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

摘要

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 degrees 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 C-3 photosynthesis to growth. In plants grown under 12h light/dark regimes of 25/17, 30/22 and 35/27 degrees C, biomass increased with temperature. Maintaining day temperature at 35 degrees C and reducing night temperature from 27 to 17 degrees C markedly lowered growth, a reduction partially reversed when roots were heated to 27 degrees C. Across all treatments, whole-shoot C-13 values ranged between -14.6 and -13.2 parts per thousand, indicating a stable proportion of CO2 was fixed at night, between 75 and 83%. Nocturnal acidification reflected growth, varying between 339 and 393mol H+ g(-1) fresh mass and 63-87mol H+ cm(-2). In outdoor open-top chambers, warming the air 3 degrees 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 C-3 and CAM probably makes this Agave, and others like it, potential species for biomass production in seasonally-dry landscapes