Native Populus Research Articles

Microbial community structure of decayed trunks of Populus euphratica desert riparian forests in the lower Tarim River, Xinjiang, China

Rich microbial communities are associated with tree decay, and they markedly impact the degradation of tree species and material cycling within ecosystems. The native Populus euphratica forests along the lower Tarim River of China are mostly mature or over-mature, with many tree trunks exhibiting features of extensive cavity decay and slow regeneration. In this study, a growth cone was used to drill a wood core at varying degrees of decay, and 16S and internal transcribed spacer techniques were used to identify the microbial structure (fungi and bacteria) within the wood core. Changes in the trunk microbial community under varying decay conditions were also examined. For healthy, lightly decayed, and heavily decayed trunk, the dominant bacterial and fungal phyla were Firmicutes and Actinobacteria, Ascomycota, and Basidiomycota, respectively. As decay progressed, the alpha diversity index of the microbial community tended to decline. The maximum number of differential species was found in healthy trunks, where leaner discriminant analysis effect size (LEfSe) of fungi and bacteria revealed 1 and 15 different species, respectively. Species network analysis showed that interspecific linkages were more complex within bacterial communities than within fungal communities, with the complexity of fungal interspecific relationship increasing as decay progressed. The microbial communities of P. euphratica trunks differed significantly with the varying degrees of decay. Microbes such as Ralstonia may also play key roles in the decay process. In addition to providing a foundation for the sustainable management of desert riparian forests, investigating the mechanisms through which microbial communities influence the deterioration of P. euphratica trunks provides information about the general health of P. euphratica forests.

Host Plant Mediated Differences in Papilio rutulus Lucas Larval Growth (Papilionidae)

Average development times differed significantly among the test plants and ranged from 27.9 days on Populus nigra to 61.5 days on Ligustrum japonicum. Average pupal mass differed significantly among the test plants and varied from 1330 mg on Prunus serotina to 740 mg on Fraxinus latifolia. There was a significant negative relationship between developmental time and percent larval survival and a significant positive relationship between larval survival and pupal mass. Fast larval development on a plant meant higher survival and heavier pupae. The growth rate of Papilio rutulus larvae varied from a high of 0.256 mg/day on Populus nigra to a low of 0.143 mg/day on Populus alba and 0.126 mg/day on Alnus tenuifolia. The larvae were able to extend their development time on some plants like Alnus tenuifolia and Prunus ilicifolia to produce heavier pupae. Biochemical flexibility in larval survival, developmental time and pupal mass allow P. rutulus larvae to utilize a wide variety of native and introduced plants and to colonize large areas in California with few to no native Populus or Salix hosts including urban areas with extensive plantings of ornamental plants and scattered individual apple and stone fruit trees, and the 651,000+ hectares of commercial California almond, stone fruit and apples. Selection of the host plants with the fastest development times allows P. rutulus to survive at high altitude areas in which there are otherwise too few heat units to allow their offspring to attain the pupal stage and overwinter.

Phenotypic Diversity and Variation in Natural Populus euphratica Populations Shaped by Environmental Factors

Phenotypic Diversity and Variation in Natural Populus euphratica Populations Shaped by Environmental Factors

Non-native tree plantations are weak substitutes for near-natural forests regarding plant diversity and ecological value

While near-natural forest stands are dramatically diminishing, monoculture tree plantations are rapidly spreading globally, including the eastern part of Central Europe. Tree plantations are regarded as simplified and species-poor ecosystems, but their functional and phylogenetic diversity and ecological value are still mostly unknown. In the present study, we investigated near-natural poplar forests and the three most common tree plantation types (native deciduous Populus alba, non-native evergreen Pinus nigra, and non-native deciduous Robinia pseudoacacia plantations) in the Kiskunság Sand Ridge, central Hungary. Our aim was to find out how different the species composition of the studied habitats is, how taxonomic, functional, and phylogenetic diversity vary among the four habitat types (i.e., near-natural forests and three types of plantations), and what the ecological value of the studied habitats is. We found that the four habitat types had significantly different species compositions. Although each habitat contained some diagnostic species, near-natural forests had the highest number of diagnostic species. While many of the diagnostic species of near-natural forests were native shrubs, tree plantations had many weeds and non-native herbs as diagnostic species. Near-natural forests had the highest per plot richness of native species and the lowest richness of non-natives. Shannon diversity, functional diversity and phylogenetic diversity were higher in the near-natural forests and two types of plantations (Populus and Pinus) compared to Robinia plantations. Based on naturalness indicator values, near-natural forests were the least degraded and Robinia plantations were the most degraded. Near-natural forests contained the most species of high conservation importance. Overall, near-natural forests proved to be much more valuable from an ecological and conservation perspective than any of the studied plantations; conservation and restoration programs should therefore focus on this type of habitat. Among the plantations, Populus alba plantations are the best substitute option in most respects, although they harbored a relatively high number of non-native species. We suggest that the native Populus alba should be preferred to non-native tree species when plantations are established. In addition, decreasing the extent of Pinus and Robinia plantations is essential on the long run if we aim to maintain the ecological integrity of the region.

新疆艾比湖胡杨凋落物与裸斑土壤代谢物差异比较

PDF HTML阅读 XML下载 导出引用 引用提醒 新疆艾比湖胡杨凋落物与裸斑土壤代谢物差异比较 DOI: 10.5846/stxb202102030358 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 绿洲生态重点实验室开放课题-胡杨冠下草本植物稀疏的机制研究(2020D04003) Comparison of soil metabolite differences between litter of Populus euphratica and bare spots in Ebinur Lake area, Xinjiang Author: Affiliation: Fund Project: Open Project of Key Laboratory of Xinjiang Uygur Autonomous Region-《Study on the Mechanisms of Herbs Sparsity under Populus euphratica Canopy》 (Grant number: 2020D04003). 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在干旱区荒漠胡杨疏林中,胡杨冠下存在草本植物极其稀疏的裸露斑块(简称裸斑)。为研究胡杨冠下裸斑形成化感机理,以裸斑内、外土壤以及冠下凋落物为研究对象,利用液相色谱-质谱联用技术对不同样本进行代谢组分析,使用PLS-DA鉴定并筛选各组代谢物差异,筛选出裸斑内、外土壤样本中差异显著的代谢物质及其代谢相关通路。研究结果显示,土壤样品中共鉴定出总代谢物质908种(615正,293负);凋落物样品中共鉴定出总代谢物质1291种(760正,531负)。通过筛选、注释并分类各组间差异显著的代谢物发现曲酸、微囊藻毒素、茶碱、辛二酸、花生四烯酸以及反式肉桂酸等化感物质相对定量值均为裸斑内显著大于裸斑外土壤;儿茶素、咖啡酸、吲哚、棕榈油酸、孜然醛、阿魏酸、反式肉桂酸、花生四烯酸、水杨醇以及香豆素等化感物质相对定量值均为凋落物样中显著大于土壤样品。以上胡杨潜在化感物质的积累可能增强植物的化感效应,导致胡杨冠下草本植物种子萌发及生长受到限制。 Abstract:The herbaceous plants are rare under the crown of the natural Populus euphratica stands (referred to as bare spots) in the arid Populus euphratica sparse forest area. To study the allelopathic formation mechanism of the bare spots under the Populus euphratica canopy, the soil inside and outside the bare spots and the litter under the canopy were used as the research objects in Ebinur Lake. We analyzed metabolomes of different samples using LC-MS technology, used PLS-DA to identify and screen metabolite differences in each group, and screened out significant differences in metabolites and their metabolic pathways in soil samples inside and outside of the bare spots. The results of the study showed that 908 total metabolites (615 positive and 293 negative) were identified in soil samples; a total of 1,291 total metabolites (760 positive and 531 negative) were identified in litter samples. By annotation and classification, it is found that the relatively quantitative values of allelochemicals such as Kojic acid, Microcystin, Theophylline, Suberic acid, Arachidonic acid and Trans-cinnamic acid were significantly higher in the bare spot than that in the soil under the tree canopy; In litter samples the relative quantitative values of allelochemicals such as Catechin, Caffeic acid, Indole, Palmitoleic acid, Cumin aldehyde, Ferulic acid, Trans-cinnamic acid, Arachidonic acid, Salicylic alcohol and Coumarin were significantly higher than that in soil samples. The accumulation of the above potential allelopathic substances in soil under Populus euphratica canopy and its litter may enhance the allelopathic effect of plants, leading to restrictions on the germination and growth of herb seeds under the Populus euphratica canopy. 参考文献 相似文献 引证文献

Models combining multiple scales of inference capture hydrologic and climatic drivers of riparian tree distributions

AbstractPredicting species geographic distributions is key to managing invasive species, conserving biodiversity, and understanding species' environmental requirements. Species distribution models (SDMs) commonly focus on climatic predictors, but other environmental factors can also be essential, particularly for species with specialized habitats defined by hydrologic, topographic, or edaphic conditions (e.g., riparian, wetland, alpine, coastal, serpentine). Here, we demonstrate a novel approach for capturing strong effects of both hydrologic and climatic predictors in SDMs for riparian plants, by merging analyses targeted at environmental drivers within riparian ecosystems and across the western USA (3.8 × 106 km2). We developed presence‐background SDMs from five algorithms for three invasive riparian trees (Tamarix ramossisima/chinensis [saltcedar], Elaeagnus angustifolia [Russian olive], and Ulmus pumila [Siberian elm]) and three native Populus spp. (cottonwoods). We used separate background datasets to develop models with different spatial scales of inference: (1) spatially filtered random points to represent available habitat across the study area and (2) target‐group points from Salix (willow) occurrences to represent available riparian habitat. Random‐background models captured hydrologic drivers of riparian tree distributions relative to the largely upland western USA, whereas Salix‐background models captured climatic drivers within the context of riparian ecosystems. Combining predictions from the two backgrounds identified hydrologically suitable habitats within climatically suitable regions, resulting in fewer false “absences” than either background alone, improving predictions over previous SDMs, and providing more complete information to guide management decisions. Surprisingly, the predicted habitat for U. pumila, a newly recognized riparian invader, was as or more extensive than Populus deltoides/fremontii, T. ramossisima/chinensis, and E. angustifolia, the most common riparian tree complexes in the western USA. Watersheds constituting 20% of U. pumila predicted habitat contained no occurrence records, indicating high risk of future and unrecognized invasions. Combining models from random and ecosystem‐specific target‐group backgrounds may improve SDMs for species from many specialized habitats, providing a method to link predicted distributions to localized geographic features while capturing broad‐scale climatic requirements.

Detection and confirmation of diagnostic microsatellite loci in Populus nigra and Populus deltoides to identify their hybrids (P. × canadensis)

Poplar cultivation has economic, social, ecological, and environmental importance in Turkey. Even though, Populus × canadensis hybrids play an important role for the commercial poplar cultivation with good growth performance and adaptability, hybrid clones introduced the different region of Turkey have started to replace the native stands of Populus nigra gradually. To continue sustainable cultivation of poplar and to conserve the native stands of P. nigra at the same time, genetic identification, and registration of the Populus cultivars from different origins are essential in breeding programs. Genetic identification and characterization of a natural population of P. nigra growing along the Melendiz River, Populus deltoides, and hybrid P. × canadensis trees were performed by 12 microsatellites loci. In addition, 18 P. nigra trees from EUFORGEN core collection were screened as reference samples. P. deltoides specific alleles were detected at four microsatellite loci previously reported as having diagnostic alleles. Several P. nigra trees from natural population and EUFORGEN core collection also included species-specific alleles of P. deltoides. It is concluded that there is an introgression event between the natural population and cultivated hybrids or P. deltoides clones in the surrounding area. Also, some members of the EUFORGEN core collection could have been mixed up or misidentified as P. nigra. The obtained results indicated that the application of the rigorous standards for reliable identification and registration with large sample size is a necessity for future breeding and conservation programs. Also, conservation of the native Populus nigra trees is an important requirement to prevent the genetic pollution of the species' gene pool and reduction of effective population size.

Intersexual segregation in winter foraging of great spotted woodpecker Dendrocopos major in riparian forests infested with invasive tree species

ABSTRACT We investigated the pre-breeding intersexual foraging habitat preferences of the great spotted woodpecker Dendrocopos major in six old, unmanaged riparian forest stands in Central Hungary, which are composed mainly of the invasive North American green ash Fraxinus pennysylvanica and boxelder Acer negundo, and native poplar Populus sp. and willow Salix sp. trees in lower abundances. With the influence of river management, the two invasive species have usurped native tree species in numerous Central European riparian forests. We studied the intersexual utilization of tree species, tree condition, stem diameter, foraging height, horizontal sections, substrate diameter, substrate condition, and foraging technique. The birds showed intersexual segregation in numerous studied variables despite the high niche overlap between sexes. Similar patterns were also found in other woodpecker species as well. We think that the most important part of this segregation could be the difference revealed in the choice of tree species, as males tended to be more specialized for native softwood tree species with rougher bark structure. Despite the high abundance of invasive tree species, neither sex preferred them. The further population decrease of native tree species could increase within-species competition and negatively affect the studied bird species.

Different sexual impacts of dioecious Populus euphratica on microbial communities and nitrogen cycle processes in natural forests

Plant-soil microbe interactions are determined by plant characters. Sexual dimorphism in root development, nitrogen (N) assimilation and resource allocation have been studied in different environments. However, how dioecious plants affect soil microbial communities in natural forests, particularly in low precipitation regions, is still poorly known. In this study, natural Populus euphratica forests were investigated in three arid regions. We hypothesized that males and females impose sex-specific impacts on physiochemical traits of soil, microbial communities and N-cycling processes. We discovered only little sex effect on most physiochemical traits, and bacterial and fungal communities in top soil (0–20 cm) in the three studied forests. However, the sex effect was greater in deep soil. Compared with fungi, the structure and composition of bacterial communities were affected more by plant sex in the rhizosphere and bulk soil. Sex indirectly affected N-cycling processes through a negative impact on the soil water content. Expressions of AOA, AOB, nifH, nirS and nirK in the rhizosphere soil were significantly affected by sex, forest site and their interactions. Proteobacteria, Actinobacteria and Firmicutes in the rhizosphere and bulk soils of P. euphratica males showed more significant effects on ammoxidation, N fixation, denitrification and protease activities when compared to females. The results suggest that sexual differences in shaping bacterial communities and affecting N-cycling processes are greater when the soil becomes drier. Thus, low precipitation causes intense sex differences in the nitrogen uptake and use efficiency. Our study highlights the importance of sexual effects on shaping specific microbial communities and N-cycling processes.

Using Sentinel-2 Images to Map the Populus euphratica Distribution Based on the Spectral Difference Acquired at the Key Phenological Stage

Populus euphratica is an important tree species in desert ecosystems. The protection and restoration of natural Populus euphratica forests requires accurate positioning information. The use of Sentinel-2 images to map the Populus euphratica distribution at a large scale faces challenges associated with discriminating between Populus euphratica and Tamarix chinensis. To address this problem, this study selected the Daliyabuyi Oasis in the hinterland of the Taklimakan Desert as the study site and sought to distinguish Populus euphratica from Tamarix chinensis. First, we determined the peak spectral difference period (optimal time window) between Populus euphratica and Tamarix chinensis within monthly Sentinel-2 time-series images. Then, an appropriate vegetation index was selected to represent the spectral difference between Populus euphratica and Tamarix chinensis within the key phenological stage. Finally, the maximum entropy method was used to automatically determine the threshold to map the Populus euphratica distribution. The results indicated that the period from 22 April to 1 May was the optimal time window for mapping the Populus euphratica distribution in the Daliyabuyi Oasis. The combination of the inverted red-edge chlorophyll index (IRECI) and the maximum entropy method can effectively distinguish Populus euphratica from Tamarix chinensis. The user’s accuracy of the Populus euphratica distribution extraction from single-data Sentinel-2 images acquired within the optimal time window was 0.83, the producer’s accuracy was 0.72, and the F1-score was 0.77. This study verified the feasibility of mapping Populus euphratica distribution based on Sentinel-2 images, and analyzed the validity of exploiting spectral differences within the key phenological stage from a single-data image to distinguish between the two species. The results can be used to extract the distribution of Populus euphratica and serve as an auxiliary variable for other plant classification methods, providing a reference for the extraction and classification of desert plants.

Reintroduced Native Populus nigra in Restored Floodplain Reduces Spread of Exotic Poplar Species.

Exotic Populus taxa pose a threat to the success of riparian forest restoration in floodplain areas. We evaluated the impact of exotic Populus taxa on softwood riparian forest development along the river Common Meuse after introducing native Populus nigra and after the re-establishment of the natural river dynamics. We sampled 154 poplar seedlings that spontaneously colonized restored habitat and assessed their taxonomy based on diagnostic chloroplast and nuclear microsatellite markers. Furthermore, by using a paternity analysis on 72 seedlings resulting from six open pollinated P. nigra females, we investigated natural hybridization between frequently planted cultivated poplars and native P. nigra. The majority of the poplar seedlings from the gravel banks analyzed where identified as P. nigra; only 2% of the sampled seedlings exhibited genes of exotic poplar species. Similarly, the majority of the seedlings from the open pollinated progenies were identified as P. nigra. For three seedlings (4%), paternity was assigned to a cultivar of P. × canadensis. Almost two decades after reintroducing P. nigra, the constitution of the seed and pollen pools changed in the study area in favor of reproduction of the native species and at the expense of the exotic poplar species. This study indicates that, although significant gene flow form exotic poplars is observed in European floodplains, restoration programs of the native P. nigra can vigorously outcompete the exotic gene flows and strongly reduce the impact of exotic Populus taxa on the softwood riparian forest development.

Discovering Biomass Structural Determinants Defining the Properties of Plant-Derived Renewable Carbon Fiber

SummaryTraditional lignocellulosic feedstock research has focused on biomass characteristics essential for improving saccharification efficiency, yet the key biomass features underlying high-quality renewable lignin materials remain unknown. Nevertheless, modern biorefinery cannot achieve sustainability and cost-effectiveness unless the lignin stream can be valorized. We hereby addressed these scientific gaps by investigating biomass characteristics defining lignin-based carbon materials properties. Lignin from eight sorghum samples with diverse characteristics was fabricated into carbon fibers (CFs). Remarkably, only lignin uniformity was found to define CF mechanical performance, highlighting the new structure-property relationship. Contrarily, lignin content and composition did not impact on carbon material properties. Mechanistic study by XRD and Raman spectroscopy revealed that higher lignin uniformity enhanced CF microstructures, in particular, turbostratic carbon content. The study for the first time highlighted lignin uniformity as an important biomass structure determinant for renewable products, which opened up new avenues for feedstock design toward diverse products enabling sustainable and cost-effective bioeconomy.

Phenotypic plasticity of natural Populus trichocarpa populations in response to temporally environmental change in a common garden

BackgroundNatural selection on fitness-related traits can be temporally heterogeneous among populations. As climate changes, understanding population-level responses is of scientific and practical importance. We examined 18 phenotypic traits associated with phenology, biomass, and ecophysiology in 403 individuals of natural Populus trichocarpa populations, growing in a common garden.ResultsCompared with tree origin settings, propagules likely underwent drought exposures in the common garden due to significantly low rainfall during the years of measurement. All study traits showed population differentiation reflecting adaptive responses due to local genetic adaptation. Phenology and biomass traits were strongly under selection and showed plastic responses between years, co-varying with latitude. While phenological events (e.g., bud set and growth period) and biomass were under positive directional selection, post-bud set period, particularly from final bud set to the onset of leaf drop, was selected against. With one exception to water-use efficiency, ecophysiology traits were under negative directional selection. Moreover, extended phenological events jointly evolved with source niches under increased temperature and decreased rainfall exposures. High biomass coevolved with climatic niches of high temperature; low rainfall promoted high photosynthetic rates evolution.ConclusionsThis work underpins that P. trichocarpa is likely to experience increased fitness (height gain) by evolving toward extended bud set and growth period, abbreviated post-bud set period, and increased drought resistance, potentially constituting a powerful mechanism for long-lived tree species in surviving unpredictably environmental extremes (e.g., drought).

Structural changes of lignins in natural Populus variants during different pretreatments

In the present study, three leading pretreatment technologies including dilute acid (DA), liquid hot water (LHW), and organosolv pretreatments (OS) were applied on two Populus natural variants with different recalcitrance. The structural features of the isolated lignins were analyzed accordingly. All the studied pretreatments reduced the molecular weights of the lignins. Aliphatic OH was reduced while phenolic OH was increased in all pretreated lignins. HSQC analysis revealed that pretreatment influenced the lignin composition and relative distribution of inter-unit linkages. The lignin S/G ratio was found to increase during DA pretreatment, while it was decreased after LHW and OS pretreatment. LHW pretreatment also resulted in much less cleavage of β-O-4 linkage than the other two pretreatments. These results could offer guidelines on appropriate selection of biomass and pretreatment technology in the future biorefinery process.

Effects of litter mixing on litter decomposition and soil properties along simulated invasion gradients of non-native trees

Plant invasions generally lead to mixtures between native and non-native litter. We assess the interactions between leaf litters from two invasive non-native trees (Robinia pseudoacia or Ailanthus altissima) and the native Populus alba on litter decomposition, nutrient release and soil properties along two gradients of invasion. Microcosms with field-collected soil covered by varying proportions of native and non-native litter simulated the two invasion gradients. We assessed the proportion of remaining litter mass and nutrient mass (N, P, C), and soil C, N-NO3−, total N, and pH, five times throughout a period of 11 months. Observed values were compared to the expected values on the assumption of no interactions. Litter mass and C mass decayed slower in Robinia and faster in Ailanthus than in Populus. The three species immobilized N and P. Soil properties did not differ across pure litters. Both litter mixture gradients showed additive or antagonistic interactions on litter decomposition, whereas N and P mass were equal or higher than expected. The proportion of non-native litter in the mixture had non-linear effects on most variables, suggesting that the impact of these non-native trees on litter decay levels off or even declines as they become more abundant. The impacts of Ailanthus and Robinia litter on soil processes should not be derived from single species experiments, both due to non-additive effects and to non-linear responses to litter abundance.

Gap dynamics of natural Populus euphratica floodplain forests affected by hydrological alteration along the Tarim River: Implications for restoration of the riparian forests

Due to climate change and excessive human activities, runoff dynamics of the Tarim River in northwest China become more pronounced. Understanding the effects of hydrological alteration on the life strategy and dynamics of the Populus euphratica riparian forests is becoming increasingly important. Forest gaps led by such disturbances change the structure and function of the desert riparian forest ecosystems. However, there is a lack of research on the gap formation and dynamics of this special forest type, for which the main driving force of the gap disturbance has always been unknown. In this study, we investigated several parameters of P. euphratica forest gap, such as gap size, gap age, gap fraction, and gap makers to quantify the gap disturbance regimes in the natural floodplain forests along the Tarim River in arid northwest China. In the middle reaches of the Tarim River, a total number of 263 gap makers and 60 gaps in six 50 m × 50 m plots with a total area of 1.5 hm2 were investigated. The result showed that gap fraction was <5%, and approximately 28.5% of the expanded gaps were from 1.0 to 1.2 in size (ratio of gap diameter to tree height), especially when formed around 1997–2006. The median size of the expanded gap (140.57 m2) in the desert riparian forests was smaller than in tropical forests. P. euphratica was the most abundant gap maker, and its share among gap makers was 12–14 times larger than another species. Furthermore, gap makers contributed to the forest gap size, as shown by a significant correlation between the number of gap makers and the size of expanded gaps, especially those that had been created 50–60 years ago (R2 = 0.455, P < 0.01). The DBH distribution of living trees versus dead trees showed that most P. euphratica mortality occurred in small size classes. However, living trees were equally frequent in large classes, which suggested that large trees were not exclusively injured or died in these P. euphratica stands that were affected by poor habitats, such as water scarcity. We concluded that climate change and anthropogenic activities (increasing water use for irrigation) since the 1970s led to the progressive decrease in water resources at the regional scale and resulted in a higher frequency of forest gaps in the riparian forests along the Tarim River. The results of this study provide useful implications for ecological restoration of P. euphratica to improve sustainable management of desert riparian forests.

Tree‐ring stable isotopes show different ecophysiological strategies in native and invasive woody species of a semiarid riparian ecosystem in the Great Plains of the United States

AbstractPersistent shifts in riparian vegetation associated with the invasion of introduced Elaeagnus angustifolia and native nonriparian Juniperus virginiana have been reported in the U.S. Great Plains, with significant impacts on ecosystem services. In Nebraska, these species have been expanding into the native Populus deltoides riparian forests along the Republican River. Using dendrochronological data and stable isotope ratios, we examined the annual growth and acclimation strategies of these three species to climatic and streamflow variability. We hypothesized that the ability of invasive species to grow under a wide range of environmental conditions favour vegetation shifts at the expense of native species. Streamflow was the strongest predictor for performance. When accompanied with above‐average annual precipitation, streamflow resulted in peak tree‐ring widths in P. deltoides. J. virginiana showed less sensitivity, and E. angustifolia showed no response. δ18O values did not differ among species, which indicates that all species compete for the same water source. δ13C ratios and WUEi were higher in J. virginiana than in P. deltoides and E. angustifolia and increased in all species over time. E. angustifolia and P. deltoides exhibit a strong stomatal control and response to relative humidity relative to J. virginiana, which showed anisohydric stomatal behaviour. Our results show that once established, J. virginiana and E. angustifolia thrive in the understory of P. deltoides using different adaptive and acclimation strategies. Based on current water flow management, which prevents high‐flood pulses through the riparian zone, these species will continue to establish and spread throughout the Republican River watershed.

First record of Entoleuca mammata in hybrid aspen plantations in hemiboreal Estonia and stand–environmental factors affecting its prevalence

Entoleuca mammata [causing Hypoxylon canker (HC)] is one of the most serious pathogens that are colonising Populus species. The area of fast-growing hybrid aspen plantations has remarkably increased in northern Europe because of the high demand for woody biomass, but the prevalence of HC and the stand-related and environmental factors that favour its presence have rarely been monitored in such monocultural plantations. The presence of E. mammata in Estonia was proven by ITS sequence on hybrid aspen. Repeated monitoring after 4 years in 24 hybrid aspen plantations found that the share of visually damaged trees by HC increased from 0.6% (15-year-old trees) to 1.6% (19-year-old trees). The mortality rate of the infected trees during the 4 years was 100%. The probability of HC incidence was favoured by tree vigour and higher soil acidity. The higher susceptibility of more vigorous trees might be related to their trade-off between productivity and defence compounds. The share of trees with clear visual symptoms of HC can be considered marginal, but the aggressive nature of the pathogen suggests the need to extend the monitoring period, especially in recently thinned sites, and to expand the observations to native Populus tremula stands.

Decoupling photo- and thermoperiod by projected climate change perturbs bud development, dormancy establishment and vernalization in the model tree Populus

BackgroundThe performance and survival of deciduous trees depends on their innate ability to anticipate seasonal change. A key event is the timely production of short photoperiod-induced terminal and axillary buds that are dormant and freezing-tolerant. Some observations suggest that low temperature contributes to terminal bud initiation and dormancy. This is puzzling because low temperatures in the chilling range universally release dormancy. It also raises the broader question if the projected climate instabilities, as well as the northward migration of trees, will affect winter preparations and survival of trees.ResultsTo gauge the response capacity of trees, we exposed juvenile hybrid aspens to a 10-h short photoperiod in combination with different day/night temperature regimes: high (24/24 °C), moderate (18/18 °C), moderate-low (18/12 °C) and low (12/12 °C), and analysed bud development, dormancy establishment, and marker gene expression. We found that low temperature during the bud formation period (pre-dormancy) upregulated dormancy-release genes of the gibberellin (GA) pathway, including the key GA biosynthesis genes GA20oxidase and GA3oxidase, the GA-receptor gene GID1, as well as GA-inducible enzymes of the 1,3-β-glucanase family that degrade callose at plasmodesmal Dormancy Sphincter Complexes. Simultaneously, this pre-dormancy low temperature perturbed the expression of flowering pathway genes, including CO, FT, CENL1, AGL14, LFY and AP1. In brief, pre-dormancy low temperature compromised bud development, dormancy establishment, and potentially vernalization. On the other hand, a high pre-dormancy temperature prevented dormancy establishment and resulted in flushing.ConclusionsThe results show that pre-dormancy low temperature represents a form of chilling that antagonizes dormancy establishment. Combined with available field data, this indicates that natural Populus ecotypes have evolved to avoid the adverse effects of high and low temperatures by initiating and completing dormant buds within an approximate temperature-window of 24-12 °C. Global warming and erratic temperature patterns outside this range can therefore endanger the successful propagation of deciduous perennials.

Green planting silver nanoparticles on Populus fibers and the catalytic application

Preparation and application of ecofriendly materials is becoming an urgent topic. In this work, a green approach for producing silver nanoparticles (AgNPs) embedded on natural Populus fibers (PF) was developed based on hydrothermal synthesis using polyamidoxime (PAO)-functionalized fibers (PF–g–PAO). Throughout the production process, PAO acts as a trapping, stabilizing, and reducing agent for AgNPs formation without involvement of any additional reagents. The effects of the hydrothermal synthesis temperature and PF–g–PAO immersion duration in silver ion solution on AgNPs formation were studied based on the morphology of the PF–g–PAO/AgNPs composites, and their application in catalytic reduction of 4-nitrophenol (4-NP) was investigated using scanning electron microscopy (SEM) and ultraviolet–visible (UV–vis) spectrophotometry. Under the optimal reaction condition, AgNPs with average size of 36 nm were embedded on the PF surface with high silver content (15.6 wt%), exhibiting high catalytic activity (2.40 s−1 g−1) and reusability (>5 cycles) in reduction of 4-NP to 4-aminophenol (4-AP). More importantly, the use of the renewable resource cellulose in this work represents a sustainable feature to reduce manufacturing cost and environmental impact.