Many factors including internal and external variables are responsible for the carbon isotopic composition (δ13C) of submersed plants and make it complex to interpret and apply in ecological studies. In order to assess the effects of temperature and dissolved inorganic carbon (DIC) concentration on the carbon isotopic fractionation in the growth of submersed plants, Potamogeton pectinatus was cultivated with tubers at sixtemperatures from 16℃to 31℃with a increment of 3℃and two DIC concentrations, 0.0001mol•L-1and 0.0001mol•L-1. Plant materials were collected and weighed after they were cultured for 50 days in illumination incubator lighting with 16∶8 (Day∶Dark). And their carbon isotopic compositions were analyzed.
In general, temperature and inorganic carbon concentration exerts a stronger influence on the growth and carbon isotopic fractionation of P.pectinatus.Net growth rates of P. pectinatus had a high positive correlation with temperature(R2>0.9). At high DIC concentration (0.001mol•L-1), net growth rates of P. pectinatus ranged from 0.64mg•min-1to 091mg•min-1with the average Q10 of 1.3, where at low DIC concentration (0.0001mol•L-1), they varied from 0.38mg•min-1 to 0.75mg•min-1with the average Q10 of 1.9. In the same time, with the increase of temperature from 16℃ to 31℃, the δ13Cvalues of P. pectinatus increase from -14.83‰ to -13.47‰ at DIC of 0.0001molL-1, where the values increase from -18.56‰ to -15.15‰ at DIC of 0.001molL-1.The difference of δ13C between the two DIC concentrations is 3.73‰ at the temperature of 16℃,and is 1.68‰ at the temperature of 31℃. The results implied that the DIC concentration has larger effects on carbon fractionation of this plant at low temperature than that at high temperature.
Carbon isotopic fractionation of P. pectinatus was modeled by using a diffusion equation. The parameters, A and B werecalculated by using the δ13C values at two DIC concentrationsof the same temperature. The results show these parameters all have highly corrective coefficients with temperatureand might be used to predict the carbon isotopic fractionation of P. pectinatus.