Long-term dynamics of soil, tree stem and ecosystem methane fluxes in a riparian forest

Funding Information: This study was supported by the Ministry of Education and Science of Estonia (SF0180127s08 grant), the Estonian Research Council (IUT2-16, PRG-352, and MOBERC20), the Czech Science Foundation (17-18112Y), SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797), the Ministry of Education, Youth and Sports of Czech Republic within the National Sustainability Program I (NPU I, grant number LO1415), the EU through the European Regional Development Fund (ENVIRON and EcolChange Centres of Excellence, Estonia, and MOBTP101 returning researcher grant by the Mobilitas Pluss programme), the European Social Fund (Doctoral School of Earth Sciences and Ecology). This work was also supported by Academy of Finland (294088, 288494), from the European Research Council (ERC) under the European Union?s Horizon 2020 research and innovation programme under grant agreement No [757695], and a Department of Energy (DOE) grant to JPM (DE-SC0008165). Funding Information: This study was supported by the Ministry of Education and Science of Estonia ( SF0180127s08 grant), the Estonian Research Council ( IUT2-16 , PRG-352 , and MOBERC20 ), the Czech Science Foundation ( 17-18112Y ), SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions ( CZ.02.1.01/0.0/0.0/16_019/0000797 ), the Ministry of Education, Youth and Sports of Czech Republic within the National Sustainability Program I (NPU I, grant number LO1415 ), the EU through the European Regional Development Fund (ENVIRON and EcolChange Centres of Excellence, Estonia, and MOBTP101 returning researcher grant by the Mobilitas Pluss programme), the European Social Fund (Doctoral School of Earth Sciences and Ecology). This work was also supported by Academy of Finland ( 294088 , 288494 ), from the European Research Council (ERC) under the European Union‘s Horizon 2020 research and innovation programme under grant agreement No [ 757695 ], and a Department of Energy (DOE) grant to JPM ( DE-SC0008165 ). Publisher Copyright: © 2021 Elsevier B.V.The carbon (C) budgets of riparian forests are sensitive to climatic variability. Therefore, riparian forests are hot spots of C cycling in landscapes. Only a limited number of studies on continuous measurements of methane (CH4) fluxes from riparian forests is available. Here, we report continuous high-frequency soil and ecosystem (eddy-covariance; EC) measurements of CH4 fluxes with a quantum cascade laser absorption spectrometer for a 2.5-year period and measurements of CH4 fluxes from tree stems using manual chambers for a 1.5 year period from a temperate riparian Alnus incana forest. The results demonstrate that the riparian forest is a minor net annual sink of CH4 consuming 0.24 kg CH4-C ha−1 y−1. Soil water content is the most important determinant of soil, stem, and EC fluxes, followed by soil temperature. There were significant differences in CH4 fluxes between the wet and dry periods. During the wet period, 83% of CH4 was emitted from the tree stems while the ecosystem-level emission was equal to the sum of soil and stem emissions. During the dry period, CH4 was substantially consumed in the soil whereas stem emissions were very low. A significant difference between the EC fluxes and the sum of soil and stem fluxes during the dry period is most likely caused by emission from the canopy whereas at the ecosystem level the forest was a clear CH4 sink. Our results together with past measurements of CH4 fluxes in other riparian forests suggest that temperate riparian forests can be long-term CH4 sinks.Peer reviewe

Tree stems are a net source of CH4 and N2O in a hemiboreal drained peatland forest during the winter period

Nutrient-rich northern peatlands are often drained to enhance forest productivity, turning peatland soils into sinks of methane (CH _4 ) and sources of nitrous oxide (N _2 O). However, further attention is needed on CH _4 and N _2 O dynamics during the winter period to fully understand the spatio-temporal variability of fluxes. Besides soil, tree stems can also emit CH _4 and N _2 O. However, stem contribution is not considered in most biogeochemical models. We determined the temporal dynamics of winter-time CH _4 and N _2 O fluxes in a drained peatland forest by simultaneously measuring stem and soil fluxes and exploring the relationships between gas fluxes and soil environmental parameters. During sampling (October 2020–May 2021), gas samples from Downy Birch ( Betula pubescens ) and Norway Spruce ( Picea abies ) trees were collected from different tree heights using manual static chambers and analysed using gas chromatography. Soil CH _4 and N _2 O concentrations were measured using an automated dynamic soil chamber system. Tree stems were a net source of CH _4 and N _2 O during the winter period. The origin of stem CH _4 emissions was unclear, as stem and soil CH _4 fluxes had opposite flux directions, and the irregular vertical stem flux profile did not indicate a connection between stem and soil fluxes. Stem N _2 O emissions may have originated from the soil, as emissions decreased with increasing stem height and were driven by soil N _2 O emissions and environmental parameters. Soil was a net sink for CH _4 , largely determined by changes in soil temperature. Soil N _2 O dynamics were characterised by hot moments—short periods of high emissions related to changes in soil water content. Tree stem emissions offset the soil CH _4 sink by 14% and added 2% to forest floor N _2 O emissions. Therefore, CH _4 and N _2 O budgets that do not incorporate stem emissions can overestimate the sink strength or underestimate the total emissions of the ecosystem

Combined effects of glacial retreat and penguin activity on soil greenhouse gas fluxes on South Georgia, sub-Antarctica

The effects of soil succession after glacial retreat and fertilisation by marine animals are known to have major impacts on soil greenhouse gas (GHG) fluxes in polar terrestrial ecosystems. While in many polar coastal areas retreating glaciers open up new ground for marine animals to colonise, little is known about the combination of both factors on the local GHG budget. We studied the magnitude of GHG fluxes (CO2, CH4 and N2O) on the combined effect of glacial retreat and penguin-induced fertilisation along a transect protruding into the world’s largest King Penguin (Aptenodytes patagonicus) colony at Saint Andrews Bay on sub-Antarctic South Georgia. GHG production and consumption rates were assessed based on laboratory incubations of intact soil cores and nutrients and water additional experimental incubations. The oldest soils along the transect show significant higher contents of soil carbon, nutrients and moisture and were strongly influenced by penguin activity. We found a net CH4 consumption along the entire transect with a marked decrease within the penguin colony. CO2 production strongly increased along the transect, while N2O production rates were low near the glacier front and increased markedly within the penguin colony. Controlled applications of guano resulted in a significant increase in CO2 and N2O production, and decrease in CH4 consumption, except for sites already strongly influenced by penguin activity. The results show that soil microbial activity promptly catalyses a turnover of soil C and atmospheric methane oxidation in de-glaciated forelands. The methane oxidizers, however, may increase relatively slowly in their capacity to oxidise atmospheric CH4. Results show also that the increase of nutrients by penguins reduces CH4 oxidation whereas N2O production is greatly increased. A future expansion of penguins into newly available ice-free polar coastal areas may therefore markedly increase the local GHG budget