Effect of temperature and nutrients on the competition between free-floating Salvinia natans and submerged Elodea nuttallii in mesocosms

In many aquatic ecosystems, free-floating plants compete with submerged plants for nutrients and light. Being on top of the water surface free-floating plants are superior competitors for light. Submerged plants can take up nutrients from the sediment and the water column, hereby reducing these levels for free-floating plants. Global warming may change chances of successful species invasion and can alter species dominance. We studied the combined effects of nutrient loading and increased temperature on the competition between the potentially invasive free-floating Salvinia natans (L.) All. and the naturalized submerged Elodea nuttallii Planch. St. John by an outdoor mesocosm experiment under temperate climate conditions (The Netherlands) over a period of 71 days. The free-floating S. natans benefited from increased temperature and increased nutrient loading and limited the chances for the submerged E. nuttallii to take advantage of these changed conditions. S. natans substantially increased temperature in the top layer, while limiting the temperature increase below the mat. Our results suggest that with global warming, invasive free-floating plants might become more successful at the expense of submerged plants.