1 Department of Sciences and Forest Engineering, Sari Agricultural Sciences and Natural Resources University, Sari, Iran
2 Department of Forestry, Tarbiat Modares University, Noor, Iran
3 Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland
Human demand for food and energy has led to significant changes in the level of reactive nitrogen (Nr) released to the atmosphere and then deposited in the biosphere. This study aimed to investigate artificial N deposition's impact on the forest floor and soil chemical properties in an oak (Quercus castaneifolia C. A. Mey) plantation in the north of Iran. Twelve plots of 200 m2 (20 m × 10 m) were set up in the study area. Four N treatments were considered: zero (control), 50 (low), 100 (medium), and 150 (high) kg N ha-1 year-1. N in the form of NH4NO3 solution was manually sprayed onto the understory plots monthly for one year. The total N, P, K, and organic C (OC) of the forest floor were measured. Soil N, available P, available K, pH, EC (electrical conductivity), OC, microbial biomass C (MBC), and urease enzme activity were measured in the 0-10 cm depth. The concentration of total N and P of the forest floor was significantly higher in the high N treatment. The total concentration of N (+36%), the urease activity (+44%), and EC (+12%) of soil increased with raising the high-N treatment compared to the control, but the MBC (-20%), available P (-28%), and available K (-15%) were significantly reduced in the high-N nitrogen treatment. The results of this short-term study indicated that high N inputs can affect the forest floor and soil chemistry in the north of Iran (Hyrcanian Forest). Our results were obtained with simulated deposition rates that exceed ambient fluxes, but ambient N deposition is nevertheless high in our study area. To assess the long-term effects of N deposition on the forest ecosystems, more aspects of the forest plantation characteristics, such as litter decomposition, microbial and fungi communities, and soil solution chemistry should be considered in future projects.
Keywords: ammonium nitrate, soil chemistry, microbial biomass carbon, urease enzyme activity, forest floor