Flooding events and rising water temperatures increase the significance of the reed pathogen <Emphasis Type="Italic">Pythium phragmitis</Emphasis> as a contributing factor in the decline of <Emphasis Type="Italic">Phragmites australis</Emphasis>

Pythium species are economically significant soilborne plant pathogens with worldwide distribution, causing seedling damping-off or root rot diseases. Pythium phragmitis is a newly described pathogen of common reed (Phragmites australis), widespread in the reed-belt of Lake Constance, Germany. It is highly aggressive towards reed leaves and seedlings, but obviously does not affect roots. In the context of ‘reed decline’ phenomena, P. phragmitis infection of reed inundated during flooding events may be of particular significance. We could show that flooding itself is not necessarily detrimental for reed plants. In the presence of the pathogen, however, most submerged leaves and plants were killed within several weeks. Clipped plants did not show regrowth in the Pythium infested treatments. Significant losses in assimilating leaf area of reeds could, thus, be the result of Pythium infection rather than of flooding alone. Therefore, we suggest that the combination of extended flooding and the presence of P. phragmitis might considerably contribute to ‘reed decline’ at Lake Constance. In parallel, we could show that pathogenicity and spread of this species are considerably favoured by rising temperatures. Since an increase in average water temperature has been found for Lake Constance, we propose that P. phragmitis could be an important factor in the dieback of reed stands likely to be promoted by predicted climate change phenomena.     

Interannual variation in rainfall,drought stress and seedling mortality may mediate monodominance in tropical flooded forests

Flood tolerance is commonly regarded as the main factor explaining low diversity and monodominance in tropical swamps. In this study we examined seedling mortality in relation to seasonality, i.e., flooding versus drought, of the dominant tree species (Prioria copaifera), and three associated species (Pterocarpus officinalis, Carapa guianensis and Pentaclethra macroloba), in seasonally flooded forests (SFF) in Darien, Panama. Seedling mortality differed among species, years and seasons. Prioria seedlings experienced the lowest overall mortality, and after 3 years many more Prioria seedlings remained alive than those of any of the associated species. In general, within species, larger seedlings had greater survival. Seed size, which can vary by close to 2 orders of magnitude in Prioria, had a confounding effect with that of topography. Large-seeded Prioria seedlings experienced 1.5 times greater mortality than small-seeded seedlings, as large-seeded Prioria seedlings were more likely to be located in depressions. This finding suggests that seed size, plant size and topography are important in understanding SFF regeneration. For all species, seedling mortality was consistently greater during the dry season than during flooding. For Prioria, dry season seedling mortality was correlated with drought stress, that is, high mortality during the long El Niño dry season of 1998 and the normal dry season of 2000, but very low dry season mortality during the mild dry season of 1999. Prioria’s ability to dominate in seasonally flooded forest of Central America is partly explained by its low drought-related mortality in comparison to associated species.     

The role of flood regime on invasive success of exotic species growing in riparian environments

To elucidate the conditions under which exotic species become invasive, we compared the performance of Veronica anagallis-aquatica (exotic) and V. undulata (native) in Kansai, southern-central Japan, where the former species is highly invasive, with performance in a region where this species is less invasive (Kanto, eastern Japan). We compared the micro-environments, including scale and frequency of flooding, of these species in both Kansai and Kanto. We also conducted growth experiments on seedlings from both regions to compare their responses to varying water conditions. Four treatments were conducted: a dry treatment where neither roots nor shoots were flooded; a flooded treatment where both roots and shoots were flooded; a moist treatment where only roots were flooded; and a variable treatment where the water level was shifted between that in the flooded and dry treatments. We found that the flooding frequency was higher in Kansai than in Kanto, whereas the flow peaks were almost four times higher in Kanto than in Kansai. The mean stem internode length was longer in the variable treatments than in the other treatments in the V. anagallis-aquatica seedlings derived from Kansai, but did not differ among treatments in both V. anagallis-aquatica and V. undulata seedlings derived from Kanto. V. anagallis-aquatica in Kansai evolved a strategy to evade flooding by stem elongation. However, that species did not show elongation traits in Kanto, possibly because it could not respond to large-scale flooding. V. anagallis-aquatica may show adaptive evolution in specific habitats where it can respond adaptively.     

Zygotic embryo cell wall responses to drying in three gymnosperm species differing in seed desiccation sensitivity

Plant cell walls (CWs) are dynamic in that they can change conformation during ontogeny and in response to various stresses. Though seeds are the main propagatory units of higher plants, little is known of the conformational responses of zygotic embryo CWs to drying. This study employed cryo-scanning electron microscopy to compare the effects of desiccation on zygotic embryo CW morphology across three gymnosperm species that were shown here to differ in seed desiccation sensitivity: Podocarpus henkelii (highly desiccation-sensitive), Podocarpus falcatus (moderately desiccation-sensitive), and Pinus elliottii (desiccation-tolerant). Fresh/imbibed (i.e. fresh Podocarpus at shedding and imbibed Pi. elliottii) embryos showed polyhedral cells with regular walls, typical of turgid cells with an intact plasmalemma. Upon desiccation to c. 0.05 g g^?1 (dry mass basis), CWs assumed an undulating conformation, the severity of which appeared to depend on the amount and type of dry matter accumulated. After desiccation, intercellular spaces between cortical cells in all species were comparably enlarged relative to those of fresh/imbibed embryos. After rehydration, meristematic and cotyledonary CWs of P. henkelii and meristematic CWs of P. falcatus remained slightly undulated, suggestive of plasmalemma and/or CW damage, while those of Pi. elliottii returned to their original conformation. Cell areas in dried-rehydrated P. henkelii root meristem and cotyledon were also significantly lower than those from fresh embryos, suggesting incomplete recovery, even though embryo water contents were comparable between the two states. Electrolyte leakage measurements suggest that the two desiccation-sensitive species incurred significant plasmalemma damage relative to the tolerant species upon desiccation, in agreement with the CW abnormalities observed in these species after rehydration. Immunocytochemistry studies revealed that of the four CW epitopes common to embryos of all three species, an increase in arabinan (LM6) upon desiccation and rehydration in desiccation-tolerant Pi. elliottii was the only difference, although this was not statistically significant. Seed desiccation sensitivity in species like P. henkelii and P. falcatus may therefore be partly based on the inability of the plasmalemma and consequently CWs of dried embryos to regain their original conformation following rehydration.     

Development and characterization of chloroplast microsatellite markers for <Emphasis Type="BoldItalic">Pinus massoniana</Emphasis> and their application in <Emphasis Type="BoldItalic">Pinus</Emphasis> (Pinaceae) species

Pinus massoniana is one of the important afforestation and pioneer tree species, which is widely distribute in southern China. Chloroplast simple sequence repeat markers (cpSSRs) have been widely used in studies of tree genetics, phylogenetic and breeding. We sequenced the whole chloroplast genome sequences of P. massoniana using PCR and Sanger sequencing. A total of 71 cpSSRs were identified, among which mononucleotide repeats were predominant (70.42%). Seventeen primer pairs were developed and amplification tests were conducted with 15 P. massoniana individuals. Also, cross-species amplification tests were conducted among 15 individuals per Pinus species, including P. elliottii, P. bungeana, P. armandii, P. caribaea, P. tabulaeformis, P. taiwanensis and P. yunnanensis which revealed polymorphic information content ranging from 0.2 to 0.8 and average of haploid diversity (h) ranging from 0.29 to 0.63. In addition, the polymorphic cpSSRs were useful in distinguishing the sampled pine species, and could be powerful tool in phylogenetic studies.     

Crustacean metamorphosis: an omics perspective

We quantified the independent impacts of flooding salinity, flooding depth, and flooding frequency on the native species, Phragmites australis and Scirpus mariqueter, and on the invasive species Spartina alterniflora in the Yangtze River Estuary, China. Total biomass of all three species decreased significantly with increasing salinity, but S. alterniflora was less severely affected than P. australis and S. mariqueter. Elevated flooding depth significantly decreased their live aboveground biomass of P. australis and S. mariqueter, while S. alterniflora still had high live aboveground biomass and total biomass even at the highest flooding depth. These findings indicated that S. alterniflora was more tolerant to experimental conditions than the two native species, and an unavoidable suggestion is the expansion of this non-native species in relation to the native counterparts in future scenarios of increased sea-level and saltwater intrusion. Even so, environmental stresses might lead to significant decreases in total biomass and live aboveground biomass of all three species, which would potentially weaken their ability to trap sediments and accumulate organic matter. However, the relatively high belowground-to-aboveground biomass ratio indicated phenotypic plasticity in response to stressful environmental conditions, which suggest that marsh species can adapt to sea-level rise and maintain marsh elevation.     

Assessment of anthropogenic pressures on South European Atlantic bogs (NW Spain) based on hydrochemical data

Cyanobacterial exudates are known to allelopathically inhibit submerged macrophytes, but the influence of the cyanobacteria growth phase on this effect is yet unknown. We compared the effect of exudates of the exponential growth phase of Microcystis aeruginosa Kütz. Elenk with exudates during the decline phase on seedlings of the macrophyte species Potamogeton crispus L. Biomass, chlorophyll content, the ratio of variable–maximum fluorescence (F _v/F _m), and light response capacity of P. crispus seedings were significantly inhibited when affected by M. aeruginosa exudates of the exponential growth phase but promoted by exudates of the decline phase. Tiller numbers of P. crispus increased by 350% under the influence of exponential phase exudates, but decreased by 60% when decline phase exudates were applied. Both exudates increased the malondialdehyde contents and decreased the activity of superoxide dismutase and peroxidase in P. crispus seedlings. We conclude that the exponential growth phase of cyanobacteria rather than the decline phase is important for disrupting photosynthesis and for inducing oxidative stress in submerged macrophytes. Planting P. crispus should thus not be applied in summer but during the cyanobacteria decline phase.     

Effects of elevated atmospheric CO<Subscript>2</Subscript> and increased tidal flooding on leaf gas-exchange parameters of two common mangrove species: <Emphasis Type="Italic">Avicennia marina</Emphasis> and <Emphasis Type="Italic">Rhizophora stylosa</Emphasis>

In this study, we examined interactive effects of elevated atmospheric CO₂, concentrations, and increased tidal flooding on two mangroves species, Avicennia marina and Rhizophora stylosa. Leaf gas-exchange parameters (photosynthesis, transpiration rates, water-use efficiency, stomatal conductance, and dark respiration rates) were measured monthly on more than 1000 two-year-old seedlings grown in greenhouses for 1 year. In addition, stomatal density and light curve responses were determined at the end of the experiment. Under elevated CO₂ concentrations (800 ppm), the net photosynthetic rates were enhanced by more than 37% for A. marina and 45% for R. stylosa. This effect was more pronounced during the warm season, suggesting that an increase in global temperatures would further enhance the photosynthetic response of the considered species. Transpiration rates decreased by more than 15 and 8% for A. marina and R. stylosa, respectively. Consequently, water-use efficiency increased by 76% and 98% for A. marina and R. stylosa, respectively, for both species, which will improve drought resistance. These responses to elevated CO₂ were minimized (by 5%) with longer flooding duration. Consequently, future increases of atmospheric CO₂ may have a strong and positive effect on juveniles of A. marina and R. stylosa during the next century, which may not be suppressed by the augmentation of tidal flooding duration induced by sea-level rise. It is possible that this effect will enhance seedling dynamic by increasing photosynthesis, and therefore will facilitate their settlements in new area, extending the role of mangrove ecosystems in carbon sequestration and climate change mitigation.     

Canopy tree species and openness affect foliar endophytic fungal communities of understory seedlings

There is growing evidence demonstrating the diversity of foliar endophytic fungi and their ecological roles in the survival of tree seedlings. However, the factors that shape fungal communities in tree seedlings within natural forest ecosystems remain poorly understood. Here, we evaluated the composition of foliar endophytic fungi growing in current-year seedlings of Cornus controversa and Prunus grayana in a cool temperate deciduous forest through a seed-sowing experiment and fungal isolation. The composition of endophytic fungi was affected by canopy tree species, canopy openness, and time after germination. In total, 27 and 22 fungal taxa were isolated from C. controversa and P. grayana seedlings, respectively. The dominant fungal taxa in both seedling species were Colletotorichum spp., and their isolation frequencies were higher under C. controversa canopies than under P. grayana canopies; the frequencies also increased with time after germination. These results suggest that overstory tree species strongly influences the endophytic fungal communities of understory seedlings.     

Titanium Dioxide Nanoparticles Affect the Percentage of Free Radical Scavenging,Protein Content and DNA Mismatch Repair Genes in <Emphasis Type="Italic">Zea mays</Emphasis> L. and <Emphasis Type="Italic">Triticum aestivum</Emphasis> L.

This paper identifies the potential molecular markers predicting the impact of nTiO₂ on plants and explores the new statistical correlations between the biomarkers and growth parameters. The quantitative mRNA expression of the three genes involved in DNA mismatch repair (MLH1) and cell division (PCNA1 and PCNA2) in Zea mays and Triticum aestivum seedlings were related to the growth parameters measured in response to five nTiO2 treatments. The results indicated that the higher concentrations were harmless to Z. mays but not to T. aestivum. nTiO₂ treatments increased the total protein levels in both species and significantly inhibited the percentage of DPPH radical scavenging in Z. mays compared with T. aestivum seedlings. The exposure to both 50 μg/ml and 30 μg/ml concentrations of nTiO₂ significantly induced the expression of MLH1 and PCNA1 genes in both species; however, the exposure to 30 μg/ml of nTiO₂ also significantly induced the expression of PCNA2 genes in T. aestivum. The exposure to 50, 70 and 140 μg/ml significantly inhibited the expression of PCNA2 in both species, while 70 and 140 μg/ml repressed the expression of MLH1 and PCNA1 in the seedlings of Z. mays. The induction and repression of the expression of the three genes were correlated with some growth parameters and biological indices in both species. This key finding suggests that the above genes may play a vital role in mediating plant stress response to nTiO₂ and could be used as sensitive molecular biomarkers indicative of the oxidative stress of nTiO₂ exposure.     

Morphological,physiological and biochemical responses to drought stress of Stone pine (<Emphasis Type="Italic">Pinus pinea</Emphasis> L.) seedlings

In this study, the effect of irrigation intervals (drought stress) on growth, predawn xylem water potential (Ψ _w), the osmotic potential at full turgor (Ψπ ₁₀₀), the osmotic potential at the turgor loss point (Ψπ _TLP), osmotic adjustment and osmotic solutes (soluble sugars and proline) of Pinus pinea L. seedlings were examined. An experiment was carried out under greenhouse conditions using four watering treatments (control, 7-, 14- and 21-day irrigation intervals) in the first growth season; from mid-July to early November. Results showed that irrigation interval had significant effect on growth characteristics, Ψ _w, water relation parameters, and osmotic solutes. The increasing irrigation interval significantly decreased the seedling height, root collar diameter, root, stem and needle dry weight, number of lateral branches, root percentage, root:shoot ratio and diameter:height ratio. Ψ _w and total soluble sugars decreased while proline content increased with the increase of drought stress. The Ψπ ₁₀₀ and Ψπ _TLP significantly decreased in drought-stressed seedlings compared to control (no stress) seedlings. The results suggest that the impact of drought stress increased with the increase of irrigation interval. Therefore, in the drought-stressed P. pinea seedlings were indicated osmotic adjustment by increasing the proline content and decreasing Ψπ ₁₀₀ and Ψπ _TLP during drought stress. Growth decreased under drought stress conditions in P. pinea seedlings.     

Light availability and soil flooding regulate photosynthesis of an imperiled shrub in lowland forests of the Mississippi Alluvial Valley,USA

Physiological responses to light availability and soil flooding on Lindera melissifolia (Walt.) Blume were studied. Shrubs were grown under 70, 37 or 5% of full sunlight with either 0, 45, or 90 d of soil flooding. We measured leaf photosynthetic rate (PN) to test the hypothesis that soil flooding reduces P _N in L. melissifolia following shrub acclimation to low light availability. Results showed that light availability and soil flooding interacted to affect P _N. In the 0 d and 45 d flooding regimes (flood water removed 36–39 d prior to measurement), P _N was similar between shrubs receiving 70% or 37% light, and these shrubs had 147% greater P _N than shrubs receiving 5% light. Shrubs receiving 90 d of soil flooding had similar low rates of area-based P _N regardless of light level. Similar P _N between 0 d and 45 d flooded shrubs indicated physiological recovery following removal of flood water.     

Ectomycorrhizal pre-inoculation of <Emphasis Type="Italic">Pinus hartwegii</Emphasis> and <Emphasis Type="Italic">Abies religiosa</Emphasis> is replaced by native fungi in a temperate forest of central Mexico

Few studies have focused on analyzing the effect of native inoculated ectomycorrhizal (ECM) fungal strains on seedlings under field conditions in temperate forests. However, it is crucial to verify that the positive effects of ECM under nursery conditions also occur in the field, favoring their performance. We evaluated the short-term effect of ECM on three-year-old seedlings of Pinus hartwegii and Abies religiosa in central Mexico by subjecting them to four treatments: inoculation with Inocybe splendens, inoculation with Suillus brevipes (both native strains), inoculation with forest soil, and non-inoculated plants. Percentage of ECM colonization, plant growth (shoot height and stem diameter), and physiological (osmotic potential, stomatal conductance, CO₂ assimilation and water use efficiency) responses were evaluated. We found that these two ECM species were partial (P. hartwegii) or totally (A. religiosa) replaced after one and a half years in the field. P. hartwegii seedlings increased their water use efficiency during the dry season, but in A. religiosa seedlings, a clear strategy for avoiding water stress was not detected. This ECM replacement had a negative effect on the physiological performance Of A. religiosa. Our results emphasize the importance of selecting compatible fungal-host species combinations for nursery inoculation and of using sources of inoculum adapted to the environmental conditions of the transplant site, ensuring root colonization prior to field transplanting to minimize seedling mortality due to water stress.     

Determination of Azole Resistance and TR<Subscript>34</Subscript>/L98H Mutations in Isolates of <Emphasis Type="Italic">Aspergillus</Emphasis> Section <Emphasis Type="Italic">Fumigati</Emphasis> from Turkish Cystic Fibrosis Patients

Background

Aspergillus fumigatus is the species section Fumigati most frequently isolated from the respiratory tract of cystic fibrosis (CF) patients. Recent studies suggest that mutations in the Cyp51 gene, particularly TR₃₄/L98H, are responsible for azole resistance.

Objectives and Methods

The focus of this study was on section Fumigati isolates isolated from the respiratory tract samples of CF patients. More specifically, the goal was to detect A. fumigatus isolates, test their antifungal susceptibility to itraconazole, voriconazole and posaconazole, and finally determine the presence of TR₃₄/L98H and other mutations in the isolates Cyp51A gene.

Results and Conclusions

A set of 31 isolates of Aspergillus section Fumigati were obtained from the sputum samples of 6 CF patients and subsequently identified to species level by microsatellite genotyping. All isolates were determined as A. fumigatus and involved 14 different genotypes. The minimal inhibitory concentrations to the three azoles were determined by the E-test method, and the Cyp51A gene was sequenced. One of the genotypes was found to be resistant to all azoles but no mutations were detected in the Cyp51A gene, especially the TR₃₄/L98H mutation. Therefore, mutations in genes other than Cyp51A or other distinct mechanisms may be responsible for this reported multiazole resistance found in a Turkish CF patient.

     

Analysis of biological functional networks during sciatic nerve repair and regeneration

Altered placental angiogenesis is implicated in the pathophysiology of preeclampsia. We have earlier reported placental regional differences in oxidative stress markers and neurotrophins. Oxidative stress and neurotrophins are reported to regulate angiogenesis. This study aims to examine protein and mRNA levels of vascular endothelial growth factor (VEGF) and VEGF receptor 1 (VEGFR1) in four regions [central maternal (CM), central fetal (CF), peripheral maternal (PM), and peripheral fetal (PF)] of the placenta in normotensive control (NC) women (n = 51) and women with preeclampsia (PE) (n = 43) [18 delivered at term (T-PE) and 25 delivered preterm (PT-PE)]. In all groups, CF region reported highest VEGF protein levels compared to all other regions. VEGF mRNA level was higher in CF region as compared to CM region in PE group (p < 0.05). VEGF levels were lower in all regions of PE, T-PE, and PT-PE groups (p < 0.05) as compared to their respective regions in NC group. VEGFR1 levels were lower in CF (p < 0.05) and PF (p < 0.01) regions as compared to CM region only in control. However, VEGFR1 levels were higher in CF (p < 0.05) and PF (p < 0.01) regions of PT-PE group as compared to control. VEGFR1 mRNA level was higher in PM region of PE group and T-PE group (p < 0.05 for both) as compared to control. VEGF levels in the PF region were positively associated with birth weight and placental weight. This study describes placental regional changes in angiogenic factors particularly highlighting increased VEGF in CF region possibly in response to hypoxic conditions prevailing in placenta.     

Can perennial dominant grass <Emphasis Type="Italic">Miscanthus sinensis</Emphasis> be nurse plant in recovery of degraded hilly land landscape in South China?

Perennial C₄ grasses, especially Miscanthus sinensis, are widely distributed in the degraded lands in South China. We transplanted native and exotic tree seedlings under the canopy of M. sinensis to assess the interaction (competition or facilitation) between dominant grass M. sinensis and tree seedlings. The results of growth, chlorophyll fluorescence, and ultrastructure showed that negative effects may be stronger in perennial dominant grass M. sinensis. Although M. sinensis buffered the air temperature, improved soil structure, and increased soil phosphorus content, these beneficial effects were outweighed by the detrimental effect, especially overshading. To ensure the establishment of target native species in M. sinensis communities in degraded lands of South China, restoration strategies should include removing aboveground vegetation, planting target species seedlings in openings to reduce the effects of canopy shading, and/or selecting competition-tolerant target species. Also, seedlings of exotic species used in restoration engineering cannot be directly planted under the canopy of M. sinensis.     

Synchronous fruiting and common seed dispersers of two endemic columnar cacti in the Caatinga,a dry forest in Brazil

This study evaluates the fruiting phenology, fruit traits, and seed dispersal in two Pilosocereus (Cactaceae) species that are widely distributed in Caatinga vegetation. We monitored the fruiting phenology of Pilosocereus gounellei and Pilosocereus chrysostele on a monthly basis for a period of 4 years (45 months from March 2009 to November 2012), including 30 individuals of each species. We also carried out focal observations, captured dispersers, and conducted germination tests, to identify the effective seed dispersers of these species. Both species exhibited sub-annual fruiting patterns and high fruiting synchrony index (O _jk 0.62), with peaks occurring from February to May for P. gounellei and February to April for P. chrysostele. In all, 248 visits by seven bird and two lizard species were recorded for P. gounellei, and 104 visits by five bird species were recorded for P. chrysostele. The two species shared five seed dispersers. The finch Lanio pileatus was the most frequently visiting bird species. The number of visits to the fruits of P. gounellei was higher than to the fruits of P. chrysostele. Passage of seeds through the digestive tracts of all bird species significantly increased the germination rate for P. chrysostele, whereas for P. gounellei, the birds Forpus xanthopterygius and L. pileatus decreased germination rates. Sub-annual fruiting patterns, similar fruit morphology, and high synchronous fruiting are factors that favor resource sharing among the dispersers of Pilosocereus in the Caatinga.     

Does a foliar endophyte improve plant fitness under flooding?

Although endophytic fungi are ubiquitous in plants, their full range of ecological effects has yet to be characterized, particularly in non-agronomic systems. In this study, we compared the responses of two congeneric bluegrass species to flooding. Both plant species co-occur in subalpine zones of the Rocky Mountains. Marsh bluegrass (Poa leptocoma) commonly hosts a vertically transmitted fungal endophyte (Epichloë sp.) and naturally grows in wetter conditions than does nodding bluegrass (Poa reflexa), which lacks an epichloid endophyte. We investigated the novel hypothesis that endophyte symbiosis promotes host fitness under flooded conditions, contributing to niche differentiation between the two bluegrass species. We used a factorial greenhouse experiment to test whether endophyte presence improved survival, growth, or reproduction of P. leptocoma under flooded versus non-flooded edaphic conditions by experimentally removing the endophyte from half of the plants. We compared P. leptocoma responses to those of the endophyte-free congener. In contrast to expectations generated from the natural distributions of the two plant species, endophyte presence was more beneficial to P. leptocoma under ambient soil moisture than under flooding. Increased benefits of symbiosis in drier soils are consistent with studies of other grass endophytes. Flooded soils also unexpectedly improved the growth of P. reflexa more than that of the wet habitat specialist, P. leptocoma. While our results demonstrate an overall benefit of fungal symbiosis in this system, ecological factors other than flooding per se likely underlie the observed geographical distributions of these congeneric grasses in nature.