Soil invertase and urease activities at different periods in subalpine forest gap in western Sichuan

As an important small scale disturbance,forest gaps are often considered to be major drivers in the natural forest regeneration. Moreover,forest gaps can play essential roles in soil processes including the dynamics of soil enzyme activity,since the snow,precipitation and sunshine duration could be redistributed in different gap location due to the effects of forest canopy. Subalpine forest in western Sichuan is a typical cold biome,which often displays sensitive responses to environment disturbance because of its fragile characters. As yet,more and more recent studies have concentrated on gap characteristics and seedling regeneration processes in this area,but little attention has been given to the effects of forest gap on soil enzyme activity. As we know,soil invertase and urease are the key enzymes involved in the soil organic carbon and nitrogen transformation,respectively,and the changes of their activities are closely associated with the carbon and nitrogen cycling. Therefore,to understand the effects of forest gap on soil invertase and urease activities at different seasons in alpine forest,a field experiment was conducted in a Picea asperata plantation forest in western Sichuan. The dynamics of soil invertase and urease activity under gap center,gap edge and under-canopy were investigated from June 2012 to May 2013.Soil samples in soil organic layer and mineral soil layer were collected in growing season( completely soil thawing stage,early stage and later stage of growing season) and freeze-thaw season( onset stage of freezing,deeply soil freezing stage and soil thawing stage). The results showed that soil invertase activity in soil organic layer was higher than that in mineral soil layer regardless of forest gap location. Soil invertase activity during the growing season in both soil organic layer and mineral soil layer showed the order: gap center under-canopy gap edge,but soil urease activity showed the order: gap center gap edge under-canopy. In comparison with gap edge and under-canopy,gap center exhibited higher soil invertase activity at onset stage of freezing and deeply soil freezing stage,while soil invertase activity in under-canopy was higher than that of gap center and gap edge at soil thawing stage. In addition,soil urease activity at onset stage of freezing and soil thawing stage was significantly higher in under-canopy than that in gap center and gap edge,although which at deeply soil freezing stage showed few differences in different gap locations. The results here imply that gap location has a profound impact on soil invertase and urease activities at different seasons in subalpine forest.