Sequential effects of acidic precipitation and drought on photosynthesis and chlorophyll fluorescence parameters of Pinus radiata d. don seedlings

We studied the sequential effect of simulated acid rain (SAR) and water str ess on net photosynthesis (A), internal CO2 concentration (Ci), stomatal co nductance (g), and instantaneous water use efficiency (A/E), and the photoc hemical damage caused by these stressors by analysing chlorophyll fluoresce nce parameters such as Fv/Fm, Fv/Fo and Fm/Fo. SAR caused inhibition of pho tosynthesis. The depletion of CO2 assimilation seems not to be solely a sto matal effect as effects on chloroplasts contribute to this photosynthetic i nhibition. No noticeable damage seems to occur to the photochemical apparat us since well-watered plants treated with acid rain did not show any change in the chlorophyll fluorescence. Water stress produced a large effect on b oth gas exchange and chlorophyll fluorescence parameters, indicating struct ural and functional damage. Interactions among SAR and drought had a larger impact on all parameters studied. However, after rewatering, significant r ecovery in both gas exchange and chlorophyll fluorescence parameters occurr ed within 6 days, although the values measured Frier to the imposition of t reatments were not recovered. We conclude that Pinus radiata exposed co aci d rain were affected in a wide range of components in the photosynthetic ap paratus, thereby modifying its response to sequential drought stress.