Influence of Temperature on the Respiration of Rice Seedlings 1

W HILE rice is normally grown only in areas with a relatively warm climate, some rice-growing areas may have wide extremes of temperature during the growing season. For instance, in California rice seedlings may be subjected to temperatures as high as 45° C. or as low as 5° C. in June (6). Since respiration rates may be taken measures of general metabolic rates, data on the effect of temperature on respiration rates would be useful for a better understanding of the behavior of the rice plant under the wide extremes of temperature to which it may be subjected. Such data have not yet appeared in the literature. Another facet of interest in rice production is the difference in adaptation of the long-grain (indica) and shortgrain (japonica) types. In general, the short-grain varieties grow more satisfactorily than the long-grain in California, while long-grain varieties are better adapted to Arkansas, Texas, and Louisiana (2). Daily temperatures during the growing season may be lower and more variable in California than they are in the southern states. For example, average daily minimum and maximum temperatures for June 1959 were: Willows, California, 15.9-33.6° C.; Stuttgart, Arkansas, 20.4-31.2° C.; Lafayette, Louisiana, 21.932.2° C.; Beaumont, Texas, 22.1-32.7° C. (6). It would thus be of interest to compare long-grain and short-grain types in their response to temperature to see if there are any basic differences in temperature effects on metabolic rates. Previous experiments concerning the respiration rates of rice plants have been on the effects of oxygen tension rather than the effects of temperature. Taylor (5) found that the oxygen uptake of rice decreased as oxygen tension was decreased from 20.8 to 0%. He found that the respiratory quotient of rice seedlings in air did not vary markedly from a value of one, indicating aerobic respiration. These findings were corroborated by Vlamis and Davis (7), who found a rapid decline in oxygen consumption as the partial pressure of oxygen goes below 9.5~.. The present experiments were carried out in air since the above results indicated that rice respiration is completely aerobic at the normal oxygen content of air. The objectives of the present experiments were twofold --to determine the temperature dependence of respiration rates in rice seedlings, and to determine any differences in respiration rates between longand short-grain types.