Abstract
BackgroundQuillaja saponaria Mol., Cryptocarya alba Mol. Looser, and Lithraea caustica Molina Hook et Arn., are common sclerophyllous species in Mediterranean Central Chile. Mesophyll conductance, gm, may strongly limit photosynthesis in these semiarid environments.ResultsSimultaneous 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, gs, were greater than those of mesophyll conductance, gm, while their ratio (gm/gs) 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.ConclusionsPhotosynthetic 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.
Highlights
IntroductionArid and semiarid lands account for 41% of Chile’s continental territory, covering about 31 million ha (Benites et al 1994)
Light response curves (Figure 3a) were very similar among species up to an irradiance level of about 500 μmol photons m−2 s−1, changing drastically thereafter with clearly distinct maximums of photosynthetic rates in the series: Q. saponaria > C. alba > L. caustica which reflects that the three species exhibited a similar initial pseudolinear slope of the A/Q curve averaging 0.033 ± 0.007 mol CO2 mol−1 quanta
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) and not significantly influenced by species
Summary
Arid and semiarid lands account for 41% of Chile’s continental territory, covering about 31 million ha (Benites et al 1994) Within this area, semiarid sclerophyllous (i.e. a woody plant with small coriaceous evergreen leaves dominant of the Mediterranean region) shrublands and forests extends from 32-36° S latitude (~345,000 ha) in Central Chile (Armesto et al 2007; CONAF 1999); exhibiting high levels of endemism, and are considered a priority for biodiversity conservation (Arroyo et al 2004). Understanding how environmental limitations are imposed on the carbon budget is relevant to accurately estimate carbon uptake and water use by sclerophyllous species
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