Ecobiological Mechanism Of Seeds Germinated In Autumn Of Erodium Oxyrhynchum In Junggar Desert

Winter annual plants are whose seeds germinate in autumn,which plays an important role in maintaining the diversity of desert areas and ecological functions such as windbreak and sand fixation.Especially with climate change,the coverage and density of winter annual plants are increasing,which plays an increasingly important role in the population.Therefore,it is great significance to study the formation mechanism of seeds germinated in autumn for further predicting desert vegetation dynamics under climate change and enriching winter annual plant seed germination strategies in temperate desert.We found that Erodium oxyrhynchum is the most common winter annual plant in Junggar desert.The existence of this species plays an important role in the stability and maintenance of desert ecosystem.Therefore,in this study,the dominant species germinated in autumn was selected.Combined with field investigation and indoor control experiment,the ecological and biological mechanism of seeds germinated in autumn was discussed from two aspects of ecological factors and biological factors,and whether seeds germinated in autumn is an important reason for the expansion and continuation of its population.The conclusions are as follows:First,important status of E.oxyrhynchum among species germinated in autumn in Junggar desertBased on the investigation of 14 sample plots in Junggar desert for two consecutive years,28 species germinated in autumn were found,accounting for 33.73% of the total species.Among them,the important value of E.oxyrhynchum was in the forefront of all species germinated in autumn,indicating that it occupied an important position in in species germinated in autumn.Second,the growth,survival and competition ability of plants germinated in autumn were significantly higher than that plants germinated in spring(1)The ecobiological characteristics of plants germinated in spring and autumn were significantly different in different growth stages.At seedling stage and mature stage,the plant height,root length,leaf number,seed number and biomass of plants germinated in autumn were significantly higher than that plants germinated in spring,but there was no significant difference in biomass allocation ratio of each organ between plants germinated in autumn and plants germinated in spring.(2)In the community,plants germinated in autumn had more survival advantages than plants germinated in spring,and the competitiveness of plants germinated in autumn was higher than plants germinated in spring.With the increase of distance level,the intraspecific and interspecific competition intensity showed a decreasing trend,and the competition was more intense in the range of 0-10 cm.Third,ecological factors of seeds germinated in autumn of E.oxyrhynchum(1)In natural habitats,the variation coefficient of precipitation in the autumn of2009-2020(9-11 months)is less than that in spring(3-5 months).It shows that the precipitation in autumn is relatively stable and the smaller the coefficient of variation of autumn rainfall,and the greater the important value and distribution frequency of E.oxyrhynchum.(2)Under natural conditions,the density and survival rate of E.oxyrhynchum germinated in autumn were positively correlated with soil water content in autumn.Indoor seed germination experiments also showed that seed germination was very sensitive to soil water content and temperature.When soil water content was 5%,seeds could not germinate,and the germination rates of seeds at 0/5 ? and 20/40 ? were significantly lower than other temperature gradients.It can be seen that high temperature and low temperature can inhibit seed germination.(3)Intraspecific competition also has a certain impact on seed germination,with the increase of planting density,the germination rate of seeds in autumn shows a downward trend;interspecific competition also has a certain impact on seed germination,with the increase of adjacent species density(Alyssum linifolium),the germination rate of seeds in autumn also shows a downward trend,indicating that intraspecific and interspecific competition will restrict the germination time of seeds.Forth,biological factors of seeds germinated in autumn of E.oxyrhynchum(1)83 species were found in the study area,including 10 fruit types.Among them,there are 7 fruit types could germinate in autumn,which are easy to spread.For example,the fruit type of E.oxyrhynchum is capsule,and its propagules have attached hairs,which can spread by wind.It is easy to crack,for example,the fruit of Brassicaceae is pod,which is easy to crack at maturity.(2)The results showed that there was no significant difference in 100 seed weight among different plant parts of 10 autumn sprouting species.There was significant difference in seed yield among different plant parts,of which 64.24% seeds were produced from the upper part of the plant.The seed germination rate of different plant parts had the trend of upper > middle > lower.The seeds produced from upper part of the plant had strong diffusion ability,and the seeds produced from middle part of the plant had strong diffusion ability The lower seeds spread nearby and the germination rate was low,which could effectively alleviate the intraspecific competition.(2)The results showed that there was no significant difference in 100 seed weight among different plant parts of 10 species germinated in autumn;there was significant difference in seed yield among different plant parts,among them,64.24% seeds were produced from the upper part of the E.oxyrhynchum;the germination rate of seeds from different plant parts had the trend of upper > middle > lower in autumn;the seeds produced from the upper part of the plant had a higher germination rate.This strategy can effectively alleviate intraspecific competition.(3)The germination rate of seeds produced in 2018 is only 15%,while the germination rate of seeds produced in 2019 and 2020 is more than 80%,indicating that the life span of seeds in soil is limited,so they must seize the appropriate germination opportunity in the limited life to improve their survival probability.(4)The results showed that there was no significant difference in germination rate between plants germinated in autumn and spring,indicating that maternal effect could not significantly affect the germination time of offspring seeds.In conclusion,the ecological factors of E.oxyrhynchum germinated in autumn were mainly due to the small fluctuation of autumn precipitation,and the suitable soil water content and temperature;The germination rate of seeds in autumn decreased with the increase of their own seed density and neighbor species density,so in order to reduce intraspecific and interspecific competition,they chose to germinate in autumn.The results showed that the main biological factor was that the fruit type was easy to crack and spread;the yield of upper position seeds was significantly higher than that of middle and lower position,and the upper seeds were easier to germinate in autumn;The germination rate of seeds decreased significantly in the third year of storage,which indicated that the life of seeds was limited.In order to improve the survival rate of seeds,it was necessary to seize the appropriate time to germinate when there was vitality;the maternal effect had no significant effect on the autumn germination of offspring seeds.The growth,survival and competitiveness of plants germinated in autumn were significantly higher than that of plants germinated in spring,which showed that the benefits of autumn germination were greater than that of spring germination.