The role of morphological changes in Microcystis adaptation to nutrient availability at the colonial level

Colony formation is a key trait facilitating the formation of Microcystis blooms. However, the role of morphological changes (e.g., colony size and tightness) in the adaptation to nutrient availability is not fully understood. In this study, we analyzed the morphological changes under both nutrient sufficiency and deficiency. Accordant morphological changes were found with both an isolated colonial strain and mixed field colonies. Colonies that were limited by nutrients became bloated and uncompacted structures, and this change was more pronounced under N deficiency. This looser morphology increased the availability of intra-colony light and relieved the size effect. When nutrients were sufficient, small colonies emerged, which helped to maintain rapid growth (0.32 day^-1). Our study highlighted probable role of morphological variations in: (1) diminishing intra-colony self-shading when facing nutrient deficiency; and (2) enlarging the population under high trophic levels by generating daughter colonies. These roles were also verified using field data from Lake Taihu, which further indicated that the seasonal succession of morphospecies was probably the result of adaptive morphological changes. Adaptive morphological changes offer advantages against fluctuations in nutrient availability, which should be considered when attempting to restrain bloom formation.