PHOTOPERIOD AND ROOT-ZONE TEMPERATURE - INTERACTING EFFECTS ON GROWTHAND MINERAL NUTRIENTS OF MAIZE

Factorial effects of photoperiod (6, 12 and 18 h) and root-zone temper atures (9, 15 and 21-degrees-C) on the growth and mineral nutrient con centration and partitioning in maize (Zea mays L.) were investigated. Strong interactions were observed between photoperiod and root-zone te mperature on the growth and concentration of numerous mineral elements in the plant tops and roots. For example, a threefold increase in pho toperiod (from 6 to 18 h) did not affect the growth of tops or roots i f the root-zone temperature was 9-degrees-C but increased them each by eightfold if the root-zone temperature was 21-degrees-C. On the other hand, raising the root-zone temperature from 9 to 21-degrees-C increa sed the growth of tops and root each by ca. threefold when plants were grown with 6 h of light. At 18 h photoperiod, however, plant growth w as increased 20- to 30-fold by the same rise in the root-zone temperat ure. The concentrations of different mineral elements in the roots and tops were affected quite differently by the interacting effects of ph otoperiod and root-zone temperature. In general, increasing the photop eriod at a given root-zone temperature decreased the concentrations of elements while increasing the root-zone temperature at a given photop eriod increased the concentrations of most elements in both roots and tops. The exceptions were K and B which reacted opposite to each other : K concentration in both tops and roots was relatively insensitive to photoperiod but very sensitive to root-zone temperature and the rever se was true for boron. The relative insensitivity of plant growth to i ncreased day length as long as the roots are subjected to suboptimal ( low) soil temperatures may have survival significance and point to the predominant role of root temperature over that of day length in the e arly growth of maize. A possible mechanism by which photoperiod and ro ot-zone temperature might interactively alter the nutrient uptake by t he roots is discussed.