Impact of arbuscular mycorrhizal fungi on the physiology of maize genotypes under variable nitrogen and phosphorus levels.

摘要

Increasing crop production to ensure future food security while reducing environmental pressure on agro-ecosystems requires improved water and nutrient use efficiency. The soil microbial community directly and/or indirectly has important consequences on food security since soil microbes participate in several soil processes. Thus, it is important to increase our understanding of AM fungal and maize genotype interactions, the impact of N and P fertilization and water condition on the symbiosis, and on the physiology and nutritional status of maize plants. In two greenhouse experiments AM inoculated plants exhibited root colonization values around 70% which was confirmed by the presence of the AM lipid biomarker (C16:1cis11). Nitrogen fertilization increased AM root colonization, but only compared to unfertilized plants. Root colonization and biomarker concentration in root and soil were similar among inoculated maize genotypes across conventional and drought tolerant hybrids. Mycorrhizal inoculation had a positive impact on maize plant P uptake, but neither increased N uptake nor chlorophyll content in leaves. Nitrogen fertilization increased P concentration in plant tissue under AM inoculation, but decreased P concentration under non-inoculated conditions. There were positive plant biomass and chlorophyll responses as N fertilization increased, but not for P fertilization. Except for increased P uptake, results from both greenhouse studies are inconclusive about why most of the parameters evaluated were unresponsive or negatively affected by AM inoculation. In a field experiment, indigenous AM fungi effectively colonized maize roots to the same magnitude regardless of maize genotype and soil water condition. Increased soil extramatrical AM biomass, suggesting greater C allocation from plant to AM fungus, was observed under water-limited conditions and also among maize genotypes. In addition, while water limitation caused a shift in the overall soil microbial community, maize hybrids influenced specific microbial groups. Bacterial and actinomycete markers, and also total microbial biomass significantly increased under water stress. Interactions among AM fungi, plants and nutrients appear to be complex making plant responses to AM fungi difficult to predict and explain. Further studies on the mechanisms involved are needed to gain further insight into the complex relationships among AM fungi, maize and soil fertility management to maximize benefit from the AM fungi/plant symbiosis.