Chlorophyll, Dry Matter, and Photosynthetic Conversion-Efficiency Relationships in Warm-season Grasses

Abstract

This study was conducted to determine the relationship between leaf chlorophyll content, dry matter production, and the photosynthetic conversion efficiency in several warm-season grasses. These included Old World bluestems (Bothriochloa spp.), eastern gamagrass [Tripsacum dactyloides (L)L.], and weeping lovegrass (Eragrostis curvula (Schradd) Nees.). Warm-season grasses usually operate on the C4-photosynthetic pathway and are considered photosynthetically more efficient than the cool-season grasses under high temperature and high light intensity conditions. Samples for chlorophyll analysis and dry matter production were taken from 3 to 5, 0.5 M2 quadrates per pasture at each phenological stage. Photosynthetically active irradiance (400-700 nm) was measured with a quantum sensor. Results indicated close correlation between chlorophyll and dry matter production. Increase in total chlorophyll was associated with increase in dry matter. Chlorophyll a/b ratio remained almost constant throughout the growing season. Solar energy conversion-efficiency ranged from 0.54% to 0.73% for various strains of Old World bluestems, 0.51% for eastern gamagrass and 0.44% for weeping lovegrass. It was demonstrated through this study that warm-season grasses, like many other plants, are not very efficient utilizers of the enormous amounts of incoming solar energy. These grasses maintained high productivity throughout the growing season by maintaining high levels of chlorophyll in the leaves.