Soil properties, labile pools of soil organic carbon and their variations under broadleaf and coniferous plantation in Hyrcanian forest, northern Iran

Afforestation, as a tool to mitigate carbon emission is constrained by available land area in several countries, but Iran has the potential of plantation. In doing so, differences in soil stocks between tree species could give an indication of the effects of future management changes. Hence, a better understanding of tree species traits on soil properties is required to predict how changes in ecosystems occur with tree species composition. This study investigated the effect of selected tree species on soil properties, carbon sequestration potential of tree species across soil profiles (0-200 cm) and evaluated the tree species effects on labile soil organic carbon pools to introduce a unique soil quality indicator. The study site was Shalman Research Station in the Hyrcanian forests, northern Iran. Our results showed significant alterations in soil properties by tree species with the greatest changes in the top soil layer. The greatest cation exchange capacity (CEC) difference (Δ 4.17) was found between A. glutinosa and J. polycarpos in 0-20 cm. The greatest differences (Δ 2.58) in mean weight diameter (MWD) of soil layers were found in the top soil layer between A. glutinosa and T. distichum. All species produced also a higher N and organic carbon concentration in the top soil layer (0-20 cm) in the following order: A. glutinosa > Q. castaneifolia > P. caspica > J. polycarpos > T. distichum > P. taeda. The varied amount of total soil organic carbon stocks was greater under Alder (A. glutinosa) and Oak (Q. castaneifolia) than other tree species with 206.24 and 195.26 (Mg.ha-1), respectively; and P. taeda had the lowest amount (136.94 Mg ha-1) across the soil profile. For all labile pools, A. glutinosa and T. distichum had the highest and the lowest percent of labile organic carbon, respectively. Consequently, the Cmin in the range of 10.11-14.04% and microbial biomass carbon in the range of 1.05-1.66% shared the highest and lowest proportion of soil organic carbon across 0-200 cm depth, respectively. We concluded that broadleaf trees had great potential for carbon sequestration across soil depth and among them; alder had high effect on soil properties and soil organic matter.