| Xanthium italicum Moretti and Xanthium sibiricum Widd are annual herbs of the genus Xanthium L.in Compositae.The X.italicum was first discovered in China in 1991.Since then,the X.italicum has spread rapidly in China,causing serious damage to the biodiversity and agricultural production in invaded areas.It was listed as an entry quarantine pest in China in 1997.A large number of studies have shown that the ecological characteristics of seeds have great significance for the growth,reproduction and diffusion of plants.Therefore,the ecological characteristics of X.italicum seeds were studied and compared with the native plant X.sibiricum,in order to explore the seed ecological basis of its successful invasion and rapid spread.The results of this experimental study are as follows:1.From the early to the middle of maturity,the weight,length and width of the fruits of the two plants showed a significant increasing trend,compared with the involucre ratio of X.sibiricum(about 61-69%).The X.italicum has a larger proportion(about 63-80%),so the fruit of the X.italicum has a larger volume and quality than the X.sibiricum,which reduces its chance of falling into the deep soil through the soil gap.At the same time,after measuring the water absorption of the two plant fruits after 10 hours of water immersion,it was found that the I X.italicum fruit can use its involucre to store more moisture(48%)than X.sibiricum(36%)in suitable conditions,which helps it to the environment effectively captures moisture and facilitates the germination of internal seeds.2.By comparing the seed vigor(germination percentage)of different maturity(early,middle and late maturity),we found that the germination percentage of X.sibiricum in the early and middle stages of maturity was low,only 50% of the X.italicum.And the seeds of X.italicum had no dormancy,the fruit is dehydrated after it matures,and it can germinate once it is placed in a suitable environment.3.The seeds of X.italicum and X.sibiricum are fully mature from September to October each year,and the canopy seed bank can be maintained for 9 months after maturity.It was found that the fruit of X.sibiricum dispersed nearly 65% of the fruit within 1 month(September-October)after full maturity,and the storing percentage of the canopy seeds was only about 16% in March of the following year.However,the dispersal percentage of X.italicum fruits in the year of maturity was only 34%,66% of the fruits stored to the next year,and intensive dispersal(56.7%)in April of the following year.In view of the fact that the seeds of X.italicum do not have dormant habits,so the large-scale canopy seed bank and centralized dispersal in spring will be important for the effective germination and seedling survival of the seeds.At the same time,the X.italicum has a more developed diffusion structure.In the wild,the fruits scattered on the surface of the earth are often distributed in groups.Therefore,animals and gravity act as their diffusion media,which make them have advantages in long-distance and short-distance diffusion.4.X.italicum and X.sibiricum showed different adaptive strategies to different environmental factors(temperature,light,soil moisture and soil salinity):(1)The temperature ecological amplitude of two plants seeds were very broad in the germination stage,and both can germinate in the environment of 10-35?.The seeds of the X.italicum had more germination advantage than X.sibiricum whether in the high temperature or low temperature environment.Among then,in the low temperature(10-15?)environment,the germination percentage of X.italicum was significantly greater than that of X.sibiricum,and in the high temperature(30-35?)environment,except the X.sibiricum upper seeds(65%),the germination percentage of other three types of seeds was as high as 100%.However,the high temperature promotes the rapid growth of X.italicum.Therefore,the X.italicum is more adaptable to the ambient temperature,and it can be quickly germinated into seedlings from the early spring to the midsummer by using any favorable conditions such as precipitation and warming.(2)The seeds of X.sibiricum were light neutral seeds,and the X.italicum was more sensitive to light than the X.sibiricum.In the deep soil environment,the germination percentage of X.italicum seeds is only 40%.However,when the seeds in the deep soil approach the surface layer of the soil due to interference,the germination percentage can reach 100%,which makes it often invade areas with frequent disturbances.At the same time,in the environment under the canopy of canopy,the germination percentage of X.italicum seeds is 66%,which may be an adaptive countermeasure for avoiding intense interspecific or intraspecific competition after seedlings are unearthed.(3)The seed germination of X.italicum and X.sibiricum has a wide tolerance to soil moisture.Under the condition of 35% PEG concentration,nearly 40% of the lower seeds of X.italicum can still germinate,and the germination index of X.italicum seeds were higher than X.sibiricum.When the soil moisture is abundant,the germination percentage of the upper and lower seeds of X.italicum and X.sibiricum can both reach 100%.When the soil water potential decreases,the germination percentage of four types seeds were significantly lower,the upper and lower seeds is,and the germination percentage of the upper seeds were significantly lower than the lower seeds,and the seeds of germination of X.italicum were higher than X.sibiricum.Therefore,the broad water demand is an important reason why the X.italicum population can expand rapidly.(4)Both X.italicum and X.sibiricum showed strong salt tolerance during the seed germination stage.With the increase of soil NaCl concentration(NaCl concentration of 160-280 mmol/L),the germination percentage of the two plant seeds decreased significantly,but the germination percentage and germination index of X.italicum were significantly higher than that of X.sibiricum.At the same time,the germination percentage of the upper and lower seeds of X.sibiricum was significantly different under most treatments,which indicated that the tolerance of X.italicum to soil salinity was significantly stronger than that of X.sibiricum in the seed germination stage,making the seeds of the exotic plants can still establish a large population in a moderately salinized soil.(5)The seeds of X.italicum are large in size and rich in nutrients.The content of soluble protein is significantly higher than that of the X.sibiricum,and the content of soluble sugar and fat in seeds is not different.This phenomenon may be the physiological advantage that the X.italicum can quickly germinate and grow rapidly.In summary,X.italicum has a large proportion of involucre,which is conducive to store more water effectively from the environment for seed germination.The canopy seed bank is remarkable,and can be maintained until the spring of the next year,so that it will fall off when the time is favorable for seed germination.The diffusion structure of involucre is developed,so it suitable for long-distance transmission by animals.X.italicum seeds are large and rich in nutrients,and the soluble protein content is significantly higher than that of the same genus X.sibiricum.The tolerance of X.italicum to temperature,soil moisture and soil salinity during seed germination stage are significantly higher than X.sibiricum.Therefore,these advantages have significantly improved the germination of X.italicum seeds and the successful colonization of seedlings,providing a guarantee for the successful invasion and rapid expansion of its population.In summary,the X.italicum has a large-scale planting seed bank,the large proportion of involucre accounts for more water;and the structure of involucre is more developed and the seeds are easy to spread and have no dormancy;the seeds are rich in nutrients,and the soluble protein content Significantly higher than the X.sibiricum.The X.italicum has strong tolerance to temperature,soil moisture and soil salinity,significantly increased the germination of its seeds and the successful colonization of seedlings,the probability of successful seedling colonization guarantees the successful invasion and rapid expansion of X.italicum. |
PDF Full Text Request