Flaveria bidentis,an exotic plant with strong invasiveness, spreads at most regions of Tianjin, Hebei, Henan and Shandong Province, China, and many evidences prove that it has high potential to expand to other provinces. According to recent studies, F. bidentis is a typical species with arbuscular mycorrhizal (AM) symbiosis and AM symbiosis can alter host plant-water relationships under both well-watered and drought stress conditions by providing water for their hosts thus enhancing the tolerance of the host plants to water deficit. F. bidentis can dominate in a wide range of habitats, such as agricultural land, orchards, lawns, roadsides, watersides and waste ground, and can rapidly form dense nearly monospecific stands within several years. However, it is not clear whether its high invasive potential is due to this plant-fungal symbiosis, especially under drought stress.
The present study is to verify the effect of AM fungi on the growth and drought resistance of F.bidentis in its invaded process, and to understand the mechanism involved. Four water conditions were designed in this pot experiment: waterlogging(soil relative water content 120%), normal irrigation(80%), moderate stress (60%) and severe stress(40%), and at each water treatment, both sterilization and no sterilization was contained through adding fungicide benomyl to control AM fungi.Each treatment was repeated three times.
The results showed that water stress significantly inhibited the growth of F.bidentis such as plant height, main root length and biomass regardless of fungicide treatment, but infection rate was not affected by water tress. Under different water regimes, fungicide significantly decreased mycorrhizal infection rate and water preservation in leaves. Activity of protective enzymes and total N, P content, soluble sugar, soluble protein significantly decreased with fungicide treatment, while leaf malondialdehyde (MDA) content was significantly increased. The utilization rate of available N and P were higher at no sterilization treatment and total N, P content of F.bidentis plant were significantly enhanced. Simultaneously, the degrees of host plant benefits from AM fungi were affected by environment conditions. The contribution rate of mycorrhizal to host plant related to the extent of water stress, being 1.84 and 1.88 times higher at severe stress than those at waterlogging condition respectively.
It is concluded that mycohrrizal associations may significantly related to the invasion history of F.bidentis in newly reclaimed habitats. Mycohrrizal associations could improve the ability of F.bidentis to withdraw the adverse conditions. AM fungi increased soil water and mineral nutrient uptake and improved plant physiological metabolic activities, thus promoting drought resistance and growth of F.bidentis.
The results provided the basis for the invasion mechanism and making effective management measures of F.bidentis, meanwhile, it is also a basic research of great significance on AM fungi.