Plant Processes and Responses to Stress

Abstract

All three photosynthetic pathways (C3, C4, and CAM) occur among North American desert plants. C3 photosynthesis is the most common type and predominates among winter-active taxa (Table 4). The C4 pathway is most often found in summer ephemerals, short-lived summer active perennials, and halophytic shrubs. Its predominance in hot and/or saline desert environments supports the purported advantages of the C4 pathway: (1) high photosynthetic temperature optima; (2) high light-saturation points; and (3) high water-use efficiencies (WUEs) (Ehleringer and Monson 1993). Crassulacean acid metabolism (CAM) is abundant in leaf- and stem-succulents of the warm deserts (see Chap. 5), but CAM plants are rare in the cold deserts. The overall distribution of CAM plants in North America is highly correlated with aridity (Teeri et al. 1978). This pattern reflects the high photosynthetic WUEs that are possible with nocturnal stomatal opening and CO2 assimilation of CAM plants.