A Study On The Adaptive Phenotypic Plasticity Of Two Elsholtiza Species

The phenotypic plasticity of Elsholtiza densa was determined under different microsites (disturbtions) in theTibetan Plateau, and estimated the vegetative and reproductive traits of Elsholtiza densa to reveal the different cause paths through the maternal investment regulating fitness in the different environments. The results showed that influences of vegetative traits on fitness changed in different environment. Individual plant size was positively related to fitness significantly in the open site and the simulated grazing pasture (P<0.05). The above biomass was positively correlated with fitness slightly only in simulated grazing pasture, but not in other sites. Delayed onset of flower was positively related to fitness slightly in no grazing pasture. Reproductive traits also displayed different regulating effect on final reproductive output across experimental environments: the amounts of spikes were positively related to fitness in the open site , but there was no spike differentiation in other sites. Spikelet amounts were positively related to fitness significantly in different environments (P<0.05). The spikelet weight were positively correlated with fitness only in the simulated grazing pasture (P<0.05), and the abortion rate was not related to fitness in different environments (P<0.05). Generally, the correlations among traits of Elsholtiza densa and the cause paths of maternal investment were plastic for the changed environments.Adaptive differences among species were often thought to result from the differences of constant developmental traits. But others believed that plastic and developmentally constant traits contribute to the adaptive differences. We compared internode lengths and node number across two field density treatments in Elsholtiza feddei and Elsholtiza densa, and analyzed the impact of two traits on the fitness. In the high-density treatment Elsholtiza densa increased internode length and had more nodes than Elsholtiza feddei, so Elsholtiza densa plants had higher fitness in this treatment. By contrast, Elsholtiza densa had more nodes than Elsholtiza feddei, and internode lengths were virtually identical in both species in the low-density treatment, so Elsholtiza densa had higher fitness in this treatment. Generally, the constant trait and the plastic traits difference jointly contributed to Elsholtiza densa's greater fitness in the high-density treatment, and the constant trait difference contributed to Elsholtiza densa's greater fitness in the low-density treatment.