Thermodynamic Characterization And Matching Research Of Algae Phosphorus Uptake Model

Algae dominates the natural aquatic ecosystems and the human industrial production,also significantly influences the global climate change as well as the element biogeochemical cycle.Physiological adaptability is an intrinsic property of algae,which spontaneously deals with external conditions change of surroundings by adjust the metabolic pathways inside algal cells.Such natural characteristic is a cognitive basis of knowing the nutrient uptake process together with the cellular nutrient status of algae,and it is also a crucial factor in cellular model construction of algae.Besides,mathematical description of algal nutrient uptake is essential core of algal ecological modeling,in which dynamic approaches are widely used and provide reliable modeling routes as well as substantial simulation data.This paper applied thermodynamic methods to quantitatively formulate the bioenergetic characteristics of algal phosphorus uptake.A thermodynamic flux formulation of algal phosphorus nutrient based on osmotic potential is derived,which underlines bioenergy metabolism instead of focusing merely on phenomenal description.Specifically,the significant biochemical processes of algal cells phosphorus uptake,storage and transform were integrated;accordingly,the principal fated materials of internal phosphorus involved those processes were confirmed.Meanwhile,the modelling procedures primarily included necessary assumptions,conditional factors,and unit system;then the linear non-equilibrium thermodynamic relation was referred to obtain the expression of phosphorus uptake flux and osmotic potential,coupling with the process of oxidative phosphorylation.Promisingly,the results of laboratory tests supported the feasibility of such formulation,to obtain the threshold of phosphorus limitation and to analyze the phosphorus limitation determination and interspecific competition of typical algae.Moreover,stoichiometry and energetics were utilized to describe three critical processes of uptake,storage and assimilation in "potential-flux" model.Macro-chemical equation was firstly provided to represent the synthesis process of algal cell,together with the formulation of energy change by AG,in order to obtain the Gibbs free energy of per unit algal cell generating(represented by △rGθ5Synthesis).Then,the relationship between ambient phosphorus concentration and △rGθsynthesis was constructed by the bridge of ATP generating rate under the function of substrate level phosphorylation,which was described by Michaelis-Menton equation.Ultimately,generating potential(μalgae)was defined as the impact of ambient phosphorus concentration on biomass of water body,in order to clearly present the contribution made by phosphorus uptake.Besides,enthalpy and entropy variation of algae uptake system under a specific range phosphorus concentration were measured by isothermal titration micro-calorimetry,and the parameters of this model were determined;therefore,the thermodynamic relationship between algae uptake and biomass increase was eventually established.Although the algae phosphorus uptake model was verified theoretically and were combined well at indoor cultivation experiments,the present conclusions of uptake characteristics as well as biomass generation yield by uptake are restricted in laboratory.As a matter of fact,the matching research of algae phosphorus uptake is supposed to play a more significant role,and can be variably modified in detail;however,its interpretation of in situ phenomena is insufficient.Promisingly,quantitative study of natural algae phenomena in water body should go a step further concerning interspecific competition and so forth.Furthermore,further efforts should be made on modeling which is conform to the law of nature and can better explain the practical situations.