Measurement of changes in labile pools of soil organic carbon and some soil properties under forest tree species in Northern Iran (Case study: Shalman Seed and Seedling of Forest Tree Species Research Station, Guilan Province)

Deep insight about the different effect of forest tree species on soil quality properties have made soil health monitoring perspective clear concerning sustainable management; however, restoration and reclamation of deteriorates inflicted on natural ecosystems may be managed through proper selection of tree species. In this study, in order to select suitable tree species in afforestation projects, Shalman Seed and Seedling of Forest Tree Species Research Station (Guilan province) was chosen as a study area to investigate carbon storage rates and effect of conifers and broadleaves on soil properties, Consequently, soil carbon labile pools were evaluated to present unique sensitive indicator of health and soil quality.
Sampling of 10 layers with thickness of 20 cm were taken from 0-200 cm depth under selected tree species plots, including Populus caspica, Oak (Quercus castaneifolia), Alder (Alnus glutinosa), Bald cypress (Taxodium distichum), Loblolly pine (Pinus taeda) and Juniper ( Juniperus polycarpos). Cation exchang capacity, mean weight diameter, EC, pH, bulk density, total nitrogen, soil organic carbon and its labile pools were analyzed in soil samples of 0-20, 20-40, 40-60 and 60-80 cm and just for carbon storage measurements all of 10 layers (0-200 cm) were considered. The experiments were of randomized complete block (RCB) designs. Data for the same soil interval were subjected to two-way analysis of variance (ANOVA). Person linear Correlation method was used to determine sensitive indicators of soil quality.
Preliminary results indicated the significant effects of tree species on soil properties during soil depth. Despite insignificant differences in EC, pH and BD, our results showed that significant alterations by tree species types were found in the 0-20 cm soil layer. However, the greatest difference on CEC and MWD values were also observed in the 0-20 cm soil thickness between Alder vs. Juniper; and Alder vs. Bald cypress, respectively. All species had also higher total nitrogen (TN) and soil organic carbon (SOC) in the top soil layer (0-20 cm) followed the order: A. glutinosa > Q. castaneifolia > P. caspica > J. polycarpos > T. distichum > P. taeda. The measured amount of total soil organic carbon as a carbon storage was the highest and the lowest under Alder (A. glutinosa) and Loblolly pine (Pinus taeda) with 206.24 and 136.94 (ton OC ha-1), respectively.
Broadleaves, especially N fixer species such as Alder had the greatest effect on soil quality properties. Broadleaves had also great potential for carbon storage with more uniform distribution during soil depth. However, among broadleaves, Alder had great effect on soil properties and soil organic matter. Finally, according to correlation values, no single and more sensitive organic carbon pool as a soil quality indicator of forest tree species changes was selected, but the complex of soil organic carbon pools could be used as sensitive indicators of soil quality and health.