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缺水的浅层土壤是植物在脆弱喀斯特地区生长和繁殖的关键限制因素.一年生草本植物是适应喀斯特地区严苛生境的先驱,但其繁殖策略对短缺水资源和有限土壤资源的双重限制响应尚不明确.因此,在这项研究中,我们通过评估果序和种子的数量、生物量和后代种子的发芽率,研究了两种一年生的菊科草本苍耳(Xanthium sibiricum)和三叶鬼针草(Bidens pilosa)在恶劣的喀斯特土壤环境中,种子和果实物候的可塑性和后代种子萌发率.苍耳和三叶鬼针草在完整的双向随机区组设计中,设置了三种土壤深度和三种水分梯度下生长.主要研究结果如下:(1)随着土壤厚度或(和)水分的降低,苍耳的子代数量(种子和果实)和生物量显著减少(P<0.05),三叶鬼针草在水分降低时增加果序和种子的生物量.(2)苍耳的亲本经历了资源减少后,种子数量和种子生物量没有相关性,而三叶鬼针草中种子数量和种子生物量之间存在显着的正相关(P<0.05).(3)三种水分处理条件下,苍耳种子的萌发率没有随土壤厚度的减少而变化.对照条件下,随着土壤厚度的减小,三叶鬼针草的种子萌发率显著降低(P<0.05).结果表明,苍耳倾向于通过确保后代的数量和质量来提高其竞争力,以适应浅层喀斯特土壤和干燥喀斯特生境.而三叶鬼针草通过风险分担策略适应了不利的喀斯特生境,它试图产生更多更大的种子以扩大生存范围,逃离不利的生存环境,但最终在岩溶土壤资源减少的情况下以较低的种子数量和后代的萌发率结束.“,”Shallow soil with low water availability is the key limiting factor for plant growth and reproduction in vul- nerable karst regions. Annual herbs are pioneers adapted to these areas; however, little is known about the re- sponses of their seeds and infructescence, and the germination of their offspring to these limited water and soil resources. In this study, we investigated how the seed and fruiting phenology plasticity and offspring seed germi- nation 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 rate. X. sibiricum and B. pilosa were grown under three soil thicknesses and three water availability levels in a full two-way randomized block design. The key results were as follows: (1) The number and biomass of progenies (infructescence and seeds) of X. sibiricum decreased with the decline of soil thickness and/or water availability (P <0.05). The infructescence and seed biomass of B. pilosa increased with the decline of water availability. (2) Seed quantity and seed biomass of X. sibiricum showed no correlation after their parents experienced resource reductions. A significant positive re- lationship between seed number and seed biomass was observed in B. pilosa (P <0.05). (3) The offspring seed germination rate of X. sibiricum did not change with the decrease of soil thickness under three levels of water treatment. However, the offspring seed germination rate of B. pilosa decreased significantly with the decrease of soil thickness under the control water level (P<0.05). The results show that X. sibiricum tends to improve its com- petitiveness by ensuring the quantity and quality of offspring in order to adapt to the shallow karst soils and dry karst habitats. In contrast, B. pilosa adapts to the unfavorable karst habitats by a risk-sharing strategy. B. pilosa produces more and bigger seeds to in an attempt to expand its survival range and escape from the unfavorable living envi- ronment, but this results in a lower seed number and germination rate of its progeny under the karst soil resource reduction.