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The American elm (Ulmus americana L.), once a dominant species in North American floodplain forests, has suffered significant population declines due to Dutch elm disease (DED). Despite this, some elms persist, potentially exhibiting disease resistance and climate-adaptive traits that could facilitate restoration. Understanding these traits is crucial for selecting genotypes suited to current and future climatic conditions, particularly in colder regions. This study evaluated the mid-winter cold tolerance of American elm genotypes across a climatic gradient to ascertain evidence of local climate adaptation. We used relative electrolyte leakage (REL) to assess mid-winter cold tolerance of current-year shoots on eleven survivor genotypes from New England and one susceptible, control genotype from Ohio. The lethal temperature, at which 50% of cellular leakage occurs (LT50), was determined and compared with 30-year climate data to identify potential climate adaptation. Genotypes from colder regions exhibited greater cold hardiness, indicating local adaptation to climate. Observed mid-winter LT50 values (−42.8 °C to −37.7 °C) were in excess of the 30-year minimum air temperature, even at the coldest source location. This calls into question whether mid-winter cold tolerance is the critical period for injury to American elm and more attention should be given to environmental conditions that cause de-acclimation to cold. By understanding the adaptive capacity of American elm, managers can better select mother trees for regional seed orchards, ensuring the long-term success of restoration initiatives. [ABSTRACT FROM AUTHOR]

Autumnal leaf anthocyanin expression is enhanced following exposure to a variety of environmental stresses and may represent an adaptive benefit of protecting leaves from those stresses, thereby allowing for prolonged sugar and nutrient resorption. Past work has shown that experimentally induced sugar accumulations following branch girdling triggers anthocyanin biosynthesis. We hypothesized that reduced phloem transport at low autumnal temperatures may increase leaf sugar concentrations that stimulate anthocyanin production, resulting in enhanced tree- and landscape-scale color change. We used refrigerant-filled tubing to cool individual branches in a mature sugar maple (Acer saccharum Marsh.) tree to test whether phloem cooling would trigger foliar sugar accumulations and enhance anthocyanin biosynthesis. Cooling increased foliar sucrose, glucose, and fructose concentrations 2- to nearly 10-fold (depending on the specific sugar and sampling date) relative to controls and increased anthocyanin concentrations by approximately the same amount. Correlation analyses indicated a strong and steady positive relationship between anthocyanin and sugar concentrations, which was consistent with a mechanistic link between cooling-induced changes in these constituents. Tested here at the branch level, we propose that low temperature induced reductions in phloem transport may be responsible for increases in foliar sugars that trigger anthocyanin displays at grander scales. Key words: fall leaf color, low temperature, sucrose, glucose, fructose, Acer saccharum. L'apparition des anthocyanines dans les feuilles a l'automne est amplifiee par l'exposition a divers stress environnementaux et pourrait representer un avantage adaptatif en protegeant les feuilles contre ces stress; ce qui permettrait par consequent de prolonger la resorption des sucres et des nutriments. Des travaux anterieurs ont montre que l'accumulation experimentalement induite des sucres apres avoir annele des branches declenche la biosynthese des anthocyanines. Nous avons emis l'hypothese que le ralentissement du transport dans le phloeme cause par les temperatures basses a l'automne pourrait augmenter la concentration des sucres; ce qui stimulerait la production des anthocyanines et entrainerait un changement de couleur plus intense a l'echelle de l'arbre et du paysage. Nous avons utilise une tubulure contenant un fluide frigorigene pour refroidir des branches dans un erable a sucre (Acer saccharum Marsh.) mature afin de tester si le refroidissement du phloeme declencherait une accumulation des sucres dans les feuilles et augmenterait la biosynthese des anthocyanines. Le refroidissement a augmente la concentration de sucrose, de glucose et de fructose dans les feuilles de 2 a pres de 10 fois (dependemment de la nature du sucre et de la date d'echantillonnage) comparativement aux branches temoins et a aussi augmente la concentration des anthocyanines dans environ la meme proportion. Les analyses de correlation montrent qu'il y a une relation positive etroite et stable entre les concentrations d'anthocyanines et de sucres qui correspond a un lien mecaniste entre les changements induits dans ces constituants par le refroidissement. Ayant teste l'hypothese a l'echelle des branches, nous sommes d'avis que le ralentissement du transport dans le phloeme cause par une temperature basse serait responsable de l'augmentation des sucres dans les feuilles qui declencherait l'apparition plus marquee des anthocyanines. [Traduit par la Redaction] Mots-cles: coloration automnale des feuilles, temperature basse, sucrose, glucose, fructose, Acer saccharum., Introduction Anthocyanins are water-soluble pigments that reside within cell vacuoles in a wide variety of plants (Archetti et al. 2009). They are responsible for the red to purple colors observed [...]

Longleaf pine (Pinus palustris Mill.) restoration in the south eastern United States offers opportunities for carbon (C) sequestration. Ecosystem C stocks are not well understood in longleaf pine forests, which are typically of low density and maintained by prescribed fire. The objectives of this research were to develop allometric equations for above- and below-ground biomass and quantify ecosystem C stocks in five longleaf pine forests ranging in age from 5 to 87 years and in basal area from 0.4 to 22.6 [m.sup.2] x [ha.sup.-1]. Live aboveground C (woody plant + ground cover) and live root C (longleaf pine below stump + plot level coarse roots + plot level fine roots) ranged from 1.4 and 2.9 Mg C x [ha.sup.-1], respectively, in the 5-year-old stand to 78.4 and 19.2 Mg C x [ha.sup.-1], respectively, in the 87-year-old stand. Total ecosystem C (live plant + dead organic matter + mineral soil) values were 71.6, 110.1, 124.6,141.4, and 185.4 Mg C x [ha.sup.-1] in the 5-, 12-, 21-, 64-, and 87-year-old stands, respectively, and dominated by tree C and soil C. In the 5- year-old stand, ground cover C and residual taproot C were significant C stocks. This unique, in-depth assessment of above and below-ground C across a series of longleaf pine stands will improve estimates of C in longleaf pine ecosystems and contribute to development of general biomass models that account for variation in climate, site, and management history in an important but understudied ecosystem. Key words: longleaf pine, carbon sequestration, allometry, roots, ground- penetrating radar. La restauration du pin des marais (Pinus palustris Mill.) dans le sud-est des Etats-Unis off re une opportunity de stocker du carbone (C). Les stocks de C de l'ecosysteme ne sont pas bien connus dans les forets de pin des marais qui ont typiquementune faible densite et se maintiennent grace au brulage dirigee. Les objectifs de ces travaux de recherche consistaient a elaborer des equations allometriques pour la biomasse aerienne et souterraine et a quantifier les stocks de C de l'ecosysteme dans cinq forets de pin des marais dont l'age allait de 5 a 87 ans et dont la surface terriere variait de 0,4 a 22,6 [m.sup.2] x [ha.sup.-1]. Le C aerien vert (plantes ligneuses + couverture vegetale) et le C des racines vivantes (souches de pin des marais + grosses racines et racines fines presentes dans les placettes) variaient respectivement de 1,4 et 2,9 Mg C x [ha.sup.-1]dans le peuplement age de 5 ans a 78,4 et 19,2 Mg C x [ha.sup.-1] dans le peuplement age de 87 ans. Le C total de l'ecosysteme (plantes vivantes + matiere organique morte + sol mineral) atteignait respectivement 71,6,110,1,124,6,141,4 et 185,4 Mg C x [ha.sup.-1] dans les peuplements ages de 5,12, 21, 64 et 87 ans et etait domine par le C des arbres et du sol. Dans le peuplement age de 5 ans, le C contenu dans la couverture vegetale et les racines pivotantes residuelles constituait un stock important de C. Cette evaluation unique et approfondie du C aerien et souterrain dans une serie de peuplements de pin des marais ameliorera les estimations du C dans les ecosystemes domines par cette essence et contribuera au developpement de modeles generaux de biomasse qui tiennent compte de la variation dans le climat, la station et l'historique d'amenagement dans un ecosysteme important mais peu etudie. [Traduit par la Redaction] Mots-cles: pin des marais, sequestration du carbone, allometrie, racines, georadar., Introduction Forests serve as a means for mitigating climate change by acting as sinks for atmospheric C[O.sub.2] and storing carbon (C) in plant biomass, detritus, and forest soils. In the [...]

: Growth, allocation to woody root biomass, wood properties, leaf physiology, and shoot morphology were examined in a 47-year-old loblolly pine (Pinus taeda L.) density trial located in Maui, Hawaii, to determine if stands continued to carry the high density, basal area, and volume reported at younger ages and to identify potential factors controlling expression of maximum growth potential. Basal area and volume were similar among spacings (square: 1.8, 2.4, 3.0, and 3.7 m) and averaged 93 [m.sup.2]*[ha.sup.-1] and 1076 [m.sup.3]*[ha.sup.-1], respectively, and were double the maxima reported for loblolly pine in its native range. Spacing had a significant influence on density, quadratic mean diameter, and height. Ring-specific gravity and percent latewood were similar among spacing treatments but values were high compared to mainland stands. Leaf light-saturated net photosynthesis, dark respiration, stomatal conductance, and quantum yield were comparable with values reported for loblolly pine in its native range. Foliar calcium concentrations, specific leaf area, and flush number were high in the Hawaii study. Higher carrying capacity in Hawaii may be related to a more favorable climate conducive to yearround leaf carbon gain, high nutrient availability, increased flushing, and less allocation to belowground mass. Resume: Nous avons etudie la croissance, l'allocation des ressources a la biomasse racinaire ligneuse, les proprietes du bois, la physiologie foliaire et la morphologie des pousses dans un peuplement de pin a encens (Pinus taeda L.) age de 47 ans situe a Maui, a Hawaii, et qui faisait partie d'une experience de densite variable. Le but de l'etude etait de determiner si les peuplements continuaient de soutenir les valeurs elevees de densite, de surface terriere et de volume observees en jeune age et d'identifier les facteurs qui pourraient etre associes a l'expression de la croissance potentielle maximale. La surface terriere et le volume n'ont pas varie selon l'espacement (espacements carres de 1,8, 2,4, 3,0 et 3,7 m) et ont respectivement atteint 93 [m.sup.2]*[ha.sup.-1] et 1076 [m.sup.3]*[ha.sup.-1], en moyenne, ce qui correspond au double des valeurs maximales observees dans l'habitat naturel du pin a encens. L'espacement a eu un effet significatif sur la densite, le diametre moyen quadratique et la hauteur des arbres. La densite du bois et le pourcentage de bois final etaient semblables parmi les traitements d'espacement, mais leurs valeurs etaient elevees comparativement aux peuplements continentaux. La photosynthese foliaire nette sous une lumiere saturante, la respiration a l'obscurite, la conductance stomatique et le rendement quantique avaient des valeurs semblables a celles qui ont ete rapportees pour le pin a encens dans son habitat naturel. La concentration foliaire en calcium, la surface foliaire specifique et le nombre de pousses etaient eleves dans l'etude hawaiienne. La plus forte capacite de support du milieu a Hawaii peut etre reliee a un climat plus favorable qui est propice a un gain foliaire en carbone a longueur d'annee, a une disponibilite elevee en nutriments, a une augmentation du nombre de pousses et a une plus faible allocation des ressources a la biomasse souterraine. [Traduit par la Redaction, Introduction Production rates of loblolly pine (Pinus taeda L.) in Hawaii, Brazil, Argentina, and South Africa indicate that full biological expression of growth potential in loblolly pine has not yet [...]

Abstract: Leaf physiology and stem growth were assessed in loblolly pine (Pinus taeda L.) in response to 10 to 11 years of treatment with weed control (W), weed control plus [...]

Inadequate cold tolerance of Eucalyptus spp. has limited a broader deployment beyond subtropical regions of the United States. We examined growth, photosynthetic rate, and cold tolerance of a cold-hardy Eucalypt (Eucalyptus benthamii) planted in North Carolina and compared the results with native Pinus taeda. After two growing seasons, E. benthamii surpassed P. taeda in both height (5.06 m, 1.34 m) and diameter (5.0 cm, 0.7 cm) growth, respectively. From April through November, E. benthamii's mean photosynthetic rate (Ps) (13.82 µmol CO2 m-2s-1) was more than twice that of P. taeda (6.21 µmol CO2 m-2s-1). Similarly, mean Ps during winter months was 6.09 µmol CO2 m-2s-1 for E. benthamii compared to 2.73 µmol CO2 m-2s-1 for P. taeda. Laboratory assessments of cold tolerance demonstrated that, unlike P. taeda, E. benthamii had a limited ability to acclimate to seasonal temperature changes. The coldest temperature (Tm) where >50% of the tissue was damaged and recovery unlikely for E. benthamii was -13.4°C for leaves and -14.3°C for stems, whereas for P. taeda it was -29.9°C for leaves and -36.5°C for stems. The exceptional productivity of E. benthamii was not without trade-offs as all trees died after experiencing air temperatures of -12.8°C on January 7, 2014. [ABSTRACT FROM AUTHOR]