Soil-tree-atmosphere CH4 flux dynamics of boreal birch and spruce trees during spring leaf-out
Elisa Vainio, Iikka Haikarainen, Kateřina Macháčová, Anuliina Putkinen, Minna Santalahti, Markku Koskinen, Hannu Fritze, Tero Tuomivirta, Mari Pihlatie
Abstract
Abstract Aims Studies on tree CH 4 exchange in boreal forests regarding seasonality and role of tree canopies are rare. We aimed to quantify the contribution of boreal trees to the forest CH 4 budget during spring leaf-out and to reveal the role of microbes in the CH 4 exchange. Methods Methane fluxes of downy birch and Norway spruce ( Betula pubescens and Picea abies ) growing on fen and upland sites were measured together with soil CH 4 flux, environmental variables and microbial abundances involved in the CH 4 cycle. Tree CH 4 fluxes were studied from three stem heights and from shoots. Results The trees emitted CH 4 with higher stem emissions detected from birch and higher shoot emissions from spruce. The stem CH 4 emissions from birches at the fen were high (mean 45 µg m −2 h −1 ), decreasing with stem height. Their dynamics followed soil temperature, suggesting the emitted CH 4 originated from methanogenic activity, manifested in high mcrA gene copy numbers, in the peat soil. Methanogens were below the quantification limit in the tree tissues. Upscaled tree CH 4 emissions accounted for 22% of the total CH 4 emissions at the fen. Conclusions The variation in stem CH 4 flux between the trees and habitats is high, and the emissions from high-emitting birches increase as the spring proceeds. The lack of detection of methanogens or methanotrophs in the aboveground plant tissues suggests that these microbes did not have a significant role in the observed tree-derived fluxes. The stem-emitted CH 4 from birches at the fen is presumably produced microbially in the soil.