INFLUENCE OF SEISMIC STRESS ON PHOTOSYNTHETIC PRODUCTIVITY, LEAF GAS EXCHANGE, AND LEAF DIFFUSIVE RESISTANCE OF GLYCINE MAX (L.) MERRILL CV WELLS II (MECHANICAL, SUSOMOROPHOGENESIS, RELATIVE GROWTH RATE)

THALIA PAPPAS, Purdue University

Abstract

Vegetative plants of soybean (Glycine max (L.) Merr. cv. Wells II) grown in a greenhouse and agitated periodically on a gyratory shaker had shorter stems, less leaf area, and lower leaf and plant dry weight than did undisturbed greenhouse-grown (GG) plants after 16 days of treatment. Outdoor-grown (OG) plants, which were subjected to additional environmental stresses, were smaller and had less dry weight than GG controls, but growth was not inhibited further by gyratory shaking. Periodic shaking of GG soybeans resulted in the same plant and leaf dry weight as for OG soybeans. Response of GG plants to mechanical stress depended on light intensity, with minimum growth reduction occurring under full light (FL) level, and maximum growth reduction occurring under lower light levels (24% to 45% FL). Seismic stress resulted in a decrease in relative growth rate (RGR), an effect which was due equally to a decrease in net assimilation rate (NAR) and leaf area ratio (LAR). In a controlled environment walk-in growth room, RGR, leaf water potential ((psi)w), whole plant transpiration rate (Tr), photosynthetic rate (Pn), and stomatal and mesophyll resistances to CO(,2) exchange were measured to determine how shaking decreases dry weight accumulation by soybean. Fifteen days of treatment decreased stem length 21%, leaf area 17%, and plant dry weight 22% relative to those of undisturbed control soybean plants. Shaking decreased RGR 3.9%, an effect which was due entirely to a decrease in NAR. Shaking also reduced Tr 17% and increased leaf (psi)w 39% 30 min after treatment. Continuous measurement of whole plant Pn showed that a decline in Pn began within seconds after the onset of shaking treatment and continued to decline to a maximum of 15.5% less than Pn of controls 20 min after shaking, at which time gradual recovery began. Pn recovered completely before the next treatment 5 h later. The transitory decrease in Pn was due entirely to a two-fold increase in stomatal resistance to CO(,2) by the abaxial leaf surface.

Degree

Ph.D.

Subject Area

Botany

COinS