PARENT SESSION
Oral Session #76: Plant Ecology: Nutrient Uptake, Movement, Use. Presiding: J. Schade.
Friday, August 10, 2001. 8:00 AM to 11:45 AM. Hall of Ideas G.

Physiological responses of roots to pulses of nutrients.

Eissenstat, David¹, Wang, Liqin¹, ¹

ABSTRACT- Plant roots commonly proliferate in nutrient-rich patches, often increasing nutrient acquisition and general plant performance. How do plant roots respond when the nutrient-rich patch disappears? In a greenhouse study, apple seedlings were grown with their roots split into two pots containing unsterilized soil collected from an orchard that had not been fertilized for at least four years. Roots in the high-nutrient pot received 4 mM nitrate while those in the low-nutrient pot received 1.6 mM nitrate twice weekly. Other seedlings had uniform low- or uniform high-nitrate addition to the two pots. Roots in the high-nitrate pot were then supplied with only low-nitrate concentrations. Both nitrate (15N) acquisition and root respiration declined within 10 d after the shift in nitrate supply. Because both costs and benefits declined in parallel, the daily root efficiency or cost of nitrate acquisition was only moderately diminished by change in nutrient supply. Root longevity was also diminished in accordance with the diminished root efficiency. Implications of the costs and benefits of root foraging in ephemeral patches will be discussed.

KEY WORDS: Malus domestica, Root foraging, Root respiration, Soil patches