The bacterial ecology and function from a sub-surface critical zone

The rock-soil interface (critical zone) is where a variety of important earth system processes occur, such as the sequestration of CO2 and pedogenesis from rock weathering. This zone is an important sub-surface region of microbial activity in extreme environments because bedrock hydrolyses providing nutrients and cations (Le. Ca2 Mg2., Na) otherwise unavailable to flora and fauna. Yet, the diversity and role of microorganisms in weathering at the critical zone is not well understood. This thesis examines microbial communities in vegetated and unvegetated critical zones near Skorradalur Lake, Iceland. A suite of analyses were carried out to determine the environmental conditions, diversity, function and trophic survival strategy employed by bacteria at the sub-surface critical zone. Molecular analysis of the bacterial 16S rRNA gene indicates that the presence of plants at the soil surface influences the bacterial diversity and composition. Cultivation of microorganisms produced several bacterial isolates; most of which were capable of mineral phosphate solubilisation. However, isolate growth rates and copper tolerance show most isolates inhabit areas of sub-optimal growth potential. Environmental factors such as temperature and pH may influence bacterial divers ity, although the presence of organics may override these other influences. The trophic conditions at sites without higher plants may have a role in bacterial weathering as the availability of organics has resulted in a diverse heterotrophic community capable of utilizing bacterial necromass as a carbon source rather than plant derived carbon. This work has shown for the first time the bacterial diversity of the sub-surface critical zone in this region. Moreover, this bacterial diversity is influenced by plants and the potentially associated organics. Areas devoid of plants harboured a diverse heterotrophic bacterial community that employ weathering as a genera list function. Experiments show that bacteria increase the rate of phosphate weathering, although it may be a generalist function rather than specific to any individual taxon.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

The Open University

Year dc:date.issued

2013

Author dc:creator

• Summers, Stephen

Language dc:language

en