What limits photosynthetic energy conversion efficiency in nature? Lessons from the oceans

Abstract

Constraining photosynthetic energy conversion efficiency in nature is challenging. In principle, two yield measurements must be made simultaneously: photochemistry, fluorescence and/or thermal dissipation. We constructed two different, extremely sensitive and precise active fluorometers: one measures the quantum yield of photochemistry from changes in variable fluorescence, the other measures fluorescence lifetimes in the picosecond time domain. By deploying the pair of instruments on eight transoceanic cruises over six years, we obtained over 200 000 measurements of fluorescence yields and lifetimes from surface waters in five ocean basins. Our results revealed that the average quantum yield of photochemistry was approximately 0.35 while the average quantum yield of fluorescence was approximately 0.07. Thus, closure on the energy budget suggests that, on average, approximately 58% of the photons absorbed by phytoplankton in the world oceans are dissipated as heat. This extraordinary inefficiency is associated with the paucity of nutrients in the upper ocean, especially dissolved inorganic nitrogen and iron. Our results strongly suggest that, in nature, most of the time, most of the phytoplankton community operates at approximately half of its maximal photosynthetic energy conversion efficiency because nutrients limit the synthesis or function of essential components in the photosynthetic apparatus.This article is part of the themed issue 'Enhancing photosynthesis in crop plants: targets for improvement'.

Plant-Growth-Promoting Bacteria Mitigating Soil Salinity Stress in Plants

“…It is one of the most common elements on Earth (second or fourth, according to different sources) [5,[114][115][116]. Despite the above, iron is not widely accessible in soils forming complexes of hydroxides and oxyhydroxides; thus, its bioavailability decreases below 10% in loamy soils [117]. In soil matrix, iron exists in two convertible states as Fe 2+ and Fe 3+ , depending on pH, oxygen, and organic matter content.…”

Siderophore-Producing Rhizobacteria as a Promising Tool for Empowering Plants to Cope with Iron Limitation in Saline Soils: A Review

“…Although widely available in nature, Fe is not always accessible to plants and it often limits biological productivity of plants (Briat et al, 2015;Falkowski et al, 2017). Fe can exist in aqueous solution in two readily inter-convertible states: Fe 2+ and Fe 3+ .…”

Photosynthesis solutions to enhance productivity

“…Moreover, the high cysteine content of the diatom proteome may allow the cell to monitor photosynthetic electron flow better in the presence of molecular oxygen and so prevent over-oxidation [7]. Within this volume, Falkowski et al [8] discuss how photosynthetic efficiency might be improved within the oceans. The phytoplankton community is shown to operate at only half maximal photosynthetic energy conversion efficiency because of poor nutrient availability that limits the synthesis or function of essential components in the photosynthetic apparatus.…”