Photosynthesis, Transpiration, and Leaf Elongation in Corn Seedlings at Suboptimal Soil Temperatures 1

The physiology of plant response to low soil temperatures is not well understood. Laboratory studies were conducted to examine the relative sensitivities of rates of leaf elongation, net photosynthesis, and transpiration and the leaf water potential of corn seedlings ( Zea mays L. ‘Pride 5’) to decreasing temperature. These parameters were simultaneously monitored, as the soil temperature was decreased from 28 to 10 C at about 4 C increments. The different soil temperatures were imposed during a 10‐hour period on 14‐day‐old plants with seven exposed leaves growing at a 27.5 C air temperature, a 55% relative humidity, and a light intensity of 753 μ E/m 2 /sec. Any decrease of the soil temperature below 28 C decreased the leaf elongation rate. This was attributed to restricted water uptake which lowered the plant water potential and to the temperature decrease of the shoot apical meristem region. Leaf elongation ceased at the plant water potential of —9 bars due to decline of leaf turgor pressure. Neither transpiration nor net photosynthesis was reduced significantly until the plant water potential reached —12 to —13 bars. Increases in both stomatal and internal resistances to CO 2 diffusion coincided with the decreased net photosynthesis at low plant water potentials. Suboptimal soil temperatures affect corn seedling growth primarily by decreasing leaf elongation.