Temporal and Spatial Variations in the Abundance of Soil Denitrifying Bacteria in Australian Sclerophyll Forests: Effects of Prescribed Burning

Abstract

Nearly one fifth of Australia’s continent is covered by forests, including 147.4 million hectares of native forest and 2.0 million hectares of forestry plantations. Australia has about 4 percent of the world’s forests on 5 percent of the world’s land area. Prescribed burning has been extensively applied to manage forest fuels in Australia since the 1960s. It greatly decreases the wildfire hazard, promotes forest regeneration and controls insects and disease. Fire modifies both the above-ground vegetation and below-ground microbial community. Despite the significant role of prescribed burning in nitrogen (N) dynamics, most studies have focused only on the responses of one or several forest components (e.g. vegetation, microbial community or soil nutrients) to fire separately. Few studies have offered an in-depth insight into the relationship between soil N cycling processes and associated functional communities in response to long-term prescribed burning. Denitrification is an important part of forest N cycling. It is a stepwise dissimilative reduction process of nitrate (NO3-) to dinitrogen gas (N2) under anaerobic conditions and the primary pathway of nitrous oxide (N2O) emission from soil. This gaseous product has a global warming potential about 298 times greater than that of carbon dioxide (CO2). The potential environmental implication of denitrification to global warming has drawn increasing scientific attention worldwide. A variety of microbial functional groups participate in the denitrification process and each of them can be measured by targeting one or more specific functional genes.