Poplar Clones Research Articles

Effects of Ozone Stress on Rhizosphere Soil of Poplar Seedlings

Near-surface O3 has negative effects on plant productivity; however there were few studies on the effects of O3 pollution on the belowground part of the ecosystem. The effect of O3 stress on the belowground parts of poplar is unclear. We investigated the effects of O3 pollution on poplar rhizosphere soil in open-top chambers (OTC). Two kinds of plants with different O3 sensitivity were selected, i.e., high-sensitive poplar clone 546 and low-sensitive poplar clone 107. The control group and high-concentration O3 group were set up: charcoal-filtered air, CF; unfiltered air + 60 ppb O3, NF. Poplar rhizosphere soil was taken after 96 days (15 June to 17 September 2020) of cultivation in OTCs. O3 stress decreased the amplicon sequence variations (ASVs) of microorganisms in poplar 107 and poplar 546 rhizosphere soil, with no significant interspecific difference. The effect of O3 fumigation on the fungal community was greater than that on the bacterial community. The correlation between the bacterial community and rhizosphere soil physicochemical indices was closer than that of the fungal community. Some fungi, such as Clitopilus hobsonii, Mortierella sp., and Minimedusa, might help poplar resist the O3 stress. O3 stress had direct impacts on the pH, nutrients, and enzyme activities of rhizosphere soil, while it had indirect negative impacts on microbial community composition by nutrients. There was no difference in sensitivity between rhizosphere soil response to O3 stress of poplar clone 107 and clone 546, which might take a longer accumulation time to show the effect. This study provides a certain basis for accurately evaluating the ecological effects of O3 pollution.

Phenology and radial growth of poplars in wide alley agroforestry systems and the effect on yield of annual intercrops in the first four years of tree age

Silvoarable agroforestry systems have the potential to combat the negative effects of climate change while also enhancing productivity per unit land. Although the growth rate of large-spaced trees remains poorly investigated and the yield of annual intercrops uncertain, silvoarable agroforestry systems with poplar are receiving an ever-growing interest. This study assessed the growth of the new HES (High Environmental Sustainability) poplar clone, Moncalvo, arranged in 40-m spaced parallel alleys with a density of 35 trees ha−1 (SA, silvoarable). Their growth was compared to those cultivated in a specialized poplar plantation (C, control) with 277 trees ha−1, and the agronomic impact on wheat and soybean as intercrops was explored. Measurements took place between 2018 and 2021 during the first 4 years, which represents the midpoint of the expected poplar rotation. Here it was demonstrated that at the end of the investigated period, diameter at breast height was significantly greater (23.8 vs. 20.5 cm, +16%) and the plant height lower (14.3 vs. 15.5 m, −8%) in poplar grown in SA as compared to those in C, likely due to reduced intraspecific competition for environmental resources. In SA, seasonal tree phenology was delayed by approximately two weeks in spring, possibly due to the high sensitivity of poplar to low soil water content and cooler night air temperatures in springtime. The grain yield of wheat was not impaired by tree shading but instead occasionally improved when neighboring the poplar alley (e.g., year 2021: +28% at 12 m from the tree row vs. full sun conditions), while soybean yield was generally reduced (maximum −38% at 6 m from the tree row). This study innovatively studied the growth response of HES poplar clones in silvoarable systems by providing valuable insights into the growth dynamics of trees grown in combination with field crops. It is concluded that poplars in wide spaced alleys of silvoarable systems in temperate climates grow faster than poplars in plantations of high population density due to enhanced access to resources, while future investigations will allow for the identification of clone-specific rotation durations. In the arable tree interrow, winter crops more readily benefit from such agroforestry system than summer crops due to reduced cycle overlap and light competition with the tree canopy.

In vitro selection of drought-tolerant white poplar clones based on antioxidant activities and osmoprotectant content.

In light of upcoming climate change, there is an urgent requirement for tree improvement regarding adaptability to drought-caused stress and the development of quick and reliable screening methodologies for genotypes' drought tolerance. White poplar is, despite its high adaptability, considered to be an endangered tree species in Serbia, which gives it special importance in the preservation and improvement of biodiversity of riparian ecosystems. The main goal of this research was to evaluate the tolerance of five white poplar clones to the presence of polyethylene glycol (PEG 6000 molecular weight 6000) (different concentrations (e.g. 0 g/L, 1 g/L, 10 g/L, 20 g/L, and 50 g/L) in Aspen Culture Medium (ACM). The tolerance of the clones was evaluated by using morphological parameters (shoot fresh and dry weight, root fresh and dry weight), photosynthetic pigments (contents of chlorophyll a, chlorophyll b, carotenoids, and chlorophyll a+b), and biochemical parameters (total phenolic content, total flavonoid content, ferric reducing antioxidant power, antioxidant activities (DPPH activity and ABTS assay), free proline content and glycine betaine content. The values of morphological and photosynthetic pigments declined with an increase in the concentration of PEG 6000. At a concentration of 50 g/L, the content of shoot fresh mass decreased by 41%, the content of Chl a by 68%, Chl b by 65%, and Car by 76% compared to the control. Also, at the same medium, there was an increase in the content of total phenols, accumulation of proline, the content of glycine betaine as well as in antioxidant activity. Based on the obtained results, it can be assumed that more drought-tolerant clones are characterized by high values for biomass, high content of photosynthetic pigments, and high content of proline and glycine betaine in conditions similar to drought in vitro. Clone L-80 showed better results in most of the tested parameters, especially compared to the reference clone Villafranca.

Analysis of Growth Trajectories and Verification of Related SNPs in Populus deltoides.

As an important timber genus with high economic and ecological values, Populus is a model for dissecting the genetic architecture of growth traits in perennial forest trees. However, the genetic mechanisms of longitudinal growth traits in poplar remain incompletely understood. In this study, we conducted longitudinal genetic analysis of height and diameter at breast height (DBH) in eleven-year poplar clones using ultra-deep sequencing datasets. We compared four S-shaped growth models, including asymptotic, Gompertz, logistic, and Richard, on eleven-year height and DBH records in terms of five metrics. We constructed the best-fitting growth model (Richard) and determined poplar ontogenetic stages by virtue of growth curve fitting and likelihood ratio testing. This study provides some scientific clues for temporal variation of longitudinal growth traits in Populus species.

Preliminary estimates of genetic parameters and familial selection for non-native poplars show good potential for genetic gains on growth, cold hardiness, trunk quality and Sphaerulina musiva susceptibility

Genetic parameters for growth, trunk quality, and susceptibility to frost and Sphaerulina musiva attack were estimated from 34 half-sib families of hybrid poplar from the crossing of non-native parents, Populus maximowiczii A. Henry, and Populus trichocarpa Torr. & Gray, 3 and 6 years after planting. The use of spatial analysis proved to be the best method for quantitative growth data. The proportion of the among-family variance to the total (phenotypic) variance as well as the high heritabilities of growth and susceptibility to frost and Spaherulina musiva showed a high potential for selection for these traits while the quality traits were under low genetic control. Some families showed gains for several traits, suggesting the possibility of developing a selection index to obtain superior families that show gain for not only growth but quality and adaptive traits as well. Type B correlations were high, suggesting that families responded in the same way regardless of the site. High type A correlation between growth traits at 3 and 6 years showed early selection potential, although these relationships should be confirmed with future measurements to evaluate this effect at maturity. These results can be integrated into the strategy for improving hybrid poplar parental populations and, in the longer term, will make it possible to optimize the selection of individuals with traits of interest for the operational deployment of hybrid poplar clones.

Optimizacija parametara proizvodnje ugušćene lamelirane furnirske građe proizvedene upotrebom urea-formaldehidne smole

This research aims to optimize densified laminated veneer lumber production parameters of compression ratio, press temperature, press time, and adhesive spread rate to maximize their mechanical properties. In the manufacturing process of densified laminated veneer lumber, I-77/51 American poplar clone (Populus deltoides) veneers and urea formaldehyde adhesive are used. The results showed that the compression rate and press time had the most significant impact on the mechanical properties of densified laminated veneer lumber. The optimal production conditions were determined as follows: 38 % compression, press temperature of 170 °C, press time of (10±3) minutes, and spread rate of 150 g/m2. Modulus of rupture, modulus of elasticity, tensile shear strength, and tensile strength perpendicular to panels surface of densified laminated veneer lumbers produced under these conditions increased by 49 %, 8 %, 71 %, and 23 %, respectively, compared to the control group of laminated veneer lumber. So, it can be said that the production parameters of densified laminated veneer lumbers can be optimized safely and effectively using Taguchi method-based grey relational analysis.

Transcriptome Analysis of Populus Overexpression in SVL Transcription Factor

Flowering is an essential part of the productive process, and flowering time is determined by endogenous genetic components and many ambient factors. SHORT VEGETATIVE PHASE (SVP), a MADS-box transcription factor, regulates floral transition by repressing floral integrator genes and is involved in ABA-mediated drought stress. In this study, we transformed the poplar (Populus) clone “84K” with the SVP-Like gene, while stable overexpression transgenic lines were obtained. Transcriptome analysis of the leaves of the transgenic lines and WT (Wide Type) poplars revealed that a total of 477 genes showed significantly altered expression, overexpressing SVL genes, including 342 upregulated and 135 downregulated genes. Ten subclusters in DEGs were analyzed, and KEGG terms of the largest subcluster were associated with two key pathways: hormone-related genes and glutathione metabolism. Meanwhile, many transcriptional factors were involved. Our results are helpful for in-depth analysis of the MADS transcriptional factor in poplars. This work provides the basis for studying woody plant growth, and development and molecular mechanisms responded to environmental stresses.

Study of Variation in Quantitative Traits of Poplar (Populus deltoides) Clones in Different Environments

Study of Variation in Quantitative Traits of Poplar (Populus deltoides) Clones in Different Environments

Transcriptome Analysis Reveals the Hormone Signalling Coexpression Pathways Involved in Adventitious Root Formation in Populus

Adventitious roots (ARs) occur naturally in many species and are important for plants to absorb nutrients and water. AR formation can also be induced from explants of trees, whose clonal propagation is needed. AR formation is gridlock for many woody plant mass propagations. Plant hormones have been regarded as playing a key role in AR formation, and the molecular regulatory mechanisms need to be elucidated. In this study, RNA-Seq was performed to reveal the molecular mechanisms in the different periods of AR formation from hybrid poplar clone 84K (Populus alba × P. glandulosa) and AUXIN SIGNALING F-BOX (PagFBL1-OE). To understand the importance of differentially expressed genes (DEGs), we found that many genes involved in signal transduction mechanisms were induced at 12, 24 and 48 h in 84K and PagFBL1-OE cells by NOG classification. We also found that many DEGs were enriched in hormone signal transduction only for the first 12 h in 84K and PagFBL1-OE by KEGG pathway enrichment. Notably, more DEGs appeared in indole-3-acetic acid (IAA), abscisic acid (ABA), ethylene (ETH), jasmonic acid (JA), brassinolide (BR), cytokinin (CTK) and gibberellin (GA) signal transduction for the first 12 h in PagFBL1-OE than in 84K. Moreover, ARF (Pop_G01G075686), IAA14 (Pop_A10G047257), SAURs (Pop_A03G019756, Pop_A12G067965, Pop_G03G055849 and Pop_G12G008821), JAR1s (Pop_A14G000375 and Pop_G14G044264), CTR1 (Pop_A17G052594 and Pop_G09G030293), CRE1s (Pop_G07G086605 and Pop_G07G086618), GID1 (Pop_A04G026477), BKI1 (Pop_A02G066155), PYR/PYLs (Pop_A03G050217 and Pop_G01G089222), and TGAs (Pop_A04G059310, Pop_G04G060065 and Pop_G05G008153) were only specifically expressed in PagFBL1-OE and could play an important role in AR formation, especially in the first 12 h under plant hormone signal transduction. These results show that the complex biological process of AR formation is primarily influenced by the hormone signalling pathway in Populus. This study reveals the initial regulation of AR formation in woody plant cuttings and thus contributes to further elucidating the molecular mechanism by which hormones interact.

Resistance against Leucoptera sinuella (Lepidoptera: Lyonetiidae) among hybrid clones of Populus spp. in central Chile.

Leucoptera sinuella (Reutti) (Lepidoptera: Lyonetiidae) is a leaf miner specialist on Salicaceae recently introduced to Chile and Argentina, where it is causing economic damage to poplar plantations. We report a field survey in a poplar nursery naturally infested showing that regardless of the poplar hybrid taxon, high variability in resistance was observed among clones within families for oviposition and leaf-mining damage. A group of susceptible and resistant hybrid poplar clones was then selected for a laboratory evaluation of oviposition (antixenosis) and leaf-mining damage (antibiosis) on potted, rooted shoot cuttings. The concentration of condensed tannins (CTs) and salicinoid phenolic glucosides (SPGs) of the leaves of the selected clones from the laboratory study was also measured. Total oviposited eggs were positively correlated with leaf area, with the lowest oviposition on TMxT 11372 clone. The lowest percentage of mined leaf area was obtained for clones TMxT 11372, TMxT 11463, and TDxD 17574, but surprisingly no correlation between the percentage of mined leaf area and concentration of CTs and SPGs was found. Resistant poplar hybrids of our study could be suitable for breeding programs aimed for L. sinuella integrated pest management.

Dar dikim aralıklarında kurulan kavak (Populus x euramericana ve Populus deltoides klonları) ağaçlandırmalarında artım ve büyüme

Bu çalışmada, levha ve kağıt endüstrisinin talebine uygun odun üretimine yönelik, dar dikim aralıklarındaki kavak ağaçlandırmalarının gelişimleri araştırılmıştır. Bu amaçla, P.x euramericana ve P. deltoides klonlarıyla (I-214, I-45/51, SAMSUN (I-77/51), İZMİT (S.307-26) ve 89.M.060) deneme ağaçlandırmaları tesis edilmiştir. Denemelerde 3m x 1,5m (4,5 m2/ağaç), 3m x 2m (6,0 m2), 3m x 3m (9,0 m2), 3m x 4m (12,0 m2) ve 3m x 5m (15,0 m2) olmak üzere, 5 değişik dikim aralığı uygulanmıştır. Tüm kavak klonları için, bonitet tabloları ve çift girişli hacim tabloları düzenlenmiştir. Ayrıca, 3 bonitet sınıfı ve 5 değişik dikim aralığına göre, 3 – 12 yaş kademesi için hasılat tabloları hazırlanmıştır. Dar dikim aralıklarındaki kavak ağaçlandırmalarında çap, boy ve meşcere unsurlarının artım ve büyüme ilişkileri ortaya konulmuştur. Analiz sonuçlarına göre, en uygun klonun 89.M.060 ve dikim aralığının 4,5 m2/ağaç olduğu belirlenmiştir.

Climate-wise models of biomass productivity for hybrid poplar clones in Europe

Climate-wise models of biomass productivity for hybrid poplar clones in Europe

Physiological harmfulness of xylophagous insects in poplar and aspen stands in the Left-Bank Forest-Steppe

Introduction
 Poplars and aspens (Populus sp.) are common in forest stands, shelterbelts, rural landscaping, and in special plantations as short-rotation woody crops; they are promising tree species for biofuel and bioenergy production. Wood-boring insects browse galleries in a stem or branches that interrupt sap circulation and promote infestation by plant pathogens. Some of these insects can additionally weaken trees using foliage, bark, or phloem for maturation feeding. All these effects comprise the physiological harmfulness of wood-boring insects, whereas their technical harmfulness depends on the size and depth of the galleries, their location at the stem, and the timber value of a given tree species.
 The approach of wood-boring insect harmfulness assessment was suggested by E. Mozolevskaya and it is implemented for oak, pine, spruce, birch, and elm. It was shown that the harmfulness of the same insect species varies significantly depending on environmental conditions and population density.
 The aim of the research was to evaluate the physiological harmfulness of xylophagous insects for Populus sp. in the Left-Bank Forest-Steppe considering the ability of these insects to colonize and damage trees under certain health, transmit the pathogens, as well as host range and occurrence.
 Materials and Methods
 The research was carried out in 2019–2022 in Poltava, Sumy, and Kharkiv regions at the archive plantation of poplar clones, forest stands, and forest shelterbelts. The collections and research of Yu. Skrylnik since 2006 in the specified territories were also included in the analysis. In the analysis, only those insect species were used, for which the development in the stems and branches of Populus sp. was proved by our research and/or supported by publications. The range of host plants and the occurrence of insects were estimated. Their physiological harmfulness was calculated as the sum of scores for their physiological activity (ability to colonize trees under certain health condition), ability to damage the trees during maturation feeding, and ability to vector the pathogens.
 Results and Conclusions
 In the study, 72 insect species were analyzed, particularly 40 Cerambycidae, 19 Buprestidae, 7 Curculionidae, 2 Sesiidae, and 3 Cossidae. The proportion of abundant species was the highest among Scolytinae: Xyleborini. Species with a high physiological activity predominate among monophagous insects, particularly, Agrilus suvorovi, Cryptorhynchus lapathi, Xyleborus cryptographus, Paranthrene tabaniformis, Acossus terebra. Only five species (S. populnea, S. octopunctata, S. perforata, S. scalaris, S. carcharias) can cause significant damage to trees during maturation feeding by foliage or bark of branches. The average score of physiological harmfulness is the highest among abundant xylophagous species, it is almost twice as low in common species, and almost two times less in rare and single species. High physiological harmfulness (10 and more) for poplars and aspens is estimated for nineteen xylophagous species, particularly, 13 for S. populnea and S. carcharias, and 12 for Cryptorhynchus lapathi, Trypodendron signatum, Tremex fuscicornis, and Xyleborini species.
 3 Tab., 4 Fig., 35 Ref.

A user-driven, reduced whole-stand growth model for major hybrid poplar clones in Spain

ABSTRACT Populus spp. clones and hybrids are commonly cultivated for timber production worldwide due to their fast growth and adaptability. In Spain, growth models are currently available for the Populus × euramericana clones ‘I-214' and ‘MC'. However, the input variables required for these models are not typically available to potential users. For the most widely used P. × interamericana clones ('Beaupre', ‘Raspalje' and ‘Unal') there is currently no growth model available in Spain or elsewhere in Europe. The aim of the present study was to develop a whole-stand growth model for these five clones. Data were obtained from a network of 134 plots and 265 trees scanned by Terrestrial Laser Scanning. The structure of the growth model was mediated by plot data typically available from forest owners: plantation age, number of trees of each clone and arithmetic mean tree diameter (dm). The main component of the growth model is a dm projection function, enabling dm to be projected at any time. Sensitivity analysis of the prediction accuracy of this function revealed that the proposed model provides satisfactory predictions for time intervals of between 5 and 10 years. The growth model was implemented in a web-based plot growth simulator, facilitating its use.

Arbuscular mycorrhizal symbiosis alleviates ozone injury in ozone-tolerant poplar clone but not in ozone-sensitive poplar clone

Tropospheric ozone (O3) is a typical air pollutant with harmful effects on plants, whereas arbuscular mycorrhizal (AM) fungi are ubiquitous plant symbionts that enhance plant resistance to various abiotic stresses. However, whether AM symbiosis decreases plant O3 sensitivity and what the underlying mechanisms are remain unclear. In this study, O3-tolerant poplar clone 107 and O3-sensitive poplar clone 546 were used as test plants. An open-top chamber experiment was conducted to investigate the effects of AM inoculation on plant growth and physiological parameters under O3 enrichment. The results showed that O3 enrichment significantly decreased plant biomass and net photosynthetic rate and increased the leaf shedding rate and malondialdehyde concentration of clone 546. Generally, clone 107 was less responsive to O3 enrichment than clone 546 was. Differences in antioxidant enzyme activity, rather than in specific leaf weight or stomatal conductance, were responsible for the differences in O3 sensitivity between the two clones. AM inoculation significantly increased the biomass and decreased the leaf shedding rate and malondialdehyde concentration of clone 107 but had no significant effect on almost all the indexes of clone 546, suggesting a species-specific mycorrhizal effect on plant O3 sensitivity. Mechanistically, AM symbiosis did not significantly affect nutrient uptake, stomatal conductance, or specific leaf weight of poplar but did significantly increase antioxidant enzyme activity. Linear regression analysis of antioxidant enzyme activities and the effect of O3 on growth and physiological parameters showed that AM symbiosis mediated antioxidant enzyme activities to mitigate O3 injury to the two poplar clones. This study improved the understanding of the protective effects of AM fungi on plants against O3 pollution.

13 years of biomass production from three poplar clones in a temperate short-rotation alley cropping agroforestry system

Farmers' interest in establishing agroforestry systems is increasing, as they are considered to have many benefits, such as the possibility of climate adaptation and crop diversification. Growing wood on agricultural land can produce biomass for energy or material purpose. Knowledge of the yield potential of the woody component in an agroforestry system is essential for informed decision making by farmers. The present study investigates the biomass production of the three poplar clones 'Max 1′, 'Koreana' and 'Hybride 275′ during the first 13 years (2008–2021) of their growth in a short rotation alley-cropping agroforestry system in Lower Saxony, Germany, on a vertic cambisol as well as a stagnosol soil. There was a high clonal effect on re-sprouting and mortality of the trees as well as on the mean annual dry matter (DM) woody biomass increment (MAI). Overall, 'Max 1′ showed highest re-sprouting, lowest mortality and highest MAI compared to the clones 'Hybride 275′ and 'Koreana'. The MAI of the three poplar clones was not affected by the rotation length of 3 or 6 years. Over the period of 13 years MAI of 'Max 1′ was 13.3 t Mg ha−1 year−1 DM, whereas that of 'Hybride 275′ and 'Koreana' was 10.2 and 9.8 t Mg ha−1 year−1 DM, respectively. The MAI was significantly determined by the factor harvest year. A low MAI was found for the 3-year rotation cycle in 2021, which was most possibly caused by drier and warmer than average vegetation periods in 2018–2020. Under the given site conditions, clone 'Max 1′ proved to be the most productive.

Sensitivity of isoprene emission rate to ozone in greening trees is concurrently determined by isoprene synthesis capacity and stomatal conductance

The sensitivity of isoprene emission rate (ISOrate) to ozone (O3) in plant suggests potentially large changes in future isoprene emissions, which will have important consequences for atmospheric chemistry. However, the interspecific variation of ISOrate sensitivity to O3 and its key drivers remain largely unknown. In this study, four urban greening tree species were exposed to two O3 treatments (charcoal-filtered air, CF; and non-filtered ambient air plus 60 ppb extra O3, EO3) in open-top chambers for one growing season. We aimed to compare the interspecific variation in O3 inhibitory effect on ISOrate and explore its physiological mechanism. EO3 decreased the ISOrate by on average 42.5 % across species. According to absolute effect size ranking, the highest ISOrate sensitivity to EO3 was observed in Salix matsudana, followed by Sophora japonica and hybrid poplar clone ‘546’, while Quercus mongolica ISOrate was the least sensitive. Leaf anatomical structures differed in tree species but did not respond to EO3. Furthermore, the ISOrate sensitivity to O3 was driven by the concurrent effects of O3 on ISO synthesis ability (i.e., dimethylallyl diphosphate and isoprene synthase contents) and stomatal conductance. Overall, the mechanistic understanding grained from this study may promote the integrity of O3 effect into process-based ISO emission models.

CRISPR/Cas9-based gene activation and base editing in Populus.

The genus Populus has long been used for environmental, agroforestry and industrial applications worldwide. Today Populus is also recognized as a desirable crop for biofuel production and a model tree for physiological and ecological research. As such, various modern biotechnologies, including CRISPR/Cas9-based techniques, have been actively applied to Populus for genetic and genomic improvements for traits such as increased growth rate and tailored lignin composition. However, CRISPR/Cas9 has been primarily used as the active Cas9 form to create knockouts in the hybrid poplar clone "717-1B4" (P. tremula x P. alba clone INRA 717-1B4). Alternative CRISPR/Cas9-based technologies, e.g. those involving modified Cas9 for gene activation and base editing, have not been evaluated in most Populus species for their efficacy. Here we employed a deactivated Cas9 (dCas9)-based CRISPR activation (CRISPRa) technique to fine-tune the expression of two target genes, TPX2 and LecRLK-G which play important roles in plant growth and defense response, in hybrid poplar clone "717-1B4" and poplar clone "WV94" (P. deltoides "WV94"), respectively. We observed that CRISPRa resulted in 1.2-fold to 7.0-fold increase in target gene expression through transient expression in protoplasts and Agrobacterium-mediated stable transformation, demonstrating the effectiveness of dCas9-based CRISPRa system in Populus. In addition, we applied Cas9 nickase (nCas9)-based cytosine base editor (CBE) to precisely introduce premature stop codons via C-to-T conversion, with an efficiency of 13%-14%, in the target gene PLATZ which encodes a transcription factor involved in plant fungal pathogen response in hybrid poplar clone "717-1B4". Overall, we showcase the successful application of CRISPR/Cas-based technologies in gene expression regulation and precise gene engineering in two Populus species, facilitating the adoption of emerging genome editing tools in woody species.

EYGFPuv-Assisted Transgenic Selection in Populus deltoides WV94 and Multiplex Genome Editing in Protoplasts of P. trichocarpa × P. deltoides Clone '52-225'.

Although CRISPR/Cas-based genome editing has been widely used for plant genetic engineering, its application in the genetic improvement of trees has been limited, partly because of challenges in Agrobacterium-mediated transformation. As an important model for poplar genomics and biotechnology research, eastern cottonwood (Populus deltoides) clone WV94 can be transformed by A. tumefaciens, but several challenges remain unresolved, including the relatively low transformation efficiency and the relatively high rate of false positives from antibiotic-based selection of transgenic events. Moreover, the efficacy of CRISPR-Cas system has not been explored in P. deltoides yet. Here, we first optimized the protocol for Agrobacterium-mediated stable transformation in P. deltoides WV94 and applied a UV-visible reporter called eYGFPuv in transformation. Our results showed that the transgenic events in the early stage of transformation could be easily recognized and counted in a non-invasive manner to narrow down the number of regenerated shoots for further molecular characterization (at the DNA or mRNA level) using PCR. We found that approximately 8.7% of explants regenerated transgenic shoots with green fluorescence within two months. Next, we examined the efficacy of multiplex CRISPR-based genome editing in the protoplasts derived from P. deltoides WV94 and hybrid poplar clone '52-225' (P. trichocarpa × P. deltoides clone '52-225'). The two constructs expressing the Trex2-Cas9 system resulted in mutation efficiency ranging from 31% to 57% in hybrid poplar clone 52-225, but no editing events were observed in P. deltoides WV94 transient assay. The eYGFPuv-assisted plant transformation and genome editing approach demonstrated in this study has great potential for accelerating the genome editing-based breeding process in poplar and other non-model plants species and point to the need for additional CRISPR work in P. deltoides.

Nitrogen addition changed the relationships of fine root respiration and biomass with key physiological traits in ozone-stressed poplars

Increasing ozone (O3) and nitrogen (N) addition may have contradictory effects on plant photosynthesis and growth. However, it remains unclear whether these effects on aboveground parts further change the root resource management strategy and the relationships of fine root respiration and biomass with other physiological traits. In this study, an open-top chamber experiment was conducted to investigate the effects of O3 alone and in combination with nitrogen (N) addition on root production and fine root respiration of poplar clone 107 (Populus × euramericana cv. ‘74/76’). Saplings were grown with (100 kg ha−1 year−1) or without (+0 kg ha−1 year−1) N addition under two O3 regimes (non-filtered ambient air or non-filtered ambient air + 60 ppb of O3). After about two to three months of treatment, elevated O3 significantly decreased fine root biomass and starch content but increased fine root respiration, which occurred in tandem with inhibited leaf light-saturated photosynthetic rate (Asat). Nitrogen addition did not change fine root respiration or biomass, neither did it alter the effect of elevated O3 on the fine root traits. However, N addition weakened the relationships of fine root respiration and biomass with Asat, fine root starch and N concentrations. No significant relationships of fine root biomass and respiration with soil mineralized N were observed under elevated O3 or N addition. These results imply that changed relationships of plant fine root traits under global changes should be considered into earth system process models to project more accurately future carbon cycle.