| More than 85% of terrestrial plant species associate with arbuscular mycorrhizal (AM) fungus. Most plant individuals stimulate nutrient availability through their fungal partner. Highly mycorrhizal-dependent plant species derive more benefits from AM fungus in comparison with plant species with a relatively low mycorrhizal dependency. Lots of research found that complex interactions among different plants species can be strongly influenced by AM fungus. Until recently, the effects of AM fungus on the competition between mycorrhizal and non-mycorrhizal plants (with high phosphate foraging ability) remained largely unclear, particularly in an environment with low phosphate bioavailability. The effects are most likely caused by alterations in the outcome of competition for soil nutrient resources between plant species that are not hosts to AM fungus and host species which can have very different response to AM symbioses in terms of changes in biomass because it is difficult to carry out long term experiments in controlled conditions. Mycorrhizal effects on plant interactions are most likely due to alterations in the soil nutrient availability. AM fungus colonization could increase nutrient (particularly phosphate) availability for host plants and consequently increase plant biomass. The larger plants are then expected to be successful competitors.In the present study, under purple soil or calcareous alluvial soil two different soil environment, different mycorrhizal-dependent plant species maize plants (Zea mays L.) or wheat (Triticum aestivuml) were cultivated with rape(Brassica napus L.) in three different interaction status, namely monoculture, intercropping and nylon net split. All the plants were inoculated with Glomus intraradices, Glomus mosseae or remained uninoculated. The strength of competition is measured as the reduction in biomass caused by the presence of a competitor. The main results as followed.(1) Maize growth and mineral nutrition was suppressed under purple soil, while the mycorrhizal dependency increased to some extent, in intercropping compared with monoculture system. In intercropping system inoculation with G. intraradices and G. mosseae significantly decreased phosphorus concentration and content of rape roots compared with non-inoculation treatments, while in contrast mycorrhizal association improved phosphorus nutrition of maize plants. The experimental results clearly showed the beneficial effects of mycorrhizal associations on AM fungus host plants in competition with non-host plants.(2) Under calcareous alluvial soil, maize and rape plants were cultivated, the results showed that mycorrhizal inoculation decreased soil inorganic phosphate significantly and transformed more Ca10-P and O-P into higher availability phosphorus form. In the intercropping treatment, the inoculation improved the growth and phosphorus uptake of maize, and meanwhile decreased the growth and phosphorus uptake of rape significantly. Our results clearly showed the strong competitive strength and phosphorus competitive strength of maize to rape, and the beneficial effects of mycorrhizal associations was due to the favorable growth of host plants over non-host plants.(3) To investigate the impacts of AM fungus on the interspecific competitions among wheat and rape, the two plants were cultivated under purple soil with the same three cropping pattern. The result showed that, inoculation with both G intraradices and G. mosseae tends to increase the shoot biomass and phosphorus uptake of wheat, also reduction shoot biomass and phosphorus uptake of rape. The results showed a strong competitive strength and phosphorus competitive strength of wheat to rape, and the beneficial effects of mycorrhizal associations was due to the favorable growth of host plants over non-host plants.(4) Under calcareous alluvial soil, wheat and rape plants were cultivated, the results showed that mycorrhizal inoculation decreased soil inorganic phosphate significantly and transformed more Cajo-P and O-P into higher availability phosphorus form. Inoculation with G. intraradices and G. mosseae significantly decreased the shoot biomass and phosphorus uptake of rape compared with non-inoculation treatments, while in contrast mycorrhizal association significantly improved shoot biomass and phosphorus uptake of wheat plants. Inoculation with AM fungus significantly increased the relative competitive strength and nutrition competitive ratio of wheat to rape. It showed beneficial effects of mycorrhizal associations to the growth coexistence of host plants and non-host plants in the ecological system. |
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