CONVERGENT SHELL MORPHOLOGY IN INTERTIDAL GASTROPODS

The functional morphology of shell infrastructure in 2 speciesof intertidal trochid was compared with that in 2 species ofnerite. The shell of Monodonta constrictais typical of the majorityof trochids. The shell is composed of 4 layers: a distal layer(calcite), anouter prismatic layer (aragonite), a nacreous layer(aragonite), and an oblique prismatic layer (aragonite). Monodontalabio lacks a distal layer and an oblique prismatic layer. Theoblique prismatic layer is replaced by an inner prismatic layerwhich forms an apertural ridge as a result of deposition andresorption. The shells of Nerita versicolor and N. tessellataconsistof 3 layers: an outer prismatic layer (calcite), a crossedlamellar layer (aragonite), and a complex crossed lamellar layer(aragonite). The complex crossed lamellar layer is covered withinclined platelets which superficially resemble the surfaceof the ique prismatic layer of trochids. In addition, the complexcrossed lamellar layer forms an apertural ridge which is similarin appearance to that of Monodonta labio. The outer surfaceof the mantle of Nerita versicolor and N. tessellata is throwninto a series of large folds which lie in contact with the inclinedplatelets of the omplex crossed lamellar layer. The interactionof the mantle folds with the inclined platelets is thought toserve as a rachet mechanism to aid in extension of themantle;a similar function has previously been proposed for trochids.The apertural ridges of Monodonta labio and Nerita are thoughtto prevent excessive desiccation when these gastropodsare exposedat low tide. ¹Contribution No. 56 of the Tallahassee, Sopchoppy & GulfCoast Marine Biological Association (Received 6 July 1979;     

Seventeen years of carbon dioxide enrichment of sour orange trees: final results

The long-term responses of trees to elevated CO₂ are especially crucial (1) to mitigating the rate of atmospheric CO₂ increase, (2) to determining the character of future forested natural ecosystems and their spread across the landscape, and (3) to determining the productivity of future agricultural tree crops. Therefore, a long-term CO₂-enrichment experiment on sour orange trees was started in 1987, and the final results after 17 years are reported herein. Four sour orange trees ( Citrus aurantium L.) were grown from seedling stage at 300 μmol mol⁻¹ CO₂ above ambient in open-top, clear-plastic-wall chambers at Phoenix, AZ. Four control trees were similarly grown at ambient CO₂. All trees were supplied ample water and nutrients comparable with a commercial orchard. After a peak 2–4 years into the experiment, there was a productivity plateau at about a 70% enhancement of annual fruit and incremental wood production over the last several years of the experiment. When summed over the duration of the experiment, there was an overall enhancement of 70% of total biomass production. Much of the enhancement came from greater numbers of fruits produced, with no change in fruit size. Thicker trunks and branches and more branches and roots were produced, but the root/shoot ratio was unaffected. Also, there was almost no change in the elemental composition of the biomass produced, perhaps in part due to the minimal responsiveness of root-symbiotic arbuscular mycorrhizal fungi to the treatment.     

Effects of long-term atmospheric CO2 enrichment on the growth and fruit production of sour orange trees

In July of 1987, we planted eight 30-cm-tall sour orange tree seedlings in a field of Avondale loam at Phoenix, Arizona and enclosed them in pairs in clear-plastic-wall open-top chambers. Since 18 November of that year, we have continuously pumped ambient air of ≈400 ppmv [CO₂] through two of these enclosures, while through the other two we have continuously pumped air of ≈700 ppmv [CO₂]. By the end of the second year of the study, the trunk plus branch volume of the [CO₂]-enriched trees was ≈2.75 times greater than that of the ambient-treatment trees. Three years later, this factor had dropped to ≈2.0; but the decline in the [CO₂]-enriched/ambient-treatment ratio of trunk plus branch volume was nearly perfectly offset by the relative fruit production advantage enjoyed by the [CO₂]-enriched trees over that period. In Years 6, 7 and 8, however, there was a moderate drop in total productivity enhancement. This decline may be a delayed acclimation response, or it could be due to enhanced self-shading in the [CO₂]-enriched trees or to the fact that, starting early in Year 6, many branches of the [CO₂]-enriched trees grew all the way to the walls of their enclosures, so that many blossoms and young fruit were destroyed by intermittent physical trauma produced by the action of wind against the taut plastic in that year and in all succeeding years. Hence, we will have to maintain our experiment for several more years for this lateral growth obstruction to occur to the same degree in the ambient-air chambers as it has in the [CO₂]-enriched chambers, in order to determine the long-term equilibrium effects of atmospheric [CO₂] enrichment in a spatially confined environment.     

Gel electrophoresis studies of proteins from leaves of photoperiodically induced and vegetative cocklebur plants

Comparisons of proteins synthesized in photoperiodically-sensitiveleaves of induced and vegetative cocklebur plants were made.Fifteen or more protein bands could be separated by polyacrylamidegel electrophoresis when polyvinylpyrrolidone was used in theextracting buffer to remove phenolics. As contrasted to resultsof others with Pharbilis nil, no differences in stained bandingpatterns could be detected in vegetative and induced plants.Radioactive leucine, lysine and phenylalanine were incorporatedinto similar leaf proteins during the last half of an inductivedark period. These experiments and dual-labeling studies with³H- and ¹⁴C-phenylalanine indicated no consistent differencesin the types of extracted proteins synthesized by leaves ofvegetative and induced plants. ¹Present address: Plant Science Dept., Utah State University,Logan 84321, U.S.A. (Received October 26, 1970; )