Ecological Response Of Seed Germination And Seedling Growth Of Scirpus Mariqueter To Salinity And N/P Ratio Gradients

Scirpus mariqueter is a endemic perennial plant of China.It mainly distributes in the Yangze River estuary at present.As a pioneer species in the wetland and intertidal zones,Scirpus mariqueter has many ecological functions,such as protecting the dam and providing habitat and food for waterfowls,thus,it has important ecological and economic values.Salt stress is one of the important environmental factors that limit plant growth in the Dongtan wetland of Chongming Island.At the meantime,the increase of nitrogen and phosphorus in the water due to the influence of human activities,affected the survival,growth and reproduction of plant.In this study,the seeds of Scirpus mariqueter populations in different field habitats were collected;based on the analysis of the basic characteristics of the seeds,the experiment was carried out under the controlled environments in the incubators.The effects of salt and N/P ratio gradient on the seed germination and seedling growth were studied.The main results were as follows:1.Significant differences were found in the hundred-grain weight,seed number per panicle and color of Scirpus mariqueter seeds from two habitats.The hundred-grain weight and the number of seeds per panicle from the habitat at high tide level were significantly lower than that from the habitat at low tide level.The seeds from the populations in the high tide habitat were mainly dark(brown,black)color,and the seeds from the populations in the low tide habitat were mainly dominated by light color,of which the proportion of the yellow seeds was close to 50%.2.The seed germination rate and germination index of the three color seeds of Scirpus mariqueter were different,the sequence from high to low was black seeds > brown seeds > yellow seeds.The sequence of seed germination rate and germination index of the three color seeds of Scirpus mariqueter in different habitats were high tide habitat > low tide habitat.3.The tolerance of the seeds of Scirpus mariqueter and Spartina alterniflora to salt stress were different.The tolerance of Spartina alterniflora seeds to salt stress which was from 0‰ to 20‰ was much higher than that of Scirpus mariqueter seeds(0‰-10‰).However,slight salt stress which was 5‰ in this study could make the seeds of the two species germinate earlier.4.The seed germination strategies of Scirpus mariqueter and Spartina alterniflora were different.The seeds of Scirpus mariqueter germinated slowly with long duration which in this study is 60 days and a few seeds could still germinate in 90 days.The seeds of Spartina alterniflora germinated quickly with short duration which took about 27 days.5.Salt stress inhibited the growth of Scirpus mariqueter seedlings.With the increase of salt stress,the growth rate,height and biomass of the seedlings decreased.6.Salt stress inhibited the clonal reproduction of Scirpus mariqueter seedlings.When the Na Cl concentration was 4‰,no ramets were produced,and 7.58% seedlings produced rhizomes.7.Salt stress changed the response of Scirpus mariqueter seedlings to planting densities.When Na Cl concentration was 0‰,the aboveground biomass and underground biomass decreased with planting density increase;when Na Cl concentration was 4‰,the aboveground biomass and underground biomass increased with planting density increase.8.The seedlings showed inferior performance in the phosphorus-limited environment.The growth rate,seedling height and biomass of the seedlings in the low N/P ratio(6.77:1)and the medium N/P ratio(14:1)conditions were significantly higher than those in high N/P ratio conditions(21:1).9.The high N/P ratio conditions inhibited the clonal reproduction of Scirpus mariqueter.At the high N/P ratio(21:1)conditions,no ramets produced in all conditions of planting densities,and only 8.91% seedlings produced rhizomes.