ABSTRACT
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.
ABSTRACT
The soil fungal community plays an important role in forest ecosystems and is crucially influenced by forest secondary succession. However, the driving factors of fungal community and function during temperate forest succession and their potential impact on succession processes remain poorly understood. In this study, we investigated the dynamics of the soil fungal community in three temperate forest secondary successional stages (shrublands, coniferous forests, and deciduous broad-leaved forests) using high-throughput DNA sequencing coupled with functional prediction via the FUNGuild database. We found that fungal community richness, α-diversity, and evenness decreased significantly during the succession process. Soil available phosphorus and nitrate nitrogen decreased significantly after initial succession occurred, and redundancy analysis showed that both were significant predictors of soil fungal community structure. Among functional groups, fungal saprotrophs and pathotrophs represented by plant pathogens were significantly enriched in the early-successional stage, while fungal symbiotrophs represented by ectomycorrhiza were significantly increased in the late-successional stage. The abundance of both saprotroph and pathotroph fungal guilds was positively correlated with soil nitrate nitrogen and available phosphorus content. Ectomycorrhizal fungi were negatively correlated with nitrate nitrogen and available phosphorus content and positively correlated with ammonium nitrogen content. These results indicate that the dynamics of fungal community and function reflected the changes in nitrogen and phosphorus availability caused by the secondary succession in temperate forests. The fungal plant pathogen accumulated in the early-successional stage and ectomycorrhizal fungi accumulated in the late-successional stage may have a potential role in promoting forest succession. These findings contribute to a better understanding of the response of soil fungal communities to secondary forest succession and highlight the importance of fungal communities during the successional process.