A comparison of physiological indicators of sublethal cadmium stress in wetland plants

Physiological indices, including photosynthesis, chlorophyll fluorescence, adenylate energy charge (AEC) ratio, and leaf reflectance, were determined for Typha domingensis and Spartina alterniflora in response to increasing c oncentrations of Cd and compared with the growth responses of these species . Leaf expansion, the live/total ratio of plant aboveground biomass, and th e aboveground regrowth rate after the initial harvests were significantly r educed with increasing Cd concentration in the growth medium. Of the four p hysiological responses measured, only photosynthesis and AEC responded to t he Cd treatment before damage was visually apparent. Also, these indices we re significantly correlated with leaf expansion rate and live/total ratio i n most instances. Except at the end of the experiment, when the most stress ed plants began to die, the Fv/Fm ratio was not significantly affected by t he Cd treatment. The leaf spectral reflectance parameters showed no signifi cant change during the entire treatment period. The significant correlation between the stress indicators and plant growth supported the findings that photosynthesis and AEC were the most responsive of the indicators tested, however, further research investigating other chlorophyll fluorescence and leaf reflectance parameters may demonstrate as well the value of these indi cators in quantifying sublethal stress. (C) 2001 Elsevier Science B.V. All rights reserved.