摘要：Shallow soil with low water availability is the key limiting factor for plant growth and reproduction in vulnerable karst *** herbs are pioneers adapted to these areas;however,little is known about the responses of their seeds and infructescence,and the germination of their offspring to these limited water and soil *** this study,we investigated how the seed and fruiting phenology plasticity and offspring seed germination rates of two annual Asteraceae herbs(Xanthium sibiricum and Bidens pilosa)respond to the harsh karst soil environment,by assessing the seed number,seed biomass and offspring seed germination *** and *** were grown under three soil thicknesses and three water availability levels in a full two-way randomized block *** key results were as follows:(1)The number and biomass of progenies(infructescence and seeds)of *** decreased with the decline of soil thickness and/or water availability(P<0.05).The infructescence and seed biomass of *** increased with the decline of water availability.(2)Seed quantity and seed biomass of *** showed no correlation after their parents experienced resource reductions.A significant positive relationship between seed number and seed biomass was observed in ***(P<0.05).(3)The offspring seed germination rate of *** did not change with the decrease of soil thickness under three levels of water ***,the offspring seed germination rate of *** decreased significantly with the decrease of soil thickness under the control water level(P<0.05).The results show that *** tends to improve its competitiveness by ensuring the quantity and quality of offspring in order to adapt to the shallow karst soils and dry karst *** contrast,*** adapts to the unfavorable karst habitats by a risk-sharing *** produces more and bigger seeds to in an attempt to expand its survival range and escape from the unfavorable living