Nutrient utilization by pine seedlings and soil microbes in oligotrophic pine barrens forest soils subjected to prescribed fire treatment

The purpose of this greenhouse experiment was to examine the short-term effects of competition between pine seedlings and the soil microbial biomass in sandy oligotrophic pine barrens upland forest soils subjected to varying levels of prescribed fire severity. Pine seedling growth performance, microbial biomass nitrogen, extractable soil nutrients and leaching loss from the soil were determined, throughout a single growing season following fire treatment. Replicate soil cores exposed to three levels of fire severity were maintained in a greenhouse with or without a pine seedling. Throughout the following growing season replicate cores from each treatment were harvested and analyzed monthly. The data allowed testing for two main effects: soil fire treatment and tree presence/absence. In no instance was a significant fire treatment X tree presence/absence interaction found. Our results indicate that biological activity strongly influences soil conditions. Reduced microbial activity resulted from the interaction of soil microbial biomass and an individual pine seedling. Increased plant growth performance correlates with reduced soil mineral nitrogen concentration and decreased pH. At the levels of fire severity utilized in this experiment immobilization due to biological uptake and abiotic soil fixation prevented significant leaching losses above that of unburned control samples. In the oligotrophic, pine barrens soils, nitrogen and phosphorus mineralized by fire are largely conserved by biological processes. These results also suggest that plant growth is subject to limitation by phosphorus availability in these soils.