Date of Award:


Document Type:


Degree Name:

Master of Science (MS)



Committee Chair(s)

Martyn M. Caldwell


Martyn M. Caldwell


Neil West


Ben Norton


Stable carbon isotope ratios of soils, roots and litter along transects stretching from nearly monospecific stands of Ceratoides lanata , a species possessing c3 photosynthesis, to nearly monospecific stands of Atriplex confertifolia, a species possessing c4 photosynthesis, were analyzed to determine i f changes in the relative dominance of the shrubs have occurred in salt-desert communities. The a13c value , which reflects the proportion of 12c and 13c in a sample of plant tissue, can be used to distinguish between c3 and c4 species. Atriolex confertifolia and Ceratoides lanata have a13c values of -13.0 ofoo and - 25 ofoo, respectively. The a13c value of litter and roots was used as a measure of current community dominance. The a13c value of soil organic matter was employed as a measure of past community dominance . The differential between a13c values of roots and soils was consistently about 3.0 ofoo in Ceratoides- dominated stands. Root a13c values were always more negative than soil a13c values. The striking uniformity in the rootsoil differential l in Ceratuitles- duninateci stands is most likely the result of fractionation of carbon isotopes during decomposition. The differential between a13c values of roots and soils in Atriplexdominated stands was more variable. This most likely indicates a lack of long- term community stability in areas na

The distribution of a13c values in relation to depth and among soil organic matter fractions was also studied. There was a trend for a13c values to become slightly less negative with depth . The a13c value of humic acid was most similar to the o13c value of the dominant vegetation. Fulvic acid was isotopically heavier than humic acid in all analyses. The implications of these trends are discussed.



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