不同氮添加对入侵植物瘤突苍耳和本地近缘植物苍耳及两者杂交种的生长影响

土壤养分对外来植物入侵过程的影响是入侵生物学研究的一个热点,但土壤养分对入侵植物和本地植物杂交后代植株特性的影响鲜有报道。本研究采用盆栽实验,通过添加不同浓度的N,改变土壤养分,比较入侵植物瘤突苍耳和本地近缘植物苍耳及两者的杂交种(杂交瘤突苍耳和杂交苍耳)在植物形态、生物量及分配、植株生长和叶片光合特性等方面的差异,探讨这些差异与入侵性的关系。结果表明,氮添加显著提高了瘤突苍耳、苍耳和杂交种的茎粗、总叶面积、总生物量、根生物量、茎生物量、根生物量比和根冠比,显著降低了4种植株的叶根比;瘤突苍耳各指标随氮含量增加而变化明显,苍耳和杂交苍耳的茎生物量比和叶生物量比下降显著;瘤突苍耳的净同化速率在不同氮处理下均显著高于苍耳,但叶面积比均显著低于苍耳;杂交后代植株的相对生长速率、净同化速率和平均叶面积比在各氮处理间均高于各母本的后代植株,同时杂交瘤突苍耳植株的各生物量指标和生长指标均显著高于杂交苍耳植株。由此可见,1)当养分是限制条件时,入侵植物瘤突苍耳相对于本地植物苍耳将较多生物量分配到根系,这种分配策略反映入侵植物对低养分环境有较高的适应性;2)以瘤突苍耳为母本的杂交后代植株较以苍耳为母本的杂交后代植株具有较强生长能力和繁殖能力,可以进一步加强其入侵。

Effect of nitrogen treatments on growth of the invasive plant Xanthium strumarium,the native plant Xanthium sibiricum,and their reciprocal crosses

The effect of soil nutrients on the invasion of alien plants is a hot topic in invasion biology research, but few studies have focused on the effects of soil nutrients on the characteristics of reciprocally crossing plants.In this study,we analyzed the differences in biomass accumulation and distribution,growth character-istics ,and photosynthetic characteristics of the invasive plant Xanthiumstrumarium,the native plant Xanthi-umsibiricum,and their reciprocal crosses (Xst♀× Xsi♂ and Xsi♀× Xst♂)under different nitrogen treat-ments,to explore the relationship between invasion and soil nutrient status.The stem diameter,total leaf are-a,total biomass,root biomass,root biomass ratio,and root mass/crown mass ratio of X.strumarium,X. sibiricum,and their reciprocal crosses (Xst♀×Xsi♂)increased significantly (P<0.05)and the leaf area to root mass ratio decreased significantly (P<0.05)with increasing nitrogen levels in the soil.The net assimila-tion rate ofX.strumariumwas significantly higher than that ofX.sibiricum(P<0.05),but its specific leaf area was significantly lower than that of X.sibiricum (P<0.05).The relative growth rate,net assimilation rate,and mean leaf area ratio were higher in the male progeny than in the female progeny (P<0.05),and the biomass index and growth index were higher in Xst♀×Xsi♂plants than in Xsi♀ × Xst♂plants.We conclu-ded that:1 )when nutrients are limited,X.strumarium distributes more biomass to the root,possibly as an ecological strategy to adapt to nutrient-heterogenous environments during invasion.2 )Compared with the hy-brid progenies of X.sibiricum,those of X.strumarium show stronger growth and increased reproductive abil-ity,which are properties that will further strengthen their invasiveness.