Abstract
Plants that use crassulacean acid metabolism (CAM) have the potential to meet growing agricultural resource demands using land that is considered unsuitable for many common crop species. Agave americana L., an obligate CAM plant, has potential as an advanced biofuel crop in water-limited regions, and has greater cold tolerance than other high-yielding CAM species, but physiological tolerances have not been completely resolved. We developed a model to estimate the growth responses of A. americana to water input, temperature, and photosynthetically active radiation (PAR). The photosynthetic response to PAR was determined experimentally by measuring the integrated leaf gas exchange over 24 h after acclimation to six light levels. Maximum CO2 fixation rates were observed at a PAR intensity of 1250 µmol photons m-2 s-1. Growth responses of A. americana to water and temperature were also determined, and a monthly environmental productivity index (EPI) was derived that can be used to predict biomass growth. The EPI was calculated as the product of water, temperature, and light indices estimated for conditions at a site in Maricopa (Arizona), and compared with measured biomass at the same site (where the first field trial of A. americana as a crop was completed). The monthly EPI summed over the lifetime of multi-year crops was highly correlated with the average measured biomass of healthy 2- and 3-year-old plants grown in the field. The resulting relationship between EPI and biomass provides a simple model for estimating the production of A. americana at a monthly time step according to light, temperature, and precipitation inputs, and is a useful tool for projecting the potential geographic range of this obligate CAM species in future climatic conditions.
Highlights
Of the three major photosynthetic pathways, crassulacean acid metabolism (CAM) has substantial advantages in semi-arid and xeric regions (Davis et al, 2014)
We developed a model to estimate the growth responses of A. americana to water input, temperature, and photosynthetically active radiation (PAR)
GHOD = GHsample / 1 − %M1o0i0sture, according to standard methods (Boundy et al, 2011).A one-way ANOVA was performed using R Studio statistical software to determine if there was any significant difference in the gross heat of combustion (GH) produced for samples from different irrigation treatments.The experimentally resolved GH values were plotted against the estimated environmental productivity index (EPI) values calculated for the Maricopa, AZ field site to determine the strength of correlation between the estimated EPI values and the energy content of the plants. Both the duration and rate of CO2 assimilation by A. americana plants over the 24 h measurement periods increased (Fig. 1A–C).When acclimated and exposed to 100 μmol photons m–2 s–1, no carbon assimilation in CAM phases 2 or 4 was evident, and assimilation only occurred during the dark periods in A. americana individuals
Summary
Of the three major photosynthetic pathways, crassulacean acid metabolism (CAM) has substantial advantages in semi-arid and xeric regions (Davis et al, 2014). Switchgrass, and sugarcane range from 5 Mg ha–1 year–1 to 26 Mg ha–1 year–1, and C3 photosynthetic species grown for biofuels such as oil palm, poplar, and willow produce between 2 Mg ha–1 year–1 and 14 Mg ha–1 year–1 (Somerville et al, 2010). While these C3 and C4 crops are restricted to mesic environments, CAM crops such as Agave can grow on suboptimal soils in very dry conditions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
