The effect of landform on soil microbial activity and biomass in a Hyrcanian oriental beech stand

Beech stands in Hyrcanian forests cover a hilly landscape with many topographical ridge-valley gradients or catenas. This study aims at providing important insights regarding the role of landscape shape and position on the drivers of soil microbial biomass and activity in these forest ecosystems. Variations in the depth profiles (0-15, 15-30 and 30-45 cm) of soil organic carbon (OC), total nitrogen (TN), soil water content (SWC), soil microbial respiration (SR), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and metabolic coefficient (qCO2) were evaluated at different slope positions (the summit, shoulder, back slope, foot slope and toe slope) along both concave (C-shaped) and convex-shaped (V-shaped) catenas. The results of our study evidenced that catena shape and slope position significantly influenced most of the parameters evaluated, confirming the importance of topography in creating heterogeneity in soil properties. In general, the significantly greater soil microbial biomass and activities observed in C-shaped with respect to V-shaped catenas, and in lower with respect to upper slope positions was related to higher SWC, OC and TN contents. We concluded that spatial variability in water and substrate availabilities are important components in determining microbial activities and the cycling of limiting nutrients for plant growth in different microsite ecosystems present in catenas.