Photosynthetic Characteristics of CAM Succulents with High Productivity

Abstract

Responses of net CO2 uptake over 24-h periods to total daily photosynthetic photon flux (PPF), day/night air temperatures, and soil water status under controlled conditions in environmental chambers have been determined for 9 species exhibiting Crassulacean Acid Metabolism (CAM) as well as one C3 and one C4 species. For the CAM species, this has enabled accurate predictions of net CO2 uptake under field conditions and the PPF responses have led to the design of field plant spacings that maximize annual net CO2 uptake per unit ground area. Two Agave species and two Opuntia species have an average measured dry weight productivity of 43 metric tons hectare−1 year−1, which exceeds that of all C3 agronomic species and C3 trees and is only slightly less than the most highly productive C4 species. The high productivity of these CAM species can be explained based on daily net CO2 exchange and cellular photosynthetic properties. However, highly productive agaves and cacti are not tolerant of low temperatures, a problem for their cultivation in regions of the United States and other countries where air temperatures annually fall below about −5°C.