Biology subjects

Virkkala, A.-M.

Publications and source records attributed to Virkkala, A.-M..

6 recordsLinked to original sources

bioRxiv2025

Microbial community composition explains wintertime greenhouse gas fluxes in an oroarctic tundra ecosystem

Microbial communities play a central role in regulating the greenhouse gas balance in soil ecosystems. Microorganisms are active in the cold, snow-covered Arctic tundra soils; however, their contribution to the greenhouse gas budget during the Arctic winter remains poorly understood. To investigate the functional activity of bacterial and archaeal communities in oroarctic tundra soils during late winter, metatranscriptomic samples were collected alongside greenhouse gas (GHG) flux measurements across key vegetation types, which represent pH and moisture gradients. The transcription of central carbohydrate metabolism genes, various stress-related genes, and high carbon dioxide (CO2) fluxes evidenced active microbial metabolism in winter. Vegetation type, soil C/N ratio, pH, and water content explained the functional activity and microbial community composition during winter. The transcription of functional marker genes for methane oxidation and denitrification, coupled with flux data, suggests that shrublands and meadows act as methane (CH4) sinks in winter, while all vegetation types function as small nitrous oxide (N2O) sources. Our results further demonstrate that the soil microbial community has a significant impact on wintertime GHG emissions in the oroarctic tundra, thereby enhancing the explanatory power of a statistical model beyond that of abiotic environmental variables alone. This represents a promising step toward developing microbial-mediated models, which are crucial for improving predictions of ecosystem responses to climate change.

microbiology↗

bioRxiv2024

An increasing Arctic-Boreal CO2 sink despite strong regional sources

The Arctic-Boreal Zone (ABZ) is rapidly warming, impacting its large soil carbon stocks. We use a new compilation of terrestrial ecosystem CO2 fluxes, geospatial datasets and random forest models to show that although the ABZ was an increasing terrestrial CO2 sink from 2001 to 2020 (mean {+/-} standard deviation in net ecosystem exchange: -548 {+/-} 140 Tg C yr-1; trend: -14 Tg C yr-1, p<0.001), more than 30% of the region was a net CO2 source. Tundra regions may have already started to function on average as CO2 sources, demonstrating a critical shift in carbon dynamics. After factoring in fire emissions, the increasing ABZ sink was no longer statistically significant (budget: -319 {+/-} 140 Tg C yr-1; trend: -9 Tg C yr-1), with the permafrost region becoming CO2 neutral (budget: -24 {+/-} 123 Tg C yr-1; trend: -3 Tg C yr-1), underscoring the importance of fire in this region.

ecology↗

bioRxiv2021

The activity and functions of subarctic soil microbial communities vary across vegetation types

Increased microbial activity in high-latitude soils due to climate change might lead to higher greenhouse gas (GHG) emissions. However, mechanisms of microbial GHG production and consumption in tundra soils are not thoroughly understood. We analyzed 116 soil metatranscriptomes from 73 sites in the Finnish sub-Arctic to investigate how the diversity and functional potential of bacterial and archaeal communities vary across vegetation types and soil layers. Soils differed in physicochemical conditions, with meadow soils being characterized by higher pH and low soil organic matter (SOM) and carbon/nitrogen ratio whereas dwarf shrub-dominated ecosystems with high SOM and low pH. Actinobacteria, Acidobacteria, Alphaproteobacteria, and Planctomycetes predominated all communities but there were significant differences on genus level between vegetation types, as plant polymer degrading groups were more active in shrub-dominated soils compared to meadows. Given that climate change scenarios predict expansion in dwarf shrubs at high latitudes, our results indicate that the rate of carbon turnover in tundra soils may increase in the future. Additionally, transcripts of methanotrophs were detected in the mineral layer of all soils, potentially moderating methane fluxes from deeper layers. In all, this study provides new insights into possible shifts in tundra microbial diversity and activity with climate change.

microbiology↗

bioRxiv2019

Plant community functional composition and diversity drive fine-scale variability in carbon cycling in the tundra

O_LIThe functional composition and diversity of plant communities are globally applicable predictors of ecosystem functioning. Yet, it is unclear how traits influence carbon cycling. This is an important question in the tundra where vegetation shifts are occurring across the entire biome, and where soil organic carbon stocks are large and vulnerable to environmental change. C_LIO_LITo study how traits affect carbon cycling in the tundra, we built a model that explained carbon cycling (above-ground and soil organic carbon stocks, and photosynthetic and respiratory fluxes) with abiotic conditions (air temperature and soil moisture), plant community functional composition (average plant height, leaf dry matter content (LDMC) and specific leaf area (SLA)), and functional diversity (weighted standard deviations of the traits). Data was collected from an observational study setting from northern Finland. C_LIO_LIThe explanatory power of the models was relatively high, but a large part of variation in soil organic carbon stocks remained unexplained. Plant height was the strongest predictor of all carbon cycling variables except soil carbon stocks. Communities of larger plants were associated with larger CO2 fluxes and above-ground carbon stocks. Communities with fast leaf economics (i.e. high SLA and low LDMC) had higher photosynthesis, ecosystem respiration, and soil organic carbon stocks. C_LIO_LIWithin-community variability in plant height, SLA, and LDMC affected ecosystem functions differently. SLA and LDMC diversity increased CO2 fluxes and soil organic carbon stocks, while height diversity increased the above-ground carbon stock. The contributions of functional diversity metrics to ecosystem functioning were about as important as those of average SLA and LDMC traits. C_LIO_LISynthesis: Plant height, SLA, and LDMC have clear effects on tundra carbon cycling. The importance of functional diversity highlights a potentially important mechanism controlling the vast tundra carbon pools that should be better recognized. More research on root traits and decomposer communities is needed to understand the below-ground mechanisms regulating carbon cycling in the tundra. C_LI

ecology↗

bioRxiv2019

Woody plants constructing tundra soils

In tundra, woody plants are expanding towards higher latitudes and altitudes due to increasingly favourable climatic conditions. Their expansion may also occur through increases in the coverage and height of the plants. These shifts may cascade further across the ecosystem, such as in the foundations of tundra: that is, in the soils. Yet, little is known about the effects woody plants have on local soil conditions. Here, we examined if the coverage and height of woody plants affect the growing-season soil moisture and temperature as well as soil organic carbon stocks. We carried out a field observation study in a dwarf shrub-dominated tundra and built a hierarchical model. We found that, after controlling for other possible factors influencing woody plants and soil conditions (namely, topography, snow, and the overall plant coverage), the coverage of woody plants inversely correlated with all three soil conditions. Yet, we found no link between the woody plant height to the soil variables. This indicates that woody plants affect local soil conditions in various ways, depending upon whether their expansion occurs though the growth of coverage or their height. Nevertheless, woody plants likely alter the very ground of the entire tundra system and feedback into the global climate system through the water, energy, and carbon cycles of tundra.

ecology↗

bioRxiv2019

Snow is an important control of plant community functional composition

The functional composition of plant communities is a critical modulator of climate change impacts on ecosystems, but it is not a simple function of regional climate. In the Arctic tundra, where climate change is proceeding the most rapidly, communities have not shifted their trait composition as predicted by spatial temperature-trait relationships. Important causal pathways are thus missing from models of trait composition change. Here, we study causes of plant community functional variation in a tundra landscape. We consider the community weighted means of plant vegetative height, as well as two traits related to the leaf economic spectrum. Specifically, we model their responses to locally measured summer air temperature, snow conditions, and soil resource levels. For each of the traits we also quantify the importance of intraspecific trait variation (ITV) for between-community functional differences and trait-environment matching. Our study shows that in a tundra landscape 1) snow is the most influential abiotic variable affecting functional composition, 2) vegetation height is under weak local environmental control, whereas leaf economics is under strong local environmental control, 3) the relative magnitude of ITV differs between traits, and 4) ITV is not very consequential for community-level trait-environment relationships.

ecology↗