Needle Traits Research Articles

Effects of Low-Temperature Stress on Physiological Characteristics and Microstructure of Stems and Leaves of Pinus massoniana L.

Pinus massoniana L. is one of the most important conifer species in southern China and is the mainstay of the forest ecosystem and timber production, yet low temperatures limit its growth and geographical distribution. This study used 30-day-old seedlings from families of varying cold-tolerance to examine the morphological traits of needles and stems, chlorophyll fluorescence characteristics, protective enzymes, and changes in starch and lignin under different low-temperature stresses in an artificial climate chamber. The results showed that the seedlings of Pinus massoniana exhibited changes in phenotypic morphology and tissue structure under low-temperature stress. Physiological and biochemical indexes such as protective enzymes, osmoregulatory substances, starch, and lignin responded to low-temperature stress. The cold-tolerant family increased soluble sugars, starch grain, and lignin content as well as peroxidase activity, and decreased malondialdehyde content by increasing the levels of actual photochemical efficiency (ΦPSII), electron transport rate (ETR), and photochemical quenching (qP) to improve the cold tolerance ability. This study provides a reference for the selection and breeding of cold-tolerant genetic resources of Pinus massoniana and the mechanism of cold-tolerance, as well as the analysis of the mechanism of adaptation of Pinus massoniana in different climatic regions of China.

Variability of Silver Fir Needle (Abies alba Mill.) Anatomical Features in the Southeast Europe Natural Populations.

The survival of marginal/peripheral silver fir (Abies alba Mill.) populations in the broader region of Southeast Europe is endangered due to climate change and population decline. This study aimed to determine the level and pattern of variability for the anatomical traits of needles and the possibility of linking the pattern of phenotypic variability with environmental factors. In most of the analyzed needle traits, the statistically significant variability between populations was determined. According to the results of the multivariate principal component analysis, it is evident that the populations are distinct from each other, in three groups. The climatic factors Hargreaves reference evaporation, mean annual temperature, and growing degree-days, were statistically significantly correlated. The altitude and heating degree-days are statistically significantly correlated with the following three environmental factors: Hargreaves reference evaporation, mean annual temperature and growing degree-days, but negatively with others. The paper's findings indicate significant moderate and high correlations between the anatomical traits of the needles' central bundle diameter with the resin duct diameter, the distance between the vascular bundle and the resin duct and the epidermis thickness with cuticle, the resin duct diameter with the distance between the vascular bundle and the resin duct and the epidermis thickness with cuticle, as well as the distance between the vascular bundle and the resin duct with the hypodermis height and the epidermis thickness with cuticle. The results of agglomerative hierarchical clustering analysis, performed for anatomical and climatic traits, confirmed the existence of three groups of tested populations according to the altitude gradient. Research results provide knowledge on the diversity and structure of Abies alba populations of Southeast Europe, important for further research and guidelines for the species' conservation and genetic variability preservation in the southern marginal distribution area and keeping in line with climate change projections.

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.

Secondary sexual dimorphism and morphological diversity in two allopatric juniper species

Juniperus L. is a very diverse genus of dioecious or monoecious conifers distributed throughout the Mediterranean region. In addition to the complex taxonomic characteristics of the genus, sexual dimorphism leads to sex-specific differences in the morphology of juniper species, which further complicates the delimitation of species. Two of these species, Juniperus oxycedrus L., which occurs in the western part of the Mediterranean, and J. deltoides R.P.Adams, which occurs in the eastern part, have only recently been delimited as separate species. To further support the delimitation of the species, we examined the phenotypic traits of the cones and needles of both species for both sexes. Three populations from the western and three from the eastern part of the Mediterranean region were sampled and a total of 2400 needles, 1200 cones and 1200 seeds were measured and analyzed. Both needles and cones of J. oxycedrus were slightly larger, longer and wider than those of J. deltoides and also less variable. Sexual dimorphism was observed in most of the needle traits measured, with the majority of traits in J. oxycedrus being larger in females than in males. Although sexual dimorphism was confirmed based on needle morphology, no consistent pattern of diversity was observed between the two species. In addition, variability among populations of J. oxycedrus was higher than that of J. deltoides. Our results confirm the previous species delimitation and open the possibility for further exploration of sex-specific differences in adaptability, as well as the potential implications for differential management and conservation of individuals of both sexes.

Utjecaj ekspozicije krošnje na morfološka svojstva iglica devet četinjača

The aim of this research was to investigate if the crown exposure of some conifers influenced to needle properties. The leaf morphological traits of sixty-six trees of nine conifers: Atlas cedar, Austrian pine, Blue spruce, Douglas fir, European spruce, European yew, Serbian spruce, Silver fir, and White fir, from six Belgrade parks, were analyzed. Five needles were measured from each of the four main crown exposures. Length, width, area and perimeter of needles were investigated. Species, parks in which they were found, as well as crown exposures, differed mostly in needle length and needle width. Correlations between measured needle traits were determined by linear regression analysis. Strong positive correlations were found between the length, perimeter, and area of needles. The differences among the species in terms of light requirement determine species for individual planting as light-loving or partial shade species (Atlas cedar, European spruce, Serbian spruce, Blue spruce, Austrian pine and Douglas fir), or for group planting as shade-loving species (Silver fir, White fir and European yew).

Needle functional features in contrasting yield phenotypes of slash pine at three locations in southern China

Pine resin, a valuable secondary metabolite, is derived from the products of photosynthesis. Pine needles, serving as the primary organ for photosynthesis and nutrient absorption, facilitate the continuous transport of nutrients to all plant organs through photosynthesis. The functional traits of pine needles exhibit a close association with the photosynthetic efficiency of pine trees, thereby affecting resin yield. The selection of superior trees with high-resin yield (RY) for slash pine (Pinus elliottii Engelm.) faces difficulties due to low selection efficiency and a high false selection rate caused by the absence of reliable indirect selection traits. The objective of this study was to systematically investigate the relationships between slash pine needle functional traits and RY in different regions. Understanding the relationship between functional traits of pine needles and RY is essential for addressing the challenges mentioned above. There were positive correlations between RY and most morphological traits, except for leaf dry matter content (LDMC), which showed a negative correlation. Moreover, low-resin yield trees exhibited lower values for most morphological variables, except for LDMC. High-yield trees exhibited higher stomata number per mm2 (STN), larger stomata diameter (STD) and size (STS), and stomata area per mm2 (STA) across all periods and sites when compared with low-yield individuals. Chloroplast pigment component analysis revealed that high yielders exhibited higher levels of chloroplast a (CHL a) and chloroplast a+b (CHL a+b) compared to low yielders, and positive correlations were found between resin yield and CHL a, chloroplast b (CHL b), and CHL a+b. Higher nutrient contents were observed in high resin yield individuals, and positive correlations were found between resin yield and most nutrients, except for potassium (K). Different needle functional traits exhibited varying periodic patterns of resin production. Most needle functional traits could be useful criteria for evaluating resin production in slash pine breeding programs, which could improve the efficiency of breeding, shorten the breeding cycle, and accelerate the breeding process.

Geographical Variation Reveals Strong Genetic Differentiation in Cryptomeria japonica var. sinensis

The adaptive capacity of tree species is crucial for their survival under environmental change. Liushan (Cryptomeria japonica var. sinensis), an allogamous conifer species, is widely distributed across southern China. However, despite its broad distribution, there have been few investigations on the geographical variation and environmental adaptability of this species. Here, we combined the phenotypic (eight needle traits) and genetic data (14 nSSR loci) to fill this gap by assessing the genetic variation of geographical populations and exploring environmental adaptations of this species. Both phenotypic and molecular genetic analyses indicated a strong genetic differentiation among geographic populations. All populations could be clustered into three groups that were consistent with their geography. Most of the needle traits showed significantly correlated with geography and environmental factors. Geographical isolation and environmental differences are the main factors that have shaped current morphological traits and patterns of genetic variation. We suggest conservation measures to be implemented on a population level with existing populations, especially those with rare phenotypes as the main goal. Our findings shed light on the geographic variation in Liushan and expanded the knowledge of its putative adaptive mechanisms, ultimately benefiting the conservation of this species.

Does distance from a sand mine affect needle features in Pinus sylvestris L.?

Needle traits of P. sylvestris exhibit high variability depending on habitat conditions and thus may be used to assess the effect of anthropopressure on tree condition in this species. The variability of 22 needle features of Scots pine, collected from populations growing at different distances from the Bełżec-Podlesina eolian sand mine located in Poland, was investigated. No similar research has been conducted to date. The needles were collected from 40 trees growing in similar habitat conditions on four study plots located at a distance of 205.281 to 997.598 m from the sand mine. In total, 3460 needles from 117 samples were measured. It was observed that the distance of the study plots from the sand mine had a statistically significant effect on all the analysed needle traits, with the most extreme values recorded for the needles coming from trees growing on the plots most distant from the sand mine. The characteristics of greatest importance for assessing the impact of the sand mine on needle condition in the studied trees included: needle length/needle width, needle length, needle length/needle thickness, number of stomata on the convex side of the needle/needle length, needle width/resin duct diameter, resin duct diameter, number of stomata on the convex side of the needle/needle width, number of stomata on the concave side of the needle/needle length and number of stomata on the convex side of the needle. The effect of the distance of a given study plot from the sand mine depended on the age of the needles. The analyses confirmed that despite the adaptability of Scots pine to local environmental conditions, the morphological and anatomical characteristics of its needles changed under the influence of anthropopressure. Thus, selected features of the assimilatory organs may be used to monitor the impact of opencast operations on this important forest-forming species.

Variability of morpho-anatomical features of black pine needles at the area of Jastrebac and Goč

In this paper the variability of morphological (needle length and needle width) and anatomical (needle thickness, resin ducts width, epidermis thickness, hypodermis height and number of the hypodermis layers) properties of black pine (Pinus nigra J.F. Arnold) needles were studied at the intra- and inter-population levels. Two mountains in Serbia, Jastrebac and Goč, were selected as experimental plots. Three black pine trees were selected from both localities (6 in total). Obtained results showed that trees on Goč had bigger dimensions of the following elements: needle length, needle width, hypodermis height, number of hypodermis layers, needle thickness and epidermis thickness. On the other hand, only resin ducts width was greater by the trees from Jastrebac. The results of the analysis of variance showed that variation between studied populations, as well as variation between trees within populations was statistically significant for all needle traits except resin ducts width and hypodermis height.

Physiological and Biochemical Traits of Needles Imply That Understory Light Conditions in the Growing Season May Be Favorable to Pinus koraiensis Trees

Light is often considered the primary factor leading to the regeneration failure of Korean pines (Pinus koraiensis) under the forest canopy. However, studies on the effect of light on Korean pines mainly focus on the use of an artificial sunshade net to control shade; field studies on the canopy are extremely scarce, and the current experimental results are contradictory. For a deeper understanding of the relationship between light conditions and understory Korean pine trees, the conditions of low, middle, high and full light (control) under the forest were tested at 18 years of age. The photosynthetic pigments, chlorophyll fluorescence, non-structural carbohydrate metabolism, antioxidant enzyme activity, and nutrient concentrations of current-year needles from Korean pine trees were measured. From June to September, light intensity and quality decreased under full light, but following leaf fall, understory light conditions improved slightly. As the light conditions improved, the photosynthetic pigments in the needles decreased, but Car/Chl were highest in the needles under full light. All light conditions had a positive correlation with glucose concentrations and Rubisco activity. Full-light needles had the highest APX activity, DPPH scavenging capacity, and proline concentration, as well as higher NPQ and lower Fv/Fm readings. This indicated that full-light Korean pine trees were stressed and inhibited photosynthesis to some extent, while the understory light environment may alleviate stress. The conservative strategy of storing more starch and using less glucose in understory Korean pine trees may be one of the reasons for the observed differences in growth rates among Korean pine trees under varying light conditions. Overall, this study implies that understory light during the growing season is not always unfavorable to 18-year-old Korean pine trees; this means that 18-year-old Korean pine trees still have shade tolerance to some extent and are capable of living under a canopy of deciduous trees.

Inter- and Intraspecific Variation Patterns of Leaf Phenotypic Traits in Two Sympatric Pine Species

Individual persistence under changing climate conditions can be aided by phenotypic plasticity. Needle morphology reflects pine species’ adaptation to their habitats, and adaptive plasticity is beneficial to pine survival. As two closely related pines, Pinusmassoniana Lamb. and Pinus hwangshanensis W. Y. Hsia sympatrically occur in the subtropical region of China, forming hilly forests (i.e., subtropical evergreen needleleaf forests) at lower elevations and montane forests (i.e., temperate evergreen needleleaf forests) at medium and high elevations. However, little is known about the intraspecific phenotypic variation patterns of the two pine species and their relationship with environmental factors. Here, we investigated the interspecific and intraspecific variation patterns of needle traits in the two sympatric pine species, focusing on six traits—i.e., leaf length, leaf thickness, leaf width, leaf area, specific leaf area, and leaf dry matter content—as well as the relationship between needle traits and environmental factors. We found significant phenotypic trait differences among populations of each species. Except for leaf length and leaf width, variation within species was greater than variation between species in the needle traits measured. Even more intriguingly, the leaf size traits (i.e., length, width, thickness) were more conservative than the leaf economic traits (i.e., specific leaf area and leaf dry matter content). In other words, the intraspecific variability of the former was weaker than that of the latter. The nature of P. massoniana needle traits was mainly shaped by latitude, while the needle traits of P. hwangshanensis were significantly affected by annual precipitation. Therefore, phenotypic plasticity may be an essential mechanism for the two pine species to better cope with changing external conditions. The intraspecific variation patterns found in the two pine species and the relationships between traits and environmental factors can provide substantial scientific data for large-scale exploration of intraspecific phenotypic variation in pine species and their breeding practice.

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.

Does leaf mass per area (LMA) discriminate natural pine populations of different origins?

Tree provenance trials are believed to be a valuable tool for assessing the adaptive potential of a population to a changing environment and ultimately for predicting the populations that are best adapted to global warming. Here, the phenotypic plasticity of morphometric traits of needles and lateral shoots of pines growing in a provenance plot in central Poland was examined to assess the inter- and intra-population variability. No significant differences were found in the measured and counted morphometric features, i.e., needle length (NL), cumulative needles length (CNL), thickness (ST), volume (SV) and shoot density (SD), number of needles per 5 cm fragment of shoot (NN), dry weight of needles (NDW) and shoot (SDW), thickness of bark (BT) and wood (WT), pith diameter (PD), and needle dry mass per area (LMA) among three pine populations while accounting for their region of origin (inter-population variability). In terms of the above-mentioned features, individual populations differed significantly from each other, except for NN and ST. We also noticed a positive, significant relationship between LMA and ST in all studied populations and based on Euclidean distances of measurable or counted traits, three population groups were identified. We concluded that LMA, which is commonly used to quantify leaf structure, is helpful in differentiating intra-population variability.

Prostorna varijabilnost morfoloških obilježja iglica populacija jele (Abies alba Mill.) na Balkanskom poluotoku u odnosu na klimatske čimbenike

Interpopulation and intrapopulation variability of three morphological needle traits (length, width and thickness) was investigated in 16 natural silver fir populations in the Balkan Peninsula. The populations represent refugial areas of silver fir (Abies alba Mill.). This paper aims to provide a comprehensive analysis of the influence of climatic factors (mean annual temperature, number of days with temperatures < 0, > 5, < 18, > 18<sup>o</sup>C, Hargreaves climatic moisture deficit and De Martonne aridity index, on the pattern of morphological needle traits within each population. Populations showed variation in the analyzed morphological needle traits, which could not be clearly defined by any of the analyzed climatic factors. The De Martonne aridity index and Hargreaves climatic moisture deficit had the greatest impact on the trait values, whereas the mean annual precipitation had the lowest. Evolutionary ecology research of the silver fir needle morphology is a valuable contribution to the comprehention of the present genetic variability as a prerequisite for adaptation to the rapid climate change and conservation of the species area in the Balkan Peninsula region.

Morphological and Comparative Transcriptome Analysis of Three Species of Five-Needle Pines: Insights Into Phenotypic Evolution and Phylogeny.

Pinus koraiensis, Pinus sibirica, and Pinus pumila are the major five-needle pines in northeast China, with substantial economic and ecological values. The phenotypic variation, environmental adaptability and evolutionary relationships of these three five-needle pines remain largely undecided. It is therefore important to study their genetic differentiation and evolutionary history. To obtain more genetic information, the needle transcriptomes of the three five-needle pines were sequenced and assembled. To explore the relationship of sequence information and adaptation to a high mountain environment, data on needle morphological traits [needle length (NL), needle width (NW), needle thickness (NT), and fascicle width (FW)] and 19 climatic variables describing the patterns and intensity of temperature and precipitation at six natural populations were recorded. Geographic coordinates of altitude, latitude, and longitude were also obtained. The needle morphological data was combined with transcriptome information, location, and climate data, for a comparative analysis of the three five-needle pines. We found significant differences for needle traits among the populations of the three five-needle pine species. Transcriptome analysis showed that the phenotypic variation and environmental adaptation of the needles of P. koraiensis, P. sibirica, and P. pumila were related to photosynthesis, respiration, and metabolites. Analysis of orthologs from 11 Pinus species indicated a closer genetic relationship between P. koraiensis and P. sibirica compared to P. pumila. Our study lays a foundation for genetic improvement of these five-needle pines and provides insights into the adaptation and evolution of Pinus species.

High Level of Phenotypic Differentiation of Common Yew (Taxus baccata L.) Populations in the North-Western Part of the Balkan Peninsula

Common or English yew (Taxus baccata L., Taxaceae) is a conifer species, native to Europe, northern Africa, Asia Minor and Caucasus. It is a dioecious, wind-pollinated and animal-dispersed tree, known for its high-quality wood and medicinal properties, albeit poisonous. The species is rare and has been legally protected at the European and national levels. In addition, its low population density and disjunct character of distribution have reinforced the need for its protection as regeneration is mostly lacking. The aim of this study was to phenotypically characterise the north-western Balkan yew populations. Phenotypic diversity was examined for seven populations, using morphometric analysis of nine phenotypic traits of needles. Descriptive and multivariate statistical analyses were conducted to evaluate the inter- and intrapopulation variability. In addition, to test correlations between geographic, climatic and phenotypic data, Mantel test was used. We identified a geographic structure across studied populations that exhibited high levels of variability on intra- and interpopulation levels. Two groups of populations have been defined and are consistent with previously described genetic divergent lineages from separate refugia. In addition, a significant correlation between phenotypic and geographic data were revealed, i.e., isolation by distance (IBD). However, the Mantel test revealed no significant correlation between morphometric and environmental data. In conclusion, our data reveal that the historical events and persistent IBD acted in combination to produce the morphological patterns observed in common yew populations in the north-western part of the Balkan Peninsula. Finally, we suggested conservation measures to be implemented on a stand level, with habitat preservation as the main goal. In addition, ex situ conservation should be considered, both in the form of collections and urban planting, as both provide additional gene pool reserves.

Population variability of scots pine (Pinus sylvestris L.) in Turkey according to the needle morphology

In the present study, needle variation of Scots pine (Pinus sylvestris L., Pinaceae) populations in Turkey was investigated. From selected eight populations, a total of 1314 needles belonging to 206 trees were examined. Four morphological needle traits were measured and analyzed to describe the population diversity and differentiation. Analyzed morphological traits showed significant variability. The trees within populations differ significantly in all analyzed needle characteristics, while the differences between populations were significant for the three of four studied characteristics. Present findings revealed that needle length, needle width and the ratio of needle length to needle width showed clinal variation in response to altitudinal gradients. Populations from higher altitudes were characterized with the smaller and wider needles as compared to the populations from lower altitudes. The results of this study could be valuable baseline data for the development of more efficient management plans for this forest tree species.

Foliage Biophysical Trait Prediction from Laboratory Spectra in Norway Spruce Is More Affected by Needle Age Than by Site Soil Conditions

Scaling leaf-level optical signals to the canopy level is essential for airborne and satellite-based forest monitoring. In evergreen trees, biophysical and optical traits may change as foliage ages. This study aims to evaluate the effect of age in Norway spruce needle on biophysical trait-prediction based on laboratory leaf-level spectra. Mature Norway spruce trees were sampled at forest stands in ten headwater catchments with different soil properties. Foliage biophysical traits (pigments, phenolics, lignin, cellulose, leaf mass per area, water, and nitrogen content) were assessed for three needle-age classes. Complementary samples for needle reflectance and transmittance were measured using an integrating sphere. Partial least square regression (PLSR) models were constructed for predicting needle biophysical traits from reflectance—separating needle age classes and assessing all age classes together. The ten study sites differed in soil properties rather than in needle biophysical traits. Optical properties consistently varied among age classes; however, variation related to the soil conditions was less pronounced. The predictive power of PLSR models was needle-age dependent for all studied traits. The following traits were predicted with moderate accuracy: needle pigments, phenolics, leaf mass per area and water content. PLSR models always performed better if all needle age classes were included (rather than individual age classes separately). This also applied to needle-age independent traits (water and lignin). Thus, we recommend including not only current but also older needle traits as a ground truth for evergreen conifers with long needle lifespan.

Морфолого-анатомические особенности хвои у семенного и разновозрастного вегетативного потомства мутационных «ведьминых метел»

The study was carried out using three objects: 1) clones of the mutational witches’ brooms and the normal crown grafted together on the same rootstock; 2) mutant seedlings of the witches’ brooms; 3) clones of the witches’ brooms mutant seedlings. It was shown that the morphological and anatomical needle characteristics are affected as by the presence and the expression of the mutation, as well as the age of the maternal tree and the presence of a rootstock. Each factor and the interaction of some factors makes a significant contribution to the differences between the groups in the main needle characteristics. The mutant seedlings and their clones formed the shortest needles; they also had smaller areas of the central cylinder, resin ducts, mesophyll and vascular cylinder. Morphological and anatomical needle traits varied between the families, the needle length was a rather conservative trait in the families. Some differences between the groups from different families of witches’ brooms were due to the natural diversity of the maternal witches’ brooms.

Instrinsic relationship among needle morphology, anatomy, gas exchanges and tree growth across 17 Picea species

The genus Picea has wide geographical range and includes species with great economic and ecological value in the northern hemisphere. Growth traits, gas exchange parameters and needle morphology and anatomy vary greatly among Picea species, but the instrinsic relationship among these traits has not been well studied for the genus Picea. We thus conducted a common garden experiment to study the relationship for these traits in 13 native and 4 exotic Picea species growing at an experimental site in Tianshui, Gansu, China. Nearly all of these traits were significantly different among the 17 species and most traits were under relatively strong genetic control. The four species introduced from abroad (P. abies, P. pungens, P. glauca and P. mariana) exhibited good growth performance in the experimental site. We found that the growth traits showed significantly positive correlation with branching characteristics. Moreover, the species with good growth performance had a relatively high photosynthetic rate. The correlation analysis based on needle morphological and anatomical traits revealed that needle traits were interrelated and needle anatomical traits might be impacted by needle size due to the increase of mesophyll area and central cylinder area with needle length. Furthermore, the relationship between needle structures and gas exchange parameters may indicate that a higher photosynthetic rate can be attributed to variations in needle structures. In addition, both the cluster analysis and principal component analysis based on needle morphology, anatomy, gas exchanges and growth traits might partially reflect the evolutionary history of the 17 Picea species. Our study represents a comprehensive survey of variation within the genus Picea to date and opens new avenues for exploring the instrinsic relationship among growth traits, needle gas exchange and needle morphology and anatomy.