Changes in soil chemical and microbial properties after a wildfire in a tropical rainforest in Sabah, Malaysia

Changes in soil caused by drought and wildfire in a Dipterocarp rainforest in Sabah, Malaysia were assessed by phosphorus fractionation, extractable nitrogen and nutrient limited respiration kinetics (after addition of glucose+N or P). Fire increased the concentration of total phosphorus (P) in the litter layer (per ha and per dry soil) by raising the 0.2 M NaOH extractable-P. In the soil organic layer, membrane exchangeable P was reduced by fire while 1.0 M HCl extractable-P, and 0.5 M NaHCO3 extractable-P increased. Microbially available P increased after the fire and was most closely related to NaOH extractable-P that has been considered available to plants only over long time-scales. Total nitrogen (N) increased in the litter layer (per ha and per dry soil) due to post-fire litter fall, while the NO3− increased up to 10-fold down to the 10 cm mineral soil. In contrast, the microbially available N decreased by 50%. Basal respiration and substrate-induced respiration increased in the litter layer and decreased in the organic horizon (per dry soil and per organic matter). P limited microbial growth resulted in a slow and non-exponential increase in respiration, presumably reflecting the P-fixing nature of the soils, while N limitation resulted in a fast exponential increase. However, higher respiration rates were eventually achieved under P limitation than under N limitation.