Previous work on a prairie population of the terrestrial orchid, Spiranthes cernua, showed that this species flowered relatively frequently. The cost of reproduction is partially compensated for by floral photosynthesis. The remaining energy must be supplied by the tuberous root system, since the plant is leafless at the time the floral spike is produced. A two-year experiment was begun in June, 1997, to investigate the effect of water and nutrient amendments on vegetative and reproductive growth. If reproduction is resource-limited, increasing the supply of nutrients should lead to greater storage in both reserve and accumulation pools. The plants could respond with increased flower production and/or an adjustment in the root/shoot ratio. Six plants were assigned at random to three treatments: control, water, water plus slow-release fertilizer. Samples sizes were small due to multiple, ongoing studies. Fertilizer was applied once and water biweekly, beginning on June 5. Initially, there were no significant size differences among the treatments. After two weeks, the total surface area (cm2) of control, fertilized, and watered plants was 8.23±3.1, 7.01±2.2 and 11.21±3.7, respectively. By the end of June, watered and fertilized plants were, on average, 5X larger than the controls (control: 0.84±0.6; fertilized: 4.13±1.8; watered: 4.46±2.5). The treatments were begun at the peak of vegetative growth, i. e., leaves normally senesce in July. The effect of the treatments was to extend the vegetative phase beyond the control plants. Four individuals flowered in 1997, including three treated and one control plant. Soil nutrient levels (ammonium and nitrate nitrogen and phosphorus) were measured before fertilizer application and on September 30. The nutrient levels in the fertilizer treatment were still 6X greater at the end of the growing season. Tissue nutrient levels will be compared across treatments and years.

Key words: nutrient experiment, orchid growth, Spiranthes cernua