Effects of Mycorrhizal Fungi on Plant and Growth Soil Properties in Trifoliate Orange Seedlings Grown in a Root-Box

Soil aggregate stability is associated with roots, arbuscular mycorrhizal (AM) hyphae, and glomalin-related soil protein (GRSP), among others. In this work, a root-box was divided into two parts: one part was the root + hyphae zone and hyphae (37-mu m mesh; root free) zone, and the other part was the no-hyphae (0.45-mu m mesh; root-and hyphae-free) zone. Trifoliate orange (Poncirus trifoliata) seedlings were planted in the root + hyphae zone and were colonized by Diversispora spurca. After 18 wk, root colonization was significantly higher under the 37-mu m mesh than under the 0.45-mu m mesh, while soil hyphal length was higher under the 0.45-mu m mesh than under the 37-mu m mesh in the root + hyphae zone. Arbuscular mycorrhizal fungi (AMF) inoculation significantly increased shoot and root biomass, and a stronger effect was observed under the 37-mu m mesh than under the 0.45-mu m mesh. AMF seedlings represented considerably higher acid, neutral, alkaline and total soil phosphatase activity, easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP) concentration, distribution of soil water-stable aggregates in the size of 2-4 mm and 1-2 mm, and mean weight diameter in the root + hyphae zone of both the 37-mu m mesh and the 0.45-mu m mesh and hyphae zone of the 37-mu m mesh. Aggregate stability was dominantly due to root biomass and root AMF colonization in the root + hyphae zone and to EE-GRSP in the hyphae zone. This result suggested that besides AMF-stimulated plant growth and phosphatase activity, mycorrhizas also strongly enhanced aggregate stability in the rhizosphere.