The Diversity Of Arbuscular Mycorrhizal Fungi In Yellow-Brown Soil Citrus Orchards

Arbuscular mycorrhizal fungi (AMF) are important components of rhizosphere microbial communities, colonizing the host plant roots and forming arbuscular mycorrhiza (AM) association. The symbioses can affect the host plant on enhancing the resistance and the competitive ability for the adverse environment or the new environment by improving plant’s absorbency on nutrients and moisture. Thus, AM symbioses take an important role in the growth, development and production of host plants. Citrus is always planted mountainous areas, and soil management has great impacts on the growth of citrus. In this study, satsuma mandarin (Citrus unshiu Marc.)/trifoliate orange (Poncirus trifoliate (L.) Raf.) was taken as material, the diversity of AMF in the soil was investigated under three management methods (straw mulch, sod culture and no-tillage), and the development of AM and the dynamics of other microbes in different soil managements, soil layers and seasons were studied to discuss the relationship between the ecological distribution of AMF in citrus and the main factors, for screening effective and dominant aboriginal strains applied in the production of citrus. The main results are as follows. 1. Arbuscular mycorrhizal fungi diversityA total of ninteen species of AM fungi belong to five genus were identified in all soil samples of the citrus orchards, including twelve species of Glomus, four species of Acaulospora, one species of Entrophospora, one species of Scutellospora and one species of Pacispora. Glomus had the most individual abundance and the highest frequency and abundance, followed by Acaulospora.Glomus, the relative abundance of which was above 90%, was the dominant genus in the rhizosphere of citrus. However dominant AM fungi species varied much in different soil managements. In the treatment of straw mulch, the dominant species were G. aggregatum, G. claroideum and G. intraradices, and G. etunicatum was common in soil samples from the rhizosphere of citrus. In the treatment of sod culture, the dominant species were G aggregatum and G. claroideum, and G diaphanum, G etunicatum, G. intraraadices, G tortuosum and G. spl were common. In the treatment of no-tillage, the dominant species was G. etunicatum, and G. aggregatum and G. claroideum were common.In the three treatments, species richness of the AM fungi in the rhizospheric soil of satsuma orange/trifoliate orange was sod culture> straw mulch> no-tillage. It suggested that, the species richness in sod culture treatment was significantly higher than it in the other two treatments, and the sod culture was more beneficial for improving the AM fungi diversity in the rhizosphere soil of satsuma mandarin/trifoliate orange. 2. Relationship between the development of AM and other microbesThe colonization rate of arbuscules, total colonization rate, spore density, activity of acid phosphatase, content of glomalin and populations of rhizospheric microbes changed with seasons and the soil depth. They were higher in summer and autumn, than in spring, which was higher than in winter, and they were highest in July and lowest in January. The colonization rate of vesicles increased in winter and spring, decreased in summer and autumn, and was higher in January and March. In the 0-10 cm soil layer, the development of AM was best and spore density were highest. In 0-30 cm soil layer, they decreased with the increase of soil depth.Compared with no-tillage, the vesicles, arbuscules and total colonization rate and spore density were higher in straw mulch and sod culture, and the populations of rhizospheric microbes were higher. It suggested that the latter two managements had beneficial effects on the development of AM and improvement of soil microenvironment. The correlation analysis showed, spore density of roots of satsuma mandarin/trifoliate orange was significantly positive correlation with arbuscules and total colonization rate (r=0.6094 and r=0.4253, respectively), and significantly positive correlation with acid phosphatase and glomalin (r=0.6984 and r=0.3501, respectively). Meanwhile, arbuscules and total colonization rate and spore density were significantly positive correlation with other rhizospheric microbes(p<0.05). Therefore, we deduced that higher arbuscules and total colonization rate and spore density had function of stimulation to other rhizospheric microbial growth and reproduction.