Date of Award:

1998

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Natural Resources

Department name when degree awarded

Rangeland Ecology

Advisor/Chair:

Martyn M. Caldwell

Abstract

Heterogeneous spatial and temporal distributions of soil resources important to plant growth have been documented in the sagebrush steppe ecosystem. There can exist as much variability in soil resources within the root zone of individual plants as exists across an entire field. The objective of this dissertation research was to evaluate how plants respond to, utilize and influence the spatial heterogeneity of soil resources. The three specific sets of questions addressed are outlined in the three main chapters of this dissertation.

My first study addressed how the number and concentration of phosphorus (P) patches in the root zone of an individual Artemisiaplant influenced the ability of the plant to increase root P uptake capacity from the enriched patches as compared to roots from unenriched soil. I found that root uptake kinetics in the most enriched patches in general was not limited by the number or concentration of phosphorus patches experienced by the plant. However, the plants could modulate the quantity of P acquired from a target patch as the number of patches experienced increased.

My second study addressed how six species common to the Great Basin, which represent three different growth forms, utilized nitrogen (N) from patches or a uniform distribution. The two species within the two perennial growth forms, shrub and tussock grass, revealed different capacities for acquiring N from concentrated patches immediately adjacent to a plant and from N applications at a distance from plants. This suggests the potential for different root foraging behavior. The two annual species used concentrated N patches more effectively than uniform applications.

My third study described decimeter scale variability of soil water potential (Ψs) in the interspace of two perennial plants at different time scales and at different soil moisture conditions. The mean Ψs was more spatially consistent in the interspace between plants during a midsummer dry period compared to an early summer period. Diel Ψs fluctuations during an early summer dry period was more spatially consistent than a midsummer dry period. When soil moisture was recharged by precipitation there were no spatial diel patterns and the mean Ψs was autocorrelated across the area evaluated.

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