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sur le développement des zones arides et semi-arides

Titre : THE EFFECT OF LEAF AREA DEVELOPMENT, LEAF PHOTOSYNTHETIC RATES AND TEMPERATURE ON GROWTH AND DRY MATTER ACCUMULATION IN CERTAIN SPECIES OF FORAGE CROPS

Auteur : El-Tabbakh, Abdelmoneim Elsayed,

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1967

Résumé partiel
A study was conducted at Tucson, Arizona during 1965 and 1966 to determine the effect of leaf area development, leaf photosyn thetic rates and temperature on growth and dry matter accumulation in certain species of forage crops. Information was obtained that would contribute to an understanding of the differential growth rates when these plants were grown under climatic conditions of the lower desert valleys in the southwestern United States. There were highly significant differences in dry matter accu mulation and leaf area development between the species of grasses and clovers and among the alfalfa varieties and strains during both spring and fall seedings. Highly significant and positive correlation coefficients of dry matter accumulation with leaf area development, in both seasons of growth, emphasized the dependence of dry matter production on the amount of active leaf area present. In most of the forage plants studied, positive and significant correlations between relative growth and net assimilation rates and leaf area ratio indicated that the growth and dry matter production was a function of both net assimilation rate and leaf area ratio. When average daily maximum and minimum temperatures were correlated with relative growth rates, net assimilation rates, and leaf area ratio, positive and significant correlations were indicated in all cases. Temperature fluctuation affected the efficiency of leaves in assimilating raw materials needed for growth as well as the distribu tion of that assimilated into living tissues of the plant. Using the Infra-Red Gas Analyzer the leaf photosynthetic rates were measured at three different temperatures (21, 27, and 32 C) under field conditions. The grasses recorded the highest rates at 21 C, while the optimum temperature for leaf photosynthetic rates in the clovers and alfalfa plants was at 27 C. Hubam sweet clover showed the highest rates and was significantly higher than Ladino, Kenland red, and Miscawi berseem clovers. In the alfalfa, plants of the variety Du Puits manifested the highest rate while those of Ranger were the lowest.

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