Assisted migration is increasingly proposed as a proactive management strategy to mitigate the consequences of maladaptation predicted under climate change. Exploring the social and academic structure of the field, its research gaps, and future research directions can help further the understanding and facilitate the implementation of assisted migration strategies. Here we used bibliometric analysis to examine the intellectual, social, and conceptual structures of assisted migration research to identify gaps and opportunities for future research. Bibliometric data based on publications on assisted migration were collected from Scopus and Web of Science databases using assisted migration and climate change or their synonyms as queries. Metadata were merged, processed and several networks were constructed.

Mesophyll conductance (gm) determines the diffusion of CO2 from the substomatal cavities to the site of carboxylation in the chloroplasts and represents a critical component of the diffusive limitation of photosynthesis. In this study, we evaluated the average effect sizes of different environmental constraints on gm in Populus spp., a forest tree model. We collected raw data of 815 A-Ci response curves from 26 datasets to estimate gm, using a single curve-fitting method to alleviate method-related bias. We performed a meta-analysis to assess the effects of different abiotic stresses on gm. We found a significant increase in gm from the bottom to the top of the canopy that was concomitant with the increase of maximum rate of carboxylation and light-saturated photosynthetic rate (Amax). gm was positively associated with increases in soil moisture and nutrient availability, but it was insensitive to increasing soil copper concentration, and it did not vary with atmospheric CO2 concentration. Our results showed that gm was strongly related to Amax and to a lesser extent to stomatal conductance (gs). Also, a negative exponential relationship was obtained between gm and specific leaf area, which may be used to scale-up gm within the canopy.

The mechanistic bases of thermal acclimation of net photosynthetic rate (A n ) are still difficult to discern, and the data sets available are scarce, particularly for hybrid poplar. In the present study, we examined the contribution of a number of biochemical and biophysical traits on thermal acclimation of A n for two hybrid poplar clones. We grew cuttings of Populus maximowiczii × Populus nigra (M×N) and Populus maximowiczii × Populus balsamifera (M×B) clones under two day/night temperature of 23°C/18°C and ?33°C /27°C and under low and high soil nitrogen level. After ten weeks, we measured leaf RuBisCO (RAR) and RuBisCO activase (RARCA) amounts and the temperature response of A n , dark respiration (R d ), stomatal conductance, (g s ), apparent maximum carboxylation rate of CO 2 (V cmax ) and apparent photosynthetic electron transport rate (J). Results showed that a 10°C increase in growth temperature resulted in a shift in thermal optimum (T opt ) of A n of 6.2±1.6 °C and 8.0±1.2 °C for clone M×B and M×N respectively, and an increased A n and g s at the growth temperature for clone M×B but not M×N. RuBisCO amount was increased by N level but was insensitive to growth temperature while RARCA amount and the ratio of its short to long isoform was stimulated by the warm condition for clone M×N and at low N for clone M×B. The activation energy of apparent V cmax and apparent J decreased under the warm condition for clone M×B and remained unchanged for clone M×N. Our study demonstrated the involvement of both RARCA, the activation energy of apparent V cmax and stomatal conductance in thermal acclimation of A n © 2019 Benomar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Intensively managed plantations are being established in a wide range of environmental conditions to satisfy the high demand for wood products and reduce the exploitation pressure on natural forests. In this study, we investigated the plasticity of four hybrid poplar (Populus spp.) clones established in 2005 along a latitudinal gradient in northwestern Quebec, Canada. The effect of latitudinal gradient on maximum rates of electron transfer (Jmax) and carboxylation (Vcmax), dark respiration (Rd), spring and fall bud phenology, net photosynthesis (Pn), specific leaf area (SLA), per mass nitrogen leaf concentration (Nm) were assessed in order to evaluate if clonal plasticity would result in increased overall productivity.

Growth season duration between the southernmost to the northernmost sites ranged 21–32 days, and was positively correlated to stem volume and negatively correlated to bud burst and bud set duration. Growth increment (stem volume) along the latitudinal gradient ranged 100–184% between the least and most productive clone. Clone 747215 had the most stable but the slowest growth. Leaf net photosynthesis decreased or did not change northwards except for the most productive clone for which it increased slightly likely due to a significant decrease in SLA. Maximum rates of carboxylation and photosynthesis electron transfer (Vcmax and Jmax) decreased northwards for three of the four clones, suggesting that photosynthesis of trees did not acclimate to lower temperatures from south to north. Plasticity of photosynthetic variables, measured with trait plasticity index was usually greater than that of SLA and Nm.

Cette thèse visait à acquérir une meilleure compréhension de l'effet des paramètres écophysiologiques (photosynthèse et nutrition minérale en particulier), en interaction avec les conditions du milieu, sur la productivité des plantations de peuplier hybride en milieu boréal. Plus spécifiquement, la thèse visait à : i) tester l'efficacité de la fertilisation basée sur la méthode DRIS (Diagnosis and Recommendation Integrated System). Cette approche est basée sur les ratios des nutriments, pour le diagnostic d'éventuelles carences nutritives en vue de déterminer plus précisément les besoins en fertilisant et optimiser le statut nutritif et la croissance du peuplier hybride, ii) déterminer l'effet de la diversité clonale sur le statut nutritif, la photosynthèse, le développement racinaire et la productivité des peupliers hybrides et iii) étudier la plasticité des clones de peuplier hybride suivant un gradient latitudinal et en réponse à l'espacement entre les arbres, et déterminer les traits physiologiques et morphologiques permettant de la caractériser.

Trois plantations expérimentales de quatre clones de peupliers hybrides ont été établies dans les régions de l'Abitibi-Témiscamingue et du Nord du Québec, Canada (747215, Populus trichocarpa Torrey & A.Gray × P. balsamifera L.; 915004 and 915005, P. balsamifera × P. maximowiczii Henry; and 915319 P. maximowiczii × P. balsamifera). Nous avons comparé l'effet de différents traitements de fertilisation sur le statut nutritif et la croissance des peupliers hybrides en plantation. Des parcelles mixtes composées des quatre clones et des parcelles monoclonales ont été établies afin de comparer l'effet des deux types de déploiement sur la productivité du peuplier hybride. Finalement, des parcelles des quatre clones ont été établies dans trois sites le long d'un gradient latitudinal et à différents espacements (1?4 m, 2?4 m et 3?4 m), afin d'évaluer, respectivement, la plasticité des clones en réponse au gradient latitudinal et à la compétition intraclonale.

Nos résultats ont montré que la fertilisation basée sur la méthode DRIS permettait de bien corriger les carences en azote, alors que les carences en phosphore n'ont pas été corrigées. L'utilisation de ce type de fertilisation n'a cependant augmenté le taux de croissance moyen des arbres que de seulement 6.1% comparativement aux arbres non fertilisés. L'utilisation de la méthode DRIS a également donné des résultats légèrement supérieurs à la dose de fertilisants traditionnelle (40N, 20P, 20K). La fertilisation basée sur DRIS apparaît globalement avantageuse par rapport à la dose traditionnelle pour corriger la carence azotée, améliorer la productivité des clones et éviter une fertilisation excessive.

En ce qui a trait au type de déploiement, la productivité des arbres était souvent supérieure dans les parcelles polyclonales comparées aux parcelles monoclonales, après cinq années de croissance, en augmentant la croissance en volume des arbres des quatre clones de 21% en moyenne. Le développement des racines différait entre les deux types de déploiements, avec un ratio de biomasse racinaire / biomasse aérienne des arbres des parcelles monoclonales supérieur à celui des parcelles polyclonales. Nous avons également observé une différence dans la distribution latérale des racines grosses et fines; La fraction des racines située à ≥ 60 cm était supérieure dans le déploiement monoclonal, ce qui suggère une compétition plus prononcée dans ce déploiement, poussant les racines à chercher les nutriments à distance. La photosynthèse nette avait tendance à augmenter dans les parcelles polyclonales chez la plupart des clones, ce qui est cohérent avec la teneur plus élevée en glucides totaux non-structuraux (TNC) des racines observées dans les parcelles polyclonales.

La date de débourrement du bourgeon terminal variait le long du gradient latitudinal et la saison de croissance raccourcissait à divers degrés selon les clones, en allant vers le nord. Le débourrement du clone 915319, le plus productif, a commencé plus tard mais duré moins longtemps que celui des autres clones, notamment le 747215, le moins productif. L'écart dans la date de débourrement entre le site du sud et celui du nord du premier clone était moins important ce qui lui a permis d'être plus productif sur tout le territoire et moins affecté par la latitude. La date de l'aoûtement a été peu influencée par le gradient latitudinal, mais différente entre les clones. Les clones ont démontré une plasticité de la capacité photosynthétique le long du gradient qui s'est traduite par une variation des vitesses maximales de carboxylation (Vcmax) et de transport photosynthétique des électrons (Jmax) le long du gradient. Ces deux paramètres étaient souvent supérieurs dans le site méridional. L'acclimatation à la compétition par la réduction de l'espacement entre les arbres s'est manifestée essentiellement par des ajustements morphologiques, particulièrement pour la surface foliaire spécifique et la hauteur des arbres plantés à 1?4 m qui étaient supérieures à celles des arbres espacés de 2?4 m ou de 3?4 m. Ces réponses à la forte densité de plantation semblaient permettre une meilleure interception de la lumière par les feuilles et une allocation de l'azote foliaire aux protéines impliquées dans la photosynthèse. Ceci était en accord avec les résultats sur l'effet de l'espacement sur la photosynthèse montrant que le taux d'assimilation nette (Pn) des feuilles était généralement supérieur dans les parcelles à densité élevée, suggérant que la plasticité morphologique a permis de réduire l'effet de l'ombrage et de la compétition pour l'azote, et d'accroitre la photosynthèse des arbres.

Cette étude a permis d'approfondir les connaissances sur la nutrition minérale des peupliers hybrides en milieu boréal, leur acclimatation à la compétition intra et inter-clonale et sur la plasticité phénotypique le long d'un gradient sud-nord. Les résultats de ce travail pourront servir à établir des recommandations dans l'aménagement des zones à production ligneuse intensive au Québec.

Mixing tree cultivars or species in forest plantations can be efficient to reduce the risk of pest damages and could have a positive effect on yields if complementarity or facilitation between trees occurs. Four hybrid poplar clones (747215, Populus trichocarpa Torrey & A.Gray × P. balsamifera L.; 915004 and 915005, P. balsamifera × P. maximowiczii Henry; and 915319 P. maximowiczii × P. balsamifera) were planted in monoclonal and polyclonal plantations in three sites located in Quebec, Canada, to assess effects of clonal diversity on (i) aboveground biomass productivity, (ii) net photosynthesis and nutrient status of trees, and (iii) root spatial distribution. Stem growth was measured over five growing seasons, while root development, foliar nutrient concentrations and photosynthesis were measured during the fifth growing season. Results showed frequent but not general overyielding of trees in the polyclonal plots compared to monoclonal plots, five years after plantation establishment. Overall, stem volumes were 21% higher in the polyclonal (7.4 m3 ha?1) vs. monoclonal (6.1 m3 ha?1) plots. Effects of clone mixing on growth were greater in sites where soil nutrients were more limiting. However, foliar macronutrient concentrations (N, P, K, Ca and Mg) in trees growing in polyclonal plots were similar to those in monoclonal plots. Root development differed between the two plot layouts, with mean root:shoot ratio being greater in monoclonal (0.41:1) vs. the polyclonal (0.35:1) plots. Mixing clones increased biomass allocation aboveground, which we attributed to reduced competition between individuals of different clones and could explain overyielding in the polyclonal plots. The root fraction most distant from the stem (?60 cm) was greater in monoclonal (67% of total root biomass) compared to polyclonal (47% of total root biomass) plots, suggesting greater belowground competition in the former, which forced roots to extend further from the stems. Effects of plot layout on net assimilation rate (Pn) depended on site, with trees in polyclonal plots having greater Pn in two of the three sites. Root total non-structural carbohydrates were greater in the polyclonal (216 mg g?1) compared to the monoclonal (159 mg g?1) plots. Mixing hybrid poplar clones often resulted in greater aboveground growth, lower root:shoot ratios, and different spatial root distributions, when compared to clones planted in monocultures.

In order to maximize early growth and establishment of planted hybrid poplars in the boreal region of Eastern Canada, growth response of four clones to fertilization was tested in two plantations. The first two fertilization treatments were based on Diagnosis and Recommendation Integrated System (DRIS), a method based on nutrient ratios: DRIS I was based on previously established norms from a study that had been conducted in the same area, and DRIS II was based on DRIS norms developed from hybrid poplars in northern Ontario, Canada. Nutrient status and growth of trees under these 2 treatments were compared to unfertilized trees and to trees under standard (STD) fertilization treatment (40 N-20P-20 K). Leaf nutrient concentrations and DRIS indices showed that fertilization treatments, and especially DRIS I corrected N deficiencies but failed to correct P deficiencies. Fertilization increased volume relative growth rate by 7.51, 4.76 and 13.25 % on average at the agricultural site for DRIS I, DRIS II and STD treatments respectively, compared to no fertilizer application. At the forest site, fertilization treatments based on DRIS indices (DRIS I and DRIS II) increased growth rates (6.67 %) slightly more than the standard treatment (5.80 %). Overall, although DRIS-based fertilization treatments generally increased growth rates, they were often equal to or less efficient than the STD treatment, and may not be as practical as using a standard fertilization recipe. © 2012 Springer Science+Business Media Dordrecht.