Tree species effects on soil chemical, biochemical and biological features in mixed Caspian lowland forests

Abstract

Tree influence on litter and soil features is detectable even in a mixed stand and the soil landscape may be considered as a mosaic of profiles reflecting the occurrence and chemical characteristics of the various tree species present. The forest soils can be strongly influenced by tree species. Many studies have addressed the effects of monocultures on soil features, but few have examined the effects of individual trees within a mixed stand. This work illustrates the differences of litter and soil characteristics in a coastal mixed forest stand in northern Iran. For this purpose, the Alnus glutinosa (AG), Populus caspica (PC), Ulmus minor (UM) and Parrotia persica (PP) species were examined; litter and soil samples were taken under tree canopy cover. Litter quality differed among the tree species, with the highest total N concentration (1.83%) and lowest organic C (38.38%) under AG species. Soil pH (7.19), EC (0.29 ds/m), total N (0.33%), available P (26.21 mg kg−1), available Ca (257.30 mg kg−1), available Mg (56.80 mg kg−1), earthworm density/biomass (4.00 n m−2 and 49.47 mg m−2, respectively), microbial respiration (0.49 mg CO2–C g soil −1 day−1), net soil ammonification (0.44 mg kg−1 day−1) and N mineralization rate (0.30 mg kg−1 day−1) were significantly higher under AG canopy whereas a higher content of available K (355.80 mg kg−1) and fine root biomass (95.02 g m−2) were found under the PC and UM tree species, respectively. Soil organic carbon and net soil nitrification were not significantly different among tree species. The results of this case study demonstrate that tree influence on litter and soil features is detectable even in a mixed stand and the soil landscape of such forests may be considered as a small-scale mosaic of profiles reflecting the occurrence and chemical characteristics of the various tree species present.