Uncovering the Differential Growth of <i>Microcystis aeruginosa</i> Cultivated under Nitrate and Ammonium from a Photophysiological Perspective
Xiaolong Yang, Wei Dong, Lihua Liu, Yonghong Bi, Wanyao Xu, Xun Wang
Abstract
Cyanobacteria have a relatively high affinity for NH 4 +, yet a NO 3 – -rich environment is comparatively conducive to their proliferation. To date, little information is available on why NO 3 – -N favors cyanobacterial biomass accumulation. This study investigated the dependence of biomass, nitrogen assimilation characteristics, and photophysiological performance of Microcystis aeruginosa on the forms of nitrogen supply, including NO 3 – -N-only, NH 4 + -N-only, and NO 3 – -N + NH 4 + -N. The results indicated that despite the retarded growth of M. aeruginosa, cells supplied with NO 3 – -N-only maintained a simultaneous promotion in the growth rate, nitrogen assimilation efficiency, and photosynthetic capacity, resulting in high biomass production. Cells supplied with NH 4 + -N-only and NO 3 – -N + NH 4 + -N were able to rapidly assimilate nitrogen during initial cell proliferation, showing a preferential use of NH 4 + -N and the inhibition of NO 3 – uptake by NH 4 + . However, growth repression occurred as cultivation time was prolonged when NH 4 + -N was excessively supplied, mainly due to PSII photodamage, intracellular redox imbalance, and increased electron energy accumulation. Thus, cells supplied with NH 4 + -N-only had to reduce light energy capture, increase photoprotection, and consume excess electrons to mitigate the damage. These findings are critical for improving our understanding of the role of different nitrogen forms in the regulation of cyanobacterial photophysiological performance and growth.