Dynamics Of Microbial Biomass In Soil Organic Layer As Affected By Alpine Forest Gap

Forest soil organic layer is the organic residues which accumulated in the soil surface from fresh litter to humified soil, including three layers as, fresh litter layer, fragmented litter layer and humified layer. Due to it is the interface between soil and air, soil organic layer is the most sensitive ecosystems to ongoing environmental change.As a result of it, the environmental gradients formed by the redistribution of precipitation and radiation form forest canopy may play an important role in dynamic of microbial biomass in soil organic layer, but so far less information has been available on it. Different levels of birch (Betula albosinensis), larch (Larix mastersiana), cypress (Sabina saltuaria) and fir (Abies faxoniana) litter are the majority components in soil organic layer in alpine forest. Therefore, microbial biomass in fresh litter layer, fragmented litter layer and humified layer were investigated in the non-growing season (onset of freezing period before snow cover, deep freezing period under snow cover,thawing period after snow cover) and the growing season (early growing season and late growing season) from2010to2012as litter decomposition proceeded. Different snow patches with different snow depths in winter were selected from uncercanopy to innergap. The results showed that:(1).Snow patches with different depths in winter which caused by forest gap significantly affected microbial biomass of soil organic layer in the alpine forest. In growing season, the redistributed rainfall and light generated largely varied hydrothermal environment, which influenced the dynamics of the microbial biomass. Both snow cover thickness in non-growing season and temperature in growing season decreased with the increase of canopy density.These observations suggested that forest canopy played a protective role in the stability of microenvironment.(2). The forest gaps significantly affected the dynamics of the microbial biomass. In non-growing season, microbial biomass increased with the increase of snow depth. In growing season, microbial biomass decreased with increaing temperature but increased with increasing humidity. Microbial biomass decreased with decreasing temperature during the non-growing season in LL, but which in FL increased. However, both LL and FL displayed the opposite sides during growing season. The stability showed the order as LL> FL> HL, which indicated that the deeper soil layer, the more stable microenvironment.(3). Forest gap significantly affected microbial biomass carbon, nitrogen and phosphorus during the fresh litter decomposition of four species, but the affected ways were different. In the non-growing season, the microbial biomass carbon, nitrogen, phosphorus of the soil organic layer increased with increasing gap sizes. Microbial biomass carbon, nitrogen and phosphorus were different among different species, i.e. microbial biomass carbon showed the order as larch>birch> fir>cypress; microbial biomass nitrogen showed the order as birch> larch> cypress> fir; and microbial biomass phosphorus showed the order as birch> larch> fir>cypress. Overall, microbial biomass carbon, nitrogen and phosphorus were higher during the decomposition of broad-leaved litter compared with coniferous litter.(4). Forest gap affected microbial biomass carbon, nitrogen, phosphorus in fragmented litter layer with different levels. During non-growing season, microbial biomass decreased with increasing gap size, but dispayed the trend as increase and then decrease during growing season. Microbial biomass carbon was relative stable throughout the year. Microbial biomass phosphorus in growing season was significantly higher than that in the non-growing season. Therfore, the microbial biomass of fragmented litter layer was relatively stable.(5). Forest gaps did also significantly affect microbial biomass carbon, nitrogen, phosphorus in the humified layer. In the non-growing season, microbial biomass increased with increasing snow thickness, while decreased with increasing gap sizes in the growing season. The volatility of microbial biomass performed as microbial biomass phosphorus>microbial biomass nitrogen> microbial biomass carbon. Humified layer, at the bottom of organic layer, still was remarkable affected by snow, which showed an increase trend in microbial biomass during the frozen period.In summary, alpine forest gaps could significantly affect microbial biomass in soil organic layer with different levels. Soil temperature is an important regulator in organic matter decompositions, and microbial biomass in the growing season was significantly higher than that in the non-growing season. Forest gaps affected microbial biomass through influencing the micro-environment of the living space of microorganisms, and further regulated microbial processes in the whole organic layer. Alpine forests are very sensitive to the changing climate. Consequently, the micro-environment of the alpine forest and the associated organic layer can be influenced by the ongoing climate change. The results provided scientific evidences for understanding the responses of organic layer in alpine ecosystems to climate change.