Study On Seed Germination Characteristics,Growth Performance,and Plant-Soil Feedback Of The Invasive Weed Sorghum Halepense In Hainan Province,China

Sorghum halepense((L.)Pers.)belongs to Sorghum of Gramineae and is perennial weed native to the Mediterranean region.It has caused serious harm worldwide and also brought great impact on food security and ecological environment in China.The first discovery of S.sorghum in Hainan was in 1921,and its populations has been outbreaking in some parts of the province since 2018.In order to clarify the causes of the outbreaking of S.halepense in some areas of Hainan,we conducted a series of common garden experiments to study S.halepense,from the points of seed germination characteristics,seedling growth and competitive ability,as well as the feedbacks of plants with soil.The main research results are as follows:1)The germination traits of seeds from outbreaking and non-outbreaking populations of S.halepense in Hainan Province were compared under different temperature,dormancy breaking and burial depth treatments.We find that the germination rate of S.halepense seeds was higher than 85%,and the germination time was shortest(2.64 d)under day and night temperature of 35℃/25℃.Concentrated sulfuric acid treatment could improve the seed germination rate.Concentrated sulfuric acid treatment,gibberellin soaking and grinding could shorten the seed germination time.The seeds on the soil surface had the highest germination rate,and germination rate decreased and germination time increased with burial depth.Under different temperature,dormancy breaking and burial depth treatments,there were no significant differences in germination rate and germination time of S.halepense seeds between outbreaking and non-outbreaking regions.2)Using the common garden approach,we compared the individual growth,competitive ability and stand-level biomass between plants of S.halepense from outbreaking populations and those from non-outbreaking populations in Hainan Province.We found that outbreaking and non-outbreaking populations of S.halepense differed in biomass when individuals were grown alone,but not when grown in competition or when three or six plants from the same population were grown together.Across populations,biomass when individuals were grown alone was negatively correlated with intra-and inter-specific competitive ability,indicating that there was a trade-off between individual growth and competitive ability.Stand-level biomass was not related to total biomass when grown alone,and intra-or inter-specific competitive ability,indicating that low biomass when grown alone and high competitive ability did not reduce the performance of S.halepense when grown in dense monocultural stands.3)Using the common garden approach,the plant-soil feedback effects of S.halepense from outbreaking and non-outbreaking populations in Hainan Province were compared.We found that the rhizosphere soil of S.halepense exerted a negative feedback effect on the growth of S.halepense.Sterilization of the rhizosphere soil could significantly increase the biomass of S.halepense,indicating that negative plant-soil feedbacks cannot limit the outbreaking of S.halepense in some regions of Hainan.Soil sample sites,S.halepense populations and population origin had no effect on the plant-soil feedback.In conclusion,on Hainan Island,the high germination rate and wide ecological breadth of germination of S.halepense seeds,the higher biomass of plants from outbreaking populations when grown alone,and the differences in environmental factors and soil management and utility regimes among different regions in Hainan,may be the important reasons why S.halepense suddenly outbreaks in some regions in Hainan in recent years.The environmental factors affected the seed germination and spread of S.halepense populations to some extent.Strengthening the planning and management of idle land in Hainan province,and controling S.halepense before the flowering and fruiting stage could be useful strategies for the prevention and control of S.halepense.