Effects Of Temperature And Water Level Changes On Enzyme Activities In North Peatlands

Wetland area in the world is only 5% of terrestrial ecosystems, but they have nearly 30% of the terrestrial ecosystem carbon storage, and this carbon pool is almost as equal as the carbon in atmosphere. It is an important carbon pool on Earth, and also the most important "carbon sinks" of the ecosystem. Because of low environmental temperature and low pH, the rate of carbon decomposition is lower than the accumulation rate in North peatlands, this kind of imbalance of carbon cycle result in a huge carbon storage in North peatlands for a long time.In wetland, organic materials, after decomposition, mainly enter atmosphere as greenhouse gases, such as CO2/CH4, or enter into hydrophytic ecosystem as dissolved organic carbon. Soil enzymes are important functional material of wetland ecosystems in decomposing organic compounds (organic carbon in the wetland). High activity of enzymes will speed up the metabolic rate of organic carbon decomposition in wetland, on the other hand, the decomposition rate of organic carbon decreased when enzyme activity is inhibited. Enzymes activities regulated by many environmental factors, including temperature, water level, pH and others. The variety of enzymes activities is consanguineous related to carbon cycling in peatland. While the small fluctuations of carbon cycle rate may result in a shock to atmospheric carbon dioxide concentration. Therefore, further understanding the effect of changes in water level and temperature conditions on soil enzymes activities in peatland will be very important for globe carbon cyclingThe activity of phosphatase is an important indicator of measurement of P elements nutrient cycling in ecosystem; and phenol oxidase is closely related with the decomposition of phenolic compounds;β-glucosidase can catalyse and hydrolyze P-glucosidase-link, mainly with cellulose degradation. These types of enzymes are key steps of organic carbon decomposition in peatland. We selected two typical peatlands in Xiaoxing'anling, which located in the northeast of China:a marsh (Carex-dominated peatland) and a swamp (sphagnum-dominated peatland) to study these three enzymes. We collected the samples at April, July, August and October in 2008. The samples were taken back to the laboratory quickly for incubation with difference temperature and water level after collected. After incubation, enzymes activity (β-glucosidase, phosphatase, phenol oxidase), pH, sample moisture content, organic matter content, the sample water-soluble phenolic content and peat soil CO2 respiration were measured.Results showed that enzyme activity was getting a closely relationship with peatland type. The same enzyme in different types of peatland show a vary value in their activity even under the same conditions of temperature and water levels. In addition, the response of enzyme activity caused by incubation temperature and water level change are large differences in difference peatland.The effect of water level and temperature changes onβ-glucosidase activity was limited, only a positive correlation of its activity and temperature has been found in marsh, August. Overall, the P-glucosidase activity is higher in marsh than in swamp. The organic matter content and quality maybe the most important factors regulating enzyme activities in peatland. However, we found that as the depth increasing, the activity of glucosidase was continuously decreasing.The effect of water level and temperature changes on phenol oxidase activity was limited too, no correlation has been found with them. However, its activity was negative correlation with phenolic compounds content in peatland. In marsh, its activity is decreasing with depth lower, and in swamp, as the depth lowering, the activity decreased at first and then increasing.The changes of water level and temperature have a great impact on phosphatase activity in both marsh and swamp, but the response of litmusless phosphatase to incubation temperature and water level fluctuate in those two peatlands. Acid phosphatase have a closely relationship with water level in both marsh and swamp, when water level lowering, its activity increasing. In addition, a positive correlation between acid phosphatase activity and incubation temperature have been found in swamp.In peatland, enzyme activities (phosphatase,β-glucosidase) changed with season varying. At different season, the value of their activities also differently. In the same peatland, those two kinds of phosphatase have the same trends of evolution with season changed. The activity of Acid phosphatase is higher than litmusless phosphatase at the same environmental condition. But when the type of peatland different, although the temperature and water level are same, the enzymes activity will be different because of their variety of physical and chemical conditions.As the incubation temperature increasing, the carbon dioxide emission in marsh and swamp has increased gradually. Carbon dioxide emission was positively correlated with temperature. The carbon dioxide emission is about 2 times in swamp than in marsh at August, and they were almost equal at October, this result indicated the type of peatland might be the key factor regulating the carbon dioxide emission in peatland.Our results showed that the enzyme activities in marsh is higher than in swamp, but the carbon dioxide emission is lower in marsh. It indicated that positive correlation between the enzymes activity and carbon dioxide emission in peatland only occured in some particular environments. As the carbon cycle is very complex in peatland, some mechanism of soil processes related with enzymes activity still need to be further studied.