Effects Of Hydrothermal Changes On Phenolic Compounds And Phenol Oxidase Activities In Peatlands

Northern peatlands mainly distribute in the North Hemisphere with the area of near 4 million square kilometers and contain a vast store of carbon (ca.450pg), consequently they are important carbon store that affecting global carbon cycle. However, global warming and frequent extreme climate events are both willing to influence northern peatlands carbon cycle, resulting in the changes of their environmental function and increasing loss of carbon to atmosphere and water system.Phenolic compounds (PC) are directly or indirectly concerned with peatland carbon cycle and exports. Lignin accounts for 50-60% dry weight of peat. PC derive from plant lignin and organic matter during their biological degradation. There are violent inhibition effects of PC to some important hydrolase enzymes (such asβ-glucosidase and phosphatase). Phenol oxidase (PO) has been found to be one of the scarce enzymes capable of decomposing PC, thus PO could indirectly promote hydrolase enzymes' activities by increasing the degradation of PC, going with the raising degradation of peatland organic matter. Here the changes of PC and PO activites under different hydrothermal conditions were studied, with the aim of determining the effects of global climate change on peatlands, and in turn, their feedback to climate change, as well as the effects of this feedback on atmosphere and water system. There are vast covers of peatlands in Northeast China, whereas few studies have been done aimed at it under the background of global climate change. Two typical peatlands, marsh and forest swamp, were choose for this study. Peat was collected in the April, July, August and October of 2008 from these two study sites, respectively. After sample-collecting, these peat cores were immediately transferred to the laboratory for water level and temperature manipulation experiments. After incubation, water soluble phenolics (WSP), phenolic acids (PAs), PO activities, pH, water content, and organic matter content were detected. According these components, along with the atmosphere, hydrology, and plants growth condition on the peat collecting time, the composition, changes and correlation of PC and PO activities under different seasons and hydrothermal conditions were studied. The results showed that: 1. The peak concentrations of WSP appeared in the depth of 0-9cm of high water level conditions in both these two peatlands, especially in the depth of 0-3cm, and the maximum Relative Standard Deviation (RSD) of WSP between different water level conditions was found in the surface (the depth of 0-6cm). These implied that high water level condition was easy for the accumulation of PC, and the effects of water level fluctuation on surface peat was more efficient than the deeper peat.2. The percentage of total PAs to WSP (TPTW) of July was higher than October after water level manipulation experiment. The temperature manipulation experiment brought marked increase to TPTW of July peat, while a significant reduce presented in October peat. These differences between July and October might be mainly attributed to the differences in litter properties, which represented one of the most important factors that affected PC concentration of peatlands.3. The RSD of WSP was higher in marsh than forest swamp. Forest swamp showed more sensitive to hydrothermal change than marsh. TPTW was higher in marsh than in forest swamp, and the maximum value of July and October appeared on 25℃of low water level condition. It suggested that Increased temperature and reduced water level accelerated carbon loss of these two peatlands. But with the extreme climate evens going on, the carbon losses of forest swamp tended to take off or even terminate, but in turn, marsh maintained its high carbon loss speed all the time. Forest swamp was much tolerant to climate change than marsh. It also showed us that the concentration and relationship of PAs and WSP responded effectively to the carbon cycle and export of peatlands.4. The maximum PO activity of marsh appeared in the depth of 0-9cm, and got a sharp decrease with the depth-increasing. PO showed a significant order with the depth, especially for the mid water level condition. But this did not appear in the forest swamp.5. The Optimum temperatures for PO activities were all near the ambient temperature of peat-sampling seasons in forest swamp, but lag behind to the corresponding season of the ambient temperature in marsh.6. There were big differences of WSP, PAs and PO between the two peatlands. The peatland types and the dominant plants were the leading factors of PC concentration and PO activities in peatland.In short, whatever for the PC and PAs, or the PO, the most remarkable difference presented between these two peatlands. Marsh was much more sensitive to hydrothermal changes than forest swamp, while forest swamp was much more tolerant to climate change. The different response of PAs to water level change proved the diversity of PAs'properties. A better knowledge of the concentrations of WSP and PAs in the downstream river and lake of peatlands would be signality to understand the water system environment changes, and its response to global climate change.