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IntroductionPhenotypic plasticity (PP) could be an important short-term mechanism to modify physiological and morphological traits in response to climate change and global warming, particularly for high-mountain tree species. The objective was to evaluate PP response of growth ring traits to temperature and precipitation in Pinus hartwegii Lindl. populations located at the ends of its elevational gradient on two volcanic mountains in central Mexico (La Malinche and Nevado de Toluca).MethodsIncrement cores collected from 274 P. hartwegii trees were used to estimate their PP through reaction norms (RN), which relate the ring width and density traits with climate variables (temperature and precipitation). We estimated the trees’ sensitivity (significant RN) to climatic variables, as well as the relative proportion of RN with positive and negative slope. We also estimated the relationship between the PP of ring width and density traits using correlation and Principal Component (PC) analyses.ResultsOver 70% of all trees showed significant RN to growing season and winter temperatures for at least one growth ring trait, with a similar proportion of significant RN at both ends of the gradient on both mountains. Ring width traits had mostly negative RN, while ring density traits tended to have positive RN. Frequency of negative RN decreased from lower to higher elevation for most traits. Average PP was higher at the lower end of the gradient, especially on LM, both for ring width and ring density traits, although high intrapopulation variation in PP was found on both mountains.DiscussionResults indicate that P. hartwegii presents spatially differentiated plastic responses in width and density components of radial growth. PP was particularly strong at the lower elevation, which has higher temperature and water stress conditions, putting these populations at risk from the continuing global warming driven by climate change.

Why this research Matters Phenotypic plasticity is a key mechanism for sedentary long‐living species to adjust to changing environment. Here, we use mature Larix decidua tree‐ring variables collected along an elevational transect in the French Alps to characterize the range of individual plastic responses to temperature. Stem cores from 821 mature Larix decidua trees have been collected from four plots distributed along a 1,000‐m elevational gradient in a natural forest to build up individual linear reaction norms of tree‐ring microdensity traits to temperature. The sign, magnitude and spread of variations of the slopes of the individual reaction norms were used to characterize variation of phenotypic plasticity among plots and traits. Results showed a large range of phenotypic plasticity (with positive and negative slopes) at each elevational plot and for each tree‐ring variable. Overall, phenotypic plasticity tends to be larger but positive at higher elevation, negative at the warmer lower sites, and more variable in the center of the elevation distribution. Individual inter‐ring reaction norm is a valuable tool to retrospectively characterize phenotypic plasticity of mature forest trees. This approach applied to Larix decidua tree‐ring micro‐density traits along an elevation gradient showed the existence of large inter‐individual variations that could support local adaptation to a fast‐changing climate.

In the long term, defoliation strongly decreases tree growth and survival. Insect outbreaks are a typical cause of severe defoliation. Eastern spruce budworm (Choristoneura fumiferana Clem.) outbreaks are one of the most significant disturbances of Picea and Abies boreal forests. Nevertheless, in boreal conifers, a 2-year defoliation has been shown to quickly improve tree water status, protect the foliage and decrease growth loss. It suggests that defoliation effects are time-dependent and could switch from favorable in the short term to unfavorable when defoliation duration exceeds 5–10 years. A better understanding of the effect of defoliation on stem radius variation during the needle flushing time-window could help to elucidate the relationships between water use and tree growth during an outbreak in the medium term. This study aims to assess the effects of eastern spruce budworm (Choristoneura fumiferana Clem.) defoliation and bud phenology on stem radius variation in black spruce [Picea mariana (Mill.) B.S.P.] and balsam fir [Abies balsamea (L.) Mill.] in a natural stand in Quebec, Canada. We monitored host and insect phenology, new shoot defoliation, seasonal stem radius variation and daytime radius phases (contraction and expansion) from 2016 to 2019. We found that defoliation significantly increased stem growth at the beginning of needle flushing. Needles flushing influenced the amplitude and duration of daily stem expansion and contraction, except the amplitude of stem contraction. Over the whole growing season, defoliation increased the duration of stem contraction, which in turn decreased the duration of stem expansion. However, the change (increase/decrease) of the duration of contraction/expansion reflects a reduced ability of the potential recovery from defoliation. Black spruce showed significantly larger 24-h cycles of stem amplitude compared to balsam fir. However, both species showed similar physiological adjustments during mild stress, preventing water loss from stem storage zones to support the remaining needles’ transpiration. Finally, conifers react to defoliation during a 4-year period, modulating stem radius variation phases according to the severity of the defoliation.

Larch budmoth (LBM) periodically defoliates alpine stands of European larch during vast outbreaks occurring generally at 8–10 year intervals. LBM outbreaks recently declined and the ongoing global warming has been pointed out as a possible cause of this decline. In this article, we reconstructed the recent history of LBM outbreaks at different elevations along a larch elevational gradient in the French Alps using direct and indirect observations based on tree-ring width and density analysis, and compared it with local climatic data. We found that LBM outbreaks time-series were better reconstructed with latewood density than with ring width. We also found that there was a recent but limited elevational shift of LBM outbreaks from medium toward higher elevations. We suggest that this elevational shift is a consequence of the variable effect of the global warming at the different elevations. Winter warming is expected to affect differently the timing of LBM egg hatch as well as that of larch bud flush, larvae being at present susceptible to emerge whereas no needles are available as food at the former optimal elevation. A better synchronization between larch and LBM may exist at higher elevations.

Until recently, the roles of plant MADS-box genes have mainly been characterized during inflorescence and flower differentiation. In order to precise the roles of AGAMOUS-LIKE 12, one of the few MADS-box genes preferentially expressed in roots, we placed its cDNA under the control of the double 35S CaMV promoter to produce transgenic walnut tree and Arabidopsis plants. In Juglans sp., transgenic somatic embryos showed significantly higher germination rates but abnormal development of their shoot apex prevented their conversion into plants. In addition, a wide range of developmental abnormalities corresponding to ectopic root-like structures affected the transgenic lines suggesting partial reorientations of the embryonic program toward root differentiation. In Arabidopsis, AtAGL12 overexpression lead to the production of faster growing plants presenting dramatically wider and shorter root phenotypes linked to increased meristematic cell numbers within the root apex. In the upper part of the roots, abnormal cell divisions patterns within the pericycle layer generated large ectopic cell masses that did not prevent plants to grow. Taken together, our results confirm in both species that AGL12 positively regulates root meristem cell division and promotes overall root vascular tissue formation. Genetic engineering of AGL12 expression levels could be useful to modulate root architecture and development.

Italy is one of the major users of cherry wood (Prunus avium L.), and its cultivation has been increasing since the early nineties, together with studies aimed at improving genotypes, with a selection usually based on growth, stem form, vigor, and tree adaptation. Here, the phenotypic correlations between growth rate and the physical and mechanical properties of wood are investigated in two wild cherry plantations. X-ray microdensitometry was also applied to analyze the age-age correlations of wood density. It was shown that growth rate did not affect wood properties, and density was confirmed to be the trait that best represents the main properties of wood. The absence of relationships between wood density and growth rate was confirmed by densitometric analysis, although an increase of wood density with an increase of ring width was detected for very narrow rings (less than 3 mm wide). The average density at age 7 to 8 was observed to be highly correlated (r > 0.90) to the average density of a 19-year-old tree, allowing reliable estimation of the wood properties of older trees by early investigation of young trees.

Tree-ring datasets are used in a variety of circumstances, including archeology, climatology, forest ecology, and wood technology. These data are based on microdensity profiles and consist of a set of tree-ring descriptors, such as ring width or early/latewood density, measured for a set of individual trees. Because successive rings correspond to successive years, the resulting dataset is a ring variables × trees × time datacube. Multivariate statistical analyses, such as principal component analysis, have been widely used for extracting worthwhile information from ring datasets, but they typically address two-way matrices, such as ring variables × trees or ring variables × time. Here, we explore the potential of the partial triadic analysis (PTA), a multivariate method dedicated to the analysis of three-way datasets, to apprehend the space-time structure of tree-ring datasets. We analyzed a set of 11 tree-ring descriptors measured in 149 georeferenced individuals of European larch (Larix decidua Miller) during the period of 1967-2007. The processing of densitometry profiles led to a set of ring descriptors for each tree and for each year from 1967-2007. The resulting three-way data table was subjected to two distinct analyses in order to explore i) the temporal evolution of spatial structures and ii) the spatial structure of temporal dynamics. We report the presence of a spatial structure common to the different years, highlighting the inter-individual variability of the ring descriptors at the stand scale. We found a temporal trajectory common to the trees that could be separated into a high and low frequency signal, corresponding to inter-annual variations possibly related to defoliation events and a long-term trend possibly related to climate change. We conclude that PTA is a powerful tool to unravel and hierarchize the different sources of variation within tree-ring datasets.

AbstractThe first and the second generation of improved maritime pine (Pinus pinaster) have produced gains of up to 30% in stem volume, a reduction of final harvesting age by 10 years and a considerable improvement of stem straightness. The third generation will include wood quality traits for different end-uses, including pulp and fibre properties. To facilitate this goal, near infrared spectroscopy (NIRS) was used to estimate chemical composition with regard to lignin, cellulose, hemicelluloses, and extractive content, and lignin quality with regard to 4-hydroxy-phenylpropane/guaiacylpropane ratio. A total of 960 samples were investigated which were collected from a large number of trees (belonging to 80 families obtained by crossing 18 mothers and 20 fathers; there are 12 trees per family). Good calibration data was obtained between NIRS and wet chemistry methods (R2values higher than 0.9 and good precision of prediction). To complete the NIRS work, kraft cookings in small scale, fibre morphology and microdensitometry investigations were also conducted. Genetic calculations indicated that for a 1% rate of selection on mothers and fathers, genetically induced changes are possible with lignin content (−3.8%), cellulose content (+1.3%), pulp yield (+1.8%), fibre length in pulps (+0.17 mm) and wood density (+50 kg m−3). [ABSTRACT FROM AUTHOR]

Abstract  In this work, we present a fast and promising method to evaluate the natural durability of wood based on X-ray microdensitometry. Tested on beech and Scots pine wood samples, our findings show that this methodology and the traditional EN standards methodology based on mass loss are strongly correlated. X-ray methodology is less time consuming (we can detect the effectiveness of the attack within 5–6 weeks) and less expensive (very cheap plastic Petri dishes instead of the expensive glass Kolle flasks); moreover, the proposed method allows to thoroughly examine the phases and the kinetics of the fungal attack, and to investigate the spatial repartition of the attack within the samples due to the low thickness of the sample. [ABSTRACT FROM AUTHOR]

Wood can be seen as a record of cambial activity. Within a ring, density variation from earlywood to latewood is a consequence of the within growing season climate changes. We propose a method to synchronize the within-ring density profile with within-growing season climate variables. Thanks to this synchronization, we show that Douglas-fir cambium reaction to the variation of the withingrowing season minimum temperature is variable and quite strongly genetically controlled. Such variation has a direct consequence on wood density, and thus on wood quality. [ABSTRACT FROM AUTHOR]

Growth and stem straightness are the two main selection criteria in the French maritime pine breeding programme. In this contribution, our objective was to study the possibility of selecting for wood density assessed at an early stage. We measured X-ray wood density, in three progeny tests, on more than 1?900 breast high increment cores. High relative expected genetic gain (from 3 to 9%) was found for wood density at mature stage. Juvenile and adult wood density estimations were well-correlated; the relative efficiency of early selection reached about 80% at 12?years old. As it would not be realistic to use the X-ray densitometer at an operational scale in a breeding programme, we tested the efficiency of using the Resistograph, an indirect method to assess wood density on live trees. High correlation between the Resistograph and density data (R2= 0.93 on familial data) was found, suggesting that wood density through Resistograph assessment could be soon integrated as a new selection criterion in our breeding programme. Peut-on efficacement s?lectionner la densit? du bois chez le pin maritime (Pinus pinaster Ait.) au stade juv?nile??. La croissance et la rectitude du tronc sont les deux principaux crit?res de s?lection dans le programme d''am?lioration g?n?tique du pin maritime en France. Cette ?tude a pour objectif d''?valuer la possibilit? de s?lectionner la densit? du bois au stade juv?nile. Plus de 1?900 arbres, provenant de trois tests, ont ?t? analys?s par microdensitom?trie. Des gains g?n?tiques relatifs ?lev?s ont ?t? mis en ?vidence pour la densit? du bois au stade adulte (3 ? 9?%). Les estimations de la densit? r?alis?es aux stades adulte et juv?nile ?tant bien corr?l?es, l''efficacit? relative de la s?lection atteint environ 80?% ? l''?ge de 12 ans. Les mesures de densit? par rayons X ne sont pas envisageables ? grande ?chelle dans le cadre d''un programme d''am?lioration, ainsi nous avons ?valu? l''efficacit? de l''utilisation du R?sistographe, une m?thode indirecte pour estimer la densit? du bois sur arbres debout. Des corr?lations ?lev?es ont ?t? mises en ?vidence entre les donn?es obtenues avec le R?sistographe et celles obtenues par microdensitom?trie (R2= 0.93 avec les donn?es familiales). Il semble donc possible d''int?grer la densit? du bois, estim?e avec le R?sistographe, comme nouveau crit?re de s?lection dans notre programme d''am?lioration. [ABSTRACT FROM AUTHOR]

The genetic control of tree ring growth in Douglas-fir in response to the drought and heat-wave that occurred in 2003 in Europe was studied with microdensity profiles in three clonal experiments located in three different French regions. The drought and heat-wave significantly affected Douglas-fir wood formation. The Chassenoix site (Northeast of Massif-Central) was more severely affected that the other two: the 2003 year-ring was narrower and less dense than in the other sites and than the previous (2002) and following (2004) year-rings in the same site: ring growth stopped earlier and latewood did not develop completely. The year-rings 2004 and 2002 were very similar in this site. There was a significant genetic control for all ring parameters in the three sites and during the three years. The heritability was highly variable between years and among sites, without any clear pattern in this variability, except in Chassenoix where it was slightly lower in the 2003 year-ring. Variables measuring the response of trees to the 2003 event, i.e., the difference in ring width between 2002 and 2003, or between 2003 and 2004, showed a very variable degree of genetic control, from very low to relatively high. Douglas-fir seemed plastic enough to acclimate to the drought and heat-wave and then to recover during 2004. Furthermore the level of heritability estimated demonstrates that Douglas-fir has an adaptive potential that could be useful for multi-generation long-term response. Contr?le g?n?tique de la r?ponse microdensitom?trique du Douglas (Pseudotsuga menziesii (Mirb.) Franco) ? la s?cheresse et canicule de 2003 en France. La r?ponse du douglas ? la canicule de 2003 en France a ?t? ?tudi?e ? l''aide de profils microdensitom?triques obtenus sur des arbres de 3 tests clonaux situ?s dans 3 r?gions diff?rentes. La canicule a significativement affect? la formation du bois du douglas. Les arbres du site de Chassenoix, situ? dans le Morvan, ont r?agi plus fortement que ceux des 2 autres : le cerne de l''ann?e de la canicule est plus ?troit et moins dense que le m?me cerne dans les 2 autres sites et plus ?troit et moins dense que les cernes imm?diatement ant?rieur (2002) et post?rieur (2004) dans le m?me site ; la formation du bois s''est arr?t?e plus t?t et le bois final ne s''est pas compl?tement d?velopp?. ? Chassenoix, le cerne de l''ann?e 2004 ressemble plus au cerne 2002 qu''au cerne 2003, ce qui traduit une r?cup?ration. Nous mettons en ?vidence un contr?le g?n?tique significatif pour toutes les variables intra-cernes dans les 3 sites, pour les 3 ann?es 2002, 2003 et 2004. Les h?ritabilit?s sont tr?s variables entre caract?res, sites et ann?es, sans structure particuli?re, sauf ? Chassenoix o? ces h?ritabilit?s sont l?g?rement plus faibles durant l''ann?e de la canicule. Des variables d?crivant la r?ponse des arbres entre 2002 et 2003 puis 2003 et 2004 sont tr?s irr?guli?rement contr?l?es g?n?tiquement, avec des h?ritabilit?s allant de 0 ? pr?s de 0,5. Le douglas semble avoir ?t? suffisamment plastique pour s''acclimater ? la s?cheresse et canicule puis pour r?cup?rer en 2004 une croissance proche de celle de 2002. De plus, son potentiel g?n?tique d?montr? par le niveau d''h?ritabilit? estim? lui donne ?galement une capacit? adaptative multi-g?n?ration ? plus long terme. [ABSTRACT FROM AUTHOR]