Limited photosynthetic plasticity in the leaf-succulent CAM plant Agave angustifolia grown at different temperatures

In Agave angustifolia Haw., a leaf-succulent constitutive crassulacean acid metabolism (CAM) plant of tropical Panama, we tested whether nocturnal CO2 uptake and growth were reduced at night temperatures above 20 C. Unlike some CAM model species from habitats with pronounced day-night temperature variations, in A. angustifolia temperature affected little the relative contributions of CAM and C3 photosynthesis to growth. In plants grown under 12 h light/dark regimes of 25/17, 30/22 and 35/27 C, biomass increased with temperature. Maintaining day temperature at 35 C and reducing night temperature from 27 to 17 C markedly lowered growth, a reduction partially reversed when roots were heated to 27 C. Across all treatments, whole-shoot dC values ranged between –14.6 and –13.2‰, indicating a stable proportion of CO2 was fixed at night, between 75 and 83%. Nocturnal acidification reflected growth, varying between 339 and 393mmol H g fresh mass and 63–87mmol H cm. In outdoor open-top chambers, warming the air 3 C above ambient at night did not reduce biomass accumulation. The persistence of a high capacity for nocturnal CO2 fixation at the expense of a limited capacity for switching between C3 and CAM probably makes this Agave, and others like it, potential species for biomass production in seasonally-dry landscapes. Additional keywords: biofuel, C3 photosynthesis, climate change, crassulacean acid metabolism, open-top chamber. Received 30 September 2013, accepted 19 February 2014, published online 28 April 2014