ROOT BIOMECHANICS AND WHOLE-PLANT ALLOCATION PATTERNS - RESPONSES OF TOMATO PLANTS TO STEM FLEXURE

Cherry tomato plants (Lycopersicon esculentum Mill.) were grown with or without stem flexure similar to that caused by wind in order to determine whether stem flexure affects whole-plant biomass allocation and increases the ability of a plant to withstand wind-induced forces. After 6 weeks of flexing (1 min, 6 days/week), whole plants were harvested. The main differences found between treatments were in the primary shoot/root axis. The stem was significantly shorter and wider near the shoot/root junction in flexed than control plants, both above- and below-ground. Flexed plants had significantly higher root/shoot dry weight ratios than controls, but flexed plants and controls did not differ significantly in total leaf area, root length, or total biomass. Lateral roots from the top 2 cm of the taproot were not affected by the flexing treatment for any of the factors studied: number of laterals, proximal diameter, elastic modulus, stress at failure, or work to failure. Lastly, the force required to uproot flexed plants did not differ significantly from that for controls. However, because their stems were shorter, flexed plants would have been subjected to smaller stem bending moments and thus less stress near their root crowns than would controls. Moreover, flexed plants have wider stem bases, and should thus be better able to resist the forces that affect stems. This suggests that in a windy situation, plants that have previously been subjected to flexing could potentially withstand more force than unflexed controls.