Populus Deltoides Research Articles

Deciphering Genetic Architecture of Adventitious Root and Related Shoot Traits in Populus Using QTL Mapping and RNA-Seq Data.

Understanding the genetic architecture of adventitious root and related shoot traits will facilitate the cultivation of superior genotypes. In this study, we measured 12 adventitious root and related shoot traits of 434 F1 genotypes originating from Populus deltoides ‘Danhong’ × Populus simonii ‘Tongliao1’ and conducted an integrative analysis of quantitative trait locus (QTL) mapping and RNA-Seq data to dissect their genetic architecture and regulatory genes. Extensive segregation, high repeatability, and significant correlation relationship were detected for the investigated traits. A total of 150 QTLs were associated with adventitious root traits, explaining 3.1–6.1% of phenotypic variation (PVE); while 83 QTLs were associated with shoot traits, explaining 3.1–19.8% of PVE. Twenty-five QTL clusters and 40 QTL hotspots were identified for the investigated traits. Ten QTL clusters were overlapped in both adventitious root traits and related shoot traits. Transcriptome analysis identified 10,172 differentially expressed genes (DEGs) among two parents, three fine rooting and three poor-rooting genotypes, 143 of which were physically located within the QTL intervals. K-means cluster and weighted gene co-expression network analysis showed that PtAAAP19 (Potri.004G111400) encoding amino acid transport protein was tightly associated with adventitious roots and highly expressed in fine-rooting genotypes. Compare with ‘Danhong’, 153 bp deletion in the coding sequence of PtAAAP19 in ‘Tongliao1’ gave rise to lack one transmembrane domain, which might cause the variation of adventitious roots. Taken together, this study deciphered the genetic basis of adventitious root and related shoot traits and provided potential function genes for genetic improvement of poplar breeding.

Modulation of Morpho-Physiological Responses in Populus deltoides by Elevated Carbon Dioxide and Temperature

AbstractRising atmospheric carbon dioxide (CO2) and temperature alter gene-expression arrays commensurate with physio-morphological changes, resulting in issues of adaptation, growth patterns, and productivity of terrestrial vegetation. An experiment was conducted to investigate the adaptive response of Populus deltoides clone G48 to the combined effect of elevated CO2 and temperature inside open-top chambers. The elevated CO2 and temperature acted as environmental cues to help express upregulated/downregulated genes involved in important metabolic pathways. As a result, P. deltoides exposed to the elevated CO2 and temperature developed adaptation to undo the effect by enhancing gaseous exchange, transpiration, and carbon assimilation and partitioning as observed on 180 days after treatment. The elevated conditions significantly enhanced stomatal density and size on adaxial/abaxial leaf surfaces, chlorophyll b that augmented photosynthesis, stomatal conductance, transpiration, and internal CO2, but decreased instantaneous and intrinsic water-use efficiency. These stimulated biomass accumulation in root, stem, and leaves. Hence, the elevated conditions of CO2 and temperature operate at the gene-expression level that acts pleiotropically for reinforcement of photosynthetic apparatus, morphological amendment for accelerated gaseous exchange, and finally growth and biomass improvement, supporting adaptive plasticity of clonal planting stock of the species to future climatic change and global warming.

Changes in growth and soil microbial communities in reciprocal grafting clones between Populus deltoides males and females exposed to water deficit conditions

Our findings highlight that male-rooted clones (M/M and F/M) of Populus deltoides are more water-deficit tolerant than female-rooted clones (F/F and M/F), as shown by a smaller decrease in total biomass and net photosynthetic rate in the male-rooted clones. It has been reported that graft clones (female scion and male rootstock) in poplars may be an option to mitigate the effects of water deficit on plants. However, the extent to which grafting mitigates the effect of soil water deficit on soil microorganisms remains poorly understood. The research was designed to investigate the effects of soil water deficit on plant growth, soil microbial communities, and soil enzymatic activities of the reciprocal graft clones of P. deltoides. Four different graft clones (female shoot scion and female rootstock, F/F; male shoot scion and female rootstock, M/F; male shoot scion and male rootstock scion, M/M; and female shoot scion and male rootstock, F/M) in P. deltoides were used. Two watering regimes, irrigation and soil water deficit (i.e., non-irrigation conditions, natural levels of precipitation) were included in the experiments. The microbial community structure was quantified using phospholipid fatty acid. Under water deficit, the decreases in total biomass, net photosynthetic rates, and leaf nitrogen content were more evident in M/M and F/M than in F/F and M/F. Bacterial phospholipid fatty acids (PLFAs) and actinomycetal PLFAs remained unaffected in the four graft clones. In contrast, during soil water deficit, fungal PLFAs were higher in M/M and F/M soil coincided with higher extracellular activities of β-1,4-N-acetyl-glucosaminidase and leucine aminopeptidase. Male-rooted clones (M/M and F/M) are more tolerant to water deficit than female-rooted clones (F/F and M/F). It is possible that the better performance of M/M and F/M, when exposed to water deficit, is associated mainly with higher fine root activity, greater specific root length and root/shoot ratio as well as increased fungal PLFAs.

Morphological, physiological and molecular analysis of Line × Tester in Populus deltoides Bartr

In the present investigation, male and female clones/strains/species of Populus deltoides procured from State Forest Department, Haldwani and Shyampur, Haridwar Forest Division and maintained in the germplasm block of Naganji nursery from which 11 male and 13 female clones were included in the reproductive study and the selected plant material of 4 females (G-48, S 1, S 7 C 8 and L-62/84) and 4 males (S 7 C 11, L-17/92, L-124/86 and S 7 C 1) clones were crossed using Line × Tester (4 × 4) mating design. Control crossing was done and seedlings were raised in the nursery at stage-1 and were evaluated for morphological characters. In stage-2 clonal cuttings of selected individuals were raised in RBD and were evaluated for morphological, physiological and wood characters. The gene action study revealed that dominance variance was observed more than the additive variance for all the parameters studied. The proportional contribution of lines was higher than individual contribution of testers or line × tester interaction except for plant height, collar diameter, internodal length, leaf area, maximum width of leaf, angle between the mid rib and 2 nd lower lateral mid rib, shoot bark thickness, root bark thickness, fresh shoot weight, dry shoot weight, dry root weight, dry root shoot ratio, root length, total fresh weight, total dry weight, stomatal conductance and fibre length. Among 18 SSR markers, fifteen markers showed monomorphic allelic pattern, the remaining three markers (PMGC-2060, PMGC-2020 and PMGC-451) showed polymorphic pattern. A close appraisal of the SSR banding pattern obtained after the amplification of genomic DNA of both the parents and their hybrids revealed that, all the hybrids were similar to their parents.

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.

Root traits and rhizosphere processes reflect differential phosphorus acquisition strategies in contrasting Populus clones

Soil phosphorus (P) availability and its distribution influence plant growth and productivity. To evaluate strategies that allow genotypes to be efficient under variable P environments, we planted six hybrid Populus deltoides clones belonging to the section Aigeiros (Aig), LL1, LL9, NL351, NL35, NL1388 and NL895, to three growth conditions in a greenhouse experiment, including low P, a high homogenous P supply and a high heterogeneous P supply. Functional traits, including foliar and root traits as well as rhizosphere processes, were measured. Large genotypic variation in shoot biomass and leaf P concentration was found in response to the P supply level and pattern. Compared with no P supply, LL1, LL9 and NL895 had a greater root length, biomass and P concentration in leaves under a homogenous P supply, while growth traits of NL351, NL35 and NL1388 were not significantly affected. A heterogeneous P supply enhanced the shoot biomass of LL1 and LL9. The root proliferation of LL1 and LL9 in P-rich patches was related to increased P acquisition in leaves. By contrast, a heterogeneous P supply did not enhance the biomass accumulation and the morphological plasticity of roots in other four genotypes, NL351, NL35, NL895 and NL1388, in P-rich patches. We found that functional traits or rhizosphere processes under low P could predict high P performance in Populus clones. Genotypes with a higher specific root length under low P can accumulate a larger biomass under a homogenous P supply. Conversely, high acid phosphatase concentrations decreased the positive impact of a heterogeneous P supply on a genotype’s performance. Our results provide implications and applications for silviculture and forest management.

Complete Genome Sequence of Terriglobus albidus Strain ORNL, an Acidobacterium Isolated from the Populus deltoides Rhizosphere.

Terriglobus albidus strain ORNL is a heterotrophic soil acidobacterium isolated from the rhizosphere of an Eastern cottonwood tree (Populus deltoides) in Tennessee. Its 6.4-Mb chromosome was completely sequenced using PacBio long reads, and it encodes 5,010 proteins and 53 RNAs.

PdWND3A, a wood-associated NAC domain-containing protein, affects lignin biosynthesis and composition in Populus

BackgroundPlant secondary cell wall is a renewable feedstock for biofuels and biomaterials production. Arabidopsis VASCULAR-RELATED NAC DOMAIN (VND) has been demonstrated to be a key transcription factor regulating secondary cell wall biosynthesis. However, less is known about its role in the woody species.ResultsHere we report the functional characterization of Populus deltoides WOOD-ASSOCIATED NAC DOMAIN protein 3 (PdWND3A), a sequence homolog of Arabidopsis VND4 and VND5 that are members of transcription factor networks regulating secondary cell wall biosynthesis. PdWND3A was expressed at higher level in the xylem than in other tissues. The stem tissues of transgenic P. deltoides overexpressing PdWND3A (OXPdWND3A) contained more vessel cells than that of wild-type plants. Furthermore, lignin content and lignin monomer syringyl and guaiacyl (S/G) ratio were higher in OXPdWND3A transgenic plants than in wild-type plants. Consistent with these observations, the expression of FERULATE 5-HYDROXYLASE1 (F5H1), encoding an enzyme involved in the biosynthesis of sinapyl alcohol (S unit monolignol), was elevated in OXPdWND3A transgenic plants. Saccharification analysis indicated that the rate of sugar release was reduced in the transgenic plants. In addition, OXPdWND3A transgenic plants produced lower amounts of biomass than wild-type plants.ConclusionsPdWND3A affects lignin biosynthesis and composition and negatively impacts sugar release and biomass production.

Tree Water Use, Water Use Efficiency, and Carbon Isotope Discrimination in Relation to Growth Potential in Populus deltoides and Hybrids under Field Conditions

We explored the relationship between tree growth, water use, and related hydraulic traits in Populus deltoides Bartr. ex Marsh.and hybrid clones, to examine potential trade-offs between growth and water use efficiency. Nine genotypes, six P. deltoides and three hybrid clones, that represented genotypes with high (Group H), intermediate (Group I), and low (Group L) growth performance were selected for study, based on year-two standing stem biomass in a replicated field trial. In year four, tree growth, transpiration (Et), canopy stomatal conductance (Gs), whole-tree hydraulic conductance (Gp), and carbon isotope discrimination (Δ13C) were measured. Tree sap flux was measured continuously using thermal dissipation probes. We hypothesized that Group H genotypes would have increased growth efficiency (GE), increased water use efficiency of production (WUEp, woody biomass growth/Et), lower Δ13C, and greater Gp than slower growing genotypes. Tree GE increased with relative growth rate (RGR), and mean GE in Group H was significantly greater than L, but not I. Tree WUEp ranged between 1.7 and 3.9 kg biomass m3 H2O−1, which increased with RGR. At similar levels of Et, WUEp was significantly greater in Group H (2.45 ± 0.20 kg m−3), compared to I (2.03 ± 0.18 kg m−3) or L (1.72 ± 0.23 kg m−3). Leaf and wood Δ13C scaled positively with stem biomass growth but was not correlated with WUEp. However, at a similar biomass increment, clones in Group H and I had significantly lower leaf Δ13C than Group L. Similarly, Group H clones had a significantly lower wood Δ13C than Group L, supporting our hypothesis of increased WUE in larger trees. Tree physiological and hydraulic traits partially explain differences in WUEp and Δ13C, and suggest that clone selection and management activities that increase tree biomass production will likely increase tree and stand WUE. However, more research is needed to discern the underlying hydraulic mechanisms responsible for the higher WUE exhibited by large trees and distinct clones.

Comportamiento Mecánico de Barras Esbeltas de Madera Laminada Encolada de Álamo ‘Australiano 129/60’ y ‘Stoneville 67’ (Populus Deltoides) del Delta del Río Paraná Sometidas a Esfuerzos de Compresión

En el año 2016 con la aprobación del primer Reglamento Argentino de Estructuras de Madera, se da un impulso importante al poner a disposición de los profesionales una normativa con criterios de diseño para estas estructuras , con valores de referencias para las especie/procedencia estudiadas, que son la Araucaria angustifolia de Misiones, el Eucalyptus grandis de Entre Ríos, el Pinus Taeda - Elliottii de Misiones y Corrientes y el Populus deltoides del delta del río Paraná. Con la utilización de elementos laminados encolados surge la necesidad de un proceso de fabricación que asegure la buena prestación. En Argentina las normas IRAM 9660/1/2 y 9661 del año 2015 establecen las pautas de fabricación y control para estos elementos estructurales. En este trabajo el objetivo del estudio es determinar el comportamiento resistente y elástico de barras esbeltas de madera laminada encolada de Populus deltoides ‘Australiano 129/60’ y ‘Stoneville 67’ cultivado en Argentina, sometidas a esfuerzos de compresión. Se desarrolló el cálculo teórico de la tensión crítica según los criterios del reglamento INTI-CIRSOC (2016a) y Eurocódigo 5 (EN 1995-1-1 2005) para barras esbeltas comprimidas en piezas de madera encolada de Populus deltoides a los efectos de evaluar el nivel de seguridad que proveen los procedimientos de cálculos, verificar las diferencias entre ambos y comparar los resultados obtenidos de los ensayos de 320 barras esbeltas.

New species of Septoria associated with leaf spot diseases in Iran

ABSTRACTSpecies of Septoria are commonly associated with leaf spot diseases of a broad range of plant hosts worldwide. During our investigation of fungi associated with leaf spot diseases in northern and northwestern Iran, several Septoria isolates were recovered from symptomatic leaves on different herbaceous and woody plants in the Asteraceae, Betulaceae, and Salicaceae families. These isolates were studied by applying a polyphasic approach including morphological and cultural data and a multigene phylogeny using a combined data set of partial sequences of the 28S nuc rRNA gene (large subunit [28S]), internal transcribed spacer regions and intervening 5.8S nuc rRNA gene (ITS) of the nuc rDNA operon, actin (actA), translation elongation factor 1-α (tef1), calmodulin (cmdA), β-tubulin (tub2), and DNA-directed RNA polymerase II second largest subunit (rpb2). Four novel species are proposed, namely, Septoria eclipticola on Eclipta prostrata, Septoria firouraghina on Cirsium arvense, Septoria guilanensis on Populus deltoides, and Septoria taleshana on Alnus subcordata. All species are illustrated, and their morphology and phylogenetic relationships with other Septoria species are discussed.

Біолого-екологічні особливості поширення омели білої (Viscum album) в умовах міста Вінниця

У межах населених пунктів, зокрема й у Вінниці, омела біла набула інтенсивного поширення. Ураження дерев омелою призводить як до погіршення стану дерев, їх подальшого всихання, так і до зниження естетичної оцінки насаджень. Незважаючи на інтенсивне пошкодження деревних насаджень омелою у Вінниці, достатньо стійкими виявилися дерева більшості хвойних видів, зокрема: сосна, ялина, дугласія. Із листяних видів достатньо високою стійкістю відрізняється дуб, граб, бук. Незначною мірою пошкоджується омелою каштан, дуб червоний, горіх та ін. Поряд із цим, більшість алейних насаджень, зокрема тополі та липи, істотно пошкоджені цим напівпаразитом. Це зумовлено не лише особливістю деревних порід, але й і їхнім віком. Зокрема, більшість дерев старшого віку із наявними пошкодженнями стовбурової частини та гілок інтенсивніше уражаються омелою. За результатами проведених досліджень виявлено, що вік дерев, які найбільш уражені омелою білою, становить 50-60 років і з віком ступінь ураження зростає, а частка ураження дерев віком 70-80 років становить 25-29 %. Ступінь ураження дерев омелою білою визначено за 5-бальною шкалою, згідно з якою найвищий бал ураження виявлено у тополі чорної та дельтовидної (5 балів), найнижчий – у ялини звичайної, липи серцелистої (1-2 бали). Розглядаючи види Populus за інтенсивністю заселення їх Viscum album, встановлено, що низький і високий ступені ураження мають 26 % дерев, середній – 28 %, а дуже високий – 30 %. Найбільшою часткою дерев з високим і дуже високим ступенем ураження відзначаються P. nigra та P. deltoids – 22 і 32 %.

Relatively rare root endophytic bacteria drive plant resource allocation patterns and tissue nutrient concentration in unpredictable ways.

Plant endophytic bacterial strains can influence plant traits such as leaf area and root length. Yet, the influence of more complex bacterial communities in regulating overall plant phenotype is less explored. Here, in two complementary experiments, we tested whether we can predict plant phenotype response to changes in microbial community composition. In the first study, we inoculated a single genotype of Populus deltoides with individual root endophytic bacteria and measured plant phenotype. Next, data from this single inoculation were used to predict phenotypic traits after mixed three-strain community inoculations, which we tested in the second experiment. By itself, each bacterial endophyte significantly but weakly altered plant phenotype relative to noninoculated plants. In a mixture, bacterial strain Burkholderia BT03, constituted at least 98% of community relative abundance. Yet, plant resource allocation and tissue nutrient concentrations were disproportionately influenced by Pseudomonas sp. GM17, GM30, and GM41. We found a 10% increase in leaf mass fraction and an 11% decrease in root mass fraction when replacing Pseudomonas GM17 with GM41 in communities containing both Pseudomonas GM30 and Burkholderia BT03. Our results indicate that interactions among endophytic bacteria may drive plant phenotype over the contribution of each strain individually. Additionally, we have shown that low-abundance strains contribute to plant phenotype challenging the assumption that the dominant strains will drive plant function.

Projected warming disrupts the synchrony of riparian seed release and snowmelt streamflow

Globally, spring phenology and abiotic processes are shifting earlier with warming. Differences in the magnitudes of these shifts may decouple the timing of plant resource requirements from resource availability. In riparian forests across the northern hemisphere, warming could decouple seed release from snowmelt peak streamflow, thus reducing moisture and safe sites for dominant tree recruitment. We combined field observations with climate, hydrology, and phenology models to simulate future change in synchrony of seed release and snowmelt peaks in the South Platte River Basin, Colorado, for three Salicaceae species that dominate western USA riparian forests. Chilling requirements for overcoming winter endodormancy were strongest in Salix exigua, moderately supported for Populus deltoides, and indiscernible in Salix amygdaloides. Ensemble mean projected warming of 3.5°C shifted snowmelt peaks 10-19d earlier relative to S.exigua and P.deltoides seed release, because decreased winter chilling combined with increased spring forcing limited change in their phenology. By contrast, warming shifted both snowmelt peaks and S.amygdaloides seed release 21d earlier, maintaining their synchrony. Decoupling of snowmelt from seed release for Salicaceae with strong chilling requirements is likely to reduce resources critical for recruitment of these foundational riparian forests, although the magnitude of future decoupling remains uncertain.

Interspecific hybridisation and LTR-retrotransposon mobilisation-related structural variation in plants: A case study

The dynamics of long-terminal-repeat retrotransposons in two poplar species (Populus deltoides and P. nigra) and in an interspecific hybrid, recently synthesized, were investigated by analyzing the genomic abundance and transcription levels of a collection of 828 full-length retroelements identified in the genome sequence of P. trichocarpa, all occurring also in the genomes of P. deltoides and P. nigra. Overall, genomic abundance and transcription levels of many retrotransposons in the hybrid resulted higher or lower than expected by calculating the mean of the parental values. A bioinformatics procedure was established to ascertain the occurrence of the same retrotransposon loci in the three genotypes. The results indicated that retrotransposon abundance variations between the hybrid and the mean value of the parents were due to i) co-segregation of retrotransposon high- or low-abundant haplotypes; ii) new retroelement insertions; iii) retrotransposon loss. Concerning retrotransposon expression, this was generally low, with only 14/828 elements over- or under-expressed in the hybrid than expected by calculating the mean of the parents. It is concluded that interspecific hybridisation between the two poplar species determine quantitative variation and differential expression of some retrotransposons, with possible consequences for the genetic differentiation of the hybrid.

Growth and physiological responses of three poplar clones grown on soils artificially contaminated with heavy metals, diesel fuel, and herbicides

We tested the growth and physiological responses of three poplar clones [Populus deltoides Bartr. ex Marsh. ‘Bora’, ‘PE 19/66’; Populus × euramericana (Dode) Guinier ‘Pannonia’] grown for 3 years on soils artificially contaminated with heavy metals, diesel fuel, and herbicides at the Experimental Estate of the Institute of Lowland Forestry and Environment (ILFE), University of Novi Sad, Serbia. Within three field blocks, clonal whole-plots were divided into seven subplots containing a non-contaminated control and six artificially-contaminated soil treatments: (1) 10.6 kg Cd ha−1, (2) 247 kg Cu ha−1, (3) 183.3 kg Ni ha−1, (4) 6,667 L diesel fuel ha−1, (5) 236 g Oxyfluorfen ha−1, and (6) 1,320 g Pendimethalin ha−1. Significant clone × treatment interactions governed growth and physiology throughout the study (p < 0.05), and the influence of inorganics versus organics varied with tree age. Heavy metals had a more substantial influence on growth and physiology as the trees matured, while diesel and herbicide treatments were most pronounced during the first growing season (p < 0.0001). Clones ‘Bora’ and ‘PE 19/66’ exhibited greater biomass than ‘Pannonia’, with trees growing in the control soils exhibiting 13.8 and 19.6 times greater biomass than ‘Pannonia’, respectively.

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.

Leaf litter identity alters the timing of lotic nutrient dynamics

Abstract The effects of resource quality on ecosystems can shift through time based on preferential use and elemental needs of biotic consumers. For example, leaf litter decomposition rates are strongly controlled by initial litter quality, where labile litter is processed and depleted more quickly than recalcitrant litters. We examined the effect of this processing continuum on stream nutrient dynamics. We added one of four different litter compositions differing in litter quality (cottonwood [Populus deltoides], labile; sycamore [Platanus occidentalis], recalcitrant; bur oak [Quercus macrocarpa], recalcitrant; and mixed [equivalent mixture of previous three species]) to 12 large (c. 20 m long, with riffle, glide and pool sections) outdoor stream mesocosms to assess the effect of litter species composition on whole‐stream nutrient uptake. Nutrients were dosed once weekly for 8 weeks to measure uptake of NH4–N, NO3–N, and PO4–P. We also measured changes in litter C, N, and P content on days 28 and 56 of the study. Nutrient uptake rates were highly variable, but occasionally very different among litter treatments (c. 5× between highest and lowest uptake rates by species). Uptake rates were generally greatest in cottonwood (labile) streams early in the study. However, during the last 4 weeks of the study, bur oak streams (recalcitrant) took up more nutrients than cottonwood streams, resulting in more cumulative NO3–N uptake in bur oak than in cottonwood streams. Cumulative NO3–N uptake was greater in mixed streams than expected (non‐additive) on two dates of measurement, but was generally additive. Changes in litter nutrient content largely corroborated nutrient uptake patterns, suggesting strong N immobilisation early in the study and some N mineralisation later in the study. P was strongly retained by most litters, but especially bur oak. Nutrient content of litter also largely changed additively, suggesting minimal evidence for non‐additive diversity effects on nutrient source/sink status. Our results demonstrate that litter species identity can have whole‐ecosystem effects on stream nutrient dynamics, with important implications for the form and fate of nutrients exported downstream. Further, diverse litter assemblages may serve as temporal stabilisers of ecosystem processes, such as nutrient sequestration, due to microbial nutrient requirements and differential decomposition rates, or the classic litter processing continuum.

The chemical composition of poplar wood in relation to the species and the age of trees

The chemical composition of poplar wood in relation to the species and age of trees. The contents of the following substances: mineral substances, extractives, cellulose, lignin, holocellulose, in wood from fastgrowing poplar species (Populus deltoides x maximowiczii and Populus trichocarpa Torr and A.Gray) aged 2.5, 3, 5 and 7 years were compared to the contents of the abovementioned substances in Populus nigra L. and Populus alba L. wood, aged about 30. According to other publications, the cellulose and lignin contents increase in line with the tree's age. On the other hand, the comparison of cellulose content in studied poplar wood showed that its content did not depend from the species of tree, age and growth environment. Whereas, the content of extractives in poplar wood was dependent from the species of tree and growth environment. The lignin content in Populus deltoides x maximowiczii and Populus trichocarpa wood did not depend from its age and was similar to the lignin content in 30-year-old P. nigra wood. 30-year-old wood of P. nigra and P. alba contained less holocellulose compared to its contents in P. deltoides x maximowiczii and P. trichocarpa wood, regardless of its age.

Rootstock determines the drought resistance of poplar grafting combinations.

To increase yield and/or enhance resistance to diseases, grafting is often applied in agriculture and horticulture. Interspecific grafting could possibly be used in forestry as well to improve drought resistance, but our understanding of how the rootstock of a more drought-resistant species can affect the grafted plant is very limited. Reciprocal grafts of two poplar species, Populus cathayana Rehder (less drought-resistant, C) and Populus deltoides Bart. ex Marsh (more drought-resistant, D) were generated. Four grafting combinations (scion/rootstock: C/C, C/D, D/D and D/C) were subjected to well-watered and drought stress treatments. C/D and D/C had a higher diameter growth rate, leaf biomass, intrinsic water-use efficiency (WUEi) and total non-structural carbohydrate (NSC) content than C/C and D/D in well-watered condition. However, drought caused greater differences between P. deltoides-rooted and P. cathayana-rooted grafting combinations, especially between C/D and D/C. The C/D grafting combination showed higher resistance to drought, as indicated by a higher stem growth rate, net photosynthetic rate, WUEi, leaf water potential, proline concentration and NSC concentration and maintenance of integrity of the leaf cellular ultrastructure under drought when compared with D/C. D/C exhibited severely damaged cell membranes, mitochondria and chloroplasts under drought. The scion genotype caused a strong effect on the root proline concentration: the P. cathayana scion increased the root proline concentration more than the P. deltoides scion (C/C vs D/C and C/D vs D/D) under water deficit. Our results demonstrated that mainly the rootstock was responsible for the drought resistance of grafting combinations. Grafting of the P. cathayana scion onto P. deltoides rootstock resulted in superior growth and biomass when compared with the other three combinations both in well-watered and drought stress conditions.