| Guangxi is the largest sugarcane growing area in China, the soils in sugarcane platations are seriously acidificated, nutrition is imbalanced and physical features are deteriorated due to continuous croping. These factors plus drought are the main limitations for sugarcane production. Previous research has proven that Arbuscular mycorrhizal (AM) fungi benefits plants by improving nutrient acquisition (especially phosphorus) and improve soil ecology. In this study, rhizosphere soils and roots of sugarcane were taken from different types of soils in sugarcane growing areas in Guangxi. AM fungi were identified/quantified by molecular method, and the basic biology of AM fungi diversity in sugarcane soils were investigated. Assessments of AM fungi colonization and infection in roots were done to elaborate the characteristic of AM fungi in roots of sugarcane in different soil types, and to analyze the effects of soil types on AM fungi diversity by soil physical and chemical properties. Based on these investigations, basic biology of AM fungi diversity in sugarcane soils and roots, and the factors that affect the AM fungi communities could be illustrated, which would provide a reference for further AM fungi utilization in sugarcane cultivation, to increase the resistance of sugarcane plants to abiotic stress and improve the efficiency of fertilizer application. The main results were as follows:1. The research collected 52 samples of sugarcane roots and 52 samples of sugarcane rhizosphere soils, including seven different types of soils in 26 cities (counties/districts) which are main sugarcane growers in Guangxi. The soil pH, organic matter, total nitrogen, available phosphorus and exchangeable Mg2+ were assessed. The results showed that the soil acidification was serious, the soils with pH6.0 or lower accounted for 61.5%, among those with pH4.0 accounted for 5.8%, pH4.0-5.0 for 28.8%, and pH5.0-6.0 for 26.9%. The soils with pH6.0-7.0 accounted for 25%, and those with pH7.0 or higher for 13.5%. The organic matter, total nitrogen and other nutrients in the soil are very low. The highest and the lowest values of the soil chemical properties were found in calcareous soil and laterite, respectively, except for available P.2. Sugarcane is a mycorrhizal type plant. The results showed that fungal hyphae infected sugarcane root epidermis efficiently. Pearson correlation analyses showed that the hyphae on root were extremely significantly and positively correlated to both internal hyphae (R=0.558, P= 0.00) and vesicles (R=0.588, P=0.588). The internal hyphae were extremely significantly and positively correlated to vesicle (R=0.435, P=0.001).3. The infection rate of fungal hyphae to sugarcane root epidermis was affected by the soil physico-chemical properties, the pH value (R=0.367, P=0.007) and the available P (R=-0.609, P=0.000) showed extremely significant negative correlation to the internal hyphae. The affected of the soil physico-chemical properties to the infection rate of fungal hyphae to sugarcane root epidermis were differences between the different soil types. The internal hyphae showed significantly negative correlations to soil organic matter (R=-0.478, P=0.028), total N (R=-0.541, P=0.011) and available P (R=-0.709, P=0.00) in latosolic red soil. Total N showed significantly negative correlation to the internal hyphae (R=-0.823, P=0.044), while the available P showed extremely significant negative correlation to the internal hyphae (R=-0.926, P=0.008)in laterite. In red soil, the pH value showed significantly positive correlation to the internal hyphae (R=0.924, P=0.008), while organic matter (R=-0.865, P=0.026), total N (R=-0.860, P=0.028) and available P (R=-0.877, P=0.022) showed significant negative correlation to the internal hyphae.4. We analyzed the molecular diversity of AM fungi using nested-PCR amplification of AM fungi 18S rDNA in sugarcane roots and rhizosphere soil samples. With 97% of the OTUs, all sequences of AM fungi were divided into 32 OTUs. They belong to 7 families, 13 genera and 32 species of AM fungi in clustering analysis, including Glomeraceae (5 genera,17 species), Diversisporaceae (2 genera,3 species), Acaulosporaceae (1 genera,1 species), Gigasporaceae (1 genera,1 species), Claroideoglomeraceae (1 genera and 5 species), Archaeosporaceae (1 genera and 2 species), Paraglomaceae (1 genera and 2 species). Among the 32 molecular species,7 are the same in morphology. Glomeraceae is dominant in all kinds of soils, followed by Claroideoglomeraceae and Paraglomaceae. Other families are relatively rare in all samples. In conclusion, the dominant family in 7 types of soils is the Glomeraceae, and Rhizophagus is the dominant genera.5. The diversity of AM fungi in different types of soils. There are 7 families,11 genera and 22 species in Latosolic red soil; 5 families,7 genera and 11 species in laterite; 4 families,8 genera and 12 species in red soil; 4 families,8 genera and 14 species in lime soil, and 5 families,9 genera and 12 species in other types of soils. The highest richness and shannon wiener index of AM fungi was found in red soil, but there were no difference in richness and shannon wiener index in the five different types of soils tested.6. Pearson correlation analysis showed that there was no significant correlation between AM fungi species richness and soil chemical properties in the lateritic, red soil, lime soil and other types of soil. In latosolic red soil, the abundance of AM fungi in roots was significantly and negatively correlated to pH (R=-0.474, P=0.03), and extremely significantly and negatively correlated to exchangeable Mg2+(R=-0.583, P=0.006).7. The distributions of AM fungi communities in roots and rhizosphere soils were significantly different. Even though there was no difference in AM fungi community structure in different kinds of rhizosphere soils, the difference of AM fungi community in the roots of latosolic red soil and lime soil was obvious. There was no correlation between AM fungi communities and soil chemical properties. |
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