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Aims: Studies on tree CH4 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 CH4 budget during spring leaf-out and to reveal the role of microbes in the CH4 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 CH4 flux, environmental variables and microbial abundances involved in the CH4 cycle. Tree CH4 fluxes were studied from three stem heights and from shoots. Results: The trees emitted CH4 with higher stem emissions detected from birch and higher shoot emissions from spruce. The stem CH4 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 CH4 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 CH4 emissions accounted for 22% of the total CH4 emissions at the fen. Conclusions: The variation in stem CH4 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 CH4 from birches at the fen is presumably produced microbially in the soil. [ABSTRACT FROM AUTHOR]

Abstract: A thinned and an unthinned treatment were compared in a 62-year-old pine stand located in northeastern Germany (Brandenburg, Ost-Prignitz, Revier Beerenbusch) (year of thinning: 1999, degree of canopy opening: [...]

A study was conducted to describe the effects of artificial acidification on the humus microbial community structure using total-community-level methods. The water content of fresh humus was correlated with the water holding capacity prior respiration studies. Dry combustion was carried out to determine total organic carbon and nitrogen while bacterial growth rates were estimated by thymidine and leucine. Results showed that the humus was acidified as a result of the acid treatments.

The microbes present in the heavy metal polluted Scandinavian coniferous forests show an increase in the concentration of branched phospholipid fatty acids (PLFAs) and a decrease in the 20:4 and 18:2-omega-6 PLFAs that are the main PLFAs in most fungi. The change in the PLFAs content is due to a bacterial tolerance to pollution. The fungal part of the microbial populations is more sensitive to heavy metals than the bacterial part. The PLFA composition analysis and the tolerance of bacteria are useful in determining heavy metal pollution in field sites.

Soil carbon sequestration has gained traction as a mean to mitigate rising atmospheric carbon dioxide concentrations. Verification of different methods' efficiency to increase soil carbon sink requires, in addition to good quality measurements, reliable models capable of simulating the effect of the sequestration practises. One way to get insight of the methods' effects on carbon cycling processes is to analyse different carbon isotope concentrations in soil organic matter. In this paper we introduce a carbon-13 isotope specific soil organic matter decomposition add-on into the Yasso soil carbon model and assess its functionality. The new 13C-dedicated decomposition is straightforward to implement and depends linearly on the default Yasso model parameters and the relative carbon isotope (13C/12C) concentration. Despite of their simplicity, the modifications considerably improve the model behaviour in a 50-year long simulation. [ABSTRACT FROM AUTHOR]