Is the photosynthetic process non-linear?
We applied two non-linear time series analysis methods to photosynthetic data obtained from a single-species population of Thalassiosira pseudonana incubated in situ in order to identify whether the time series were generated predominantly by linear or non-linear processes. The tests used to make these distinctions involved a comparison of the predictability of the observed data under a non-linear hypothesis versus a linear hypothesis. Two records were analyzed. For the first data segment taken in the morning, the linear method performed as well or better than the nonlinear methods. Although a weak non-linearity was detected in the second data set observed in the afternoon, the time series is dominantly linear. The best embedding dimension, whose value suggests the number of participating independent parameters in the system, is 2 for the moming data and 7 for the afternoon data. These results are true for aggregate productivity measures (1.8 x 108 cells) on a time scale of 1 5 min. Ci
