Plants and algae in nature perform photosynthesis in a dynamically fluctuating environment, yet most mechanistic studies of photosynthesis take place in a static laboratory environment. Laboratory tools capable of simulating nature-like environments are required to identify the mechanisms which confer robustness to photosynthesis. To this end, I present three technologies for measuring photosynthesis in a simulated environment. The IDEA spectrophotometer provides detailed fluorometric and spectrophotometric measurements of individual plant leaves. The DEPI chamber cultivates small plants such as Arabidopsis thaliana in a reproducible simulated environment while simultaneously monitoring their photosynthesis by fluorescence image analysis. The ePBR cultivates microalgae in a simulated production pond environment.These tools were employed to examine the mechanisms of hyperoxia sensitivity in an algal production pond setting. Such ponds are supplemented with mineral nutrients and CO2 to maximize photosynthetic productivity. The high rates of day-time photosynthesis in these ponds inevitably leads to the accumulation of dissolved O2 to hyperoxia, which inhibits the photosynthetic growth and productivity of algae despite the CO2 supplementation. Using the ePBRs, I identified hyperoxia tolerant and sensitive strains of Chlamydomonas reinhardtii and compared their photosynthetic efficiencies in normoxia and hyperoxia ePBR cultivation. Photorespiration is often cited as a mechanism of hyperoxia sensitivity in algae, yet the hyperoxia sensitive strain was less prone to photorespiration than the tolerant strain and overall rates of photorespiratory glycolate production amounted to only a small fraction of the total light-dependent oxygen consumption observed in the sensitive strain. This indicates that the hyperoxia sensitive strain is diverting a larger fraction of its photosynthetic electron flux to the reduction of oxygen, possibly via the Mehler cycle or flavodiiron proteins. There also appears to be a trade-off between hyperoxia tolerance and low-CO2 performance, in which case algae strain selection strategies based on maximum performance under air cultivation may be unintentionally selecting against pond hyperoxia performance.
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