Ecohydrology of CAM plants: environmental co-benefits for agroecosystems

In spite of their potential as low input crops in arid and semi-arid regions, limitations in CAM (Crassulacean Acid Metabolism) modeling have made it difficult to compare the productivity and water use of CAM crops with their C3 and C4 counterparts on a consistent basis. Using the Photo3 model, which adds a malic acid storage and circadian rhythm to the widely accepted Farquhar et al. model for C3 photosynthesis, we analyze the coupling of CAM carbon assimilation and transpiration with the soil-plant-atmosphere continuum at an hourly timescale to explore the potential of prickly pear and agave in several semiarid locations. Model results are compared with experimental data and contrasted with results generated using the widely used and empirically based Environmental Productivity Index introduced by Park Nobel in 1980. Using model results for CAM as well as C3 and C4 species, we explore how agricultural productivity in these locations may be optimized by diversifying planting strategies among the three photosynthetic pathways. This work aims to assist in better understanding the potential of CAM for food and biofuel production in arid and semiarid regions of the world accounting also for environmental co-benefits related to enhanced carbon sequestration and reduced water demand in semi-arid, marginal lands.