ALGAL C-14 AND TOTAL CARBON METABOLISMS .1. MODELS TO ACCOUNT FOR THEPHYSIOLOGICAL PROCESSES OF RESPIRATION AND RECYCLING

A consistent set of equations has been written to describe the net rat e of algal (CO2)-C-14 uptake (and where appropriate respiration and ph otosynthesis) which take into account separately complications due to respiration of the labelled photosynthetic products and the recycling of respiratory CO2. Written specifically into the equations is the con cept of 'new' and 'old' carbon, the coefficient q is used in the respi ration model to allow for the differential respiration of organic mate rial from the 'new' and 'old' carbon pools. Analytical integrals have been found for respiration and recycling models, and the behaviour of the models studied over periods of 12 h (i.e. up to 70% of the intrins ic generation time). The rate constant for respiration has a greater e ffect on the behaviour of the recycling than the respiration model. Ov er short time courses (up to 30% of the intrinsic generation time), th e effects of respiration and recycling on net (CO2)-C-14 uptake are qu ite distinct, especially at high P/R ratios, and not complicated by as sumptions over the value of q. Although the value of q will have a tim e-dependent secondary effect on the modelled total carbon-specific res piration rate, this was found not to give rise to major problems of in terpretation. Beyond 50% of the intrinsic generation time, the separat e treatment of respiration and recycling in the models becomes less sa tisfactory. It was concluded that the present equations, which are not constrained by mass balance considerations, would not be appropriate for a model that combines the two processes. The pattern of recycling at low P/R values is identified as one of the major uncertainties in p roducing models of C-14 uptake. The effect of the release of dissolved organic material can be anticipated in a general way. The models have been used to define an experimental strategy to establish the separat e effects of respiration and recycling on the time course of net C-14 uptake. The initial rates give the dearest resolution of the two proce sses and it would appear that with photosynthetic rates in the region of 1 day(-1),incubation periods up to 3-6 h would be suitable to deter mine the importance of recycling in controlling net C-14 uptake. With the present models, only in the absence of recycling could the effect of respiration be studied and the value of q established.