Genetic and environmental influences on root development in cuttings of selected <Emphasis Type="Italic">Salix</Emphasis> and <Emphasis Type="Italic">Populus</Emphasis> clones – a greenhouse experiment

Aims

This study investigated how genetic determination of adventitious root development compared in experimental hybrid and parental Salix and Populus clones, and how soil bulk density influenced root development.

Methods

Cuttings of 11 Salix clones and 10 Populus clones were grown in pots with water, a low bulk density soil and a high bulk density soil for 4 (water) or 10 weeks (soils). Parameters relating to root development were measured.

Results

Root initiation, total root length (RL), and dry mass (DM), as well as root: shoot relationships in Salix clones exceeded that of Populus clones in all media. For Salix clones RL and DM were highest in S. matsudana?×?pentandra and for Populus clones RL and DM were generally higher in hybrid clones having P. trichocarpa parentage. Mean RL and DM for all clones were generally greater in the low bulk density soil than in the high bulk density soil. There were a greater proportion of thinner roots in the low bulk density soil than in the high bulk density soil.

Conclusions

There were significant differences in root initiation, RL, and DM among clones within each genus. Increasing soil bulk density significantly reduced root development in both Salix and Populus clones. Evaluating cutting root development in pot trials could be a useful clone selection tool in willow and poplar breeding.

     

Effects of Sewage Sludge Application on Biomass Production and Concentrations of Cd,Pb and Zn in Shoots of <Emphasis Type="Italic">Salix</Emphasis> and <Emphasis Type="Italic">Populus</Emphasis> Clones: Improvement of Phytoremediation Efficiency in Contaminated Soils

Fast-growing clones of Salix and Populus species have been studied for phytoremediation of soils contaminated by risk elements (REs) using short-rotation coppice plantations. Biomass yield, accumulation and removal of RE (Cd, Pb and Zn) by highly productive willow (S1—(Salix schwerinii × Salix viminalis) × S. viminalis, S2—Salix × smithiana) and poplar (P1—Populus maximowiczii × Populus nigra, P2—P. nigra) clones were investigated with and without sewage sludge (SS) application. The precise field experiment was established in April 2008 on moderately Cd-, Pb- and Zn-contaminated soil. Initially, shoots were harvested after four seasons in February 2012 and then after two more seasons in February 2014. The application of SS limited plant growth during the first years of the experiment in the majority of treatments, mainly due to weed competition and higher concentrations of available soil nutrients causing lower yields than those of control (C) treatments. Well-developed roots were able to take advantage of SS applications, and shoot yield was mainly higher in SS treatments in the second harvest, reaching up to 15 t dry matter (DM)?ha^?1. Willows performed better than poplars. Application of SS reduced RE shoot concentrations compared to the C treatment. The removal of RE was significantly higher in the second harvest for all clones and elements (except the P2 clone), and the biomass yield was the major driving force for the amount of RE removed by shoots. Well-developed plantations of fast-growing trees showed better suitability for the phytoextraction of moderately contaminated soils for Cd and partly for Zn but not for Pb, which was less available to plants. From the four tested clones, S2 showed the best removal of Cd (up to 0.94 %) and Zn (up to 0.34 %) of the total soil element content, respectively, and this clone is a good candidate for phytoextraction. SS can be a suitable source of nutrients for Salix clones without any threat to the food chain in terms of biomass contamination, but its application to the soil can result in an increased incidence of some weeds during the first years of plantation.     

First-Rotation Performance of Five Short-Rotation Willow Cultivars on Different Soil Types and Along a Large Climate Gradient

The establishment of short-rotation willow coppice plantations for bioenergy production is proposed as a land management practice to reduce the use of fossil fuels. However, there is little information on the performance of different willow (Salix spp.) cultivars on various types of soils and over climate gradients. This study aimed to determine which set of soil, climatic conditions, and cultivars are conducive to greater growth in eastern Canada. The performance of five willow cultivars was followed over three growing seasons on eight sites representing a large hydroclimatic gradient. Both geographic location and cultivar had a significant effect on annual yields. Annual yields were on average greater in the southern part of the climatic gradient. Across all cultivars, annual yields were positively correlated to average annual temperature (r = 0.23), total annual precipitation (r = 0.77), average growing season temperature (r = 0.21), average growing season precipitation (r = 0.47), and degree days (r = 0.18), as well as soil pH (r = 0.37) and soil extractible P (r = 0.38), and negatively correlated to soil clay content (r = 0.33). Cultivars of the SX group (i.e., Salix miyabeana SX61, SX64, and SX67) showed greater yield than did cultivars of the SV group (i.e., Salix × dasyclados SV1 and Salix viminalis SV5027). These results indicate that at the landscape level, climate variables, especially climate-related variables, largely explain the yield of the selected willow cultivars. Nonetheless, soil pH, extractable P, and clay content likely play an important role in plantation yield.     

<Emphasis Type="Italic">PAD4</Emphasis>, <Emphasis Type="Italic">LSD1</Emphasis> and <Emphasis Type="Italic">EDS1</Emphasis> regulate drought tolerance,plant biomass production,and cell wall properties

Key message

Arabidopsis and poplar with modified PAD4, LSD1 and EDS1 genes exhibit successful growth under drought stress. The acclimatory strategies depend on cell division/cell death control and altered cell wall composition.

Abstract

The increase of plant tolerance towards environmental stresses would open much opportunity for successful plant cultivation in these areas that were previously considered as ineligible, e.g. in areas with poor irrigation. In this study, we performed functional analysis of proteins encoded by PHYTOALEXIN DEFICIENT 4 (PAD4), LESION SIMULATING DISEASE 1 (LSD1) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) genes to explain their role in drought tolerance and biomass production in two different species: Arabidopsis thaliana and Populus tremula × tremuloides. Arabidopsis mutants pad4-5, lsd1-1, eds1-1 and transgenic poplar lines PAD4-RNAi, LSD1-RNAi and ESD1-RNAi were examined in terms of different morphological and physiological parameters. Our experiments proved that Arabidopsis PAD4, LSD1 and EDS1 play an important role in survival under drought stress and regulate plant vegetative and generative growth. Biomass production and acclimatory strategies in poplar were also orchestrated via a genetic system of PAD4 and LSD1 which balanced the cell division and cell death processes. Furthermore, improved rate of cell division/cell differentiation and altered physical properties of poplar wood were the outcome of PAD4- and LSD1-dependent changes in cell wall structure and composition. Our results demonstrate that PAD4, LSD1 and EDS1 constitute a molecular hub, which integrates plant responses to water stress, vegetative biomass production and generative development. The applicable goal of our research was to generate transgenic plants with regulatory mechanism that perceives stress signals to optimize plant growth and biomass production in semi-stress field conditions.

     

Anthropogenic signature in the incidence and distribution of an emerging pathogen of poplars

The introduction and establishment of non-native plant pathogens into new areas can result in severe outbreaks. Septoria leaf spot and canker caused by Sphaerulina musiva is one of the most damaging poplar diseases in northeastern and north-central North America. Stem and branch cankers can be devastating on susceptible trees, leading to tree death and reduced biomass in commercial plantations. In the Pacific Northwest region of North America, the first report of the disease was made in 2006 in the Fraser Valley of British Columbia (BC), Canada. To investigate the incidence and distribution of S. musiva from its point of introduction into BC, five plantations of Populus trichocarpa (black cottonwood), 500 P. trichocarpa trees from natural populations, and 23 plantations of hybrid poplars were surveyed by using real-time PCR assays targeting S. musiva and its native sister species, S. populicola. Our survey suggests a strong anthropogenic signature to the emergence of the non-native S. musiva. Detection frequency of S. musiva was high in hybrid poplar plantations (116 trees infected, 54.2 % of the sampled trees), while detection of the native S. populicola was limited to 13.1 % (22 trees infected). By contrast, in natural stands of P. trichocarpa, less than 2 % of the trees were positive for S. musiva (7 trees) while ~75 % were positive for S. populicola (433 trees). All the S. musiva detections in natural stands of the native P. trichocarpa were from trees located in the vicinity (<2.5 km) of hybrid poplar plantations. Identification of the genotypes found in the hybrid poplar plantations revealed that they are in majority F1 progeny from P. trichocarpa × P. deltoides (T × D) (82 %) and P. nigra × P. maximowiczii (N × M) (7.8 %) crosses, which are generally susceptible (intermediate level of susceptibility between the two parental species) to the canker disease. Our results suggest that the emergence of S. musiva in BC is related to the planting of susceptible hybrid poplars. Even if the disease has not yet established itself in natural poplar populations outside of the Fraser Valley, infected plantations could act as a reservoir that could promote its spread into nearby native P. trichocarpa populations.     

Trabala Vishnou Gigantina Yang (Lepidoptera: Lasiocampidae) Larval Fitness on six Sympatric Plant Species in Sea-Buckthorn Forest

Trabala vishnou gigantina Yang (Lepidoptera: Lasiocampidae) is a major pest that damages the sea-buckthorn, Hippophae rhamnoides. We observed and compared the feeding preferences of T. vishnou gigantina larvae on six sympatric plant species in a two-choice test. We also compared T. vishnou gigantina fitness, as measured by the following variables: larvae weight, developmental period, pupae versus adult weight, longevity, and fecundity rates. Between host and non-host plants, larvae showed a strong preference for their natural host (sea-buckthorn), followed by apricot, poplar, and willow. Caragana and locust were the least preferred plants when the natural host plant was not present. Larvae reared on sea-buckthorn possessed greater pre-pupal weight, had lower mortality, and developed more quickly into heavier pupae than either poplar-raised or willow-raised larvae. Fecundity was highest on sea-buckthorn, second highest on apricot, and lowest on poplar. Longevity (of both females and males) was not significantly different across plant species. These results clearly demonstrate that T. vishnou gigantina larvae are able to distinguish between host versus non-host plants, and that their preference translates to increased fitness. Possible, non-mutually exclusive explanations for observed preference and fitness differences include variation in required nutritional content across plant species or the presence of plant traits (morphological features or chemical metabolites) that negatively affect larval development. While the exact mechanisms are unknown, these data may be useful for the development of appropriate counter-measures to the damage caused by T. vishnou gigantina on sea-buckthorn.     

Sexual reproduction of clonal dwarf shrubs in a forest–tundra ecotone

Successful sexual reproduction may be more important for regeneration of clonal species in high-latitude and -altitude areas than has been previously suggested. We investigated the potential of Vaccinium myrtillus, V. vitis-idaea and Empetrum nigrum ssp. hermaphroditum (E. hermaphroditum) for sexual reproduction at three sites in the forest–tundra ecotone in Finnish Lapland. We studied whether the potential differs between plant communities, whether disturbance enhances germination, and whether seedling emergence is limited by seed availability. We established a field experiment with disturbance and sowing treatments, and monitored seed and seedling numbers and survival rates for two years. The number of mature seeds of V. myrtillus was higher in plants from the tundra heath than in those from the coniferous and mountain birch forests. The number of mature seeds and seedlings emerging from the seed bank of E. hermaphroditum tended also to be higher in the tundra heath. Disturbance marginally increased the seedling emergence of V. myrtillus and E. hermaphroditum, whereas sowing generally increased the seedling numbers. The seedling number of V. myrtillus was lower in the tundra heath and that of E. hermaphroditum was lower in the coniferous forest than at the other sites. Seedling survival was equal for all plant species at all sites. We conclude that the capacity for sexual reproduction varies among plant communities, and seed availability is a stronger constraint than microsite availability for the studied species. Once the crucial early phase of seedling establishment is overcome, seedling survival enables successful recruitment of V. myrtillus, V. vitis-idaea and E. hermaphroditum in the subarctic area.     

The benefits of foliar inoculation with <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> in soybean are explained by an auxin signaling model

Azospirillum sp. is one of the most studied genera of plant growth-promoting rhizobacteria (PGPR). The ability of Azospirillum sp. to promote plant growth has been associated with its ability to produce several phytohormones, such as auxins, gibberellins and cytokinins, but mainly indole-3-acetic acid (IAA). It has been propoosed that the production of IAA explains the positive effects of co-inoculation with Azospirillum sp. on the rhizobia-legume symbiosis. In this study, we constructed an IAA-deficient mutant of A. brasilense Az39 (ipdC ^? ) by using a restriction-free cloning method. We inoculated soybean seeds with 1·10⁶ cfu·seed^?1 of Bradyrhizobium japonicum E109 and co-inoculating leaves at the V3 stage with 1·10⁸ cfu.plant^?1 of A. brasilense Az39 wt or ipdC ^? or inoculated leaves with 20 μg.plant^?1 synthetic IAA. The results confirmed soybean growth promotion as there was increased total plant and root length, aerial and root dry weight, number of nodules on the primary root, and an increase in the symbiosis established with B. japonicum E109. Nodule weight also increased after foliar co-inoculation with the IAA- producer A. brasilense Az39. The exogenous application of IAA decreased aerial and root length, as well as the number of nodules on primary roots in comparison with the Az39 wt strain. These results allow us to propose a biological model of response to foliar co-inoculation of soybean with IAA-producing rhizobacteria. This model clearly shows that both the presence of microorganism as part of the colonization process and the production of IAA in situ are co-responsible, via plant signaling molecules, for the positive effects on plant growth and symbiosis establishment.     

The role of expansin genes <Emphasis Type="Italic">PtrEXPA3</Emphasis> and <Emphasis Type="Italic">PnEXPA3</Emphasis> in the regulation of leaf growth in poplar

The genes of α-expansins of woody plants are of great interest for genetic engineering, since they can potentially be used to improve the tree growth parameters. In the flora of Russia, model woody plants for plant biotechnology are aspen (Populus tremula L.) and black poplar (Populus nigra L.). The objective of this study was to determine the role of α-expansin-encoding genes, aspen PtrEXPA3 and black poplar PnEXPA3, in the regulation and maintenance of woody plant growth. To achieve this goal, the PtrEXPA3 expression level were determined upon exogenous phytohormone treatment, the action of stress factors, and constitutive expression of the PnARGOS-LIKE gene. In addition, transgenic aspen plants with constitutive expression of the black poplar PnEXPA3 gene were generated, and their morphological analysis was carried out. The highest PtrEXPA3 mRNA level was detected in young intensely growing aspen leaves, and furthermore, expression of the gene was induced by exogenous cytokinins and auxins. In response to NaCl and constitutive expression of the PnARGOS-LIKE gene, the PtrEXPA3 mRNA level decreased. Transgenic aspen plants with constitutive PnEXPA3 expression were characterized by the decreased size of leaves, petioles, and internodes, as well as the increased size of leaf epidermal cells, while the stem size remained unchanged. Taken together, the data obtained enable the suggestion that the PtrEXPA3 and PnEXPA3 genes encode cytokinin- and auxin-regulated, leaf-specific expansins that are involved in the cell expansion.     

Overexpression and oral immunogenicity of a dengue antigen transiently expressed in <Emphasis Type="Italic">Nicotiana benthamiana</Emphasis>

To understand the genetic and expression stability of transgenic insect-resistant poplar 741, this study compared the experimental plantations of transgenic insect-resistant poplar 741 lines (pb1, pb6, pb11, pb17, and pb29) with non-transgenic poplar 741, P. tomentosa Carr.f.yixianensis (poplar 84 K) and transgenic hybrid progeny lines cultured from immature embryos. The insect resistance and growth stability of transgenic poplar 741 were investigated by detecting exogenous genes by polymerase chain reaction (PCR), measuring the diameter at breast height (DBH) and volume growth, and performing insect-resistance tests against Clostera anachoreta and Hyphantria cunea. The inheritance and expression of the exogenous gene was also examined in transgenic hybrid progeny lines. The results revealed that the exogenous gene was stable, remaining stable in 8–10-year-old transgenic poplar 741 trees. No significant difference was found between the height of 10-year-old transgenic poplar 741 and non-transgenic poplar 741 in the experimental plantations in Baoding, China. The DBH and volume growth of pb17 was significantly greater than that of pb29 and pb11. The 8-year-old transgenic poplar 741 pb29 grown in Zhuozhou showed no significant difference from poplar 741 in terms of height growth, DBH, and volume. From 1999 to 2013, pb29-fed larvae (C. anachoreta larvae and H. cunea) exhibited stable mortality rates >79%. Likewise, pb11-fed larvae showed stable mortality rates (C. anachoreta larvae had mortality rates >75%, and H. cunea larvae exhibited rates >80%). pb17 conferred low insect-resistant stability, showing mortality rates that varied from 28.2 to 99.27% in C. anachoreta and H. cunea larvae. Among the hybrid progeny lines acquired by hybridization of pb1, pb29, and pb11 with 84 K poplar, the ratios of PCR-positive to PCR-negative lines for the BtCry1Ac gene were 1.31, 1.15, and 0.86, respectively. X ² tests showed that the ratio was consistent with the Mendelian law of 1:1 segregation controlled by an allele pair. The hybrid progeny of pb6?×?84 K had a segregation ratio of 3:1. The nptII gene followed the same segregation rule as Cry1Ac. The transgenic hybrid progeny that contained Cry1Ac gene exhibited the same insect resistance as the parent plants.     

Glutathione improves survival of cryopreserved embryogenic calli of <Emphasis Type="Italic">Agapanthus praecox</Emphasis> subsp. <Emphasis Type="Italic">orientalis</Emphasis>

The effect of supplementation of reduced glutathione (GSH) to cryoprotectant solution on the generation of reactive oxygen species (ROS) (e.g., H₂O₂, OH^·, and O ₂ ^·? ) and antioxidants (e.g., SOD, POD, CAT, AsA, and GSH), as well as membrane lipid peroxidation (i.e., MDA content) mitigation in cryopreserving of embryogenic calli (EC) of Agapanthus praecox subsp. orientalis was investigated. The vitrification-based cryopreservation method was used in this study. The addition of GSH at a final concentration of 0.08 mM to the cryoprotectant solution has significantly improved cryotolerance of A. praecox EC. The EC post-thaw survival rate increased by 68.34 % using the cryoprotectant solution containing 0.08 mM GSH as compared to the control (GSH-free). EC treated with GSH displayed the reduction in  OH^· generation activity and the contents of H₂O₂ and MDA, as well as enhancement in the inhibition of O ₂ ^·? generation and the antioxidant activity. Treatment with exogenous GSH also increased endogenous AsA and GSH contents after dehydration step. Expression of stress-responsive genes, e.g., peroxidase (POD), peroxiredoxin, ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and glutathione peroxidase (GPX), was also increased during cryopreservation processes. The expression of DAD1 (Defender against apoptotic cell death) was elevated, while cell death-related protease SBT was suppressed. These results demonstrated that the addition of GSH to cryoprotectant solution affects the ROS level and could effectively improve survival of A. praecox EC through enhancing antioxidant enzyme activities and decreasing cell death.     

Regulation of secondary xylem formation in young hybrid poplars by modifying the expression levels of the <Emphasis Type="Italic">PtaGLIMa</Emphasis> gene

Due to the importance of wood in many industrial applications, a tremendous amount of research has focused on the regulation of secondary xylem formation and wood properties. In this study, we performed functional analysis of PtaGLIM1a, a LIM gene that is predominantly expressed in the differentiation of secondary xylem of the hybrid poplar (Populus tremula × P. alba). With no growth retardation, transgenic poplar plants with increased and reduced expression levels of PtaGlim1a exhibited enhanced and diminished secondary growth, respectively, accompanied by a corresponding change in their lignin abundance. This study demonstrates that the wood-associated PtaGlim1a acts as a positive regulator of secondary xylem formation in poplar trees and could potentially be utilized in modifying the synthesis of plant secondary wall lignin.     

Growth and photosynthetic responses in Jatropha curcas L. seedlings of different provenances to watering regimes

Seedlings from four provenances of Jatropha curcas were subjected to 80, 50, and 30% of soil field capacity in potted experiments in order to study their responses to water availability. Our results showed that with the decline of soil water availability, plant growth, biomass accumulation, net photosynthetic rate, stomatal conductance (g_s), and transpiration rate (E) decreased, whereas leaf carbon isotope composition (δ¹³C), leaf pigment contents, and stomatal limitation value increased, while maximal quantum yield of PSII photochemistry was not affected. Our findings proved that stomatal limitation to photosynthesis dominated in J. curcas under low water availability. The increase of δ¹³C should be attributed to the decrease in g_s and E under the lowest water supply. J. curcas could adapt to low water availability by adjusting its plant size, stomata closure, reduction of E, increasing δ¹³C, and leaf pigment contents. Moreover, effects of provenance and the interaction with the watering regime were detected in growth and many physiological parameters. The provenance from xeric habitats showed stronger plasticity in the plant size than that from other provenances under drought. The variations may be used as criteria for variety/provenance selection and improvement of J. curcas performance.     

Invasive plants decrease microbial capacity to nitrify and denitrify compared to native California grassland communities

Exotic plant invasions are a major driver of global environmental change that can significantly alter the availability of limiting nutrients such as nitrogen (N). Beginning with European colonization of California, native grasslands were replaced almost entirely by annual exotic grasses, many of which are now so ubiquitous that they are considered part of the regional flora (“naturalized”). A new wave of invasive plants, such as Aegilops triuncialis (Barb goatgrass) and Elymus caput-medusae (Medusahead), continue to spread throughout the state today. To determine whether these new-wave invasive plants alter soil N dynamics, we measured inorganic N pools, nitrification and denitrification potentials, and possible mediating factors such as microbial biomass and soil pH in experimental grasslands comprised of A. triuncialis and E. caput-medusae. We compared these measurements with those from experimental grasslands containing: (1) native annuals and perennials and (2) naturalized exotic annuals. We found that A. triuncialis and E. caput-medusae significantly reduced ion-exchange resin estimates of nitrate (NO₃ ^?) availability as well as nitrification and denitrification potentials compared to native communities. Active microbial biomass was also lower in invaded soils. In contrast, potential measurements of nitrification and denitrification were similar between invaded and naturalized communities. These results suggest that invasion by A. triuncialis and E. caput-medusae may significantly alter the capacity for soil microbial communities to nitrify or denitrify, and by extension alter soil N availability and rates of N transformations during invasion of remnant native-dominated sites.     

Physiological,biochemical, antioxidant and growth characterizations of gibberellin and paclobutrazol-treated sweet leaf (<Emphasis Type="Italic">Stevia rebaudiana</Emphasis> B.) herb

A greenhouse experiment was designed to study the responses of Stevia rebaudiana herb to paclobutrazol (PBZ) and gibberellin (GA) treatments. GA and PBZ treatments caused no significant impact on photosynthesis pigments while they increased carbohydrates, amino acids and protein metabolites. Stevia showed a potent antioxidant activity through scavenging DPPH, NO^·; O ₂ ^·? and OH^· radicals which was highlighted in GA and PBZ treatments. The enzymatic and non-enzymatic antioxidant system of Stevia plant showed a significant increase in response to PBZ and GA treatments. PBZ treatment decreased plant growth while GA treatment had no significant effect on it. Collectively, both GA and PBZ treatments effectively increased metabolites and antioxidant property of Stevia herb.     

Nutrient allocation and photochemical responses of <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">canadensis</Emphasis> ‘Neva’ to nitrogen fertilization and exogenous <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> inoculation

Arbuscular mycorrhizal fungi (AMF) can promote plant growth performance, but their effectiveness varies depending on soil nitrogen (N) availability. To clarify the effectiveness of exogenous AMF along an N-fertilization gradient (0, 2, 10, 20, and 30 mM), the impacts of exogenous Rhizophagus irregularis and N on the growth, photochemical activity, and nutritional status of Populus?×?canadensis ‘Neva’ in natural soil were evaluated in a pot experiment. The results showed that the 10 mM N level was the optimal fertilization regime with the highest promotion effect on plant growth and the maximum quantum yield of photosystem II (PSII) (F_v/F_m). Excess N (20 and 30 mM) fertilization reduced the actual quantum yield of PSII (ФPSII) and the F_v/F_m of the plants. Regardless of the N availability, inoculated plants exhibited greater F_v/F_m values than did non-inoculated plants. The biomass of inoculated plants was significantly higher compared with the control under low N levels (0 and 2 mM). Under high N levels, inoculated plants showed significant increases in ФPSII. Moreover, the nutrient imbalance of plants inoculated with exogenous R. irregularis was eased by increasing P, Fe, Mn and Cu uptake in roots and higher P, Ca, Mg, Fe, Mn and Zn concentrations in leaves. Moreover, the F_v/F_m and ФPSII exhibited positive correlations with P, Ca, Mg and Zn concentrations in leaves. In conclusion, inoculation with exogenous R. irregularis can benefit plant fitness by improving the photochemical capacity and nutrient composition of poplar under different N levels.     

A major QTL controlling the tolerance to manganese toxicity in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.)

Waterlogging stress disturbs plant metabolism through increased ion (manganese and iron) toxicity resulting from the changes in the soil redox potential under hypoxic conditions. Our previous study found a significant correlation between the tolerance to Mn²⁺ toxicity and waterlogging stress tolerance in barley, suggesting that waterlogging tolerance could be increased by improving the tolerance to Mn²⁺ toxicity. In this study, a doubled-haploid (DH) population from the cross between barley varieties Yerong and Franklin (waterlogging-tolerant and -sensitive, respectively) was used to identify QTL controlling tolerance to Mn²⁺ toxicity based on chlorophyll content and plant survival as selection criteria. Four significant QTL for plant survival under Mn²⁺ stress (QSur.yf.1H, QSur.yf.3H, QSur.yf.4H, and QSur.yf.6H) were identified in this population at the seedling stage. Two significant QTL (QLC.yf.3H and QLC.yf.6H) controlling leaf chlorosis under Mn²⁺ stress were identified on chromosomes 3H and 6H close to QSur.yf.3H and QSur.yf.6H. The major QTL QSur.yf.3H, located near the marker Bmag0013, explained 21% of the phenotypic variation. The major QTL for plant survival on 3H was validated in a different DH population (TX9425/Naso Nijo). This major QTL could potentially be used in breeding programmes to enhance tolerance to both manganese toxicity and waterlogging.     

Feasibility of SRC Species for Growing in Mediterranean Conditions

The suitability of poplar (Populus × canadensis Moench.—genotype ‘Neva’), black locust (Robinia pseudoacacia L.), and eucalyptus (Eucalyptus bridgesiana R. Baker) growing in short rotation coppice (SRC) system in a Mediterranean area (southern Italy), and under two management regimes, was evaluated in terms of survival, biomass yield, biomass quality, and soil fertility. The high management regime (H treatment) consisted of high plant density (6667 trees ha^?1) and a 2-year harvesting cycle; the low management regime (L treatment) consisted of low plant density (1667 trees ha^?1) and a 4-year harvesting cycle. The dry biomass production was 36, 13, and 9 t dry matter (dm)?ha^?1 in the H treatment and 25, 14, and 7 t dm ha^?1 in the L treatment for eucalyptus, black locust, and poplar, respectively. The analysis of the biomass showed a superior quality for the black locust feedstock because of its low moisture and ash percentages, high heating value (HHV), and low alkali metal concentrations, although, from an environmental point of view, the high N (12.3 g kg^?1) and S (0.7 g kg^?1) biomass concentrations would increase the pollutant emissions generated by combustion. Eucalyptus showed a high HHV, especially for the H treatment (18.70 MJ kg^?1). Its high concentrations of K (4 g kg^?1) and Mg (0.8 g kg^?1) could provoke slagging and fouling in combustion equipment, and the high concentrations of S and N, if leaves are considered in the harvested biomass, indicate the low quality of its feedstock. No specific poplar feedstock stood out, although it had a good HHV (19.02 MJ kg^?1). The soil fertility was not affected negatively after the 4-year SRC cycle, while S content in soil showed a tendency to increase in the case of black locust cultivation.     

Accumulation and tolerance characteristics of lead in <Emphasis Type="Italic">Althaea rosea</Emphasis> Cav. and <Emphasis Type="Italic">Malva crispa</Emphasis> L.

Two ornamental plants of Althaea rosea Cav. and Malva crispa L. were exposed to various concentrations of lead (Pb) (0, 50, 100, 200 and 500 mg·kg^?1) for 70 days to evaluate the accumulating potential and the tolerance characteristics. The results showed that both plant species grown normally under Pb stress, and A. rosea had a higher tolerance than M. crispa, while M. crispa had a higher ability in Pb accumulation than A. rosea. Besides, lower Pb concentration (50 mg·kg^?1) stimulated the shoot biomass in both plant species. Pb accumulation in plants was consistent with the increase of Pb levels, and the main accumulation sites were the roots and the older leaves. In addition, the photosynthetic pigments content and chlorophyll fluorescence parameters were influenced by Pb stress. In such case, both of the plants could improve the activities of antioxidant enzymes of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), and the contents of the total soluble sugar and soluble protein, which reached the highest value at Pb 100 mg·kg^?1, as well as the accumulation of the total thiols (T-SH) and non-protein thiols (NP-SH) to adapt to Pb stress. Thus, it provides the theoretical basis and possibility for ornamental plants of A. rosea and M. crispa in phytoremediation of Pb contaminated areas.