Crassulacean acid metabolism (CAM) offers sustainable bioenergy production and resilience to climate change

Abstract

Biomass production on low-grade land is needed to meet future energy demands and minimize resource conflicts. This, however, requires improvements in plant water-use efficiency (WUE) that are beyond conventional C3 and C4 dedicated bioenergy crops. Here we present the first global-scale geographic information system (GIS)-based productivity model of two highly water-efficient crassulacean acid metabolism (CAM) candidates: Agave tequilana and Opuntia ficus-indica. Features of these plants that translate to WUE advantages over C3 and C4 bioenergy crops include nocturnal stomatal opening, rapid rectifier-like root hydraulic conductivity responses to fluctuating soil water potential and the capacity to buffer against periods of drought. Yield simulations for the year 2070 were performed under the four representative concentration pathway (RCPs) scenarios presented in the IPCC's 5th Assessment Report. Simulations on low-grade land suggest that O. ficus-indica alone has the capacity to meet ‘extreme’ bioenergy demand scenarios (>600 EJ yr⁻¹) and is highly resilient to climate change (−1%). Agave tequilana is moderately impacted (−11%). These results are significant because bioenergy demand scenarios >600 EJ yr⁻¹ could be met without significantly increasing conflicts with food production and contributing to deforestation. Both CAM candidates outperformed the C4 bioenergy crop, Panicum virgatum L. (switchgrass) in arid zones in the latitudinal range 30°S–30°N.

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