# Interactive effects of CO2 , temperature, and nitrate limitation on the growth and physiology of strain CCMP 1334 of the marine cyanobacterium Synechococcus (Cyanophyceae)

## TL;DR

This study examines how CO2 levels, temperature, and nitrate availability affect the growth and physiology of a marine cyanobacterium, Synechococcus.

## Contribution

The study reveals how Synechococcus adapts to combined environmental stressors, particularly under climate change conditions.

## Key findings

- Higher CO2 levels increased growth rates across all temperatures.
- Carbon:nitrogen ratios decreased with increasing temperature.
- The cyanobacterium shows resilience to warming and elevated CO2 levels.

## Abstract

The marine cyanobacterium Synecococcus sp. (CCMP 1334) was grown in a continuous culture system on a 12:12 h light:dark cycle at all combinations of low and high pCO2 (400 and 1000 ppmv, respectively), nutrient availability (nitrate‐limited and nutrient‐replete conditions), and temperatures of 21, 24, 28, 32, and 35°C. The maximum nutrient‐replete growth rate was ~1.15 day−1 at 32–35°C. Median nutrient‐replete growth rates were higher at 1000 ppmv than at 400 ppmv pCO2 at all temperatures. Carbon:nitrogen ratios were independent of pCO2 at a fixed relative growth rate (i.e., growth rate ÷ nutrient‐replete growth rate) but decreased with increasing temperature. Carbon:chlorophyll a ratios were decreased monotonically with increasing temperature and were higher under nitrate‐limited than nutrient‐replete conditions. Ratios of phycoerythrin to chlorophyll a were independent of growth conditions. Productivity indices were independent of temperature and nutrient limitation but were consistently higher at 1000 ppmv than 400 ppmv pCO2. Both growth rates and dark respiration rates were positively correlated with temperature, and the associated Q
10 values were 2.2 and 2.3, respectively. A model of phytoplankton growth in which cellular carbon is allocated to structure, storage, or the light or dark reactions of photosynthesis accounted for the general patterns of cell composition and growth rate. This strain of Synechococcus appears well suited to changes in environmental conditions that are expected as the climate warms in response to anthropogenic emissions of CO2.