Responses of Soil Dynamics under Two Contrasting Oak and Pine Stands in a Korean Temperate Forest

Abstract

Recently, forest environments have been continuously changed by the impacts of human activities such as industrialization and land-use changes. In forest ecosystems, maintaining a proper nutrient circulation system is essential for increasing forest productivity because organic matter properties, such as different plant residues, nutrient quality, and microbial activity, affect nutrient processes. The main environmental problems impacting forest soils are soil nitrogen deposition and deforestation. Therefore, the purpose of this study is to evaluate forest soil problems by assessing tree species, soil carbon, pH, and phosphorus. To do so, I developed four hypotheses.<br/> First, experiments using 15N-labeled urea were conducted for three years to assess the effect of nitrogen deposition on soil carbon and nitrogen dynamics under oak and pine forest stands in natural field conditions. Through this study, I revealed that the increases in total carbon and nitrogen contents due to nitrogen deposition were greater under coniferous forest stands than those under deciduous forest stands as a result of the greater mixing of new carbon substrates into the soil profile in this temperate forest. Second, I evaluated the effects of nitrogen treatment on the soils of two different forest floors on different sizes of soil aggregates and on soil organic carbon decomposition patterns. Through this study, I revealed that N treatments affect the decomposition of organic matter and soil aggregate distributions and that these effects depend on the tree species. Third, I evaluated the effects of nitrogen treatments on the soils of two different forest floors on humic substances and soil organic functional group patterns by soil aggregate size fraction. Through this study, I revealed that N treatment affects humic substances and soil organic functional groups and that these effects depend on the tree species. Fourth, I challenged the widely held notion that phosphorus availability increases due to liming by hypothesizing that an increase in soil pH induced by liming would instantaneously disturb the chemical equilibria among inorganic P species through extensive interactions with increased Ca2+ due to the dissolution of CaCO3 and with displaced Al3+ and Fe3+. Through this study, I revealed that the application of lime has an unexpected opposite impact on Al-, Fe- and Ca-P compounds, at least in the early stage of equilibrium disturbances.<br/> These results suggest that the soil carbon and phosphorus of forest soils are responsive to nitrogen application and liming and provide a foundation for investigating the impacts of tree species, soil aggregates, humic substances, soil organic functional groups, and phosphorus speciation.