Facultative grazing and bioturbation by macrodetritivores alter saltmarsh plant-plant interactions under stress

The importance of positive plant-plant interactions is generally suggested to increase towards more stressful conditions, due to mutual stress amelioration between plants. Bioturbating macrodetritivores can also ameliorate stress through bioturbation, but can also become selective herbivores under food-limited conditions, making the outcome of plant-plant interactions under stress in the presence of macrodetritivores unclear. We studied how combining environmental stress (waterlogging) with the presence of the soil macrodetritivore Orchestia gammarellus affected the outcome of the interaction between two salt marsh plants: the tall, late successional Elytrigia atherica and the shorter, early successional Festuca rubra. In a replacement design competition experiment under controlled conditions, we found that soil redox potential was negatively affected by waterlogging and positively affected by the presence of O. gammarellus. The survival and shoot biomass of E. atherica was not signific...