Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → États-Unis → 1997 → Studies on biomass, productivity and nanoclimate of desert pavement cyanobacteria

Florida State University (1997)

Studies on biomass, productivity and nanoclimate of desert pavement cyanobacteria

Allen, Mary Elizabeth

Titre : Studies on biomass, productivity and nanoclimate of desert pavement cyanobacteria

Auteur : Allen, Mary Elizabeth

Université de soutenance : Florida State University

Grade : Doctor of Philosophy (PhD) 1997

Résumé
The hypolithic (under stones) habitat is one of the principal microbial habitats in deserts that are covered by desert pavements. These are ground surfaces covered by pebble-size stones lying close together and half embedded in soil. Hypolithic microorganisms, which are mostly photosynthetic, colonize the lower surfaces of translucent stones of the desert pavement. Conditions of light and humidity under stones create an environment that is suitable for growth and survival, in contrast to the extreme conditions on the soil surface. Lethal light intensities are filtered through the translucent stones to suitable levels, and slower evaporation rates under stones result in small water reservoirs utilized by the microorganisms. I compared hypolithic microbial communities, composed of cyanobacteria and heterotrophic bacteria, from the Gobi Desert in Mongolia and the Negev Desert in Israel. Many of the cyanobacteria in the two deserts were the same, and the general morphology of the communities was similar. However, microorganisms from the Negev Desert experience a more extreme environment. They receive more moisture, but must contend with higher temperatures, and winter rainfall. Under these conditions respiration rates are high but photosynthetic rates will be at their lowest because of low light levels. More extreme than the Negev Desert is the Atacama Desert in Chile, which has no hypolithic microbial flora because there is never moisture under stones. In the most arid regions of the Gobi Desert hypolithic cyanobacteria are the only primary producers. They are productive here because of their extreme dessication tolerance and ability to carry out photosynthesis over a broad temperature range. They are limited most by moisture availability. However, additional rainfall has little impact on yearly productivity because combinations of light and temperature, which have a large effect on physiological rates, are unpredictable. Where sparse individuals of the plant Iljinia regelii are present, they have a biomass and productivity comparable to that of hypolithic cyanobacteria. Even so, the cyanobacteria have the greatest impact on soil formation and binding, and the prevention of soil erosion, because they are distributed more evenly across the soil surface.

Mots clés : Ecology, hypolithic habitat, Gobi desert, Negev desert, heterotrophic bacteria, Microbiology Biological sciences

Proquest Dissertations & Theses

Page publiée le 6 mars 2015, mise à jour le 13 septembre 2017