Current and Historical Resource Nitrogen Supply Affects the Eco-Physiological Traits and the Ionome of a Diazotrophic Cyanobacterium

Diazotrophic cyanobacteria can overcome nitrogen (N)-limitation by fixing atmospheric N₂; however, this increases their energetic, iron, molybdenum, and boron costs. It is unknown how current and historic N-supplies affect cyanobacterial elemental physiology beyond increasing demands for elements involved in N-fixation. Here, we examined the changes in pigment concentrations, N-storage, and the ionome (i.e., multivariate elemental composition) of the freshwater diazotroph Dolichospermum flosaquae adapted to an N-gradient for two temporal scales: 27 days and 45 months. We found short-term adaptation of Dolichospermum to low N-supply decreased pigment concentrations, N-storage, N:carbon (C), and increased boron:C, calcium:C, and magnesium:C than high N-supply adapted populations. Dolichospermum adapted to low N-supplies for 45 months had higher pigment concentrations, N-storage, and lower boron:C, calcium:C, magnesium:C, and phosphorus:C than the short-term adapted populations when grown in low N-supplies. Our results highlight the connections between the ionome and physiology, identifying the previously unrecognised roles of elements that can be used to advance physiological patterns.