Comparing soil microbial eco-physiological and enzymatic response to fire in the semi-arid Zagros woodlands

Fire is a major ecological factor altering soil properties that may remain for a long time. Little is known about the sensitivity to fire and post-fire recovery in soil microbial and biochemical properties in the semi-arid woodlands. The main objective of this study was to compare the changes in some microbial and biochemical properties in different years after fire. This study was conducted across a wildfire chronosequence in the semi-arid Zagros oak woodlands. We considered three fire treatments including 1, 3, and 10 years after fire. Then the soil samples were collected in a completely random design from each of the treatments. Soil microbial eco-physiological and enzymatic activities were measured for all the treatments and their relevant unburned control. The results indicated that soil organic carbon (Corg) decreased 1 year after fire (27%) and still remained lower for 3 years after fire (22%) and even for 10 years after (21%) compared to the controls. Microbial biomass carbon (Cmic) significantly decreased (77%) 1 year after the fire, whereas the value of basal respiration (BR) remained unchanged. The value of Cmic for the treatments 3 and 10 years after fire recovered to the unburned level. 1 year after the fire the ratio of BR to Cmic (qCO2) was three times as much as the control. Although the value of BR was lower (p < 0.05) for the treatment 3 years after the fire, the value of qCO2 was higher (p < 0.05) compared to the control. The value of absolute enzyme activities was generally lower (p < 0.05) 1 year after the fire. However, it recovered 3 years after the fire to the unburned level. In comparison to the absolute enzyme activity, the specific enzyme activity showed a different trend and generally increased 1 year after the fire. The absolute activity of acid phosphatase (ACP) was significantly lower (p < 0.05) 10 years after the fire, while the ratio of ACP/Corg was higher (p < 0.05) compared to the control. It was concluded that specific activity of enzymes are more efficient indicators to reveal the post-fire changes in soil quality in medium and long-term studies.