Effects of Inoculating Arbuscular Mycorrhizal Fungi on the Growth and Soil Structure Characteristics of Robinia pseudoacacia under Different Garden Waste Treatment Methods

Taking Robinia pseudoacacia as the research object, this study explores the effects of inoculating arbuscular mycorrhizal fungi (AMF) on the growth, photosynthesis, and rhizosphere soil structure characteristics of R. pseudoacacia under different garden waste treatment methods. Under four different addition methods, including no addition of garden waste (CK), coverage of garden waste (WM), addition of garden waste (WI), and addition of ammoniated garden waste (AWI), AMF inoculum of Claroideoglomus etunicatum and non-inoculated control (N-AMF) were applied, resulting a total of eight treatments. The results show that different methods of adding garden waste had a significant impact on AMF mycorrhizal infection rate, spore count, invasion site count, and vesicle count. Compared with CK, WM, WI, and AWI addition methods all significantly increased AMF mycorrhizal infection rate and spore count, whereas there was no significant difference in invasion site count and vesicle count between CK and WM. Among all waste addition methods, AWI had the highest mycorrhizal infection rate, spore count, invasion site count, and vesicle count. Compared with CK, WM, WI, and AWI all promoted the growth of R. pseudoacacia to varying degrees. Under the addition of AWI, the height, base diameter, relative growth rate, and root-shoot ratio of R. pseudoacacia treated with AMF increased by 12.9%, 4.6%, 5.0%, and 20.9%, respectively. The chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and water use efficiency (WUE) of R. pseudoacacia leaves increased by 11.2%, 18.9%, 15.0%, 6.4%, and 27.9%, respectively, compared to N-AMF treatment. The effects of WM, WI, and AWI addition methods on the physicochemical properties of R. pseudoacacia soil are different. Under different waste addition methods, the AWI addition method has the highest soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), available phosphorus (SP), and available potassium (SK) content, while the nitrate nitrogen (NO₃^--N) content to be the lowest. There is no significant difference in TN content between AMF treatment and N-AMF treatment under AWI addition method. Compared to N-AMF treatment, the SOC, NH₄⁺-N, NO₃^--N, SP, and SK content of AMF treatment increased by 33.8%, 7.8%, 27.2%, 8.3%, and 8.3%, respectively. The activities of soil peroxidase (S-CAT), amylase (S-SC), soil urease (S-UE), and soil alkaline phosphatase (S-ALP) increased by 7.9%, 14.5%, 15.2%, and 23.4%, respectively. The effect of waste addition methods on soil water stable aggregates varies with different diameters. Under the same addition method, inoculation with AMF promoted the formation of soil water stable aggregates in R. pseudoacacia as a whole, but had no significant effect on the content of aggregates with diameters < 0.25 mm. The conclusion is that the addition of ammoniated garden waste and inoculation with AMF is an effective measure to promote the growth of R. pseudoacacia, improve soil structure characteristics and effectively utilize garden waste.