Deformation of the stem of containerized black spruce seedlings

When containerized black spruce seedlings (Picea mariana (Mill.) B.S.P.) are grown rapidly, they often bend over, grow horizontally and become deformed. This phenomenon, commonly referred to as spiralization, has had a severe impact on the containerized seedling industry in Quebec, particularly for producers using heated greenhouses. Research programs at Universite Laval and the Universite du Quebec a Chicoutimi have attempted to determine causes as well as possible solutions. The physiological basis of stem spiralization appears to be associated with a redubed capacity of root systems to convert the amino acid, phenylalanine, into lignin precursors that will permit the stem to lignify in a normal manner. High light levels together with an aerobic root environment were found to stimulate lignin synthesis in black spruce. The development cf spiralized stems was found to result from the sum total of a series of relatively small bending movements as well as minor corrective movements (i.e. 0-15°) measured every 2 to 3 days but integrated over the production cycle. A direct relationship was found between the maximal angle of bending and the risk that the seedling would have a significant defect at the end of the production cycle. A seedling which bent at more than 90° from the vertical at any time nearly always was classified as a defective seedling at the end of the production period. Vector analyses of seedling movements indicated that seedlings tended to move in the direction of the dominant light source. Le gauchissement de la tige est un défaut de croissance, provenant d'une verse partielle ou complète du semis pendant sa phase de croissance exponentielle. Cette déformation se retrouve principalement sur les semis d'épinette noire (Picea mariana (Mill.) B.S.P.) en récipients, produits en serre pendant l'hiver. Le gauchissement de la tige entraîne des pertes importantes pour l'industrie du plant en récipient au Québec. Les travaux de recherche effectués a l'Université Laval et a l'Université du Québec a Chicoutimi ont démontré que le gauchissement de la tige était associé a la diminution du taux de transformation d'un acide aminé, le phénylalanine, en un composé qui est un précurseur de la lignine. De plus, il a été démontré que la combinaison des traitements de forte intensité lumineuse et d'oxygénation du substrat racinaire augmentait la lignification des semis d'épinette noire. La mesure de Tangle et de l'orientation de la tige, tous les 2 à 3 jours pendant la période de production, a démontre que le gauchissement de la tige résultait dune sommation de mouvements de faible amplitude (i.e. 0-15°). L'angle de la tige à la fin de la période de production était corrélé avec l'angle maximal atteint par le semis pendant sa croissance. Ainsi, un semis ayant atteint un angle supérieur à 90° pendant sa croissance était presque toujours classé inacceptable pour le reboisement, avec un angle de la tige supérieur a 15° à la fin de la période de production. L'analyse vectorielle des mouvements du plant a démontré que l'orientation de la source lumineuse dominante avait un effet significatif sur l'orientation des mouvements de la tige

Deformation of the stem of containerized black spruce seedlings

When containerized black spruce seedlings (Picea mariana (Mill.) B.S.P.) are grown rapidly, they often bend over, grow horizontally and become deformed. This phenomenon, commonly referred to as spiralization, has had a severe impact on the containerized seedling industry in Quebec, particularly for producers using heated greenhouses. Research programs at Universite Laval and the Universite du Quebec a Chicoutimi have attempted to determine causes as well as possible solutions. The physiological basis of stem spiralization appears to be associated with a redubed capacity of root systems to convert the amino acid, phenylalanine, into lignin precursors that will permit the stem to lignify in a normal manner. High light levels together with an aerobic root environment were found to stimulate lignin synthesis in black spruce. The development cf spiralized stems was found to result from the sum total of a series of relatively small bending movements as well as minor corrective movements (i.e. 0-15°) measured every 2 to 3 days but integrated over the production cycle. A direct relationship was found between the maximal angle of bending and the risk that the seedling would have a significant defect at the end of the production cycle. A seedling which bent at more than 90° from the vertical at any time nearly always was classified as a defective seedling at the end of the production period. Vector analyses of seedling movements indicated that seedlings tended to move in the direction of the dominant light source. Le gauchissement de la tige est un défaut de croissance, provenant d'une verse partielle ou complète du semis pendant sa phase de croissance exponentielle. Cette déformation se retrouve principalement sur les semis d'épinette noire (Picea mariana (Mill.) B.S.P.) en récipients, produits en serre pendant l'hiver. Le gauchissement de la tige entraîne des pertes importantes pour l'industrie du plant en récipient au Québec. Les travaux de recherche effectués a l'Université Laval et a l'Université du Québec a Chicoutimi ont démontré que le gauchissement de la tige était associé a la diminution du taux de transformation d'un acide aminé, le phénylalanine, en un composé qui est un précurseur de la lignine. De plus, il a été démontré que la combinaison des traitements de forte intensité lumineuse et d'oxygénation du substrat racinaire augmentait la lignification des semis d'épinette noire. La mesure de Tangle et de l'orientation de la tige, tous les 2 à 3 jours pendant la période de production, a démontre que le gauchissement de la tige résultait dune sommation de mouvements de faible amplitude (i.e. 0-15°). L'angle de la tige à la fin de la période de production était corrélé avec l'angle maximal atteint par le semis pendant sa croissance. Ainsi, un semis ayant atteint un angle supérieur à 90° pendant sa croissance était presque toujours classé inacceptable pour le reboisement, avec un angle de la tige supérieur a 15° à la fin de la période de production. L'analyse vectorielle des mouvements du plant a démontré que l'orientation de la source lumineuse dominante avait un effet significatif sur l'orientation des mouvements de la tige

Applicability of the bulk-transfer approach to estimate evapotranspiration from boreal peatlands

In northern landscapes, peatlands are widespread and their hydrological processes are complex. Furthermore, they are typically remote, limiting the amount and accuracy of in situ measurements. This is especially the case for evapotranspiration ET, which strongly influences watershed hydrology. The objective of this paper is to demonstrate the validity of the bulk-transfer approach to estimate ET over boreal peatlands. The simplicity of the model relies on four assumptions: (i) near-neutral atmospheric conditions; (ii) wet surface; (iii) constant momentum roughness length depending on vegetation height; and (iv) constant water vapor roughness length, with the last two assumptions implying a constant water vapor transfer coefficient CE. Using eddy covariance data from three Canadian peatlands—Necopastic (James Bay, Québec), Mer Bleue (Ottawa, Ontario), and Western Peatland (Athabasca, Alberta)—this paper shows that these sites are characterized by frequent occurrences of near-neutral atmospheric conditions, especially the Necopastic site, with nearly 76% of the 30-min data segments occurring under near-neutral stratification. The analysis suggests these near-neutral conditions occur as a result of strong mechanical turbulence and weak buoyancy effects. The bulk-transfer approach gives promising results for 30-min and daily ET in terms of mean error and correlation, with performances similar to the Penman equation, without requiring net radiation data. The accuracy of the approach is likely related to the number of near-neutral periods and the elevated position of the water table, which backs up the wet surface assumption

Recent climate and fire disturbance impacts on boreal and arctic ecosystem productivity estimated using a satellite-based terrestrial carbon flux model

Warming and changing fire regimes in the northern (≥45°N) latitudes have consequences for land-atmosphere carbon feedbacks to climate change. A terrestrial carbon flux model integrating satellite Normalized Difference Vegetation Index and burned area records with global meteorology data was used to quantify daily vegetation gross primary productivity (GPP) and net ecosystem CO2 exchange (NEE) over a pan-boreal/Arctic domain and their sensitivity to climate variability, drought, and fire from 2000 to 2010. Model validation against regional tower carbon flux measurements showed overall good agreement for GPP (47 sites: R = 0.83, root mean square difference (RMSD) = 1.93 g C m−2 d−1) and consistency for NEE (22 sites: R = 0.56, RMSD = 1.46 g C m−2 d−1). The model simulations also tracked post-fire NEE recovery indicated from three boreal tower fire chronosequence networks but with larger model uncertainty during early succession. Annual GPP was significantly (p \u3c 0.005) larger in warmer years than in colder years, except for Eurasian boreal forest, which showed greater drought sensitivity due to characteristic warmer, drier growing seasons relative to other areas. The NEE response to climate variability and fire was mitigated by compensating changes in GPP and respiration, though NEE carbon losses were generally observed in areas with severe drought or burning. Drought and temperature variations also had larger regional impacts on GPP and NEE than fire during the study period, though fire disturbances were heterogeneous, with larger impacts on carbon fluxes for some areas and years. These results are being used to inform development of similar operational carbon products for the NASA Soil Moisture Active Passive (SMAP) mission

Can a Satellite-Derived Estimate of the Fraction of PAR Absorbed by Chlorophyll (FAPAR(sub chl)) Improve Predictions of Light-Use Efficiency and Ecosystem Photosynthesis for a Boreal Aspen Forest?

Gross primary production (GPP) is a key terrestrial ecophysiological process that links atmospheric composition and vegetation processes. Study of GPP is important to global carbon cycles and global warming. One of the most important of these processes, plant photosynthesis, requires solar radiation in the 0.4-0.7 micron range (also known as photosynthetically active radiation or PAR), water, carbon dioxide (CO2), and nutrients. A vegetation canopy is composed primarily of photosynthetically active vegetation (PAV) and non-photosynthetic vegetation (NPV; e.g., senescent foliage, branches and stems). A green leaf is composed of chlorophyll and various proportions of nonphotosynthetic components (e.g., other pigments in the leaf, primary/secondary/tertiary veins, and cell walls). The fraction of PAR absorbed by whole vegetation canopy (FAPAR(sub canopy)) has been widely used in satellite-based Production Efficiency Models to estimate GPP (as a product of FAPAR(sub canopy)x PAR x LUE(sub canopy), where LUE(sub canopy) is light use efficiency at canopy level). However, only the PAR absorbed by chlorophyll (a product of FAPAR(sub chl) x PAR) is used for photosynthesis. Therefore, remote sensing driven biogeochemical models that use FAPAR(sub chl) in estimating GPP (as a product of FAPAR(sub chl x PAR x LUE(sub chl) are more likely to be consistent with plant photosynthesis processes

A first record of Pestalotiopsis clavispora in Argan mass cutting propagation: Prevalence, prevention and consequences for plant production

A trial involving the mass propagation of Argania spinosa cuttings was established following two protocols: in mini-bouturathèques without mist and in a greenhouse under mist. Symptoms of petiole necrosis, foliar yellowing and abundant black acervuli were observed under both protocols. These symptoms were responsible for a 90% mortality rate in the mini-bouturathèques while under the mist treatment premature fatal necrosis of the apical buds resulted in 100% mortality. The disease’s causal agent, Pestalotiopsis clavispora, was identified on the basis of its morphological characteristics and by molecular analysis. Alternating weekly treatments of systemic and contact fungicides resulted in a 41% success rate in controlling this pathogen, described for the first time on argan cuttings.Deux approches différentes de bouturage de masse d’Argania spinosa ont été utilisées. La première consistait à enraciner les boutures dans des mini-bouturathèques sans brumisation, tandis que la deuxième consistait à utiliser une serre dotée d’un brumisateur. Des symptômes de nécrose des pétioles et de jaunissement des feuilles ainsi qu’une production abondante d’acervules noires ont été observés dans les deux protocoles. Dans les mini-bouturathèques, ces symptômes ont entraîné un taux de mortalité de 90 % des boutures, alors que sous brumisateur la nécrose précoce et fatale des bourgeons apicaux a engendré 100 % de mortalité. L’agent causal de la maladie, Pestalotiopsis clavispora, décrit pour la première fois sur les boutures d’arganier, a été identifié à partir de ses caractères morphologiques et par analyse moléculaire. Un traitement hebdomadaire à base de fongicide systémique et de fongicide de contact utilisés en alternance a permis de maîtriser cet agent pathogène avec un taux de réussite de 41 %

Modeling Analysis of Primary Controls on Net Ecosystem Productivity of Seven Boreal and Temperate Coniferous Forests Across a Continental Transect

Process-based models are effective tools to synthesize and/or extrapolate measured carbon (C) exchanges from individual sites to large scales. In this study, we used a C- and nitrogen (N)-cycle coupled ecosystem model named CN-CLASS (Carbon Nitrogen-Canadian Land Surface Scheme) to study the role of primary climatic controls and site-specific C stocks on the net ecosystem productivity (NEP) of seven intermediate-aged to mature coniferous forest sites across an east–west continental transect in Canada. The model was parameterized using a common set of parameters, except for two used in empirical canopy conductance–assimilation, and leaf area–sapwood relationships, and then validated using observed eddy covariance flux data. Leaf Rubisco-N dynamics that are associated with soil–plant N cycling, and depend on canopy temperature, enabled the model to simulate site-specific gross ecosystem productivity (GEP) reasonably well for all seven sites. Overall GEP simulations had relatively smaller differences compared with observations vs. ecosystem respiration (RE), which was the sum of many plant and soil components with larger variability and/or uncertainty associated with them. Both observed and simulated data showed that, on an annual basis, boreal forest sites were either carbon-neutral or a weak C sink, ranging from 30 to 180 g C m−2 yr−1; while temperate forests were either a medium or strong C sink, ranging from 150 to 500 g C m−2 yr−1, depending on forest age and climatic regime. Model sensitivity tests illustrated that air temperature, among climate variables, and aboveground biomass, among major C stocks, were dominant factors impacting annual NEP. Vegetation biomass effects on annual GEP, RE and NEP showed similar patterns of variability at four boreal and three temperate forests. Air temperature showed different impacts on GEP and RE, and the response varied considerably from site to site. Higher solar radiation enhanced GEP, while precipitation differences had a minor effect. Magnitude of forest litter content and soil organic matter (SOM) affected RE. SOM also affected GEP, but only at low levels of SOM, because of low N mineralization that limited soil nutrient (N) availability. The results of this study will help to evaluate the impact of future climatic changes and/or forest C stock variations on C uptake and loss in forest ecosystems growing in diverse environments.Earth and Planetary Science

Taking Stock of Circumboreal Forest Carbon With Ground Measurements, Airborne and Spaceborne LiDAR

The boreal forest accounts for one-third of global forests, but remains largely inaccessible to ground-based measurements and monitoring. It contains large quantities of carbon in its vegetation and soils, and research suggests that it will be subject to increasingly severe climate-driven disturbance. We employ a suite of ground-, airborne- and space-based measurement techniques to derive the first satellite LiDAR-based estimates of aboveground carbon for the entire circumboreal forest biome. Incorporating these inventory techniques with uncertainty analysis, we estimate total aboveground carbon of 38 +/- 3.1 Pg. This boreal forest carbon is mostly concentrated from 50 to 55degN in eastern Canada and from 55 to 60degN in eastern Eurasia. Both of these regions are expected to warm >3 C by 2100, and monitoring the effects of warming on these stocks is important to understanding its future carbon balance. Our maps establish a baseline for future quantification of circumboreal carbon and the described technique should provide a robust method for future monitoring of the spatial and temporal changes of the aboveground carbon content

Performance of Linear and Nonlinear Two-Leaf Light Use Efficiency Models at Different Temporal Scales

remote sensin

What eddy-covariance measurements tell us about prior land flux errors in CO₂-flux inversion schemes

To guide the future development of CO₂-atmospheric inversion modeling systems, we analyzed the errors arising from prior information about terrestrial ecosystem fluxes. We compared the surface fluxes calculated by a process-based terrestrial ecosystem model with daily averages of CO₂ flux measurements at 156 sites across the world in the FLUXNET network. At the daily scale, the standard deviation of the model-data fit was 2.5 gC·m⁻²·d⁻¹; temporal autocorrelations were significant at the weekly scale (>0.3 for lags less than four weeks), while spatial correlations were confined to within the first few hundred kilometers (<0.2 after 200 km). Separating out the plant functional types did not increase the spatial correlations, except for the deciduous broad-leaved forests. Using the statistics of the flux measurements as a proxy for the statistics of the prior flux errors was shown not to be a viable approach. A statistical model allowed us to upscale the site-level flux error statistics to the coarser spatial and temporal resolutions used in regional or global models. This approach allowed us to quantify how aggregation reduces error variances, while increasing correlations. As an example, for a typical inversion of grid point (300 km × 300 km) monthly fluxes, we found that the prior flux error follows an approximate e-folding correlation length of 500 km only, with correlations from one month to the next as large as 0.6