The Study Of Variation In Resource Allocation And Reproductive Strategies Of Two Species Of Saussurea DC. With Elevation In Qinghai-Tibet Plateau

It is very important to understand and forecast the changing of plant structure and vegetation zones shift in global change.There are limitative resources during the plant whole life,so the plant has to allocate resources among growth,survival and reproduction.The mode of resources allocation can reflect the character of the plant life history,which is the core to study of plant life history.In recent years,the research on plant resource allocation mainly focuses on reproductive allocation and sex allocation.Among them,the reproductive allocation mainly focuses on the proportions of the resources allocated to breeding parts to the total resources,the factors which affects the proportions and the relationship between reproductive allocation and these factors.Sex allocation is about optimal allocation of reproductive resources between the male and female.The unique geographical and climatic conditions of the Qinghai-Tibet Plateau have created many unique biological groups.However,how these plants adapt to the stress environment of the Qinghai-Tibet Plateau and showing what kind of resource allocation strategy has aroused great interest of breeding ecologists and evolutionary ecologists.In view of this,in this paper,aimed at Saussurea katochaete Maxim,and Saussurea stella Maxim(the common species of the genus Saussurea DC and also widely distributed in Qinghai and Tibet),we measure and the analyse their growth and reproduction traits,to study the relationship between resource allocation and altitude in the population of S.katochaete and S.stella in this area.This paper explores the resource allocation patterns of two species and attempts to reveal the adaptation strategies of the two species to the alpine meadow environment.The results showed:(1)With the increase of altitude,the individual size,the number of tubular florets,and the number of pollen in the populations of S.katochaete and S.stella gradually decreased,while the weight of the tubular florets and the weight of the petals gradually increased.In a resource-constrained environment at high altitudes,two species responded to the ecological environment of alpine meadows by reducing the number of tubular florets and pollen and increasing the weight of tubular florets and petals.(2)There were different levels of allometry between the R and V at differentaltitudes.The allometric slope(exponent)of the R-V relationship decreased significantly with increasing altitude for S.katochaete;however,there was a increasing trend of relationship for S.stella.We also found a significant positive relationship between the intercept of the regression of log R on log V and elevation for S.katochaete and S.stella.The slope of two species varies with altitude,indicating that the adaptation strategy of reproductive allocation is different.(3)The variation of reproductive allocation of populations of S.katochaete was influenced by altitude and individual size.However,the variation of reproductive allocation of S.stella was mainly affected by the change of individual size.The effect of altitude was insignificant.That is,the two species have different reproductive allocation strategies at different altitudes.Due to micro environmental effects,the same altitude of the same population will produce different size of plants,thus forming different patterns of reproductive allocation.Therefore,we should pay more attention to the effect of individual size on reproductive allocation when we study reproductive allocation of plant in the alpine area.(4)The distribution of two plants in low altitude area is consistent with the theoretical prediction of SDS,larger individuals are more inclined to invest in female organs.However,in high altitude areas,larger individuals invest more resources to male functions,showing a partial male sex allocation.Even if the impact of the size for the individual is controlled,the effect of altitude on sex allocation is still significant.Therefore,external environmental factors may play a more important role in the change of sex allocation than the internal resource situation.(5)There is a trade-off relationship between the number of tubular florets and the weight of tubular florets of S.katochaete and S.stella.The larger individual size plants,the greater the number of tubular florets,but there was no consistent increase or decrease in the weight of tubular florets.Only the number of tubular florets is size-dependent.(6)With the increase of altitude,two species of pollen gradually decreased in number,by increasing the length of the style and style branches to improve the perception of stigma pollination insects to compensation,so as to compensate the influence broughtby high altitude pollinators to reduce the number of adverse factors,to some extent to improve the success rate and reproduction the ability to adapt to environmental stress.(7)The resource allocation patterns of S.katochaete Maxim.and S.stella Maxim.are closely related to the phylogeny and origin of the species.As the altitude rises,the more evolutionary S.katochaete Maxim(compared to the original S.stella Maxim)pays more attention to the output of reproduction,so as to get the greatest fitness in the limited life history.At the same time,phylogeny affects the pattern of reproductive allocation and sex allocation of two plants to change in a certain direction(both increase).