Populus Deltoides Cv Research Articles

Spatial Heterogeneity of Total and Labile Soil Organic Carbon Pools in Poplar Agroforestry Systems

Agroforestry systems are considered effective methods of carbon sequestration. In these systems, most of the carbon is stored in the soil, and the pattern of tree planting can influence the spatial distribution of organic matter input into the soil. However, limited information is available about the extent of this influence. In this study, the horizontal and vertical distributions of soil organic carbon (SOC) and labile fractions were investigated in four planting systems: a pure poplar (Populus deltoides cv. “35”) planting system, a wide-row (14 m spacing) poplar and wheat (Triticum aestivum L.) agroforestry system, a narrow-row (7 m spacing) poplar and wheat agroforestry system, and a pure wheat field. The results showed that although the poplar system had the highest vegetation biomass (147.50 t ha−1), the agroforestry systems overall had higher SOC contents than the pure poplar system and wheat fields. Especially in the wide-row agroforestry system, the SOC, readily oxidizable carbon, and dissolved organic carbon contents were, respectively, 25.3%, 42.4%, and 99.3% higher than those of the pure poplar system and 60.3%, 148.7%, and 6.3% higher than those of the wheat field in a 1 m soil profile, and it also had the highest fine root biomass. However, the microbial biomass carbon content was highest in the pure poplar system. The SOC of the three poplar planting systems was spatially heterogeneous, with the highest values occurring at 1.5 m in the narrow-row systems and within the tree rows in the wide-row system, similar to the distribution of fine root biomass. Additionally, we found that the larger the diameter at the breast height of the trees, the greater their positive effect on SOC at greater distances.

Deforestation for Agriculture Temporarily Improved Soil Quality and Soil Organic Carbon Stocks

Deforestation for agricultural development or extension is a common land-use problem that may cause a series of changes in the ecological environment and soil carbon stock in planting systems. However, the response of soil physical, chemical properties and carbon stocks in agricultural systems in the initial period after deforestation have not been thoroughly examined, especially in the subsoil. We investigated the variations in the soil physicochemical properties and organic carbon stocks to a depth of 100 cm in a poplar (Populus deltoides cv. 35) plantation, a summer maize (Zea mays L.) followed by winter wheat (Triticum aestivum L.) field after 1 year of deforestation of a poplar plantation, and a wheat–maize rotation field used for decades. The soil bulk density and pH decreased, and the soil total nitrogen (TN), total phosphorus, and total potassium contents increased considerably. The soil organic carbon (SOC) content and stocks (to 100 cm) increased by 32.8% and 20.1%, respectively. The soil TN content was significantly (p < 0.001) positively correlated with the SOC content, and the C:N ratio increased for the field following deforestation. Furthermore, the nitrogen in the poplar plantation and the field following deforestation was limited. We recommend increasing the amount of nitrogen fertilizer following deforestation to improve fertility and this will be beneficial to SOC storage.

Whole-plant compensatory responses of isoprene emission from hybrid poplar seedlings exposed to elevated ozone

It is still unclear whether the responses of isoprene (ISO) emission to elevated O3 vary with biological organization level (i.e. leaf and whole-plant). To study such responses and the possible reasons explaining their variation, we investigated the effect of O3 (CF: charcoal-filtered ambient air; E-O3: non-filtered ambient air enriched with O3) on ISO emission rate (ISOrate), net photosynthetic rate (Pn), leaf nitrogen and carbon contents, and leaf growth traits in poplar seedlings (Populus deltoides cv. 55/56 × P. deltoides cv. Imperial) during one growing season. Opposite effects of E-O3 on Pn were found between upper leaves (positive effect) and lower leaves (negative effect). Compared to CF, E-O3 significantly decreased leaf mass per area, number of leaves, and leaf biomass, but increased leaf nitrogen content and individual leaf size. In the framework of such compensatory responses, poplar seedlings further increased ISOrate in upper leaves and decreased ISOrate in lower leaves, thus preventing significant decrease in the overall whole-plant ISOrate by E-O3. The measured whole-plant ISOrate also showed that the simplistic estimation approaches based on the linear regression between chlorophyll content indicated by soil plant analysis development meter (SPAD value) and leaf-level ISOrate could not accurately reflect the true response of whole plant to elevated O3. For more accurate predictions, the potential ISO compensatory response to increasing O3 concentration should be incorporated into the climate biogeochemical models related to ISO emission.

Combined transcriptome and proteome analysis provides insights into anthocyanin accumulation in the leaves of red-leaved poplars.

Anthocyanin was highly accumulated in the leaves of red-leaved poplars; Many structural genes involved in anthocyanin synthesis were significantly up-regulated in 'Quanhong' and 'Xuanhong'; TTG2, HYH, and HY5 may be directly involved in the regulation of anthocyanin synthesis in both red-leaved poplars. The red-leaved poplar cultivars 'Quanhong' and 'Xuanhong' are bud mutations of Populus deltoides cv. 'Zhonglin 2025'. These cultivars are valued for their beautiful shape, lack of flying catkins, and ornamental leaf colors. However, the understanding of the molecular mechanism of anthocyanin accumulation in the leaves of red-leaved poplars is still unclear. Here, we profiled the changes of pigment content, transcriptome and proteome expression in the leaves of three poplar cultivars and the results showed that the ratios of anthocyanin to total chlorophyll in both red-leaved poplars were higher than that in 'Zhonglin 2025', indicating that the anthocyanin was highly accumulated in the leaves of red-leaved poplars. Based on the results of combined transcriptome and proteome analysis, 15 and 11 differentially expressed genes/proteins involved in anthocyanin synthesis were screened in 'Quanhong' and 'Xuanhong', respectively, indicating that the two red-leaved poplar cultivars have slightly different patterns of regulating anthocyanin biosynthesis. Among the 120 transcription factors, 3 (HY5, HYH, and TTG2), may be directly involved in the regulation of anthocyanin synthesis in both red-leaved poplars. This study screens the candidate genes involved in anthocyanin accumulation in the leaves of red-leaved poplars and lays a foundation for further exploring the molecular mechanism of leaf red coloration in red-leaved poplars.

Soil Fungal Community Structure and Functional Diversity in a Copper Tailing Dam and Its Surrounding Areas

Soil fungal communities are reconstructed under heavy metal stress. This study was conducted to explore the structural and functional diversity of soil fungal communities under different land-use patterns, namely grassland and farmland, in 15-year-old or 10-year-old poplar plantations (Populus deltoides cv. 'zhonghuahongye') near the Shibahe copper tailing dam and the surrounding area, located in Yuanqu County, Shanxi. The results indicated that the abundance and diversity of fungal communities were the highest in the 15-year-old poplar plantation and lowest in the grassland on the tailing dam. The dominant fungal groups in the study area were Ascomycota, Basidiomycota, and Mortierellomycota. The Ascomycota members were the most abundant at all four sampling sites, reaching 92.92% of the fungal community in the grassland on the tailing dam. The highest functional diversity of carbon utilization was found in the soil fungal communities of the 15-year-old poplar plantations; moreover, the diversity in the grassland on the tailing dam was significantly higher than that in the farmland and in the 10-year-old poplar plantation. Meanwhile, we also observed the highest glucoside carbon source utilization efficiency in the grassland. Notably, the correlation analysis revealed that Ascomycota was significantly correlated with the utilization efficiency of the glucoside carbon source in our study area. Moreover, the soil total nitrogen content, but not the soil heavy metal content, was significantly correlated with the abundance of the soil fungal community. There were significant correlations between the cadmium and arsenic contents and the soil fungal community diversity indices. Our results indicated that the soil fungal communities were more influenced by soil fertility and land use than by the soil heavy metal content. This study underlies the application of soil fungal communities in soil remediation of heavy metal-contaminated areas.

Ozone Pollution, Nitrogen Addition, and Drought Stress Interact to Affect Non-structural Carbohydrates in the Leaves and Fine Roots of Poplar

Ground-level ozone (O3) pollution frequently co-occurs with drought and nitrogen (N) deposition during the growing season. It is important to understand how the carbon dynamics of plants respond to O3 pollution in drier and N-enriched environments. Here we present the patterns of non-structural carbohydrates and its components (soluble sugar and starch) in the leaves and fine roots in poplar clone 546 (Populus deltoides cv. '55/56'×P. deltoides cv. 'Imperial') for one growing season at two O3 concentrations (control, charcoal-filtered air, and elevated O3, non-filtered air+40 nmol·mol-1 of O3), two watering regimes (well-watered and reduced watering at 40% of well-watered irrigation), and two soil nitrogen addition treatments[no addition and the addition of 50 kg·(hm2·a)-1]. The results showed that O3 stress significantly increased the content of soluble sugar in leaves and starch in fine roots but decreased the content of starch and total non-structural carbohydrate (NSC) in leaves. Drought stress significantly reduced the content of starch and total NSC in leaves but increased the contents of soluble sugar and total NSC in fine roots. Nitrogen addition had no significant effect on NSC and its components in leaves and fine roots. NSC and its components in leaves and fine roots were positively correlated with photosynthetic rate and biomass. With an increase in the number of environmental stress factors, NSC in leaves showed a significant downward trend while NSC in fine roots showed a significant upward trend. The study demonstrates that environmental stress can promote the transformation of starch into soluble sugars in plant leaves and the transfer of NSC from leaves to roots for storage, which may be a coping strategy for plants exposed to environmental stress.

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.

Water stress rather than N addition mitigates impacts of elevated O3 on foliar chemical profiles in poplar saplings

Tropospheric ozone (O3) pollution can alter tree chemical profiles, and in turn, affect forest ecosystem function. However, the magnitude of these effects may be modified by variations in soil water and nutrient availability, which makes it difficult to predict the impacts of O3 in reality. Here we assessed the effects of elevated O3 alone, and in combination with soil water deficit and N addition, on the phytochemical composition of hybrid poplar (Populus deltoides cv. ‘55/56’ × P. deltoides cv. ‘Imperial’). Potted trees were grown in open-top chambers (OTCs) under either charcoal-filtered air or elevated O3 (non-filtered air +40 ppb of O3), and trees within each OTC were grown with four combinations of water (well-watered or water deficit) and nitrogen (with or without N addition) levels. We found that elevated O3 alone stimulated the accumulation of foliar nitrogen, soluble sugar, and lignin while inhibiting the accumulation of starch, but had limited impacts on condensed tannins and salicinoids in poplar saplings. Graphical vector analysis revealed that these changes in concentrations of nitrogen, starch and lignin were due largely to altered metabolic processes, while increased soluble sugar concentration related mainly to decreased leaf biomass in most cases. The effects of O3 on poplar foliar chemical profiles depended on soil water, but not soil N, availability. Specifically, O3-mediated changes in carbohydrates and lignin were mitigated by decreased soil water content. Taken together, these results suggested that nitrogen acquisition, carbohydrates mobilization and lignification play a role in poplar tolerance to O3. Moreover, the impacts of elevated O3 on phytochemistry of poplar leaves can be context-dependent, with potential consequences for ecosystem processes under future global change scenarios. Our results highlight the needs to consider multi-factors environments to optimize the management of plantations under changing environments.

Comparative metabolomics analysis reveals different metabolic responses to drought in tolerant and susceptible poplar species.

Drought is one of the critical factors limiting tree growth and survival. Clarifying the adaptation to drought will facilitate the cultivation of drought-tolerant varieties. Metabolites, as direct signatures of biochemical functions, can uncover the biochemical pathways involved in drought responses. Here, we investigated the physiological and metabolic responses of drought-tolerant Populus simonii and drought-susceptible Populus deltoides cv. 'Danhong' to drought. Under drought conditions, P. simonii grew better and had a higher photosynthetic rate than P. deltoides cv. 'Danhong'. Global untargeted metabolite profiling was analyzed using gas chromatography time-of-flight mass spectrometry system. A total of 69 and 53 differentially accumulated metabolites were identified in drought-stressed P. simonii and P. deltoides cv. 'Danhong', respectively. The metabolisms of carbohydrate, amino acid, lipid and energy were involved in the drought responses common to both poplar species. The citric acid cycle was significantly inhibited to conserve energy, whereas multiple carbohydrates acting as osmolytes and osmoprotectants were induced to alleviate the adverse effects of drought stress. Unlike P. deltoides cv. 'Danhong', P. simonii underwent a specific metabolic reprogramming that enhanced non-enzymatic antioxidants, coordinated the cellular carbon/nitrogen balance and regulated wax biosynthesis. These results provide a reference for characterizing the mechanisms involved in poplar response to drought and for enhancing the drought tolerance of forest trees.

Leaf Cuticle Can Contribute to Non-Host Resistance to Poplar Leaf Rust

The plant leaf cuticle is a chemically complex but largely waxy outer shell that limits water loss and also prevents some pathogens from gaining access to internal mesophyll. Rust fungi are obligate parasites, and most bypass the cuticle by thigmotropically locating stomata, growing through the stomatal openings, and then parasitizing mesophyll cells with haustoria. It is thought that even non-hosts of a given rust fungus do not resist until their mesophyll cells are contacted in this way. In other words, it is thought that the cuticle plays no role in non-host resistance. Here, we tested the hypothesis that poplar leaf cuticles might contribute to non-host resistance to rust fungi by chemically impeding the germination and growth of urediniosporelings of Melampsora larici-populina. Following an initial survey in China of the resistance of 36 genotypes of various species and interspecific hybrids of Populus to M. larici-populina, we selected three genotypes for the initial test of hypothesis: (1) A Populus purdomii genotype that is fully susceptible; (2) a Populus deltoides cv. ‘I-69′ that is incompletely resistant (i.e., a resistant host); and (3) a Populus tomentosa genotype that is a non-host to M. larici-populina. Urediniospores were assayed for germination in extracts of the cuticles of the three genotypes. Germination was most reduced by the P. tomentosa non-host cuticular extracts that also reduced the growth of germ tubes to 36 times less than that in controls or in the extract of the susceptible P. purdomii. Four cuticular components were identified as putative defense compounds given greater concentrations in P. tomentosa than in P. purdomii: Aucubin, hexakis(trimethylsilyl) ether, catechol, 7,9-Di-tert-buty l-1-oxaspiro (4,5) deca-6, 9-diene-2,8-dione and trifluoroacetamide. These four compounds were then tested, and they reduced urediniospore germination and uredinial density in inoculations of normally susceptible P. purdomii with Melampsora larici-populina. Thus, the cuticle of P. tomentosa can contribute to pre-haustorial, non-host resistance to M. larici-populina.

The First Record of a North American Poplar Leaf Rust Fungus, Melampsora medusae, in China

A wide range of species and hybrids of black and balsam poplars or cottonwoods (Populus L., sections Aigeiros and Tacamahaca) grow naturally, or have been introduced to grow in plantations in China. Many species of Melampsora can cause poplar leaf rust in China, and their distributions and host specificities are not entirely known. This study was prompted by the new susceptibility of a previously resistant cultivar, cv. ‘Zhonghua hongye’ of Populus deltoides (section Aigeiros), as well as by the need to know more about the broader context of poplar leaf rust in China. Rust surveys from 2015 through 2018 in Shaanxi, Sichuan, Gansu, Henan, Shanxi, Qinghai, Beijing, and Inner Mongolia revealed some samples with urediniospores with the echinulation pattern of M. medusae. The morphological characteristics of urediniospores and teliospores from poplar species of the region were further examined with light and scanning electron microscopy. Phylogenetic analysis based on sequences of the rDNA ITS region (ITS1, 5.8S rRNA gene, and ITS2) and the nuclear large subunit rDNA (D1/D2) was used to further confirm morphology-based identification. Based on combined analyses, five of the fifteen fully characterized samples were identified as Melampsora medusae: one from Shaanxi and four from Sichuan. Two of the five were from Populus deltoides cv. ‘Zhonghua hongye’. Three others were identified on Populus szechuanica, P. simonii, and P. yunnanensis. Additional samples of M. medusae were collected in Shaanxi in 2017 and 2018, and from Henan in 2015 through 2018. Altogether these findings show that this introduced pathogen is widespread and persistent from year to year in China. This is the first report of this North American poplar leaf rust species, Melampsora medusae, in China. It has previously been reported outside North America in Argentina, Europe, Australia, New Zealand, Japan, and Russia.

The effects of elevated ozone on the accumulation and allocation of poplar biomass depend strongly on water and nitrogen availability

Ozone (O3) pollution can alter carbon allocation and reduce tree growth - both above and below ground, but the extent of these effects depends on the variation in soil water and nutrient availability. Here we present the accumulation and allocation of biomass in poplar clone 546 (Populus deltoides cv. ‘55/56’ × P. deltoides cv. ‘Imperial’) for one growing season at two O3 concentrations (charcoal-filtered air [CF] and non-filtered air + 40 ppb of O3 [E-O3]), two watering regimes (well-watered [WW] and reduced watering at 40% of WW irrigation [RW]) and two soil nitrogen addition treatments (no addition [N0] and the addition of 50 kg N ha−1 year−1 [N50]). We found that the deleterious effects of E-O3 depended on the supply of water and nitrogen. Specifically, when the supplies of water and/or N (WW and/or N50) were abundant, E-O3 significantly reduced whole plant biomass by >15% but had no significant effect on biomass when these supplies were limited (RW and N0). A significant reduction of biomass by E-O3 occurred earlier in fine roots than in other plant organs, indicating greater sensitivity of fine root to E-O3. These results suggest that rising O3 concentrations may not ubiquitously lead to a large reduction in plant biomass since plant growth is often jointly constrained by water and nutrients.

Effects of elevated ozone concentration and nitrogen addition on ammonia stomatal compensation point in a poplar clone

The stomatal compensation point of ammonia (χs) is a key factor controlling plant-atmosphere NH3 exchange, which is dependent on the nitrogen (N) supply and varies among plant species. However, knowledge gaps remain concerning the effects of elevated atmospheric N deposition and ozone (O3) on χs for forest species, resulting in large uncertainties in the parameterizations of NH3 incorporated into atmospheric chemistry and transport models (CTMs). Here, we present leaf-scale measurements of χs for hybrid poplar clone ‘546’ (Populusdeltoides cv. 55/56 x P. deltoides cv. Imperial) growing in two N treatments (N0, no N added; N50, 50 kg N ha−1 yr−1 urea fertilizer added) and two O3 treatments (CF, charcoal-filtered air; E-O3, non-filtered air plus 40 ppb) for 105 days. Our results showed that χs was significantly reduced by E-O3 (41%) and elevated N (19%). The interaction of N and O3 was significant, and N can mitigate the negative effects of O3 on χs. Elevated O3 significantly reduced the light-saturated photosynthetic rate (Asat) and chlorophyll (Chl) content and significantly increased intercellular CO2 concentrations (Ci), but had no significant effect on stomatal conductance (gs). By contrast, elevated N did not significantly affect all measured photosynthetic parameters. Overall, χs was significantly and positively correlated with Asat, gs and Chl, whereas a significant and negative relationship was observed between χs and Ci. Our results suggest that O3-induced changes in Asat, Ci and Chl may affect χs. Our findings provide a scientific basis for optimizing parameterizations of χs in CTMs in response to environmental change factors (i.e., elevated N deposition and/or O3) in the future.

Proteomics analysis identified a DRT protein involved in arsenic resistance in Populus.

A DRT protein was identified and proved to be involved in the poplar arsenic resistance through comparative proteomics analysis between arsenic sensitive and resistant cultivars. Arsenic pollution in soil has been a serious problem all over the world. It is very important to dissect plants arsenic stress-response mechanisms in phytoremediation. In this study, arsenate-tolerant Populus deltoides cv. 'zhonglin 2025' and arsenate-sensitive Populus×euramericana cv. 'I-45/51' were screened from 10 poplar varieties. Systematic comparisons between these two cultivars demonstrated that 'zhonglin 2025' exhibited slighter morphological and structural injury, lower ROS and MDA accumulation, and higher photosynthesis and ROS scavenging ability under arsenate stress, compared with 'I-45/51'. Through comparative proteomics analysis, we detected that most of the identified arsenate-responsive proteins were stress and defense related. Among these proteins, PdDRT102 was found to be only highly induced in 'zhonglin 2025' under arsenate stress. Heterologous over-expression of PdDRT102 in Arabidopsis conferred to enhanced tolerance to arsenate and sodium chloride. PdDRT102 localizes to the plasma membrane and the nucleus in Arabidopsis. Interestingly, the remarkably increased fluorescence protein signals in the nucleus were found during arsenate stress. Together, these results not only provided an overall understanding on poplar response to arsenate stress, but also revealed that DRT102 protein might involve in protecting poplar against this stress.

Anatomy and ultrastructure adaptations to soil flooding of two full-sib poplar clones differing in flood-tolerance

Flooding stress always depressed plants survival and growth in flood-affected areas. To explore anatomy and ultrastructure adaptations to hypoxia stress, two full-sib poplar clones differing in flood-tolerance LS1 (flood-tolerant) and LS2 (flood-susceptible) were compared for waterlogging effects on them. The two clones LS1 and LS2 originated from Populus deltoides cv. Lux ex. I-69/55×P. simonii. Morphological, ecophysiological and growth parameters, as well as anatomy and ultrastructure characteristics of their seedlings were subjected for 15days to flooding treatment, followed by a three-day drainage and recovery stage. Results showed that flooding stress adversely influenced all characteristics aforementioned in all flooded plants. Compared with LS1, LS2 suffered clearly more severe flood injury during hypoxia and slower recovery ability after drainage, illustrated by morphology, biomass accumulation, gas exchange, chlorophyll fluorescence, root metabolism, and relative membrane permeability and malonaldehyde content of roots. Correspondingly, more pronounced anatomy and ultrastructure damages in leaves and roots were found in flooded LS2 as well, including palisade cell deformation in leaves, as well as serious lysis of cortical parenchyma cells and decompositions of nucleus and organelles in roots. Our results showed that morphological, ecophysiological and growth responses to soil flooding paralleled their anatomy and ultrastructure adaptations in leaves and roots. Stable intercellular and intracellular structures in leaves and roots, especially in the latter, helped the flood-tolerant clone behaved better than the flood-susceptible clone. Roots suffered more severe anatomy and ultrastructure injury than leaves under hypoxia stress. The flood-tolerant clone kept a stable cross-section anatomy with normal aerenchyma and ultrastructure in roots, which enable plant-internal aeration so that maintain aerobic respiration and basic root activities under flooding condition. The flood-susceptible clone was prone to lost normal cross-section anatomy under soil flooding caused by serious cortical parenchyma cell lysis and ultrastructure destruction, which resulted in root disorganization and dysfunction.

Interaction of drought and ozone exposure on isoprene emission from extensively cultivated poplar.

The combined effects of ozone (O3 ) and drought on isoprene emission were studied for the first time. Young hybrid poplars (clone 546, Populus deltoides cv. 55/56 x P. deltoides cv. Imperial) were exposed to O3 (charcoal-filtered air, CF, and non-filtered air +40 ppb, E-O3 ) and soil water stress (well-watered, WW, and mild drought, MD, one-third irrigation) for 96 days. Consistent with light-saturated photosynthesis (Asat ), intercellular CO2 concentration (Ci ) and chlorophyll content, isoprene emission depended on drought, O3 , leaf position and sampling time. Drought stimulated emission (+38.4%), and O3 decreased it (-40.4%). Ozone increased the carbon cost per unit of isoprene emission. Ozone and drought effects were stronger in middle leaves (13th-15th from the apex) than in upper leaves (6th-8th). Only Asat showed a significant interaction between O3 and drought. When the responses were up-scaled to the entire-plant level, however, drought effects on total leaf area translated into around twice higher emission from WW plants in clean air than in E-O3 . Our results suggest that direct effects on plant emission rates and changes in total leaf area may affect isoprene emission from intensively cultivated hybrid poplar under combined MD and O3 exposure, with important feedbacks for air quality.

Roots play a vital role in flood-tolerance of poplar demonstrated by reciprocal grafting

Poplar is one of the most important multipurpose afforestation trees in river floodplains and arable farmland which are subject to frequent flooding. To determine the relative roles that the roots and shoots have in responses to waterlogging, six root-shoot grafting combinations of full-sib poplar clones LS1 (flood-tolerant) and LS2 (flood-susceptible) were compared for waterlogging effects on them, using reciprocal and self-grafts. Plants of the six combinations comprised non-grafted (LS1) and (LS2), self-grafted (LS1/LS1) and (LS2/LS2), LS1 grafted onto LS2 (LS1/LS2), and LS2 grafted onto LS1 (LS2/LS1) experimental plants. The two clones LS1 and LS2 originated from Populus deltoides cv. Lux ex. I-69/55 (flood-tolerant)×P. simonii (flood-susceptible). Growth, morphological and ecophysiological parameters of plants belonging to the six grafting combinations were subjected for 21 days to flooding, followed by a six-day drainage and recovery stage. Results showed that flooding stress affected adversely growth, biomass accumulation, morphological and ecophysiological characteristics in all flooded plants. The more severe influences were found in the plants with LS2 roots (LS1/LS2, LS2/LS2, LS2), whereas plants having roots of LS1 (LS2/LS1, LS1/LS1, LS1) were less negatively affected. At the end of the study, 100%, 100%, 93.3%, 26.7%, 6.7% and 20% survival rates, respectively, were observed in flooded plants of LS1, LS1/LS1, LS2/LS1, LS1/LS2, LS2/LS2 and LS2. In conformity with the results for growth, biomass accumulation and morphology, responses to flooding of gas exchange, chlorophyll fluorescence, relative membrane permeability of leaves, the overall root metabolism parameter dehydrogenase activity (TTC assay), as well as malonaldehyde contents of leaves and roots also indicated that flood injury was significantly more pronounced in plants having LS2 roots than in those with LS1 roots. Plants with roots of LS1 displayed clearly faster recovery after flooding than the plants with LS2 roots. The results indicate that flooding-tolerance of poplar is based more on influences from the rootstock than on those of the scion. It is thus the root genotype that plays the decisive role in flood-tolerance of poplar.

Ecophysiological and morphological adaption to soil flooding of two poplar clones differing in flood-tolerance

Responses to soil flooding of two poplar clones differing in flood-tolerance were studied to elucidate ecophysiological and morphological adaptation to hypoxia. Results showed that Populus deltoides cv. Lux ex. I-69/55 (Lux) was flood-tolerant, whereas P. simonii was flood-susceptible, based on structural and functional differences. They differed in morphological, ecophysiological, and anatomical characteristics when subjected to flooding. The difference between cv. Lux and P. simonii became particular obvious with increased length of the flooding period (8–22 days), but responses to flooding differed already during the first week of flooding. Ecophysiologically, in the beginning of flooding cv. Lux kept a high level of photosynthesis, showed a high free water content and water use efficiency at reduced leaf conductances and leaf water potentials. Chlorophyll content of cv. Lux was reduced so that sunlight absorption was lower as well and destruction of the photosynthesis system by photooxidation was avoided. Free protein content of Lux under flooding was also low, probably in favor of synthesis of other substances that enforce flood tolerance. On the contrary, in P. simonii transpiration only slowly decreased due to slow stomatal closure of leaves in the first day of flooding, and water potential decreased slowly, accompanied with high transformation rate of free water into bound water and low water use efficiency. Slow decomposition of chlorophyll of P. simonii resulted in overabundant light energy absorption and serious destruction of photosynthesis system II (PSII). Net photosynthesis of P. simonii seriously decreased under flooding. At the morphological level, cv. Lux developed many small and obviously functional hypertrophied lenticels throughout the flooding treatment. Bigger hypertrophied lenticels of P. simonii inclined to become rotten. Under complete submergency, cv. Lux could keep an intact leaf structure, whereas epidermis and structure of leaves of P. simonii were destroyed severely. Anatomically, the ultrastructures of leaves of cv. Lux were still intact at the end of flooding, whereas those of P. simonii were destroyed seriously, and many organelles were decomposed.The flood-tolerant poplar clone showed better mechanisms of avoiding oxygen scarcity and tolerating oxygen scarcity. By contrast, the flood-susceptible poplar clone possessed such mechanisms to an insufficient degree. Under soil flooding, rapid formation and maintenance of fine hypertrophied lenticels, a quick decrease of water potential and stomatal closure, keeping for some days still a high level of photosynthesis and water use efficiency, and maintaining intact structures of leaves and roots, etc. were critical traits to survival and growth of the flooding-tolerant poplar clone.

Cadmium and zinc localization by SIMS in leaves of Populus deltoides (cv. Lena) grown in a metal polluted soil

AbstractPoplar (Populus) species can relatively accumulate high concentrations of heavy metals such as cadmium and zinc in their aboveground tissues. Cd accumulation in poplar is 30 times higher as compared to other woody species. Zn concentrations in leaves ranged from 200 to 1000 mg kg−1 dry weight (DW) and Cd concentrations from 10 to 70 mg kg−1 DW on metal polluted sites. These plants possess effective mechanisms for heavy metal translocation into aerial parts. However cellular localization of zinc and cadmium is still unknown in these species. In order to elucidate the precise localisation of these elements, leaves of poplar (Populus deltoides cv. Lena) was grown on metal polluted soil and analysed by SIMS. Using primary gallium source (FIB) mounted on IMS‐6f, it was possible to performed secondary ions positives images with a lateral resolution above to 100 nm. In this study, SIMS analysis has been performed on cross section of leaves. Results were compared with global measurement performed by ICP‐AES on reference sample (no contaminated) and poplar exposed to metals. Elemental maps of cadmium and zinc were obtained which revealed the high concentrations of metals in both the mesophyll and in the epidermal cell layer. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Function and Chromosomal Localization of Differentially Expressed Genes Induced by Marssonina brunnea f. sp. multigermtubi in Populus deltoides

A total of 1,160 differentially expressed genes induced by Marssonina brunnea f. sp. multigermtubi were identified in Populus deltoides cv. ‘Lux’ (I-69/55) with two-colour cDNA microarray including 2,952 cDNAs from two cDNA libraries constructed with 72 h inoculated poplar leaves. Functional analysis showed that 1,160 genes were classified into 11 functional categories that are involved in metabolism (15.9%), signal transduction (9.5%), transcription and replication (8.7%), and cell rescue and defense (7.8%). Among them, 926 genes were sporadically localized on 19 linkage groups. Chromosome 2 contained 102 (11%) differentially expressed genes, followed by chromosome 1 which contains 93 genes (10%), and chromosome 17 had the least number of differentially expressed genes. Clustering of expressed sequence tags (ESTs) in poplar genome was observed at the terminal regions of several chromosomes. The relationship between cluster of genes and plant defense response would be further studied.