Modelling Si-N-limited growth of diatoms

Abstract

A mechanistic model for silicon (Si) physiology is developed, interfaced with a model of nitrogen IN) physiology, which is capable of simulating the major documented facets of Si-N physiology in diatoms. The model contains a cell cycle component that is involved in regulating the timing ol the synthesis of valves, girdles and setae. In addition to reproducing the timing of diatom cell division within a light- dark cycle, the model simulates the following features seen in real diatoms. Synthesis of valves only occurs during G 2 interphase and M, while the girdles and (if appropriate) setae are synthesized during G 1 Si stress alone results in a loss of setae, followed by a thinning of the valves in successive generations until a minimum Si cell quota is attained. After this point, the duration of G 2 increases and growth is Si limited. Concurrently, the carbon (C) cell quota increases, offering the capability to simulate the documented increase in sinking rates with Si stress. N stress alone results in an increase in the duration of G 1 and G 2 interphases, and high Si cell quotas, From this complex model which must be run for arrays of subpopulations to simulate non-synchronous growth, a simpler model is developed. This is capable of reproducing similar growth dynamics, although with no reference to component parts of the frustule. When allied to a photoacclimative submodel, a prediction of the model is that diatoms starved of Si will release increased amounts of dissolved organic C because cell growth is halted more rapidly than the photosystems can be degraded.