Effects of micro-climatic conditions on soil properties along a climate gradient in oak forests, west of Iran: Emphasizing phosphatase and urease enzyme activity

Abstract

Climatic characteristics are among most important factors influence on soil properties. Changes in climatic characteristics could be derived in different scales such as local-scale changes in topographical factors (i.e., slope aspect, known as micro-climate). However, the effects of micro-climate condition on soil properties (especially enzyme activity that are effective on nutrient cycles) along climatic gradient have rarely been investigated in arid and semi-arid forest ecosystems. For this purpose, soil sampling was carried out using 60 composite soil samples in three regions with different climate conditions including slightly-arid, moderately-arid and semi-arid in two slope aspects (north vs. south) in oak forests, western Iran. The results showed that urease and phosphatase enzymes activity significantly varied as a function of climate condition, with humped-shaped patterns through the climate gradient. Soil respiration (R), substrate induced respiration (SIR) and microbial biomass carbon (MBC) simultaneously reflected the influence of the climate condition and slope aspect (p < 0.05). From slightly-arid to semi-arid areas, the soil chemical, biological (R and SIR), and physical (saturation point) properties significantly increased while, soil lime, EC, pH, and silt declined (p < 0.05). Structural equation modelling showed that, the soil's chemical and biological properties were the best mediators for indirect effects of climate condition and slope aspects on soil enzyme activities. The results also revealed that the phosphatase enzyme is indirectly influenced by climatic condition (β = 0.114 and P-value = 0.029) and slope aspect (β = -0.067 and P-value = 0.05), while the urease enzyme was directly and indirectly affected by climate condition and slope aspect, respectively. The principal component analysis indicated that it was easier to separate the climatic region than to separate them based on the slope's aspect. This study suggested that on a large scale, climatic characteristics play a more critical role in changing soil properties. Still, on a small scale, the slope aspect determines changes in soil biology.