Effects Of Arbuscular Mycorrhizas Fungi Of Robinia Pseudoacacia On Soil Nutrition And Structure Stability

The relationship between arbuscular mycorrhizal fungi (AMF) and soil factors in different layers of Robinia pseudoacacia plantation at different ages was studied in the hilly region of the Loess Plateau. A greenhouse pot experiment was carried to investigate the influence of two AMF(Glomus versiforme; Glomus intraradices) on growth of R. pseudoacacia, root and soil structure characteristics. The main conclusions included as follows:1. Mycorrhizal infection rate and spore density of R. pseudoacacia plantation at the same age were higher in0-20cm soil layer than that in20-40cm soil layers. Moreover, mycorrhizal infection rates in the upper and lower soil layers and spore density in20-40cm soil layer were increased at early stage and then declined with the increasing of tree age. As to the spore density in0-20cm soil layer, it was gradually reduced after two peaks with the increasing of tree age. The highest mycorrhizal infection rate and the maximum spore density were found in the21-and26-year-old plantation, respectively.2. A significantly positively correlation was observed between mycorrhizal infection rate, spore density and urease activities. Spore density showed a highly significantly positive correlation with available N, available P and alkaline phosphatase activities, but showed a significantly negative correlation with soil pH. Total glomalin (TG) and easily extractable glomalin (EEG) had a highly significant positive correlation with soil organic carbon. Principal component analysis showed that available N, available P, available K and alkaline phosphatase activities were the key factors affecting mycorrhizal development of R. pseudoacacia and reflecting soil nutrition status in the hilly region of the Loess Plateau.3. R. pseudoacacia inoculated with AMF significantly increased total root length, mean diameter, surface area, root volume, number of root tips and forks, while decreased specific root length. R. pseudoacacia inoculated with AMF had significantly higher percentage of root length in both the0.5-1.0mm and>1.0mm diameter classes, and lower percentage of root length in the0-0.2mm diameter class, the root became thicker, and AMF improved root tensile ability.4. The plant biomass, hyphal length and glomalin content were significantly improved after AMF inoculation. R. pseudoacacia inoculated with AMF significantly increased the mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates, and mycorrhizal effect of G. intraradices was more prominent. The hyphal length, the content of TG and EEG showed a significantly positive correlation with MWD. There was a highly significant positive correlation between hyphal length and the amount of larger macroaggregates>0.25mm (R0.25). AMF infection played an important role in the formation and stabilization of soil aggregates.