The effects of fire and seasonal variations on soil properties in Juniperus excelsa M. Bieb. stands in the Alborz Mountains, Iran

Abstract

This study was conducted in Juniperus excelsa stands on the southern slopes of Iran's Alborz Mountains, to determine the effects of fire and seasonal variations on soil physicochemical properties and enzyme activities. A total of 64 composite soil samples were randomly collected in the spring and fall from two burned and unburned sites at depths of 0−10 and 10−20 cm. The results of a two-way ANOVA analysis indicate that fire increased the organic carbon (OC), total nitrogen (TN), and available phosphorus (P_ava) contents of the soil by 16%, 59%, and 53%, respectively. Similarly, when burned sites were compared to unburned sites, the activities of acid phosphatase (ACP) and urease enzymes increased by 73% and 12%, respectively. Nevertheless, fire did not affect soil texture, bulk density (BD), pH, electric conductivity (EC), exchangeable potassium (K_exc), or the activities of alkaline phosphatase (ALP) and dehydrogenase. According to two-way ANOVA results, OC, TN, P_ava, K_exc, and EC values were significantly higher in the fall, whereas pH and ALP values were significantly higher in the spring. Additionally, phosphorous and dehydrogenase activity were significantly different in selected soil factors at 0−10 and 10–20 cm depths. The interaction of fire, season, and soil depth were significant for phosphorous and urease. Moreover, the activity of ALP correlated well with pH (r = 0.68), P (r =  − 0.74), OC (r =  − 0.53), and TN (r =  − 0.37), whereas the activity of ACP correlated significantly with OC (r = 0.64) and TN (r = 0.71). Two years after the fire, soil properties in J. excelsa stands had either improved or remained unaffected, returning to pre-fire levels. Additionally, soil chemical properties varied significantly across sampling seasons, which should be considered when comparing and interpreting soil data in future research.

Keywords

Dehydrogenase / Acid & alkaline phosphatases / Seasonal variations / Soil physicochemical properties / Urease