Aluminum-induced changes in the net carbon fixation and carbon decomposition of a nitrogen-fixing cyanobacterium Trichodesmium erythraeum

Abstract

Recent studies suggest aluminum (Al) likely plays a role in the ocean carbon cycle by altering the biological carbon xation and carbon decomposition of marine diatoms. However, it remains speculative whether Al has similar effects on other ecologically important phytoplankton groups such as the globally important nitrogen-xing cyanobacterium, Trichodesmium. Here we report the in uence of Al on carbon xation and decomposition in non-axenic cultures of Trichodesmium erythraeum IMS101 (CCMP 1985). By using radiocarbon, and adding oceanic relevant amounts of dissolved Al (yielding concentrations of 40 and 200 nM) along with non-Al-amended controls, we investigated the changes in particulate organic carbon (POC) of Trichodesmium (> 2 µm, Trichodesmium POC), and free-living bacteria (0.2-2 µm, bacterial POC), and dissolved organic carbon (< 0.2 µm, DOC) over a 116-day growth period. The results showed that the rates of increase of POC in the declining growth phase of T. erythraeum were signi cantly higher (by 11-14%) in the Al-enriched treatments than in the control, and this Al-enhanced carbon xation is consistent with previous observations on marine diatoms. On the other hand, unlike diatoms, the POC from T. erythraeum decomposed faster in the Al-enriched treatments during the rst decay phase when bacterial POC and DOC increased along with the decomposition of Trichodesmium POC. Further addition of the same amounts of Al (again calculated to increase the Al concentration by 40 and 200 nM) was performed on day 71. This treatment was designed to mimic Al supply from sediment after the settling of Trichodesmium colonies to the ocean bottom. Following this second addition, the decomposition rate of both Trichodesmium POC and DOC slowed down by 20-27% and 31-62%, respectively, during the second decay phase, when DOC and bacterial POC decreased. The study suggests that Al fertilization in the surface ocean via dust deposition may increase the net carbon xation and nitrogen xation by Trichodesmium, and thus the supply of new nitrogen to the euphotic zone, whereas Al from sediment may decrease the decomposition rate of decaying Trichodesmium settled to the ocean bottom.

Natural ocean iron fertilization and climate variability over geological periods

“…Although aluminum is not an essential nutrient for phytoplankton, aluminum plays an important role in enhancing the BCP by maintaining iron bioavailability and increasing the carbon export of major marine primary producers, such as diatoms and nitrogen-fixing cyanobacteria Trichodesmium spp. (Zhou et al, 2018(Zhou et al, , 2021Zhou, Liu, et al, 2023). In special geological periods, especially the glacial-interglacial cycle, natural fertilization from atmospheric dust deposition contained both iron and aluminum, and the content of aluminum based on ice core records was even higher than the iron content.…”

Promoting effects of aluminum addition on chlorophyll biosynthesis and growth of two cultured iron‐limited marine diatoms

“…Moreover, Al has long been known to decrease the dissolution rate of diatom frustules (Lewin 1961;Dixit et al 2001;Tian et al 2023). Aluminum addition at environmentally relevant levels has also been reported to decrease the decomposition rates of marine diatoms (Zhou et al 2021) and decaying cyanobacterium Trichodesmium (Zhou et al 2023b). Aluminum may also contribute to the long-term preservation and sequestration of carbon in microfossils and sediments (Blattmann et al 2019;Hemingway et al 2019;Anderson et al 2020).…”