Effects Of Light And Nutrient Treatements On Three Plants Of Saussurea DC. On The Eastern Alpine Meadow Of Qinghai-Tibet Plateau

It is expected an important effect of light and nutrienrt on plant growth, livability and reproductive success within populations. The question of which resource will be selected to ensure reproductive success has attracted many researchers, especially in reference to plants in alpine environments. There are a lot of unique plants on the Eastern Alpine Meadow of Qinghai-Tibet Plateau. How to adapt to the special environment here, and what reproductive strategies appear for these species, which provide a special chance for ecologists and evolutionists. In the paper, we studied the emergence and survival rate, reproductive phenophase, reproductive allocation, traits of capitulum and seed, and the relationship between size and number of capitulum and seeds of three species of Saussurea DC. (Saussurea japonica, Saussurea parviflora and Saussurea purpurascens) under different light and nutrient levels on the eastern alpine meadow of Qinghai-Tibet plateau. The aim of this research is to understand the reproductive strategies of the plant under the extreme environment and its possible mechanism. The results showed:1. Light has significant effect on the emergence and survival rate of the three species, while the effect of nutrients is not significant. Shading can improve the emergence and survival rate while high level of light has the opposite effect.2. The flowering phenophase of this three species varied significantly under different light levels, but not varied significantly under different nutrient levels. Shading resulted in the delay of time of flowering and made the duration of flowering shorter. When the nutrient decreased, the time of fruiting turned to be delayed, and increased the percent of seed abortion furtherly.3. Different light and nutrient levels have significant effects on the traits of capitulum and seed of this three species, but each species has different response. The capitulum and seed of Saussurea japonica and Saussurea purpurascens turn to be less but bigger under lower light and nutrient level. Saussurea parviflora turn to produce bigger and more capitulums and seeds under lower light level, while turn to produce smaller but more capitulum and smaller and less seeds under lower nutrient level.4. The reproductive allocation of all three species decreased when the nutrient level decreased in both of flower stage and fruit stage. The reproductive allocation of three species has different responses to the light level. Under the shading situation, the reproductive allocation of Saussurea japonica and Saussurea purpurascens decreased, but Saussurea parviflora increased. These different responses among the three species may because of the adaption to the different natural environment.5. There is size-number trade-off of capitulum and seed of Saussurea japonica and Saussurea purpurascens, and this is related to the resource availability. Absence of resource would enhance the trade-off. There is a positive relationship between the size and number of capitulum and seeds of Saussurea parviflora, and there is no size-number trade-off and no correlation to resource level. The size-number trade-off of capitulum and seeds of Saussurea japonica and Saussurea purpurascens indicates the dependence to the environment. The plant can response to the environmental change, and maximize its fitness by adjusting the reproductive investment. To the Saussurea parviflora, there is no trade-off in its reproductive strategy. This also indicated the adaption to the shading environment.