Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration

Vegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site‐years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two‐stream albedo submodel provided accurate predictions of boreal needle‐leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two‐stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r²=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r²=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two‐stream albedo model and foliage nitrogen concentration. These nitrogen‐based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.     

The Effect of Vitamin A on Cellular Differentiation and Mucous Glycoprotein Synthesis in Long-Term Rat Tracheal Organ Cultures

Rat tracheal explants maintained as organ cultures exhibited a normal mucociliary epithelium for at least 46 days in the presence of retinyl acetate. In the absence of vitamin A the explant epithelium became quiescent or underwent a metaplastic change to a keratinizing squamous epithelium. This process was accelerated if explants were derived from vitamin A-deficient animals. Autoradiographic examination showed that [³H]glucosamine label accumulated in various cell types in the explant, but especially in the epithelium. It was found that the explants secreted mucous glycoproteins into the medium and that the production and biochemical characteristics of a specific mucin fraction were dependent upon the vitamin A status of the explant.     

The postcranial skeleton of Kingoria nowacki (von Huene) (Therapsida: Dicynodontia)

A new specimen of Kingoria nowacki (von Huene) with a complete pelvic girdle and hindlimb is reconstructed and the method of locomotion analysed. It is concluded that the hindlimb was modified from the normal dicynodont pattern in a direction comparable to that of advanced mammal-like reptiles which are presumed to have given rise to mammals. The pectoral girdle also had a modified form, but the humerus was probably conservative in its morphology. The hindlimb stride relied on protraction and retraction to effect movement while the forelimb relied on long axis rotation of the humerus. Possible reasons for the difference in morphology and function of the fore-and hindlimbs are discussed, and a functional sequence for the generation of the Kingoria pelvic girdle from that of other Permian dicynodonts is suggested.