Mohammed S. Lamhamedi

Managing irrigation to reduce nutrient leaching in containerized white spruce seedling production.

Increasing irrigation efficiency and reducing groundwater contamination from agricultural and nursery runoff are important components in environmentally compatible plant production practices. The objectives of this study were to quantify mineral leaching from containerized (2+0) white spruce seedlings grown under three different irrigation regimes (30, 40 and 55% V/V) and to determine the effect of irrigation regime on growth, nutritional status, and gas exchange. To negate the effect of environmental variables, a completely randomized block experiment was installed in a normal production run of air-slit containerized white spruce seedlings grown under an unheated polyethylene tunnel. Whereas substrate water content was monitored daily, biweekly measurements of tissue and substrate fertility and seedling morphophysiological variables were made over the course of the growing season. Leaching of mineral nutrients was continuously monitored throughout the experimental period. Reducing volumetric substrate water content from 55 to 30% did not have a significant effect on seedling growth, carbon allocation, tissue nitrogen content, or end-of-season morphology. This irrigation strategy also resulted in a 20% reduction in water usage and, more importantly, reduced the total leachate volume by 65% and the quantity of N leached by 52%. Maintaining rhizosphere water content of (2+0) white spruce seedlings at 40% V/V compromises neither plant growth nor physiological processes. This strategy limits leaching of water and mineral nutrients, and reduces the risk of groundwater contamination, thus enabling growers to meet both quality and environmental standards for seedlings grown in northern forest nurseries.

Genetic Adaptation vs. Ecophysiological Plasticity of Photosynthetic-Related Traits in Young Picea glauca Trees along a Regional Climatic Gradient

Assisted population migration (APM) is the intentional movement of populations within a species range to sites where future environmental conditions are projected to be more conducive to growth. APM has been proposed as a proactive adaptation strategy to maintain forest productivity and to reduce the vulnerability of forest ecosystems to projected climate change. The validity of such a strategy will depend on the adaptation capacity of populations, which can partially be evaluated by the ecophysiological response of different genetic sources along a climatic gradient. This adaptation capacity results from the compromise between (i) the degree of genetic adaptation of seed sources to their environment of origin and (ii) the phenotypic plasticity of functional trait which can make it possible for transferred seed sources to positively respond to new growing conditions. We examined phenotypic variation in morphophysiological traits of six seed sources of white spruce (Picea glauca [Moench] Voss) along a regional climatic gradient in Québec, Canada. Seedlings from the seed sources were planted at three forest sites representing a mean annual temperature (MAT) gradient of 2.2°C. During the second growing season, we measured height growth (H2014) and traits related to resources use efficiency and photosynthetic rate (Amax). All functional traits showed an adaptive response to the climatic gradient. Traits such as H2014, Amax, stomatal conductance (gs), the ratio of mesophyll to stomatal conductance, water use efficiency, and photosynthetic nitrogen-use efficiency showed significant variation in both physiological plasticity due to the planting site and seed source variation related to local genetic adaptation. However, the amplitude of seed source variation was much less than that related to plantation sites in the area investigated. The six seed sources showed a similar level of physiological plasticity. H2014, Amax and gs, but not carboxylation capacity (Vcmax), were correlated and decreased with a reduction of the average temperature of the growing season at seed origin. The clinal variation in H2014 and Amax appeared to be driven by CO2 conductance. The presence of locally adapted functional traits suggests that the use of APM may have advantages for optimizing seed source productivity in future local climates.

Fine-scale geographic variation in photosynthetic-related traits of Picea glauca seedlings indicates local adaptation to climate

Climate-related variations in functional traits of boreal tree species can result both from physiological acclimation and genetic adaptation of local populations to their biophysical environment. To improve our understanding and prediction of the physiological and growth responses of populations to climate change, we studied the role of climate of seed origin in determining variations in functional traits and its implications for tree improvement programs for a commonly reforested boreal conifer, white spruce (Picea glauca (Moench) Voss). We evaluated growth, root-to-shoot ratio (R/S), specific leaf area (SLA), needle nitrogen (N(mass)), total non-structural carbohydrates (NSC) and photosynthetic traits of 3-year-old seedlings in a greenhouse experiment using seed from six seed orchards (SO) representing the different regions where white spruce is reforested in Québec. Height and total dry mass (TDM) were positively correlated with photosynthetic capacity (A(max)), stomatal conductance (g(s)) and mesophyll conductance (g(m)). Total dry mass, but not height growth, was strongly correlated with latitude of seed origin (SO) and associated climate variables. A(max), g(s), g(m) and more marginally, photosynthetic nitrogen-use efficiency (PNUE) were positively associated with the mean July temperature of the SO, while water use efficiency (WUE) was negatively associated. Maximum rates of carboxylation (V(cmax)), maximum rates of electron transport (J(max)), SLA, N(mass), NSC and R/S showed no pattern. Our results did not demonstrate a higher Amax for northern seed orchards, although this has been previously hypothesized as an adaptation mechanism for maintaining carbon uptake in northern regions. We suggest that gs, gm, WUE and PNUE are the functional traits most associated with fine-scale geographic clines and with the degree of local adaptation of white spruce populations to their biophysical environments. These geographic patterns may reflect in situ adaptive genetic differences in photosynthetic efficiency along the cline.

Differences in growth and mineral nutrition of seedlings produced from ten white spruce seed orchards

To meet the needs for improved spruce seeds in the province of Quebec, Canada, 17 first-generation white spruce seed orchards (SO) were established. These SOs are located in different bioclimatic domains and contain seed trees originating from geographically and genetically distinct sources. To evaluate the influence of SO on seedling growth and morphology, seedlings produced with seeds originating from the ten most commonly used first-generation white spruce SO in Quebec were raised under similar nursery conditions. Tissue nutrient concentrations of seedlings evolved similarly among seed orchards during the second growing season. At the end of the growing season, only shoot phosphorus concentrations were significantly different. When modeled with a logistic function, there was a significant difference between height and diameter growth curve parameters of seedlings from distinct SO during the second growing season. These differences led to significant differences in the height and shoot dry mass of the seedlings at the end of their second growing season, but not in their diameter or root dry mass. The ten SOs were clustered in two groups according to the above-ground characteristics of their progeny. This limited amount of morphological diversity suggests that expanding the size of the present seed zones may be an appropriate course of action for white spruce seed production in Quebec.

Are composts from shredded leafy branches of fast-growing forest species suitable as nursery growing media in arid regions?

The morpho-physiological quality of seedlings is negatively affected by the wide scale use of forest soils as substrates in developing countries. With the objective of finding long-term sustainable supply of growing media, compost was produced from shredded branches of three fast growing species (Acacia cyanophylla (AA), Acacia cyclops (AS) and Eucalyptus gomphocephala (EG). The composting process covered three different periods over the course of a year. Pile temperatures were monitored daily and the composts were routinely sampled and analyzed for 19 chemical variables. Although composting is feasible year-round in arid climates, compost produced in the humid cool conditions of autumn, winter and early spring reaches the maturation phase more quickly than compost produced under hot, dry summer conditions. It also requires less turning and water. The evolution of the composting process and quality of the final product can be assessed using three chemical variables (C/N, pH, EC). Seed germination rates in the three types of compost were similar to that in a peat:vermiculite substrate and vigorous high quality seedlings were produced in the two acacia composts. However, compost-grown seedlings had significantly smaller shoots and root systems than those produced in peat substrate. Principal components analyses showed that the quality of a compost-based substrate is reproducible and that its final chemical composition can be predicted from its raw organic materials. The EG composts had higher pH than the acacia composts, whereas the AA and EG composts were higher in mineral salts than the AS.

Genetic parameters and clonal variation in growth and nutritional traits of containerized white spruce somatic seedlings

Abstract Clonal forestry can significantly increase forest productivity and its establishment requires a high level of clonal variation to maximize genetic gain and diversity. An evaluation of the genetic parameters of clones at a juvenile stage is necessary to better understand the amplitude of clonal variability and the degree of genetic control. The analysis of variance of white spruce clones showed a highly significant clonal effect for the majority of the growth characters at the end of both growing seasons and for the mineral status at the 2+0 stage. Our results reveal that height exhibits a high clonal heritability value which remained stable over the two growing seasons (H2 c= 0.60). Strong genotypic and phenotypic correlations were observed between height and diameter at the end of the first growing season and between height and the rest of the growth characters at the end of the second growing season. The strong clonal variation, genetic control and genetic correlation particularly of height found in this study indicate that the selection ability of the best performing clones is possible for intensive forest management.

Frost tolerance of two-year-old Picea glauca seedlings grown under different irrigation regimes in a forest nursery

Abstract This study examined the impact of increased irrigation efficiency on the hardening and frost tolerance of 2-year-old containerized white spruce seedlings in the context of groundwater protection, irrigation management and the maintenance of seedling quality in northern climates. The seedlings were grown under three different irrigation regimes (IR =30%, 40% and 55% v/v; cm3 H2O/cm3 substrate) and were hardened under conditions of natural photoperiod and temperature. After being subjected to artificial frost tests on four sampling dates during autumn, the seedlings were compared for bud development and frost tolerance. IR had no influence on frost tolerance as determined by measurements of physiological (electrolyte leakage, root water loss) and morphological (shoot damage, root initiation) variables. At the end of the second growing season, there was no significant difference between IRs in seedling height, root collar diameter, shoot dry mass and root dry mass. The results indicate that the amount of water applied to large-dimension 2-year-old white spruce seedlings during the growing season can be significantly decreased without prematurely impeding their growth or hindering their acquisition of frost tolerance.

Relationships between frost hardiness, root growth potential, and photosynthesis of nursery-grown white spruce seedlings

Abstract• ContextRoot growth is a characteristic to which nursery personnel is particularly attentive. The increase in root growth of white spruce seedlings in the autumn relies on the current season’s photosynthates. Needle hardening or a decrease in the mass of photosynthetically active foliage as a result of early frost may negatively affect the seedling’s photosynthetic capacity and its ability to fuel root growth.• AimsThis study evaluated the relationship between cold hardiness, root growth potential, and photosynthesis of 2-year-old white spruce seedlings.• MethodsAt the end of their second growing season under standard cultural practices in a forest nursery, seedlings were hardened under natural conditions of photoperiod and temperature. After being subjected to artificial freezing tests on four sampling dates during the fall, the seedlings were compared for cold tolerance and recovery of gas exchange.• ResultsThe effect of artificial freezing treatments on seedling photosynthesis varied with frost intensity and degree of needle hardening. The mass of new roots formed over a 21-day cultivation test period following the freeze tests was positively related to the photosynthetic capacity of the seedlings and negatively related to the proportion of damaged needles.• ConclusionThese results imply that autumnal cold damage to needles directly affects seedling root growth and emphasize the importance of maintaining seedlings in an environment favorable for photosynthesis during the fall to promote root growth.

Morpho-physiological variation of white spruce seedlings from various seed sources and implications for deployment under climate change

Because of changes in climatic conditions, tree seeds originating from breeding programs may no longer be suited to sites where they are currently sent. As a consequence, new seed zones may have to be delineated. Assisted migration consists of transferring seed sources that match the future climatic conditions to which they are currently adapted. It represents a strategy that could be used to mitigate the potential negative consequences of climate change on forest productivity. Decisions with regard to the choice of the most appropriate seed sources have to rely on appropriate knowledge of morpho-physiological responses of trees. To meet this goal, white spruce (Picea glauca [Moench] Voss) seedlings from eight seed orchards were evaluated during two years in a forest nursery, and at the end of the first growing season on three plantation sites located in different bioclimatic domains in Quebec. The morpho-physiological responses obtained at the end of the second growing season (2+0) in the nursery made it possible to cluster the orchards into three distinct groups. Modeling growth curves of these different groups showed that the height growth of seedlings from the second-generation and southern first-generation seed orchards was significantly higher than that of those from other orchards, by at least 6%. A multiple regression model with three climatic variables (average growing season temperature, average July temperature, length of the growing season) showed that the final height of seedlings (2+0) from the first-generation seed orchards was significantly related to the local climatic conditions at the orchard sites of origin where parental trees from surrounding natural populations were sampled to provide grafts for orchard establishment. Seedling height growth was significantly affected by both seed source origins and planting sites, but the relative ranking of the different seed sources was maintained regardless of reforestation site. This knowledge could be used, in conjunction with transfer models, to refine operational seed transfer rules and select the most suitable sites in an assisted migration strategy.

Évaluation de la structure et de la variabilité génétiques des populations naturelles du pin d'Alep (Pinus halepensis Mill.) au Maroc à l'aide de marqueurs isoenzymatiques

Abstract Aleppo pine (Pinus halepensis Mill.) is a species threatened by anthropogenic overexploitation due to climate change. To contribute to its conservation, we evaluate the structure and the genetic diversity of the natural pine populations. We studied the genetic diversity of 14 populations (Rif, Middle Atlas, eastern Morocco and High Atlas) using an isoenzymatic marker. The results of the analysis indicated that the genetic variation of pine in Morocco is modest in comparison with other Mediterranean provenances. However, the study revealed a high coefficient of differentiation among populations (Fst = 9.5%). Two main population groups were identified based on genetic distances: South—West and North-East.