Why some stems are red: cauline anthocyanins shield photosystem II against high light stress

Red-stemmed plants are extremely common, yet the functions of cauline anthocyanins are largely unknown. The possibility that photoabatement by anthocyanins in the periderm reduces the propensity for photoinhibition in cortical chlorenchyma was tested for Cornus stolonifera. Anthocyanins were induced in green stems exposed to full sunlight. PSII quantum yields (ФPSII) and photochemical quenching coefficients were depressed less in red than in green stems, both under a light ramp and after prolonged exposures to saturating white light. These differences were primarily attributable to the attenuation of PAR, especially green/yellow light, by anthocyanins. However, the red internodes also had less chlorophyll and higher carotenoid:chlorophyll ratios than the green, and when the anthocyanic periderm was removed, small differences in the ФPSII of the underlying chlorenchyma were retained. Thus, light screening by cauline anthocyanins is important, but is only part of a set of protective acclimations to high irradiance. Hourly measurements of ФPSII on established trees under natural daylight indicated a possible advantage of red versus green stems under sub-saturating diffuse, but not direct sunlight. To judge the wider applicability of the hypothesis, responses to high light were compared for red and green stems across five further unrelated species. There was a strong, linear, interspecific correlation between photoprotective advantage and anthocyanin concentration differences among red and green internodes. The photoprotective effect appears to be a widespread phenomenon

An experimental study of intermodulation effects in an atomic fountain frequency standard

The short-term stability of passive atomic frequency standards, especially in pulsed operation, is often limited by local oscillator noise via intermodulation effects. We present an experimental demonstration of the intermodulation effect on the frequency stability of a continuous atomic fountain clock where, under normal operating conditions, it is usually too small to observe. To achieve this, we deliberately degrade the phase stability of the microwave field interrogating the clock transition. We measure the frequency stability of the locked, commercial-grade local oscillator, for two modulation schemes of the microwave field: square-wave phase modulation and square-wave frequency modulation. We observe a degradation of the stability whose dependence with the modulation frequency reproduces the theoretical predictions for the intermodulation effect. In particular no observable degradation occurs when this frequency equals the Ramsey linewidth. Additionally we show that, without added phase noise, the frequency instability presently equal to 2x10-13 at 1s, is limited by atomic shot-noise and therefore could be reduced were the atomic flux increased

Born to run? Vegetative spread of the invasive plant Phragmites australis via stolons (runners)

Phragmites australis is a highly invasive wetland grass species that dominates nearly any ecosystem that it invades, this is due to its incredibly dense foliage which makes it hard for plants and animals to live in the vicinity of phragmites. Phragmites can grow in versatile environments and are extremely durable. Therefore, once phragmites establish itself, it is very difficult to remove it. On top of that, Phragmites spreads very quickly by utilizing both sexual and asexual reproduction

Edge influence on forest composition in a pine-oak forest in central Mexico

Deforestation in central Mexico comes as a direct consequence of the increase in agriculture demand and has resulted in the creation of more habitat edges. Changes in land usage for agriculture and resource extraction has resulted in habitat destruction and degradation; these same mechanisms have led to habitat fragmentation by producing smaller, and isolated fragments separated by human-transformed land cover. The loss of continuous area has resulted in greater exposure to human dominated landscapes resulting in changes to the structure and function of the remaining fragment. To quantify, document, and describe the edge influence on forest composition fragmented by an agriculture field, I sampled 6 transects with 3, 10, 20, 30, & 40m data points per transect. My results reveal an edge influence on forest composition from an agriculture field

Experimental demonstration of intermodulation effects in a continuous cesium fountain microwave frequency standard

International audienceThe short-term stability of passive atomic frequency standards, particularly ones operated sequentially, is often limited by local oscillator noise via intermodulation effects. This article describes an experimental demonstration of the intermodulation effect on the frequency stability of a continuous atomic fountain standard usually imperceptible under normal operating conditions. To make the effect observable, we increase the phase instability of the microwave field interrogating the clock transition.We measure the frequency stability of the locked, commercial local oscillator, for both square-wave phase modulation and squarewave frequency modulation of the microwave field. The observed degradation of the stability depends on the modulation frequency in a way that agrees with our earlier theoretical predictions. Most significantly, no degradation is observed when the modulation frequency is made equal to the Ramsey linewidth. When no extra phase noise is added, the frequency instability, currently 2.0x10-13 at 1 s, is limited only by atomic shot-noise. This shows the potential to reduce it via the use of a higher atomic flux

Honolulu Moon

With Ukulele arrangement. Contains advertisements and/or short musical examples of pieces being sold by publisher.https://digitalcommons.library.umaine.edu/mmb-vp/7085/thumbnail.jp

A Preliminary Look into Regional Primary Succession in the DePauw University Nature Park Quarry

Quarries are anthropogenic landscapes that when abandoned, leave a blank slate in the environment for species to come in and repopulate the area. This gives way to primary succession, a process that re-vegetates areas devoid of soil. The goal of this research is to investigate where the abandoned limestone quarry at the DePauw University Nature Park is in terms of its successional phase since extraction stopped in 1977. Throughout the summer of 2020, plant species were identified along with the specific region and sub-habitat, the main sub-habitats being the temporary ponds, quarry spoils, talus slopes, flat limestone areas, and damp or low spots. Other information including plant form, life history, native and wetland status, and invasive rank was recorded for each species using the USDA website. Of the 98 species collected, 73% are native plants. Of the 27 non-native species, 7 have been identified as highly invasive, 2 are medium, and 1 is low. Nineteen of the 75 species with labeled wetland statuses are commonly found in wetlands, having facultative wetland and obligate wetland statuses. The majority of the species we identified are herbaceous in plant form and have perennial life history. According to an article by Girardelli et al. (2016) regarding assigning successional phases in limestone quarries, an area undergoing primary succession that is dominated by perennials is indicative of late phase succession while shrubs tend to replace herbaceous plants in later phases of succession. While the majority of the species are native, herbaceous, perennials, and have a facultative upland status, we do not yet know whether these species are representative of the total coverage on the quarry bottom. Moving forward with this information, a pilot study has been started as a basis for my research in the fall semester that will estimate species diversity in the quarry bottom as well as relate species diversity and composition to abiotic conditions

A Comparison of Invasive and Native Plants in an Abandoned Limestone Quarry

The abandoned limestone quarry in the DePauw Nature Park is a site of interest for research into plant community establishment due to the harsh, heterogenous, and fluctuating environment. Because the limestone floor of the quarry is a novel anthropogenic environment, every plant species in the quarry had to be introduced somehow. Perhaps native species that are able to establish populations in the quarry are more likely to share traits with invasive species. Using information collected from scientific articles, I compared traits of three pairs of plants with similar forms to compare their life history traits to see if any patterns emerge. I compared Erigeron annuus (native) to Pilosella caespitosa (invasive), Celastrus scandens (native) to Rosa multiflora (invasive), and Phragmites australis to Typha angustifolia which are both invasive, but Phragmites is more prevalent in the quarry. All six species exhibited traits that are associated with invasiveness. They all can reproduce asexually. All but two of the species have seeds that are wind dispersed. Rosa multiflora is the only one that lacks multiple distinct means of seed dispersal. Lastly, four of the species have high genetic and/or phenotypic plasticity. The initial comparisons indicate that species that establish on the quarry floor tend to exhibit traits associated with invasiveness, regardless of whether those species are native to Indiana. Future empirical research comparing the traits these three species groups taking into account other groups with which quarry plants could share traits such as natural calcareous and primary successional species would broaden our understanding of the intersection between natural calcareous, primary successional, invasive, and quarry species

Stressed, but doing fine. An Investigation of Apocynum Canabinum Patches and Individuals

Apocynum cannabinum (hemp dogbane) is a native Indiana plant that is abundant in the DePauw University Nature Park’s quarry, a heterogeneous site that contains stretches of dry, rocky terrain in addition to many temporary ponds. In 2023, I mapped the distribution of A. cannabinum in the quarry to see if its habitats are associated with elevation and/or the presence of temporary ponds. I also conducted a study of diurnal pollinator visitation, and an examination of damage caused by the dogbane saucrobotys moth (Saucrobotys futilalis)