Journal of Applied Bacteriology

Abstract Key message Seed germination responses to variation in temperature and light differed among six dry forest species, results that will inform ecological restoration and climate change adaptation projects. Abstract In dry forests, where opportunities for plant establishment occur in a narrow window of opportunity, seeds must respond to cues to germinate when conditions for growth are suitable. Knowledge of the strategies and adaptations of seeds to the seasonal dry-forest ecosystems, being under constant threat, is needed to guide restoration and management actions in the face of climate change. We investigated the effects of scarification, temperature and light in germination percentage, germination time and synchrony of six woody Fabaceae species. The species have ecological potential for restoration and are of cultural or economic importance for the local people in the Tehuacán-Cuicatlán Valley, Mexico. We carried out a multifactorial germination experiment with five temperatures, two light regimes and two scarification conditions for Mimosa luisana, M. polyantha, M. adenantheroides, M. lactiflua, Acaciella angustissima and Vachellia constricta. All germinated in a wide range of temperatures (10–40 °C), and mechanical scarification highly increased the germination percentage. Higher temperature increased and speeded up germination in dark conditions for most of the species, but they exist heterogeneous responses in their germination synchrony. Studied species had high germination percentages in warm temperatures, but their recruitment in nature might be negatively affected by warmer and drier conditions, and by the loss of shade and seed dispersers due to deforestation and changes in land use. It is crucial to study not just germination percentage and time but also other aspects of the germination process such as the germination synchrony, since it might reveal useful information for management actions.

Abstract Key message Distance from the tree tip strongly influences axial variations in the elasticity (MOE) and strength (MOR) of fresh Scots pine wood, with both properties increasing towards the base of the stem. Abstract Scots pine (Pinus sylvestris L.), one of Europe's most used timber species, is valued in the construction, furniture, and paper industries. The anatomical structure of Scots pine wood follows the universal conduit widening model, where tracheid lumen size increases in each tree ring from the tip to the base of the stem, enhancing hydraulic efficiency. However, whether the physical and mechanical properties of the wood mirror its axial anatomical pattern remains unclear. For this study, we sampled an 8.6 m tall Scots pine and analysed its fresh wood mechanical, physical and anatomical properties of the outermost growth ring along the stem. In addition to the expected axial increase in tracheid size towards the base, we observed axial variations in latewood percentage and the density of rays and resin ducts. These anatomical differences correspond to axial trends in physical and mechanical properties, which show predictable patterns described by power law scaling. All three measured physical and mechanical traits, namely basic wood density, modulus of elasticity (MOE), and modulus of rupture (MOR), decrease from the stem base towards the tip. Mechanical properties correlate more strongly with distance from the tree tip than basic density or latewood proportion. These findings have practical implications for optimising timber selection in load-bearing applications and inspire new avenues for research and innovation in wood material science.

Seed morphological traits and antioxidant defense mechanisms determine desiccation sensitivity differences between Quercus species, enabling development of species-specific seed storage protocols. Despite extensive research on the desiccation sensitivity of Quercus seeds, the factors and physiological mechanisms driving interspecific variations remain poorly understood. This study investigated the differences in desiccation sensitivity between Q. chenii and Q. acutissima seeds by examining the effects of desiccation on seed moisture content, detecting reactive oxygen species production, antioxidant enzyme activities, soluble sugars and proteins, and exploring the relationships among initial seed traits, water loss rates, and seed viability. Results showed that despite similar initial moisture content (41.9% for Q. chenii and 42.9% for Q. acutissima), Q. acutissima seeds exhibited more rapid water loss under identical desiccation conditions (same seed: silica gel ratio and temperature), primarily due to their larger scar area and seed mass, leading to a decline in germination percentage below 80% within just 7 days, while Q. chenii seeds maintained high germination percentage for up to 27 days. Regarding physiological mechanisms, Q. chenii seeds demonstrated a more efficient antioxidant defense system, characterized by higher superoxide dismutase activity and early increased catalase activity, which effectively reduced hydrogen peroxide accumulation and membrane lipid peroxidation. Additionally, Q. chenii showed significantly increased soluble protein content during early desiccation stages. These findings contribute to a deeper understanding of desiccation sensitivity mechanisms and their interspecific variations in recalcitrant seeds, providing physiological bases for optimizing recalcitrant seed conservation strategies.

Clones originating from the young seed progeny of mutational witches’ broom have a compact crown and no flowering phenotype caused by the combined effect of the mutation and biological age of the source plant material. Mutational witches’ broom (WB), which is formed on trees, is a bud sport that has a modified crown structure. Phenotypically, it differs from the normal crown part in its high density, abundant branching and usually shorter needles. Grafted WBs have a high ornamental value and are propagated for landscaping purposes. WB seed progeny and their clones have also been successfully used in breeding for a long time. However, it is still unknown how the two types of clones differ from each other. To reveal the differences, a comparative analysis of clones from the original mature 170–200-year-old trees of Pinus sibirica with cone-bearing WBs and clones from the 9-year-old mutant seed progeny was carried out in the uniform environment of a common garden. Unlike the initial WB clones, the derivative clones did not flower, which was the most pronounced influence of the age of the source plant material. The growth of derivative WB clones was also affected by the age of the source plant material, which reduced linear growth in addition to the mutation. They were 1.5 times less than in the initial clones, and their crowns were even more compact due to the decreased branching threshold and apical dominance. Significant variation was observed amongst groups of derivative clones derived from different saplings in the progeny of an original WB. The obvious source of the variation was the effect of recombination in the WB seed progeny, which gave rise to the clones. Thus, the influence of the age of the source plant material is fully manifested in the WB of Pinus sibirica, just as it occurs in normal trees. Together with great variation in morphological traits, this made the WB seed progeny an almost inexhaustible source of material for ornamental breeding.

Abstract Key message Urban trees can acclimate to their growth environment through changes in vessel anatomy. Vessel lumen area and vessel frequency following a gradient from park trees to inner-city street trees. Abstract Urban trees stand in potentially stressful growth environments occurring along gradients of urban heat and impermeable surface cover and, to survive, can adjust their function and structure. The consequent tree-to-tree variations in hydraulic xylem traits can shed light on tree hydraulics and capacity to acclimate to diverse conditions, as well as identify limitations to tree growth and survival. Using microscopic analysis of increment cores, we compared early wood vessel traits of the ring-porous angiosperm Celtis occidentalis in three urban site types: central streets, residential streets and parks, within the city of Montreal. We explored differences in vessel traits (mean vessel lumen area, vessel frequency, vessel grouping index and derived variables) between site types, vessel trait intercorrelations and correlations with monthly temperature, precipitation and heat-moisture index over 10 years. The vessel traits significantly differed between site types. Park trees had the largest and central street trees had the smallest vessel lumen area and theoretical hydraulic conductivity; traits supporting efficient water transport. Central street trees had the largest vessel frequency and smallest theoretical vulnerability to cavitation; traits connected to hydraulic safety. Residential street tree traits were in between. Among central and residential street trees, water transport efficiency traits correlated positively with cool springs or arid summers, whereas among park trees, mainly vessel frequency and grouping index responded to climate variations. These results highlight the capacity of C. occidentalis to acclimate to urban environments and the potential of anatomical traits for quantifying the effects of urban environments on tree functioning. Graphical Abstract

Abstract Key message Austropuccinia psidii infection and increase in diseased leaf area resulted in a reduction of photosynthesis, an upregulation of stomatal conductance, and an increase in leaf starch and sucrose content. Abstract Austropuccinia psidii is a biotrophic rust pathogen that causes myrtle rust, affecting over 480 species in the Myrtaceae family. The development of chlorotic and necrotic leaf areas following A. psidii infection has been shown to affect leaf gas exchange. In this study, we quantified photosynthesis, stomatal conductance, and non-structural carbohydrates in seedlings of a long-lived tree, Metrosideros excelsa (pōhutukawa), following A. psidii infection in a glasshouse experiment (infected and control seedlings) conducted over 20 weeks. The diseased leaf area rose from 8% in week 2 to 95% in week 20 after A. psidii inoculation. The photosynthetic rate declined by over 90% within 6 weeks after inoculation and was associated with biochemical damage in CO2 fixation. Stomatal conductance decreased over the first 4 weeks after inoculation and then increased. An increase in lesions and necrotic cells may inhibit stomatal regulation. Starch content was threefold higher in infected than control leaves 20 weeks after inoculation. Increased starch accumulation in the infected leaf area could be due to reduced export of newly fixed carbon from the infected leaves. Meanwhile, glucose + fructose content was 31% lower in infected leaves at the experiment’s end, likely because of leaf necrosis. If the pathogen-induced damage and loss of leaves, reduction in photosynthesis and changes in non-structural carbohydrates shown in this study also occur in wild M. excelsa seedlings and reduces their biomass, this may in turn reduce their competitive ability in the primary successions that they currently often dominate.

Abstract 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. Abstract 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.

Abstract Key message Terrestrial laser scanning data of trees combined with models of heartwood content proportion of woody disks can provide precise characterization of total aboveground tree sapwood and heartwood volume. Abstract Quantifying sapwood and heartwood content of trees is challenging. Previous studies have primarily characterized main stem wood composition, while branches have rarely been studied. Terrestrial Laser Scanning (TLS) can provide precise representations of the entire above-ground tree structure, non-destructively, to help estimate total tree sapwood and heartwood volume. In this study, we used TLS to scan above-ground portions of twenty-four open-grown, urban Gleditsia triacanthos trees on Michigan State University campus. TLS data were used to generate quantitative structure models that provided comprehensive characterizations of the total tree woody surface area (WSA) and volume. A subsample of trees was harvested (after scanning) and main stem and branch woody disks were collected to build models of heartwood content proportion. Models were applied to measurements from TLS to quantify complete heartwood and sapwood volume of each tree, including main stem and branches. From the base to the top of the trees, the largest portion of stem vertical cumulative volume was heartwood, whereas vertical cumulative volume of branches showed the opposite pattern. Absolute heartwood volume declined monotonically toward zero from stem base to stem top, while absolute sapwood volume declined sharply from stem base up to near the crown base and then remained relatively constant within crown. We also found that tree WSA increased with sapwood volume for both branches and main stem. This study developed a novel, general method for quantifying total aboveground sapwood and heartwood volume of trees and provided new insights into urban tree growth and structure.

Abstract Key message The temperature sensitivity of maximum latewood density measurements in pine trees from a high-elevation site in the Spanish Pyrenees increases with tree age. Detrending modulates the intensity of the effect. Abstract Tree-rings are the prime archive for high-resolution climate information over the past two millennia. However, the accuracy of annually resolved reconstructions from tree-rings can be constrained by what is known as climate signal age effects (CSAE), encompassing changes in the sensitivity of tree growth to climate over their lifespans. Here, we evaluate CSAE in Pinus uncinata from an upper tree line site in the Spanish central Pyrenees, Lake Gerber, which became a key location for reconstructing western Mediterranean summer temperatures at annual resolution. We use tree-ring width (TRW) and maximum latewood density (MXD) measurements from 50 pine trees with individual ages ranging from 7 to 406 years. For MXD, temperature sensitivity increases significantly (p < 0.01) with tree age from r = 0.31 in juvenile rings with a cambial age < 100 years to r = 0.49 in adult rings > 100 years. Similar CSAE are not detected in TRW, likely affected by the overall lower temperature signal (r TRW = 0.45 vs. r MXD = 0.81 from 1951 to 2020). The severity of CSAE is influenced by the approach used to remove ontogenetic trends, highlighting the need to assess and consider potential biases during tree-ring standardization. Our findings reveal CSAE to add uncertainty in MXD-based climate reconstructions in the Mediterranean. We recommend studying CSAE by sampling diverse age classes in dendroclimatic field campaigns.

Abstract Key message The effects of MJ on pine trees are species-specific and trigger a resistant phenotype to the PWN. A more dynamic response of hormones and gene expression in Pinus pinea explains the high resistance to Bursaphelenchus xylophilus of this species. Abstract Knowledge on hormonal and genetic mechanisms of pine trees in response to the pinewood nematode (PWN; Bursaphelenchus xylophilus) is limited. To describe tree defence strategies against B. xylophilus, this study used the plant stress hormone methyl jasmonate (MJ) on four pine species with different susceptibility (Pinus pinaster < P. radiata ≈ P. sylvestris < P. pinea). Three-year-old trees were sprayed with MJ at 0, 25, and 50 mM, and 2 months later challenged with the PWN. Multiple samples were taken to assess nematode content, oxidative stress, secondary metabolites, phytohormone levels, and stress-related gene expression. Nematode infestation in trees correlated negatively with the water content of needles and phenolics of stems, and positively with the concentration of indole-3-carboxylic acid in stems. MJ spray reduced in a dose-dependent manner the nematode content in P. pinaster and P. sylvestris. The effects of MJ were species-specific, although a more pronounced impact was observed in the susceptible P. pinaster species, leading to a decrease of chlorophyll and water loss and to the upregulation of the gene involved in the biosynthesis of terpenoids (AFS). After MJ spray, increased levels of JA-Ile were observed in P. pinea only. Hormone profiling, predisposition to activate antioxidant response, and gene expression in P. pinea trees provide evidence of why this species is highly resistant to B. xylophilus. On the contrary, the lack of effective hormonal changes in P. pinaster explained the lack of defence responses to B. xylophilus of this susceptible species. This study is a first approach to explore biochemical, molecular, and hormonal interactions between Pinus species and the PWN, and presents unprecedented insights into alterations induced by exogenous MJ in regulating defence mechanisms in pine trees.

Resin production and growth in Pinus pinaster and Pinus pinea show a trade-off under varying environmental conditions, impacting future resin yields under climate change. Resin production in pines constitutes an important defense mechanism against biotic and abiotic factors, and it is also an important forestry product. In Portugal, resin is mainly extracted from Pinus pinaster and to a lesser extent from Pinus pinea, the two most widespread pine species in the country. The resin tapping season coincides with the growing season, from spring to autumn. Thus, growth and resin production may compete for carbon, although their response to environmental conditions can differ. This study investigates how the daily growth and biweekly resin production of P. pinaster and P. pinea in a mixed stand respond to environment over the 2021 growing season. During the resin tapping period, growth of both species showed a positive correlation with temperature, soil moisture, air relative humidity and radiation. Resin yield of both species showed a positive relation with soil temperature, and a negative relation with growth, suggesting a trade-off between growth and resin yield. Our results indicate that both growth and resin yield increase with temperature, with growth being more sensitive to soil moisture and relative humidity. Under a scenario of rising temperatures and precipitation reduction, both functions (growth and resin yield) are expected to be affected positively. However, resin production depends on carbon assimilation and allocation, both of which are reduced or altered during periods of extreme drought. This can lead to increasing competition for carbon allocation between growth, storage and resin yield, making resin yield responses to climate change scenarios uncertain.