[Effects of seasonal freeze-thaw on the enzyme activities in Abies faxoniana and Betula platyphylla litters].

To understand the effects of seasonal freeze-thaw on the ecological processes of subalpine forest ecosystem, the enzyme activities in Abies faxoniana and Betula platyphylla litters under freeze-thaw were measured from October 2006 to October 2007 by the method of litter bags. There was an obvious monthly change in the enzyme activities, but the peak time varied with enzymes. Compared to the control, freeze-thaw had significant effects on the activities of invertase, urease, cellulase, and dehydrogenase in the litters (P < 0.05). Over a growth season, the invertase, cellulase, and urease activities in fir litter increased by 66.1%, 14.8%, and 76.3%, respectively while dehydrogenase activity decreased by 18.4%, and the invertase activity in birch litter increased by 39.4% while the urease, cellulase and dehydrogenase activities decreased by 18.2%, 28.7% and 15.6%, respectively. As for the activities of peroxidase and polyphenol oxidase in fir and birch litters, they were less affected by freeze-thaw. All of these revealed that seasonal freeze-thaw had definite effects on the litter decomposition of subalpine forest, which closely related to the kind of litter and its decomposition stage.

[Forest litter decomposition and its responses to global climate change].

Litter decomposition is one of the important processes in forest ecosystem, which is controlled by both biotic and abiotic factors such as climate, litter quality, and soil organisms. Up to now, numerous studies have been made on the dynamics of aboveground litter in different forest ecosystems, nutrient release during its decomposition, and effects of biotic and abiotic factors on the decomposition, but less information has been reported on the decomposition of belowground forest litter. Recently, the responses of forest litter decomposition to global climate change characterized by elevated atmospheric CO2 concentration and temperature have got worldwide concern, but there remains uncertainty in research results. In the further study, more attention should be paid on the contribution of forest litter decomposition to soil organic carbon sequestration, the physical, chemical and biological processes of below- and above-ground litter decomposition, the responses of forest litter decomposition to the ecological factors (e.g. seasonal freeze-thaw cycle and drying-rewetting cycle) and their interactions, and the mechanisms of litter (especially belowground litter) decomposition responses to global climate change.