Resumen de Mesophyll conductance constrains photosynthesis in three common sclerophyllous species in Central Chile

Carla E Brito, Horacio E Bown, Juan-Pablo Fuentes, Nicolás Franck, Jorge F. Perez-Quezada

• BACKGROUND: Quillaja saponaria Mol., Cryptocarya alba Mol. Looser, and Lithraea caustica Molina Hook et Arn., are common sclerophyllous species in Mediterranean Central Chile. Mesophyll conductance, g m, may strongly limit photosynthesis in these semiarid environments. RESULTS: Simultaneous measurements of gas exchange and chlorophyll fluorescence were carried out in 45 nursery plants from these species to determine diffusional and biochemical limitations to photosynthesis. Values of stomatal conductance, g s, were greater than those of mesophyll conductance, g m, while their ratio (g m/g s) was not influenced by species being on average 0.47. Relative limitations posed by mesophyll conductance to photosynthesis, Lm, (0.40 ± 0.02) were high compared to those imposed by stomata, Ls (0.07 ± 0.01). The average CO2 concentration in the intercellular air spaces (Ci) was 32 µmol mol-1 lower than in the atmosphere (Ca), while the average CO2 concentration in the chloroplasts (Cc) was 131 µmol mol-1 lower than Ci independent of species. Maximal rates of Rubisco carboxylation, Vcmax, and maximal electron transport rates driving regeneration of RuBP, Jmax, ranged from 13 to 66 µmol CO2 m-2 s-1 and from 33 to 148 µmol electrons m-2 s-1, respectively, and compare well to averages for C3 plants. CONCLUSIONS: Photosynthetic performance was in the series: Q. saponaria > C. alba ≥ L. caustica, which can be attributed first to mesophyll conductance limitations, probably mediated by leaf anatomical traits and then to species specific foliage N partitioning strategies.