Potential Increase in Photosynthetic Efficiency from the Redistribution of Solar Radiation in a Crop

The efficiency of the conversion of photosynthetically activeradiation by C₃ plants falls off with increasing intensity.Hypothesis: an increase in the productivity of direct solarenergy will be achieved if, by redistribution, it is interceptedat a more uniform and lower intensity by a greater proportionof the leaf area of a crop. A model is developed which usesestimates of the proportions of clear and overcast conditionsfrom site records of solar radiation to calculate the resultantphotosynthetic productivity. The amounts of diffuse light anddirect light are estimated for clear conditions. The model predictsthat redistributing direct solar radiation over twice the leafarea at half the intensity would give an increase of 22% inannual productivity. The model gives reasonable values for theproductivity reductions reported for two shading regimes. Tomato plants were grown for 21 d in three cabinets under regimesthat differed from each other only in the distribution of PARenergy over the daily photoperiod: (a) 103 W m^–2 for halfthe photoperiod followed by 13 W m^–2, (b) 13 W m^–2followed by 103 W m^–2 and (c) 58 W m^–2 for the wholephotoperiod. The dry matter increase of plants under the uniformregime was 33% greater than the average of those in the twoasymmetric regimes. It is suggested that, in protected cultivation, screens of partiallyreflective material could be used to redistribute solar radiationfrom leaves exposed to high intensities on to shaded leavesand so raise the photosynthetic efficiency. Assuming an absorptionof direct light by the screens of 0.10, the increase in productivityis estimated to be 17%. Key words: Photosynthesis, C₃, canopy, solar energy, solar redistribution, light interception, partial reflection, growth cabinet, glasshouse, tomato     

Modeling Cretaceous-Tertiary boundary events with extant photosynthetic plankton: effects of impact-related acid rain

Griffis, K. & Chapman, D. J. 1990 10 15: Modeling Cretaceous-Tertiary boundary events with extant photosynthetic plankton: effects of impact-related acid rain. Lethaia , Vol. 23, pp. 379–383. OSIO. ISSN 0024–1164.
An acid rain phenomenon has previously been proposed as one of the consequences of a bolide impact contributing to the extinctions at the Cretaceous-Tertiary boundary. This hypothesis has been tested by observing the growth responses of four organisms under simulated acid rain conditions. Two of these phytoplankton, Ditylum (a diatom) and Thoracosphaera (a dinoflagellate). are genera that persisted through the boundary, while the other two, Coccolithus (a coccolithophorid) and Gonyaulax (a dinoflagellate), are post-boundary genera. Ditylum and Coccolithus survive the acid rain simulation. but with the loss of scales in Coccolithus . The two dinoflagellate are sensitive to acid rain simulations. with Gonyaulax unable to survive beyond seven days. The results indicate that acid rain may have contributed to the Cretaceous-Tertiary boundary extinctions. but that the changes resulting from the acid rain were not as severe as postulated or were short-lived and quickly dissipated. ▭ Acid rain, coccolithophorids. Cretaceous/Tertiary extinctions, diatons, dinoflagellates, phytoplankton .     

Development of Amblyospora campbelli (Microsporida: Amblyosporidae) in the Mosquito Culiseta incidens (Thomson)

The complete life cycle of Amblyospora campbelli (Kellen and Wills, 1962) (Microsporida: Amblyosporidae) requires a two-host system involving the mosquito host, Culiseta incidens (Thomson), and an obligatory intermediate copepod host. The parasite has dimorphic spore development producing meiospores (haploid condition) and binucleated spores (diploid condition), either as an exclusive infection or simultaneously (within females only). This is the 1st known report of concurrent spore development within an adult mosquito host, and, therefore, shows the Amblyospora campbelli system to be uniquely different from other Amblyospora spp. cycles previously described. The significance of dimorphic spore development is discussed. In females, diplokaryotic meronts may invade oenocytes, causing a benign-type of infection. A blood-meal is required to initiate sporulation of the binucleate spore. The binucleate spore contains the sporoplasm involved in transovarial transmission. A 2nd sporulation sequence, primarily in adipose tissue, may involve both males and females. In this sequence, repeated merogonic division greatly increased the density of diplokaryotic meronts and generally involved most of the body of the host. Production of meiospores, unlike that for the binucleate spore, appeared to be spontaneous (i.e. no obligatory blood meal). Survivorship of male and female larval mosquitoes was nearly equal. Adult females spread the parasite in three ways: transovarial, transovum, and by meiospore deposition.     

Population subdivision in Australian temperate marine invertebrates: Larval connections versus historical factors*

This paper reviews the use of genetic data, in combination with manipulative experimentation, to infer the mode of reproduction and the extent and directionality of dispersal for a range of Australian temperate marine invertebrates. Local populations of obligately sexually reproducing species have been inferred to be strongly interconnected by larval dispersal, over distances of thousands of kilometres. Their larvae may be subject to strong post-settlement selection, but this selection is independent of obvious geographic or intertidal gradients. Within local populations selection may therefore result in apparently chaotic genetic patchiness which is eliminated by the effects of sexual reproduction and the widespread dispersal and mixing of the colonizing larvae of each generation. In partial contrast, local populations of species which rely on asexual reproduction for the maintenance of populations show evidence of similar larval connections, but no recent settlement of their sexually generated larvae has been demonstrated. The apparent connectedness of these populations may reflect either historical events or a more episodic pattern of settlement by sexually generated larvae. Local populations of these species are more highly differentiated as a result of the continued asexual replication of a limited number of genotypes. In one of these species, reciprocal transplantation of the clones within and among populations has revealed that resident clones can be highly locally adapted (as reflected by much higher asexual fecundity), which implies that selection is an important determinant of the composition of local populations. Nevertheless, the failure to detect continuing sexual recruitment into these populations obscures the evolutionary significance of this finding.     

A review of the fossil record of the Pomacentridae (Teleostei: Labroidei) with a description of a new genus and species from the Eocene of Monte Bolca, Italy

The fossil record of the Pomacentridae has been based on species from six genera. The status of these taxa is reviewed. Only two are tentatively accepted as belonging to the Pomacentridae: Chromis savomini from the Miocene of Algeria and Izuus nakamurai from the Miocene of Japan. In addition, a new genus and species Palaeopomacentrus orphae is described from the lower Middle Eocene of Monte Bolca, Northern Italy. This is the first substantiated record of a pomacentrid from the Eocene, and represents the oldest record of the family.     

Effects of social conditions on Juvenile Hormone mediated reproductive development in Bombus terrestris workers

Abstract. During the annual life cycle of the bumble bee Bombus terrestris (L.) colony, there is a stage characterized by worker reproduction in the presence of the queen. It has been proposed that this is a result of a decrease in queen inhibition. This hypothesis was examined by studying the effects of queens taken from colonies at different stages of development on several aspects of worker physiology and behaviour: rates of Juvenile Hormone (JH) release in vitro , ovary development, and behaviour associated with reproduction. After optimizing and validating the radiochemical assay for JH release for bumble bee workers, we found that queenless workers had significantly more developed ovaries and higher rates of release of JH than did queenright workers, confirming and extending previous findings that suggest that bumblebee ovarian development is under JH control. Mated queens, separated from their colony and brood, can have the same inhibitory effect on the reproductive development of callow workers. In contrast, workers confined with virgin queens or in queenless groups demonstrated a significantly higher rate of release of JH, overt aggression and threatening behaviours. However, there were no differences in rates of release of JH between workers confined in groups in the laboratory with queens taken from colonies either before or after the onset of worker reproduction. Furthermore, overt aggression and threatening behaviours were similar and low in both types of groups. These results gave no support to the hypothesis that a decrease in queen inhibition is associated with the onset of worker reproduction. We also show that young workers reared in colonies either before or after worker reproduction occurs, or in queenless colonies, all demonstrated similar, low rates of release of JH. These results suggest that older workers may inhibit the corpora allata of younger workers in queenless colonies.