Populus Genotypes Research Articles

Willow, Poplar, and Black Locust Debarked Wood as Feedstock for Energy and Other Purposes

Solid biomass can be used for energy generation and the production of various renewable bioproducts. The aim of this study was to determine the yield and characteristics of wood obtained as debarking residue from 14 genotypes of short-rotation woody crops (SRWCs). These included five Populus genotypes, one Robinia genotype, and eight Salix genotypes, harvested in both annual and quadrennial cycles. The results showed that the highest dry wood yield (12.42 Mg ha−1 y−1 DM) and yield energy value (244.34 GJ ha−1 y−1) were obtained from willow (cultivar Żubr) harvested in a quadrennial cycle. The best effect among the poplar genotypes was achieved for the Hybryda275, and it was particularly marked in the quadrennial harvest cycle. The poorest results were determined for black locust. The Robinia characteristics included the significantly lowest moisture content (31.6%), which was a positive attribute from the energy point of view, but, on the other hand, it had some adverse characteristics—the highest levels of sulfur (0.033% DM), nitrogen (0.38% DM), and ash (0.69% DM). More beneficial properties in this respect were determined for willow and poplar wood. Moreover, willow and poplar wood contained more cellulose—51.8 and 50.0% DM, respectively—compared with black locust. Extending the SRWC shoot harvest cycle from annual to quadrennial resulted in an increase in cellulose, lignin, and carbon, higher heating value, and a decrease in nitrogen, sulfur, ash, and moisture content. Therefore, extending the harvest cycle improved the parameters of SRWC wood as an energy feedstock.

Unveiling the Molecular Arsenal: Identification and Characterization of Sphaerulina musiva Effectors Targeting Populus Genotypes.

Unveiling the Molecular Arsenal: Identification and Characterization of Sphaerulina musiva Effectors Targeting Populus Genotypes.

Genotypic and tissue-specific variation of Populus nigra transcriptome profiles in response to drought

Climate change is one of the most important challenges for mankind in the far and near future. In this regard, sustainable production of woody crops on marginal land with low water availability is a major challenge to tackle. This dataset is part of an experiment, in which we exposed three genetically differentiated genotypes of Populus nigra originating from contrasting natural habitats to gradually increasing moderate drought. RNA sequencing was performed on fine roots, developing xylem and leaves of those three genotypes under control and moderate drought conditions in order to get a comprehensive dataset on the transcriptional changes at the whole plant level under water limiting conditions. This dataset has already provided insight in the transcriptional control of saccharification potential of the three Populus genotypes under drought conditions and we suggest that our data will be valuable for further in-depth analysis regarding candidate gene identification or, on a bigger scale, for meta-transcriptome analysis.

Short rotation woody crops as a source of bioactive compounds depending on genotype and harvest cycle

Short rotation woody crops (SRWC) are one of the available sources of renewable feedstock which can be used in the medical, chemical and power industries. The current study evaluated the usability of the bark from different SRWC genotypes as a source of bioactive compounds. The specific objectives were to determine the concentrations of six bioactive substances in bark, bark yield and potential bioactive substance yield. A two-factorial field experiment was carried out in north-eastern Poland and comprised 14 SRWC genotypes, including one Robinia genotype, five Populus genotypes, seven clones and one variety of the genus Salix and two cycles of biomass harvest: annual and quadrennial. The genetic variability had a significant impact on the qualitative and quantitative composition of the bioactive substances in the bark of the studied SRWC, whereas the biomass harvest cycle determined the quantitative concentration of individual bioactive substances. Extending the biomass harvest rotation decreased the mean concentration of the substances under analysis by ca. 20%. The highest total concentration of bioactive substances was found in poplar bark obtained from P. balsamifera. Among the six studied bioactive substances, the highest mean concentration was determined for salicin (20.61 mg g−1 d.m.), followed by salicortin (12.58 mg g−1 d.m.). A significantly lower concentration was determined for salicylic acid (2.74 mg g−1 d.m.) and salireposide (2.51 mg g−1 d.m.), whereas kaempferol and quercetin were determined in trace amounts. The total potential yield of the analyzed bioactive compounds varied significantly, both with respect to genetic variability and biomass harvest cycle.

Differences in Environmental and Hormonal Regulation of Growth Responses in Two Highly Productive Hybrid Populus Genotypes

Phenotypic plasticity, in response to adverse conditions, determines plant productivity and survival. The aim of this study was to test if two highly productive Populus genotypes, characterised by different in vitro etiolation patterns, differ also in their responses to hormones gibberellin (GA) and abscisic acid (ABA), and to a GA biosynthesis inhibitor paclobutrazol (PBZ). The experiments on shoot cultures of ‘Hybrida 275′ (abbr. H275; Populus maximowiczii × P. trichocarpa) and IBL 91/78 (Populus tremula × P. alba) were conducted by either modulating the physical in vitro environment or by adding specific chemicals to the nutrient medium. Our results revealed two main sets of differences between the studied genotypes in environmental and hormonal regulation of growth responses. First, the genotype H275 responded to darkness with PBZ-inhibitable shoot elongation; in contrast, the elongation of IBL 91/78 shoots was not affected either by darkness or PBZ treatment. Secondly, the explants of H275 were unable to recover their growth if it was inhibited with ABA; in contrast, those of IBL 91/78 recovered so well after the temporal inhibition by ABA that, when rooted subsequently, they developed longer shoots and roots than without a previous ABA treatment. Our results indicate that GA catabolism and repressive signalling provide an important pathway to control growth and physiological adaptation in response to immediate or impending adverse conditions. These observations can help breeders define robust criteria for identifying genotypes with high resistance and productivity and highlight where genotypes exhibit susceptibility to stress.

A k-mer based approach for classifying viruses without taxonomy identifies viral associations in human autism and plant microbiomes

Viruses are an underrepresented taxa in the study and identification of microbiome constituents; however, they play an essential role in health, microbiome regulation, and transfer of genetic material. Only a few thousand viruses have been isolated, sequenced, and assigned a taxonomy, which limits the ability to identify and quantify viruses in the microbiome. Additionally, the vast diversity of viruses represents a challenge for classification, not only in constructing a viral taxonomy, but also in identifying similarities between a virus’ genotype and its phenotype. However, the diversity of viral sequences can be leveraged to classify their sequences in metagenomic and metatranscriptomic samples, even if they do not have a taxonomy. To identify and quantify viruses in transcriptomic and genomic samples, we developed a dynamic programming algorithm for creating a classification tree out of 715,672 metagenome viruses. To create the classification tree, we clustered proportional similarity scores generated from the k-mer profiles of each of the metagenome viruses to create a database of metagenomic viruses. The resulting Kraken2 database of the metagenomic viruses can be found here: https://www.osti.gov/biblio/1615774 and is compatible with Kraken2. We then integrated the viral classification database with databases created with genomes from NCBI for use with ParaKraken (a parallelized version of Kraken provided in Supplemental Zip 1), a metagenomic/transcriptomic classifier. To illustrate the breadth of our utility for classifying metagenome viruses, we analyzed data from a plant metagenome study identifying genotypic and compartment specific differences between two Populus genotypes in three different compartments. We also identified a significant increase in abundance of eight viral sequences in post mortem brains in a human metatranscriptome study comparing Autism Spectrum Disorder patients and controls. We also show the potential accuracy for classifying viruses by utilizing both the JGI and NCBI viral databases to identify the uniqueness of viral sequences. Finally, we validate the accuracy of viral classification with NCBI databases containing viruses with taxonomy to identify pathogenic viruses in known COVID-19 and cassava brown streak virus infection samples. Our method represents the compulsory first step in better understanding the role of viruses in the microbiome by allowing for a more complete identification of sequences without taxonomy. Better classification of viruses will improve identifying associations between viruses and their hosts as well as viruses and other microbiome members. Despite the lack of taxonomy, this database of metagenomic viruses can be used with any tool that utilizes a taxonomy, such as Kraken, for accurate classification of viruses.

Obtaining mutants of highly productive genotypes of Populus × canescens using the method of induced mutagenesis in vitro

Obtaining mutants of highly productive genotypes of Populus × canescens using the method of induced mutagenesis in vitro

Comparative transcriptome analyses define genes and gene modules differing between two Populus genotypes with contrasting stem growth rates

BackgroundWood provides an important biomass resource for biofuel production around the world. The radial growth of tree stems is central to biomass production for forestry and biofuels, but it is challenging to dissect genetically because it is a complex trait influenced by many genes. In this study, we adopted methods of physiology, transcriptomics and genetics to investigate the regulatory mechanisms of tree radial growth and wood development.ResultsPhysiological comparison showed that two Populus genotypes presented different rates of radial growth of stems and accumulation of woody biomass. A comparative transcriptional network approach was used to define and characterize functional differences between two Populus genotypes. Analyses of transcript profiles from wood-forming tissue of the two genotypes showed that 1542, 2295 and 2110 genes were differentially expressed in the pre-growth, fast-growth and post-growth stages, respectively. The co-expression analyses identified modules of co-expressed genes that displayed distinct expression profiles. Modules were further characterized by correlating transcript levels with genotypes and physiological traits. The results showed enrichment of genes that participated in cell cycle and division, whose expression change was consistent with the variation of radial growth rates. Genes related to secondary vascular development were up-regulated in the faster-growing genotype in the pre-growth stage. We characterized a BEL1-like (BELL) transcription factor, PeuBELL15, which was up-regulated in the faster-growing genotype. Analyses of transgenic Populus overexpressing as well as CRISPR/Cas9-induced mutants for BELL15 showed that PeuBELL15 improved accumulation of glucan and lignin, and it promoted secondary vascular growth by regulating the expression of genes relevant for cellulose synthases and lignin biosynthesis.ConclusionsThis study illustrated that active division and expansion of vascular cambium cells and secondary cell wall deposition of xylem cells contribute to stem radial increment and biomass accumulation, and it identified relevant genes for these complex growth traits, including a BELL transcription factor gene PeuBELL15. This provides genetic resources for improving and breeding elite genotypes with fast growth and high wood biomass.

Aphid Gall Interactions with Forest Tree Genotypes Influence Leaf Litter Decomposition in Streams

Genetic variation within a dominant riparian forest tree affects susceptibility to a leaf-galling aphid (Pemphigus betae), which induces phytochemical and structural changes in leaf tissue. Research Highlights: We show here that these changes to tree leaf tissue alter adjacent in-stream leaf litter decomposition rates and the aquatic macroinvertebrate community associated with litter in the stream for some Populus genotypes. Background and Objectives: Naturally occurring hybrid cottonwoods (Populus fremontii × Populus angustifolia) are differentially susceptible to aphid attack and vary in induced phytochemistry following attack. When leaves are galled by aphids, foliar tissue is altered structurally (through the formation of pea-sized gall structures) and phytochemically (through an increase in foliar condensed tannin concentrations). Materials and Methods: To examine the effect of aphid-galled leaves on forest stream processes, we collected both galled and un-galled leaves from five clones of three hybrid cottonwood genotypes in an experimental forest. We measured in-stream litter decomposition rates, aquatic fungal biomass and aquatic macroinvertebrate community composition. Results: Decomposition rates differed among genotypes and the galled litter treatments, with a 27% acceleration of decomposition rate for the galled litter of one genotype compared to its own un-galled litter and no differences between galled and un-galled litters for the other two genotypes. Genotype by foliar gall status interactions also occurred for measures of phytochemistry, indicating a prevalence of complex interactions. Similarly, we found variable responses in the macroinvertebrate community, where one genotype demonstrated community differences between galled and un-galled litter. Conclusions: These data suggest that plant genetics and terrestrial forest herbivory may be important in linking aquatic and terrestrial forest processes and suggest that examination of decomposition at finer scales (e.g., within species, hybrids and individuals) reveals important ecosystem patterns.

Microscopic, Biochemical, and Molecular Comparisons of Moderately Resistant and Susceptible Populus Genotypes Inoculated with Sphaerulina musiva.

Sphaerulina musiva, the causal agent of Septoria leaf spot and stem canker, is responsible for mortality and yield loss in Populus plantations. However, little is known about the mode of infection and the mechanisms of resistance in this pathosystem. To characterize these phenomena, microscopic, biochemical, and transcriptome comparisons were performed between leaves of moderately resistant and susceptible genotypes of Populus inoculated with S. musiva conidia. Using scanning electron, cryofracture, and laser-scanning confocal microscopy, the infection and colonization of Populus leaves by S. musiva were examined across five time points (48 h, 96 h, 1 week, 2 weeks, and 3 weeks). The infection process was similar regardless of the host genotype. Differences in host colonization between susceptible and moderately resistant genotypes were apparent by 1 week postinoculation. However, the germination of conidia was greater on the susceptible than on the moderately resistant genotype (P < 0.008). Diaminobenzidine staining, a measure of hydrogen peroxide accumulation, was different (P < 0.001) between the host genotypes by 2 weeks postinoculation. Transcriptome differences between genotypes indicated that the speed and amplitude of the defense response were faster and more extensive in the moderately resistant genotype. Changes in gene expression support the microscopic and biochemical observations.

Contingency rules for pathogen competition and antagonism in a genetically based, plant defense hierarchy.

Plant defense against pathogens includes a range of mechanisms, including, but not limited to, genetic resistance, pathogen‐antagonizing endophytes, and pathogen competitors. The relative importance of each mechanism can be expressed in a hierarchical view of defense. Several recent studies have shown that pathogen antagonism is inconsistently expressed within the plant defense hierarchy. Our hypothesis is that the hierarchy is governed by contingency rules that determine when and where antagonists reduce plant disease severity.Here, we investigated whether pathogen competition influences pathogen antagonism using Populus as a model system. In three independent field experiments, we asked whether competition for leaf mesophyll cells between a Melampsora rust pathogen and a microscopic, eriophyid mite affects rust pathogen antagonism by fungal leaf endophytes. The rust pathogen has an annual, phenological disadvantage in competition with the mite because the rust pathogen must infect its secondary host in spring before infecting Populus. We varied mite–rust competition by utilizing Populus genotypes characterized by differential genetic resistance to the two organisms. We inoculated plants with endophytes and allowed mites and rust to infect plants naturally.Two contingency rules emerged from the three field experiments: (a) Pathogen antagonism by endophytes can be preempted by host genes for resistance that suppress pathogen development, and (b) pathogen antagonism by endophytes can secondarily be preempted by competitive exclusion of the rust by the mite. Synthesis: Our results point to a Populus defense hierarchy with resistance genes on top, followed by pathogen competition, and finally pathogen antagonism by endophytes. We expect these rules will help to explain the variation in pathogen antagonism that is currently attributed to context dependency.

Mortality of Different Populus Genotypes in Recently Established Mixed Short Rotation Coppice with Robinia pseudoacacia L.

Short rotation coppices play an increasing role in providing wooden biomass for energy. Mixing fast-growing tree species in short rotation coppices may result in complementary effects and increased yield. The aim of this study was to analyze the effect on mortality of eight different poplar genotypes (Populus sp.) in mixed short rotation coppices with three different provenances of the N-fixing tree species black locust (Robinia pseudoacacia L.). Pure and mixed stands were established at two sites of contrasting fertility. Survival of poplar was assessed for each tree two times a year, for a period of three years. In the first two years, high variation in mortality was observed between the genotypes, but no significant differences between pure and mixed stands were identified. However, three years after planting, higher mortality rates were observed in the mixtures across all poplar genotypes in comparison to pure stands. The expected advantage on growth of combining an N-fixing tree with an N-demanding tree species, such as poplar, was overshadowed by the Robinia’s dominance and competitiveness.

Poplar Transformation.

First publications of successful Agrobacterium-mediated transformation of tobacco were published more than 30 years ago. Protocols for Agrobacterium-based transformation as well as biolistic bombardment and PEG transformation of protoplasts are available for more than 150 plant species from various plant families. Also for many Populus species and hybrids, adapted transformation protocols have been published. The standard protocol for Agrobacterium-mediated transformation of different Populus genotypes is the leaf-disc method. Here, we first describe the transfer of genes into poplar by using the Agrobacterium-based leaf disc methods. In addition, alternative basic transformation methods, namely, biolistic bombardment and PEG transformation of protoplasts, are also described. Further, we present improved poplar transformation protocols by simplifying the transformation procedure and optimizing tissue preparation and plant regeneration.

Genotypic differences in biomass production during three rotations of short-rotation coppice

Short-rotation coppice (SRC) will play a major role in meeting the predicted demands for woody biomass, but data on genotype-specific biomass productivity and growth parameters are still largely missing. These data are, however, important for assessing the expected revenue, but also for predicting the choice of harvester. Therefore, an operational SRC with 12 Populus genotypes was yearly monitored over its first seven years (three rotations). Inventories of shoot diameters at 22 cm above the ground, of number of shoots per stump and stump mortality were converted to above-ground woody biomass (AGWB) with allometric relations. The dataset was based on 23,656 sampled stumps for determining the number of shoots per stump, while 36,792 shoots were measured to determine their diameter. An AGWB productivity of 3.43, 11.13, and 16.49 Mg ha−1 y−1 was reached in the first (two-year), second (two-year), and third (three-year) rotation, respectively. Within each rotation, the AGWB productivity increased yearly, while rotations (after the establishment rotation) reached comparable AGWB productivities over the same (two-year) duration. Significant genotypic and spatial variation in shoot diameters, number of shoots per stump and AGWB were found within and among the seven sampled years. Additionally, repeated sampling at breast height in the second and third year of the third rotation was comparable to sampling at 22 cm above the soil. Lastly, a shoot diameter measurement accuracy of 0.01 mm proved exagerrated for biomass assessments and could be limited to an accuracy of 1 mm.

Differences in Al sensitivity affect establishment of Populus genotypes on acidic forest land.

Forest lands hold great potential for Populus plantations, but in native boreal forests, soils normally have low pH and thus higher levels of aluminum ions (Al3+ and hydroxides). Aluminum (Al) is one of the major factors limiting plant growth on these soils by inhibiting root growth, thus reducing water and nutrient uptake and slowing growth. There is a large variation in Al resistance both among and within species. In this study, growth responses of greenhouse-grown hybrid aspen (P. tremula × tremuloides) and poplar (P. trichocarpa hybrids) were monitored in relation to changes in Al concentrations. In quartz sand, hybrid aspen was more tolerant to exogenous application of Al than P. trichocarpa hybrids. This difference in Al-tolerance was further confirmed by hematoxylin staining of the roots, with hybrid aspen displaying less staining after Al treatment than poplar clones. When planted on forest land with low pH, hybrid aspen increased growth after planting and showed low mortality. This was not the case for poplar clones; plant height decreased after planting and mortality increased. Together, our results suggest that differences in initial growth and survival on forest land among hybrid aspen and the tested poplar clones may be connected to differences in Al tolerance. Our findings that staining with hematoxylin can identify Al-tolerant Populus genotypes may help identify Al-tolerant genotypes suitable for forest land.

THE APPLICATION OF METHODS OF IN VITRO TISSUE CULTURE FOR PROPAGATION OF CULTIVARS OF THE POPULUS × СANADENSIS MOENCH

The development of an effective technology of mass reproduction of fungal and bacterial diseases-free plants of the cultivars Populus × canadensis Moench, valuable in the plantation aspect, is one of the urgent tasks of today. At present, microcloning of valuable genotypes of genus Populus L. is carried out both by foreign and domestic scientists. Currently, the scientific literature does not contain protocols on micropropagation of investigated plants. The aim of the study was to develop a method of introduction the cultivars P. × canadensis 'Tardif de Champagne', P. × canadensis 'Ι-45/51', P. × canadensis 'Dorskamp', P. × canadensis 'Robusta' and P. × canadensis 'Blanc du Poitou' to in vitro culture for their mass microclonal reproduction. The parts of one-year shoots 10‑20 cm long harvested from 20-year-old cultivars in the spring-summer period of 2017 were used for research. The following methods were used: statistical, in vitro plant tissue culture. The conditions for obtaining a significant number of aseptic viable explants in the spring-summer period have been established. The optimal conditions for induction of callus formation in leaf blade tissues of cultivars P. × canadensis 'Tardif de Champagne', P. × canadensis 'Dorskamp' and P. × canadensis 'Blanc du Poitou' with a frequency of more than 90 % and active growth of tissues were created on MS medium with the addition of 1.0 mg·L -1 BAP and 0.5 mg·L -1 NAA and during the cultivation in a thermostat without light. An active microshoots formation by direct morphogenesis in the tissues of leaf blades of cultivars P. × canadensis 'Tardif de Champagne', P. × canadensis 'Ι-45/51', P. × canadensis 'Dorskamp', P. × canadensis 'Robusta' was fixed on MS medium modified with 1.0 mg·L -1 BAP and 0.5 mg·L -1 NAA in bright light mode. An actively growing microshoots of stem origin of the cultivar P. × canadensis 'Tardif de Champagne' were obtained on MS medium with 0.1 mg·L -1 BAP and 1.0 mg·L -1 IAA and 7.5 mg·L -1 glucose. The further studies are aimed at obtaining stably growing in vitro cultures of cultivars P. × canadensis 'Tardif de Champagne', P. × canadensis 'Ι-45/51', P. × canadensis 'Dorskamp', P. × canadensis 'Robusta' and P. × canadensis 'Blanc du Poitou' on modified basic nutrient medium for mass microclonal propagation with the following adaptation to the conditions in vitro .

Growth response of hybrid aspen (Populus × wettsteinii) and Populus trichocarpa to different pH levels and nutrient availabilities

Populus plantations are mainly established on agricultural land, but natural forests soils typically have lower pHs and nutrient contents. In this study, growth responses of two commonly used Populus genotypes, hybrid aspen (Populus × wettsteinii Hamet-Ahti) and black cottonwood (Populus trichocarpa Torr. & A. Gray ex Hook.), were monitored in the greenhouse in relation of changes in pH and fertilizer levels in quartz sand and forest moraine soil. In quartz sand, changes in pH had no impact on growth or mortality of the two species. In forest soils, the lowest pH values, i.e., 3.5 and 4.0, caused plant mortality for P. trichocarpa but not for P. × wettsteinii. Growth optimum of P. trichocarpa occurred at a pH range of 5.5–6.5, whereas P. × wettsteinii showed a broader growth optimum at a pH range of 4.0–7.0. Fertilization expanded the pH range of optimum growth for P. trichocarpa but not for P. × wettsteinii. In both species, foliar content of nitrogen and potassium content increased after fertilization, ...

Coupling aquaculture with forest plantations for food, energy, and water resiliency

Freshwater aquaculture and forest bioenergy markets are expanding globally in areas concurrently experiencing human population growth, urbanization and water shortages. Coupling these agroecosystems can improve food, energy, and water resiliency by enhancing ecosystem services through fertilization, water-reuse, carbon storage, and bioenergy via biomass production. This study evaluated how a model aquaculture-managed forest plantation could (1) provision fish and woody biomass; (2) regulate carbon, groundwater infiltration, and groundwater quality; and (3) support nutrient cycling over a two-year period. A 0.5-hectare hardwood bioenergy plantation was established with 12 Populus spp. genotypes adjacent to a 0.6-hectare freshwater aquaculture operation (hybrid striped bass, Morone chrysops×M. saxatilis); pond waters were land-applied on the plantation for two years. The aquaculture operation produced ~3.5Mg of fish and trees yielded 5.9Mgha−1yr−1 of oven-dry biomass, sequestered 2.9Mg carbon (C) ha−1yr−1 and stored 0.028Mg nitrogen (N) ha−1yr−1. Biomass productivity, carbon storage, and nitrogen storage differed significantly among the evaluated Populus genotypes. Land application of pond water increased groundwater infiltration by 60% relative to the previous year. The integrated system regulated chlorophyll a, total organic carbon, and nitrogen in groundwater at concentrations below regulatory limits. This study demonstrated that coupled agroecosystems could deliver productive yields of food and bioenergy as well as support water re-use while meeting water quality regulations. More research is needed to evaluated long-term sustainability and economic viability of this coupled system and other land management practices that seek to improve food, energy, and water resiliency.

Sub-Soiling and Genotype Selection Improves Populus Productivity Grown on a North Carolina Sandy Soil

This study reports the stem volume of 10 Populus genotypes in a randomized split-plot design with different tillage treatments (disking versus sub-soiling) after two years of growth. Height, diameter at breast height (DBH), stem aboveground volume index, survival, Melampsora rust resistance, leaf area index (LAI), chlorophyll content, and foliar nitrogen concentration (Foliar N) were measured to identify how tillage treatments might alter poplar growth. Stem volume index and LAI were positively correlated and differed significantly among tillage treatments, taxa, and genotypes. Melampsora rust resistance was also positively correlated with volume index, but significant differences were only detected among taxa and genotypes. Foliar N and chlorophyll did not correlate to stem volume for genotypes or tillage treatments. Overall, sub-soiling yielded 37% more estimated volume compared to disking. Within the sub-soiled treatments, four genotypes (140, 176, 185, and 356) had high survival (&gt;80%) and produced substantial stem volume (&gt;32 dm3·tree−1). These findings show that tillage practices do impact poplar stem volumes after two years and that sub-soiling improves productivity for poplar short rotation woody crops on loamy fine-sandy soils.

Effect of short rotation coppice plantation on the performance and chips quality of a self-propelled harvester

The performance of coppice harvesting machines is influenced by parameters such as field yield, the shape and size of the plantation and the space for turning at the headland. The quality of chips and the effect of the dendrometric characteristic of nine different species (Fraxinus angustifolia, Robinia pseudoacacia, Salix alba, Eucalyptus occidentalis, Populus nigra L. and four genotypes of Populus x euroamericana (Grimminge, Hoogvorst, Muur, Vesten) grown in the same flat plot of about 4.5 ha on the performance rate and quality of the work, was evaluated. Field yields ranged from 33 t ha−1 to ∼95 t ha−1, for the S. alba and E. occidentalis, respectively. The harvester worked with an average speed of 0.91 m s−1 (±0.22) and average productivities of 0.98 ha h−1 (±0.24) and 45.25 t h−1 (±5.56). There was a satisfactory linear correlation between the working speed of the machine and field yield. The quality of the chips showed some variability with values of moisture content ranging between 42.7% and 57.3% (for R. pseudoacacia and S. Alba respectively) and values of bulk density from 273 kg m−3 to 313 kg m−3 (for Populus euroamericana Vesten and E. occidentalis respectively).