The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform
Ian J. Alexander - One of the best experts on this subject based on the ideXlab platform.
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A study of ageing of spruce [Picea Sitchensis (Bong.) Carr.] ectomycorrhizas. III. Phosphate absorption and transfer in ageing Picea Sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
New Phytologist, 1992Co-Authors: J. W. G. Cairney, Ian J. AlexanderAbstract:summary Phosphate absorption and transfer to the host was studied in seedlings of Picea Sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex root observation chambers. Phosphate absorption into excised mycorrhizas was reduced in older compared with young mycorrhizas, kinetic analysis indicating physiological differences in phosphate absorption between the two age classes over a range of external concentrations up to 1000μM. Individual young mycorrhizas labelled directly with 32P transferred more 32P to the host than older mycorrhizas in the same intact root system. There was variation in the ratio (young:older) suggesting a progressive reduction in nutrient transfer to the host as the mycorrhiza ages. The results are discussed in relation to nutrient accumulation in the field.
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A study of ageing of spruce [Picea Sitchensis (Bong.) Carr.] ectomycorrhizas. II. Carbohydrate allocation in ageing Picea Sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
New Phytologist, 1992Co-Authors: J. W. G. Cairney, Ian J. AlexanderAbstract:summary Translocation of 14C-labelled photosynthate was studied in seedlings of Picea Sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex observation chambers. Although translocation to young and older mycorrhizas was observed, accumulation of current 14C-labelled photosynthate was reduced in older compared with young mycorrhizas in the same root system. Non-structural carbohydrate components of P. Sitchensis/T. fibrillosa and undefined beech ectomycorrhizas collected from the field were quantified by gas-liquid chromatography. Relative differences in accumulated carbohydrates were identified between P. Sitchensis/T. fibrillosa and beech mycorrhizas. Levels of total soluble and insoluble carbohydrate were lower in older compared with young P. Sitchensis/T. fibrillosa mycorrhizas. The soluble sugars arabitol, glucose and mannitol were detected in significantly lower quantities in older mycorrhizas whilst fructose and trehalose content was similar to that of young mycorrhizas. These results are discussed in relation to the physiology of the ageing mycorrhiza.
Jon Lloyd - One of the best experts on this subject based on the ideXlab platform.
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variations in 13c discrimination during co2 exchange by Picea Sitchensis branches in the field
Plant Cell and Environment, 2007Co-Authors: Lisa Wingate, Ulli Seibt, Paul G. Jarvis, John Moncrieff, Jon LloydAbstract:We report diurnal variations in 13C discrimination (13Δ) of Picea Sitchensis (Bong.) Carr. branches measured in the field using a branch chamber technique. The observations were compared to predicted 13Δ based on concurrent measurements of branch gas exchange. Observed 13Δ values were described well by the classical model of 13Δ including isotope effects during photorespiration, day respiration and CO2 transfer through a series of resistances to the sites of carboxylation. A simplified linear of model 13Δ did not capture the observed diurnal variability. At dawn and dusk, we measured very high 13Δ values that were not predicted by either of the said models. Exploring the sensitivity of 13Δ to possible respiratory isotope effects, we conclude that isotopic disequilibria between the gross fluxes of photosynthesis and day respiration can explain the high observed 13Δ values during net photosynthetic gas exchange. Based on the classical model, a revised formulation incorporating an isotopically distinct substrate for day respiration was able to account well for the high observed dawn and dusk 13Δ values.
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Variations in 13C discrimination during CO2 exchange by Picea Sitchensis branches in the field
Plant Cell and Environment, 2007Co-Authors: Lisa Wingate, Ulli Seibt, John B. Moncrieff, Paul G. Jarvis, Jon LloydAbstract:We report diurnal variations in C-13 discrimination ((13)Delta) of Picea Sitchensis (Bong.) Carr. branches measured in the field using a branch chamber technique. The observations were compared to predicted (13)Delta based on concurrent measurements of branch gas exchange. Observed (13)Delta values were described well by the classical model of (13)Delta including isotope effects during photorespiration, day respiration and CO2 transfer through a series of resistances to the sites of carboxylation. A simplified linear of model (13)Delta did not capture the observed diurnal variability. At dawn and dusk, we measured very high (13)Delta values that were not predicted by either of the said models. Exploring the sensitivity of (13)Delta to possible respiratory isotope effects, we conclude that isotopic disequilibria between the gross fluxes of photosynthesis and day respiration can explain the high observed (13)Delta values during net photosynthetic gas exchange. Based on the classical model, a revised formulation incorporating an isotopically distinct substrate for day respiration was able to account well for the high observed dawn and dusk (13)Delta values.
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non steady state effects in diurnal 18o discrimination by Picea Sitchensis branches in the field
Plant Cell and Environment, 2006Co-Authors: Ulli Seibt, Lisa Wingate, Joseph A. Berry, Jon LloydAbstract:We report diurnal variations in 18O discrimination (18Δ) during photosynthesis (18ΔA) and respiration (18ΔR) of Picea Sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18Δ (18Δpred) based on concurrent measurements of branch gas exchange to evaluate steady state and non-steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the δ18O of atmospheric CO2. The non-steady state approach substantially improved the agreement between 18Δpred and observed 18Δ (18Δobs) compared with the assumption of isotopic steady state (ISS) for the δ18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18Δ values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of δ18O of CO2.
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Non‐steady state effects in diurnal 18O discrimination by Picea Sitchensis branches in the field
Plant cell & environment, 2006Co-Authors: Ulli Seibt, Lisa Wingate, Joseph A. Berry, Jon LloydAbstract:We report diurnal variations in 18O discrimination (18Δ) during photosynthesis (18ΔA) and respiration (18ΔR) of Picea Sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18Δ (18Δpred) based on concurrent measurements of branch gas exchange to evaluate steady state and non-steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the δ18O of atmospheric CO2. The non-steady state approach substantially improved the agreement between 18Δpred and observed 18Δ (18Δobs) compared with the assumption of isotopic steady state (ISS) for the δ18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18Δ values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of δ18O of CO2.
Jorg Bohlmann - One of the best experts on this subject based on the ideXlab platform.
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Behavioral and Reproductive Response of White Pine Weevil (Pissodes strobi) to Resistant and Susceptible Sitka Spruce (Picea Sitchensis).
Insects, 2010Co-Authors: Jeanne A. Robert, Jorg BohlmannAbstract:White pine weevil (Pissodes strobi, Peck.) is a native forest insect pest in the Pacific Northwest of North America that attacks species of spruce (Picea spp.) and pine (Pinus spp.). Young Sitka spruce [Picea Sitchensis (Bong.) Carr.] trees are particularly susceptible to weevil attack. Pockets of naturally occurring Sitka spruce resistance have been identified in high weevil hazard areas in coastal British Columbia. In this study, we characterize behavioral, physiological and reproductive responses of weevils to an extremely resistant Sitka spruce genotype (H898) in comparison to a highly susceptible genotype (Q903). The experiments relied on a large number of three-year-old clonally propagated trees and were therefore restricted to two contrasting Sitka spruce genotypes. When exposed to resistant trees, both male and female weevils were deterred during host selection and mating, females showed delayed or reduced ovary development, and successful reproduction of weevils was prevented on resistant trees.
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The Multigene Dirigent Family of Sitka Spruce (Picea Sitchensis): Differential Gene Expression in Response to Wounding
2005Co-Authors: Ji-young Park, Jorg Bohlmann, Steven G. Ralph, Shawn D MansieldAbstract:We have isolated, cloned and characterized the expression of the multigene dirigent family from Sitka Spruce (Picea Sitchensis). To-date, this family consists of dirigent genes that can be separated into two distinct clads by phylogenetic analysis. One clad was shown to be spatially and temporally up-regulated in response to external stimuli, including mechanical wounding and insect attack, while the other clad seem to be display significantly higher basal levels of gene expression. The wound-inducible clad possess coding regions of 194-195 amino acids with a predicted molecular mass of ca. 22 - 23 kDa, and all contain a putative hydrophobic signal peptide as part of their secretory system. The primary structure of the isoforms displayed a high degree of amino acid homogeneity (81-91%), while the deduced isoelectric points for the isoforms ranged from 5.4 to 7.9.
Charles Cartwright - One of the best experts on this subject based on the ideXlab platform.
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genetic resistance of sitka spruce Picea Sitchensis populations to the white pine weevil pissodes strobi distribution of resistance
Forestry, 2004Co-Authors: John N King, René I. Alfaro, Charles CartwrightAbstract:Summary Sitka spruce (Picea Sitchensis) is highly susceptible to leader damage by the white pine weevil (Pissodes strobi). Population differences for resistance have been previously noted from older IUFRO provenance trials both from hybrid sources (the natural hybrids of Sitka and white spruce), but also in populations of pure Sitka from dryer ecological zones. It was postulated that this resistance might be common within this high hazard ‘dry’ zone because of potentially higher selection pressures from increased weevil density. Results from a population transect of this zone, established as an openpollinated progeny/provenance trial, show that resistance is not broadly based but is centred about one of the original IUFRO resistant sources. Although hazard-zone differences were significant, sources within zone, had the strongest effect in our model; particularly evident was a strongly defined population effect around the original IUFRO source. Heritability estimates for resistance were also affected by this strong source population effect.
J. W. G. Cairney - One of the best experts on this subject based on the ideXlab platform.
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A study of ageing of spruce [Picea Sitchensis (Bong.) Carr.] ectomycorrhizas. III. Phosphate absorption and transfer in ageing Picea Sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
New Phytologist, 1992Co-Authors: J. W. G. Cairney, Ian J. AlexanderAbstract:summary Phosphate absorption and transfer to the host was studied in seedlings of Picea Sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex root observation chambers. Phosphate absorption into excised mycorrhizas was reduced in older compared with young mycorrhizas, kinetic analysis indicating physiological differences in phosphate absorption between the two age classes over a range of external concentrations up to 1000μM. Individual young mycorrhizas labelled directly with 32P transferred more 32P to the host than older mycorrhizas in the same intact root system. There was variation in the ratio (young:older) suggesting a progressive reduction in nutrient transfer to the host as the mycorrhiza ages. The results are discussed in relation to nutrient accumulation in the field.
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A study of ageing of spruce [Picea Sitchensis (Bong.) Carr.] ectomycorrhizas. II. Carbohydrate allocation in ageing Picea Sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
New Phytologist, 1992Co-Authors: J. W. G. Cairney, Ian J. AlexanderAbstract:summary Translocation of 14C-labelled photosynthate was studied in seedlings of Picea Sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex observation chambers. Although translocation to young and older mycorrhizas was observed, accumulation of current 14C-labelled photosynthate was reduced in older compared with young mycorrhizas in the same root system. Non-structural carbohydrate components of P. Sitchensis/T. fibrillosa and undefined beech ectomycorrhizas collected from the field were quantified by gas-liquid chromatography. Relative differences in accumulated carbohydrates were identified between P. Sitchensis/T. fibrillosa and beech mycorrhizas. Levels of total soluble and insoluble carbohydrate were lower in older compared with young P. Sitchensis/T. fibrillosa mycorrhizas. The soluble sugars arabitol, glucose and mannitol were detected in significantly lower quantities in older mycorrhizas whilst fructose and trehalose content was similar to that of young mycorrhizas. These results are discussed in relation to the physiology of the ageing mycorrhiza.