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Light stimulates the assimilation of nitrate and nitrite by two green algae, Chlorella pyrenoidosa and Ankistrodesmus braunii. Assimilation can be observed when the algae are illuminated in the absence of carbon dioxide under both aerobic and anaerobic conditions. The rates of assimilation by Chlorella do not depend on the presence of carbon dioxide, but Ankistrodesmus assimilates nitrate and nitrite more rapidly when cultures are illuminated in the presence of carbon dioxide than in its absence. The ratios of O(2) : NO(3') and O(2) : NO(2') vary from one experiment to the other and, with the exception of Chlorella cultures reducing nitrite they are higher than the 'expected' values of 2.0 and 1.5 respectively. Oxygen evolution accompanying nitrate and nitrite by algae illuminated in the absence of carbon dioxide is completely inhibited by DCMU at concentrations of 4 × 10(-6) M. However, nitrite assimilation by both Ankistrodesmus and Chlorella and nitrate assimilation by Ankistrodesmus are less sensitive to the inhibitor.

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A dynamic simulation model of the soil-water-atmosphere-plant system is developed as a tool for optimal irrigation decision making under a stochastic weather regime and when water supplies are limited. Crop yield, foliage development, plant water deficits, and irrigation decisions have been treated as interdependent processes. Yield susceptibility of the crop to water deficit is a function of crop growth stage. The stomatal regulation of transpiration by the crop has been taken into account also. The model is a closed loop dynamic system, in which past irrigation decisions and weather conditions affect the current as well as the future response of the crop system and, consequently, the future irrigation decisions and the overall water use efficiency. The specific illustration in this paper pertains to grain sorghum grown under weather conditions typical for south central Texas. 1095-1099, 1973a. van Bavel,.C.H.M., D. W. DeMichele, and J. Ahmed, A model of gas and energy exchange regulation by stomatal action in plant leaves, Publ. MP-1078, Texas Agr. Exp. Sta., Texas A&M Univ., College Station, 1973b.

No abstract