Modelling Si-N-limited growth of diatoms

Abstract

A mechanistic model for silicon (Si) physiology is developed, interfaced with a model of nitrogen (N) 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 of 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 G2 interphase and M, while the girdles and (if appropriate) setae are synthesized during G1. 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 G2 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 G1 and G2 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.