Type of Document	Dissertation
Author	Campbell, James Harold
Author's Email Address	james.campbell@ttu.edu
URN	etd-07072006-112747
Title	Distributions and nutrient responses of soil oligotrophic bacteria along an elevational gradient in the Chihuahuan Desert
Degree	Doctor of Philosophy
Department	Biology
Advisory Committee	Advisor Name Title John C. Zak Committee Co-Chair Randall M. Jeter Committee Co-Chair Abdul N. Hamood Committee Member Michael J.D. San Francisco Committee Member Richard E. Zartman Committee Member
Keywords	arid copiotroph soil Chihuahuan Desert bacteria
Date of Defense	2006-06-07
Availability	restricted
Abstract Oligotrophic bacteria can metabolize, divide and grow when carbon concentrations are in the parts per million (mg/L) range. Oligotrophs have been isolated from marine, freshwater, soil, clinical and indoor environments, yet understanding the factors controlling of their distributions remains unclear. Distributional studies of oligotrophic bacteria in soils of arid environments have not been reported. Moreover, effects of environmental parameters on bacterial responses to nutrient concentrations have not been elucidated. To address abiotic influences on oligotroph distributions, bacteria were isolated from soils sampled from five sites along the Pine Canyon Watershed in the Big Bend National Park region of the Chihuahuan Desert. Analyses indicated statistically significant effects of soil pH, soil organic matter, microbial biomass carbon, soil moisture, extractable nitrate and extractable ammonium on plate counts of oligotrophic bacteria. Oligotroph distributions in three sites sampled demonstrated good congruence to soil characteristics, whereas distributions in two forested sites did not correspond to measured parameters. It is likely that dense vegetation in these two sites alleviated nutritional constraints upon bacterial growth, and species interactions might underlie bacterial community structures. Oligotroph distributions were most strongly influenced by soil pH and extractable ammonium concentrations. Soil organic matter, a major pool of bioavailable soil carbon, was rarely a determinant of oligotroph abundances. Oligotrophic bacteria isolated during the distributional study were monitored for growth in four broths with carbon contents that ranged logarithmically from 12-12,000 mg/L. Unexpectedly, most isolates grew optimally in the broth highest in nutrients, and approximately equal numbers of bacteria were found to grow optimally in the two media with mid-range nutrient concentrations. Few bacteria grew optimally in the most oligotrophic medium. Optimal growth of bacteria at the community level appeared to be related to site, season, isolation temperature and soil chemistry measurements. However, growth of individual isolates was influenced primarily by soil characteristics. While statistically significant, all responses to experimental treatment or edaphic parameters were weak. These data contradict widely held beliefs that most soil bacteria cannot grow optimally in high nutrient concentrations and that growth on synthetic laboratory media is unrelated to in situ conditions.
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