Using Real-Time Quantitative PCR to Examine the Dynamics of Soil Fungi and Bacteria in Response to Ecosystem Warming.

As atmospheric trace gas concentrations and global temperatures climb, scientists are challenged to determine how microbial communities may mediate plant response to future climate change. To this end, a Temperature Free-Air Controlled Enrichment (T-FACE) experiment was implemented in a spring wheat (Triticum aestivum) field in Maricopa, Arizona. The T-FACE system features infrared-heater-based warming of the canopy by 3 and 1.5 ^oC during night-and daytime, respectively. Following a December 2008 planting, soil samples were collected on 13 Jan, 30 Jan, and  18 Feb 2009 at three different depths (0-5; 5-10; and 10-15 cm) from heated plots, non-heated open control plots, and  reference plots with “dummy” non-functional heaters. Following soil DNA extraction, real-time PCR was used to quantify bacterial and fungal markers. Results from the first sampling revealed strong responses in microbial biomass to soil heating, averaging 2.3 x 10⁷ (bacterial) and 6.0 x 10⁵ (fungal) markers g^-1 dry soil in the 0-15 cm depth of heated soils, and 9.0 x 10⁵ (bacterial) and 1.3 x 10⁴ (fungal) markers in control soils. Increases in fungal markers under T-FACE were largest in the 0-5 cm depth, averaging 5.3 x 10⁶ and 3.2 x 10³ markers g^-1 dry soil in heated and control plots, respectively, while bacterial markers increased most dramatically in the 10-15 cm depth (4.4 x 10⁷ and 7.7 x 10⁵ g^-1 dry soil in heated and control, respectively). No statistical differences were found in microbial markers between control and reference plots. Work quantifying microbial markers later in the growing season is currently underway. Knowledge of microbial response to increased temperatures will aid our ability to predict the interactions of plant species with their biological and physical environments in response to future climate change.