Effect Of Population Density And Water Variation On Sex Allocation And Phenotypic Plasticity Of Two Sagittaria Species

Sagittaria(Alismataceae)is one of the most primitive monocots plant in Alismataceae.There are more than 30 species,mostly distribute in subtropical area.In China there are about 8 species,which is divided into Lophotocarpus Subgenus and Sagittaria subgenus.The small arrowhead Sagittaria potamogetifolia and Sagittaria trifolia are kinds of weed,associated with the growth environment accompanied by crop,which are main harmful weeds.We studied S.potamogetifolia and S.trifolia as a great fecundity in different environment levels,to explore the formation and the evolutionary trend of sex and phenotypic plasticity.S.potamogetifolia belong to the evolutionary mode of the intermediate state,having both of outcrossing and selfing mating system.It is more evolutionary than the S.guayanensis,which is selfing only;Dominant mating system of S.trifolia is outcrossing reproduction,is more evolutionary species in Sagittaria genus.Evolution of gender approaches generally divided into two ways,in which hermaphroditic evolution to the intermediate state monoecy which evolving into the dioecious gender system.And Sagittaria is in the evolution of sex on andromonoecious-Gynomonoecious-dioecious gender system.It has great research value in the field of gender phenotypic.The size-dependence sex allocation has focus on male and female fitness components between the optimal allocation of resources,this kind of male and female separation species in Sagittaria genus is a good study material.However,in recent years more and more SDS theory is questioned by researches,which argue plant size is not the only reason of sex modification.The interaction between the Sagittaria and environment were studied for a period of two years,the purpose is to clarify resource allocation model and the reason.The first step in order to investigate the population density is the influence on plant resource allocation and distribution.We investigate S.potamogetifolia and S.trifolia which were carried out in Greenhouse of Wuhan University for control experiments.The S.potamogetifolia made 5 different densities populations of a total of 120 ramets and S.trifolia made 4 different densities populations of the total 80ramets which were observed and recorded for a year.Phenotypic gender(G_i)is measured by the individual plant.Through the variance analysis results showed that the size dependent sex ratio is not the only influencing factor of sex allocation.In addition,with population density decreases the number of male floral display show far more number than female floral display,resulting in a decline in male fitness gain curve.The results showed that in different population density will lead to the difference between male and female proportion is one of the important factors that cause these species phenotypic plasticity and then change to the evolution of sex and life history of plants and the reasons provided some evidence.Secondly,the depth of the water level in the study of biomass allocation of aquatic plants has been shown to play an important role.Past researches have shown that with the increase of water depth,the biomass of underground part of the plant will be reduced,and the part on the ground will increase with the increase of water depth,resulting in vegetative plants which tend to be developed,sexual propagation will allocate fewer resources.People tend to focus on the biomass and nutrient distribution,but little attention to the depth of aquatic plants for the influence of gender.Adaptive dynamic network put forward the theory of plant phenotypic changes with environmental factors to a count of equilibrium position.Therefore,we assume that the size dependent sex allocation is not only able to influence factors of distribution,to explore the depth of the water level of the aquatic plants directly or indirectly influence.To test this hypothesis,we conducted experiments on the depth of the water level control in Greenhouse of Wuhan University:(1)two very strong size difference species S.potamogetifolia and S.trifolia set five different water depth,the compared to daily floral display number,to test the fitness gain curve.(2)Length of inflorescence and sex ratios were recorded every day and analysis one by one.The results showed that in deep water level the inflorescence of plant is longer;so this result enables us to have the opposite conclusions of previous studies.The relationship between plant species and environmental factors are more concerned about most of the reproductive allocation of resources,resource allocation and sex is not enough attention.However,studies have shown that the plant will produce a series of changes with the plasticity of the density effect of population and water pressure effect.Our study focuses on the two kinds of Sagittaria in the evolution of different degree.The results showed that,two kinds of environmental factors changes phenotypic plasticity of different species which can produce two kinds of sex ratios in sagittaria.Size dependent sex allocation is one of the most important factors of plant sex allocation,but if you consider the size of the plant only will make mistakes.We realize that we should not only consider the modification of size-dependent sex allocation,but also consider other factors,such as pollination environment,water pressure and density of population.