Date of Award:

5-1980

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Department name when degree awarded

Range Science

Committee Chair(s)

Martyn M. Caldwell

Committee

Martyn M. Caldwell

Committee

Neil West

Committee

Ben Norton

Abstract

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 if changes in the relative dominance of the shrubs have occurred in salt-desert communities. The 𝛿13C 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 𝛿13C values of -13.0 o/∞ and -25 o/∞, respectively. The 𝛿13C 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 𝛿13C values of roots and soils was consistently about 3.0 o/∞ in Ceratoides- dominated stands. Root 𝛿13C values were always more negative than soil 𝛿13C values. The striking uniformity in the root-soil 𝛿13C differential in Ceratoides-dominated stands is most likely the result of fractionation of carbon isotopes during decomposition. The differential between 𝛿13C values of roots and soils in Atriplex-dominated stands was more variable. This most likely indicates a lack of long- term community stability in areas now dominated by Atriplex. In addition some samples of soil carbon from Atriplex-dominated stands had 𝛿13C values more negative than root 𝛿13C values. This suggests the presence of C3-derived carbon in areas currently dominated by the C4 species Atriplex. These trends indicate that Atriplex has been increasing in importance in this salt-desert community.

The distribution of 𝛿13C values in relation to depth and among soil organic matter fractions was also studied. There was a trend for 𝛿13C values to become slightly less negative with depth . The 𝛿13C value of humic acid was most similar to the 𝛿13C 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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