Document: DAV-3-6-3

Root foraging in nutrient-rich patches: Interactions with rhizosphere organisms.

EISSENSTAT, D.M.* ¹ and L.WANG ¹

Dept. of Horticulture and Intercollege Graduate Program in Plant Physiology, Penn State University, University Park, PA, USA 16802-4200 ¹
Environmental and Resource Science/370, University of Nevada, Reno, NV, USA 89557 ²

Abstract:
The roots of plants commonly proliferate in nutrient-rich patches, increasing nutrient acquisition and general plant performance. This can result in an accumulation of young, densely populated roots that may be very susceptible to root-feeding organisms. Interactions among soil organisms and roots can have dramatic effects on root longevity. For example, application of fungicide and insecticide more than doubled median lifespan of fine roots in a 60-year-old sugar maple stand. Maple roots that had grown into locally fertilized patches also had much longer lifespans than untreated roots, suggesting that active production of defense compounds of healthy roots helps protect them from root-feeding organisms. Other evidence that plants can exert controls over root longevity comes from a greenhouse study where apple seedlings were grown in split-pots containing unsterilized soil. Roots in the high-nutrient pot received 4 mM nitrate while those in the low-nutrient pot received 1.6 mM nitrate twice weekly. Control seedlings had uniform low- or uniform high-nitrate addition. Root longevity was longest in the uniform-high and heterogeneous-high pots and lowest in the heterogeneous-low pots with longevity in the uniform-low pot intermediate. For the plants exposed to heterogeneous nitrate supply, patterns of longevity were similar to patterns of nitrogen acquisition efficiency of the roots. We conclude that rhizospheric organisms may exert a major effect on patterns of root longevity. Plants foraging for nutrients not only must expend energy on root growth and nutrient uptake processes, but also on defense from the abundant root-feeding organisms in the rhizosphere.

Keywords: root turnover, root lifespan, soil microbes, nutrient uptake, root efficiency, root plasticity

This abstract is being presented at: 9:15 AM in session:
Symposium # 21: The Rhizosphere: Top-Down and Bottom-Up Approaches.