Effects Of Seed Mucilage On Germination And Seedling Establishment Of Nepeta Micrantha

In the Gurbantunggut Desert of Northwest China,the life cycle of ephemeral plants in early spring can be completed in 2?3 months,which play an important role in the stabilization of wind erosion on the surface of sand dunes in spring.Nepeta micrantha is an ephemeral plant in Gurbantunggut Desert.As an important seed trait,seed mucilage layer plays an important ecological role in plant life history.Studies on the ecological functions of seed mucilage layer mainly focused on mucilage composition,seed dispersal and seed settlement,while studies on the ecological functions of seed mucilage layer in the process of seed germination and seedling growth are less to known.Through field investigation and indoor pot experiments,the morphological structure of seed mucilage layer in N.micrantha,meanwhile,the ecological function of mucilage on seed germination,seedling emergence and growth of N.micrantha were systematically studied and revealed.The results were as follows:1.The seed mucilage of N.micrantha is a flocculent fiber attached to the seed coat before absorbing water,and then wrapped on the seed surface as a divergent fiber after absorbing water.There are three stages of seed water absorption:(1)faster water absorption,(2)slower water absorption and(3)stopped water absorption.The water absorption rate and maximum water absorption of seeds with mucilage are significantly higher than those of seeds without mucilage.2.The germination rate of N.micrantha seeds was the lowest under dark conditions,and the mucilage layer had no significant effect on the germination rate of seeds under different light conditions;the seed germination rate of N.micrantha firstly increased and then decreased with the increase of temperature change cycle.The optimum germination temperature was 10/25~oC under 12/12 h light/dark condition,and the germination rate could reach 76%.The mucilage had no significant effect on the seed germination under different temperature change cycle.3.The germination rate of intact and demucilaged seeds decreased with the increase of PEG concentration.However,at the same PEG concentration,there was no significant difference in the germination rate between the intact and demucilaged seeds except for 15%PEG.After 15%PEG treatment,the germination rate and final germination rate of intact seeds were significantly higher than those of demucilaged seeds.The germination rate of intact and demucilaged seeds decreased with the increase of Na Cl concentration.At the same Na Cl concentration,there was no significant difference in germination rate between intact and demucilaged seeds except for 100 mmol/L Na Cl treatment.Under100 mmol/L Na Cl treatment,the germination rate of intact seeds was significantly lower than that of demucilaged seeds.4.In terms of seedling emergence,compared with low water(80 ml)and high water(160 ml),medium water(120 ml)treatment had higher dry matter accumulation.Soil microorganisms and seed mucilage could significantly promote seedling emergence under three water conditions,and the interaction between them was more significant under low water conditions.The biomass of N. micrantha seedlings with mucilage seeds was the highest under the condition of soil microorganism and medium water content.5.The interaction of water,mucilage and soil microorganisms significantly affected the aboveground biomass of N.micrantha.The dry matter accumulation of medium water(120 ml)treatment was higher than that of low water(80 ml)and high water(160 ml)treatment.Soil microorganisms and seed mucilage could significantly promote plant growth under low and medium water conditions.The plant biomass of N.micrantha was the highest under the conditions of medium moisture,soil microorganism and intact seed.The above results showed that seed mucilage played a key role in the process of water absorption,which helped to absorb water quickly and effectively.The results showed that seed mucilage could significantly reduce the germination rate and final germination rate under moderate osmotic stress,suggesting that seeds of N.micrantha would adopt"cautious strategy"under osmotic stress and "opportunity strategy"after releasing stress,which is a mixed strategy under extreme desert conditions with unpredictable precipitation.Under drought conditions,mucilage can interact with soil microbes to promote the early emergence of plants.