How do water depth and harvest intensity affect the growth and reproduction of Elodea nuttallii(Planch.)st.John?

Aims both high and low densities of macrophyte vegetation can impair its ecosystem service function.Harvesting is often applied to macrophyte vegetation to maintain an appropriate density.Vegetation harvesting has occasionally gone awry and caused catastrophes,such as vegetation disappearance and cyanobacterial dominance in waterways and lakes.because water depth influences macrophyte density at all life stages,the simultaneous influences of harvesting and water depth should be carefully examined.Thus,this study aims to quantify the effects of differently harvesting Elodea nuttal-lii on its growth and reproduction at different water depths in field experiments.Methods Four harvest intensities(harvesting E.nuttallii plant heights equal to 25%,50%,75%and 100%of the water depth)were applied to E.nuttallii growing at four different water depths(60,90,120 and 150 cm).Plant length and root length were measured.The node number,root number of each plant and number of floating plants were counted before harvesting.The harvested plant were dried to a constant weight for dry weight determination.Important Findings The rate of increase in the length and shoot number of E.nuttallii varied from−0.012 to 0.440 day^(−1) and from−0.020 to 0.639 day^(−1),respec-tively.Water depth>150 cm would limit E.nuttallii growth.Elodea nuttallii responded to increasing water depths and low-intensity har-vesting by increasing internodal length and decreasing shoot number.The larger internodal length of E.nuttallii observed in relatively deeper water was also induced by the physical strain generated by its buoy-ancy as its specific gravity was less than water’s.The physical mecha-nism of removing the plant canopy by harvesting decreased E.nuttallii buoyancy and prevented floating.Harvesting increased plant produc-tion in shallow waters<90 cm deep.moreover,it is also necessary to perform three medium-intensity harvests at a water depth of 120 cm and one low-intensity harvest or no harvesting at a water depth of 150 cm to achieve longer lifetimes and less biomass near the water surface when the plants reach or approach the water surface.