CANCELLED - Plant zonation along a freshwater flooding gradient: The relative importance of flooding, competition, and grazing

Background/Question/Methods

Vegetation zonation is a common phenomenon along the flooding gradients of wetlands. It is reported that an inherent trade-off in species between competitive ability and stress tolerance restricts species to a certain range of the flooding gradient. Herbivory also plays a large role in shaping plant community structures. However, studies of the relative importance of flooding, competition and herbivory in shaping plant zonation have been lacking. In this study, we conducted both field and greenhouse experiments to investigate the role of flooding, competition and herbivory in determining the zonation patterns of two dominated plants in a lakeshore marsh surrounding Liangzi Lake in China. Along the flooding gradient, Carex japonica tends to dominate higher marshes while Eleocharis valleculosa often dominates lower marshes and shallow water areas. In the field experiment, treatments were created by reciprocally transplanting E. valleculosa and C. japonica into adjacent zones, as well as into their own zone, with neighbor plants either removed or not. Eleocharis valleculosa plants received an additional simulated grazing (clipping) treatment. In the greenhouse experiment, both species were planted both with and without surrounding vegetation and with and without clipping treatment in soils that were either drained or flooded.

Results/Conclusions

In the field experiment, E. valleculosa performed well in C. japonica’s zone in comparison to its own, but performed poorly when both competition and clipping was imposed. Carex japonica plants transplanted to the E. valleculosa zone did not grow as vigorously as transplants in its own zone, especially when E. valleculosa plants were removed. The greenhouse experiment showed that clipping reduced the biomass of E. valleculosa, and neighbor competition reduced its biomass only when the soil was drained. No significant interaction was found between competition and clipping for E. valleculosa. Eleocharis valleculosa competition had no effect on the above-ground biomass of C. japonica when soils were flooded. Clipping appeared to have no effect—or even a positive effect—on the above-ground biomass of C. japonica plants in drained and flooded conditions, respectively. Our results showed that biotic and abiotic factors play a significant role in mediating the plant zonation patterns of the species E. valleculosa and C. japonica in a lakeshore marsh environment. Carex japonica species are restricted to high marshes by flooding stress, while E. valleculosa species are excluded from high marshes by the combined effects of competition and grazing.