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This study was initiated to determine the itiuence of vesiculararbuscular mycorrhizal (VAM) fungi on a rhizobhun-legume interaction. Inoculation of subclover with Glomus fascicddus resulted in 2 times as many rhizobium nodules on roots as on nonmycorrhizal controls. Inocuhtion with Glomus mosseue resulted in 1.4 times greater nodule formation compared to the noninoculated controls. Plants inoculated with G. mosseue + G. fusckulatus had 1.9 times more nodules than the controls. Furthermore, inoculation with G. fasciculatus or G. mosswe+ G. fasciculatus resulted in shoot weights and total plant weights nearly double that of the controls. The conclusion is that inoculation with the correct VAM fungal species is as important as the selection of the rhizobium species for subclover growth and development. The increased demand for energy resources has resulted in large tracts of arid and semiarid rangelands being disturbed by the quest for coal and oil shale. Both the 1972 federal mining law and state regulations require the reclamation of these lands to acceptable standards for forage and wildlife habitat. Western rangelands are generally deficient in nitrogen and phosphorus throughout their soil profiles; as a result, standard rehabilitation operations must use large applications of these inorganic fertilizers to establish site productivity (Bauer et al. 1978). However, the costs of fertilizer often exceed the actual benefits derived from their use in reseeding projects in arid locations. Abbott and Robson studied the growth of subterranean clover inoculated with two types of vesicular arbuscular endophytes and compared them with that of noninoculated plants at 5 levels of applied superphospate in a high phosphate fixing soil. A greater growth response of plants inoculated with a fungus resembling G. mosseue was associated with a greater amount of mycorrhizal roots. Responses in nodulation closely paralleled responses in growth. This study was initiated to determine the potential of using existing biological systems in place of expensive fertilizer applications for site rehabilitation. Legumes will, with associated rhizobium, fix large quantities of nitrogen; this association might be useful as a biological system for supplying nitrogen. However, the legume-rhizobium interaction requires relatively high levels of phosphorus (van Schreven 1958). Since vesicular-arbuscular mycorrhizal (VAM) fungi increase the uptake of phosphorus by their host plants, a study was initiated to determine the influence of VAM fungis on a rhizobium-legume assoc$tion under low phosphorus conditions. The use of mist chambers for root studies Authors arc. respectively, associate professor, graduate research assistant, and former student. Debartment of Ranne Manaeement. Humboldt State Universitv. Arcata, Califorttia 45521, and projecy leader, ‘kocky ‘Mountain Forest and Ran& Experiment Station. Albuquerque,, New Mexico 87106. William Beavis is presently a research assistant. Iowa State Untversity, Ames Xl01 I. This research was funded by the Rocky Mountain Forest and Range Experiment Station, at the Station’s Research Work Unit in Albuquerque, incooperation with the University of New Mexico. Station headquarters is in Fort Collins. in cooperation with Colorado State University. Manuscript received December 4. 1981. avoids the confounding effects of edaphic factors (Graham et al. 1976). Materials and Methods Spores of Glomus mosseae (Nichol. and Gerd.) Gerdemannand Trappe and Glomusfascicuhtus (7haxter sensu Gerdemann) Gerdemann and Trappe, collected in the state of Washington, were multiplied in pot culture on wheat (Graham et al. 1976). Spores were extracted by wet sieving and decanting (Gerdemann and Nicholson 1963) and stored in Ringer’s solution (Daniels and Graham 1976) for about 3-5 months before use. Seeds of subclover (Trifolium subterranean L. cv. Mount Barker) were surface disinfected in a 0.5% sodium hypochlorite solution and rinsed 5 times in sterile, distilled water. The moistened seeds were inoculated with a commercial preparation of Rhizobium trifolii (Dungeard) by placing them in the preparation and thoroughly coating each seed. The inoculated seeds were then planted in 3-inch pots containing a 1 to I mixture (vol/vol) of sterile autoclaved sand and vermiculite. When the seedlings reached the two-leaf stage, they were carefully tapped out of the pots, and the roots were rinsed free of sand and vermiculite with tap water. The seedlings were then placed in 3-inch pots with one root subtended through a l/2-inch hole drilled in the base of each pot. One to 3 lateral roots were left confined within the pot. The confined roots were covered with l/2-inch of moistened vermiculite, and the potted plants were then placed in a misted-root culture chamber (Hansen et al. 1979). The roots were sprayed continuously with a fine mist of a 40-fold dilution of a modified Hoaglands number 2 solution to allow healing of any abrasions on the roots (Graham et al. 1976). After 7 days, the vermiculite covering the confined roots was carefully rinsed out of the pots with tap water. Roots of the plants used for controls were recovered with moistened vermiculite and placed back on the misted-root chambers. Plants for the VAM fungi treatments were inoculated by placing lo-15 spores of each selected VAM fungal species directly on the rootlets confined within the pot. The inoculated roots were covered with moistened vermiculite, and the pots again placed in the root-chamber and misted with the same diluted Hoglands solutions (available phosphorus maintained at 10e6 M concentration). Treatments, in addition to the R. trifolii inoculation already done, were (1) control-no VAM inoculation; (2) G. mosseae; (3) G. fasciculatus; (4) G. mosseae -IG.fascicularus-inoculated with 15 spores each of the VAM fungi G. mosseae and G. fasciculatus. All root lengths were measured every 2 weeks until all of the plants were harvested 12 weeks following inoculation, when the following data were also collected: Number of nodules/root system, root dry weight, shoot dry weight, and total plant dry weight. Presence of VAM mycelium was determined by trypan blue staining techniques. Two completely randomized blocks of 92 plants/block were used, which represents a total of 23 plants per treatment, replicated twice. 576 JOURNAL OF RANGE MANAGEMENT 36(5), September 1963

Influence of Vesicular-Arbuscular Mycorrhizal Fungi on the Nodulation and Growth of Subclover