Call number: LD2668 .T4 1966 H799 / Master of Science

Microbial decomposition of soil organic matter (SOM) releases around 98 Pg of C (as CO2) to the atmosphere annually. Quantifying CO2 emissions from SOM is necessary to monitor and manage them but is complicated by proximate respiration of CO2 from plant roots, and by the influence of roots on SOM decomposition rate. Differences in the natural abundance of 13C in root and SOM-derived respiration (of < 10 ‰ in most temperate ecosystems) can be used to apportion their contributions to soil-surface CO2 efflux. However, this is challenging because all three δ13CO2 measurements are susceptible to significant sampling errors, which this study set out to identify and resolve, as follows. Respired CO2 sampled from excised roots is 13C-depleted by 1.8 ‰ (± 0.47) compared to intact roots due to the contribution of CO2 from root wounds. Root-respired δ13CO2 is more reliably measured using chambers around live, intact roots. These chambers also permit detection of diurnal changes in root-respired δ13CO2. Soil disturbance during sampling and root removal changes the carbon substrates available to microbes and this is reflected in a rapid (1-2 hours) decrease in δ13C of respiration of c. 4 ‰. This change can be regressed to estimate the δ13CO2 of microbial respiration from undisturbed soil. Techniques for measuring soil-surface efflux δ13CO2 induce method-specific biases of as much as 5 ‰, as measured in intact mesocosm soil and when simulated using a numerical diffusion model. Discrepancies between measurements and model predictions may be due to complexities of gas transport not currently accommodated in diffusion models, namely, near-surface advection and non-uniform soil diffusivity. Using improved techniques, this study used natural abundance 13C partitioning to assess priming effects, identify distinct environmental drivers of root-respired and SOM-derived CO2 fluxes, and detect differences in soil carbon cycling between tree species, possibly attributable to mycorrhizal type.

No description available.

Chemolithotrophic oxidation of ammonia to nitrate via nitrite (autotrophic nitrification) is a key link in the cycling of nitrogen in the biosphere.  It is facilitated by diverse communities of microorganisms including the autotrophic ammonia oxidising bacteria (AOB).  A good understanding of niche differentiation among members of such communities will aid in the prediction of how a community structure and function may respond to environmental change. The work presented here aims to extend the available ecophysiological data on soil AOB with an emphasis on comparative observations between organisms under the same conditions.  Under a set of standardised conditions, several potentially ecologically relevant traits were quantified and comparisons were made between organisms in the context of their phylogenetic relationships.  <i>Nitrosomonas europaea </i>ATCC 19718, <i>Nitrosomonas europaea </i>ATCC 25978, <i>Nitrosospira </i>‘Apple Valley’, <i>Nitrosospira briensis </i>C-128, <i>Nitrosospira multiformis </i>ATCC 25196, <i>Nitrosospira tenuis </i>NV-12, and <i>Nitrosospira </i>40KI in pure culture were examined. Specific growth rates in batch culture, maximum velocities, Michaelis constants and specific oxidation velocities of ammonia oxidation, AMO transcript decay half-life and transcriptional and metabolic response to re-supply of ammonia following energy starvation were quantified.  Significant phenotypic diversity was observed and hypotheses were tested with respect to trade-offs in niche adaptation and the influence of phylogeny.  It is hoped these new data will aid in the formation and testing of further ecological and evolutionary hypotheses and will contribute to the long term goal of developing predictive models for biogeochemical cycling.

by Jimmy Siu-hung Tsang. / Bibliography: leaves 124-148 / Thesis (M.Ph.)--Chinese University of Hong Kong

No description available.

Ericoid mycorrhizal fungi form mycorrhizal associations with Ericaceae plants and are regarded as essential to the ecological fitness of the plants in extremely nutrition-poor soils world-wide. The culturable fungible assemblages associated with hair roots of Epacris pulchella and Rhododendron lochiae (Ericaceae) from different forest habitats in eastern Australia were investigated using rDNA internal transcribed spacer (ITS) restriction fragment length polymorphisms (RFLPs) and sequence analysis, and the abilities of the fungi to form ericoid mycorrhizas were tested. The functional significance of members of the H. ericae complex, Sebacinaceae and the ectomycorrhizal basidiomycetes are discussed particularly in regard to the possibility of symbiont sharing between Ericaceae and ectomycorrhizal hosts. / Doctor of Philosophy (PhD)

No description available.

No description available.

Thesis (Ph.D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ.123-127)