Cadmium tolerance in Schinus molle trees is modulated by enhanced leaf anatomy and photosynthesis

Low concentrations of cadmium cause anatomical responses in leaf chlorenchyma enhancing Schinus molle photosynthesis and tolerance. This work is aimed to evaluate the effects of cadmium (Cd) on leaf anatomy and photosynthesis in Schinus molle, a species that can cope with harsh environments. Seven-month-old S. molle plants were exposed over 90 days to varying Cd concentrations (0, 10, 20, 50, 125 or 250 A mu M using Cd(NO3)(2) as the Cd source). The plants were placed in vases containing washed sand and vermiculite as the substrate and nutrient solution. Throughout the experiment, the substrate was maintained at field capacity, and the nutrient solution was replaced at 15-day intervals. After 90 days, leaves were collected and processed for anatomical analysis using typical plant microtechniques. In addition, plant growth, photosynthesis, chlorophyll content and A/Ci curve were evaluated using an infrared gas analyzer. S. molle growth was not affected by Cd. Lower Cd concentrations (10 and 20 A mu M) resulted in greater net photosynthesis, stomatal conductance and density, Vcmax, Jmax and mesophyll thickness. However, Cd concentrations of 50 A mu M or greater resulted in a reduction of most of the evaluated characteristics to levels close to control. All of the tested Cd concentrations resulted in reduced chlorophyll content and stomatal size. Therefore, the effect of Cd in a tolerant species such as S. molle is concentration dependent, and at low Cd concentrations, these plants can cope with the toxicity by adjusting leaf structure and function.