The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Liisa Kulmala - One of the best experts on this subject based on the ideXlab platform.
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inter and intra annual dynamics of photosynthesis differ between Forest Floor vegetation and tree canopy in a subarctic scots pine stand
Agricultural and Forest Meteorology, 2019Co-Authors: Pasi Kolari, Jukka Pumpanen, Liisa Kulmala, Sigrid Dengel, Frank Berninger, Kajar Koster, Laura Matkala, Anni Vanhatalo, Timo VesalaAbstract:Abstract We studied the inter- and intra-annual dynamics of the photosynthesis of Forest Floor vegetation and tree canopy in a subarctic Scots pine stand at the northern timberline in Finland. We tackled the issue using three different approaches: 1) measuring carbon dioxide exchange above and below canopy with the eddy covariance technique, 2) modelling the photosynthesis of the tree canopy based on shoot chamber measurements, and 3) upscaling the Forest Floor photosynthesis using biomass estimates and available information on the annual cycle of photosynthetic capacity of those species. The studied ecosystem was generally a weak sink of carbon but the sink strength showed notable year-to-year variation. Total ecosystem respiration and photosynthesis indicated a clear temperature limitation for the carbon exchange. However, the increase in photosynthetic production was steeper than the increase in respiration with temperature, indicating that warm temperatures increase the sink strength and do not stimulate the total ecosystem respiration as much in the 4-year window studied. The interannual variation in the photosynthetic production of the Forest stand mainly resulted from the Forest Floor vegetation, whereas the photosynthesis of the tree canopy seemed to be more stable from year to year. Tree canopy photosynthesis increased earlier in the spring, whereas that of the Forest Floor increased after snowmelt, highlighting that models for photosynthesis in the northern area should also include snow cover in order to accurately estimate the seasonal dynamics of photosynthesis in these Forests.
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Forest Floor co 2 flux measurements with a dark light chamber
Biogeosciences Discussions, 2009Co-Authors: Harry Lankreijer, Liisa Kulmala, Anders Lindroth, Monika Stromgren, Jukka PumpanenAbstract:An automatic closed chamber system for measuring net carbon flux from the Forest Floor was equipped with both a transparent and an opaque cover. The system was operated in such way that a measurement session with transparent chamber was followed by a session with dark chamber. This made it possible to estimate besides total daytime respiration and nighttime respiration also the gross assimilation of the vegetation enclosed in the chamber. The chamber was used at two locations, Hyytiala in Finland and Norunda in Sweden. Results were compared to estimation of gross assimilation by extrapolation of nighttime respiration and the difference between daytime and nighttime respiration was analyzed. Estimated gross photosynthesis from the darkening sessions by the chamber resulted in a higher gross photosynthesis then obtained by extrapolation from nighttime respiration for Norunda, but not for Hyytala. Comparison of obtained gross photosynthesis rates indicated that the Forest Floor vegetation contributed up to 30% of maximum net ecosystem uptake.
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Forest Floor vegetation plays an important role in photosynthetic production of boreal Forests
Forest Ecology and Management, 2006Co-Authors: Pasi Kolari, Jukka Pumpanen, Liisa Kulmala, Hannu Ilvesniemi, Eero Nikinmaa, Tiia Gronholm, Pertti HariAbstract:Abstract We estimated gross photosynthetic production (GPP) of the Forest Floor vegetation in a 40-year-old Scots pine stand in southern Finland with three different methods: measurements of CO2 exchange of single leaves of field and ground layer species, measurement campaigns of Forest Floor net CO2 efflux at different irradiances with a manually operated soil chamber, and continuous measurements of Forest Floor net CO2 efflux with an automatic transparent chamber system. We upscaled the measured light response curves from the manual soil chambers using the biomass distribution of the Forest Floor species, a modelled seasonal pattern of photosynthetic capacity and a model of light extinction down the canopy. Leaf gas exchange measurements as well as measurements of net CO2 efflux with the manual chamber indicated saturation of photosynthesis at relatively low (50–400 μmol m−2 s−1) light levels. Leaf and patch level measurements gave similar rates of photosynthetic CO2 fixation per unit leaf biomass suggesting that reduction in photosynthetic production due to within-patch shading was small. Upscaling of photosynthetic production to the stand level and continuous measurements with the automatic soil chambers indicated that momentary photosynthetic production by the Forest Floor vegetation in the summer was typically about 2 μmol m−2 (ground) s−1. Cumulative upscaled GPP over the period of no snow (from 20 April to 20 November) in year 2003 was 131 g C m−2. Continuous measurements with the automatic soil chamber system were in line with the upscaling, the cumulative GPP being 83 g C m−2 and the seasonal pattern of photosynthetic rate similar to that of the upscaled photosynthesis.
Timo Vesala - One of the best experts on this subject based on the ideXlab platform.
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inter and intra annual dynamics of photosynthesis differ between Forest Floor vegetation and tree canopy in a subarctic scots pine stand
Agricultural and Forest Meteorology, 2019Co-Authors: Pasi Kolari, Jukka Pumpanen, Liisa Kulmala, Sigrid Dengel, Frank Berninger, Kajar Koster, Laura Matkala, Anni Vanhatalo, Timo VesalaAbstract:Abstract We studied the inter- and intra-annual dynamics of the photosynthesis of Forest Floor vegetation and tree canopy in a subarctic Scots pine stand at the northern timberline in Finland. We tackled the issue using three different approaches: 1) measuring carbon dioxide exchange above and below canopy with the eddy covariance technique, 2) modelling the photosynthesis of the tree canopy based on shoot chamber measurements, and 3) upscaling the Forest Floor photosynthesis using biomass estimates and available information on the annual cycle of photosynthetic capacity of those species. The studied ecosystem was generally a weak sink of carbon but the sink strength showed notable year-to-year variation. Total ecosystem respiration and photosynthesis indicated a clear temperature limitation for the carbon exchange. However, the increase in photosynthetic production was steeper than the increase in respiration with temperature, indicating that warm temperatures increase the sink strength and do not stimulate the total ecosystem respiration as much in the 4-year window studied. The interannual variation in the photosynthetic production of the Forest stand mainly resulted from the Forest Floor vegetation, whereas the photosynthesis of the tree canopy seemed to be more stable from year to year. Tree canopy photosynthesis increased earlier in the spring, whereas that of the Forest Floor increased after snowmelt, highlighting that models for photosynthesis in the northern area should also include snow cover in order to accurately estimate the seasonal dynamics of photosynthesis in these Forests.
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continuous voc flux measurements on boreal Forest Floor
Plant and Soil, 2013Co-Authors: Hermanni Aaltonen, Juho Aalto, Mari Pihlatie, Pasi Kolari, Jukka Pumpanen, Eero Nikinmaa, Markku Kulmala, Timo Vesala, Jaana BäckAbstract:Background and Aims Volatile organic compound (VOC) emissions from biogenic sources are important contributors to chemical reactions in the air. Soil/Forest Floor VOCs contribute significantly to the ecosystem scale emissions, however, these emissions and their temporal and spatial variations are poorly characterised. The below-canopy VOC emissions have been measured mainly in campaigns; continuous measurements over the whole growing season are rare.
Ke Chen - One of the best experts on this subject based on the ideXlab platform.
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slower rates of litter decomposition of dominant epiphytes in the canopy than on the Forest Floor in a subtropical montane Forest southwest china
Soil Biology & Biochemistry, 2014Co-Authors: Wenyao Liu, Liang Song, Ke ChenAbstract:Epiphytes constitute a substantial proportion of the canopy biomass in subtropical montane Forests, and their decomposition has not been adequately addressed, especially in the canopy relative to the Forest Floor compartments. The rates of litter decomposition and nutrient release of five epiphytes (macrolichens Everniastrum nepalense, Nephromopsis ornata and Usnea florida, moss Homaliodendron flabellatum, and fern Phymatopteris connexa) and two tree species (Castanopsis wattii and Lithocarpus xylocarpus) were quantified over a two-year period using litterbags in the canopy and on the Forest Floor in an evergreen broad-leaved Forest in the subtropical Ailao Mountains in southwest China. After two years, all litter in the canopy decayed 15e30% slower than on the Forest Floor, with 17e69% and 2e51% of initial masses remaining respectively. Nutrient concentration varied regularly as decay proceeded in the canopy while nutrient amount underwent regular variation on the Forest Floor. Decay rate and nutrient release differed significantly among functional groups and the order of decay rate was lichen > tree > fern > bryophyte. Lichens had the fastest decay rates, and the fruticose U. florida decayed faster than the other two foliose species. The rate of lichen decomposition was significantly correlated with morphology and initial N and P concentrations. The bryophyte species had the lowest decay rate, but with relatively rapid release of N and P, while the fern had high net N and P immobilization. K was rapidly released from litter. Ca and Mg eventually decreased with variable concentrations during decomposition. Our results highlight the potential importance of nonvascular epiphytes in increasing nutrient availability, especially N and P, in the canopy soil environment, and the probable role of epiphytic bryophytes and ferns in accumulating organic matter.
Pasi Kolari - One of the best experts on this subject based on the ideXlab platform.
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inter and intra annual dynamics of photosynthesis differ between Forest Floor vegetation and tree canopy in a subarctic scots pine stand
Agricultural and Forest Meteorology, 2019Co-Authors: Pasi Kolari, Jukka Pumpanen, Liisa Kulmala, Sigrid Dengel, Frank Berninger, Kajar Koster, Laura Matkala, Anni Vanhatalo, Timo VesalaAbstract:Abstract We studied the inter- and intra-annual dynamics of the photosynthesis of Forest Floor vegetation and tree canopy in a subarctic Scots pine stand at the northern timberline in Finland. We tackled the issue using three different approaches: 1) measuring carbon dioxide exchange above and below canopy with the eddy covariance technique, 2) modelling the photosynthesis of the tree canopy based on shoot chamber measurements, and 3) upscaling the Forest Floor photosynthesis using biomass estimates and available information on the annual cycle of photosynthetic capacity of those species. The studied ecosystem was generally a weak sink of carbon but the sink strength showed notable year-to-year variation. Total ecosystem respiration and photosynthesis indicated a clear temperature limitation for the carbon exchange. However, the increase in photosynthetic production was steeper than the increase in respiration with temperature, indicating that warm temperatures increase the sink strength and do not stimulate the total ecosystem respiration as much in the 4-year window studied. The interannual variation in the photosynthetic production of the Forest stand mainly resulted from the Forest Floor vegetation, whereas the photosynthesis of the tree canopy seemed to be more stable from year to year. Tree canopy photosynthesis increased earlier in the spring, whereas that of the Forest Floor increased after snowmelt, highlighting that models for photosynthesis in the northern area should also include snow cover in order to accurately estimate the seasonal dynamics of photosynthesis in these Forests.
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continuous voc flux measurements on boreal Forest Floor
Plant and Soil, 2013Co-Authors: Hermanni Aaltonen, Juho Aalto, Mari Pihlatie, Pasi Kolari, Jukka Pumpanen, Eero Nikinmaa, Markku Kulmala, Timo Vesala, Jaana BäckAbstract:Background and Aims Volatile organic compound (VOC) emissions from biogenic sources are important contributors to chemical reactions in the air. Soil/Forest Floor VOCs contribute significantly to the ecosystem scale emissions, however, these emissions and their temporal and spatial variations are poorly characterised. The below-canopy VOC emissions have been measured mainly in campaigns; continuous measurements over the whole growing season are rare.
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Forest Floor vegetation plays an important role in photosynthetic production of boreal Forests
Forest Ecology and Management, 2006Co-Authors: Pasi Kolari, Jukka Pumpanen, Liisa Kulmala, Hannu Ilvesniemi, Eero Nikinmaa, Tiia Gronholm, Pertti HariAbstract:Abstract We estimated gross photosynthetic production (GPP) of the Forest Floor vegetation in a 40-year-old Scots pine stand in southern Finland with three different methods: measurements of CO2 exchange of single leaves of field and ground layer species, measurement campaigns of Forest Floor net CO2 efflux at different irradiances with a manually operated soil chamber, and continuous measurements of Forest Floor net CO2 efflux with an automatic transparent chamber system. We upscaled the measured light response curves from the manual soil chambers using the biomass distribution of the Forest Floor species, a modelled seasonal pattern of photosynthetic capacity and a model of light extinction down the canopy. Leaf gas exchange measurements as well as measurements of net CO2 efflux with the manual chamber indicated saturation of photosynthesis at relatively low (50–400 μmol m−2 s−1) light levels. Leaf and patch level measurements gave similar rates of photosynthetic CO2 fixation per unit leaf biomass suggesting that reduction in photosynthetic production due to within-patch shading was small. Upscaling of photosynthetic production to the stand level and continuous measurements with the automatic soil chambers indicated that momentary photosynthetic production by the Forest Floor vegetation in the summer was typically about 2 μmol m−2 (ground) s−1. Cumulative upscaled GPP over the period of no snow (from 20 April to 20 November) in year 2003 was 131 g C m−2. Continuous measurements with the automatic soil chamber system were in line with the upscaling, the cumulative GPP being 83 g C m−2 and the seasonal pattern of photosynthetic rate similar to that of the upscaled photosynthesis.
Neil J Loader - One of the best experts on this subject based on the ideXlab platform.
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Forest Floor chemical transformations in a boreal Forest fire and their correlations with temperature and heating duration
Geoderma, 2016Co-Authors: Cristina Santin, Stefan H Doerr, Agustin Merino, Robert Bryant, Neil J LoaderAbstract:Boreal soils account for ~30% of the global soil organic carbon (C) stock. Wildfires are an important perturbation of this C pool, particularly affecting the top organic soil layer, which constitutes the Forest Floor. Alterations to the Forest Floor by fire are relevant to the soil C balance and have profound implications for soil properties. However, relationships between Forest Floor transformations and actual wildfire characteristics have not been established to date due to the logistical challenges of obtaining the necessary fire behaviour data, together with associated pre- and post-fire sample material. We used a high-intensity experimental wildfire to address this research gap, which enabled us to determine Forest Floor chemical transformations in a Canadian boreal Forest in relation to temperature-time profiles for 18 sampling points during the fire. Forest Floor samples taken pre- and post-fire were characterized using elemental and δ13C analysis, differential scanning calorimetry and 13C nuclear magnetic resonance. During this typical boreal crown fire average maximum temperature (Tmax) at the Forest Floor was 745°C (550 300°C being 176s (65 600-700°C, which is higher than the range of 300-500°C for aromaticity development previously reported from laboratory experiments. One reason for this discrepancy could be the generally much longer heating durations used in laboratory studies, and we therefore advise caution when extrapolating findings from laboratory studies to wildfire conditions. Almost half of the initial total C stock in the Forest Floor (20MgCha-1) was affected by fire, with ~24% of this fire-affected C transformed to pyrogenic organic matter. This pyrogenic material possessed variable, yet distinct, chemical characteristics when compared to unburnt Forest Floor, including higher recalcitrance and associated resistance to biological degradation. As some boreal regions already show a rise in fire severity and area burned linked to climate change, our findings suggest a potential accompanying increase in the more stable organic carbon stock, with important implications for the functioning and turnover of organic matter in boreal soils.