Effect of Vesicular-Arbuscular Mycorrhizal Fungi on the Growth, Photosynthesis, Transpiration and the Distribution of Photosynthates of Bearing Satsuma Mandarin Trees

The response of satsuma mandarin (Citrus unshiu Marc. cv. Okitsu wase) on trifoliate orange (Poncirus trifoliata Raf.) rootstocks to inoculation of vesicular-arbuscular mycorrhizal (VAM) fungi, such as Glomus ambisporum Smith and Schenck, Gloumus fasciculatum (Thaxter) Gerdemann and Trappe emend. Walker and Koske, Glontus mosseae (Nicolson and Gerdemann) Gerdemann and Trappe, and Gigaspora ramisporophara Spain was studied at low phosphorus (P) application. Under high air temperature stress conditions in August, the photosynthetic (Pn) and transpiration (Tr) rates of VAM-inoculated trees were faster than non VAM ones. But in September when air temperature decreased, the Pn and Tr rates did not differ significantly between VAM-inoculated trees and non infected ones. In general, infected trees had larger leaf area and higher leaf P concentration and the tree growth was more vigorous than was that of non infected ones. When 13CO2 was fed to fruit-bearing trees under the optimal air temperature conditions, fruits were the strongest sink for photosynthates and new leaves were the second strongest. The leaves of VAM and non VAM trees assimilated 13CO2 equally fast per unit leaf area, and the distribution of 13C into various parts of the bearing trees did not differ. VAM trees, however, had 3 times more photoassimilates per tree than uninfected ones because the former had a leaf area 3 times larger than the latter and grew more vigorously.