PARENT SESSION
Contributed Oral Session 166: Soil Communities and Plant-Root Interactions
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal

Costs of root foraging: An experiment with drought and a comparison with herbivory and environmental stress.

Jones, Robert¹, Moore, Sean¹, Neatrour, Matthew¹, Stevens, Glen¹, ¹ Department of Biology, Blacksburg, Virginia, USA

ABSTRACT- Many plant species proliferate fine roots into nutrient-rich patches. This proliferation requires investment of carbon to build and maintain roots. Other costs that have not yet been thoroughly investigated include susceptibility to drought or flooding stress, and increased levels of root herbivory. Here we report a recent greenhouse experiment using two herbaceous species, Erechtites hieracifolia (an annual) and Solidago nemoralis (a perennial), to determine whether there is greater risk of drought associated with the proliferation response. Each plant received fertilizer either spread homogeneously throughout the pot or concentrated in one quarter of the pot. After watering the plants daily for two months we ceased watering entirely to simulate drought conditions. Each plant was harvested upon wilting. Both species responded to nutrient heterogeneity by concentrating root growth in the nutrient-rich quarter (ANOVA, P<0.001), but only S. nemoralis produced finer roots in the nutrient-rich quarter than in the rest of the pot (ANOVA, P<0.0001). S. nemoralis also wilted significantly faster in the heterogeneous treatment compared with the homogeneous treatment (ANCOVA, P=0.015), while E. hieracifolia did not show a difference in days to wilting between the two treatments. These results suggest that preferential proliferation into nutrient-rich patches increases susceptibility to drought stress for S. nemoralis but not for E. hieracifolia. A previous study with less statistical power showed the same results. This study, combined with other recent studies in our laboratory on root herbivory and root responses to soil anoxia, show that root proliferation may have several types of costs to plants.

Key words: heterogeneity, nitrogen, herbivory, anoxia