Effects of Temperature and Humidity on Foliar Absorption and Translocation of 2,4 -Dichlorophenoxyacetic Acid and Benzoic Acid

Abstract

Little is known concerning the effect of humidity on the absorption of foliarly applied materials or their subsequent translocation. It is generally believed that the higher the humidity at any one temperature, the larger the amount of a foliarly applied material that penetrates the leaf per unit time. Most of the evidence for such an effect has been obtained indirectly. Koontz and Biddulph (16) found that the amount of phosphorus translocated from a given compound seemed to be related to the drying time of the solution on the leaf. By adding glycerine to the treatment solution, the translocation of P32 from an application of KH,PO4 solution was increased. Other workers have reported increased penetration of foliarly applied materials by additives which increase moisture retention. The recent review by Currier and Dybing (7) covers this work. It has been suggested that thin aqueous films on the leaf surface are important in promoting the absorption of nutrient sprays, the existence of the film depends upon the vapor pressure gradient at the leaf surface (4). In general, increasing temperature, within physiological limits, has been found to result in increased penetration. Rice (19) using red kidney bean plants studied the absorption of the ammonium salt of 2,4-D. He found that the amount absorbed was positively correlated with temperature over a three-level range of 46 to 580 F, 79 to 820 F and 86 to 920 F. Other workers using soybeans as the test plant found that with increasing temperature, there was an increase in the absorption of the sodium salt of 2,4-D (5,10). Barrier and Loomis (2) reported a temperature effect on the absorption of 2,4-D by soybean seedlings, but no effect upon the absorption of P32. Increased rates of absorption with increasing temperature have been reported for Co60 (9) and manganese (18). Known quantities of maleic hydrazide have been applied on several species of plants; the time course of absorption followed as it was affected by temperature and humidity (21). A variation in temperature at controlled humidities was found to have less effect on the absorption rate than a variation in humidity at controlled temperatures. Either an increase in 1 Received December 5, 1959. temperature or humidity gave an increase in absorption of the maleic hydrazide. The preponderance of evidence to date indicates a maximum in translocation over the range of 20 to 300 C. At temperatures below and above this range translocation is reduced (2, 12, 22). MATERIALS AND METHODS Selected seed of Phlaseolus vulgaris L. var. Red Kidney was used. Seeds were germinated at 250 C in Vermiculite saturated with distilled water. All temperatures reported are accurate within ± 10 C and relative humidities are accurate to + 3 % as measured by a hair hygrometer calibrated periodically with a hand phychrometer. Forty to 42 hours after sowing , 90 germinated seeds with radicles between 1.5 cm and 1 cm long were selected and planted in 4 inch pots containing Yolo clay loam soil fertilized with 16 ppm N and 6 ppm P on an oven dry weight basis. After subirrigation the pots were transferred to a growth chamber where they remained at 250 C until the 5th day after sowing, when the lights were turned on at 5:30 A.M. At this time the beans were in the crook stage. Subsequent growth conditions were: 1 5Y2 hours light, temperature 250 C, relative humidity 60 to 76 % and 8/2 hours dark, temperature 15° C, relative humidity 85 to 95 %. Light was obtained from a fluorescent-incandescent source giving 1.100 to 1.300 ft-c at the level of the unifoliate leaves. The beginning of the experimental temperature and humidity regimes coincided with initiation of the light period on the 9th day after planting the dry seeds. Generally, 60 selected plants were treated between 9:00 and 12:00 A.M. The first trifoliate leaves were beginning to unfurl from the bud at this time. Plants were watered before treating; in experiments at lower humidities, they also were watered several hours later. Treatment consisted of applying two 5 Al droplets on each side of a unifoliate leaf, approximately 2/3 cm from the major vein and 1 Y2 cm from the base of the leaf. The treatment solution contained 10 ug acid equivalent of the triethanolamine salt of 2,4-dichlorophenoxyacetic acid or 5.52 ug acid equivalent of triethanolamine benzoate in water with 0.1 % Vatsol OT (sodium dioctyl sulfosuccinate). The C14 activity of carboxyl-labelled 2,4-D and ben-zoic acid was 6.03 mc/mM and 1.0 mc/mM, respectively. Ten replications of every treatment were harvested at 2, 4, 6, and, in two experiments, 8 hours after treatment. The harvest consisted of washing out the root systems and then simultaneously removing two 1 cm sections from the epicotyl by means of a three-bladed knife. The first cut was made as close 575