by Claire Morin | 30 January 2019
Published in Geoderma 145: 410-418
The pedological mass balance (PMB) model is still among the best quantitative geochemical approaches to estimate chemical weathering and pedogenesis. This one-dimensional vertical approach permits estimation of the enrichment factor for a given element in a soil layer, based on changes in 1) residual enrichment, 2) strain, and 3) mass transport. The first two components represent the “closed-system” contributions to the enrichment factor since they occur without movement of the element under consideration. The last component represents the “open-system” contribution that results from net element mass movement across soil layer boundaries. Modelling the mass transport function represents a crucial step in soil pedogenesis model definitions and in the estimation of soil chemical weathering rates. We present here a method to empirically model this mass transport function based on the change in soil horizon composition within a soil profile, taking base cations (Ca, Mg, K, and Na) and Ti composition in three northern forest soil profiles as showcase. The empirically modelled compositional trends explained between 81 and 94% of the change in element composition within the soil profiles. Among the studied elements, Ti was the most recalcitrant one, except at one site where K, tended to accumulate (relatively to Ti). The results suggest that changes in composition within soil profiles are mostly linear. The calculated degree of weathering (k) of a given soil horizon was linearly related to the calculated gain/loss of base cations in the three soils using the PMB model, and was correlated to observed soil organic matter, carbon and N concentrations and its texture, pH, and bulk density. Although the modelled trend can successfully predict mass transport changes with depth as the composition of soil horizons changes upon weathering, the question of time function for this process to operate remains to be quantified.
by Claire Morin | 30 January 2019
Published in Forest Ecology and Management 255: 3460-3468
Soil properties, regeneration, sugar maple (SM, Acer saccharum Marsh.) crown dieback, and light interception were evaluated following dolomitic lime application (CaMg(CO3)2; 0, 2, 5, 10 and 20 t ha-1) in a base-poor and declining northern hardwood stand of Québec (Canada). Ten years after liming, soil pH, cation exchange capacity and base saturation increased with the lime rate. Meanwhile, concentrations of exchangeable K, Na, and acidity (0–20 cm) decreased. Concentrations and content of total carbon, organic matter, and total N decreased in the top sampled soil layer, mainly for the highest lime rate. Mean crown dieback of SM ranked from 0 to 3.4% among lime treatments, while it ranked 18.4% for the unlimed controls. Light interception by the canopy responded with an opposite pattern to crown dieback, with higher interception in lime treatments and lower in control. Proportion and diameter of SM regeneration stems increased with lime rate while proportion of American beech (AB, Fagus grandifolia Ehrh.) regeneration stems decreased in the understory. Height and stem diameter of the three taller regeneration stems (mainly AB) in each plot were inversely correlated with lime rate. Overall, the results suggest that the increase in soil fertility following liming had a beneficial effect on SM regeneration within 10 years, even if light availability was lower under treated SM than under control, and had an overall negative impact on AB regeneration.
by Claire Morin | 30 January 2019
Published in Plant Cell, Tissue and Organ Culture 42: 39-46
The physiological and osmotic roles of sucrose during black spruce (Picea mariana (Mill.) B.S.P.) embryo maturation were investigated. The results showed that when both sucrose and mannitol were present in the medium, the optimum sucrose concentration varied between 4% and 6%. From these data, mannitol does not apparently replace sucrose during the maturation of somatic embryos and therefore it might not be a suitable osmoticum. For the media supplemented with 4% to 12% sucrose and various concentrations of mannitol, the osmotic pressure of the medium rose during maturation, particularly for the highest sucrose concentrations (7% to 12%). Medium containing 3% each of fructose and glucose produced fewer mature embryos compared to the medium with 6% sucrose. An increment in the osmotic potential was observed in medium with 6% sucrose in contrast to that containing 3% each of fructose and glucose. Sugar analysis revealed that the sucrose hydrolysis in the medium was detectable within 1 week of incubation and continued throughout the maturation period. Moreover, no significant uptake of the sugars was detected, since the total amount of fructose, glucose and sucrose remained constant. Our results indicate that the action of sucrose on embryo maturation is mostly achieved through an osmotic control.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 256: 1780-1784
In Canada’s eastern boreal forest, the stagnant growth of black spruce (Picea mariana (Mill.) BSP) seedlings is often observed in the presence of ericaceous shrubs such as Kalmia angustifolia L. Many mechanisms, including allelopathic interference, reduced soil N mineralization, soil enzymes inhibition, and direct resource competition have been proposed to explain poor spruce growth in the presence of Kalmia. However, the relative importance of direct competition versus indirect interference remains unclear. Our objective was thus to adequately isolate the ‘‘Kalmia effect’’ from other growth-limiting factors and to determine if removal of Kalmia also resulted in fundamental changes in the biochemical properties of the forest floor. By sampling plots established in 2000, we evaluated how Kalmia eradication and spot fertilization influenced soil nutrient availability, N mineralization rates, microbial basal respiration and biomass, as well as planted black spruce seedling growth, dimensions, and foliar nutrient concentrations 6 years later.We measured higher extractable-P, mineralizable-N, seedling dimensions and growth rates, as well as lower extractable-K, total-K, basal respiration and microbial biomass, in plots without Kalmia than in those where Kalmia had been maintained from 2000 to 2006. Our results thus confirmed that Kalmia eradication over 6 years not only improved the growth and nutrition of black spruce seedlings, but also resulted in fundamental changes in the biochemical properties of the forest floor. We demonstrated that along with direct competition for resources, Kalmia interferes indirectly with black spruce by modifying nutrient cycling and energy fluxes in soil. Higher indices of available C in plots with Kalmia corroborates that Kalmia tannins or rhizodeposition may reduce N mineralization by stimulating microbial immobilization, a relation that however needs to be confirmed with longer term laboratory incubations.Our results indicated that although it had a positive influence on seedling growth, the fertilization effect was confined to the first few years following treatment application, and failed to influence soil processes as did Kalmia eradication. Further monitoring will indicate if the increased litterfall in fertilized plots will eventually initiate a second wave of fertilizer-induced changes to soil processes, as observed in other ecosystems.
by Claire Morin | 30 January 2019
Published in Theoretical and Applied Genetics 86: 81-87
The usefulness of random amplified polymorphic DNA (RAPD) in assessing the genetic stability of somatic embryogenesis-derived populations of black spruce [Picea mariana (Mill.) B.S.P.] was evaluated. Three arbitrary 11-mer primers were successfully used to amplify DNA from both in-vivo and in-vitro material. Twenty-five embryogenic cell lines, additional zygotic embryos and megagametophytes from three controlled crosses involving four selected genotypes of black spruce were used for the segregation analysis of RAPD variants. Ten markers were genetically characterized and used to evaluate the genetic stability of somatic embryos derived from three embryogenic cell lines (one cell line per cross, 30 somatic embryos per cell line). No variation was detected within clones. The utilization of RAPD markers both for the assessment of genetic stability of clonal materials and to certify genetic stability throughout the process of somatic embryogenesis is discussed.
