The effects of natural forest succession on soil respiration in Bieszczady National Park (south-eastern Poland)

The Polish Carpathian Mountains characterise the unique landscape containing high valuable seminatural mountain meadows. However, due to land abonnement, especially decrease agriculture and pasture activity, land cover changes occur. As a result of such changes, natural forest succession in the Carpathians become more and more widespread process. Despite, landscape transformations the natural forest succession is an important issue of science in the context of carbon sequestration. It is well known, that soil organic carbon is the largest terrestrial organic carbon pool in the world. Land cover transformations are regarded as the most dynamic factors of soil organic carbon changes. So far, studies have presented no clear organic carbon accumulation pattern, there is a lack of study covered different land use conversions.

Soil microbiota is the major factor influence on decomposition and transformation of organic matter in the soil. One of the predominantly measured parameters of microbial activity is soil respiration. Moreover, soil respiration is widely used as an indicator of soil quality, degree of development and especially the carbon cycling dynamics. Furthermore, understanding the mechanism controlling microbial respiration is critical to efforts to model carbon cycling at a regional and global scale. The purpose of this study was to investigate the influence of natural forest succession on microbial respiration.

The study area was located in Bieszczady National Park in south-eastern Poland. The samples from two layers (0-10 cm and 10-20 cm) in the four transects each consisted of a meadow, a succession (covered by 30-60 years trees) and a forest (more than 150 years old trees) were taken. Microbial respiration was determined by the incubation method. Respiration was measured for 5 weeks in closed vials. During the three days, the soil was carried in the vial with the small baker containing NaOH and hermetically closed. After this period the baker was removed and trapped CO₂ was quantified by titration with HCl and with participation BaCl₂. Additionally, based on the first-order kinetic model of microbial respiration cumulative respiration, the content of carbon available for microbial respiration present at the start of the experiment and the rate constant were calculated. Moreover, other microbiological, chemical and physical soil properties were determined in previous research.

Soil respiration C-CO₂ after the first week of incubation was significantly higher in the 0-10 cm layer compare to 10-20 cm, however, after the fifth week of incubation differences between investigated layers were no significant differences. In the 0-10 cm layer, the highest cumulative respiration was observed in succession (74.9 mgC-CO₂ g^-1 h^-24) and the lowest in forest (51.9 mgC-CO₂ g^-1 h^-24). However, in the 10-20 cm layer meadow characterised the highest cumulative respiration (42.0 mgC-CO₂ g^-1 h^-24) and forest the lowest (26.8 mgC-CO₂ g^-1 h^-24). Following cumulative respiration, significant the highest content of carbon available for microbial respiration was observed in succession and meadow, in the 0-10 and 10-20 cm layers respectively. Cumulative respiration of investigated soils was positively correlated with total nitrogen content, microbial biomass carbon as well as dehydrogenase and cellulase activity.