Arbuscular Mycorrhizal Ecology Of An Indicator Species Of Vegetation Degragation, Ligularia Virgaurea, In Alpine Meadow Ecosystems

Ligularia virgaurea (Asteraceae), a perennial toxic forb for livestock, can dominate in degraded alpine meadows and is regarded as an indictor species of vegetation degradation. In the past decades, the large spreading of L. virgaurea has resulted in serious loss of ecological and economic services in alpine meadow ecosystem. Recently, the biological and ecological traits of L. virgaurea, such as population characteristics and life history strategies, have been well elucidated to establish the therotical basis for invatigating the spreading pathes and mechanisms of their populations, but less is known about arbuscular mycorrhizal (AM) fungi that are related tightly with their growth and competition. What is the relationship between the assemblage of AM fungi and population spreading of L. virgaurea? How does AM fungi colonizing the roots of L. virgaurea response to abotic factors? Whether are AM fungi involving the spreading of L. virgaurea? Based on above questions, we investigated the dynamics and driving mechanisms of AM fungal community during the spreading of L. virgaurea, and revealed the interactive influences of soil fertility and light intensity on mutualistic association between AM fungi and L. virguarea’s population. The main results of this dissertation are listed below.(1) To investigate the relationship between the assemblage of AM fungi and spreading of L. virgaurea’s population, the species composition and phylogenetic structure of AM fungal communities colonizing the roots of L. virgaurea, and its neighborhood plants, were analyzed in patches with different individual densities of L. virgaurea (represents the spreading degree). The spreading of L. virgaurea significantly reduced arbuscualr colonization, increased vesicular colonization in the roots of their neighborhood plants, but did not affect the AM colonization in the roots of themselves. Community compositions of AM fungi in both root systems were changed significantly by the L. virgaurea spreading. AM fungal communities were not only correlated with plant species composition, P availability and soil ratio of C/N, but also fitted the neutral model very well. AM fungal communities in patches with the absence and presence of L. virgaurea were phylogenetically random and clustered, respectively, suggesting that the principal ecological process determining AM fungal assemblage shifted from stochastic process to environmental filtering when this toxic plant was present.(2) To elucidate the response mechanism of AM fungi in the roots of L. virgaurea to abiotic factors, a three-year controlling experiment in an alpine meadow was conducted to test the interactive influences of light intensity and soil ferlity on AM fungi at two L. virgaurea’s density. Results showed that there were no significant effects of individual density on all measured AM variables; Shade reduced AM colonization of roots, fertilization consistently reduced the abundance of hyphae in the soil, and both factors reduced the species richness of AM fungi inside plant roots. Fertilization exacerbated the negative impacts of shade on AM fungal abundance and diversity. We observed fifteen phylotypes of AM fungi inside plant roots and ten morphotypes of AM fungal spores in the soil. Moreover, there was little congruence between the responses of fungi inside the roots and in the spore community, and active AM fungi within plant roots is more sensitive to our treatments than the asexual reproductive spores.Our results suggest that the spreading of L. virgaurea not only change the species composition of AM fungal community, but also change the main ecological processes driving AM fungal assemblage; both shade and fertilization weaken the mutualistic association between AM fungi and L. virgaurea, but the two factors have different impact strength. Our findings indicate that the spreading of L. virgaurea, soil fertility and light intensity involve indirectly in the formation of L. virgaurea’s population via regulating the mutualistic association between AM fungi and L. virgaurea. This study reported systematically the relationship between the assemblage of AM fungi and apreading of virgaurea’s population, and elucidated interactive influences of soil fertility and light intensity on the mutualistic association between AM fungi and L. virgaurea. Moreover, it provided the corresponding theoretic basis for investigating the relationship between AM fungi and formation of L. virgaurea’s population, and unserstanding the spreading mechanism of L. virgaurea from the perspective of mycorrhizal fungi.