Even though the mycorrhizal relationship is thought to be important in nutr
ient and water uptake by plants, earlier work showed that soybean cultivars
differ in responsiveness, The reasons for cultivar differences are unclear
. The objective of this growth-chamber study was to relate plant-growth par
ameters and rooting characteristics of three soybean cultivars to mycorrhiz
al dependency (MD), The soybean cultivars were chosen from a preliminary st
udy to represent a range in MD values from high (Glycine soja Sieb, & Zucc.
PI 468916; referred to hereafter as Soja), to intermediate [G, max (L.) Me
rr. cv. Mandarin] and low (G, max cv. Swift). Shoot weight, P percentage in
shoot tissue, total shoot P uptake, P use efficiency, rate of growth, and
root acid phosphatase activity were measured at three harvests when plants
were grown at three relative P levels, each with and without mycorrhizal fu
ngal (Gigaspora margarita Becker & Hall) colonization, Soja developed an ac
tive symbiosis more quickly than Swift or Mandarin, and mycorrhizae clearly
aided in P uptake, When averaged across harvests at low P, mycorrhizal Soj
a had 7.8 times greater total shoot P than nonmycorrhizal Soja. Comparable
values were 2.4 for Mandarin and 1.5 for Swift. Soja roots showed higher ph
osphatase activity and a higher percentage increase in phosphatase activity
with mycorrhizal colonization than did the other two cultivars, Nonmycorrh
izal Soja root lengths (avg. 1401 cm) at 5-wk growth were significantly sho
rter than Mandarin (2303 cm) and Swift (2236 cm) root lengths. The mean dia
meter of lateral roots of Soja (0.38 mm) was greater than that of Mandarin
or Swift (approximate to 0.26 mm), Root lengths and root surface areas were
negatively correlated (P < 0.01) with MD.