Factors controlling short-term soil microbial response after laboratory heating. Preliminary results

Soil microbial response after fire is controlled by numerous variables which conclude with a mosaic of results depending on organic carbon alterations or pH fire-induced changes. This fact has complicated the studies focused on post-fire microbial response, compiling high variability of opposite result in the bibliography. Soil laboratory heating cannot emulate a real wildfire effect on soil but lead us the possibility to control several variables and it is a valid tool to clarify the relative weight of different factors controlling microbial response after soil heating. In this preliminary study different heated treatments were applied to unaltered forest soil samples, obtaining 4 different heating treatments to simulate a range of fire intensities: unaltered-control (UH), and soil heated at 300, 450 and 500 ºC. In order to isolate possible nutrient availability or pH heating-induced changes, different culture media were prepared using soil:water extract from each heating treatments and adding different supplements to obtain the total of 11 different culture media: unheated soil without supplements (UH-N-), unheated soil with nutrient supplement (UH-N+), soil heated at 300 ºC without supplements (300-N-), soil heated at 300 ºC with nutrient supplement (300-N+), soil heated at 300 ºC with nutrient supplement and pH-buffered (300-N+pH); soil heated at 450 ºC without supplements (450-N-), soil heated at 450 ºC with nutrient supplement (450-N+), soil heated at 450 ºC with nutrient supplement and pH-buffered (450-N+); soil heated at 500 ºC without supplements (500-N-), soil heated at 500 ºC with nutrient supplement (500-N+), soil heated at 500 ºC with nutrient supplement and pH-buffered (500-N+). Each media was inoculated with different dilutions of a microbial suspension from the original unaltered soil, and the abundance of viable and cultivable microorganisms were measured by plate count method. In addition, the analysis of heating-induced soil organic matter alterat