Needle Age Research Articles

Coniferous Tree Species Identity and Leaf Aging Alter the Composition of Phyllosphere Communities Through Changes in Leaf Traits

Phyllosphere microorganisms are essential for plant growth and health. Although there are an increasing number of studies showing that the composition of phyllosphere communities varies among different plant species, it remains unclear whether and how their bacterial and fungal community composition predictably varies with plant traits and leaf age. In this study, we used high-throughput sequencing to explore the diversity and composition of phyllosphere communities in needles of different ages (originating from different cohorts) for three evergreen coniferous species (Pinus koraiensis, Picea koraiensis, and Abies nephrolepis). Our results indicated that Gammaproteobacteria (bacteria) and Dothideomycetes (fungi) were dominant in newly formed needles, whereas Actinobacteria (bacteria) and Eurotiomycetes (fungi) were dominant in perennial needles. Tree species identity and needle age were the main factors explaining the variations of the α diversity (species richness of phyllosphere communities) and β diversity (dissimilarity among phyllosphere communities). In particular, we found that leaf dry matter content, leaf mass per area, and total phosphorus content emerged as key predictors of composition and diversity of phyllosphere microbial communities, underscoring the major influence of tree species identity and needle age on phyllosphere communities through changes in plant functional traits. Finally, we found that the interaction between tree species identity and needle age also contributed significantly to explaining the diversity and composition of phyllosphere communities, probably because differences in plant functional traits or environmental conditions between new and perennial needles depend on tree growth rates and resource acquisition strategies. These findings provide new insights into the mechanisms of community assembly among different evergreen tree species and offer a better understanding of the interactions between plant traits and phyllosphere microorganisms during needle aging.

Effect of Needle Age and Location on the Volatile Composition of Essential Oils from Juniperus communis L.: A Chemometric Study

AbstractProfiles of the volatile organic compound (VOC) content of essential oils (EOs) extracted from young and old Juniperus communis L. needles were generated via gas chromatography combined with mass spectrometry (GC‐MS) and flame ionization detection (GC‐FID) and subsequently processed using multivariate statistical methods. These were then used to differentiate the EOs according to needle age and geographical origin. From a total 49 of VOCs identified, statistically significant differences (p<0.05) between young‐ and old‐needle EOs were found for 21 VOCs. Most of the EOs from the young needles showed higher (p<0.05) contents of α‐ and β‐pinene and sesquiterpenes (β‐ and γ‐elemene, germacrene D and B, α‐muurolene, and δ‐cadinene) and their oxygenated derivatives (α‐ and τ‐cadinol), while most of the monoterpenes (α‐thujene, sabinene, terpinolene, β‐myrcene, β‐phellandrene, and p‐cymene) were present in higher quantities (p<0.05) in the EOs from the old needles. The volatiles germacrene D, α‐ and β‐pinene, α‐cadinol, and sabinene were identified via stepwise and canonical discriminant analysis as the most valuable for EO discrimination according to needle age and geographical origin. Recognition and prediction ability tests of the EOs achieved 100 % accuracy in EO classification according to the above mentioned criterion.

Effects of legacy mining on mercury concentrations in conifer needles and mushrooms in northern Palatinate, Germany

Due to integrated pollution prevention and control measures and the reduced burning of coal, air concentrations of mercury (Hg0) are currently levelling off. In the future, however, evasion from land surfaces will probably reverse this trend. Reasons are the rising temperatures and the loss of forest cover caused by calamities, droughts, storms and wildfires. Plant leaves constitute an important matrix for the accumulation of gaseous mercury and uptake and re-volatilisation by plants depends on the species, the vitality and the age and morphology of leaf organs. It has been shown that older conifer needles show higher concentrations than young needles and Hg accumulation is increasing throughout the season.In present study, we collected branches from Norway Spruce (Picea abies) in a former cinnabar mining region in Northern Palatinate, where artisanal and small-scale mining left innumerable waste dumps. While mining, smelting and processing of the ores were terminated during WWII, high total mercury concentrations remained in the top soils locally, with presumably only small fractions being plant available. In the lab, up to seven needle age classes were analysed. 1000 needle weights increased with age and as expected, also the Hg concentrations were elevated in the older needles. Needle concentrations were higher than those reported from other national biomonitoring programs confirming the regional imprint from legacy mercury. To complement our biomonitoring study, we collected edible mushrooms in former mining areas. Hg concentrations in most samples exceeded the EU maximum residue levels (MRL), while only a few broke the existing cadmium and lead limits. Tolerable weekly intake (TWI) for inorganic mercury would be surpassed with the consumption of a small portion of mushrooms. Further studies should be performed on the outgassing of Hg from mine wastes and the incorporation of Hg in the local food web, including its methylation and biomagnification.

Gas-chromatographic analyses of volatile organic compounds in essential oils extracted from Slovak juniper berries and needles (Juniperus communis L.)

Juniper essential oils (EOs) are mainly extracted from berries; however, nowadays studies point to needles as a viable source of EOs. Total qualitative-quantitative profiles of individual volatile organic compounds (VOCs) of EOs extracted from berries, old and young needles, gathered from the same locality, were obtained by GC–MS and GC–FID analyses. Moreover, qualitative-quantitative differences were determined among particular EOs within two subsequent years. Generally, VOC profiles of EOs were mainly represented by monoterpenes, sesquiterpenes and their oxygenated derivatives. Depending on the harvest year, α-pinene (27.70–35.42 %) was the most abundant VOC in juniper berry EOs, followed by germacrene D, sabinene, myrcene, germacrene B and β-pinene. Overall, needle EOs were primarily characterised by sabinene, α-pinene, γ-terpinene and terpinen-4-ol, but with an intense dependence on the needle age and harvest year. β-Ylangene and α-cubebene were specific to berry EOs, whereas trans-2-hexenal was specific to needle EOs. Discriminant analysis achieved 100 % accuracy of correctly classified EOs according to the raw material and harvest year. α-Cubebene, germacrene B, γ-muurolene, one unknown compound and trans-2-hexenal were identified as the most significant for discrimination according to the source, while juniper camphort, cis-2-p-menthen-1-ol, terpinen-4-ol and β-elemene played dominant roles in discrimination according to the harvest year.

Histologic, metabolomic, and transcriptomic differences in fir trees from a peri-urban forest under chronic ozone exposure.

Urbanization modifies ecosystem conditions and evolutionary processes. This includes air pollution, mostly as tropospheric ozone (O3), which contributes to the decline of urban and peri-urban forests. A notable case are fir (Abies religiosa) forests in the peripheral mountains southwest of Mexico City, which have been severely affected by O3 pollution since the 1970s. Interestingly, some young individuals exhibiting minimal O3-related damage have been observed within a zone of significant O3 exposure. Using this setting as a natural experiment, we compared asymptomatic and symptomatic individuals of similar age (≤15 years old; n = 10) using histologic, metabolomic, and transcriptomic approaches. Plants were sampled during days of high (170 ppb) and moderate (87 ppb) O3 concentration. Given that there have been reforestation efforts in the region, with plants from different source populations, we first confirmed that all analyzed individuals clustered within the local genetic group when compared to a species-wide panel (Admixture analysis with ~1.5K SNPs). We observed thicker epidermis and more collapsed cells in the palisade parenchyma of needles from symptomatic individuals than from their asymptomatic counterparts, with differences increasing with needle age. Furthermore, symptomatic individuals exhibited lower concentrations of various terpenes (ß-pinene, ß-caryophylene oxide, α-caryophylene, and ß-α-cubebene) than asymptomatic trees, as evidenced through GC-MS. Finally, transcriptomic analyses revealed differential expression for 13 genes related to carbohydrate metabolism, plant defense, and gene regulation. Our results indicate a rapid and contrasting phenotypic response among trees, likely influenced by standing genetic variation and/or plastic mechanisms. They open the door to future evolutionary studies for understanding how O3 tolerance develops in urban environments, and how this knowledge could contribute to forest restoration.

Effects of nitrogen addition and leaf age on needle traits and the relationships among traits in Pinus koraiensis

Leaf functional traits are essential for the growth and adaptation of trees to environmental changes. However, how needle traits and trait–trait relationships respond to different nitrogen (N) addition rates and leaf ages remain unclear for evergreen coniferous species. Our study aimed to investigate the effects of N addition and leaf age on needle traits and their bivariate correlations. Understanding resource utilization and distribution strategies during tree growth under the background of increased N deposition is important. We conducted a six-year manipulative field experiment in a Pinus koraiensis plantation in northeastern China with variable N addition levels: control (no N addition, CK); 20 kg N ha−1yr−1 (low-N, LN); 40 kg N ha−1yr−1 (medium-N, MN); and 80 kg N ha−1yr−1 (high-N, HN). The needle trait data were collected in September. The morphological traits, i.e., specific leaf area (SLA) and leaf dry matter content (LDMC); and chemical traits, i.e., leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC), and leaf nonstructural carbohydrates (NSC) concentrations, were measured to investigate the changes in needle traits and their bivariate correlations. We found that N addition and needle age significantly affected needle traits, and the effect of needle age was much stronger than that of N addition. N addition and needle age had no significant interaction effects on any of the traits except for the LNC. Due to the dispersal trait values of current-year needles, there were almost no significant bivariate correlations between traits under different N addition rates. The SLA–LDMC and LDMC–LNC relationships were found to differ among the various N addition rates, and other traittrait relationships may be relatively stable because of the weak plasticity of older needles. Additionally, needle age significantly affected the slope of the SLA–LDMC relationship and the elevation of the LDMC–LPC and NSC–LNC relationships, indicating differences in the ecological strategies of needles at different ages. In summary, our findings emphasize that trait–trait relationships in current-year and older needles were inconsistent in response to N addition and that the optimal allocation of resources in needles was based on their functional needs during leaf aging.

Transcriptome Analysis of Picea crassifolia in Response to Rust Infestation.

This study examines the relationship between needle age and rust resistance in Picea crassifolia, focusing on the needle morphology, including size, shape, and physiological traits. One-year-old spruce needles are more susceptible to rust, while two-year-old needles show effective resistance. Using RNA-seq on the Illumina HiSeq500 platform, we analyzed both healthy and diseased one-year-old needles (N and B), as well as healthy one-year-old and two-year-old needles (N and L). We applied a fold change (FC) threshold of ≥2 and a false discovery rate (FDR) of <0.01, alongside GO annotation and KEGG pathway enrichment, to identify differentially expressed genes (DEGs). In N vs. B, DEGs were significantly enriched in processes such as metabolism, cellular function, catalysis, binding, ribosomal function, plant-pathogen interactions, endoplasmic reticulum protein processing, and signal transduction, revealing a polygenic network regulating the rust response. Similarly, in N vs. L, electron microscopy highlighted morphological differences in the wax layers of needles, with subsequent transcriptome sequencing uncovering genes involved in the development of one-year-old and two-year-old needles. DEGs were primarily found in pathways related to cutin, suberin, wax biosynthesis, fatty acid metabolism, photosynthesis, and phenylalanine synthesis. Two-year-old needles displayed reduced stomatal density, higher lignin content, and a thicker wax layer compared to one-year-old needles. Validation of the RNA-seq data through RT-qPCR on 10 DEGs confirmed the consistency of gene expression trends, enhancing our understanding of Picea crassifolia's genetic response to rust and supporting future research into its disease resistance.

Needle bacterial community structure across the species range of limber pine.

Bacteria on and inside leaves can influence forest tree health and resilience. The distribution and limits of a tree species' range can be influenced by various factors, with biological interactions among the most significant. We investigated the processes shaping the bacterial needle community across the species distribution of limber pine, a widespread Western conifer inhabiting a range of extreme habitats. We tested four hypotheses: (i) Needle community structure varies across sites, with site-specific factors more important to microbial assembly than host species selection; (ii) dispersal limitation structures foliar communities across the range of limber pine; (iii) the relative significance of dispersal and selection differs across sites in the tree species range; and (iv) needle age structures bacterial communities. We characterized needle communities from the needle surface and tissue of limber pine and co-occurring conifers across 16 sites in the limber pine distribution. Our findings confirmed that site characteristics shape the assembly of bacterial communities across the host species range and showed that these patterns are not driven by dispersal limitation. Furthermore, the strength of selection by the host varied by site, possibly due to differences in available microbes. Our study, by focusing on trees in their natural setting, reveals real needle bacterial dynamics in forests, which is key to understanding the balance between stochastic and deterministic processes in shaping forest tree-microbe interactions. Such understanding will be necessary to predict or manipulate these interactions to support forest ecosystem productivity or assist plant migration and adaptation in the face of global change.

Nonlinear model prediction of needle chlorophyll content of Picea koraiensis Nakai at different needle ages based on hyperspectral features

Pigment content is a critical assessment indicator in the study of plant physiological metabolism, stress resistance, ornamental characteristics, and forest health. Spectral imaging technology is widely used for rapid and non-destructive determination of plant physicochemical parameters. To address the shortcomings of previous models of spectral reflectance prediction of chlorophyll content of needles only from the perspective of traditional algorithms and ignoring physical models, this research integrates variable complexity and refined classification of physical models to validate the increased accuracy of both the conventional partial least squares (PLS) method and the traditional neural network algorithm. The results of the conifer chlorophyll models of Picea koraiensis Nakai with different needle ages based on spectral reflectance and vegetation index parameters showed that the improved nonlinear state transition algorithm-backpropagation (STA-BP) neural network model approach (R2 of 0.73–0.89) and the nonlinear Stacking partial least squares (Stacking-PLS) model approach (R2 of 0. 67–0.85) is slightly more robust than the traditional algorithms nonlinear BP model (R2 of 0.63–0.82) and linear PLS model (R2 of 0.60–0.76). This finding suggests that the nonlinear fitting of chlorophyll content in needles of different needle ages in P. koraiensis Nakai surpasses the traditional linear model fitting methodology. Furthermore, the model fitting of chlorophyll content in conifers of different needle ages outperforms the mixed P. koraiensis Nakai model, suggesting that chlorophyll models using needle refinement classification help to improve model robustness. This study provides data and theoretical support for rapid and non-invasive characterization of physiological and biochemical properties of needles of different needle ages using spectral imaging techniques to predict growth and community structure productivity of forest trees in the coming years.

Seasonal changes in foliar calcium oxalate concentrations in conifer and hardwood trees: a potentially bioavailable source of cellular calcium and/or oxalate under stress

The present study compared seasonal changes in the concentrations of calcium oxalate (CaOx) crystals and total calcium (Ca) in the foliage of red spruce (Picea rubens Sarg.), white pine (Pinus strobus L.), black oak (Quercus velutina L.), and sugar maple (Acer saccharum Marshall) trees. Samples were collected from the same four replicate trees of each species starting in June 2014 through September 2015 for a total of six times for conifers and four times for hardwoods. Calcium oxalate was extracted from tissues using a method developed in our laboratory in 2015. The purity of the extracted CaOx was indicated by an r2 of 0.98 between Ca and oxalate (Ox) for the data pooled across all species and all sampling times. As expected, the concentrations of CaOx varied between species. We hypothesized that the only role of CaOx crystals is to bind excess Ca, so based on this hypothesis the concentrations of CaOx would increase over the growing season both in conifer and hardwood trees, and in conifers, its quantities would be higher in the older relative to the younger needles. However, we found, that for most species, CaOx concentrations were not significantly different from each other for all collection times. In addition, relative to total Ca, the percent of Ca that existed in the form of CaOx varied widely with species, time of collection within a species, and needle age. Thus, no specific trend was observed for CaOx accumulations with changes in seasons. Concentrations of CaOx were indeed higher in older spruce and pine needles. Based on the available literature on this topic and our data, this could mean that CaOx amounts are dynamic and are continuously being adjusted according to the metabolic needs of cells for either Ca or Ox while still performing the function of shedding off excess Ca.

What matters most? Assessment of within-canopy factors influencing the needle microbiome of the model conifer, Pinus radiata

The assembly and function of the phyllosphere microbiome is important to the overall fitness of plants and, thereby, the ecosystems they inhabit. Presently, model systems for tree phyllosphere microbiome studies are lacking, yet forests resilient to pests, diseases, and climate change are important to support a myriad of ecosystem services impacting from local to global levels. In this study, we extend the development of model microbiome systems for trees species, particularly coniferous gymnosperms, by undertaking a structured approach assessing the phyllosphere microbiome of Pinus radiata. Canopy sampling height was the single most important factor influencing both alpha- and beta-diversity of bacterial and fungal communities (p < 0.005). Bacterial and fungal phyllosphere microbiome richness was lowest in samples from the top of the canopy, subsequently increasing in the middle and then bottom canopy samples. These differences maybe driven by either by (1) exchange of microbiomes with the forest floor and soil with the lower foliage, (2) strong ecological filtering in the upper canopy via environmental exposure (e.g., UV), (3) canopy density, (4) or combinations of factors. Most taxa present in the top canopy were also present lower in tree; as such, sampling strategies focussing on lower canopy sampling should provide good overall phyllosphere microbiome coverage for the tree. The dominant phyllosphere bacteria were Alpha-proteobacteria (Rhizobiales and Sphingomonas) along with Acidobacteria Gp1. However, the P. radiata phyllosphere microbiome samples were fungal dominated. From the top canopy samples, Arthoniomycetes and Dothideomycetes were highly represented, with abundances of Arthoniomycetes then reducing in lower canopy samples whilst abundances of Ascomycota increased. The most abundant fungal taxa were Phaeococcomyces (14.4% of total reads) and Phaeotheca spp. (10.38%). A second-order effect of canopy sampling direction was evident in bacterial community composition (p = 0.01); these directional influences were not evident for fungal communities. However, sterilisation of needles did impact fungal community composition (p = 0.025), indicating potential for community differences in the endosphere versus leaf surface compartments. Needle age was only important in relation to bacterial communities, but was canopy height dependant (interaction p = 0.008). By building an understanding of the primary and secondary factors related to intra-canopy phyllosphere microbiome variation, we provide a sampling framework to either explicitly minimise or capture variation in needle collection to enable ongoing ecological studies targeted at inter-canopy or other experimental levels.

Foliar water uptake in Pinus species depends on needle age and stomatal wax structures.

Foliar water uptake (FWU) has been documented in many species and is increasingly recognized as a non-trivial factor in plant-water relationships. However, it remains unknown whether FWU is a widespread phenomenon in Pinus species, and how it may relate to needle traits such as the form and structure of stomatal wax plugs. In this contribution, these questions were addressed by studying FWU in current-year and 1-year-old needles of seven Pinus species. We monitored FWU gravimetrically and analysed the needle surface via cryo-scanning electron microscopy. Additionally, we considered the effect of artificial wax erosion by application of the surfactant Triton X-100, which is able to alter wax crystals. The results show for all species that (1) FWU occurred, (2) FWU is higher in old needles compared to young needles and (3) there is substantial erosion of stomatal wax plugs in old needles. FWU was highest in Pinus canariensis, which has a thin stomatal wax plug. Surfactant treatment enhanced FWU. The results of this study provide evidence for (1) widespread FWU in Pinus, (2) the influence of stomatal wax plugs on FWU and (3) age-related needle surface erosion.

Needle age and precipitation as drivers of Hg accumulation and deposition in coniferous forests from a southwestern European Atlantic region

Vegetation and climate are critical in the biogeochemical cycle of Hg in forest ecosystems. The study assesses the influence of needle age and precipitation on the accumulation of Hg in needle biomass and its deposition by litterfall in thirty-one pine plantations spread throughout two biogeographical regions in SW Europe. Well-developed branches of Pinus pinaster were sampled and pine needles were classified according to 4 age classes (y0, y1, y2, y3). The concentration of total Hg (THg) was analyzed in the samples and Hg content in needle biomass and its deposition by litterfall were estimated. The concentration of total Hg (THg) increased with needle age ranging from 9.1 to 32.7 μg Hg kg−1 in the youngest and oldest needles, respectively. The rate of Hg uptake (HgR) three years after needle sprouting was 10.2 ± 2.3 μg Hg kg−1 yr−1, but it decreased with needle age probably due to a diminution in photosynthetic activity as needles get older. The average total Hg stored in needle biomass (HgWt) ranged from 5.6 to 87.8 mg Hg ha−1, with intermediate needle age classes (y1 and y2) accounting for 70% of the total Hg stored in the whole needle biomass. The average deposition flux of Hg through needle litterfall (HgLt) was 1.5 μg Hg m−2 yr−1, with the y2 and y3 needles contributing most to the total Hg flux. The spatial variation of THg, HgWt and HgLt decreased from coastal pine stands, characterized by an oceanic climate, to inland pine stands, a feature closely related to the dominant precipitation regime in the study area. Climatic conditions and needle age are the main factors affecting Hg accumulation in tree foliage, and should be considered for an accurate assessment of forest Hg pools at a regional scale and their potential consequences in the functioning of terrestrial ecosystems.

Effect of Scots pine needle age on preference, performance, and overwintering of pine-tree lappet larvae—the distaste for the oldest foliage

The choice of a host and feeding site is particularly interesting in the case of species feeding on conifers, where the larvae usually have a choice of several age classes of needles. The subject of this research is to answer whether the larvae have a specific preference for a certain needle age class, as well as how such foraging decisions influence larval performance and overwintering. We present the results of food choice tests and the influence of food quality (different age classes of Scots pine Pinus sylvestris needles) on the performance and overwintering of Dendrolimus pini larvae. The obtained results indicate that larvae fed with the youngest needles have the highest performance; however, in the food choice tests, one year old needles were chosen significantly more often. It was also shown that feeding on one year old needles led to the best overwintering survival. Differences in the contents of elements and metabolites explained the cause of the worst food, the oldest needles, and also the differentiation between current year and one year old needles. Water content may be of key importance, which is lower in one year old needles than in current year needles; its lower content may elevate the concentration of cryoprotectant substances.

Crown closure affects endophytic leaf mycobiome compositional dynamics over time in Pseudotsuga menziesii var. menziesii

Old-growth Pseudotsuga menziesii var. menziesii forests produce complex environmental and spatial gradients along which biota assemble. Given this, it has been proposed that changes in the crown microenvironment are associated with different community assembly outcomes for needle fungi. Using high-throughput sequencing, the endophytic mycobiomes of needles were characterized for increasing ages of needles sampled along the boles of eight coastal Douglas-fir trees. Leveraging airborne light detection and ranging (LiDAR) data to create three-dimensional “point cloud” representations of tree crowns revealed that crown closure accounted for more fungal compositional variation than height in crown, and fungal richness and diversity were positively correlated with increasing crown closure. Supplementing the point clouds of each climbed tree with clouds from >5,000 randomly selected trees in the study area showed that fungal communities from closed portions of the crown were increasingly structured with needle age. These findings highlight the importance of the crown microenvironment in the development of foliar fungal communities for a foundation tree species.

Genotoxic effects of transboundary pollutants in Pinus mugo in the high mountain habitats

This study evaluated the environmental genotoxic load of mountain and alpine habitats of Slovak mountains caused by the total mixture of air pollutants at 69 sites using the phytoindicator Pinus mugo. The level of overall genotoxicity was determined by pollen grain abortion assay. This shows that the test is sensitive enough to detect contamination from more distant sources, including long-range transboundary pollutants. It extends the applicability of this test to mountain environments. Soil and plant samples (pollen, one-two year old needles) were collected during a three-year growing period (2011–2013). The study identified source regions of pollutants by assessments at different altitudes and slope exposures. The highest genotoxicity was found in the Little Fatra Mts. on Suchy Mt., with pollen abortivity 3.52 % which represented a 23.5 times higher genotoxic load than at the control site. Samples from mountain peaks showed a higher genotoxicity in 2012 than in 2011 on most mountains. A gradual increase of pollen abortivity and needle Pb content (one year old) with increasing altitude was found in the vertical transect in Belian Tatras. The influence of subsoil type was analysed; higher genotoxicity and Pb content in soil and needles were found on limestone subsoil (Sivy vrch Mt.) and higher values of needle Cd were on granite (Brestova Mt.). The highest Pb and Cd concentrations in needles were measured in the Great Fatra Mts. on Krizna Mt. situated between highly-industrialized areas. The other mountain ranges with the high loading by Pb, Cd were Chocske vrchy Mts. and Low Tatra Mts. The lead content increased with needle age, but the correlation between soil Pb and needle Pb was not confirmed. The positive correlation between soil Pb and abortivity was found only at mountain peaks. The results showed a significant impact of both local industrial and transboundary sources of pollutants. Based on the results, the studied Slovak mountains were not strongly burdened by Pb, Cd and an overall mixture of air pollutants. This methodological approach may contribute to the assessment of urban exposome by comparing the external exposure in urban environment of big cities with background - mountain areas, where the only possible source is long-range transport.

Comparative Genomics of Seasonal Senescence in Forest Trees.

In the course of evolution, both flowering plants and some gymnosperms have developed such an adaptation to winter and unfavorable living conditions as deciduousness. Of particular interest is Siberian larch (Larix sibirica Ledeb.), which is the only species in the pine family (Pinaceae) with a seasonal deciduousness. New generation sequencing technologies make it possible to study this phenomenon at the genomic level and to reveal the genetic mechanisms of leaf and needle aging in angiosperms and gymnosperms. Using a comparative analysis of the genomes of evergreen and deciduous trees, it was found that the genes that control EXORDIUM LIKE 2 (EXL2) and DORMANCY-ASSOCIATED PROTEIN 1 (DRM1) proteins are most represented in Siberian larch, while an excess of genes that control proteins acting as immune receptors were found in evergreens. Orthologs from the family of genes that control leucine-rich repeat receptor-like kinases (LRR-RLK) contributed mostly to the distinction between evergreens and deciduous plants.

Variations of leaf nonstructural carbohydrates in an evergreen coniferous species: Needle age and phenology dominate over life history

Non-structural carbohydrates (NSCs), including soluble sugar (SS) and starch (ST), are essential for the growth and survival of plants. However, few studies have investigated the effects of phenology, needle age, and life history together on NSCs. We measured NSCs of leaves for 120 Pinus koraiensis individuals of various sizes (0.3–100 cm diameter at breast height, DBH) across needle age and during three leaf development periods to evaluate the effects of phenology, needle age, and life history on NSCs. Concentration ranges were 6.60–12.07, 2.38–8.90 and 10.97–16.18 g·100 g−1 dry mass for SS, ST, and NSC, respectively. Needle age accounted for most of the variations (42.2%-84.4%) of NSCs, followed by phenology (9.2%-46.8%), while life history accounted for only a small proportion. In general, NSC reached its maximum value during the leaf unfolding period and the shift between SS and ST occurred during the leaf fall period. The slope of NSC with phenology generally increased with increasing needle age (absolute value). With increasing needle age, NSC and its components showed gradual upward trends. The slope of NSC with needle age decreased with leaf development (except during the leaf fall period). Life history had significant effects on NSCs in the leaf fall period for both current year and perennial needles, and in the leaf unfolding period only for the current year needles. Needle age significantly affected the correlations of NSC and SS (or ST) only at the leaf unfolding period. Phenology had significant effects on the correlations of NSC and SS (or ST) only for current year needle. Our results clearly showed that the variations of NSC and its components were highly dependent on needle age, followed by phenology. Unexpectedly, the effects of life history on NSCs were much less than those of needle age and phenology. Therefore, needle age and phenology dominate over life history in influencing NSCs, and the ecological significance of NSCs variations need to be reconsidered by effects of incorporating needle age and phenology.

Distribution of a Foliage Disease Fungus Within Canopies of Mature Douglas-Fir in Western Oregon.

Nothophaeocryptopus gaeumannii is a common native, endophytic fungus of Douglas-fir foliage, which causes Swiss needle cast, an important foliage disease that is considered a threat to Douglas-fir plantations in Oregon. Disease expression is influenced by fungal fruiting bodies (pseudothecia), which plug the stomata and inhibit gas exchange. Trees are impacted when pseudothecia plug stomates on 1-year-old and older needles resulting in early needle abscission. Mature (100 years+) trees appear to be less impacted from disease, and we hypothesize this is due to the greater emergence of pseudothecia on older than younger needles, which allows for more needle retention. We measured the density of pseudothecia occluding stomates across 2- to 5-year-old needles from upper, middle, and lower canopy positions of mature trees at three sites in the Oregon Coast Range and two sites in the western Oregon Cascade Mountains. Binomial generalized linear mixed model (GLMM) was used to test for the effects of canopy position (upper, middle, and lower), sites, needle age (2-5 years old), and years (2016 and 2017), and their interactions on the pseudothecia density. Pseudothecia density varied annually depending on sites, needle age and canopy positions. Pseudothecia density peaked on 3-, and 4-year-old needles, however, needles emerging from the same year, like 2-year-old needles in 2016 and 3-year-old needles in 2017 both emerged in 2014, had consistently similar patterns of pseudothecia density for both years, across site and canopy positions. Canopy position was important for 3-, and 4-year-old needles, showing less pseudothecia in the lower canopy. This research confirms that N. gaeumannii pseudothecia density is greatest in 3- and 4-year old needles in mature trees in contrast to plantations where pseudothecia density usually peaks on 2-year-old needles, and that pseudothecia density (disease severity) is generally lower in mature trees. Something about mature forest canopies and foliage appears to increase the time it takes for pseudothecia to emerge from the needles, in contrast to younger plantations, thus allowing the mature trees to have greater needle retention.

Diurnal and seasonal variations in photosynthetic rates of dwarf pine Pinus pumila at the treeline in central Japan

ABSTRACT It is important to develop a convenient method for predicting photosynthetic rates in cold regions such as high elevations. Dwarf pine Pinus pumila is a representative treeline species in Japan. In this study, we investigated how environmental factors affect diurnal and seasonal variations of the in situ photosynthetic rate of P. pumila. Five environmental factors (photosynthetic photon flux density [PPFD], air temperature [T a], soil temperature [T s], vapor pressure deficit [VPD], and soil water content [SWC]) were examined. Photosynthetic measurements were conducted for four needle ages at hourly intervals on fifteen days from July to October 2018. The net photosynthetic rate decreased with needle age and changed seasonally and diurnally for each needle age. The net photosynthetic rate showed unimodal patterns with T a, T s, and SWC. The seasonal and diurnal changes in the net photosynthetic rate were related to seasonal changes in the four environmental factors (PPFD, T a, T s, SWC); the net photosynthetic rate decreased in mid-summer when T a, T s, and PPFD were high due to a decrease in SWC. Seasonal and diurnal changes in net photosynthetic rates could be reproduced by the multiplicative model of the four environmental factors and needle age. Therefore, the photosynthetic rate of P. pumila can be explained and predicted using these environmental factors and needle age. This information will be useful for predicting the effects of climate change on the photosynthetic production of plants in cold regions.