Carbon Dioxide, Methane and Nitrous Oxide Fluxes from Tree Stems in Silver Birch and Black Alder Stands with Drained and Naturally Wet Peat Soils

Abstract

The aim of this study was to evaluate the impact of groundwater level, soil temperature and general soil chemistry on greenhouse gas (GHG)—carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)—fluxes from tree stems in deciduous stands with nutrient-rich naturally wet and drained peat soils. In total, nine sample plots were established in the central and north-eastern part of Latvia. The studied tree species were silver birch (Betula pendula Roth.) and black alder (Alnus glutinosa (L.) Gaertb.). Tree stands of different ages and tree dimensions were selected for the study. GHG fluxes were measured with a circular-type non-transparent chamber of fixed area and volume, which was connected to the “Gasmet DX4040” mobile spectrometer. Ambient and soil temperature at a depth of 10 cm were measured, soil parameters (pH and content of carbon (C), nitrogen (N), potassium (K), phosphorus (P)) down to 30 cm depth were analyzed, and groundwater levels and weather conditions (wind, cloudiness, precipitation) were determined. The study found that CO2 fluxes from tree stems show a distinct seasonal pattern and a strong positive correlation with soil temperature. Significant differences in CO2 fluxes were found between temperature ranges below and above 5 °C, indicating that this temperature represents a threshold value. CH4 emissions from the tree stems increased with increasing groundwater levels. The impact of groundwater level becomes insignificant if the depth of the groundwater exceeds 30 cm. No significant N2O fluxes from tree stems were detected for most of the study period, except for March, April and June in black alder stands. As with CH4, N2O emissions exhibit an increase as groundwater levels rise. The C and N contents in soil have a significant impact on N2O fluxes from tree stems. There is a tendency for the N2O flux to increase along with increasing C and N contents in soil.