The integrated productivity of a Macrocystis integrifolia plant

The relative contributions of various plant parts to the integrated productivity of Macrocystis integrifolia Bory were determined by extrapolating the net photosynthetic capacity of each part, as observed in vitro, to its proportional contribution to the biomass of a M. integrifolia kelp bed. The nongrowing plant parts (primarily mature and senescing blades) which represented 66% of the total plant biomass were responsible for 58% of the plant's net productivity. This productivity was assumed, in part, to support growing portions of the plant and, in part, to be stored as reserves for the initiation of late-winter growth. Within the three classes of blades studied (growing, mature, and senescing), which constituted 79% of the total plant biomass, there were no significant differences in photosynthetic pigment concentrations or in net photosynthetic rates. Dark respiration rates were significantly different between these three classes of blades: the older the blade, the lower the respiratory rate. Macrocystis integrifolia optimized its productivity by reducing the respiratory demands of the fully grown tissue, and by having all blades contribute to the net photosynthate pool. These adaptations vary from those of the deeper-water Macrocystis pyrifera (L.) C. Ag., which has been shown by others not to have differential respiratory rates and to have net productivity generally restricted to the shallow-water canopy.