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Light inhibition of foliar respiration in response to soil water availability and seasonal changes in temperature in Mediterranean holm oak (Quercus ilex) forest
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Edité par CCSD ; CSIRO Publishing -
International audience. In the present study we investigated variations in leaf respiration in darkness (R-D) and light (R-L), and associated traits in response to season, and along a gradient of soil moisture, in Mediterranean woodland dominated by holm oak (Quercus ilex L.) in central and north-eastern Spain respectively. On seven occasions during the year in the central Spain site, and along the soil moisture gradient in north-eastern Spain, we measured rates of leaf R-D, R-L (using the Kok method), light-saturated photosynthesis (A) and related light response characteristics, leaf mass per unit area (MA) and leaf nitrogen (N) content. At the central Spain site, significant seasonal changes in soil water content and ambient temperature (T) were associated with changes in M-A, foliar N, A and stomatal conductance. R-D measured at the prevailing daily T and in instantaneous R-T responses, displayed signs of partial acclimation and was not significantly affected by time of year. R-L was always less than, and strongly related to, R-D, and R-L/R-D did not vary significantly or systematically with seasonal changes in T or soil water content. Averaged over the year, R-L/R-D was 0.66 +/- 0.05 s.e. (n = 14) at the central Spain site. At the north-eastern Spain site, the soil moisture gradient was characterised by increasing M-A and R-D, and reduced foliar N, A, and stomatal conductance as soil water availability decreased. Light inhibition of R occurred across all sites (mean R-L/R-D= 0.69 +/- 0.01 s.e. (n = 18)), resulting in ratios of R-L/A being lower than for R-D/A. Importantly, the degree of light inhibition was largely insensitive to changes in soil water content. Our findings provide evidence for a relatively constrained degree of light inhibition of R (R-L/R-D similar to 0.7, or inhibition of similar to 30%) across gradients of water availability, although the combined impacts of seasonal changes in both T and soil water content increase the range of values expressed. The findings thus have implications in terms of the assumptions made by predictive models that seek to account for light inhibition of R, and for our understanding of how environmental gradients impact on leaf trait relationships in Mediterranean plant communities.
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