The impact of Persian oak (Quercus brantii Lindl.) on soil characteristics in a declining forest

Root activity has an important impact on soil development but we have little knowledge of the interaction of the root zone and soil genetic horizons. The aim of this investigation was to study the interactions between soil chemical characteristics and root zone processes in a declining Persian oak forest (Quercus brantii Lindl.). A randomized complete block design was used to investigate the long-term effect of Persian oak on soil horizons, and the chemical and biological properties in two soil zones (under and outside the canopy). Results indicate that the rhizosphere zone had significantly higher total organic carbon (TOC) than outside the canopy soil in the upper soil horizons. In subsurface horizons, water-extractable organic carbon values were significantly higher in rhizosphere than in non-rhizospheric zone. Microbial biomass carbon (MBC) values in the rhizospheric zone decreased from the first to the second horizon. The MBC/TOC ratio indicated significant differences between the rhizosphere and soils outside of the canopy, with the exception of the subsurface horizon. In the subsurface horizon of the rhizosphere, there was greater respiration of organic carbon (∑CO2/TOC) than in outside of canopy soil. In addition, root processes influenced pH, nitrogen fractions, and availability of phosphorus, potassium, iron, zinc and manganese. Differences in soil characteristics between rhizospheric and non-rhizospheric zones were significant in surface horizons due to higher root density than in deeper soil layers. The findings indicate that Persian oak (Quercus brantii Lindl.) roots influenced the main soil chemical properties, even in calcareous soils.