PHOTOSYNTHETIC PATHWAYS OF HESPERALOE-FUNIFERA AND H-NOCTURNA (AGAVACEAE) - NOVEL SOURCES OF SPECIALTY FIBERS

Hesperaloe funifera and H. nocturna are currently being studied as pot ential new sources of fibers for specialty papers. This study investig ated canopy architecture and light interception in H. funifera, and ga s exchange in both species. H. funifera is an acaulescent rosette spec ies with stiff, upright leaves. Mean leaf angle for 3-year-old plants was 70-degrees from horizontal, and more than 90% of the leaf surface was at angles greater than 50-degrees. Vertical orientation of leaves reduced seasonal variation in light interception and midday light inte rception during summer months. High leaf angles are interpreted as an adaptation to arid habitats that could reduce this species' suitabilit y for cultivation in more humid areas. Both H. funifera and H. nocturn a had leaf-tissue water contents and mesophyll-succulence values inter mediate between previously investigated Agavaceae known to be either C 3 or Crassulacean acid metabolism (CAM) plants. Both species proved to have CAM, however. Gas exchange characteristics varied with leaf age, with older leaves having higher assimilation rates, greater water-use efficiency, and a higher proportion of nighttime CO2 uptake. Interest ingly, these older leaves had mesophyll succulence values closer to th ose of typical C3 species. These Hesperaloe species can thus be charac terized as nonsucculent CAM plants. Both species showed CO2 uptake rat es of 5-8 mumol m-2 sec-1 expressed on a total-surface-area basis and 10-18 mumol m-2 sec-1 expressed on a projected-leaf-area basis. Expand ed cultivation of species possessing CAM in marginal areas has been re commended recently; the physiological studies reported here along with previous studies of their economic botany identify these Hesperaloe s pecies as good crop candidates for dry regions.