The Structuring Roles Of Submerged Macrophytes In Shallow Lakes And Its Response To Elevated Temperatures

Submerged macrophytes are important primary producers and play an important role in maintaining the clear-water state in shallow lakes.During the different stages of life history,submerged macrophytes have distant morphological structures and physiological activities,and these characteristics will directly or indirectly affect the habitat heterogeneity of water column.The presence of submerged macrophytes can influence the community composition of aquatic organisms,for instance periphyton,phytoplankton,zooplankton,benthic communities,bacteria,fish and so on,which can be called the structuring role of submerged macrophytes.In order to describe the structuring role of submerged macrophytes in shallow lakes,we would better combine macrophytes,environmental variables and aquatic organisms together.Climate warming significantly affects the structure of shallow lake,changes the interaction between submerged plants and other aquatic organisms,and influences the relationships among aquatic organisms.Therefore,the structuring roles of submerged macrophytes and the main feed-back loops among aquatic organisms in shallow lakes were also affected by warming.In this study,to demonstrate the structuring role of submerged macrophytes and the interactions among submerged macrophytes,water environment and biotic communities,we conducted a series of experiments:(1)How the structuring role of submerged macrophytes respond to the interactions among submerged macrophytes?(2)How the structuring role of submerged macrophytes respond to the growth forms(morphological structure)of plants?(3)How the structuring role of submerged macrophytes respond to nutrients,temperatures and plant types?(4)The effects of elevated temperatures on the structuring role of submerged macrophytes and the community of phytoplankton.(5)The effects of elevated temperatures on the interactions among primary producers in shallow lake.Our results showed:(1)Interactions among submerged macrophytes significantly affects the structuring role of submerged macrophytes in shallow lakes.Competition was more intense between macrophytes belonging to the same growth form,which can affect the structuring role of submerged macrophytes through reducing their biomass and/or height.(2)The structuring roles of submerged macrophytes differed significantly among macrophytes with different growth forms.Periphyton abundance was positively related to the leaf structural complexity of submerged macrophytes,while phytoplankton community and environmental variables did not differ notably among the growth forms of macrophytes.(3)The structuring roles of submerged macrophytes were different among seasons,which results in the different responses of periphyton community to nutrients,temperatures and plant types.In autumn and winter,periphyton community respond significantly to the morphological structure of submerged macrophytes,but not in spring and summer.(4)The presence of submerged plants can increase the resistance of phytoplankton community to winter warming,which is also a performance of the structuring roles of submerged macrophytes in lakes.(5)The structuring roles of submerged macrophytes can also be affected by the interactions among the primary producers in shallow lakes,as well as the temperature change.Warming reduced the survival and accelerated the decline of P.crispus,and also facilitated the shift from a clear-state dominated by P.crispus to a clear-state dominated by filamentous algae.Based on these results,we concluded that the morphological structure(such as growth form,leaf structure complexity and texture)and physiological characteristics(such as leaf polarity,allelochemical and nutrients release)of macrophytes,the interactions between submerged macrophytes,the interactions between macrophytes and other primary producers,and the environmental conditions(such as temperature,nutrient and seasonality)were all of great importance for the structuring roles of submerged macrophytes.The differences in the structuring roles of submerged macrophytes mainly reflect in the community structure of aquatic organisms(such as periphyton,phytoplankton and zooplankton)and the relationships between aquatic organisms and macrophytes.Our results revealed the mechanisms of the structuring roles of submerged macrophytes and its response to warming in shallow lakes.These results provide the basis for field investigations on the structuring roles of submerged macrophytes,and offer theoretical guidance for the further field investigations that how the structuring roles of submerged macrophytes and the dynamic of shallow lakes respond to global warming.