The Radiation Budget of a Subarctic Woodland Canopy

Open woodland is a major sub-type of the circum global boreal forest zone. In Canada it dominates the basins of a number of large hydroelectric schemes in which snowmelt is a critical phase of the hydrologic cycle. The forest vegetation strongly influences the radiant energy flux to the snow and is therefore important in the production of snowmelt runoff and its prediction. The radiation budget of a subarctic open woodland canopy in northern Quebec is computed from measurements of net allwave, solar and longwave radiation components over the snowpack at treeless and woodland sites. The canopy gains solar radiation both directly and from solar radiation reflected off the snowpack, the latter enhanced by the larger spacing between tree crowns. Canopy heating from absorbed solar radiation leads to a considerable longwave flux being emitted by the tree crowns. Overall, the radiant energy exchange in the open woodland behaves differently than for a closed crown forest. This is believed to be a function of a variety of canopy characteristics, not solely of tree crown density.Key Words: snowmelt, open woodland, radiation budget, northern QuebecMots clés: fonte des neiges, forêt claire, taux de rayonnement, nord du Québe

Axial force imparted by a current-free magnetically expanding plasma

The axial force imparted from a magnetically expanding, current-free, radiofrequency plasma is directly measured. For an argon gas flow rate of 25 sccm and an effective rf input power of ∼800W, a maximum force of ∼6mN is obtained; ∼3mN of which is transmitted via the expanding magnetic field. The measured forces are reasonably compared with a simple fluid model associated with the measured electron pressure. The model suggests that the total force is the sum of an electron pressure inside the source and a Lorentz force due to the electron diamagnetic drift current and the applied radial magnetic field. It is shown that the Lorentz force is greatest near the magnetic nozzle surface where the radial pressure gradient is largest.A part of this work is financially supported by an Australian Research Council Discovery grant (DP 1096653), an Australian Research Council Linkage grant (LP 0883456), a Grant-in-Aid for Young Scientists (A 22684031) from MEXT in Japan, and the TEPCO Research Foundation

The Annual Carbon Budget for Fen and Forest in a Wetland at Arctic Treeline

Three separate research efforts conducted in the same wetland-peatland system in the northern Hudson Bay Lowland near the town of Churchill, Manitoba, allow a comparison of two carbon budget estimates, one derived from long-term growth rates of organic soil and the other based on shorter-term flux measurements. For a tundra fen and an open subarctic forest, calculations of organic soil accumulation or loss over the last half-century indicate that while the fen on average has lost small amounts of carbon from the ecosystem, the adjacent forest has gained larger amounts of atmospheric carbon dioxide. These longer-term data are supported by shorter-term flux measurements and estimates, which also show carbon loss by the fen and carbon uptake by the forest. The shorter-term data indicate that the fen's carbon loss is largely attributable to exceptionally dry years, especially if they are warm. The forest may gain carbon at an increased rate as it matures and during warm growing seasons. Also, the changes in relief of the dynamic hummock-hollow landscape in the fen may inhibit photosynthesis.Trois travaux de recherche distincts portant sur le même système de marécages/tourbières situés dans la partie septentrionale des basses-terres de la baie d'Hudson, près de la ville de Churchill au Manitoba, permettent de comparer deux estimations du budget de carbone, l'une tirée des taux de croissance à long terme du sol organique et l'autre fondée sur des mesures du flux à plus court terme. Pour une tourbière basse de toundra et une forêt claire subarctique, les calculs de l'accumulation ou de la perte de sol organique au cours des cinquante dernières années révèlent que, si la tourbière basse a perdu en moyenne de petites quantités du carbone présent dans l'écosystème, la forêt adjacente a acquis des quantités plus grandes de bioxyde de carbone atmosphérique. Ces données établies sur une période relativement longue sont étayées par des mesures et estimations du flux à plus court terme, qui révèlent également une perte de carbone par la tourbière basse et une absorption de carbone par la forêt. Les données à plus court terme montrent que la perte de carbone par la tourbière basse est due en grande partie à des années de sécheresse exceptionnelle, surtout s'il fait chaud. Il se peut que la forêt acquière du carbone à une vitesse accrue en devenant mature et au cours des saisons de croissance chaudes. Il est en outre possible que les changements dans le relief dynamique en bosses et en creux de la tourbière basse bloquent la photosynthèse

Carbon dioxide fluxes of tundra vegetation communities on an esker top in the low-Arctic

Previous studies have shown that carbon dioxide fluxes vary considerably among Arctic environments and it is important to assess these differences in order to develop our understanding of the role of Arctic tundra in the global carbon cycle. Although many previous studies have examined tundra carbon dioxide fluxes, few have concentrated on elevated terrain (hills and ridge tops) that is exposed to harsh environmental conditions resulting in sparse vegetation cover and seemingly low productivity. In this study we measured carbon dioxide (CO2) exchange of four common tundra communities on the crest of an esker located in the central Canadian low-Arctic. The objectives were to quantify and compare CO2 fluxes from these communities, investigate responses to environmental variables and qualitatively compare fluxes with those from similar communities growing in less harsh lowland tundra environments. Measurements made during July and August 2010 show there was little difference in net ecosystem exchange (NEE) and gross ecosystem production (GEP) among the three deciduous shrub communities, Arctous alpina, Betula glandulosa and Vaccinium uliginosum, with means ranging from −4.09 to −6.57 μmol·m−2·s−1 and −7.92 to −9.24 μmol·m−2·s−1, respectively. Empetrum nigrum communities had significantly smaller mean NEE and GEP (−1.74 and −4.08 μmol·m−2·s−1, respectively). Ecosystem respiration (ER) was similar for all communities (2.56 to 3.03 μmol·m−2·s−1), except the B. glandulosa community which had a larger mean flux (4.66 μmol·m−2·s−1). Overall, fluxes for these esker-top communities were near the upper range of fluxes reported for other tundra communities. ER was related to soil temperature in all of the communities. Only B. glandulosa GEP and ER showed sensitivity to a persistent decline in soil moisture throughout the study. These findings may have important implications for how esker tops would be treated in construction of regional carbon budgets and for predicting the impacts of climate change on Arctic tundra future carbon budgets

F.A.R.O.G. FORUM, Vol. 5 No. 6

https://digitalcommons.library.umaine.edu/francoamericain_forum/1018/thumbnail.jp

Hypoxia drives glucose transporter 3 expression through HIF-mediated induction of the long non-coding RNA NICI

Hypoxia inducible transcription factors (HIFs) directly dictate the expression of multiple RNA species including novel and as yet uncharacterized long non-coding transcripts with unknown function. We used pan-genomic HIF-binding and transcriptomic data to identify a novel long non-coding RNA NICI (Non-coding Intergenic Co-Induced transcript) on chromosome 12p13.31 which is regulated by hypoxia via HIF-1 promoter-binding in multiple cell types. CRISPR/Cas9-mediated deletion of the hypoxia-response element revealed co-regulation of NICI and the neighboring protein-coding gene, solute carrier family 2 member 3 (SLC2A3) which encodes the high-affinity glucose transporter 3 (GLUT3). Knock-down or knock-out of NICI attenuated hypoxic induction of SLC2A3 indicating a direct regulatory role of NICI in SLC2A3 expression, which was further evidenced by CRISPR/Cas9-VPR mediated activation of NICI expression. We also demonstrate that regulation of SLC2A3 is mediated through transcriptional activation rather than post-transcriptional mechanisms since knock-out of NICI leads to reduced recruitment of RNA polymerase 2 to the SLC2A3 promoter. Consistent with this we observe NICI-dependent regulation of glucose consumption and cell proliferation. Furthermore, NICI expression is regulated by the VHL tumour suppressor and is highly expressed in clear cell renal cancer, where SLC2A3 expression is associated with patient prognosis, implying an important role for the HIF/NICI/SLC2A3 axis in this malignancy

Relationship between ecosystem productivity and photosynthetically active radiation for northern peatlands

We analyzed the relationship between new ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density of PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe. NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data set for all peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola (NEE = PPFD P max (PPFD + PMAX) + R) better described the NEE-PPFD relationships ,while bogs had lower respiration rates (R = -2.0 umol m-2 s-1 for bogs and -2.7 umol m-2 s-1 for fens) and lower NEE at moderate and high light levels (Pmax = 5.2 umol m-2 s-1) than the upland exosystems (closed canopy forest, grassland, and cropland) summarized by Ruimy et al. [1995]. Despite this low productivity, northern peatland soil carbon pools are generally 5-50 times larger than upland ecosystems because of slow rates of decomposition caused by litter quality and anaerobic, cold soils

Interannual and spatial impacts of phenological transitions, growing season length, and spring and autumn temperatures on carbon sequestration: A North America flux data synthesis

Understanding feedbacks of ecosystem carbon sequestration to climate change is an urgent step in developing future ecosystem models. Using 187 site-years of flux data observed at 24 sites covering three plant functional types (i.e. evergreen forests (EF), deciduous forests (DF) and non-forest ecosystems (NF) (e.g., crop, grassland, wetland)) in North America, we present an analysis of both interannual and spatial relationships between annual net ecosystem production (NEP) and phenological indicators, including the flux-based carbon uptake period (CUP) and its transitions, degree-day-derived growing season length (GSL), and spring and autumn temperatures. Diverse responses were acquired between annul NEP and these indicators across PFTs. Forest ecosystems showed consistent patterns and sensitivities in the responses of annual NEP to CUP and its transitions both interannually and spatially. The NF ecosystems, on the contrary, exhibited different trends between interannual and spatial relationships. The impact of CUP onset on annual NEP in NF ecosystems was interannually negative but spatially positive. Generally, the GSL was observed to be a likely good indicator of annual NEP for all PFTs both interannually and spatially, although with relatively moderate correlations in NF sites. Both spring and autumn temperatures were positively correlated with annual NEP across sites while this potential was greatly reduced temporally with only negative impacts of autumn temperature on annual NEP in DF sites. Our analysis showed that DF ecosystems have the highest efficiency in accumulating NEP from warmer spring temperature and prolonged GSL, suggesting that future climate warming will favor deciduous species over evergreen species, and supporting the earlier observation that ecosystems with the greatest net carbon uptake have the longest GSL