EFFECTS OF DEPTH, DURATION AND FREQUENCY OF INUNDATION ON THE EARLY GROWTH OF AN AQUATIC PLANT (MYRIOPHYLLUM OGURAENSE SUBSP. YANGTZENSE WANG)

Abstract

In lakeshore areas,inundation events are relatively unpredictable and may vary greatly in timing and duration,affecting the growth of the majority of aquatic and wetland plants.Myriophyllum oguraense subsp.yangtzense Wang is a submerged macrophyte endemic in China and grows readily in lakeshore wetlands and shallow waters of the lower Yangtze River basin.To investigate how inundation affects the early growth of this endemic species,we manipulated plants in plastic pots of 16 cm in diameter and 12.5 cm in depth respectively,and subjected to varied inundation treatments of depth(0,10,and 60 cm),duration(1 week and 2 weeks) and frequency(1 time and 2 times) in an outdoor experiment.Results showed that inundation significantly decreased plant biomass and the production of side branches,and greatly increased plant height.In contrast,plants which were never inundated had the highest plant biomass and side branch number,and had the shortest plant height.Plant biomass,branch number,and plant height significantly decreased with the increasing of water depth.On the other hand,as duration of inundation increased,plant biomass and side branch number decreased significantly.Plant height was affected by both water depth and duration.As the duration of inundation prolonged,plant height increased in shallow water treatments(10 cm) but decreased in deep water treatments(60 cm).With increasing frequency of inundation,plant biomass increased in shallow water × long-lasting duration treatments(10 cm,2 weeks) and deep water × short-lasting duration treatments(60 cm,1 week),and more side branches were produced.Additionally,plant height was affected by the interaction of water depth and frequency of inundation.Under high frequency of inundation,plant height decreased in shallow water treatments(10 cm) and increased in deep water treatments(60 cm).Notably,root mass ratio,leaf mass ratio and branch mass ratio decreased while stem mass ratio increased under inundation treatments.Our data revealed that inundation greatly depressed both the production of plant biomass and number of side branches,but facilitated the elongation of stem.Specifically,prolonged inundation improved plant height,whereas short-lasting inundation resulted in a lower biomass and less number of side branches,and higher inundation frequency improved an increase of biomass and number of side branches.This indicated that the early growth performance of the studied species depended on the specific characteristics of the inundation conditions,which might shed light on the environment-plant interaction in relation to inundation regime.