posted on 2020-03-10, 15:30authored byYunfei Sun, Xingxing Zhang, Lu Zhang, Yuan Huang, Zhou Yang, David Montagnes
Solar
ultraviolet-B (UVB) radiation reaching the earth’s
surface is increasing due to stratospheric ozone depletion. How the
elevated UVB affects the trophic interactions is critical for predicting
the ecosystem functioning under this global-scale stressor. Usually,
inducible defenses in phytoplankton stabilize community dynamics within
aquatic environments. To assess the effects of elevated UVB on induced
defense, we examined the changes in antigrazer colony formation in Scenedesmus obliquus under environmentally relevant
UVB. S. obliquus exposed to Daphnia infochemicals consistently formed multicelled colonies,
traits confirmed to be adaptive under predation risk. However, the
suppressed photochemical activity and the metabolic cost from colony
formation resulted in the severer reductions in algal growth by UVB
under predation risk. The transcriptions of key enzyme-encoding genes,
regulating the precursor synthesis during polysaccharide production,
were also inhibited by UVB. Combination of the reduced production
of daughter cells and the ability of daughter cells to remain attached,
the antigrazing colony formation was interrupted, leading to the dominant
morphs of algal population shifting from larger-sized colonies to
smaller ones at raised UVB. The present study revealed that elevated
UVB will not only reduce the phytoplankton growth but also increase
their vulnerability to predation, probably leading to potential shifts
in plankton food webs.