C and N cycle monitoring under Quercus castaneifolia plantation

In temperate forests, oak (Quercus castaneifolia) is an important species that grows along an elevation gradient from the flood prone plains to high topographical positions of the landscape. This study was aimed to monitor the effect of oak plantation on the soil C and N cycles and dynamics in the north of Iran. We tested the following hypotheses: (i) reclamation of deforested areas, planting of oak can improve topsoil fertility via forest floor inputs in the long-term, (ii) soil C and N microbial indices can be enhanced under oak plantation, 25 years after planting. For this purpose, three afforested oak stands with 15, 20, and 25 years old, besides a site without plantation, were selected and thirty samples per each site were taken from forest floor and soil (20 x 20 x 10 cm) layers and their physicochemical, biological, and enzymatic properties were assessed. The acquired data demonstrated that forest floor quality, physicochemical and biological properties and enzymatic activities (i.e. urease, acid phosphatase, arylsulfatase and invertase) have been changed over time of oak plantation. Moreover, the microbial activity of soil C and N include basal respiration (BR), substrate inducted respiration (SIR), microbial biomass carbon (MBC), Metabolic quotient (qCO(2)), microbial entropy (MBC/C), carbon availability index (CM), carbon management index (CMI), particle organic carbon (POC) and dissolved organic carbon (DOC) were significantly higher in the plantation areas than without plantation site. Oak plantation significantly improved the N microbial characteristics [NH4+, NO3-, N mineralization, microbial biomass nitrogen (MBN), particle organic nitrogen (PON) and dissolved organic nitrogen (DON)]. Under different land covers, soil microbial activities were more affected by variations in forest floor and soil chemical properties with higher ratio of C, N and available nutrients. Taken together, plantation with suitable native broadleaved species could be considered to rehabilitate degraded natural forests through improving soil quality. Findings also highlighted the importance of understanding C and N cycles in the plantation areas which could involve in global warming phenomena.