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 studies explained the effects of both resource and non-resource stress gradients on the facilitation between species. We conducted a controlled experiment to study the effects of nutrient stress gradient on the interspecific relationship between Phormidium corium and Scenedesmus quadricauda under different calcium concentration. The results showed that when the calcium concentration was high, the change of interspecific relationship between the two algae along the nutrient stress gradient accorded with the SGH theory, that is, the competitive interaction changed into positive interaction. The reason for this phenomenon may be that in the stress environment, the population density is low and the encounter rate is low; secondly, facilitation may improve the harsh environment and make it more beneficial to the beneficiary species, which may enable the beneficiary species to survi...