Studies in Stomatal Behaviour: VIII. STOMATAL RESPONSES TO TEMPERATURE AND CARBON DIOXIDE CONCENTRATION IN ALLIUM CEPA L., AND THEIR RELEVANCE TO MID-DAY CLOSURE

It has been reported in the literature that onion leaf stomatatend to close at noon (Loftfield, 1921) and that the minimumcarbon dioxide concentration () in onion leaf tissue rises from0.012 per cent to 0.024 per cent. When the leaf temperatureincreases from 30°C. to 35°C (light intensity 900.f.c.)(Heath and Orchard, 1957). Experiments were therefore carried out of test the hypothesisthat raising the left temperature above about 30°C. causesstomatal closing movements in onion leaves (e.g. mid-day closure)by increasing the carbon dioxide concentration in the leaf tissue.This hypothesis has been supported by the results of these experiments.Another and diametrically opposed effect of temperature on stomatalmovements in onion leaves has, however, been discovered, Namelythat, provided the final width of stomatal pores.     

Solar radiation interception by leafless, semi-leafless and leafed peas (Pisum sativum) under contrasting field conditions

Foliage composition, photosynthetic area index (PAI) and radiation interception were measured for crop canopies of leafless (var. Filby), semi-leafless (var. BS3) and leafed (var. Birte) peas (Pisum sativum). Tendrils and petioles contributed more than 60% of total leaf area for leafless peas but less than 30% for semileafless and leafed pea canopies. PAI was related to radiation interception by calculating attenuation coefficients which indicated that leafless peas intercepted more radiation per unit PAI than either semi-leafless or leafed peas. Data interpretation, however, was complicated because of difficulties in estimating the tendril and petiole surface area contribution to PAI. Radiation interception was related to dry matter accumulation by calculating photosynthetic efficiencies. Leafless and semi-leafless peas converted intercepted radiation into dry matter as efficiently as leafed peas. Under conditions of moisture stress, leafed and leafless peas both intercepted radiation more effectively but converted it into dry matter with reduced photosynthetic efficiency.     

Convergence and parallelism among cicadas of Argentina and the southwestern United States (Hemiptera: Cicadoidea)

Cicadas of the genera Derotettix in Argentina and Okanagodes in the south-western United States resemble each other in colour, live on salt-tolerant plants ( Atriplex spp. etc.), nearly match the colour of their respective host plants and produce songs above the range of avian hearing. The Argentine cicadas are smaller, but have nearly identical thermal limits for activity measured by the minimum temperature for flight (20–24 °C) and a body temperature at heat torpor (48–49 °C). The species shift activity from basking sites to shade at temperatures above 37 °C, although O .  gracilis rises to a significantly higher temperature (40.7 °C) than its congener (38.2 °C) or Derotettix (37.2 °C). The thermal tolerances are the highest reported for cicada species. A third group using halophytes in Argentina ( Babras sonorivox ) has similar temperature tolerances and is cryptically coloured. The genera are convergent with respect to morphology, coloration, body size, behaviour, habitat choice and host plant selection. The similarities of thermal tolerances and their influence on behaviour can be viewed as parallelism because the underlying mechanisms are the same in all species studied.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 281–288.     

Carbon Assimilation at Low Carbon Dioxide Levels: II. THE PROCESSES OF APPARENT ASSIMILATION

The relation of the net uptake or output of carbon dioxide bydetached leaves of Pelargonium zonale or wheat to ambient carbondioxide concentration was investigated at two or three lightintensities. The statistics of fitted curves were used as datain analysis of variance. For Pelargonium the results were consistentwith a hypothesis of a ‘straight balance’ betweena rate of photosynthetic uptake proportional to concentrationand a constant rate of respiratory production. For wheat, however,the curve was steeper near than at lower carbon dioxide levels;this disproved the ‘straight balance’ hypothesisand was consistent with an increase in carbon dioxide fixationor a reduction in output over a limited concentration rangeon either side of . The characteristics of light respiration, possibly carbon dioxidedependent, were investigated further in an experiment on theeffect of oxygen concentrationupon r values for two species(P. zonale and Hydrangea sp.) at two light intensities; theywere also studied by measuring the ‘burst’ of carbondioxide output when leaves were darkened after illuminationat four different light intensities and at two temperatures. was linearly related to oxygen tension up to 610 mm partialpressure of mercury and a fivefold increase in light intensityhad only a very small effect indicating that photoxidation wasnot important. The carbon dioxide burst on darkening showedrelations to temperature and previous light intensity quitedifferent from those of which should be proportional to lightrespiration. These results, therefore, do not support the viewthat the burst represents the persistence of an enhanced lightrespiration.     

American Kestrel reproduction: evidence for the selection hypothesis and the role of dispersal

Many hypotheses attempt to explain why younger, less experienced birds have a relatively low reproductive output. We evaluated reproductive patterns of marked American Kestrels Falco sparverius nesting in boxes in southwestern Idaho from 1992 to 2006 to test predictions of these hypotheses. Results were consistent with the selection (differential mortality) hypothesis and did not support the constraint, restraint or recruitment hypotheses. Most known-age Kestrels nested in their first year of life, and there was no apparent short-term or long-term reproductive advantage to delayed breeding. The number of years that Kestrels nested in study area boxes ranged from 1 to 6 years, with most Kestrels nesting in only 1 year. Reproductive rates were higher for birds with at least 1 year of nesting experience than for birds nesting in boxes for the first time. After 2 years of nesting, reproductive rates levelled off; there was no evidence for additional improvement or for senescence. Differences in reproductive output with experience/age were due to variation among and not within individuals. Individuals that nested in more than 1 year had similar reproductive rates in their first and second years. Poor producers either died or dispersed after 1 year of nesting in study area boxes. Successful females that nested early in the season and successful males that had been produced locally had the highest probability of returning to nest in a subsequent year.