Warming and increased nitrogen concentrations are expected scenarios in the near future as consequences of the global climatic changes. This may reduce submerged macrophyte growth due to an increase in periphyton biomass, which could significantly affect the function of freshwater ecosystems. However, little is known about the role of increased nitrogen for the growth of macrophytes under warming in shallow phosphorus-enriched lakes. 

To investigate the effects of warming on the growth of two macrophyte species (Potamogeton crispus Linn. and Elodea canadensis Michx.) and periphyton on the two species in eutrophic experimental mesocosms with high phosphorus levels, Ph.D. student LIU Yang, supervised by Prof. CAO Yu and Juan Pablo Pacheco from the Wuhan Botanical Garden, conducted a microcosm study on plant and periphyton traits by using an experimental heating facility across warming in spring and early summer (summer showed higher nitrogen loading) in Denmark.  

The experimental heating facility has run for a period of 15 years where mesocosms are warmed up according to Intergovernmental Panel on Climate Change scenarios (IPCC) A2 (ca. + 3 ℃) and A2 +50% (ca. + 4.5 ℃, called A3 in this study) relative to ambient conditions (CK).    

Results revealed that the plant traits of P. crispus and E. canadensis responded differently to warming and that the growth of E. canadensis and asexual reproduction of P. crispus increased with warming in both seasons. 

Interestingly, they also found that periphyton biomass was low in the A3 treatment in early summer, but not in spring.  

This study indicates that the two macrophytes show different growth patterns under warming, E. canadensis will spread more in warming future, while P. crispus will produce more turions instead. In addition, warming negatively affects periphyton biomass in early summer under high nitrogen loading.  

This research was supported by the National Natural Science Foundation of China. Results have been published in Hydrobiologia entitled "Responses of submerged macrophytes and periphyton to warming under two nitrogen scenarios: A microcosm study". 

Experimental design with natural P. crispus (white triangles) and E. canadensis (white squares) and their artificial mimics (in blue) (Image by LIU Yang)