Various processes that occur in forest soils have significant roles in the forest carbon cycle and contribute to soil CO2 efflux. Soil CO2 efflux occurs via a combination between the metabolism of soil microorganisms and the respiration of plant roots. It releases around 10 times more CO2 than all anthropogenic factors combined. For this reason, diurnal and seasonal carbon efflux rates were measured in Lithuanian Scots pine (P. sylvestris) forests to determine soil CO2 efflux rates and the relative importance of various climatic factors that can influence belowground conditions. The aim of this study was to determine the factors that have the strongest influence on variation in forest soil CO2 efflux and the mutual influence between the factors, in order to attain a clearer understanding of C sinks. We took measurements of soil CO2 efflux to examine diurnal and seasonal variation. For the continuous measurement of CO2 efflux, an ADC BioScientific LCpro+ soil respiration analysis system was used. The main parameters that were measured were CO2 efflux (μmol m-2 s-1), air temperature (°C) in the chamber, soil temperature (°C) at a depth of 10 cm and water evaporation (mmol m-2 s-1). The diurnal rate values fluctuated within a certain range (2.78–6.17 μmol m-2 s-1), while seasonal variations fluctuated more, but the average CO2 efflux rate was between 2 - 4 μmol m-2 s-1. The highest CO2 efflux rate recorded during daytime was from 16:00–20:00, and the lowest one was early in the morning, between 05:00–08:00. During the seasonal soil CO2 efflux study, it was found that peak forest growth was related to peak efflux rates. These rates were observed from early to mid-June. The collected data suggest that SM (soil moisture) has a weaker connection with the efflux rate but had an impact on Ts (soil temperature), dampening its effect on soil CO2 efflux. These results demonstrate that the soil CO2 efflux of P. sylvestris forests in the cool climatic zone of Lithuania depend most heavily on soil temperature and soil moisture.

26.3.2021