by Marie-Claude Boileau | 16 July 2020
Published in Tree Physiology 14: 759-768
A computer-controlled whole-plant cuvette system is described that allows precise and independent control of temperature (± 0.05 °C), vapor pressure (± 0.02 kPa), CO2 concentration (± 2 mmol mol-1) and photosynthetic photon flux density (± 5 mmol m-2 s-1), and allows the continuous measurement of net photosynthesis and transpiration rates. Vapor pressure is controlled by circulating chamber air through a CaSO4 desiccant column supported on a digital balance. Transpiration rate is calculated from the change in desiccant mass with time. Photosynthesis rate is measured by integrating the output of a mass flow controller used to inject CO2 into the chamber to compensate for that assimilated by the plant.
The control system can be driven by set points that can be varied, for example, as a function of time, or held constant. We were able to simulate weather data obtained from climate stations and accurately follow, in real time, the output of sensors measuring outside conditions.
Experiments on well-watered one- and two-year-old nursery-raised western red cedar (Thuja plicata Donn.) and white spruce (Picea glauca (Moench) Voss) seedlings showed that if the mean daily temperature was increased from 20 to 22 °C with vapor pressure remaining constant at 1 kPa, CO2 concentrations must almost double to compensate for the decrease in net photosynthesis rate.
by Audrey Verreault | 15 July 2020
Published in Journal of Economic Entomology 87(1): 96-100
Variations in concentrations of ground white pine bark incorporated into artificial diet were studied to determine their effect on egg laying and feeding behavior of white pine weevils, Pissodes strobi (Peck). Significant differences in feeding and egg laying responses were detected between adults fed diets containing 5 and 10% ground bark. White pine weevil larvae reared on the diet containing 1% ground bark had a higher mortality level than those reared on the diet containing 5% ground bark. Weevil females fed the diet containing 5% ground bark were significantly heavier than those reared on the diet with 1% ground bark. Insect development times did not differ significantly between the two concentrations of ground bark. Adults exposed to a natural substrate were stimulated to oviposit, and viable eggs were laid.
by Marie-Claude Boileau | 16 June 2020
Published in Canadian Journal of Soil Science 75: 343-348
A Podzolic soil from an old-growth maple hardwood forest in eastern Canada was systematically sampled from a 16.5-m-long trench in 1975. ln 1986, the upper 10 cm of the B horizon was resampled from two sampling lines located on each side and parallel to the 1975 trench, one at a distance of 1 m downhill and the other at a distance of 4 m uphill. Total N, organic C, pH, and exchangeable Ca, Mg and K were measured. The objectives were to evaluate the change in the chemical status of the B horizon from 1975 to 1986 and to characterize the spatial variability of the horizon. No significant change was found in the soil chemical properties tested during this 11-yr period. No significant autocorrelation was observed between soil samples 60 cm apart, except for the downhill sampling line, which was located 1 m from the trench. For most properties, the magnitude of the difference between two soil sampling units was not proportional to the distance separating them over the range of 0.6-4.2 m. Except for pH, a difference in soil properties of more than 30% was observed in 37-56% of sampIe pairs 60 cm apart. Resampling near (1 m) an old soil pit may not be valid because of possible local modifications of soil properties created by the pit, even when it is filled in.
by Audrey Verreault | 16 June 2020
Published in New Forests 9: 261-272
Paper bags equipped with a polyethylene window were placed on branchlets 6 and 9 weeks before the time of pollen dispersal of Japanese larch and Jack pine, respectively. This technique produced a localized greenhouse effect around the branchlets, accelerating male cone development. For Jack pine trees, buds in bags with the window oriented upward had the shortest maturation time. ln fact, it was possible to collect these pollen cones about 11 days before the unbagged control without decreasing the production of pollen. The mean germination rate of the pollen from the bags with the window pointed upward, however, was significantly lower than the control, by about 15%. Buds in bags with the window oriented downward had an accelerated development of about 9 days (compared to the control) but did not experience a decrease in pollen production or quality. This same technique caused the abortion of male cones of the Japanese larch trees. Thermal probes in the bags enabled us to follow the progression of temperature inside and outside the bags during the development of the male cone in each species. They revealed that the bags increased mean temperature, daily temperature range, and degree-day accumulation, and that this effect was most pronounced for Jack pine, when the polyethylene window was oriented upward.
by Audrey Verreault | 12 June 2020
Published in Grana 34: 367-370
ln Québec, 83 first-generation seed orchards destined to produce seeds from genetically improved trees have been established since 1973. Consequently, the Tree Genetic Improvement Program uses a very large quantity of pollen in order to carry out the controlled pollination projects in those seed orchards. Moreover, controlled pollination is carried out within a very short time-frame and very often the receptivity period occurs before the time of pollen dispersion. It is for these reasons that the pollen bank was created in Québec. This manuscript summarize the process of long term preservation of a large quantity of tree pollen. It is possible to preserve the pollen of coniferous trees on a large scale for up to five years. lt is more difficult to manipulate the pollen of deciduous trees.
