The effect of environmental factors on phytoplankton growth: Temperature and the interactions of temperature with nutrient limitation1

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Abstract
The combined stress of nutrient limitation and suboptimal temperature on growth was studied with turbidostat and chemostat cultures of Scenedesmus sp. and Asterionella formosa. The combined effects were greater than the sum of individual effects and were not multiplicative. In N‐ and P‐limited Scenedesmus sp. and A. formosa the cell (q) of both limiting and nonlimiting nutrients increased with decreasing temperature. At a given temperature cell quotas of limiting nutrients also increased with the growth rate (µ) and followed a saturation function. Higher values of the minimum cell quota (qo) at lower temperatures show that cells require more nutrient with decreasing temperature. The change of qo with temperature varies with the type of limiting nutrient. This change for N and P in Scenedesmus sp. suggests that their optimum ratio, the ratio at which one limitation changes over to the other, is higher at suboptimal temperatures.Cell quotas of nutrient‐sufficient cultures (qm) for C, N, and P and cellular chlorophyll a concentration increased with decreasing temperature. The quota of each nonlimiting nutrient in nutrient‐limited cultures had the same value as qm. The rate of protein synthesis per unit RNA decreased with temperature.The highest apparent maximum N uptake was observed at 15°C for N‐limited Scenedesmus sp. growing at 0.5·d‒1. The optimal growth temperature range, however, was 20°–25°C. The highest apparent maximum P uptake in A. formosa was found at 19°–20°C, when µ = 0.4·d‒1. These temperatures were also optimal for growth.