Marginal land bioethanol yield potential of four crassulacean acid metabolism candidates (Agave fourcroydes,Agave salmiana,Agave tequilana and Opuntia ficus‐indica) in Australia

The Nobel environmental productivity index (EPI) was used as a framework for the development of a predictive geospatial model to estimate the bioethanol yield potential of four crassulacean acid metabolism (CAM) candidates in Australia (Agave fourcroydes, Agave salmiana, Agave tequilana, and Opuntia ficus‐indica). GIS software was used to integrate climate datasets with titratable acidity responses to changes in photosynthetically active radiation (PAR), temperature, and water availability. Additional refinements to Nobel's approach were made to accommodate spatial and temporal fluctuations in soil water potential (ψs) as a function of soil particle size distribution and precipitation, and CO₂ uptake response to a range of day and night temperatures. A scalar factor for CO₂ persistence during periods of drought was also introduced to model the capacity of succulent species of Agave to buffer against fluctuations in ψs. Macro‐scale criteria were applied to estimate environmentally responsible (ER) bioethanol yield potential on lands that are not suitable for food production. Consideration was given to indigenous vascular plant species richness and endemism scores at ER sites of interest. The highest mean ER bioethanol yield was achieved by A. fourcroydes (μ: 3.89, max. 7.17 kL ha^‐1 yr^‐1) while the highest maximum yield was achieved by A. tequilana (μ: 3.78, max. 7.63 kL ha^‐1 yr^‐1). This research indicated the CAM pathway may produce significant yields (≥≥ 5 kL ha^‐1 yr^‐1) at ER sites totalling 57,700 km² (0.7% land area of Australia).