Wheat root morphology, root anatomy, and hydraulic conductivity as affected by temperature

Plant root growth and hydraulic properties affect the total supplies of water to plant. They are under genetic control, but can be environmentally modified. The objectives of this study were to: (1) evaluate the effects of temperature on morphological and anatomical development of wheat root system, (2) establish prediction equations based on plant age and temperature, (3) develop equations to describe the distribution pattern in length and number of lateral roots along seminal axes. The experiments were conducted in a controlled environmental growth chamber. Winter wheat was grown at constant air temperatures of 10, 20, 25 and 30° C. Three plants from each temperature were randomly harvested daily beginning at 4 days after planting for 30 days. Results indicate that the 30° C temperature restricted formation of seminal root axes. The 10° 0 temperature inhibited production of crown root axes. Length and dry weight of wheat roots increased with temperature from 10 to 25° C, then declined at 30° C. Root to shoot ratio was much greater at 10° C than at 20, 25, and 30° C. The primary lateral roots: (1) emerged earlier and were more closely spaced along the seminal axis at higher temperatures, (2) had distribution patterns in length and number following a logistic function and quadratic polynomial regression, respectively, and (3) were fewest in number and least in length at lO°C, greatest in number and length at 25°C, and were intermediate in length and number at 20°C and 30°C. Diameter of late metaxylem elements and stele decreased with an increase in temperature. Lignification of xylem elements commenced further toward the root apex at higher temperatures. The relative conductivity of seminal roots, calculated from Poiseuille's equation, decreased as temperature increased. The prediction equations developed accounted for 76, 81, 86, 78, 72 and 81% of the observed variation in length, number of root axes, root dry weight, mean length of seminal axes, and total length, number of primary lateral roots, respectively.