Calcium Concentration Regulates Interspecific Interaction of Algae Along the Nutrient Gradient

Although many studies have focused on the influence of abiotic stress gradients on biological interactions, few have examined the effects of both resource and non‐resource stresses on facilitation.

We conducted a controlled experiment to study the effects of nutrient stress on the interspecific interaction between Phormidium corium and Scenedesmus quadricauda along calcium gradient.

The results showed that elevated calcium concentration changed the interspecific relationship among algae with nutrient stress. When the calcium stress was low, the relationship between P. corium and S. quadricauda changed from competition to facilitation with the increase of nutrient stress gradient. In a nutrient‐stress environment, the population density and the encounter rate are typically low. Facilitation improves these harsh environments and makes them more beneficial for the beneficiary species.

When the calcium stress was high, facilitation peaked under medium resource stress. This phenomenon may be caused by the interaction between salt stress and nutrients. High calcium stress is conducive to the absorption of nutrients by algae. The facilitation effect is strongest in a medium calcium stress environment owing to relatively sufficient resources.

These results emphasize the importance of non‐resource stress in interspecific relationships, highlight a new direction for the study of facilitation, and provide theoretical guidance for studying the influencing factors of algal competition.