Document: MIC-3-33-21

Physiological and demographic response of the desert perennial, Cryptantha flava, to simulated Mule deer excretions.

PEEK, M.S* and I.NFORSETH

University of Maryland, College Park, MD 20742 USA ¹

Abstract:
Patterns of resource acquisition and allocation represent major means of adaptation for plants. Allocation patterns have immediate impacts on fitness as well as impacts on future fitness and survival. A challenge facing ecologists is to determine how allocation patterns impact immediate fitness returns and the consequences for survival and long term fitness for perennial plants. In cold deserts, plants are generally considered to be most limited by water. However, during the spring thaw and intermittent precipitation events when water availability is high, nitrogen has been shown to limit plant growth. Plants are able to exploit these nitrogen pulses by increasing uptake kinetics or fine root production. In 1998 an experiment was conducted to determine the physiological and demographic response of the desert perennial, Cryptantha flava, to nitrogen pulses simulated from Mule deer excretions. Five treatments were applied to 1 to 3 year old, non-reproductive plants. Treatments consisted of a control, deionized water, simulated urine application, feces application, and both a feces and urine application. Plants treated with the urine showed consistently higher photosynthetic rates across the season as well as increased leaf nitrogen concentrations. In the following year, mean size of urine treated plants increased from 5.7 to 8.4 rosettes, whereas non-urine treated plants showed no significant increase in size. In addition to increasing in size, plants treated with simulated urine were more likely to initiate reproduction (²<0.0001). Flowering response for urine treated individuals was 45% as compared to 15% for non-treated plants. Additionally, fruit production was also affected by urine application with 38% developing multiple ovules versus only 12% developing multiple ovules for non-urine treated plants. However, there was no difference in germination percentage between the two treatments, 57% and 50% for urine and no urine respectively. The positive growth and flowering response to these nutrient pulses resulted in changing size hierarchies in the population. In addition, since 5.6% of the population was found to naturally encounter an excretion, the positive effects of these stochastic nutrient pulses could be a mechanism maintaining genetic diversity within the population.

Keywords: resource allocation, nitrogen pulses, genetic diversity, size hierarchies

This abstract is being presented at: 9:30 AM in session:
Oral Session #61: Plant Responses to Nutrients.