Cutting affects growth of Potamogeton lucens L. and Potamogeton compressus L

Abstract

Effects of cutting on the growth of Potamogeton lucens L. and Potamogeton compressus L. were studied indoor under experimental conditions. Plants were cut every time they reached the water surface, applying three depth treatments at which the plants were cut; halfway down the water column, at three-quarters down the water column and at the sediment–water interface. For both species short term negative effects of cutting on biomass production and survival were observed. P. lucens seemed to be the more tolerant species as only below-ground biomass was significantly lower when cutting biomass at the sediment–water interface together with a downward trend in shoot biomass at increasing cutting depth. The low below-ground biomass (less than 20% of that in the controls) was caused by the death of most plants in this treatment. P. compressus was more vulnerable with every treatment resulting in significantly lower below-ground and green shoot biomass production. The lowest biomass for P. compressus was observed when plants were cut at the sediment–water interface with values more than 80% lower compared to the controls, while cutting halfway and at three-quarters resulted in values 30–50% lower compared to the controls. Long term effects of cutting on P. lucens might occur through decreased development of the rhizome network. Long term effects on reproduction of P. compressus might be expected as flowering decreased when cut at the sediment–water interface, while turion formation only occurred in the uncut controls. Additionally, the decreased biomass production by P. compressus may lead to a competitive disadvantage in the field as fast-growing, disturbance tolerant species such as Elodea nuttallii (Planch.) St. John may outcompete the species. Creating patchiness in mowing height and frequency or applying a mowing regime that leads to reduced biomass development while species still survive might create opportunities to both maintain the water transporting function of drainage ditches while preserving the species in the system.