The response of Vicia faba to enhanced UV-B radiation under low and near ambient PAR levels

The effects of enhanced UV-B are often overestimated in greenhouse studies due to low levels of photosynthetically active radiation (PAR). For this reason, we studied effects of enhanced UV-B (12 kJ m^–2 d^–1) at low and near ambient PAR levels on young vegetative plants of Vicia faba, in the greenhouse. It was hypothesized that near ambient PAR levels could reduce the negative UV-B effects on growth, due to higher amounts of UV-B absorbing compounds in the leaves and to morphological changes attenuating UV-B damage.We found that effects of enhanced UV-B on the growth were not negative. We found an increase in biomass in response to enhanced UV-B at low and near ambient PAR levels. The increase in biomass was related to increased branching, which leads to a higher interception of PAR. Enhanced irradiance of both PAR and UV-B had similar photomorphogenic effects: thicker and smaller leaves and reduced plant height and internode length. Moreover, the concentration of UV-B absorbing compounds was increased. We conclude that in this study effects of enhanced UV-B were mainly photomorphogenic effects, which were also induced by radiation in the PAR region.     

A Vegetation, Climate and Environment Reconstruction Based on Palynological Analyses of High Arctic Tundra Peat Cores (5000–6000 years BP) from Svalbard

As a reference for ongoing studies reconstructing past vegetation, climate and environment, pollen spectra in tundra peat profiles from Svalbard, were investigated. The base of tundra peat cores collected from Ny Ålesund, Stuphallet, Blomstrand and Isdammen has been ¹⁴C dated to 350–490 BP, 5710 BP, 4670 BP and 700–900 BP, respectively. The Stuphallet and Blomstrand (Brøggerhalvøya) peat profiles were composed of a peat developed in a nutrient enriched and wet tundra environment of steep birdcliffs. Pollen concentrations were low, Brassicaceae pollen dominated the whole profile. In contrast, the Ny Ålesund and Isdammen profiles contained high pollen concentrations and suggest a nutrient-poor, dry tundra environment. Pollen of the polar willow, Salix polaris, occurred commonly throughout all four peat profiles. In the relatively high resolution (10 years per peat core sample) analysis of the Ny Ålesund core, starting before or at the beginning of the Little Ice Age (LIA, 16th-mid 19th century), dominance of Saxifraga oppositifolia indicates a cold and dry climate, followed by a decline of Saxifraga oppositifolia and gradual increase of Salix polaris after the LIA, which indicates a moist and milder climate.     

Dispersal and life span spectra in plant communities: a key to safe site dynamics, species coexistence and conservation

Dispersal and life span of individual plant species within five plant communities were assessed to obtain a characterization of these communities in this respect. Such a characterization is important in the context of restoration and maintenance. The most frequent species of five communities were ranked in eight classes according to their level of seed dispersal capability, their seed bank formation (dispersal in time and space) and their individual life span. In the communities, all eight classes were found, but communities differed in the distribution of the species over the classes.
A theoretical framework was constructed to use the level of specialization of plant species in terms of dispersal in space and time, and life span, to define the characteristics of safe site dynamics within communities. Following simple rules, the relative reliability of the occurrence of safe sites in space and time was defined. After that, the relative reliability of the habitat was linked to the best fitting combination of trait specialization level. Having defined this link, communities could be characterized in a comparative way by their level and pattern of reliability of the opportunities for recruitment in space and time.
The meaning of the coexistence of a range of trait combinations in one community was discussed. It was postulated that habitat reliability can explain this by assuming that the habitat of the community is part of a larger system, or consists of several “subsystems”. These insights need to be considered in nature conservation. Succession and also specializations beyond the scope of dispersal and life span may influence the occurrence of species in a seemingly unfit habitat (for instance the occurrence of semi parasitic annuals in a community of perennials, because they use the perennial root system of other species). Finally, the meaning of safe site reliability in space and time in the context of restoration of communities was discussed. The reliability in space and time may be different today from that of the past, which restricts the feasibility of restoration of communities.     

The combined effects of elevated CO2 levels and UV-B radiation on growth characteristics ofElymus athericus (= E. pycnanathus)

Elymus athericus (Link) Kerguélen, a C₃ grass, was grown in a greenhouse experiment to determine the effect of enhanced atmospheric CO₂ and elevated UV-B radiation levels on plant growth. Plants were subjected to the following treatments; a) ambient CO₂-control UV-B, b) ambient CO₂-elevated UV-B, c) double CO₂-control UV-B, d) double CO₂-elevated UV-B. Elevated CO₂ concentrations stimulated plant growth, biomass production was 67% higher than at ambient CO₂. Elevated UV-B radiation had a negative effect on growth, biomass production was depressed by 31%. Enhanced CO₂ combined with elevated UV-B levels caused a biomass depression of 8% when compared with the control plants. UV-B induced growth depression can be modified by a growth stimulus caused by high CO₂ concentrations. Growth analysis has been performed and possible physiological mechanisms behind changing growth parameters are discussed.     

Quantification of UV-B flux through time using UV-B-absorbing compounds contained in fossil Pinus sporopollenin

UV-B radiation currently represents c. 1.5% of incoming solar radiation. However, significant changes are known to have occurred in the amount of incoming radiation both on recent and on geological timescales. Until now it has not been possible to reconstruct a detailed measure of UV-B radiation beyond c. 150 yr ago. Here, we studied the suitability of fossil Pinus spp. pollen to record variations in UV-B flux through time. In view of the large size of the grain and its long fossil history, we hypothesized that this grain could provide a good proxy for recording past variations in UV-B flux. Two key objectives were addressed: to determine whether there was, similar to other studied species, a clear relationship between UV-B-absorbing compounds in the sporopollenin of extant pollen and the magnitude of UV-B radiation to which it had been exposed; and to determine whether these compounds could be extracted from a small enough sample size of fossil pollen to make reconstruction of a continuous record through time a realistic prospect. Preliminary results indicate the excellent potential of this species for providing a quantitative record of UV-B through time. Using this technique, we present the first record of UV-B flux during the last 9500 yr from a site near Bergen, Norway.     

Outlier Removal and the Relation with Reporting Errors and Quality of Psychological Research

Background

The removal of outliers to acquire a significant result is a questionable research practice that appears to be commonly used in psychology. In this study, we investigated whether the removal of outliers in psychology papers is related to weaker evidence (against the null hypothesis of no effect), a higher prevalence of reporting errors, and smaller sample sizes in these papers compared to papers in the same journals that did not report the exclusion of outliers from the analyses.

Methods and Findings

We retrieved a total of 2667 statistical results of null hypothesis significance tests from 153 articles in main psychology journals, and compared results from articles in which outliers were removed (N = 92) with results from articles that reported no exclusion of outliers (N = 61). We preregistered our hypotheses and methods and analyzed the data at the level of articles. Results show no significant difference between the two types of articles in median p value, sample sizes, or prevalence of all reporting errors, large reporting errors, and reporting errors that concerned the statistical significance. However, we did find a discrepancy between the reported degrees of freedom of t tests and the reported sample size in 41% of articles that did not report removal of any data values. This suggests common failure to report data exclusions (or missingness) in psychological articles.

Conclusions

We failed to find that the removal of outliers from the analysis in psychological articles was related to weaker evidence (against the null hypothesis of no effect), sample size, or the prevalence of errors. However, our control sample might be contaminated due to nondisclosure of excluded values in articles that did not report exclusion of outliers. Results therefore highlight the importance of more transparent reporting of statistical analyses.     

The applicability of the rooting technique measuring salt resistance in populations ofFestuca rubra andJuncus species

Summary Indices of salt resistance, based on the measurement of the Mean Relative Growth Rate of the total plant biomass were shown to be more reliable and easily obtained than those based on the rooting technique. Adaptation to salinity stress (NaCl toxicity, osmotic stress) differs essentially from heavy metal stress (mainly ion-toxicity). Extension of the root system under saline conditions should therefore be regarded as a compensatory growth mechanism rather than the direct result of salt stimulation. The application of the rooting technique for optimum measurement of salt resistance is questioned. The index of salt resistance technique may be applied to all vascular plants, while unmodified application of the rooting technique is confined to certain groups of the Monocotyledonae.     

Nutrient availability influences UV-B sensitivity of Plantago lanceolata

Seeds of Plantago lanceolata were collected in a dune grassland ecosystem in the Netherlands. Plants were grown in a greenhouse for 61 days under either low or high nutrient conditions and were exposed to four different levels of biologically effective UV-B radiation. The highest UV-B exposure level simulated 30% reduction of the stratospheric ozone layer during summertime in the Netherlands. Total biomass production of plants at low nutrient supply was 50% lower compared to plants grown at high nutrient supply, while net photosynthesis was decreased by only 12%. Increased levels of UV-B reduced biomass production under non-limiting nutrient conditions only. Biomass production of plants grown at limited nutrient supply was not affected by UV-B. This response was correlated to increased accumulation of carbohydrates under nutrient limitation, which agrees well with the carbon/nutrient balance hypothesis. It is concluded that the increased accumulation of carbon in nutrient-stressed plants, may lead to a reduction of UV-B induced damage because of increased foliar UV-B absorbance by enhanced accumulation of phenolic compounds and leaf thickening.     

The effect of a single injection of irinotecan on the development of enamel in the Wistar rats

Cancer is the second most frequent cause of death in children. Because the prognosis for childhood malignancies has improved, attention has now focused on long‐term consequences of cancer treatment. The immediate effects of chemotherapy on soft tissues have been well described; however, there is less information about long‐term effects of chemotherapy on the development of dental tissues. To test the association between the effect of chemotherapy on enamel development, we examined two groups of rats: one that had received an intraperitoneal dose of 200 mg/kg of irinotecan, whereas the other (control) group had received vehicle only. Rats were killed at 6, 48 and 96 hr post‐injection; the mandibles dissected out, fixed for histological evaluation and scanned for mineralization defects by Micro‐CT. Our results showed structural changes in the ameloblast layer along with a significant reduction in mineralization and thickness of enamel at 96 hr after chemotherapy. These data demonstrate that irinotecan induces structural changes in forming enamel that become apparent after anticancer chemotherapy treatment.     

The impact of elevated UV-B (280–320 nm) radiation levels on the reproduction biology of a highland and a lowland population of Silene vulgaris

A highland (altitude 1600 m) and a lowland (altitude –2 m) population of the perennial herb Silene vulgaris were tested on the effects of elevated levels of UV-B radiation on their reproductivity. Highland populations receive higher natural UV-B doses than lowland populations. Therefore adaptation to high UV-B levels of the highland population is to be expected. The lowland population showed a decrease in the number of seed producing flowers and the number of seeds produced per plant under elevated UV-B levels. The highland population increased the number of seeds per plant under elevated UV-B levels. In both populations individual seed mass as well as seed germination percentages were unaffected by the UV-B flux received by the parental plant. Possible effects of UV-B induced alterations in reproductivity on the geographical distribution of the different populations are discussed.