Spatio-temporal variability in the photosynthetic characteristics of Zostera tasmanica measured by PAM

Rapid light curves (RLCs), based on pulse amplitude modulated (PAM) fluorometry, were used to investigate the spatio-temporal variability in photosynthesis versus irradiance parameters (α, Ik and Pmax) and the Fv/Fm ratio of the seagrass Zostera tasmanica (formerly Heterozostera tasmanica). Spatial variation was examined across scales ranging from within a leaf (cms) to across the bed (ms), using a nested analysis of covariance sampling design. Overall, significant variation was identified at all scales examined, excluding the largest scale (area). Patterns of variability differed among individual parameters; however a high percentage of the variation was consistently assigned to the covariates, age (within and between leaves) for all parameters, except Pmax.Using these results, a sampling strategy focusing on the leaf level was used to examine temporal changes to the photosynthesis parameters and the Fv/Fm ratio and to minimize spatial considerations. Both Pmax and the Fv/Fm ratio showed a significant relationship with in situ irradiance. However, a large percentage of the variation, for all parameters, was left unexplained by in situ irradiance. When the effect of in situ irradiance was removed there was no autocorrelation between measurements, taken at 3 min intervals, of the photosynthesis parameters and the Fv/Fm ratio. These results suggest that small-scale spatial and not temporal variation must be taken into account when seeking to characterise Z. tasmanica photosynthetic performance using PAM fluorometry.