Hybrid Poplar Research Articles

Hybrid and Environmental Effects on Gene Expression in Poplar Clones in Pure and Mixed with Black Locust Stands

Mixed cropping might be seen as an alternative to monocultures by better protecting biodiversity and improving ecosystem services and resources. In the presented study, we tested the genetic and ecological effects of pure and mixed propagation of different poplar hybrids planted together with black locust trees. Poplar (Populus) hybrids are widely used for bioenergy in monoculture systems due to their rapid and high biomass production. Black locust (Robinia pseudoacacia L.) is a species with the ability to fix nitrogen and seen as a promising candidate for mixed cultivation. Eight different poplar hybrids and black locust trees from three provenances planted in two study sites with different environmental conditions were tested in varying combinations in pure and mixed stands to observe effects of the different hybrids and genotypes, site conditions and the mixed growing on the performance of poplar and its gene expression. Transcriptome analyses of leaves from four poplar clones selected according to their divergent growth performance were conducted to study differential gene expression that can be an important indicator of differences in growing conditions and success. Differences in gene expression were most pronounced among hybrids and different genotypes of the same hybrid, followed by the study site influence, and were least pronounced between mixed and pure stands. The genotypes of the same hybrid were clearly separated from each other. Clear separation between the study sites for all clones was also observed. Only a few genes were differently expressed in pure vs. mixed stand comparisons for each clone, but there were no common genes that were differently expressed in pure vs. mixed stands in all clones. In total, 199 genes showed differential expression between the study sites regardless of poplar clone or type of stands. The analysis suggested that plant genotypes and environmental conditions were more important at the early stage of stand development than pure or mixed cultivation.

Biological and economic features of the ‘Voronezh Giant’ hybrid poplar

The purpose of this publication is to generalize the available experimental data on the survival, growth, stability, technical and other characteristics of this hybrid and to clarify proposals for its practical use. Long-term studies have been carried out on the five variety testing sites in various soil and climatic zones of the South-Eastern part of Russia and in Ukraine. The survival rate of this poplar were quite high (from 75 to 96%), on average 81%. The age of economic exploitability in the forest-steppe zone with a 20 m2 feeding area per tree was equal to 29 years. To this age the ‘Voronezh Giant’ accumulated stem wood stock of 550-640 m3/ha. The duration of shoot growth was 146 days, and the growing season was 177 days. It was distinguished by high winter hardiness, relative drought resistance, wind resistance, low damage by primary and secondary entomopests, and affection with phytodiseases, but a low straight trunk. It has a fairly high timber density, the length of the wood fiber and the cellulose content, which is important for the pulp and paper industry. The freshly picked green leaves of this poplar are close to the nutritional value of meadow herbs and lucerne. In general, the poplar ‘Voronezh Giant’ is promising for growing wood pulp, introducing into energy, shelter-belts, roadsides, riversides and other reclamation plantings. Given into account its male gender and high decorativeness, it can be also recommended in the greenery landscaping.

Wood forming tissue-specific expression of PdSuSy and HCHL increases holocellulose content and improves saccharification in Populus

Development of strategies to deconstruct lignocellulosic biomass in tree species is essential for biofuels and biomaterials production. We applied a wood forming tissue-specific system in a hybrid poplar to express both PdSuSy (a sucrose synthase gene from Populus deltoides × P. euramericana that has not been functionally characterized) and HCHL (the hydroxycinnamoyl-CoA hydratase-lyase gene from Pseudomonas fluorescens, which inhibits lignin polymerization in Arabidopsis). The PdSuSy-HCHL overexpression poplars correspondingly driven by the promoters of Arabidopsis AtCesA7 and AtC4H resulted in a significant increase in cellulose (> 8%), xylan (> 12%) and glucose (> 29%) content, accompanying a reduction in galacturonic acid (> 36%) content, compared to control plants. The saccharification efficiency of these overexpression poplars was dramatically increased by up to 27%, but total lignin content was unaffected. These transgenic poplars showed inhibited growth characteristics, including > 16% reduced plant height, > 10% reduced number of internodes, and > 18% reduced fresh weight after growth of 4 months, possibly due to relatively low expression of HCHL in secondary xylem. Our results demonstrate the structural complexity and interaction of the cell wall polymers in wood tissue and outline a potential method to increase biomass saccharification in woody species.

Interactive effects of ozone exposure and nitrogen addition on the rhizosphere bacterial community of poplar saplings

It is widely documented that elevated ground-level ozone (O3) has negative effects on tree physiological characteristics, and in return, affects forest ecosystem function. However, the effect may be modified by soil nitrogen (N) availability. Numerous studies have focused on the aboveground part of trees under elevated O3 alone or in combination with soil N; however, little is known about the response of soil bacterial communities. Here, we investigated the effects of O3 (charcoal-filtered air, CF, versus ambient air +40 ppb of O3, E-O3), N addition (0 kg ha−1 yr−1, N0, versus 200 kg ha−1 yr−1, N200), and their combination on rhizosphere soil bacterial communities of hybrid poplar, using an MiSeq targeted amplicon sequencing of the bacterial 16S rRNA gene. E-O3 significantly decreased bacterial abundance, and N200 significantly decreased the α-diversity. The negative impacts of N200 on α-diversity were alleviated by E-O3. Nitrogen and E-O3-N200 combination altered bacterial community composition, with a significant increase in the relative abundance of Proteobacteria and Bacteroidetes and a decrease in the abundance of Firmicutes. From an ecological network analysis, E-O3, alone and in combination with N200, complicated the co-occurrence network of bacterial communities by inducing a microbial survival strategy, shifting the hub species from RB41 to Bacillus and Blastococcus. Conversely, N200 led to simplification and decentralization of the co-occurrence network. These findings demonstrate that the rhizosphere bacterial communities exhibit divergent responses to E-O3 and N200, suggesting the need to consider the stability of the belowground ecosystem to optimize plantation management in response to environmental changes.

Trading tree growth for soil degradation: Effects at 10 years of black plastic mulch on fine roots, earthworms, organic matter and nitrate in a multi-species riparian buffer

This study assessed the effects of two vegetation management treatments (black polyethylene mulch and a control treatment) on tree growth, fine root biomass of trees and of competing vegetation, earthworms, and physiochemical soil properties in a 10 year-old agricultural riparian buffer planted in southern Québec (Canada) with five trees species: Populus × canadensis Moench (hybrid poplar), Fraxinus pennsylvanica Marsh. (red or green ash), Quercus macrocarpa Michx. (bur oak), Quercus rubra L. (red oak), and Pinus strobus L. (eastern white pine). Vegetation management treatments had a significant effect on tree growth, fine root biomass, earthworms and on many soil properties. Overall, the use of plastic mulch increased tree growth in all species (not to the same extent), but locally decreased soil organic matter, total soil carbon, total soil nitrogen, earthworm biomass and abundance, competing vegetation fine root biomass and the biomass of the total pool of fine roots. Also, more than three times more soil nitrate was measured under mulch despite the higher tree growth. Lower soil phosphorus availability (in some species), base cation saturation and moisture content under the mulch suggested higher uptake of these soil resources to sustain high tree growth. Across treatments and species, significant and strong correlations were observed between total fine root biomass and soil carbon, between competing vegetation fine root biomass and earthworm biomass, and between total soil carbon and earthworm biomass. These highlight the central role of the total pool of fine roots in maintaining or enhancing soil carbon, the importance of understory herbaceous vegetation for earthworm populations and the importance of organic matter as a factor limiting earthworm activity. Species × Treatment interactions were observed on tree growth, fine roots, and earthworms. Pine growth was little enhanced by the mulch and its fine root biomass peaked in the control treatment, suggesting plasticity in allocation to fine roots in response to resource limitations. Pine had similar earthworm biomass across both vegetation management treatments, with two to three times less earthworm biomass than other tree species observed in control plots, reflecting its low needle litter quality. Only poplar and ash had higher tree fine root biomass under the mulch. Red oak was the species the most negatively affected by herbaceous competition. In practice, plastic mulch is rarely removed from tree plantation sites. This should change in a context where plastic mulch is increasingly used as an alternative to herbicide, and where riparian agroforestry projects need to meet both timber and non-timber objectives (carbon sequestration in the soil and in tree biomass, N and P storage in woody biomass, soil quality restoration), while minimizing their impacts in terms of nitrate leaching. Identifying alternative mulching materials and strategies that would provide high growth benefits without degrading the soil or water quality is a priority to optimize ecosystem services provision in tree plantations and riparian buffers.

The effect of cutting technique on the mortality and resprouting vigor of poplar stumps in short-rotation plantations

Mechanical felling is the most cost-effective solution for harvesting short-rotation poplar plantations, but the damage inflicted by conventional shear-cutting devices on tree stumps has raised concerns about stump mortality and resprouting vigor, both of which are crucial to coppice regeneration. To determine whether such concerns are justified, this experiment monitored the survival and resprouting vigor of 11 sample blocks composed of two 10-stump row segments that were cut according to one of two methods: (1) a chainsaw or (2) an excavator-mounted shear. The sample blocks were located within the same plantation, established 7 years earlier with hybrid poplars (Populus nigra × Populus deltoides) belonging to the AF8 clone. One year after cutting, no differences were found between treatments in terms of stump mortality, number of shoots per stump, shoot diameter at 30 cm from the insertion, or shoot height. These results support the use of mechanical shears to fell short-rotation poplar coppice. However, further studies should be conducted on multiple fields and clones in order to safely generalize these preliminary findings.

Carbon Budget of an Agroforestry System after Being Converted from a Poplar Short Rotation Coppice

Poplar (Populus L. spp.) Short Rotation Coppice systems (SRCs) for bioenergy production are being converted back to arable land. Transitioning to Alley Cropping Systems (ACSs) could be a suitable strategy for integrating former tree rows and arable crops. A field trial (Pisa, Central Italy) was set up with the aim of assessing the C storage of an ACS system based on hybrid poplar and sorghum (Sorghum bicolor L. Moench) and comparing it with that of an SRC cultivation system. The carbon budget at the agroecosystem scale was assessed in the first year of the transition using the net biome production (NBP) approach with a simplified method. The overall NBP for the SRC was positive (96 ± 40 g C m−2 year−1), highlighting that the system was a net carbon sink (i.e., NBP > 0). However, the ACS registered a net C loss (i.e., NBP < 0), since the NBP was −93 ± 56 g C m−2 year−1. In the first year of the transition, converting the SRC into an ACS counteracted the potential beneficial effect of C storage in tree belowground biomass due to the high heterotrophic respiration rate recorded in the ACS, which was fostered by the incorporation of residues and tillage disturbance in the alley. Additional years of heterotrophic respiration measurements could allow for an estimate of the speed and extent of C losses.

Comparative analysis of SNP data and hybrid taxa information by using a classificatory linear mixed model to study the genetic variation and heritability of initial height growth in selected poplar hybrids

Advances in genomics increase the possibility of using SNP markers in selecting new parental genotypes for poplar breeding or new poplar varieties for commercial deployment. Here, we use a classificatory linear mixed model and a quantitative genetic approach for the combined analysis of SNP and phenotypic data from poplar hybrids at the beginning of their testing program. The main objective was to compare genetic parameters estimated based on two classification criteria: original (hybrid) taxa and SNP clustering. Height growth measurements obtained in three consecutive years from a poplar trial planted in 2002 in the center of Chile were included. In 2016, DNA was extracted from leaves of the same hybrids and genotyped by sequencing. An increasing number of clusters based on the similarity of SNP information was obtained. Broad sense heritability values observed at all levels of genomic clustering were larger than the only estimate obtained by using the original taxa classification. Thus, the method can help to predict a higher genetic gain in the early selection of poplars, based on initial height growth. The method did not affect the accuracy of the heritability estimation. The systematic increment in the intra-clonal covariance with the clustering level also suggests a highly positive genotype-by-time interaction effect at high levels of SNP clustering, which can also be positive for selection purposes. We concluded that the use of SNP clustering allowed the expression of larger genetic differences among hybrids in initial height growth, regardless of the original hybrid taxa.

Қазақстандық терек будандарын көбейту әдістері

The combination of clonal micropropagation method with container growing allows accelerating the provision of elite planting material of poplar hybrids for forestry needs. The object of the study was poplar hybrids obtained in Kazakhstan during hybridization: Kazakhstani, 1967, Excellent, 39/64, 1/86. To obtain aseptic plants of poplar hybrids in an in vitro culture, first thoroughly washed with a soap solution, then the most effective was to use as a sterilizing agent Belizna (1:1) 10 min, 70% ethyl alcohol 5 min, 0.1% mercuric chloride (HgCl2) 5 min. Rinse thoroughly 3 times with sterile distilled water. After these procedures, 3 times were thoroughly washed with sterile distilled water. In addition to saprophytic microflora, pathogenic microflora can develop in plants, which does not die during sterilization. During cloning, the basal portion of explants, sterile from saprophytic microflora was also tested for infectious microflora using VISS medium. The Murasige and Skoog medium was optimal for intensive growth and propagation of explants of poplar shoots with a slight change: vitamin B1 0.5 mg/l, BAP cytokinin – 0.1 mg/l, gibberellic acid (HA) – 0.02 mg/l, replacement sucrose glucose 20 g/l. Intensive root (95 %) formation of shoots of poplar hybrids was noticeable on the nutrient medium Woody Plant Medium c NUC 0,2 mg/l. The shoots of all hybrids rooted 95%. The shoots showed a high survival rate when transferred in vivo to a soil substrate with a composition of 10% sand, 40% peat, 50% chernozem.Key words: poplar, micropropagation, shoots, hybrids, in vitro, in vivo introduction, explant. 

Soil nutrient availability and microclimate are influenced more by genotype than by planting stock type in hybrid poplar bioenergy buffers on farmland

Bioenergy buffers planted with fast-growing woody crops such as hybrid poplars (Populus spp.) are increasingly integrated into agricultural land to enhance the provision of ecosystem services. Genotype and planting stock type selection may influence buffer establishment success and soil properties, which may affect buffer functions such as soil nutrient removal, hydrological regulation (i.e. soil dewatering) or local climate regulation (i.e. temperature reduction). This farm-scale study tested the effects of two unrelated hybrid poplar genotypes (P. deltoides × P. nigra, genotype D × N-3570 and P. maximowiczii × P. balsamifera, genotype M × B-915311) and two planting stock types (unrooted whips and bare-root stocks) on biomass growth, soil nutrient availability and soil microclimate in 15 m wide bioenergy buffers located downslope of hayfields in the cold temperate region of southern Québec, Canada. Poplar genotype had an important effect on biomass growth, soil microclimate and the supply rates of several macronutrients and micronutrients, while planting stock type had little effect on these variables. The P. maximowiczii × P. balsamifera genotype produced the highest biomass and had generally lower nutrient availability in the soil, but not for soil NO3, which was less available under the P. deltoides × P. nigra genotype. Compared to the hayfield soils, only the P. maximowiczii × P. balsamifera genotype maintained a lower supply rate of available P in the buffer soil. Compared to the hayfield soils, NH4 supply rates were lower in the buffers for both genotypes, while NO3 supply rates were similar or higher. Both genotypes had the capacity to maintain cooler soil temperatures and lower moisture content in the soil of the buffer compared to the adjacent hayfields, but this capacity was greater for the P. maximowiczii × P. balsamifera genotype. Because plant-soil interactions are strongly affected by hybrid poplar genetics, genotype selection is an important consideration in the design of multifunctional agricultural buffers. In temperate agroecosystems, future studies should try to identify productive poplar genotypes that would decrease topsoil NO3 and P availability and reduce soil water content in order to minimize potential N and P losses from buffer soils during runoff events.

Soil respiration and net ecosystem productivity in a chronosequence of hybrid poplar plantations

Forest stand age can affect ecosystem carbon (C) cycling and net ecosystem productivity (NEP). In Canada, establishment of short-rotation plantations on previously agricultural lands has been ongoing, but the effect of stand development on soil respiration (Rs) and NEP in such plantations is poorly understood. These types of data are essential for constraining ecosystem models that simulate C dynamics over the rotation of a plantation. We studied Rs (including autotrophic, Ra, and heterotrophic, Rh) and NEP in 2008 and 2009 in a chronosequence of 5-, 8-, 14-, and 16-yr-old (ages in 2009) hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) plantations in northern Alberta. The highest Rs and NEP were generally found in the 14-yr-old stand. Seasonal variations in Rs were similar among the plantations, with most of the variation explained by soil temperature at the 10 cm depth in 2008 with far less explained in 2009, a much drier year. In diurnal measurements, hysteresis was found between soil respiration and soil temperature, with the patterns of hysteresis different among stand ages. Soil respiration in the 14-yr-old plantation had the greatest sensitivity to temperature changes. Stand age did not affect the Rh:Rs ratio, whereas the NEP exhibited strong inter-annual variability. We conclude that stand age was a major factor affecting Rs and NEP, and such effects should be considered in empirical models used to simulate ecosystem C dynamics to evaluate potentials for C sequestration and the C source–sink relationship in short-rotation woody crop systems.

First Report of Erysiphe adunca Causing Foliar Powdery Mildew on Poplar in China

Hybrid poplars are important economic plants and sources of biofuel all over the world. Poplars are subjected to a wide range of diseases (Cellerino 1999). In September 2019, powdery mildew was observed on the hybrid poplar Populus davidiana × P. alba var. pyramidalis, a fast-growing elite poplar cultivar widely planted in the northeast of China, in one poplar nursery room in the Northeast Forestry University in China (45.7266°N, 126.6380°E). Disease incidence during September and October was only 5 to 15% but gradually increased to 100% during November and December. The symptom of white circular powdery spots with diameters of up to 12 mm appeared on the upper surface of the mature leaves of poplar plants over 40 days old. Under nursery conditions (50 to 65% humidity, 20 to 25°C, and 16-h/8-h day/night cycles), the diameter of a mildew spot could develop from merely visible to 10 mm in 3 days. The mildew site was observed with a stereomicroscope (Leica DVM6S, Germany). A single fungal species demonstrating characteristics of the obligate pathogens Erysiphe spp. was observed. The conidiophores grew straight upward on the leaf surface until reaching 102 to 165 μm in length (n = 30). Then, even-looking, ellipse-shaped conidia were developed, forming a singular, curved string of up to tens of conidia, on top of each conidiophore. Conidia (n = 30) measured 29.4 to 35.1 × 18.1 to 21.0 μm. Appressoria were lobed or nipple-shaped and appeared in pairs or singular. The germ tubes were slightly curly unbranched tubes pointing at one direction near the long axis of the conidium. We carefully collected the mildew by scraping it off the upper surfaces of fresh diseased leaves with a scalpel and extracted the genomic DNA. The internal transcribed spacer rDNA region was amplified according to the method of Siahmard et al. (2017). The resulting nucleotide sequence (deposited in GenBank as MN998572) displayed 99.84% identity with that of Erysiphe adunca (KY653179.1). Hence, we identified the causal pathogen of this poplar powdery mildew as an E. adunca strain. Furthermore, an Mcm7 sequence (deposited as MN998573) and a Chs sequence (deposited as MN998574) were cloned according to the method of Ellingham et al. (2019). A voucher specimen and the sequence information have been deposited in the Northeast Forestry University Culture Collection (NECC) and named as NECCFP001. Pathogenicity was tested in the nursery, by merely placing healthy 40-day-old plants next to diseased plants (n = 10, with a 15 cm distance between plants), and by pressing the mildew sites of diseased leaves onto each mature leaf of the healthy plants (n = 10, also with 15 cm distance). The same symptoms appeared on heathy plants after 10 to 15 days, and 6 to 8 days, respectively. The induced mildew was confirmed morphologically to be NECCFP001 by microscopic examination. E. adunca occurs on aspen, willow, and Populus spp. throughout temperate regions of the Northern Hemisphere and forms fruiting bodies (chasmothecia) to overwinter (Horst 2001; Sinclair and Lyon 2005). However, chasmothecia were not observed in our case, suggesting no sexual morph under the nursery conditions. Incidents of powdery mildew on hybrid poplars caused by Phyllactinia populi had been reported in Jiangsu and Shandong provinces of China (Zhao et al. 2013). This is the first report of E. adunca causing poplar powdery mildew in Heilongjiang, China.

PtKTI12 genes influence wobble uridine modifications and drought stress tolerance in hybrid poplar.

The multisubunit Elongator complex plays key roles in transcription by interacting with RNA polymerase II and chromatin modeling. Kti proteins have been identified as the auxiliary protein for the Elongator complex. However, our knowledge of Kti proteins in woody plants remains limited. In this study, in total 16 KTI gene homologs were identified in Populus trichocarpa. Among them, the two KTI12 candidates were named PtKTI12A and PtKTI12B. Although PtKTI12A and PtKTI12B were largely different in gene expression level and tissue specificity, both genes were induced by heat and drought stresses. PtKTI12A and PtKTI12B RNAi transgenic poplar plants showed reduced levels of modified nucleosides, in particular 5-carbamoylmethyluridine and 5-methoxycarbonylmethyl-2-thiouridine. Meanwhile, their tolerance to drought was improved when subjected to withdrawal of watering. Also, the protein products of PtKTI12A and PtKTI12B had similar subcellular localization and predicted tertiary structure. The results suggest that Kti12 proteins are involved in tRNA wobble uridine modification, stress response and drought stress tolerance in hybrid poplar.

Intensive Mechanical Site Preparation to Establish Short Rotation Hybrid Poplar Plantations—A Case-Study in Québec, Canada

Because they generate more wood per area and time, short rotation plantations are likely to play an increasing role in meeting the global increase in the demand for wood fiber. To be successful, high-yield plantations require costly intensive silviculture regimes to ensure the survival and maximize yields. While hybrid poplar (Populus spp.) is frequently used in intensive, short rotation forestry, it is particularly sensitive to competition and resource levels. Mechanical site preparation is thus of great importance to create microsites that provide sufficient light levels and adequate soil water and nutrient availability. We conducted an experiment in Québec (Canada) to compare two intensive site preparation treatments commonly used to establish hybrid poplar. We compared the effects of double-blade site preparation (V-blade), mounding and a control on hybrid poplar growth and nutritional status four growing seasons after planting on recently harvested forested sites. We also evaluated the effects of site preparation and planted poplar on inorganic soil N. Our results confirmed general positive effects of site preparation on the early growth of hybrid poplar clones. After four growing seasons, survival was higher in the mounding treatment (99%) than in the V-blade (91%) and the control (48%). Saplings planted in the V-blade and in the mounding treatments had mean diameters that were respectively 91% and 155% larger than saplings planted in the control plots. Saplings were 68% taller in the mounding treatment than the control plots, but differences between the V-blade and controls were not significant. We did not detect significant effects of site preparation or the presence of planted hybrid poplar on soil inorganic N. Sapling foliar nutrient concentrations were not influenced by the site preparation treatments. Based on these results, mounding appears to be a good management approach to establish hybrid poplar plantations under the ecological conditions we have studied, as it is less likely to cause erosion because of the localized nature of the treatment. However, these environmental benefits need to be balanced against economic and social considerations.

Assessing wood properties on hybrid poplars using rapid phenotyping tools

There is a growing interest in improving wood properties through clonal selection. However, traditional methods for determining wood properties are difficult to implement at the scale required for large-scale selection programs. In this study, we used rapid phenotyping methods (i.e., drill resistance (DR) and stress wave velocity (SWV)) for assessing wood quality in a 3-year-old clonal trial containing 125 clonal poplar hybrids. These hybrids belong to interspecific crosses of Populus deltoides [D], P. trichocarpa [T], P. nigra [N], and P. maximowiczii [M]. We estimated clonal variation and correlations among DR, SWV, basic density (BD), and dynamic modulus of elasticity (MOEd). Clonal repeatabilities were moderate for all traits, but were higher for BD and DR (i.e., R2 = 0.45 and 0.46, respectively) than for SWV and MOEd (i.e., R2 = 0.30 and 0.35, respectively). Clonal mean phenotypic correlations were high between BD and DR (rc = 0.84) and between SWV and MOEd (0.87), and the clonal correlations (rg) were 0.90 and 0.96, respectively. Overall, there was a weak relation between BD and MOEd (rc = 0.23 and rg = 0.29, respectively). Results support the use of DR and SWV as tools for the selection of poplar clones oriented to improve solid wood properties.

A novel aqueous gallic acid-based natural deep eutectic solvent for delignification of hybrid poplar and enhanced enzymatic hydrolysis of treated pulp

Natural deep eutectic solvent (NADES) emerged as a promising solvent used for lignocellulosic biomass dissolution and lignin separation. In this work, we prepared an aqueous NADES from choline chloride and a type of aromatic hydrogen bond donor, gallic acid-monohydrate, according to the possible solute-solvent interactions where phenyl-based NADES possessed favorite interactions with lignin aromatic compounds. Aqueous gallic acid-based NADES induced a high lignin removal (50.0%) of poplar and enhancement of enzymatic hydrolysis yield of treated pulp (69.1%). Presence of water aided in decreasing NADES viscosity and improving mass transfer. Various characterization approaches of extracted lignin were employed to investigate changes of molecular weights, types and amounts of hydroxyl groups and crucial linkages. The aqueous gallic acid-based NADES exploited in this work exhibited desirable delignification performance. Formation of considerable hydrogen bonds and hydrophobic interactions between the aromatic gallic acid-based NADES and lignin contributed to the reduced re-aggregation and condensation of separated lignin fragments.

Structure and Monomer Ratio of Lignin in C3H and HCT RNAi Transgenic Poplar Saplings

AbstractWild type poplar hybrid (Populus alba × P. glandulosa cv‘84k′), p‐coumaroyl shikimate 3′‐hydroxylase (C3H) downregulated transgenic poplar and hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) downregulated transgenic poplar were used as experimental materials. The techniques of two‐dimensional heteronuclear single‐quantum coherence nuclear magnetic resonance (2D‐HSQC‐NMR) spectroscopy and pyrolysis coupled to gas chromatography‐mass spectrometry (Py‐GC/MS) were used for the analysis and comparison of the lignin structure and monomer ratio between the wild type poplar hybrid and transgenic plants. The results of these analyses showed that the lignin of all poplar samples contained β‐O‐4′ aryl ether linkages and their derivative substructures, resinol substructures, spirodienone substructures, phenylcoumarane substructures, p‐hydroxycinnamyl alcohol end groups, syringyl units, p‐hydroxyphenyl units, guaiacyl units, p‐hydroxybenzoate substructures, and ferulate. Downregulation of C3H and HCT in double transgenic poplar reduced the β‐O‐4′ relative content of lignin in poplar. The S unit, H unit, and S/G ratio in the C3H‐downregulated transgenic poplar were increased, while its G unit was decreased. The S unit and S/G ratio in HCT‐downregulated transgenic poplar were decreased while its G unit was increased. The C3H‐downregulated transgenic poplar was a superior material for biomass energy, pulping, and papermaking than the HCT‐downregulated transgenic poplar.

Transgenic Poplar Designed for Biofuels.

Members of the genus Populus (i.e., cottonwood, hybrid poplar) represent a promising source of lignocellulosic biomass for biofuels. However, one of the major factors negatively affecting poplar's efficient conversion to biofuel is the inherent recalcitrance to enzymatic saccharification due to cell wall components such as lignin. To this effect, there have been efforts to modify gene expression to reduce biomass recalcitrance by changing cell wall properties. Here, we review recent genetic modifications of poplar that led to change cell wall properties and the resulting effects on subsequent pretreatment efficacy and saccharification. Although genetic engineering's impacts on cell wall properties are not fully predictable, recent studies have shown promising improvement in the biological conversion of transgenic poplar to biofuels.

Over-expression of transcription factor ARK1 gene leads to down-regulation of lignin synthesis related genes in hybrid poplar \u2018717\u2019

Improving wood growth rate and wood quality are worthy goals in forest genetics and breeding research. The ARK1 gene is one member of the ARBORKNOX family in all plants, which play an essential role in the process of plant growth and development, but the mechanism associated with its gene network regulation is poorly investigated. In order to generate over-expression transgenic hybrid poplar, the agrobacterium-mediated transformation was used to obtain transgenic hybrid poplar ‘717’ plants to provide insight into the function of the ARK1 gene in poplar. Moreover, the morphology of transgenic plants was observed, and transcriptome analysis was performed to explore the ARK1 gene function. The results showed that there were significant differences in pitch, stem diameter, petiole length, leaf width, leaf length and seedling height between ARK1 transgenic seedlings and non-transgenic seedlings. The transgenic seedlings usually had multiple branches and slender leaves, with some leaves not being fully developed. The results of transcriptome analysis showed that the differentially expressed genes were involved in the growth of poplars, including proteins, transcription factors and protein kinases. Genes related to the positive regulation in plant hormone signal transduction pathways were up-regulated, and the genes related to lignin synthesis were down-regulated. The RT-qPCR analysis confirmed the expression levels of the genes involved in the plant hormone signal transduction pathways and phenylpropanoid pathway. In conclusion, the ARK1 gene had a positive regulatory effect on plant growth, and the gene’s coding enzymes related to lignin synthesis were down-regulated.

Successive organic solvent fractionation and structural characterization of lignin extracted from hybrid poplar by deep eutectic solvent for improving the homogeneity and isolating narrow fractions

Deep eutectic solvent (DES) treatment emerged as an efficient way to separate lignin at a moderate condition via acidolysis and hydrophobic interaction. In the attempt to realize lignin’s upgrading, this work employs successive organic solvent fractionation in DES-extracted lignin to obtain fragments with a narrow molecular weight distribution and relatively homogeneous structure. The polydispersity was decreased from 2.26 to 1.35. Purity and thermal stability were enhanced. Ethyl acetate-extracted lignin possessed the highest content of phenolic hydroxyls (3.23 mmol/g) but the lowest content of aliphatic hydroxyls of 1.10 mmol/g β-O-4 linkages were partly cleaved during DES separation and fragments containing more C–C bonds tended to be dissolved in ethyl acetate through hydrophobic interaction. The successive fractionation performed effectively in obtaining lignin fragments with diversity in main linkages and functional groups. This approach provided lignin fractions with versatility in preparation and application in thermos-plastics, lignin-derived carbon materials, antioxidants and aromatic fuels and chemicals.