Variation in species composition and species richness within Phragmites australis dominated riparian zones

In riparian wetlands total standing crop often fails to account for a significant part of the observed variation in species richness and species composition within communities. In this study, we used abundance of the dominant species instead of total standing crop as the biotic predictor variable and investigated its relationships with species composition and species richness in communities dominated by Phragmites australis (Cav.) Trin. ex Steudel. This was done by measuring soil organic matter content, litter cover and elevation, Phragmites abundance (standing crop and stem density) and species composition in 78 relevés. In addition, we tried to identify the environmental boundaries of Phragmites communities by sampling relevés in neighbouring communities.Two gradients were related to a decline in Phragmites abundance: one gradient, perpendicular to the shoreline, was mainly related to increased elevation and the second gradient ran parallel to the shoreline and was related to increased amounts of soil organic matter. Within the relevés dominated by Phragmites, stem density of Phragmites and litter cover were the only factors significantly related to species composition in the RDA solution. Litter cover and standing crop of the dominant accounted for 64% of the variation in species richness within the Phragmites-dominated community. These results show that dead and living biomass of the dominant species may account for a substantial part of the variation in species composition and species richness within a single community.     

Diagnostic value of the electrocardiogram in the assessment of prior myocardial infarction

BackgroundThe best available imaging technique for the detection of prior myocardial infarction (MI) is cardiac magnetic resonance (CMR) with late gadolinium enhancement (LGE). Although the electrocardiogram (ECG) still plays a major role in the diagnosis of prior MI, the diagnostic value of the ECG remains uncertain. This study evaluates the diagnostic value of the ECG in the assessment of prior MI.MethodsIn this retrospective study, data from electronic patient files were collected of 1033 patients who had undergone CMR with LGE between January 2014 and December 2017. After the exclusion of 59 patients, the data of 974 patients were analysed. Twelve-lead ECGs were blinded and evaluated for signs of prior MI by two cardiologists separately. Disagreement in interpretation was resolved by the judgement of a third cardiologist. Outcomes of CMR with LGE were used as the gold standard.ResultsThe sensitivity of the ECG in the detection of MI was 38.0% with a 95% confidence interval (CI) of 31.6–44.8%. The specificity was 86.9% (95% CI 84.4–89.1%). The positive and negative predictive value were 43.6% (95% CI 36.4–50.9%) and 84.0% (95% CI 81.4–86.5%) respectively. In 170 ECGs (17.5%), the two cardiologists disagreed on the presence or absence of MI. Inter-rater variability was moderate (κ 0.51, 95% CI 0.45–0.58, p < 0.001).ConclusionThe ECG has a low diagnostic value in the detection of prior MI. However, if the ECG shows no signs of prior MI, the absence of MI is likely. This study confirms that a history of MI should not be based solely on an ECG.     

A primary culture of distal convoluted tubules expressing functional thiazide-sensitive NaCl transport

Studying the molecular regulation of the thiazide-sensitive Na(+)-Cl(-) cotransporter (NCC) is important for understanding how the kidney contributes to blood pressure regulation. Until now, a native mammalian cell model to investigate this transporter remained unknown. Our aim here is to establish, for the first time, a primary distal convoluted tubule (DCT) cell culture exhibiting transcellular thiazide-sensitive Na(+) transport. Because parvalbumin (PV) is primarily expressed in the DCT, where it colocalizes with NCC, kidneys from mice expressing enhanced green-fluorescent protein (eGFP) under the PV gene promoter (PV-eGFP-mice) were employed. The Complex Object Parametric Analyzer and Sorter (COPAS) was used to sort fluorescent PV-positive tubules from these kidneys, which were then seeded onto permeable supports. After 6 days, DCT cell monolayers developed transepithelial resistance values of 630 ± 33 Ω·cm(2). The monolayers also established opposing transcellular concentration gradients of Na(+) and K(+). Radioactive (22)Na(+) flux experiments showed a net apical-to-basolateral thiazide-sensitive Na(+) transport across the monolayers. Both hypotonic low-chloride medium and 1 μM angiotensin II increased this (22)Na(+) transport significantly by four times, which could be totally blocked by 100 μM hydrochlorothiazide. Angiotensin II-stimulated (22)Na(+) transport was also inhibited by 1 μM losartan. Furthermore, NCC present in the DCT monolayers was detected by immunoblot and immunocytochemistry studies. In conclusion, a murine primary DCT culture was established which expresses functional thiazide-sensitive Na(+)-Cl(-) transport.     

The influence of pH on concentrations of protein and phenolics and resource quality of decomposing floating leaf material of Nymphaea alba L. (Nymphaeaceae) for the detritivore Asellus aquaticus (L.)

Summary Senescent floating leaf material of Nymphaea alba L., collected in an acidified moorland pool, was used in decomposition studies in two aquatic systems that differed greatly in pH, alkalinity and nutrient concentration. Concentrations of extractable protein and phenolics in the decomposing leaf material were measured during the incubation period. Protein levels were not significantly different in the leaf material from the two study sites, whereas the concentrations of phenolics in the degrading leaf blades from the acid site remained higher than in the material from the alkaline site. The resource quality of the decomposing leaf material was estimated by feeding tests using Asellus aquaticus (L.) in the laboratory. The effect of an artificially increased level of tannin on the feeding activity of A. aquaticus was also studied. Material from the acid system was consumed at a lower rate than material from the other system. The phenolic content of the material was found to be the most important feeding cue. The protein level of the leaf blade detritus seems to be of less importance. The structure of the decomposing leaf blades may have influenced the resource quality in the later stages of the experiment.     

Quantitative trait loci associated with seed and seedling traits in Lactuca

Seed and seedling traits related to germination and stand establishment are important in the production of cultivated lettuce (Lactuca sativa L.). Six seed and seedling traits segregating in a L. sativa cv. Salinas x L. serriola recombinant inbred line population consisting of 103 F8 families revealed a total of 17 significant quantitative trait loci (QTL) resulting from three seed production environments. Significant QTL were identified for germination in darkness, germination at 25 and 35°C, median maximum temperature of germination, hypocotyl length at 72 h post-imbibition, and plant (seedling) quality. Some QTL for germination and early seedling growth characteristics were co-located, suggestive of pleiotropic loci regulating these traits. A single QTL (Htg6.1) described 25 and 23% of the total phenotypic variation for high temperature germination in California- and Netherlands-grown populations, respectively, and was significant between 33 and 37°C. Additionally, Htg6.1 showed significant epistatic interactions with other Htg QTL and a consistent effect across all the three seed production environments. L. serriola alleles increased germination at these QTL. The estimate of narrow-sense heritability (h²) of Htg6.1 was 0.84, indicating potential for L. serriola as a source of germination thermotolerance for lettuce introgression programs.     

The effect of flooding on the recruitment of reed marsh and tall forb plant species

Recruitment of plant species in wetlands dominated by Phragmites australis often results in a zonation of two vegetation types. A development of reed marshes takes place in the shallow flooded parts where the dominant P. australis becomes accompanied by interstitial marsh species. The vegetation on higher elevations becomes dominated by tall forbs. We investigated whether this zonation is related to the effects of flooding on the recruitment of component species of both vegetation types. All but one species had maximum germination at field capacity and germination was strongly reduced in drier soils and flooded soils. Nearly all seedlings of reed marsh species, irrespective of whether they initially supported two or six true leaves, survived eight weeks of total inundation. Survival of tall forbs was however significantly decreased by inundation. At both seedling stages a considerable number of Cirsium arvense lost their leaves when submerged, but all plants were able to recover when drained. Eupatorium cannabinum suffered extra mortality when transferred from flooded to drained conditions, whereas only young seedlings of Epilobium hirsutum died. Of all investigated species E. hirsutum was the only one with a significantly increased stem length after one week of submergence. Root porosities did not differ between reed marsh species and tall forbs but stem porosities of the reed marsh species Mentha aquatica and Lycopus europaeus were significantly higher than those of the tall forbs C. arvense and E. cannabinum. It was concluded that both reed marsh species and tall forbs require lowered water levels for germination. Flooding during the seedling stage will assign species to their position on the elevation gradient. Reed marsh species establish at lower elevations because they are best able to survive flooding and because their higher stem porosities allows them to withstand higher levels of partial submergence.     

Differential responses of germination and seedling establishment in populations of Tragopogon pratensis (Asteraceae)

The establishment phase is an important bottleneck in the life cycle of plants. It consists of two steps that are rarely separated, i.e., the germination of seeds and the establishment of seedlings. Here we report the results of two experiments in which we independently investigated germination and seedling establishment in the greenhouse, under different grass vegetation treatments representing different regeneration niches. Seeds of Tragopogon pratensis from six populations and two habitat types were studied, three from roadside verges and three from hayfields. Germination percentages and germination speed were higher for seeds from roadside verges than for seeds from hayfields, but were little affected by treatment. In contrast, seedling growth was much lower in the tall grass vegetation, than in the short grass and especially the bare soil treatment. Seedling sizes were generally similar for different populations and habitat types. Our results thus show that the two early steps in the establishment phase of plants may respond very differently to the micro-environment, and may have a different selection history. Insight into the ecology and evolution of life histories may require that germination and establishment are considered separately.     

Selection on phenotypic plasticity of morphological traits in response to flooding and competition in the clonal shore plant Ranunculus reptans

Adaptive evolution of phenotypic plasticity requires that plastic genotypes have the highest global fitness. We studied selection by spatial heterogeneity of interspecific competition and flooding, and by temporal heterogeneity of flooding on morphological plasticity of 52 genotypes of the clonal shore plant Ranunculus reptans. Competition reduced clone size, rosette size, leaf length and stolon internode thickness. Flooding had similar effects and reduced competition. Differences in selection between environments imply potential for either local adaptation or for indirect evolution of phenotypic plasticity. We also detected direct selection for plastic reductions in internode length in response to flooding and for a plastic increase in internode length in response to competition. Plastic responses of some morphological traits to flooding were in line with selection thereon, suggesting that they indeed are adaptive and might have evolved in response to direct selection on plasticity.     

Distribution of alfalfa weevil (Coleoptera: Curculionidae) larvae among postcutting locations

A field study was conducted in 1996 and 1997 to determine survival and spatial patterns of alfalfa weevil, Hypera postica (Gyllenhal), larvae within and between windrows of swathed alfalfa, Medicago sativa L., forage as dry matter concentration increased. After harvest, the percentage of live weevil larvae residing in swathed forage decreased as swath dry matter percentage increased. Conversely, larval populations in stubble between windrows increased with increasing swath dry matter. Larval populations in stubble under windrowed forage increased slightly as windrowed forage dry matter increased. Applications of these results for the development of alfalfa harvest systems for improved cultural control of alfalfa weevil are discussed.