Selected coccal green algae are not affected by the humic substance Huminfeed® in term of growth or photosynthetic performance

Abstract

Humic substances (HSs) have been shown to influence growth, photophysiology, and redox homeostasis in phototrophs. However, many ecological studies deliver controversial results indicating inhibitory or stimulating effects depending on the kind of phototrophic organism or type of HSs applied. Here we analyzed the effect of Huminfeed Ò (HF), a preparation from leonardite associated with lignite deposits, on growth and photosynthetic performance of three different coccal green algae. Concentrations of HF in the range of 2-20 mg l -1 dissolved organic carbon (DOC) did neither affect the growth rate nor the light-adapted photosynthetic electron transport. Even photoinhibitory light intensities of 1,600 lmol photons m -2 s -1 , representing the tenfold of growth light intensity, did not result in a decline of the maximal photosynthetic rate in HF-treated algae. In HF-grown algae, a very subtle decrease by about 10% could be observed in thermoluminescent light emission, a sensitive method to detect changes in photosystem II (PSII) chemistry. However, thermoluminescence (TL) represents only 3% of the light-induced charge separated states in PSII. Hence, rather small changes will not have significant effects on overall photosynthetic performance and growth. Therefore, the physiological effect of HSs on freshwater phototrophs has to be revisited.

Colored organic matter increases CO2 in meso‐eutrophic lake water through altered light climate and acidity

“…Four treatments were set up: (1) addition of DOC concentrated from a humic stream draining a forested wetland (59°92′N, 17°34′E), with a DOC concentration of 37.7 (± 0.49 SE) mg L −1 ; the stream water was filtered (0.2 μ m) with a submersible pump through 10‐in. filter cartridges, and DOC was concentrated by reverse osmosis using a Real Soft PROS/2S unit as described by Serkiz and Perdue (), to a final concentration of approximately 800 mg L −1 (i.e., reverse osmosis); (2) DOC from HuminFeed® (Humintech, GmbH), an alkaline extract of Leonardite, which has previously been used as a humic matter source in aquatic studies (Heinze et al ; Rasconi et al ) (i.e., HuminFeed); (3) a mix of reverse osmosis concentrate and HuminFeed adding equal amounts of DOC from the two sources (i.e., mixed); and (4) no addition of DOC (i.e., control) (Fig. a).…”

“…(2) DOC from HuminFeed ® (Humintech, GmbH), an alkaline extract of Leonardite, which has previously been used as a humic matter source in aquatic studies (Heinze et al 2012;Rasconi et al 2015) (i.e., HuminFeed); (3) a mix of reverse osmosis concentrate and HuminFeed adding equal amounts of DOC from the two sources (i.e., mixed); and (4) no addition of DOC (i.e., control) ( Fig. 2a).…”

Humic Substances as Microalgal Biostimulants—Implications for Microalgal Biotechnology

“…At higher concentrations, HS cause plastid homeostasis imbalance due to the destructuration of the proton gradient across the inner chloroplast membrane [ 80 ]. This proton gradient is fundamental for converting light energy into chemical energy (ATP) and is essential for the efficient functioning of photosystem II [ 81 ].…”