Date of Award:

5-1977

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

John J. Skujins

Committee

John J. Skujins

Committee

Frederic J. Post

Committee

Raymond I. Lynn

Committee

Jerome J. Jurniak

Committee

Neil E. West

Abstract

The inputs and losses of nitrogen from Great Basin arid soils were studied using the acetylene reduction and 15N techniques. Filamentous blue-green algae were observed to be the predominant algal group in the soil crusts. The bacterial association with this group of algae suggest a phycosphere-like effect, thus allowing heterotrophic nitrogen fixation and denitrification to occur. Up to 17.5 mg N/100 g soil was found to have been fixed in surface soils (0 to 3 cm) during a three week incubation period, while 45.9 mg N/100 g soil was fixed in a five-week incubation period. Ammonium sulfate and ammonium sulfate plus plant material amendments reduced the gain in nitrogen by 41 to 100 percent. Fifty to sixty percent of the applied 15NH_4+-N and 15N0_3--N was denitrified during the first week of incubation while 70 to 80 percent of the 15NH_4+-N was lost in a three- to five-week incubation period. These data suggest that a potential for heterotrophic nitrogen fixation exists, and under optimal conditions, significant gains in soil nitrogen may be achieved. However, in the presence of allelochemic agents, the potential gain in soil nitrogen may be reduced or inhibited. In addition, the denitrification potentials of these soils may also limit the input of nitrogen.

The application of protein (casein) to these soils resulted in an ammonification rate of 50 to 60 percent. Fixed 15N_2 indicated a 21 to 48.8 percent ammonification rate, thus suggesting that the mineraliztion of NH+4 was the rate limiting step for nitrogen loss.

Ammonia volatilization accounted for less than a five percent nitrogen loss, regardless of experimental conditions.

The inhibitory effects of plant material and litter extracts, and ''N-Serve" on heterotrophic nitrogen fixation has been assessed. The data suggest that the nitrogen fixing population is sensitive to the inhibitory effects of such agents.

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