High Productivity of Certain Agronomic CAM Species

Abstract

Plant productivity varies with the vegetation type and the environmental conditions. For native species in deserts, the aboveground dry-weight productivity averages only 1 Mg hectare⁻¹ year⁻¹ (Lieth and Whittaker 1975), whereas annual crops usually have productivities of 6 to 20 Mg ha⁻¹ yr⁻¹ (Evans 1975; Loomis and Gerakis 1975; Beadle et al. 1985; Nobel 1991)¹. About 92% of all vascular plant species use the C₃ photosynthetic pathway (Fig. 16. la) in which the first stable product of photosynthesis is a 3-carbon compound (3-phospho- glyceric acid; Ting 1985; Winter 1985; Lüttge 1987; Nobel 1991; Salisbury and Ross 1991). The highest productivities for C₃ crops range from 34 to 45 Mg ha⁻¹ yr⁻¹ (Table 16.1). For plants with the C₄ pathway (Fig. 16.1b), the first products formed are C₄ acids (e. g. oxaloacetic acid and malic acid). The highest productivities are 47 to 88 Mg ha⁻¹ yr⁻¹ for C₄ crops and 51 to 94 Mg ha⁻¹ yr⁻¹ for C₄ floodplain grasses (Table 16.1). Although the values for floodplain grasses are initial estimates, the high values for sugarcane (Saccharum officinarum) have been confirmed by multiple studies.