SUMMARYMicroscopic analysis of infection development hy Gloynus in sugar maple roots revealed changes in the cortical cells similar to those reported by other workers using either herbaceous or woody plant hosts. Few cortical cells contained exclusively terminate hyphal structures. Instead, large intracellular hyphae entered and exited cortical cells while arbuscules formed from initiation points at various places on the intracellular hyphae. Intercellular hypbae were rare and vesicles were not observed. The beaded root morphology observed did not seem to influence the infection process. Beaded roots are formed from repeated constrictions in feeder roots due to major reductions in cell size. Tbe relationship between the constrictions and moisture stress is discussed. The living arbuscule seemed to be tbe site of transfer between tbe host and endophyte, implying that the process is an active one.

The response of sweetgum (Liquidambar styraciflua L.) seedlings grown either without or inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Gigaspora margarita 'Becker' and 'Hall' to 25, 50, and 100 ppm soil phosphorus (P) and adjusted soil pHs of 4.5, 5.5, 6.5, and 7.8 was observed during the first growing season. The best seedling growth for both VAM and noninoculated seedlings occurred at soil pH 4.5 and 100 ppm of soil P where mean heights and top dry weights averaged > 28 cm and 8 g, respectively. As soil pH increased, seedling growth decreased significantly and at pH 7.8 the seedlings averaged < 4 cm in height regardless of the soil P level or mycorrhizal condition. Seedling growth at all pH levels, except pH 7.8, decreased with decreasing soil P. Inoculated seedlings were significantly larger than noninoculated seedlings at 25 ppm soil P and pHs 4.5 and 5.5. Soil P, soil pH, and mycorrhizal condition significantly influenced nutrient levels in plant parts. Soil nutrient levels varied significantly with soil pH. ABSTRACTThe response of sweetgum (Liquidambar styraciflua L.) seedlings grown either without or inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Gigaspora margarita 'Becker' and 'Hall' to 25, 50, and 100 ppm soil phosphorus (P) and adjusted soil pHs of 4.5, 5.5, 6.5, and 7.8 was observed during the first growing season. The best seedling growth for both VAM and noninoculated seedlings occurred at soil pH 4.5 and 100 ppm of soil P where mean heights and top dry weights averaged > 28 cm and 8 g, respectively. As soil pH increased, seedling growth decreased significantly and at pH 7.8 the seedlings averaged < 4 cm in height regardless of the soil P level or mycorrhizal condition. Seedling growth at all pH levels, except pH 7.8, decreased with decreasing soil P. Inoculated seedlings were significantly larger than noninoculated seedlings at 25 ppm soil P and pHs 4.5 and 5.5. Soil P, soil pH, and mycorrhizal condition significantly influenced nutrient levels in plant parts. Soil nutrient levels varied significantly with soil pH.

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Hanover, 1981).Webb (1976) investigated the effects of light intensity and photoperiod on root elongation rates and found that active root growth proceeded at the expense of shoot growth followed by a period of increased shoot growth and reduced root growth.The cyclic nature of these processes allowed for the maintenance of a relatively stable root to shoot ratio. Reduction in light intensity to a point that limited photosynthesis severely inhibited root growth, while a return to adequate light intensities resulted in normal rates of growth. It appeared that root growth was dependent on photosynthate supply. During a period of inactivity, roots became suberized. This was followed by the growth of white roots from these suberized tips during an active period. Taylor and Dumbroff (1975) and Dumbroff and Brown (1976) found that root growth in sugar maple continued through the winter ceasing only when the ground was frozen in December and January. A surge of root growth was observed in late February to early April indicating that this species prepares for spring growth very early in the year. In fact, sugar maple seeds are often observed to germinate under snow cover in early spring. An increase in cytokinin activity, just before bud break, followed this early root activity. It was suggested that synthesis of cytokinins is not the initial step leading to the breaking of shoot dormancy since cytokinin Bonfante-Fasolo, P., J. Dexheimer, S. Gianinazzi, V. Gianinazzi-Pearson, and S. Scannerini. 1981. Cytochemical modifications in the host-fungus interface during intracellular interactions in vesicular-arbuscular mycorrhizae. Plant Sci. Letters 22:13-21. Buwalda, J. G. and K. M. Goh. 1982. Host-fungus competition for carbon as a cause of growth depressions in vesiculararbuscular mycorrhizal ryegrass. Soil Biol. Biochem. 14:103-106.