Woody Biomass Production Research Articles

Enhanced woody biomass production in a mature temperate forest under elevated CO2

Enhanced CO2 assimilation by forests as atmospheric CO2 concentration rises could slow the rate of CO2 increase if the assimilated carbon is allocated to long-lived biomass. Experiments in young tree plantations support a CO2 fertilization effect as atmospheric CO2 continues to increase. Uncertainty exists, however, as to whether older, more mature forests retain the capacity to respond to elevated CO2. Here, aided by tree-ring analysis and canopy laser scanning, we show that a 180-year-old Quercus robur L. woodland in central England increased the production of woody biomass when exposed to free-air CO2 enrichment (FACE) for 7 years. Further, elevated CO2 increased exudation of carbon from fine roots into the soil with likely effects on nutrient cycles. The increase in tree growth and allocation to long-lived woody biomass demonstrated here substantiates the major role for mature temperate forests in climate change mitigation.

Biomass Production and Metal Remediation by Salix alba L. and Salix viminalis L. Irrigated with Greywater Treated by Floating Wetlands

As an alternative wood source for biochar and a cost-effective renewable energy source, sustainable biomass production based on fast-growing willows irrigated with treated wastewater has been explored. Salix alba L. and Salix viminalis L. were selected for assessment of their potentially high woody biomass productivity and phytoremediation efficiency when irrigated with greywater treated by floating treatment wetlands. Both Salix species produced significantly (p < 0.05) high woody biomass in the second harvest, with a significantly higher fresh woody biomass weight with higher water content (53%) for S. viminalis compared to S. alba. The dry biomass weight of S. alba was greater than of S. viminalis at the first harvest. The element accumulations in substrates changed significantly after irrigation, with greywater compared to the raw substrate following this order: Mg > Fe > Al > Cr > Mn > Cd > Cu > B. Element concentrations accumulated in twigs of S. alba following this order: Ca > Mg > Na > Mn > Zn > Fe > Al > Cd > Cu > Cr > Ni > B, but for S. viminalis the order was Ca > Mg > Mn > Zn > Na > Fe > Al > Cd > Cu > Ni > Cr > B. The accumulations of Al, B, Ca, Fe, Mg, Mn, and Ni were significantly greater in S. alba leaves compared to their twigs, which showed significantly high accumulations of Na and Zn. The accumulations of Al, B, Ca, Fe, Mg, Mn, and Na were significantly greater in S. viminalis leaves compared to their twigs.

Ectopic Expression of PtrLBD39 Retarded Primary and Secondary Growth in Populus trichocarpa.

Primary and secondary growth of trees are needed for increments in plant height and stem diameter, respectively, affecting the production of woody biomass for applications in timber, pulp/paper, and related biomaterials. These two types of growth are believed to be both regulated by distinct transcription factor (TF)-mediated regulatory pathways. Notably, we identified PtrLBD39, a highly stem phloem-specific TF in Populus trichocarpa and found that the ectopic expression of PtrLBD39 in P. trichocarpa markedly retarded both primary and secondary growth. In these overexpressing plants, the RNA-seq, ChIP-seq, and weighted gene co-expression network analysis (WGCNA) revealed that PtrLBD39 directly or indirectly regulates TFs governing vascular tissue development, wood formation, hormonal signaling pathways, and enzymes responsible for wood components. This regulation led to growth inhibition, decreased fibrocyte secondary cell wall thickness, and reduced wood production. Therefore, our study indicates that, following ectopic expression in P. trichocarpa, PtrLBD39 functions as a repressor influencing both primary and secondary growth.

Contrasting drivers of aboveground woody biomass and aboveground woody productivity in lowland forests of Colombia

The relative importance of abiotic and biotic factors in shaping forest biomass stocks and fluxes remains a controversial issue. Here, using data gathered from 39 1 ha plots located in flooded and terra firme mature tropical lowland forests of the Amazon and Orinoquia regions of Colombia, we evaluated the importance of climate, soil fertility, and flooding, as well as tree taxonomic/phylogenetic diversity and forest structural properties, in determining the aboveground biomass stocks (AGB; Mg ha−1) and aboveground woody productivity (AWP; Mg ha−1 year−1). Using information‐theoretic multimodel inference and variance partitioning we found that forest structural features such as the number of trees with diameter at breast height ≥ 70 cm, and wood density, are the main drivers of variation in AGB. However, taxonomic diversity also contributes to AGB because it is associated with more large trees in these forests. In contrast, the key drivers of AWP in these forests were soil P and Mg concentrations, with no significant effects of diversity indices. These findings emphasize the need to include major soil cations other than N and P (e.g. Mg) in experimental studies to improve our understanding about the extent to which soil fertility can modulate increases in forest AWP due to climate change. Terra firme forests had higher AGB stocks than flooded forests, but both had similar AWP; and we found similar results for the drivers of AGB and AWP between flooded and terra firme forests. Our results provide limited evidence for strong effects of plant diversity on AGB or AWP. Therefore, we call for caution on generalizations of nature‐based initiatives aiming to preserve diversity based on maximizing carbon stocks and productivity, due to the complex nature of the processes controlling carbon accumulation and carbon fluxes in tropical forests.

Constraining long-term model predictions for woody growth using tropical tree rings.

The strength and persistence of the tropical carbon sink hinges on the long-term responses of woody growth to climatic variations and increasing CO2 . However, the sensitivity of tropical woody growth to these environmental changes is poorly understood, leading to large uncertainties in growth predictions. Here, we used tree ring records from a Southeast Asian tropical forest to constrain ED2.2-hydro, a terrestrial biosphere model with explicit vegetation demography. Specifically, we assessed individual-level woody growth responses to historical climate variability and increases in atmospheric CO2 (Ca ). When forced with historical Ca , ED2.2-hydro reproduced the magnitude of increases in intercellular CO2 concentration (a major determinant of photosynthesis) estimated from tree ring carbon isotope records. In contrast, simulated growth trends were considerably larger than those obtained from tree rings, suggesting that woody biomass production efficiency (WBPE = woody biomass production:gross primary productivity) was overestimated by the model. The estimated WBPE decline under increasing Ca based on model-data discrepancy was comparable to or stronger than (depending on tree species and size) the observed WBPE changes from a multi-year mature-forest CO2 fertilization experiment. In addition, we found that ED2.2-hydro generally overestimated climatic sensitivity of woody growth, especially for late-successional plant functional types. The model-data discrepancy in growth sensitivity to climate was likely caused by underestimating WBPE in hot and dry years due to commonly used model assumptions on carbon use efficiency and allocation. To our knowledge, this is the first study to constrain model predictions of individual tree-level growth sensitivity to Ca and climate against tropical tree-ring data. Our results suggest that improving model processes related to WBPE is crucial to obtain better predictions of tropical forest responses to droughts and increasing Ca . More accurate parameterization of WBPE will likely reduce the stimulation of woody growth by Ca rise predicted by biosphere models.

The Use of Forest Biomass for Energy Purposes in Selected European Countries

The utilization of primary and secondary woody biomass resources, despite controversies, is being promoted to reduce dependence on fossil fuels and due to the need to diversify energy sources and ensure energy security in European Union countries. Forest biomass is one of the renewable and sustainable energy sources that can be used for electricity, heat, and biofuel production. In the context of the ongoing energy crisis in Europe, an attempt was made to analyze the production and consumption of woody biomass for energy purposes (fuel wood, chips, and pellets). Specifically, an analysis of similarities between European countries in terms of biomass utilization was conducted. The analysis was complemented by a forecast of primary biomass production in selected European countries. The similarity analysis was conducted using the Ward method. Artificial neural networks (ANNs), including multi-layer feedforward perceptron (MLP) and radial basis function (RBF) models, were used to predict fuelwood extraction. The study showed that woody biomass remains an important source of bioenergy in Europe, and its significance as a strategic resource guaranteeing energy security is likely to increase. Fuel wood harvesting in Europe generally shows an upward trend, particularly in the Czech Republic, Germany, Estonia, Denmark, and the UK. A decreasing trend was observed in France, Spain, Greece, and Cyprus. The analysis revealed differences between countries in terms of woody biomass consumption. The ANN-based forecasts of fuelwood supply generally showed an increase in primary biomass harvesting.

Natural regeneration offers an effective way for large‐scale restoration of degraded lands in Tigray, Ethiopia

AbstractLand rehabilitation through exclosures has been recognized as a promising practice in the restoration of degraded drylands. This study evaluated woody species density, diversity, cover, and biomass production from three regeneration approaches (EMTs): (1) Naturally Regenerated (ENR) exclosures, (2) exclosures with Soil and Water Conservation Structures (ECNR), and (3) those enriched with exotic and local plant species in addition to SWC structures (ECP) among which empirical evidence of comparisons are lacking for appropriate decision making of which restoration strategy to promote. Primary data were collected from a total of 72 study plots located across transects laid within exclosures and in adjacent grazing areas with similar ecological condition. Interview with 331 households and focus groups was used to further understand the effects. Regression analysis revealed that the mean difference in herbaceous and canopy cover, herbaceous and woody biomass, and woody species density and diversity of the three EMTs was statistically significantly higher than in the adjacent open grazing areas. Moreover, herbaceous biomass in ECP differed significantly from that of ECNR. The results indicated that ENR and ECP equally enhanced the selected vegetation parameters. This is predominantly attributed to the comparable responsiveness of many degraded areas to natural regeneration as they do to active regeneration approaches. Implementation of natural regeneration is suitable for immediate recruitment of strategy in terms of resources, time, and meeting objectives before decisions are made for assisted models of exclosure that require massive campaigns to construct soil and water conservation structures and huge seedling production in the dryland areas.

Coppice growth traits in sand dune willow (Salix cordata) and comparisons with two common North American shrub willows used for biomass production

Among eight native North American willow species examined for coppice growth performance, the sand dune willow, Salix cordata Michx. (COR) has proved to be one of the most productive and useful for woody biomass production. In a common garden study, clones from the eastern and southwestern regions of Ontario, Canada, outperformed those from northern populations. Geographic region, populations within regions, and clones within populations all accounted for large portions of total variation in coppice growth traits that were compared with two other willows commonly used for biomass production, S. discolor Muhl. and S. eriocephala Muhl. Each species varied significantly in coppice structure and growth. The number of coppice stems per plant (coppice stem number) showed strong positive relationships to stem dry mass in 1- and 3-year-old coppices. Female COR plants were often slightly larger than male plants in this dioecious species, but these differences were not statistically significant, and provided no evidence of a reproductive cost expressed as a differential reduction in subsequent vegetative growth in female vs. male plants. This indicated that a zero sum model in which reproductive and vegetative structures compete for assimilates was not supported by our results. In all three species, clonal selection for growth and commercial biomass production, coppice stem number (not plant sex, longest stem length or corresponding basal stem diameter) was the best criteria for selecting superior willow clones.

Socioecological effects of swidden management in traditional Maya agroforests in the Selva Lacandona of Chiapas, Mexico

For millennia, Maya farmers (i.e., milperos) throughout Mesoamerica have managed milpa: sequential agroforests initiated by slashing and burning patches of secondary forest and then cultivating a diverse polyculture of trees and annual crops. To reduce greenhouse gas emissions associated with deforestation, the Mexican government and non-governmental organizations have urged milperos to cease burning. We collaborated with Maya milperos in several communities in the Montes Azules Biosphere Reserve region in Chiapas, Mexico to determine carbon retained as char in traditional milpas, carbon loss associated with burning, and effects of burning on soil quality. We found the carbon retention of char in Maya milpas (24 ± 6.5% of C in vegetation) is 4–1400% higher than other slash-and-burn agroecosystems reported in the literature. Burning resulted in significant carbon loss of 12.6 (±3.6) t C ha−1 yr−1, but this was partially mitigated by char production (3.0 [±0.6] t C ha−1 yr−1) and incomplete combustion of woody biomass. The effects of burning on soil were minimal, with the only significant changes observed being increases in pH, potassium availability, and cation exchange capacity (2, 100, and 7%, respectively). The mean residence times of charred materials were at least double that of uncharred biomass. While there is a risk that shortening fallow periods would undermine the sustainability of Maya swidden agroecology, proper management and secure land tenure can help maintain intensive production without enduring environmental degradation. The char produced in these swiddens and successional management could allow this agroforestry system to be a long-term carbon sink.

Exploring the Seasonal Dynamics and Molecular Mechanism of Wood Formation in Gymnosperm Trees.

Forests, comprising 31% of the Earth's surface, play pivotal roles in regulating the carbon, water, and energy cycles. Despite being far less diverse than angiosperms, gymnosperms account for over 50% of the global woody biomass production. To sustain growth and development, gymnosperms have evolved the capacity to sense and respond to cyclical environmental signals, such as changes in photoperiod and seasonal temperature, which initiate growth (spring and summer) and dormancy (fall and winter). Cambium, the lateral meristem responsible for wood formation, is reactivated through a complex interplay among hormonal, genetic, and epigenetic factors. Temperature signals perceived in early spring induce the synthesis of several phytohormones, including auxins, cytokinins, and gibberellins, which in turn reactivate cambium cells. Additionally, microRNA-mediated genetic and epigenetic pathways modulate cambial function. As a result, the cambium becomes active during the summer, resulting in active secondary xylem (i.e., wood) production, and starts to become inactive in autumn. This review summarizes and discusses recent findings regarding the climatic, hormonal, genetic, and epigenetic regulation of wood formation in gymnosperm trees (i.e., conifers) in response to seasonal changes.

A review on the application of machine learning in production of woody biomass from natural and planted forests

The forest is considered as a significant source of woody biomass production. Sustainable production of wood, lower emittance of CO2 from burning, and lower amount of sulfur and heavy metals are the advantages of woods rather than fossil fuels. The utilization of biomass, as an energy resource, is required four main steps of production, pretreatment, bio-refinery, and upgrading. This work reviews Machine Learning applications in the production of the woody biomass raw material in forests because investigating numerous related works concluded that there is a considerable reviewing gap in analyzing and collecting the applications of Machine Learning in the woody biomass. To fill this gap in the current work, the origin of woods is explained and the application of Machine Learning in this section is scrutinized. Then, the multidisciplinary enhancement approaches in the production of plants as well as the role of Machine Learning in each of them are reviewed. Meanwhile, the role of natural and planted forests in the production of woody biomass is explained and the application of Machine Learning in these areas is surveyed. Summarily, after analysis of numerous papers, it is concluded that Machine Learning and Deep Learning is widely utilized in the production of woody biomass to enhance the wood production quantity and quality, improve the predictions, enhance the harvesting techniques, and diminish the losses.

Are absorptive root traits good predictors of ecosystem functioning? A test in a natural temperate forest.

Trait-based approaches provide a useful framework to predict ecosystem functions under intensifying global change. However, our current understanding of trait-functioning relationships mainly relies on aboveground traits. Belowground traits (e.g. absorptive root traits) are rarely studied although these traits are related to important plant functions. We analyzed four pairs of analogous leaf and absorptive root traits of woody plants in a temperate forest and examined how these traits are coordinated at the community-level, and to what extent the trait covariation depends on local-scale environmental conditions. We then quantified the contributions of leaf and absorptive root traits and the environmental conditions in determining two important forest ecosystem functions, aboveground carbon storage, and woody biomass productivity. The results showed that both morphological trait pairs and chemical trait pairs exhibited positive correlations at the community level. Absorptive root traits show a strong response to environmental conditions compared toleaf traits. We also found that absorptive root traits were better predictors of the two forest ecosystem functions than leaf traits and environmental conditions. Our study confirms the important role of belowground traits in modulating ecosystem functions and deepens our understanding of belowground responses to changing environmental conditions.

Enhanced Photosynthetic Efficiency for Increased Carbon Assimilation and Woody Biomass Production in Engineered Hybrid Poplar

Increasing CO2 levels in the atmosphere and the resulting negative impacts of climate change have compelled global efforts to achieve carbon neutrality or negativity. Most such efforts focus on carbon sequestration through chemical or physical approaches. Harnessing the power of synthetic biology to enhance the natural ability of carbon sequestration in plants, especially non-annuals, provides a biological approach to further reduce CO2 levels in the air. Here, we selected a photorespiration bypass pathway and tested its effectiveness on photosynthetic enhancement in a hybrid poplar, INRA717-IB4. The design includes an RNAi strategy to reduce the transportation of the photorespiration byproduct, glycolate, out of chloroplast and a shunt pathway to metabolize the retained glycolate back to CO2 for fixation through the Calvin-Benson cycle. Molecular and physiological data collected from two separate growth experiments indicate that transgenic plants expressing genes in the photorespiration bypass pathway have increased photosynthetic efficiency, leading to faster plant growth and elevated biomass production. One lead transgenic event accumulated 35%–53% more above-ground dry biomass over four months of growth in a controlled environment. Our results provide a proof of concept for engineering trees to help combat climate change.

Tetraploidization promotes radial stem growth in poplars.

Somatic polyploidization often increases cell and organ size, thereby contributing to plant biomass production. However, as most woody plants do not undergo polyploidization, explaining the polyploidization effect on organ growth in trees remains difficult. Here we developed a new method to generate tetraploid lines in poplars through colchicine treatment of lateral buds. We found that tetraploidization induced cell enlargement in the stem, suggesting that polyploidization can increase cell size in woody plants that cannot induce polyploidization in normal development. Greenhouse growth analysis revealed that radial growth was enhanced in the basal stem of tetraploids, whereas longitudinal growth was retarded, producing the same amount of stem biomass as diploids. Woody biomass characteristics were also comparable in terms of wood substance density, saccharification efficiency, and cell wall profiling. Our results reveal tetraploidization as an effective strategy for improving woody biomass production when combined with technologies that promote longitudinal stem growth by enhancing metabolite production and/or transport.

The 2018 hot drought pushed conifer wood formation to the limit of its plasticity: Consequences for woody biomass production and tree ring structure.

Hot droughts are expected to increase in Europe and disturb forest ecosystem functioning. Wood formation of trees has the potential to adapt to those events by compensatory mechanisms between the rates and durations of tracheid differentiation to form the typical pattern of vital wood anatomical structures. We monitored xylogenesis and measured wood anatomy of mature silver fir (Abies alba Mill.) and Scots pine (Pinus sylvestris L.) trees along an elevational gradient in the Black Forest during the hot drought year of 2018. We assessed the kinetics of tracheid differentiation and the final tracheid dimensions and quantified the relationship between rates and durations of cell differentiation over the growing season. Cell differentiation kinetics were decoupled, and temperature and water availability signals were imprinted in the tree ring structure. The sudden decline in woody biomass production provided evidence for a disruption in carbon sequestration processes due to heat and drought stress. Growth processes of Scots pine (pioneer species) were mainly affected by the spring drought, whereas silver fir (climax species) growth processes were more disturbed by the summer drought. Our study provides novel insights on the plasticity of wood formation and carbon allocation in temperate conifer tree species in response to extreme climatic events.

The effects of stand density, standards and species composition on biomass production in traditional coppices

Traditional coppices and coppice-with-standards were widely used throughout Europe and Asia for centuries but were largely abandoned in the second half of the 19th century, especially in central and northwestern Europe. In last decades, there has been a renewed interest in traditional coppicing for nature conservation and most often, for rapid woody biomass production. However, there is little information on biomass productivity of traditional coppices and what affects it. Here, we focused on the effects of stand density, standards and tree species composition on sprout biomass production in newly restored coppices in the Czech Republic. We measured sprouts and calculated sprout biomass 7 years after the harvest from 2013 resprouting stumps in two 4 ha experimental plots. Each plot was divided into 64 subplots with different densities of standards and sprouting stumps. Total sprout biomass declined with increasing density of standards, but the effect of standards differed significantly among studied species. Whereas increasing density of standards decreased sprout biomass in Quercus petraea and Carpinus betulus, it did not affect sprout biomass productivity in Acer campestre and Tilia cordata. Sprout biomass on stand level increased linearly with increasing number of sprouting stumps and we observed no levelling of this relationship even in the highest densities of stumps. We also found significant shift in tree species composition with steeply declining relative abundance of Qurcus in favor of other studied tree species.

Allometric equations for estimating on-farm fuel production of Gliricidia sepium (Gliricidia) shrubs and Cajanus cajan (pigeon pea) plants in semi-arid Tanzania

BackgroundFuelwood is considered to be the primary source of cooking energy in Tanzania and, due to ongoing deforestation, access to fuelwood is becoming more cumbersome. On-farm agroforestry systems can reduce dependency on off-farm fuel; however, the output of on-farm produced fuel is typically uncertain as production potentials are often not known. In this paper, we have developed allometric equations to model the above-ground woody biomass (AGWB) production from intercropped Gliricidia sepium (Jacq.) Kunth ex Walp (Gliricidia) shrubs and Cajanus cajan (L.) Millsp. (pigeon pea) plants.MethodsWe used a destructive sampling approach, for measuring the dendrometric characteristics, such as the root collar diameter at a 20 cm stem height (RCD20) and the stem height to estimate the AGWB production. The models are based on 112 Gliricidia and 80 pigeon pea observations from annually pruned plants. Seven allometric equations were fitted to derive the best-fit models for the AGWB production.ResultsWe found that using a natural log-transformed linear model with RCD20 as a single predictor variable provides the highest explanatory value to estimate the AGWB production (Gliricidia: R2 = 95.7%, pigeon pea: R2 = 91.4%) while meeting Ordinary Least Square (OLS) estimator requirements. Adding stem height as an additional variable to predict the AGWB production does not improve model accuracy enough to justify the extra work for including it.ConclusionsWhile on-farm pigeon pea plants produced a stable amount of woody biomass per annum, annual fuelwood production from Gliricidia shrubs increased over the years. Compared to the annual fuelwood consumption data from the literature, our results show that on-farm produced fuelwood can substantially offset the demand for off-farm fuel, potentially resulting in household fuelwood autarky.

Woody and Foliage Biomass, Foliage Traits and Growth Efficiency in Young Trees of Four Broadleaved Tree Species in a Temperate Forest.

The main goal of this study is to analyse and interpret interspecific differences in foliage biomass/area and woody parts biomass as well as the ratio between quantities of foliage and woody components (i.e., branches, stem and roots). The study was principally aimed at determining basic biomass allocation patterns and growth efficiency (GE) of four broadleaved species, specifically common aspen (Populus tremula L.), European hornbeam (Carpinus betulus L.), silver birch (Betula pendula Roth.) and sycamore (Acer pseudoplatanus L.) in young growth stages. We performed whole-tree sampling at 32 sites located in central and northern parts of Slovakia. We sampled over 700 trees and nearly 4900 leaves to quantify biomass of woody parts and foliage traits at leaf and tree levels. Moreover, we estimated specific leaf area in three parts of the crown, i.e., the upper, middle and lower thirds. We found that hornbeam had the largest foliage biomass and the lowest foliage area of all investigated species, while its biomass of woody parts did not differ from aspen and sycamore. Birch had the lowest biomass of woody parts, although its foliage properties were similar to those of aspen. Intraspecific differences of foliage were related to tree size and to leaf position along the vertical crown profile. Growth efficiency (GE), expressed as woody biomass production per foliage area unit, was evidently larger in hornbeam than in the other three broadleaves. We suggest that future GE modelling should utilize real values of stem diameter increment measured in a current year, bio–sociological position of trees and competition indicators as inputs. Such an approach would elucidate the role of stand structure and tree species mixture for ecological and production properties of forest stands.

Multifunctions of fine root phenology in vegetative and reproductive growth in mature beech forest ecosystems

AbstractMasting, a large interannual variation of reproductive investment spatially synchronized within perennial plants, is an important factor for understanding the use and storage of carbon and nutrient resources in various forest ecosystems. Fine roots play essential roles in water and nutrient uptake but also consume a large amount of net primary production (NPP) during growth. Understanding masting mechanisms requires knowledge of how masting trees succeed in abundant fructification by adjusting resource acquisition via fine roots and how mast seeding influences fine root dynamics. The aims of the present study were to estimate interannual variations in NPP, including belowground production, over several years while evaluating fine root phenology and to suggest possible relationships between fine root growth and the production of nuts, leaves, and woody biomass in mature forest ecosystems. Nut and leaf production was quantified using litter traps in two beech forests located at different altitudes of 550 and 1500 m, and woody biomass increment was estimated using allometric equations. Seasonal and mass‐based annual fine root production was determined using minirhizotrons and soil cores. Correlations between seasonal fine root and aboveground production were analyzed using the state‐space model, which can verify masting effects on fine root production between flower bud formation and mast seeding. NPP estimates exhibited almost biennial or irregular masting behavior. Nut production was positively correlated with fine root production in autumn of the previous year in the lower site but showed negative correlations with that in the early growing season of the same year in the upper site. The former indicated enhanced fine root production to absorb nutrients prior to mast seeding, and the latter suggested the suppression of fine root production due to resource depletion during masting. Fine root production increased with increasing leaf production in the early growing season in both sites, indicating the corresponding water transport between them. Thus, fine root phenology has distinct multiple functions to ensure water and nutrient resources in supporting aboveground vegetative and reproductive growth, resulting in variable seasonal patterns of fine root production.

Field evaluation of transgenic hybrid poplars with desirable wood properties and enhanced growth for biofuel production by bicistronic expression of PdGA20ox1 and PtrMYB3 in wood-forming tissue

BackgroundTo create an ideotype woody bioenergy crop with desirable growth and biomass properties, we utilized the viral 2A-meidated bicistronic expression strategy to express both PtrMYB3 (MYB46 ortholog of Populus trichocarpa, a master regulator of secondary wall biosynthesis) and PdGA20ox1 (a GA20-oxidase from Pinus densiflora that produces gibberellins) in wood-forming tissue (i.e., developing xylem).ResultsTransgenic Arabidopsis plants expressing the gene construct DX15::PdGA20ox1-2A-PtrMYB3 showed a significant increase in both stem fresh weight (threefold) and secondary wall thickening (1.27-fold) relative to wild-type (WT) plants. Transgenic poplars harboring the same gene construct grown in a greenhouse for 60 days had a stem fresh weight up to 2.6-fold greater than that of WT plants. In a living modified organism (LMO) field test conducted for 3 months of active growing season, the stem height and diameter growth of the transgenic poplars were 1.7- and 1.6-fold higher than those of WT plants, respectively, with minimal adverse growth defects. Although no significant changes in secondary wall thickening of the stem tissue of the transgenic poplars were observed, cellulose content was increased up to 14.4 wt% compared to WT, resulting in improved saccharification efficiency of the transgenic poplars. Moreover, enhanced woody biomass production by the transgenic poplars was further validated by re-planting in the same LMO field for additional two growing seasons.ConclusionsTaken together, these results show considerably enhanced wood formation of our transgenic poplars, with improved wood quality for biofuel production.