Annual variability of soil, microbial, and root respiration rates in a mixed oriental beech-hornbeam stand (Case study: Shast-Kalateh forest of Gorgan)

Soil respiration is the first way to return the carbon dioxide fixed in the vegetation into the atmosphere and plays an important role in the respiration of terrestrial ecosystems. This study aims to investigate the monthly and seasonal variability of soil respiration and its components (microbial and root respiration) rates in a mixed oriental beech stand located at Hyrcanian forests using a dynamic closed chamber system and root exclusion method. A total number of six locations with an area of 400 square meters were selected randomly at the canopy gaps and its adjacent closed canopy at Shast-kalateh forest, Gorgan. One sample plot with an area of 9 square meters (3×3) was installed at each location. Soil, microbial, and root respiration rates and some environmental factors were monthly measured during one year (from October 2016 to September 2017). The amount of soil, microbial, and root CO2 efflux ranges were 0.66-4.81, 0.3-3.41, and 0.36-1.43 μmol m-2 s-1, respectively. The highest increase in the soil, microbial, and root respiration rates were in summer (4.29, 2.86 and 1.34 μmol m-2 s-1, respectively), while the lowest rates were observed in winter (0.94, 0.54 and 0.41 μmol m-2 s-1, respectively). We found that the microbial respiration rate in the canopy gaps was greater than that of the closed canopy, but the rate of root respiration under the closed canopy was higher. Soil respiration rate had a positive significant correlation with soil temperature but had a negative significant correlation with soil moisture content. Variation in soil moisture content and soil temperature could change the soil biological characteristics, consequently soil fertility, and chemical properties. Therefore, we suggest the measurement of soil biological properties in the artificial gap with different areas for modeling the process of soil characteristics changes in the gap.