Date of Award

12-1-1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Atriplex oanescens, a facultatively evergreen dioecious shrub inhabiting cold and warm winter deserts of western United States, was studied at four sites in the Great Basin. The species was commonly a co-dominant in communities throughout its distribution, and was frequently found with other members of the Chenopodiaceae and members of Compositae. It was found to resprout vigorously and experiments indicated that seeds from all sites germinated easily in wetted, well 3 aerated soil. The mean plant size ranged from 0.62±0.48 to 7.05±2.19 m . 3 -1 Density and cover ranged from 400 to 1.022 X 10 plants ha , and from 5.7 to 38.4% of the ground space, respectively.

Atviplex oanescens had a significant influence on the chemical and physical properties of the soil. Vegetated soils had significantly higher moisture content, organic matter, electrical conductivity, alkaline earth carbonates, nitrogen, potassium, sodium, calcium, magnesium and manganese than unvegetated soils. Both organic matter and nitrogen of unvegetated soils from the four study sites were typical of semi- arid environments, generally below 0.7 and 0.03%, respectively. Fertile islands beneath the shrub canopies provided microclimates favorable to the growth of ephemeral grass species.

Major cations in plant parts were in the order K > Ca > Mg > Na. Concentrations of these cations in plant parts decreased thus: leaves, fruits, twigs, middle and old growth. The mean of major cations in leaf tissue was 317.96±42.78 me 100 g_1 dry weight. Major anions in leaf tissue followed the order Cl > C20^ > N > P. The mean sum of major anions in leaf tissue was 116.15±15.54 me 100 g-* dry weight. High K/Na ratios were found in plant tissue, in contrast to low K/Na ratios in unvegetated soils. Leaf chloride content of Atriplex oanesoens was negatively correlated with total oxalate but positively correlated with the sum of major cations in the leaf.

Water potential (^) measurements of Atriplex oanesoens at Tipton revealed a range of -15.5 to -45.1 bars. Minimum values coincided with the lowest air and soil temperatures, maximum with the greatest atmospheric evaporative demand. Change in $ exceeded 12 bars hr-1 during periods of rapidly moving storm systems. Changes in ^ appeared to be independent of plant size, age, sex and the spatial location of plants. Chemical analyses revealed that expressed sap was up to three times more concentrated at high than at low \p. The increase in water movement accounted for the dilution of the concentration of sap solutes. Together, K, Ca, Mg and Na contributed 58% of the mean osmolality of the expressed sap; the dominant ions, however, were K and Cl.

Productivity of Atriplex oanesoens at southern warm-desert sites was significantly greater than that at the cold-desert locations. Net annual productivity estimated from species-specific prediction equations ranged from 0.203 X 10^ to 2.482 X 10^ kg ha * yr Potassium had the highest rate of return of any single element in plant litter. Rates of potassium mobilization from leaf litter at the cold-desert site ranged from 3.94 to 11.12 g K yr ■*". Data suggest that K and N, and possibly other elements are redistributed to other plant parts from leaves prior to leaf senescence.

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