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This experiment as undertaken to determine the efects of soil drying around the nodal and/or seminal root systems on the shoot growth of wheat (Triticum aestivum L.). Two split-root experiments were conducted, the first on newly emerged nodal roots of 18-day-old wheat plants, the second on 25-day-old plants. In both experiments, nodal and seminal roots were isolated from one another and water was withheld from either the nodal root chamber, the seminal root chamber, or both, over 6 days. In the first experiment, leaf growth was unaffected by withholding water from very short nodal roots, even though leaf relative water content of the droughted plants decreased. By comparison, both leaf elongation rate and relative water content decreased by withholding water from the seminal roots. On plants that were 1 week older, leaf growth rate and leaf relative water content decreased when nodal roots were drought-stressed. Leaf growth rate of seminal root droughted plants was more impaired than their nodal root counterparts, even though leaf relative water contents of the two treatments were the same. In both experiments, drought stress applied to the nodal root system enhanced nodal root growth more than seminal roots. These results suggest that seminal and nodal roots perceive and respond to drought stress differently with respect to the nature of the message conveyed to the shoots.

Flexible-and rigid-walled minirhizotron techniques were compared for estimating root length density of 14-to 28-day-old Pinto bean (Phaseolus vulgaris L.) and spring whet (Triticum aestivum L.) plants in soil boxes under controlled environment conditions at three soil bulk densities (1.3, 1.5 and 1.7g cm-3). The flexible-tube system consisted of bicycle inner tubes inflated inside augered access holes and removed only when measurements were taken. Rigid tubes were constructed of extruded polybutyrate plastic. In both cases tubes were oriented horizontally. Despite similar root densities for wheat and beans based on measurements obtained from soil cores, root densities estimated from both types of minirhizotron were higher in bean than in wheat in uncompacted soil. Estimates of root density by the flexible tube minirhizotron were more closely correlated with soil core image analysis estimates than were those by the rigid minirhizotron system. At high soil bulk density, rigid tube measurements consistently overestimated actual rooting density of both wheat and bean. The relationship between estimated and actual rooting densities in the case of flexible tube measurements was not significantly influenced by soil bulk density. These findings were consistent with the theory that preferential root growth is induced by gaps at the soil-observation tube interface, inherent in the rigid tube technique, and was accentuated under conditions of high soil strength.

VOLKMAR, K. M., and WOODBURY, W. 1989. Effects of soil temperature and depth on colonization and root and shoot growth of barley inoculated with vesicular-arbuscular mycorrhizae indigenous to Canadian prairie soil. Can. J. Bot. 67: 1702 -1707. The ability of vesicular-arbuscular mycorrhizae indigenous to the Canadian prairie to colonize roots and promote growth of barley in 38 x 11 cm plastic tubes at soil temperatures of 12, 16, or 20°C was examined. Mycorrhizal inoculum was placed 5 cm below the soil surface (PI) or dispersed throughout the soil (DI) prior to planting. Plants were harvested at stage 10.1 (Feeke's scale). Infection levels on PI and DI treatments were about 2 and 7 %, respectively, with more infection occurring on DI roots. Soil temperature did not influence infection of DI plants but infection development beyond the inoculum source was greatest at 12OC in PI plants. The dry shoot mass of DI plants was larger, but root mass was smaller than the PI and control plants irrespective of soil temperature. Root lengths of PI and DI plants were about 80 and 40% of control plants, irrespective of soil temperature with root length declining with soil depth on PI and control plants but not on DI treatments. Low infection level despite high inoculum potential indicated either a low rate of overwinter inoculum survival or an incompatibility between the host and endophyte. Significant growth promotion in spite of low levels of infection suggests that the mycorrhizal species that do colonize the root could be of economic value. VOLKMAR, K. M., et WOODBURY, W. 1989. Effects of soil temperature and depth on colonization and root and shoot growth of barley inoculated with vesicular-arbuscular mycorrhizae indigenous to Canadian prairie soil. Can. J. Bot. 67 : 1702 -1707. Cette Ctude a Ct C entreprise afin de dCterminer la capacitt de champignons endomycorhiziens ?I vCsicules et arbuscules indigbnes ?I la prairie canadienne B coloniser les racines et i stimuler la croissance de l'orge; les exptriences ont ttC effectutes dans des grands pots, B trois temperatures du sol. L'inoculum mycorhizien a Ct C plact soit ?I 5 cm sous la surface du sol (PI) ou soit dispersC dans I'ensemble du substrat (DI) dans des pots de 38 x 11 cm. Les plantes ont ttC rCcoltCes au stade 10.1 (tchelle de Feeke). La masse sbche des plantes DI est plus Clevte, mais la masse des racines et leur longueur sont plus faibles que chez les plants PI et les plants tCmoins. L'intensitC de la colonisation dans les traitements PI et DI Ctaient d'environ 2 et 7 % respectivement. Les faibles valeurs de colonisation en dtpit d'un fort pouvoir inoculant pourraient indiquer une perte de vitalit6 ou uneincapacitC pour la plupart des spores B passer l'hiver dans un climat froid ou une incompatibilitt entre l'h6te et l'endophyte. La stimulation significative de la croissance observCe malgrC une faible colonisation, suggkre que les espbces mycorhiziennes qui colonisent la racine pourraient &tre importantes Cconomiquement.[Traduit par la revue]

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