PHOTOSYNTHETIC PATHWAYS OF HESPERALOE FUNIFERA AND H. NOCTURNA (AGAYACEAE): NOVEL SOURCES OF SPECIALTY FIBERS.

Abstract

Hesperaloe funifera and H. nocturna are currently being studied as potential new sources of fibers for specialty papers. This study investigated canopy architecture and light interception in H. funifera, and gas exchange in both species. H. funifera is an acaulescent rosette species with stiff, upright leaves. Mean leaf angle for 3-year-old plants was 70° from horizontal, and more than 90% of the leaf surface was at angles greater than 50°. Vertical orientation of leaves reduced seasonal variation in light interception and midday light interception during summer months. High leaf angles are interpreted as an adaptation to arid habitats that could reduce this species' suitability for cultivation in more humid areas. Both H. funifera and H. nocturna had leaf-tissue water contents and mesophyll-succulence values intermediate between previously investigated Agavaceae known to be either C3 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. Interestingly, these older leaves had mesophyll succulence values closer to those of typical C3 species. These Hesperaloe species can thus be characterized as nonsucculent CAM plants. Both species showed CO2 uptake rates of 5-8 μmol m-2 sec-1 expressed on a total-surface-area basis and 10-18 μmol m-2 sec-1 expressed on a projected-leaf-area basis. Expanded cultivation of species possessing CAM in marginal areas has been recommended recently; the physiological studies reported here along with previous studies of their economic botany identify these Hesperaloe species as good crop candidates for dry regions.