Vegetation Influence and Environmental Controls on Greenhouse Gas Fluxes from a Drained Thermokarst Lake in the Western Canadian Arctic

Abstract. Thermokarst features are widespread in ice-rich regions of the circumpolar Arctic. The rate of thermokarst lake formation and drainage is anticipated to accelerate as the climate warms. However, it is uncertain how these dynamic features impact the terrestrial Arctic carbon cycle. Methane (CH4) and carbon dioxide (CO2) fluxes were measured during peak growing season using eddy covariance and chambers at Illisarvik, a 0.16 km2 thermokarst lake basin that was experimentally drained in 1978 on Richards Island, Northwest Territories, Canada. Vegetation in the basin differs markedly from the surrounding dwarf-shrub tundra and included patches of tall shrubs, grasses and sedges with some bare ground and a small pond in the centre. During the study period, temperature and wind conditions were highly variable and soil water content decreased steadily. Basin scaled net ecosystem exchange (NEE) measured by eddy covariance was −1.5 [CI95 % ± 0.2] g C-CO2 m−2 d−1; NEE followed a marked diurnal pattern with no trend during the study period. NEE was primary controlled by photosynthetic photon flux density and influenced by vapor pressure deficit, volumetric water content and the presence of shrubs. By contrast, net methane exchange (NME) was low (8.7 [CI95 % ± 0.4] mg CH4 m−2 d−1 and had little impact on the carbon balance of the basin during the study period. NME displayed high spatial variability, sedge areas in the basin were the strongest source of CH4 while upland areas outside the basin were a net sink. Soil moisture and temperature were the main environmental factors influencing NME, having a positive and negative effect respectively.

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Vegetation influence and environmental controls on greenhouse gas fluxes from a drained thermokarst lake in the western Canadian Arctic

Biogeosciences ◽

10.5194/bg-17-4421-2020 ◽

2020 ◽

Vol 17 (17) ◽

pp. 4421-4441

Author(s):

June Skeeter ◽

Andreas Christen ◽

Andrée-Anne Laforce ◽

Elyn Humphreys ◽

Greg Henry

Keyword(s):

Water Content ◽

Eddy Covariance ◽

Vapour Pressure Deficit ◽

Growing Season ◽

Photon Flux ◽

Photon Flux Density ◽

Lake Basin ◽

Thermokarst Lake ◽

Environmental Controls ◽

Lake Formation

Abstract. Thermokarst features are widespread in ice-rich regions of the circumpolar Arctic. The rate of thermokarst lake formation and drainage is anticipated to accelerate as the climate warms. However, it is uncertain how these dynamic features impact the terrestrial Arctic carbon cycle. Methane (CH4) and carbon dioxide (CO2) fluxes were measured during peak growing season using eddy covariance and chambers at Illisarvik, a 0.16 km2 thermokarst lake basin that was experimentally drained in 1978 on Richards Island, Northwest Territories, Canada. Vegetation in the basin differs markedly from the surrounding dwarf-shrub tundra and included patches of tall shrubs, grasses, and sedges with some bare ground and a small pond in the centre. During the peak growing season, temperature and wind conditions were highly variable, and soil water content decreased steadily. Basin-scaled net ecosystem CO2 exchange (NEE) measured by eddy covariance was −1.5 [CI95 %±0.2] g C−CO2 m-2d-1; NEE followed a marked diurnal pattern with no day-to-day trend during the study period. Variations in half-hourly NEE were primarily controlled by photosynthetic photon flux density and influenced by vapour pressure deficit, volumetric water content, and the presence of shrubs within the flux tower footprint, which varied with wind direction. Net methane exchange (NME) was low (8.7 [CI95 %±0.4] mgCH4m-2d-1) and had little impact on the growing season carbon balance of the basin. NME displayed high spatial variability, and sedge areas in the basin were the strongest source of CH4 while upland areas outside the basin were a net sink. Soil moisture and temperature were the main environmental factors influencing NME. Presently, Illisarvik is a carbon sink during the peak growing season. However, these results suggest that rates of growing season CO2 and CH4 exchange rates may change as the basin's vegetation community continues to evolve.

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Analyzing the major drivers of NEE in a Mediterranean alpine shrubland

Biogeosciences ◽

10.5194/bg-7-2601-2010 ◽

2010 ◽

Vol 7 (9) ◽

pp. 2601-2611 ◽

Cited By ~ 30

Author(s):

B. R. Reverter ◽

E. P. Sánchez-Cañete ◽

V. Resco ◽

P. Serrano-Ortiz ◽

C. Oyonarte ◽

...

Keyword(s):

Net Ecosystem Exchange ◽

High Elevation ◽

Photosynthetic Photon Flux Density ◽

Photon Flux ◽

Photon Flux Density ◽

Precipitation Pattern ◽

Key Factors ◽

Cold Temperatures ◽

Carbon Sequestration Potential ◽

Sequestration Potential

Abstract. Two years of continuous measurements of net ecosystem exchange (NEE) using the eddy covariance technique were made over a Mediterranean alpine shrubland. This ecosystem was found to be a net source of CO2 (+ 52 ± 7 g C m−2 and + 48 ± 7 g C m−2 for 2007 and 2008) during the two-year study period. To understand the reasons underlying this net release of CO2 into the atmosphere, we analysed the drivers of seasonal variability in NEE over these two years. We observed that the soil water availability – driven by the precipitation pattern – and the photosynthetic photon flux density (PPFD) are the key factors for understanding both the carbon sequestration potential and the duration of the photosynthetic period during the growing season. Finally, the effects of the self-heating correction to CO2 and H2O fluxes measured with the open-path infrared gas analyser were evaluated. Applying the correction turned the annual CO2 budget in 2007 from a sink (− 135 ± 7 g C m−2) to a source (+ 52 ± 7 g C m−2). The magnitude of this change is larger than reported previously and is shown to be due to the low air density and cold temperatures at this high elevation study site.

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Environmental controls over methanol emission from leaves

Biogeosciences Discussions ◽

10.5194/bgd-4-2593-2007 ◽

2007 ◽

Vol 4 (4) ◽

pp. 2593-2640 ◽

Cited By ~ 3

Author(s):

P. Harley ◽

J. Greenberg ◽

Ü. Niinemets ◽

A. Guenther

Keyword(s):

Stomatal Conductance ◽

Leaf Growth ◽

Dry Mass ◽

Leaf Temperature ◽

Photon Flux ◽

Photon Flux Density ◽

Emission Model ◽

Production Term ◽

Methanol Production ◽

Environmental Controls

Abstract. Methanol is found throughout the troposphere, with average concentrations second only to methane among atmospheric hydrocarbons. Proposed global methanol budgets are highly uncertain, but all agree that at least 60% of the total source arises from the terrestrial biosphere and primary emissions from plants. However, the magnitude of these emissions is also highly uncertain, and the environmental factors which control them require further elucidation. Using a temperature-controlled leaf enclosure, we measured methanol emissions from leaves of six plant species by proton transfer reaction mass spectrometry, with simultaneous measurements of leaf evapotranspiration and stomatal conductance. Rates of emission at 30°C varied from 0.3 to 38 μg g (dry mass)−1 h−1, with higher rates measured on young leaves, consistent with the production of methanol via pectin demethylation in expanding foliage. On average, emissions increased by a factor of 2.4 for each 10°C increase in leaf temperature. At constant temperature, emissions were also correlated with co-varying incident photosynthetic photon flux density and rates of stomatal conductance. The data were analyzed using the emission model developed by Niinemets and Reichstein (2003a, b), with the incorporation of a methanol production term that increased exponentially with temperature. It was concluded that control of emissions, during daytime, was shared by leaf temperature and stomatal conductance, although rates of production may also vary diurnally in response to variations in leaf growth rate in expanding leaves. The model, which generally provided reasonable simulations of the measured data during the day, significantly overestimated emissions on two sets of measurements made through the night, suggesting that production rates of methanol were reduced at night, perhaps because leaf growth was reduced or possibly through a direct effect of light on production. Although the short-term dynamics of methanol emissions can be successfully modeled only if stomatal conductance and compound solubility are taken into account, emissions on longer time scales will be determined by rates of methanol production, controls over which remain to be investigated.

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Analyzing the major drivers of NEE in an alpine Mediterranean shrubland

Biogeosciences Discussions ◽

10.5194/bgd-7-671-2010 ◽

2010 ◽

Vol 7 (1) ◽

pp. 671-696 ◽

Cited By ~ 2

Author(s):

B. R. Reverter ◽

E. P. Sánchez-Cañete ◽

V. Resco ◽

P. Serrano-Ortiz ◽

C. Oyonarte ◽

...

Keyword(s):

Environmental Changes ◽

Net Ecosystem Exchange ◽

Daily Basis ◽

Photosynthetic Photon Flux Density ◽

Photon Flux ◽

Exchange Potential ◽

Photon Flux Density ◽

Precipitation Pattern ◽

Carbon Sequestration Potential ◽

Sequestration Potential

Abstract. Two years of continuous measurements of net ecosystem exchange (NEE) using the eddy covariance technique were made over a Mediterranean alpine shrubland. These ecosystems are little studied, since they have little CO2 exchange potential. Nevertheless, their high susceptibility to environmental changes is far from being understood, introducing some uncertainty in terrestrial CO2 and water vapour assessments. High altitude sites might be undergoing a transition from sink to source of CO2, due to their high vulnerability to climate change. Indeed, this ecosystem was found to be a net source of CO2 (+52 g C m-2 and +48 g C m-2 for 2007 and 2008) during the two-year study period. To understand the reasons underlying this net release of CO2 into the atmosphere, we analysed the drivers of seasonal variability in NEE across these two years. We observed that the soil water availability – driven by the precipitation pattern – and the photosynthetic photon flux density (PPFD) are the key factors for understanding both the carbon sequestration potential and the duration of the photosynthetic period during the growing season. Finally, the effects of the Burba correction for both NEE and evapotranspiration (ET) are evaluated. This correction can sometimes be neglected on a daily basis, but becomes rather important in long-term assessments. For instance, the annual CO2 budget in 2007 turned from sink (-136 g C m-2) to source (+52 g C m-2) when the Burba correction was taken into account.

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Environmental controls over methanol emission from leaves

Biogeosciences ◽

10.5194/bg-4-1083-2007 ◽

2007 ◽

Vol 4 (6) ◽

pp. 1083-1099 ◽

Cited By ~ 72

Author(s):

P. Harley ◽

J. Greenberg ◽

Ü. Niinemets ◽

A. Guenther

Keyword(s):

Stomatal Conductance ◽

Leaf Growth ◽

Dry Mass ◽

Leaf Temperature ◽

Photon Flux ◽

Photon Flux Density ◽

Emission Model ◽

Production Term ◽

Methanol Production ◽

Environmental Controls

Abstract. Methanol is found throughout the troposphere, with average concentrations second only to methane among atmospheric hydrocarbons. Proposed global methanol budgets are highly uncertain, but all agree that at least 60% of the total source arises from the terrestrial biosphere and primary emissions from plants. However, the magnitude of these emissions is also highly uncertain, and the environmental factors which control them require further elucidation. Using a temperature-controlled leaf enclosure, we measured methanol emissions from leaves of six plant species by proton transfer reaction mass spectrometry, with simultaneous measurements of leaf evapotranspiration and stomatal conductance. Rates of emission at 30°C varied from 0.2 to 38 μg g (dry mass)−1 h−1, with higher rates measured on young leaves, consistent with the production of methanol via pectin demethylation in expanding foliage. On average, emissions increased by a factor of 2.3 for each 10°C increase in leaf temperature. At constant temperature, emissions were also correlated with co-varying incident photosynthetic photon flux density and rates of stomatal conductance. The data were analyzed using the emission model developed by Niinemets and Reichstein (2003a, b), with the incorporation of a methanol production term that increased exponentially with temperature. It was concluded that control of emissions, during daytime, was shared by leaf temperature and stomatal conductance, although rates of production may also vary diurnally in response to variations in leaf growth rate in expanding leaves. The model, which generally provided reasonable simulations of the measured data during the day, significantly overestimated emissions on two sets of measurements made through the night, suggesting that production rates of methanol were reduced at night, perhaps because leaf growth was reduced or possibly through a direct effect of light on production. Although the short-term dynamics of methanol emissions can be successfully modeled only if stomatal conductance and compound solubility are taken into account, emissions on longer time scales will be determined by rates of methanol production, controls over which remain to be investigated.

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The impact of chamber transparency on estimation of peatland net ecosystem exchange

ITM Web of Conferences ◽

10.1051/itmconf/20182300033 ◽

2018 ◽

Vol 23 ◽

pp. 00033

Author(s):

Marcin Stróżecki ◽

Anshu Rastogi ◽

Radosław Juszczak

Keyword(s):

Research Work ◽

Net Ecosystem Exchange ◽

Photosynthetic Photon Flux Density ◽

Photon Flux ◽

Photon Flux Density ◽

Atmospheric Conditions ◽

Measuring Chamber ◽

The Impact ◽

Modelling Process ◽

Selection Of

The purpose of this work was to quantify the variation of chamber transparency over the period of one month of measurements and its impact on estimates of peatland net ecosystem exchange. The automated transparent closed (non-steady-state) chambers are widely used for quantifying net carbon dioxide (CO2) fluxes exchanged between different canopies and the atmosphere. However, it is known that the transparency of the chamber, and hence the amount of radiation reaching the surface, is changing over time and depends on several factors, such as solar angle, obstacles, and cleanness of the chamber surface which is exposed to the environmental conditions. The objective of this research work was to determine if the material from which the measuring chamber is made maintains constant parameters for reduction of incoming radiation in the form of photosynthetic photon flux density (PPFD) inside the chamber. Based on the obtained results, it can be stated that during the specific atmospheric conditions, the average transparency of the measuring chamber of the automatic chamber system can drop even up to 20%. If not considered, it may lead to incorrect estimation of net ecosystem exchange (NEE). In case of our experiment, non-corrected NEE flux rates were five times higher than the same fluxes after corrections. For this reason, it is important to apply correction coefficients, which allow the selection of the appropriate value for PPFD during the NEE modelling process.

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Land use affects the net ecosystem CO<sub>2</sub> exchange and its components in mountain grasslands

Biogeosciences Discussions ◽

10.5194/bgd-6-11435-2009 ◽

2009 ◽

Vol 6 (6) ◽

pp. 11435-11462

Author(s):

M. Schmitt ◽

M. Bahn ◽

G. Wohlfahrt ◽

U. Tappeiner ◽

A. Cernusca

Keyword(s):

Land Use ◽

Ecosystem Respiration ◽

Net Ecosystem Exchange ◽

Co2 Exchange ◽

Photon Flux ◽

Major Influence ◽

Photon Flux Density ◽

Response Curves ◽

Area Index ◽

Mountain Grasslands

Abstract. Land-use change has been strongly affecting mountain grasslands, however, its controls on the net ecosystem exchange of CO2 (NEE) and its components have not yet been well documented. We analyzed chamber-based estimates of NEE, gross primary productivity (GPP), ecosystem respiration (R) and light use efficiency (LUE) of six mountain grasslands differing in land use, as measured during the growing seasons from 2002 to 2008. The main findings of the study are that: (1) land use affected seasonal NEE, GPP, R and LUE, which all decreased from managed to unmanaged grasslands; (2) these changes were explained by altered leaf area index (LAI), biomass and physiology; (3) diurnal variations of NEE were primarily controlled by photosynthetically active photon flux density (GPP) and soil and air temperature (R), seasonal variations were associated with changes in LAI; (4) parameters of light response curves were generally closely coupled, and the ratio R/GPP was nearly constant across the sites; (5) similarly to our study, GPP and R for other grasslands on the globe decreased with land-use intensity, while their ratio remained largely unchanged. We conclude that land use exerts a major influence on the net ecosystem CO2 exchange and its components in mountain grasslands.

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Effect of Pre-Harvest Supplemental UV-A/Blue and Red/Blue LED Lighting on Lettuce Growth and Nutritional Quality

Horticulturae ◽

10.3390/horticulturae7040080 ◽

2021 ◽

Vol 7 (4) ◽

pp. 80

Author(s):

Triston Hooks ◽

Joseph Masabni ◽

Ling Sun ◽

Genhua Niu

Keyword(s):

Blue Light ◽

Nutritional Quality ◽

Uv Light ◽

Ultra Violet ◽

Photon Flux ◽

Photon Flux Density ◽

Daily Light Integral ◽

Lettuce Growth ◽

Supplemental Lighting

Blue light and ultra-violet (UV) light have been shown to influence plant growth, morphology, and quality. In this study, we investigated the effects of pre-harvest supplemental lighting using UV-A and blue (UV-A/Blue) light and red and blue (RB) light on growth and nutritional quality of lettuce grown hydroponically in two greenhouse experiments. The RB spectrum was applied pre-harvest for two days or nights, while the UV-A/Blue spectrum was applied pre-harvest for two or four days or nights. All pre-harvest supplemental lighting treatments had a same duration of 12 h with a photon flux density (PFD) of 171 μmol m−2 s−1. Results of both experiments showed that pre-harvest supplemental lighting using UV A/Blue or RB light can increase the growth and nutritional quality of lettuce grown hydroponically. The enhancement of lettuce growth and nutritional quality by the pre-harvest supplemental lighting was more effective under low daily light integral (DLI) compared to a high DLI and tended to be more effective when applied during the night, regardless of spectrum.

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Light Quality Affects Water Use of Sweet Basil by Changing Its Stomatal Development

Agronomy ◽

10.3390/agronomy11020303 ◽

2021 ◽

Vol 11 (2) ◽

pp. 303

Author(s):

Sungeun Lim ◽

Jongyun Kim

Keyword(s):

Stomatal Conductance ◽

Blue Light ◽

Water Use ◽

Growth Parameters ◽

Stomatal Density ◽

Photon Flux ◽

Photon Flux Density ◽

Stomatal Development ◽

Sweet Basil ◽

Stomatal Responses

Different light qualities affect plant growth and physiological responses, including stomatal openings. However, most researchers have focused on stomatal responses to red and blue light only, and the direct measurement of evapotranspiration has not been examined. Therefore, we quantified the evapotranspiration of sweet basil under various red (R), green (G), and blue (B) combinations using light-emitting diodes (LEDs) and investigated its stomatal responses. Seedlings were subjected to five different spectral treatments for two weeks at a photosynthetic photon flux density of 200 µmol m−2 s−1. The ratios of the RGB light intensities were as follows: R 100% (R100), R:G = 75:25 (R75G25), R:B = 75:25 (R75B25), R:G:B = 60:20:20 (R60G20B20), and R:G:B = 31:42:27 (R31G42B27). During the experiment, the evapotranspiration of the plants was measured using load cells. Although there were no significant differences in growth parameters among the treatments, the photosynthetic rate and stomatal conductance were higher in plants grown under blue LEDs (R75B25, R60G20B20, and R31G42B27) than in the R100 treatment. The amount of water used was different among the treatments (663.5, 726.5, 728.7, 778.0, and 782.1 mL for the R100, R75G25, R60G20B20, R75B25, and R31G42B27 treatments, respectively). The stomatal density was correlated with the blue light intensity (p = 0.0024) and with the combined intensity of green and blue light (p = 0.0029); therefore, green light was considered to promote the stomatal development of plants together with blue light. Overall, different light qualities affected the water use of plants by regulating stomatal conductance, including changes in stomatal density.

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LED Illumination Spectrum Manipulation for Increasing the Yield of Sweet Basil (Ocimum basilicum L.)

Plants ◽

10.3390/plants10020344 ◽

2021 ◽

Vol 10 (2) ◽

pp. 344

Author(s):

Md Momtazur Rahman ◽

Mikhail Vasiliev ◽

Kamal Alameh

Keyword(s):

Growth Rate ◽

Fold Increase ◽

Photosynthetic Photon Flux Density ◽

Ocimum Basilicum ◽

Photon Flux ◽

Photon Flux Density ◽

White Led ◽

Experimental Conditions ◽

Sweet Basil ◽

Optimal Illumination

Manipulation of the LED illumination spectrum can enhance plant growth rate and development in grow tents. We report on the identification of the illumination spectrum required to significantly enhance the growth rate of sweet basil (Ocimum basilicum L.) plants in grow tent environments by controlling the LED wavebands illuminating the plants. Since the optimal illumination spectrum depends on the plant type, this work focuses on identifying the illumination spectrum that achieves significant basil biomass improvement compared to improvements reported in prior studies. To be able to optimize the illumination spectrum, several steps must be achieved, namely, understanding plant biology, conducting several trial-and-error experiments, iteratively refining experimental conditions, and undertaking accurate statistical analyses. In this study, basil plants are grown in three grow tents with three LED illumination treatments, namely, only white LED illumination (denoted W*), the combination of red (R) and blue (B) LED illumination (denoted BR*) (relative red (R) and blue (B) intensities are 84% and 16%, respectively) and a combination of red (R), blue (B) and far-red (F) LED illumination (denoted BRF*) (relative red (R), blue (B) and far-red (F) intensities are 79%, 11%, and 10%, respectively). The photosynthetic photon flux density (PPFD) was set at 155 µmol m−2 s−1 for all illumination treatments, and the photoperiod was 20 h per day. Experimental results show that a combination of blue (B), red (R), and far-red (F) LED illumination leads to a one-fold increase in the yield of a sweet basil plant in comparison with only white LED illumination (W*). On the other hand, the use of blue (B) and red (R) LED illumination results in a half-fold increase in plant yield. Understanding the effects of LED illumination spectrum on the growth of plant sweet basil plants through basic horticulture research enables farmers to significantly improve their production yield, thus food security and profitability.

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