Effects of a surface wildfire on soil nutrient and microbial functional diversity in a shrubbery

The aim of the study was to determine effects of a wildfire on soil nutrients and soil microbial functional diversity in short-term time scales. Burned and unburned control soil samples were collected 1 day, and 2, 4, 8, 10, 12 and 15 months after a shrubbery fire in Yumin county of Xinjiang, Northwest China. Nutrients of soil in each sampling time were detected and soil microbial functional diversity was measured by Biolog Eco plates. Results of the study showed that soil nutrients were significantly affected by fire. Soil pH increased immediately after the wildfire and was higher than that of unburned soil during 15 months post fire. Soil organic matter and total N significantly decreased immediately after the fire and was even lower than control soil at the 15th month post fire. Soil available P level increased sharply during the 4th month after the fire, and later reached to the maximum value with eight times higher than that of unburned soil. Soil available N and available K were more than the control site in 2 months after the fire, then decreased, but available N began to increase, when vegetations restored 1 year after the fire. Soil microbial activity and functional diversity recovered gradually after fire. The average well color development (AWCD) and functional diversity indices (Shannon index, Simpson index, and McIntosh index) decreased significantly 1 day after the fire, but then increased and were similar to that of undisturbed soil 15 months after the fire, when plant started to regenerate in burned area. The changes in soil nutrients after the fire affected soil microbial activity and functional diversity. Correlation analysis revealed that AWCD was negatively correlated with soil pH and positively correlated with soil total N and available N, Shannon and Simpson index had positive significantly correlation with soil total N and McIntosh index had positive significantly correlation with available N. Result of principal component analysis based on the data of carbons metabolism showed that microbial catabolic profiles of burned soils of each sampling time after the wildfire were different and all were distinct from those of unburned soils, which might suggest that microbial community structure of fire-impacted area changed dynamically on monthly scale and was distinct from that of the control site in 15 months after fire, although microbial activity or richness showed similar to pre-fire level at the 15th month post-fire.