by Marie-Claude Boileau | 12 June 2020
Published in Soil Science Society of America Journal 59(1): 38-43
With the recent development of improved time domain reflectometry (TDR) probe design, measurement systems, and calibration procedures, it is now possible to detect and quantify the effect of temperature on the soil apparent dielectric constant (Ka). We investigated measurement errors in Ka associated with soil temperature variations and compared measured changes in Ka with those predicted by a dielectric mixing model. After confirming the accuracy and resolution of our measurement system with a series of measurements on distilled water, we measured changes in Ka with temperature for a range of soil types, including sand, loam, and peat, at soil water contents (qv) ranging from 0.09 to 0.81 m3 m-3. The measured variation with temperature in the dielectric constant of distilled water (0.322°C-1) was very close to that reported in the literature (0.356°C-1). ln soils, changes in Ka with temperature were highest at high water contents. For soils near saturation, the overall changes observed in Ka with temperature were lower than those predicted by the dielectric mixing model by 17% for sand, 24% for loam, and 39% for peat. These results suggest that the temperature dependence of the dielectric constant of water in a soil matrix is lower than that of bulk water. Absolute water content errors increased linearly with the size of the water fraction, ranging from 8.75 x 10-5 m3 m-3°C-1 at 0.05 m3 m-3 soil water content to 1.40 x 10-3 m3 m-3°C-1 at 0.80 m3 m-3 soil water content. To obtain the highest measurement accuracy, particularly at higher qv, we suggest that a temperature correction of 0.00175qv°C-1 be employed.
by Marie-Claude Boileau | 12 June 2020
Published in Canadian Journal of Forestry Research 25: 536-544
The advance regeneration often present following clear-cutting in black spruce (Picea mariana (Mill.) B.S.P.) stands is generally composed of individuals of various heights. This initial height difference is hypothesized to affect the yield of the future stand. Height of the advance regeneration at time of release was determined on several black spruce trees within 33 stands distributed across the boreal forest of the province of Québec, Canada. From these data, a regeneration structure index was developed and used to explain a part of the variation in subsequent stand yield. Dominant trees of stands developing for 38 to 65 years since clear-cutting generally originated from the tallest advance regeneration at time of release. Stands with the tallest regeneration at time of release produced the largest yields for a given site quality and number of years since harvesting. A 3-m increase in advance-regeneration height resulted in a similar yield gain as a 3-m increase in site index. Site indices calculated from age-height relationships of dominant trees originating from tall advance regeneration were less than those calculated from trees that have undergone a relatively short period of suppression. These results suggest that traditional management tools developed for fire-origin black spruce stands, i.e., stands mainly composed of seed-origin trees established after perturbation, should be adjusted for clearcut-origin stands that largely develop from advance regeneration.
by Audrey Verreault | 12 June 2020
Published in Journal of Economic Entomology 88(3): 640-643
A method was developed for rearing Dioryctria abietivorella (Grote) under aseptic artificial conditions. Larvae fed with artificial diet completed their development from first instar to pupae with a survival level of 59.7 ± 2.5% (mean ± SEM). Development time, recorded in an incubator set at 25°C, 60% RH, and a photoperiod of 16:8 (L:D) h from first instar through pupation, was 22.54 ± 0.56 d for males and 22.80 ± 0.80 d for females. Larval development included five instars, and 25.6% of the time there was an additional sixth instar. Instars were identified by head-capsule width measurements. Sex identification was done by observation with a binocular microscope of the eighth and ninth abdominal segments of pupa. Fifty pairs of insects were placed per cage for mating. Adult cages for mating and oviposition were used successfully and a mean number of 24.68 ± 2.02 viable eggs were laid per female.
by Audrey Verreault | 12 June 2020
Published in Plant Disease 80(5): 494-499
Erwinia carotovora and pectolytic pseudomonads are the most prevalent bacteria associated with soft rot of plants. A procedure based on random amplified polymorphic DNA (RAPD) analysis was developed to distinguish these bacteria rapidly and easily. Forty bacterial strains isolated from diseased plants in the province of Québec were used to screen RAPD primers. Two primers were chosen based on cost considerations and on their capacity to discriminate between the bacterial strains. The combination of the two primers was sufficient for adequate distinction of Erwinia carotovora from pectolytic, fluorescent Pseudomonas spp. Furthermore. E. carotovora subsps. atroseptica and carotovora could also be distinguished from each other. To simplify the identification work, a quantitative identification tool was elaborated, based on selected markers produced with the two primers. To verify the RAPD analysis accuracy, 49 additional soft rot bacteria from diseased plants were submitted to the RAPD procedure and all the identifications were in agreement with those produced by standard biochemical tests. In addition, the RAPD analysis correctly identified 25 bacteria from collections outside of Québec.
by Marie-Claude Boileau | 12 June 2020
Published in Plant, Cell and Environment 19: 949-957
Sudden but transient changes in the fraction of illuminated foliage area in a well-watered 7-year-old Pinus radiata D. Don tree were imposed by completely covering either the upper 22% or the lower 78% of the foliage for periods of up to 36 h. Measurements of transpiration flux density (E), tree conductance (gt), stomatal conductance (gs) and net photosynthesis (A) were made to test the hypothesis that compensatory responses would occur in the remaining illuminated foliage when the cover was installed. When the lower foliage was covered there was an immediate decrease in gt. However, when tree conductance was normalized with respect to the illuminated leaf area (gt‘), it increased between 50 and 75%, depending on the value of air saturation deficit (D). The effect was also apparent from concurrent measurements of increases in gs and A up to 59 and 24%, respectively, for needles in the top third of the crown. When the cover was removed these effects were reversed. The changes in the lower foliage when the upper foliage was covered were much smaller. Changes in bulk needle water potential were small. It is suggested that the observed responses occurred because of a perturbation to the hydraulic pathway in the xylem that could have triggered the action of a chemical signal to regulate stomatal conductance and photosynthesis.
