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Losses of leaf area owing to abiotic stress along the leaf economics spectrum: implications for carbon gain at the branch level

Mediavilla, Sonia, García-Cunchillos, Iván, Andrés-Rivera, Carmen, Escudero, Alfonso
Trees 2018 v.32 no.2 pp. 559-569
abiotic stress, carbon, carbon dioxide, carbon sequestration, chlorosis, economics, leaf area, leaves, longevity, models, necrosis, photosynthesis, trees
KEY MESSAGE: The differences in premature loss of leaf area between coexisting tree species have significant impacts on the duration of the functional photosynthetic machinery, therefore, this aspect should be included in the predictive models of carbon sequestration capacity. The competition between tree species with different leaf habits has attracted the attention of numerous researchers. It has been frequently reported that the lower instantaneous rates of assimilation of the leaves of the evergreen species are compensated by a longer duration of the leaves. Traditionally, the duration of the photosynthetic machinery has been thought to be equivalent to the longevity of the individual leaves. However, when the leaves experience injuries that result in premature loss of healthy leaf area, the duration of the photosynthetic machinery may be less than the mean duration of the individual leaves. During 3 years, the leaf area affected by chlorosis and necrosis in seven evergreen Mediterranean tree species was measured, and the mean leaf life span and leaf mass per unit area were determined. Previously published data on the instantaneous photosynthetic capacity for the same species were used to estimate the impact of the loss of leaf area on photosynthetic capacity at the branch level. The percentage of leaf area damaged decreased with the increase in leaf life span. At the branch level, the loss of CO₂ assimilation associated with the loss of healthy leaf area was almost insignificant for the species with a longer leaf life span, but amounted to 13% in the species with shortest leaf duration. It can be concluded that the negative impact of the premature losses of leaf area on the duration of the photosynthetic machinery tends to decrease with the increase in leaf life span. This trend could modify the slope of the relationships between the duration of the photosynthetic machinery and instantaneous CO₂ assimilation rates, which determine the competitive equilibrium between species differing in leaf life span.