Soil microbial activity in response to fire severity in Zagros oak (Quercus brantii Lindl.) forests, Iran, after one year

The Zagros forest ecosystem is being threatened by increasing number of forest fires. These forests are generally in coppice form and oak sprout clumps occupy forest area like patches. We examined some microbial and physical-chemical properties of burned soil to understand the response of soil microbial activity to different fire severities one year after burning. Soil collected from areas subjected to different fire severities was visually classified as: unburned-inside of sprout clumps (UI), unburned-outside of sprout clumps (UO), burned with low severity-outside of sprout clumps (BLO), burned with moderate severity-inside of sprout clumps (BMI), and burned with high severity-inside of sprout clumps (BHI). Increases in soil pH and available P and decreases in soil N and C/N ratio occurred only at BHI. SOC decreased in BHI and BMI compared to UI but no change was observed in BLO compared to UO. The areas subjected to high severity burn contained the most bacterial and the least fungal colony forming units (CFUs). Basal respiration decreased in BMI and BHI while substrate-induced respiration (SIR), and alkaline and acid phosphatase activities were only decreased in BHI compared UI. Discriminate analysis showed that the linear combination of acid and alkaline phosphatase activity, fungal CFUs, and SIR were respectively the most effective variables to differentiate the treatments. We concluded that acid and alkaline phosphatase activities can efficiently represent the degree of fire impact on soil even one year after fire.