Calcium concentration regulates interspecific interaction of algae along the nutrient gradient

Abstract Although many studies have focused on the influence of abiotic stress gradients on biological interactions, few studies explained the effects of both resource and non-resource stress on the facilitation. We conducted a controlled experiment to study the effects of nutrient stress on the interspecific between Phormidium corium and Scenedesmus quadricauda along calcium gradient. The results showed that when the calcium concentration was high, the competitive interaction changed into positive interaction along the nutrient stress. In the stress environment, the population density is low and the encounter rate is low. Moreover, facilitation may improve the harsh environment and make it more beneficial to the beneficiary species. When the calcium concentration was low, the facilitation reached the peak under medium resource stress. This phenomenon may be caused by the interaction between salt stress and nutrient. When calcium stress was high, it may not be conducive to the absorption of nutrients by algae. While the facilitation effect may be strongest in the medium stress environment due to the relatively sufficient resource. These results emphasized the importance of non-resource stress in interspecific relationships, pointed out a new direction for the study of facilitation, and provided theoretical guidance for the prevention of freshwater blooms.