Winter survival of extraradical hyphae and spores of
arbuscular mycorrhizal fungi in the ®eld
Terence P. McGonigle
*
, Murray H. Miller
Department of Land Resource Science, University of Guelph, Guelph, Ont., Canada N1G 2W1
Received 28 May 1998; accepted 29 October 1998
Abstract
The ability of the extraradical mycelium (EM) of arbuscular mycorrhizal (AM) fungi to colonize spring-sown seedlings in
temperate regions requires that this EM survive winter conditions. We studied the production and winter survival of such an
EM and its associated spores at its site of synthesis in a ®eld soil. Pouch-like nylon mesh bags of sieved and pasteurized soil
were buried in a ®eld below where a maize (Zea mays L.) crop was then grown. A mesh size of 45 mm prevented the entry of
roots into the pouches. Extraradical hyphae and spores of AM fungi were formed in these pouches. The density of trypan-blue
staining hyphae in the pouches increased from 16.3 to 60.0 m g
À1
between planting and maize-harvest time, but it then fell to
one-third of this value over the following winter. The density of ¯uorescein diacetate staining hyphae in the pouches were also
highest at maize-harvest time, at 38.1 m g
À1
. In contrast, the density in soil of newly produced AM spores with cytoplasm was
maximal earlier, reaching 28.8 g
À1
during the grain-®lling period; this density in soil had been halved by the time of maize
harvest. At various times before and after winter, pouches were excavated from the ®eld and used for growth-chamber
bioassays. The extraradical component of the AM fungi retained over winter its capacity to colonize roots. Arbuscular
colonization of sudangrass (Sorghum sudanense Staph.) bioassay plants at 28 days ranged from 36.5% to 69.3% root length,
and colonization of plants in bioassays after the winter was similar to that for bioassays before the winter. Disturbance of
pouch soil after excavation reduced the P content of bioassay shoots, relative to pouches with undisturbed soil. We show here
that extraradical structures of AM fungi can survive the winter in the soil at their site of synthesis. Reductions in soil densities
of spores in autumn, and of hyphae over winter, did not affect the capacity of the extraradical mycorrhizal system to colonize
plants swiftly in the spring, even after the elimination of any potential contribution from the part of the mycorrhizae inside the
roots. However, disturbance of soil was a potent means of hindering the subsequent development by the plant of a functional
mycorrhizal P-acquisition system. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Soil disturbance; Colonization; Extraradical mycelium; Fluorescein diacetate; Trypan blue
1. Introduction
Tillage has been shown to reduce early season
maize (Zea mays L.) plant-P absorption (Miller et
al., 1995a; McGonigle and Miller, 1996a; Gavito and
Miller, 1998b). This effect of soil disturbance requires
Applied Soil Ecology 12 (1999) 41±50
*Corresponding author. Present address: Faculty of Agriculture,
Gifu University, Gifu 501-1193, Japan. Tel.: +81-58-293-2842; fax:
+81-58-293-2842; e-mail: tmcgonig@cc.gifu-u.ac.jp
0929-1393/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S0929-1393(98)00165-6