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Increased summer drought will exacerbate the regeneration of many tree species at their lower latitudinal and altitudinal distribution limits. In vulnerable habitats, introduction of more drought-tolerant provenances or species is currently considered to accelerate tree species migration and facilitate forest persistence. Trade-offs between drought adaptation and growth plasticity might, however, limit the effectiveness of assisted migration, especially if introductions focus on provenances or species from different climatic regions. We tested in a common garden experiment the performance of Pinus sylvestris seedlings from the continental Central Alps under increased temperatures and extended spring and/or summer drought, and compared seedling emergence, survival and biomass allocation to that of P. sylvestris and closely related Pinus nigra from a Mediterranean seed source. Soil heating had only minor effects on seedling performance but high spring precipitation doubled the number of continental P. sylvestris seedlings present after the summer drought. At the same time, twice as many seedlings of the Mediterranean than the continental P. sylvestris provenance were present, which was due to both higher emergence and lower mortality under dry conditions. Both P. sylvestris provenances allocated similar amounts of biomass to roots when grown under low summer precipitation. Mediterranean seedlings, however, revealed lower phenotypic plasticity than continental seedlings under high precipitation, which might limit their competitive ability in continental Alpine forests in non-drought years. By contrast, high variability in the response of individual seedlings to summer drought indicates the potential of continental P. sylvestris provenances to adapt to changing environmental conditions.

Pine nuts are not only the important agent of pine reproduction and afforestation, but also the commonly consumed nut with high nutritive values. However, it is difficult to distinguish among pine nuts due to the morphological similarity among species. Therefore, it is important to improve the quality of pine nuts and solve the adulteration problem quickly and non-destructively. In this study, seven pine nuts ( Pinus bungeana , Pinus yunnanensis , Pinus thunbergii , Pinus armandii , Pinus massoniana , Pinus elliottii and Pinus taiwanensis ) were used as study species. 210 near-infrared (NIR) spectra were collected from the seven species of pine nuts, five machine learning methods (Decision Tree (DT), Random Forest (RF), Multilayer Perceptron (MLP), Support Vector Machine (SVM) and Naive Bayes (NB)) were used to identify species of pine nuts. 303 images were used to collect morphological data to construct a classification model based on five convolutional neural network (CNN) models (VGG16, VGG19, Xception, InceptionV3 and ResNet50). The experimental results of NIR spectroscopy show the best classification model is MLP and the accuracy is closed to 0.99. Another experimental result of images shows the best classification model is InceptionV3 and the accuracy is closed to 0.964. Four important range of wavebands, 951–957 nm, 1,147–1,154 nm, 1,907–1,927 nm, 2,227–2,254 nm, were found to be highly related to the classification of pine nuts. This study shows that machine learning is effective for the classification of pine nuts, providing solutions and scientific methods for rapid, non-destructive and accurate classification of different species of pine nuts.

Mountain pine beetle (MPB, Dendroctonus ponderosae) is a significant mortality agent of Pinus, and climate-driven range expansion is occurring. Pinus defenses in recently invaded areas, including high elevations, are predicted to be lower than in areas with longer term MPB presence. MPB was recently observed in high-elevation forests of the Great Basin (GB) region, North America. Defense and susceptibility in two long-lived species, GB bristlecone pine (Pinus longaeva) and foxtail pine (P. balfouriana), are unclear, although they are sympatric with a common MPB host, limber pine (P. flexilis). We surveyed stands with sympatric GB bristlecone–limber pine and foxtail–limber pine to determine relative MPB attack susceptibility and constitutive defenses. MPB-caused mortality was extensive in limber, low in foxtail and absent in GB bristlecone pine. Defense traits, including constitutive monoterpenes, resin ducts and wood density, were higher in GB bristlecone and foxtail than in limber pine. GB bristlecone and foxtail pines have relatively high levels of constitutive defenses which make them less vulnerable to climate-driven MPB range expansion relative to other highelevation pines. Long-term selective herbivore pressure and exaptation of traits for tree longevity are potential explanations, highlighting the complexity of predicting plant–insect interactions under climate change.

As climates change, thermal limits may no longer constrain some native herbivores within their historical ranges. The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a tree-killing bark beetle native to western North America that is currently expanding its range. Continued eastward expansion through the newly invaded and novel jack pine (Pinus banksiana Lamb.) trees of the Canadian boreal forest could result in exposure of several species of novel potential host pines common in northeastern North America to this oligophagous herbivore. Due to the tightly co-evolved relationship between mountain pine beetle and western pine hosts, in which the insect utilizes the defensive chemistry of the host to stimulate mass attacks, we hypothesized that lack of co-evolutionary association would affect the host attraction and acceptance behaviors of this insect among novel hosts, particularly those with little known historical association with an aggressive stem-infesting insect. We studied how beetle behavior differed among the various stages of colonization on newly cut logs of four novel potential pine host species; jack, red (P. resinosa Ait.), eastern white (P. strobus L.) and Scots (P. sylvestris L.) pines, as well as two historical hosts, ponderosa (P. ponderosa Dougl. ex. Laws. var. scopulorum Engelm.) and lodgepole (P. contorta Dougl. var. latifolia Engelm.) pines. Overall, we found that beetle colonization behaviors at each stage in the colonization process differ between pine hosts, likely due to differing chemical and physical bark traits. Pines without co-evolved constitutive defenses against mountain pine beetle exhibited reduced amounts of defensive monoterpenoid chemicals; however, such patterns also reduced beetle attraction and colonization. Neither chemical nor physical defenses fully defended trees against the various stages of host procurement that can result in tree colonization and death.

Until very recently, complete characterization of the megagenomes of conifers has remained elusive. The diploid genome of sugar pine (Pinus lambertiana Dougl.) has a highly repetitive, 31 billion bp genome. It is the largest genome sequenced and assembled to date, and the first from the subgenus Strobus, or white pines, a group that is notable for having the largest genomes among the pines. The genome represents a unique opportunity to investigate genome “obesity” in conifers and white pines. Comparative analysis of P. lambertiana and P. taeda L. reveals new insights on the conservation, age, and diversity of the highly abundant transposable elements, the primary factor determining genome size. Like most North American white pines, the principal pathogen of P. lambertiana is white pine blister rust (Cronartium ribicola J.C. Fischer ex Raben.). Identification of candidate genes for resistance to this pathogen is of great ecological importance. The genome sequence afforded us the opportunity to make substantial progress on locating the major dominant gene for simple resistance hypersensitive response, Cr1. We describe new markers and gene annotation that are both tightly linked to Cr1 in a mapping population, and associated with Cr1 in unrelated sugar pine individuals sampled throughout the species’ range, creating a solid foundation for future mapping. This genomic variation and annotated candidate genes characterized in our study of the Cr1 region are resources for future marker-assisted breeding efforts as well as for investigations of fundamental mechanisms of invasive disease and evolutionary response.

Key message Understanding bark allocation in juvenile stages of commercially viable Pinus trees can be useful in dating wood formation, thus improving the accuracy of correlating wood quality to environmental factors. Bark is an important and multifunctional part of plant anatomy that has been researched mostly in the context of fire history, timber resource assessments and more recently as a bioresource. Few studies have comprehensively examined bark thickness in some commercially valuable Pinus species. More importantly, the role of bark in accurately dating wood formation has seldom been researched. This study was conducted to model and compare bark thickness variation between different species of young South African-grown Pinus trees including Pinus radiata var. radiata D. Don., Pinus elliottii Engelm., Pinus elliottii  ×  Pinus caribaea var. hondurensis , Pinus patula  ×  Pinus tecunumanii (Low Elevation), and Pinus patula  ×  Pinus tecunumanii (High Elevation). Measurements were taken at 1.6 and 2.3 years including absolute and relative bark thickness and distribution along the stem. Results showed species-specific variation in absolute and relative bark thickness with the highest means recorded in Pinus elliottii  ×  Pinus caribaea and lowest in Pinus radiata . A positive linear relationship was observed between bark thickness and diameter, consistent with all species and ages. Absolute bark thickness decreased along the stem from bottom to top while more nuanced patterns of variation were observed for relative bark thickness. These findings underscore the importance of understanding bark thickness in young trees for various applications, including dating wood formation, anticipatory breeding strategies for quality wood and predicting stand quality among others.

Background Studying the physiological growth status of Pinus yunnanensis Franch and Pinus elliottii Engelm. seedlings under different karst fissure thicknesses and rainfall distributions is of great significance for the management, vegetation restoration, and tree species selection in karst rocky desertification areas. In this study, we used a two-factor block experiment and set different rainfall durations, namely reduced rainfall duration (I 3d ), natural rainfall duration (I 6d ), and extended rainfall duration (I 9d ); Different karst small habitats, i.e., stone-free soil (S 0 ), less stone and more soil (S 1/4 ), and half stone and half soil (S 1/2 ), are simulated at these three levels. Analyze the changes in physiological growth and photosynthetic characteristics in two coniferous seedlings under different treatments with different karst thicknesses. Results The results showed that with the increase of karst thickness, the growth volumes of height and diameter of P. yunnanensis seedlings, the biomass of various organs, and the accumulation of K + , Ca 2+ , Na + , and Mg 2+ showed a significant change pattern of first increasing and then decreasing ( P  < 0.05); P. elliottii seedlings show a gradually decreasing trend (except for Ca 2+ ). The biomass accumulation of each organ in two coniferous seedlings showed that leaves > stems > roots. The K + , Ca 2+ , and Mg 2+ content in various organs of P. yunnanensis seedlings showed that leaves > roots > stems, while Na + shows the order of roots > leaves > stems. The accumulation of mineral elements in various organs of P. elliottii seedlings is manifested as roots > stems > leaves and the accumulation of mineral elements in both coniferous seedlings is manifested as Ca 2+ > Mg 2+ > K + > Na + . Root length, root volume, root surface area, root diameter, SOD, POD, SP, photosynthetic pigment content, fluorescence parameters, and gas exchange parameters of P. yunnanensis seedlings gradually increase with the increase of karst thickness (except for the 9-day rainfall duration), while those of P. elliottii seedlings gradually decrease. The light saturation point of P. yunnanensis seedlings is highest under the I 6d S 1/2 treatment, while that of P. elliottii is highest under the I 3d S 0 treatment. Conclusions In summary, prolonging rainfall duration has an inhibitory effect on the growth of two types of coniferous seedlings. Increasing karst thickness inhibits the growth of P. elliottii seedlings, and to some extent, promotes the growth and development of P. yunnanensis seedlings. I 6d S 1/4 and I 3d S 0 treatments have the best growth effects on P. yunnanensis and P. elliottii seedlings. Therefore, we give priority to P. yunnanensis as the tree species for vegetation restoration or rocky desertification management in karst areas. Our study reveals the role of limestone-filled different karst fissures in mitigating the effects of drought as “containers” for plant growth. These findings help us understand the response of plants to drought stress and provide valuable insights for vegetation restoration in karst environments affected by global climate change. Therefore, further experiments with various karst fissure sizes are necessary to test the universality of the reactions of various plants under different karst fissures.

Scots pine (Pinus sylvestris) is one of the main sources of timber in the boreal zone of Eurasia. Commercial pine plantations are vulnerable to root and butt rot disease caused by the fungus Heterobasidion annosum. The pathogen affects host growth rate, causes higher mortality and decreases in timber quality, resulting in considerable economic losses to forest owners. Genetic and biochemical factors contributing to Scots pine tolerance against H. annosum infection are not well understood. We assessed the predictive values of a set of potential genetic and chemical markers in a field experiment. We determined the expression levels of 25 genes and the concentrations of 36 terpenoid compounds in needles of 16 Scots pine trees randomly selected from a natural population prior to artificial infection. Stems of the same trees were artificially inoculated with H. annosum, and the length of necrotic lesions was documented 5 months post inoculation. Higher expression level of four genes included in our analysis and encoding predicted a-pinene synthase (two genes), geranyl diphosphate synthase (GPPS), and metacaspase 5 (MC5), could be associated with trees exhibiting increased levels of necrotic lesion formation in response to fungal inoculation. In contrast, concentrations of two terpenoid compounds, β-caryophyllene and α-humulene, showed significant negative correlations with the lesion size. Further studies with larger sample size will help to elucidate new biomarkers or clarify the potential of the evaluated markers for use in Scots pine disease resistance breeding programs.

Natural hybridization can manifest different evolutionary results, such as accelerating differentiation and facilitating speciation through the rapid origin of new biochemical compounds, physiological or morphological phenotypes that allow hybrid species to occupy new habitats, which for parental species would be inaccessible. However, these expectations are not always fulfilled, because natural hybridization between divergent populations can lead to inadequate or unviable hybrids and, therefore, lower forest stability and productivity. Using pure species Pinus arizonica, P. cembroides, P. durangensis, P. engelmannii, P. leiophylla, P. lumholtzii and P. teocote trees and their natural hybrids, this study aims to determine for the first time: (i) morphological differences between pure pine trees and their hybrids molecularly detected, (ii) differences in vigor between 1970 seeds from trees of pure pine species and their hybrid trees (hereinafter called pure and hybrid parents), (iii) differences in vigor between 3465 seedlings from 1421 pure and hybrid parents, and (iv) whether growth of seedlings of hybrid parents is differently associated to parent tree’s environmental conditions, than growth of seedlings of pure parents. The seedlings grew under equal nursery conditions. Our results show some significant differences in morphological traits between the seed trees of pure species and their respective putative hybrid seed trees, and in seed and seedling fitness indices. In contrast to the mean growth of seedlings of hybrid parents, the mean growth of seedlings from pure parents was significantly associated with the parent tree’s bioclimatic conditions studied (R2 = 0.70 vs 0.83). There were only some individuals that presented hybrid superiority.

AIM: Large‐scale patterns of limitations in tree recruitment remain poorly described in the Mediterranean Basin, and this information is required to assess the impacts of global warming on forests. Here, we unveil the existence of opposite trends of recruitment limitation between the dominant genera Quercus and Pinus on a large scale and identify the key ecological drivers of these diverging trends. LOCATION: Spain METHODS: We gathered data from the Spanish National Forest inventory to assess recruitment trends for the dominant species (Pinus halepensis, Pinus pinea, Pinus pinaster, Pinus nigra, Pinus sylvestris, Pinus uncinata, Quercus suber, Quercus ilex, Quercus petraea, Quercus robur, Quercus faginea and Quercus pyrenaica). We assessed the direct and indirect drivers of recruitment by applying Bayesian structural equation modelling techniques. RESULTS: Severe limitations in recruitment were observed across extensive areas for all Pinus species studied, with recruitment failure affecting 54–71% of the surveyed plots. In striking contrast, Quercus species expanded into 41% of the plots surveyed compared to only 10% for Pinus and had a lower local recruitment failure (29% of Quercus localities compared to 63% for Pinus species). Bayesian structural equation models highlighted the key role of the presence of Q. ilex saplings and the increase in the basal area of Q. ilex in limiting recruitment in five Pinus species. The recruitment of P. sylvestris and P. nigra showed the most negative trends and was negatively associated with the impacts of fire. MAIN CONCLUSIONS: This study identified Q. ilex, the most widespread species in this area, as a key driver of recruitment shifts on a large scale, negatively affecting most pine species with the advance of forest succession. These results highlight that the future expansion/contraction of Q. ilex stands with ongoing climate change will be a key process indirectly controlling the demographic responses of Pinus species in the Mediterranean Basin.