Euramericana Cv Research Articles

Effects of site conditions on growth and wood properties of Populus × euramericana cv. ‘74/76’

Effects of site conditions on growth and wood properties of Populus × euramericana cv. ‘74/76’

Correlation Analysis of the Bacterial Community and Wood Properties of Populus × euramericana cv. "74/76" Wet Heartwood.

Wetwood disease of poplar limits the processing and manufacturing of poplar, and the pathogenic bacteria of wet heartwood are poorly known. We used high-throughput sequencing methods to analyze the bacterial community of the heartwood, sapwood, root tissue, and rhizosphere soil of Populus × euramericana cv. “74/76” (poplar 107) in wetwood trees and healthy trees to explore the cause of poplar wetwood disease. Bacterial diversity and community structure were analyzed, and the correlation between wood properties and bacterial relative abundance was analyzed to explore their relationship. Two alpha-diversity indices of endophytic bacteria in the heartwood of wetwood trees were significantly (p < 0.05) lower than that in the heartwood of healthy trees, and the community structure between the two types of trees was significantly different. No significant differences in the alpha-diversity indices nor community structure were observed in the sapwood, root tissue, or rhizosphere bacterial community of diseased and healthy trees. The distribution of dominant bacteria genus in the heartwood of diseased and healthy trees differed. Proteiniphilum, Actinotalea, and Methanobacterium were the dominant genera in diseased trees’ heartwood. Proteiniphilum, Dysgonomonas, and Bacteroides were the dominant genera in healthy trees’ heartwood. The relative abundance of Proteiniphilum, Actinotalea, and Methanobacterium was significantly higher in the heartwood of wetwood trees than those of healthy trees. A db-RDA analysis found that these three bacterial genera were positively correlated with the rate of wet heartwood. These three bacterial genera may be the main pathogens causing poplar wetwood disease.

Elevated Ozone Concentration and Nitrogen Addition Increase Poplar Rust Severity by Shifting the Phyllosphere Microbial Community.

Tropospheric ozone and nitrogen deposition are two major environmental pollutants. A great deal of research has focused on the negative impacts of elevated O3 and the complementary effect of soil N addition on the physiological properties of trees. However, it has been overlooked how elevated O3 and N addition affect tree immunity in face of pathogen infection, as well as of the important roles of phyllosphere microbiome community in host–pathogen–environment interplay. Here, we examined the effects of elevated O3 and soil N addition on poplar leaf rust [Melampsora larici-populina] severity of two susceptible hybrid poplars [clone ‘107’: Populus euramericana cv. ‘74/76’; clone ‘546’: P. deltoides Í P. cathayana] in Free-Air-Controlled-Environment plots, in addition, the link between Mlp-susceptibility and changes in microbial community was determined using Miseq amplicon sequencing. Rust severity of clone ‘107’ significantly increased under elevated O3 or N addition only; however, the negative impact of elevated O3 could be significantly mitigated when accompanied by N addition, likewise, this trade-off was reflected in its phyllosphere microbial α-diversity responding to elevated O3 and N addition. However, rust severity of clone ‘546’ did not differ significantly in the cases of elevated O3 and N addition. Mlp infection altered microbial community composition and increased its sensitivity to elevated O3, as determined by the markedly different abundance of taxa. Elevated O3 and N addition reduced the complexity of microbial community, which may explain the increased severity of poplar rust. These findings suggest that poplars require a changing phyllosphere microbial associations to optimize plant immunity in response to environmental changes.

Chemical changes of steamed timber during short-term photodegradation monitored by FTIR spectroscopy

Black locust (Robinia pseudoacacia L.), beech (Fagus sylvatica L.), poplar (Populus x euramericana cv. pannonia) and spruce (Picea abies Karst.) wood samples were treated in saturated steam at 100, 110 and 120 °C for 2 days. Steamed and unsteamed (control) specimens were irradiated using a UV emitter mercury lamp in order to determine the chemical changes generated by UV irradiation. The main goal of the research was to find out if steaming can improve the UV resistance of wood. Chemical changes were determined by diffuse reflectance FTIR spectroscopy. Steaming deacetylated the hemicellulose molecules of hardwood species. Steamed spruce specimens showed the same photodegradation properties as the unsteamed ones. Steaming reduced the photodegradation sensitivity of lignin considerably for black locust only. Steamed hardwood specimens presented greater absorption increase at 1705 cm−1 compared to unsteamed samples, which corresponds to the photodegradation of hemicelluloses.

T-DNA integration and its effect on gene expression in dual Bt gene transgenic Populus ×euramericana cv. Neva

The integration of Bacillus thuringiensis (Bt) genes is often accompanied by unintended effects along with the improved resistance to targeted pests. The insertion information of transfer DNA (T-DNA) and the expression information of upstream and downstream genes are of great significance for related research on unexpected effects and molecular-level mechanisms. In this study, six dual Bt transgenic Populus × euramericana cv. Neva (poplar 107) lines were used as research objects. We determined growth and physiological indices, and characterized the T-DNA integration using next-generation sequencing technology. The transgenic and non-transgenic lines showed no significant difference in growth index. However, while insect resistance was enhanced, effects related to the integration sites of the Bt gene occurred. A total of 15 insertion sites were detected among the six transgenic lines, and T-DNA preferentially inserted into AT-rich regions of the poplar genome. RNA sequencing and weighted gene co-expression network analysis were used to explore the effects of T-DNA insertion on the gene expression of poplar 107. As a result, the metabolic pathways most affected by the Bt gene were starch and sucrose metabolism and pentose and gluconate conversion. The expression of exogenous Bt had a greater impact than the insertion position or copy number on poplar 107 gene expression, and the Cry1Ac toxin protein also played a major role. This study provides theoretical support for the cultivation and management of poplar 107 new varieties, and provides reference for Poplar insect resistance breeding and its molecular response to Bt gene.

Soil and Atmospheric Microclimate Research in Poplar Forestry Intercropping System in Hungary

Climate change presents growing environmental, economic, and social problems for the industrializing and developing world. Applying new technologies and transitioning to a cleaner, more flexible economy are essential to solving these problems. These solutions focus on climate change mitigation and work toward a complete transformation in line with sustainable development goals. Agroforestry systems are used for climate change adaptation and to support biodiversity. They also help combat desertification and soil erosion. Practical experiences show that applying forestry alley cropping systems can contribute to the climate adaptation of young forest stocks. The present study examined a historical forestry intercropping method known as Vákáncsos following the effects of microclimate stress on poplar seedlings (Populus × euramericana cv. I-214). This study investigated the background of previous observations concerning the practice of using intermediate crops in forest conditions – and the favorable results from these – and compared the stress effects on seedlings. When assessing the microclimate of the system, we used the EC tester (EC–electrical conductivity) to measure soil temperature and conductivity. We employed an agrometeorological hand-held instrument to measure air temperature, humidity, and wind speed. The results show that the agroforestry system significantly reduces temperature extremes and provides more favorable humidity. The agroforestry system reduced soil temperature values by 1–14 Co in the warmest period of the year. Experience and measurements indicate that the applied agroforestry practice can increase stress tolerance, afforestation efficiency, land use maximization, and profitability. Applied agroforestry can also serve other purposes like ecosystem services and feeding. Forestry alley cropping systems can be combined with resource efficiency.

Measurements of the Load-bearing Structural Aspects of Pannónia Poplar from Sites in Western Transdanubia, Hungary

This study summarises the test results of Pannónia poplar (Populus × euramericana cv. Pannónia) originating from three plantation sites in Győr-Moson-Sopron County in the Western Transdanubia region of Hungary: Újrónafő 11G, Győr 540B, and Kapuvár 35A. The research primarily aimed to clarify the characteristics of radial growth depending on the plantation site and to predict the selected physical and mechanical properties of the xylem. Measuring the time-of-flight (TOF) in trees was performed with a non-destructive test technique using a “Fakopp” TreeSonic device. The stress wave velocity (SWV) values calculated from TOF data are significant in estimating the dynamic modulus of elasticity (MOE) of the xylem and, therefore, in the prediction of timber suitability for structural applications. During the on-site measurements, 50 trees – as random samples from every site – were investigated to determine the diameter at breast height (DBH) and the stress wave velocity in sapwood parallel to the grain. In addition to the non-destructive measurements, the laboratory analysis of the xylem from harvested logs (three logs per site, random sample) was also performed to determine the radial growth rate and density. The one-way ANOVA results revealed significant differences in SWV values between certain plantation groups. The difference between the average values of young and old plantations is 136.8 m/s, which is a significant difference. Similar findings occurred for the middle-aged and old plantation trees. The average values of the young and the middle-aged trees can be considered the same at the 0.05 level of significance. We also established that the trees in the young (22 years old) plantation site, Újrónafő 11G, planted with the closest spacing (3 m × 4 m), had the lowest average diameter of breast height naturally and showed the highest average value of SWV. Nevertheless, the sap- and heartwood samples from this plantation site had the highest average density values in a normal climate; therefore, the highest dynamic modulus of elasticity of the xylem can be expected in logs originating from this plantation site.

Dynamic monitoring of the impact of insect-resistant transgenic poplar field stands on arthropod communities

The safety of genetically modified forest trees is an important ecological issue worldwide, and concerns about genetic modification are one factor hindering in-depth research and large-scale planting of genetically modified trees. This study evaluated the impact of transgenic poplars on the ecosystem by analyzing differences in arthropod communities, target arthropods, and nontarget arthropods in transgenic (BtCryIAc) and non-transgenic experimental forests of Populus × euramericana cv. “74/76” (hereafter, tPE and ntPE, respectively). Five years of dynamic monitoring showed that the tPE had stable and lasting insect resistance to Lepidoptera, especially Arctiidae. However, the insertion of exogenous genes also had a negative impact on certain tPE line. The principle response curves (PRC) indicated that the genetic modification contributed much less to the community difference than the year factor (7% vs. 60%, respectively), and nontarget arthropods may be more sensitive to interannual variations. Nontarget arthropods that respond sharply to the PRC curve include Aphididae and Tenthredinidae (species weight > 0.5), but this difference appears only in certain years or lines. Our research shows that the tPE had no obvious adverse effects on nontarget arthropods. In areas with severe lepidopteran pests, the tPE could help to increase the diversity and stability of arthropod communities, while providing greater ecological and economic benefits than non-transgenic poplars.

Soil pH drives poplar rhizosphere soil microbial community responses to ozone pollution and nitrogen addition

AbstractGround‐level ozone (O3) pollution frequently coincides with the deposition of anthropogenic nitrogen (N), and both factors can influence the structure and functionality of both above‐ and belowground ecosystems. Elevated O3 levels have been shown to adversely impact plants in many prior reports, but the interacting effects of high O3 levels and N addition on exposed plants remain to be clearly defined, and the changes in rhizosphere microbial community composition in this context have yet to be studied. The direct and indirect mechanisms and interactions among plants, microbes, and the soil that shape these O3 and N responses are also poorly understood. Herein, we explored the interactive effects of O3 exposure (five levels) and soil N (four levels) on the composition of rhizosphere soil microbial communities associated with poplar trees (Populus euramericana cv. ‘74/76’). In these analyses, exposure to higher levels of O3 was linked to significant decreases in bacteria, fungi, arbuscular mycorrhizal fungi, and to a reduction in the ratio of fungi‐to‐bacteria, whereas soil N addition had no impact on these parameters. No interactive effects between O3 and N were observed in the context of alterations in soil microbial community composition, and equivalent performance was observed for concentration‐based (AOT40, cumulative exposure to hourly O3 concentrations &gt;40 ppb) and flux‐based [POD1 and POD7, cumulative stomatal uptake of O3 &gt; 1 or 7 nmol O3 m−1 PLA (projected leaf area) s−1] dose–response analyses. Structural equation modelling revealed that changes in the composition of the microbial community were attributable to changes in soil pH but unrelated to plant characteristics. Overall, these findings indicated that increased O3 levels can induce soil alkalinisation and thereby influence soil microbial communities such that soil pH is a reliable predictor of O3 pollution‐related changes in these communities.Highlights Elevated O3 exhibited an overall negative influence on microorganisms. AOT40‐, POD1‐ and POD7‐based dose–responses performed equally well. Soil pH is a reliable predictor of O3 pollution‐related changes in microbial communities. N addition failed to affect O3 effects on soil microbial community.

COMPARATIVE ANALYSIS OF STATIC AND DYNAMIC MOE OF PANNÓNIA POPLAR TIMBER FROM DIFFERENT PLANTATIONS

The aim of this study has been to investigate the suitability of Pannónia poplar (Populus × euramericana cv. Pannónia) timber for structural purposes. Static and dynamic modulus of elasticity (MOE) has been determined on samples of 4 different Hungarian plantation origins. The results of the dynamic test showed the same range as the static test, showing a good correlation of the two measurements. As result it can be stated that the domestic Hungarian Pannónia poplar species have in average 11000 N.mm-2 modulus of elasticity. This exceeds considerably the threshold limit value (7000 N.mm-2) necessary for structural applications according to Eurocode 5. Therefore Pannonia poplar is suitable for structural applications, and are a good alternative of the widely used coniferous species in construction sector.

The relationship between the hydrothermal response of yield stress and the formation of sandwich compressed wood

The effects of yield stress of poplar ( Poplar × euramericana cv. ‘Neva’) on temperature (60–210°C), moisture content (oven dry-30%) and grain response mechanism and as well as its role in the formation of sandwich compressed wood were studied in this paper. The results showed that the yield stress of wood was significantly affected by moisture content(MC), temperature and their interaction. Compared with temperature, the relative change rate of yield stress was nearly 10 times higher for each 1% increase in MC than for each 1°C increase in temperature. The experimental data revealed that the relative change rate of yield stress depended on the softening effect of wood by moisture and temperature. The asymmetry of yield stress in different grain direction also depended on wood hydrothermal softening effect. Raising the temperature or increasing the MC could make wood radial vs tangential asymmetry decrease and radial vs radial tangential asymmetry disappear. In the process of hydrothermal compression, the yield stress gradient caused by the hydrothermal softening inside the wood was the main reason for the formation of sandwich compressed wood, and provided a scientific basis for the controllability of the position and thickness of the compressed layer(s).

Physical and Mechanical Properties of Poplar Clones and Rapid Prediction of the Properties by Near Infrared Spectroscopy

In order to understand the physical and mechanical properties of poplar clones, and explore a method for their quick evaluation, the air dry density, modulus of rupture (MOR), modulus of elasticity (MOE), and compressive strength parallel to grains of three new bred poplar clones were explored and the prediction models with the highest accuracy were established by near infrared spectroscopy (NIRs). Clone 50 (Populus deltoides CL. ‘55/65′) had the highest air dry density, MOR, MOE, and compressive strength parallel to grains in the three clones. For clone 50 and 108 (Populus euramericana cv. ‘Guariento’), the mechanical properties of sapwood were better than those of heartwood, and the sapwood of clone 50 also had a better air dry density than that of heartwood. There were significant positive correlations between the air dry density and mechanical properties, with correlation coefficients above 0.68. Prediction models with better effects could be obtained by using information on the cross section for the air dry density and mechanical properties. First derivative+ Savitzky–Golay (S-G) smoothing methods were employed for the air dry density and MOR, and multiple scattering correction (MSC)+ S-G smoothing methods were used when establishing prediction models of MOE and compressive strength parallel to grains.

Comparative studies on lignin structures in normal and tension wood of Populus × euramericana cv. “74/76”

Tension wood is a type of defect of wood, however, it has some especial character and structure. In this study, cellulase lignin structures in normal and tension wood of Poplar 107 (Populus × euramericana cv. ‘74/76’) were compared using ultraviolet (UV), Fourier transform infrared (FT-IR), Raman and magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and elemental analysis. The results showed that the lignins in both normal and tension wood were dominated by syringyl units, followed by guaiacyl and p-hydroxyphenyl units. The FT-IR result presented that the relative intensity of syringyl units in normal and tension wood were 0.87 and 0.90. The contents of aliphatic hydroxyl, methoxyl, condensed phenolic hydroxyl and carboxyl of lignin in tension wood were higher than those of phenolic hydroxyl groups and β-5. The contents of β-O-4, β-β and β-1 in tension wood were similar with those in normal wood. The average per-C9-unit formulae of the lignin in normal and tension wood of Poplar 107 were C9H7.21O1.79 (OH)1.17_x0001_(OCH3)1.55 and C9H7.23O1.76(OH)1.25_x0001_(OCH3)1.62, respectively.

Nonlinear responses of foliar phenylpropanoids to increasing O3 exposure: Ecological implications in a Populus model system

Plant phenolic compounds (phenylpropanoids) act as defense chemicals against herbivores and can mediate ecosystem processes. Tropospheric ozone (O3) pollution alters concentrations of plant phenolics; however, little is known about how these phytochemicals respond to different levels of O3 exposure. Here, we investigated the effects of five different O3 exposure levels on foliar concentrations of phenylpropanoids (53 compounds in total) and antioxidative capacity in hybrid Populus (Populus euramericana cv. ‘74/76’) saplings grown in the presence of high or low soil nitrogen (N) load. Increasing O3 exposure initially increased and then decreased total concentrations of phenolic compounds, revealing a biphasic exposure-response profile (hormetic zone: 1.1–36.3 ppm h AOT40). This biphasic response pattern was driven by changes in a subset of phenylpropanoids with high antioxidative capacity (e.g. condensed tannins) but not in phenolics with low antioxidative capacity (e.g. salicinoids). The O3 exposure-response relationships of some phenylpropanoids (e.g. flavonoids and chlorogenic acids) varied in response to soil N, with hormesis occurring in high N soil but not in low N soil. Collectively, our findings indicated that plant phenolic compounds exhibit nonlinear responses to increasing O3 exposure, and that the responses vary in relation to phenolic compound class, antioxidative capacity, and soil nitrogen conditions. Our findings further suggest that the impact of O3 on ecological processes mediated by phenolics will be concentration-dependent, highlighting the complexity of the ecological effects of ground-level O3 pollution.

Effects of Bt-Cry1Ah1 Transgenic Poplar on Target and Non-Target Pests and Their Parasitic Natural Enemy in Field and Laboratory Trials

Increasing areas of artificial afforestation and poplar monoculture in China have led to serious problems with insect pests. The development of genetic engineering technology, such as transgenic modification with Bacillus thuringiensis (Bt) genes, provides novel solutions to the pest problem. We generated a Bt-Cry1Ah1 gene incorporating codon optimization and transferred it into Populus deltoides × P. euramericana cv “Nanlin895” using an Agrobacterium-mediated method. The resulting Bt-Cry1Ah1 transgenic poplars were planted in the field with permission from the State Forestry Administration in 2017. Field and laboratory studies were conducted in Jiangsu, China, to investigate the effects of these transgenic poplars expressing the Cry1Ah1 protein on target and non-target pests and their parasitic natural enemy. Target pests included Hyphantria cunea (Lepidoptera, Arctiidae), Micromelalopha troglodyta (Lepidoptera, Notodontidae), and Clostera anachoreta (Lepidoptera, Notodontidae). Plagiodera versicolora (Coleoptera, Chrysomelidae) served as the non-target pest. Laboratory trials showed that the six transgenic poplar lines exhibited resistance against the target insects. The corrected mortality rates of the target pest larvae fed leaves from the six lines were as high as 87.0%, significantly higher than that of the control. However, the corrected mortality rate of the non-target pest larvae was markedly lower and did not differ significantly from that of the control. Field experiments showed that transgenic poplar exhibited resistance against H. cunea and M. troglodyta. Field mortality rates were slightly higher than laboratory mortality rates. In addition, we investigated Chouioia cunea (Hymenoptera, Eulophidae) as a parasitoid of H. cunea pupae that had been fed transgenic poplar leaves. The emergence time, parasitism rate, and abundance of C. cunea did not differ significantly from those of the control. Therefore, Bt-Cry1Ah1 transgenic poplar can be used to effectively control damage by target insect pests without negatively affecting non-target insects and parasitoids.

Assessment of environmental microbial effects of insect-resistant transgenic Populus × euramericana cv. ‘74/76’ based on high-throughput sequencing

Pests and diseases present major obstacles to poplar growth, which have been overcome via transgenic engineering applications. However, given the long growth cycle of transgenic poplars, long-term environmental safety assessments are needed for transgenic poplars planted in the field. Therefore, we investigated the effects of exogenous genes in transgenic poplar on the diversity of endophytic and rhizosphere soil bacterial communities in poplars. The composition and diversity of bacterial communities in trunk tissue, root tissue, and rhizosphere soil samples of transgenic Populus × euramericana cv. ‘74/76’ containing the high-resistance gene HPb1 (hereafter, HPb1) and non-transgenic Populus × euramericana cv. ‘74/76’ (hereafter, 107) in a 4-year-old experimental forest were analyzed using high-throughput sequencing. In terms of bacterial abundance at the phylum level, in trunk tissue, Bacteroidetes was the dominant phylum in both poplar lines (HPb1: 32.17%; 107: 47.42%). In root tissue, Proteobacteria was the dominant phylum in both lines (HPb1: 67.52%; 107: 65.96%). In rhizosphere soil, Proteobacteria was the dominant phylum in both lines (HPb1: 39.75%; 107: 37.98%). There were no significant differences in the richness and diversity of bacterial communities between HPb1 and 107. Finally, the bacterial community compositions in root tissue and rhizosphere soil were highly similar, both of which differed somewhat from that in trunk samples. This study provides a reference for ecological safety assessments of transgenic poplars and allows for a more systematic understanding of the potential ecosystem risk posed by environmental release of transgenic poplars.

Emission Characteristics of Biogenic Volatile Compounds (BVOCs) from Common Greening Tree Species in Northern China and Their Correlations with Photosynthetic Parameters

In order to understand the emission characteristics of common greening trees in Beijing and analyze their correlations with photosynthetic parameters, including the net photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (ci), and transpiration rate (Tr), we collected samples of biogenic volatile organic compounds (BVOCs) using a dynamic sampling technique from 14 species of deciduous trees. The results showed that there were significant differences in isoprene and total BVOC emissions between family or genus levels (P<0.01). With the exception of Lonicera maackii Maxim and Ulmus pumila L., all species were found to emit isoprene, monoterpenes, and sesquiterpenes, of which, species from the Salicaceae (e.g., Populus deltoides cv. '55/56'× P.deltoides cv. 'Imperial', P. euramericana cv. '74/76', Populus simonii Carr, and Salix babylonica) and Legume (Sophora japonica, Robinia pseudoacacia, and S. japonica Linn. var. japonica f. pendula Hort) families were the higher isoprene emitters, with emission rates that ranged from (30.1±4.3) μg·(g·h)-1 to (91.8±10.0) μg·(g·h)-1. Plants from the Oleaceae (e.g., Fraxinus chinensis Roxb and Syringa oblata Lindl), Begonia (Malus prunifolia), Sapindaceae (Koelrenteria paniculate), and Aceraceae (Acer truncatum Bunge) families mainly emitted monoterpenes and sesquiterpenes. Among them, Fraxinus chinensis Roxb and Acer truncatum Bunge were the highest emitters with emission rates of (10.6±4.8) μg·(g·h)-1 and (11.8±6.4) μg·(g·h)-1, respectively. Ocimene and β-pinene were the two main monoterpenes emitted from greening tree species. No significant correlations were found between the emission of BVOCs and Pn or gs, while the emission rate of isoprene (r=0.681; P<0.01) and the total BVOC (r=0.698; P<0.01) from the Salicaceae family increased with increasing Tr. Moreover, leguminous plants showed a significant positive correlation between the total BVOC emission rate and ci (P=0.04). This study provides a scientific reference for the selection and configuration of urban greenery, and a theoretical basis for exploring the mechanism of BVOC emissions.

Effects of Changes in Biopolymer Composition on Moisture in Acetylated Wood

To investigate the effects of changes in biopolymer composition on moisture in acetylated poplar wood (Populus euramericana Cv.), the acetylation of control wood was compared to the acetylation of wood with reduced hemicellulose or lignin content (about 9% reduction of total specimen dry weight in both cases). Time-domain nuclear magnetic resonance relaxometry of water-saturated wood gave spin–spin relaxation times (T2) of water populations, while deuteration in a sorption balance was used to characterize the hydroxyl accessibility of the wood cell walls. As expected, the acetylation of pyridine-swelled wood reduced hydroxyl accessibility and made the cell wall less accessible to water, resulting in a reduction of cell wall moisture content by about 24% compared with control wood. Hemicellulose loss per se increased the spin–spin relaxation time of cell wall water, while delignification had the opposite effect. The combined effect of hemicellulose removal and acetylation caused more than a 30% decrease of cell wall moisture content when compared with control wood. The acetylated and partially delignified wood cell walls contained higher cell wall moisture content than acetylated wood. An approximate theoretical calculation of hydroxyl accessibility for acetylated wood was in the low range, but it agreed rather well with the measured accessibility, while acetylated and partially hemicellulose-depleted and partially delignified wood for unknown reasons resulted in substantially lower hydroxyl accessibilities than the theoretical estimate.

Response of isoprene emission from poplar saplings to ozone pollution and nitrogen deposition depends on leaf position along the vertical canopy profile

We investigated isoprene (ISO) emission and gas exchange in leaves from different positions along the vertical canopy profile of poplar saplings (Populus euramericana cv. ‘74/76’). For a growing season, plants were subjected to four N treatments, control (NC, no N addition), low N (LN, 50 kg N ha−1year−1), middle N (MN, 100 kg N ha−1year−1), high N (HN, 200 kg N ha−1year−1) and three O3 treatments (CF, charcoal-filtered ambient air; NF, non-filtered ambient air; NF + O3, NF + 40 ppb O3). Our results showed the effects of O3 and/or N on standardized ISO rate (ISOrate) and photosynthetic parameters differed along with the leaf position, with larger negative effects of O3 and positive effects of N on ISOrate and photosynthetic parameters in the older leaves. Expanded young leaves were insensitive to both treatments even at very high O3 concentration (67 ppb as 10-h average) and HN treatment. Significant O3 × N interactions were only found in middle and lower leaves, where ISOrate declined by O3 just when N was limited (NC and LN). With increasing light-saturated photosynthesis and chlorophyll content, ISOrate was reduced in the upper leaves but on the contrary increased in middle and lower leaves. The responses of ISOrate to AOT40 (accumulated exposure to hourly O3 concentrations > 40 ppb) and PODY (accumulative stomatal uptake of O3 > Y nmol O3 m−2 PLA s−1) were not significant in upper leaves, but ISOrate significantly decreased with increasing AOT40 or PODY under limited N supply in middle leaves but at all N levels in lower leaves. Overall, ISOrate changed along the vertical canopy profile in response to combined O3 and N exposure, a behavior that should be incorporated into multi-layer canopy models. Our results are relevant for modelling regional isoprene emissions under current and future O3 pollution and N deposition scenarios.

Roots play a key role in drought-tolerance of poplars as suggested by reciprocal grafting between male and female clones

Drought stress influences the growth of plants and thus grafting has been widely used to improve tolerance to abiotic stresses. Poplars possess sex-specific responses to drought stress, but how male or female rootstock affect the grafted plant is little known. To explore the mechanisms underlying changes in drought tolerance caused by grafting, we investigated the changes in growth, leaf traits, gas exchange and antioxidant enzyme activities of reciprocally grafted seedlings between Populus euramericana cv. "Nanlin895" (NL-895) (female) and Populus deltiodes cv."3412" (NL-3412) (male) under water deficit stress with 30% field capacity for 30 d. Results showed that drought stress affected adversely growth, morphological, and physiological characteristics in all seedlings studied. Grafted seedlings with male roots can effectively alleviated the inhibition of growth induced by drought stress, as shown by higher WUE, activities of SOD, POD and CAT, and lower levels of lipid peroxidation. Male seedlings with female roots were found to be less tolerance to drought than non-grafted male clones and female scions with male roots, but more tolerance than non-grafted female clones. This results suggested that drought tolerance of grafted seedlings is primarily caused by the rootstock, although the scion also affects the grafted plant. Thus, paying attention on the root genotype can provide an important means of improving the drought tolerance of poplars.