有重要作用,受土地利用方式影响强烈。喀斯特地区具有岩石出露面积广和土层浅薄不连续的特点,且随着人为干扰强度的增加而加剧。但是目前关于土壤碳氮循环酶活性对出露岩石(土壤-岩石界面)的响应受土地利用变化的影响的研究还较为薄弱。以贵州省喀斯特地区陈旗和天龙山流域为研究区域,探讨了原生林、次生林、弃耕地和耕地4种不同干扰梯度下土壤-岩石界面的土壤有机质水解酶活性的差异以及影响机制。研究结果表明:(1)当土地利用方式从森林转化为弃耕地或耕地后,土壤有机碳(SOC)、全氮(TN)、硝态氮(NO3^——N)、铵态氮(NH4^+-N)含量和SOC/TN随着人为干扰强度的增加呈现降低的趋势。在4种不同干扰强度的土地中,岩土界面的pH、SOC和NH4^+-N含量较高。(2)土壤酶活性在不同干扰梯度下土壤-岩石界面和非交界处有明显的分异。与碳循环有关的β-1,4-葡萄糖苷酶(βG)、β-1,4-木糖苷酶(βX)、纤维素二糖水解酶(CBH)和α-1,4-葡萄糖苷酶(αG)酶活性均表现为弃耕地和耕地高于原生林和次生林。与氮循环有关的β-1,4-N-乙酰葡糖氨糖苷酶(NAG)和亮氨酸氨基肽酶(LAP)在原生林和弃耕地中表现出更高的活性。所有水解酶均在弃耕地的土壤-岩石交界处活性最高。(3)RDA分析表明,可溶性有机碳(DOC)的含量对土壤水解酶活性影响最大,贡献率为33.4%(P=0.002)。土壤pH、SOC和NH4^+-N与酶活性显著相关。综上,土地利用方式和岩石裸露显著影响土壤的理化性质和水解酶活性;同时弃耕地的土壤-岩石界面维持了较高的碳氮周转酶活性,反映出长期恢复下土壤的养分循环功能仍然存在,表明退耕还林还草对喀斯特地区生态系统恢复和土地资源可持续利用具有重要意义。

Effect of soil-rock interface on soil organic matter hydrolase activity under different disturbance gradients in Karst Critical Zone

Soil enzymes play an important role in the material cycle and energy flow of soil ecosystem,and are strongly affected by land use patterns.Karst area has the characteristics of wide exposed area of rock and shallow discontinuity of soil layer,and increased with the aggravation of human interference intensity.However,the progress on the response of soil enzymes related to carbon and nitrogen cyclingto exposed rock(soil rock interface)under different land use disturbance gradients is weak.In this study,we selected Chenqi and Tianlongshan river basins in karst area of Guizhou Province as the research areas to explore the differences of soil organic matter hydrolase activities and their driving factors of soil-rock interface under four different disturbance gradients:primary forest,secondary forest,abandoned farmland and cultivated land.The results showed that:(1)when the land use pattern changed from forest to abandoned farmland or cultivated land,the content of soil organic carbon(SOC),total nitrogen(TN),nitrate nitrogen(NO3^--N),ammonium nitrogen(NH4^+-N)and SOC/TN decreased with the increase of human disturbance intensity.The pH,SOC and NH4^+-N contents of the soil-rock interface were higher in the four soils with different disturbance intensities.(2)Soil enzyme activities differed significantly between soil-rock interface and bulk soil under different disturbance gradients.The activities of β-1,4-glucosidase(βG),β-1,4-xylanase(βX),cellulose disaccharide hydrolase(CBH)and α-1,4-glucosidase(αG)related to carbon cycle were higher in abandoned farmland and cultivated land than in primary and secondary forests.The β-1,4-N-acetylglucuronidase(NAG)and leucine aminopeptidase(LAP)related to nitrogen cycle showed higher activity in primary forest and abandoned farmland.All the hydrolases had the highest activity at the rock-soil interface of abandoned farmland.(3)RDA analysis showed that the content of dissolved organic carbon(DOC)had the greatest influence on soil hydrolase activity,and contributed to the variation of 33.4%(P=0.002).Soil pH,SOC and NH4^+-N were significantly correlated with enzyme activities.In conclusion,land use and rock exposure significantly affected the physical and chemical properties and hydrolase activity of soil;at the same time,the soil rock interface of the abandoned farmland maintained a high carbon and nitrogen turnover enzyme activities,which reflected that the nutrient cycling function of soil still existed under long-term restoration.The results further indicates that returning farmland to forest and grassland are of great significance to ecosystem restoration and sustainable use of land resources in karst areas.