Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 14, 2012
Publication Date: February 3, 2013
Citation: 2013. Summer fire increases plant-available nitrogen and phosphorus in the Northern Great Plains. Society for Range Management Meeting Oklahoma City, OK. February 3-7, 2013. Abstract #0191. Technical Abstract: Fire is an important process maintaining ecosystem functioning in grasslands. Most wildfires in the western U.S. burn during summer and coincide with the greatest fire danger. Consequently, experimental data are lacking and little is known about the impacts of summer fire on ecosystem function. Since nitrogen is the primary limiting nutrient in terrestrial ecosystems, understanding its response to fire is critical. We sampled soils from August 2011 - October 2012 to quantify the effects of summer fire on available soil nutrients (resins), total soil nutrients (cores), and used quantitative PCR (qPCR) of nitrogen-fixation (nifH gene) quantity (DNA) and activity (RNA) in the northern Great Plains. Comparisons were made using three replicate plots exposed to various summer fire return intervals (1.5-yr, 3-yr, 6-yr, and non-burned) assessed seasonally throughout the year. Residual nitrogen pools (cores) remained low and were similar across treatments. However, plant-available nitrogen pools (resins) were greater in burned plots (1.5 – 4-fold greater). A similar response was observed for plant-available phosphorus (1.2 – 2.0-fold increases), while the inverse was true for iron (14 – 40% declines). In burn treatments, available nutrient levels often remained elevated. Burning assessments with qPCR on the nifH gene indicated additional nitrogen was not coming from soil microbial communities. Return interval also influenced the abundance (DNA) and activity (RNA) of nitrogen-fixing bacterial genes in soils, with recently burned plots showing decreased gene abundance and activity. Results suggest burns cause persistent changes in available soil nutrients which might facilitate plant recovery and increase forage quality post-fire.