Seasonal variation in RuBPcase activity and N allocation in the chlorophyte seaweeds ulva curvata (kutz.) de toni and Codium decorticatum (Woodw.) Howe

Seasonal variation in ribulosebisphosphate carboxylase (RuBPCase) activity and cellular N allocation in Ulva curvata (Kutz.) De Toni and Codium decorticatum (Woodw.) Howe was followed over two annual cycles. Because apparent seasonal variation may result from random sampling of a coherent pattern of shorter-term variation, estimating the magnitude of seasonal variation in seaweed N allocation requires sampling over a range of time scales. Such sampling reveals annual ranges of variation in N allocation to be greater than those measured at time scales of hours to days. RuBPCase activity in both U. curvata and C. decorticatum peaks in winter and summer, with fall and spring lows. Total N and C exhibit pronounced winter highs and summer lows in C. decorticatum, with less predictable variation in U. curvata. Growth is controlled by temperature in both species, while N uptake is only loosely coupled to temperature or light. Seasonal variations in N allocation are driven by interactive effects of N supply, temperature, and light on growth and N uptake. These effects are largely independent of morphological and genetic differences between species.