Changes Of Soil Carbon Dioxide Concentration And Soil Enzymes Activities In Karst Area And Their Relationship

Soil enzymes are important components and active participants in the soil biochemical processes, and the most vigorous biological-active substances in the process of material circulation and energy flow in the soil ecosystem. They also are very important for the underground ecological processes of terrestrial ecosystems. The carbon dioxide concentration in karst soil is high, which is tens or hundreds times of atmospheric carbon dioxide concentration. The concentration of soil carbon dioxide in karst area is higher than the non-karst area, for the particularly geological background in the karst zone. Previous studies were focused on atmospheric carbon dioxide concentration affected on soil enzyme activities, rarely discussed the changes in soil carbon dioxide concentration and its effect on soil enzyme activities. It is important for revealing the difference in the soil and ecosystem between karst and non-karst zone, and the rational development of agricultural economy and ecological restoration in karst area to study on this relationship.Qingmuguan karst valley in Chongqing is selected as the study area in this research. According to research needs to avoid interference complex factors, we choose the less affected area by human activities, from the Caofangwan to Jinzhuwan which covers the upper and middle stream of Qingmuguan underground river as the main study zone. During winter, summer, and autumn;we select three main land use types at depressions and slopes:grassland, shrub land and bamboo land, and at 0-20cm,20-40cm,40-60cm,60-80cm we sampling and monitoring the soil carbon dioxide concentration,and then testing their soil enzymes activity. According to the data, we reveal the rule of the concentration of soil carbon dioxide in karst valley in the vertical distribution and seasonal variation; and reveal the rule of soil enzymes activity in karst valley in the vertical distribution and seasonal variation;and reveal the relationship between the concentration of soil carbon dioxide concentration and activity of soil enzymes in karst valley, and then discuss the soil carbon dioxide concentration effect on soil enzyme activities. Thus, it revealing the particularity of ecological environment in karst zone and providing scientific supporting for rational development of ecological agriculture in karst zone.By a one-year field monitoring of soil carbon dioxide concentration in Qingmuguan karst valley, we get the karst valley soil carbon dioxide concentration trend figure during one year, which is in the different landscape positions and different land use patterns. The variation of soil carbon dioxide concentration in Qingmuguan karst valley in the general is:With the increase of soil depth, soil carbon dioxide concentration increased. In a same month, the soil carbon dioxide concentration was highest at the bottom and lowest at the surface. The concentration of soil carbon dioxide is different in different landform position:soil carbon dioxide concentration at depressions is higher than at slopes. The variation amplitude of soil carbon dioxide concentration is different under different vegetation types:the grass soil carbon dioxide concentrations have the largest increase, followed by shrub land, and then bamboo ground.In this issue,135 soil samples were tested in soil invertase activities,soil urease activities,soil alkaline phosphatase activities,soil amylase activities and soil catalase activities. And we got these soil enzymes activity values in different seasons and different depths. This study fonud the general rule of soil invertase, urease, alkaline phosphatase and amylase were surface enzyme activities were larger than bottom, some samples to bottom by surface gradually decreasing vertical distribution situation. And the four enzyme activity changes with the season variety. But the variations of soil catalase activities in temporal and spatial distribution were not obvious. There was no obvious change rules form surface to bottom and no obvious change rules between each season. In addition, depression sites have more significant vertical distribution and seasonal variation than slope sites.The results show that soil carbon dioxide concentration has a certain relationship with soil enzyme activity in Qingmuguan karst valley by the correlation, path analysis. Even more, regardless of different seasons or different soil layers, the soil carbon dioxide concentration will have an impact on soil enzyme activities. From the seasonal analysis, soil carbon dioxide concentrations have larger effect on soil enzyme activities, and mainly indirectly impact the enzymes activities through the other chemical properties. This impact was most obviously on invertase and urease. The strength values of these two enzymes were over 0.3. and others were between 0.1 and 0.2. Soil carbon dioxide concentration shows directly influence on soil enzyme activities by analysis different layers of soil, and have most significant impact on invertase and urease in each layers, the value was about 0.3. The amplitude of soil air concentration would affect soil enzymes activities. Lager amplitude has a significant impact on soil enzymes activities and mainly shows indirectly influence on soil enzymes activities, otherwise smaller amplitude has a minor impact on soil enzymes activities and mainly shows directly impact. Thus. Soil carbon dioxide concentration has significant impact on soil hydrolysis enzymes, and mostly on invertase. Amylase and alkaline phosphatase were less affected, urease was least affected, and catalase of soil redox enzymes was greater affected by soil carbon dioxide concentration.The soil-vegetation system and terrain ecosystem was affected by soil carbon dioxide concentration, for its impacts on soil enzymes activities. The positive influence on invertase by variation of soil carbon dioxide concentration would attribute to promote the ecosystem status; the inhibition on amylase and alkaline phosphatase would cause negative influence on ecosystem; the variation of soil carbon dioxide concentration has less impact on urease., thus there was litter influence on ecosystem.And soil carbon dioxide concentration had greater impact on catalase and it would cause negative influence on ecosystem.