Popis: |
The enhanced mutualism hypothesis postulates that invasive plants promote self-growth by enriching beneficial microbes to establish a positive soil feedback. However, the roles of soil microorganisms may vary with increasing time for plant growth. Research on changes in soil microbial communities over time has important implications for understanding the mechanisms underlying plant invasion. Due to the difficulty in evaluating the duration of plant growth, few studies have quantified the changes in soil microorganisms with increasing plant age. This study focuses on the invasive weed Phytolacca americana L., which has growth rings in the main root. We conducted a two-stage experiment in the field and greenhouse to explore the soil feedback changes with duration of plant growth. We determined the effects of P. americana at different ages on the soil microbial community and soil properties and performed a soil inoculation experiment to quantify the influence of soil microbes on seed germination and seedling performance. We found that the content of some soil nutrients, namely total nitrogen, total phosphorus, nitrate-N, and available phosphorus, significantly decreased with increasing growth age of P. americana, whereas the available potassium showed an opposite increasing trend. The P. americana growth age also significantly influenced the soil bacterial community structure. However, this phenomenon did not occur in the fungal community. In the bacterial community, the relative abundance of plant growth-promoting bacteria showed an increasing trend. The soil inoculation experiment had high seed germination rates and biomass accumulation when the plants were grown in conditioned soil from P. americana growth within 5 years, suggesting a positive plant-soil feedback. However, the promoting effect disappeared in conditioned soil from 10 years of age. Our findings demonstrate that plant growth-promoting bacteria significantly accumulated in the soil during the early stages of P. americana invasion, and that the strength of enhanced positive feedback may play a crucial role in facilitating P. americana invasion. This study highlights the changing nature of plant-microbe interactions during biological invasion and illustrates how bacteria could contribute to the initial success of P. americana, providing new insights into the underlying mechanisms of plant invasion.促进共生假说(Enhanced mutualism hypothesis)指出,外来入侵植物可以通过富集有益微生物建立正向土壤反馈来促进自身生长。然而,土壤微生物的作用效果可能会随植物生长时间的延长而发生变化,进一步研究这种变化对理解植物入侵机制无疑具有重要意义,但由于确定入侵植物生长时长存在诸多困难,相关研究难以开展。本研究以主根有年轮结构的多年生草本入侵植物美洲商陆为研究对象,设计了野外采样和实验室分析两部分试验以判定不同生长年限美洲商陆对土壤理化性质和土壤微生物群落的影响,并进行了土壤接种试验以量化不同生长年限美洲商陆根际土壤微生物对其自身种子萌发和幼苗生长的影响。研究结果表明,土壤中全氮、全磷、硝态氮和速效磷含量随美洲商陆生长年限的增加而显著降低,而速效钾含量则呈现明显增加趋势。研究同时发现,美洲商陆的生长年限对土壤细菌群落结构有显著影响,主要表现为一些促进植物生长的细菌类群的相对丰度呈现增加趋势,如具有解钾功能的伯克霍尔德菌属细菌,而对真菌群落结构则无明显影响。此外,土壤接种试验结果表明,接种生长1-5年生美洲商陆根际土壤的盆栽中,美洲商陆种子发芽率和幼苗生物量积累显著增加,表现出正向的植物-土壤反馈作用。然而,接种生长10年的美洲商陆根际土壤则不会产生上述促进效果。综上认为,在入侵的早期阶段,美洲商陆通过在土壤中富集生长促进菌,驱动土壤正反馈作用,从而促进其成功入侵。这项研究强调了植物入侵过程中植物-微生物相互作用效果的变化,说明了细菌在美洲商陆成功入侵中的作用,丰富了对植物入侵潜在机理的认识。. |