Spectral dependence of the inhibition of photosynthesis under simulated global radiation in the unicellular green alga Dunaliella salina

The inhibition of photosynthesis after exposure to simulated solar radiatio n has been investigated in the marine green alga Dunaliella salina by monit oring the chlorophyll fluorescence parameter, Delta F/F-m', and the maximum Light utilization efficiency for oxygen production. 40 different irradiati on regimes have been applied by combining two different levels of UV radiat ion with two different levels of photosynthetically active radiation (PAR), and by using 10 coloured glass filters with decreasing cut-off wavelengths ranging from 400 to 295 nm. After a 30 min exposure both Delta F/F-m' and the efficiency of oxygen production decrease under all irradiation conditio ns. Inhibition increases when the cut-off is shifted towards short waveleng ths. The fit of the experimental data with an analytical model describing i nhibition of photosynthesis as a function of a linear combination of the ph oton flux densities in the UV-B, UV-A and PAR allows the average weighting factors for inhibition of photosynthesis by the three spectral ranges (abou t 1.6, 1.9 x 10(-2) and 1.8 x 10(-4) (mu mol m(-2) s(-1))(-1) for UV-B, UV- A and PAR, respectively) to be calculated. The experimental data and the de rived weighting factors are in agreement with previous results obtained und er natural solar radiation. In addition, the data allow an estimation of a biological weighting function in the UV range to be made. (C) 1999 Elsevier Science S.A. All rights reserved.