Scaling carbon dioxide and water vapour exchange from leaf to canopy in a deciduous forest. II. Model testing and application

The scaling of CO₂ and water vapour transfer from leaf to canopy dimensions was achieved by integrating mechanistic models for physiological (photosynthesis, stomatal conductance and soil/root and bole respiration) and micrometeorological (radiative transfer, turbulent transfer and surface energy exchanges) processes. The main objectives of this paper are to describe a canopy photosynthesis and evaporation model for a temperate broadleaf forest and to test it against field measurements. The other goal of this paper is to use the validated model to address some contemporary ecological and physiological questions concerning the transfer of carbon and water between forest canopies and the atmosphere. In particular, we examine the role of simple versus complex radiative transfer models and the effect of environmental (solar radiation and CO₂) and ecophysiological (photo-synthetic capacity) variables on canopy-scale carbon and water vapour fluxes.     

The Fine Structure of the Sporozoite of Lankesteria culicis

SYNOPSIS. The sporozoite of Lankesteria culicis was studied by light and electron microscopy, after excystation in the intestine of Aedes aegypti 1st stage larvae. The sporozoite was 9.5–10.0 μ long with a blunt anterior end and a tapered posterior region. The organism was enclosed by a typical pellicle consisting of an outer and an inner membrane with underlying subpellicular microtubules. The anterior end had a conoid with 2 associated rings, a polar ring which served as a termination of the subpellicular microtubules and a flask-shaped structure situated internal and posterior to the conoid. A micropyle consisting of a collar formed from the inner membrane and lacking an invagination of the outer membrane was present near the anterior end of the parasite. The nucleus was centrally located and had a peripheral concentration of chromatin and a central nucleolus. One or more mitochondria were observed in the vicinity of the nucleus.     

Effects of growth under elevated UV-B on photosynthesis and isoprene emission in Quercus gambelii and Mucuna pruriens

Increasing surface levels of UV-B resulting from stratospheric ozone reduction directly affect tropospheric photochemistry. There may also be indirect tropospheric effects due to changes in emission of organic compounds from vegetation. We treated woody and herbaceous isoprene-emitting species in the field with supplemental UV-B simulating 30% ozone depletion. For Quercus gambelii, photosynthesis and isoprene emission were significantly greater in elevated UV-B treatments when expressed on a leaf area basis, but not on a leaf mass basis. Leaves of Mucuna pruriens, however, showed no significant differences in photosynthesis or isoprene emission between treatments, nor when exposed for 45 min to acute high levels of UV-B. Elevated UV-B during growth did not elicit significant isoprene emission from Acer platanoides, a non-emitting species. Other potential UV-B effects, such as changes in leaf area or species composition, which may influence regional isoprene emissions, should be examined.     

An explosive pollination mechanism in Eriope crassipes, a Brazilian labiate

The first recorded case of an explosive pollination mechanism in the Labiatae is reported. This was discovered in Eriope crassipes Benth., a frequent herb of the South and Central Brazilian savanna. Observations made on the sequence of events associated with pollination by the bee Epanthidioidesgregarium (Schrottky) are described in detail, and it is demonstrated that the whole process from flower opening to corolla fall is normally completed in a single day. Finally, the possible occurrence of this mechanism in other species of Eriope , and in related genera, is discussed.