Effects of mycorrhizal fungi on high temperature root stress of container grown nursery crops

Abstract

The effects of high medium temperatures and vesicular-arbuscular mycorrhizal fungi on selected container grown woody plants were studied. Root-zone medium temperature profiles were established for nursery production plots on white and black ground surfaces. White surfaces increased medium temperatures 2 to 4°C in plots of plants with open canopies. Berberis thunbergii DC. 'Atropurpurea', Pinus eldarica Medw., Pittosporum tobira (Thunb.) Ait. 'Wheeler', and Buxus microphylla Seibold and Zucc. japonica were established to be highly intolerant, intolerant, moderately intolerant, and resistant, respectively, to high medium temperatures (40 to 50°C), under field conditions. Root growth was less in the southern and western plot exposures. P. tobira plants, colonized with Glomus etunicatus Baker and-Gerd. and Glomus fasciculatum (Thax. sensu Gerd.) Gerd. and Trappe, under field conditions had increased shoot and root growth in protected plot regions. Colonization did not improve plant growth in the southern and western plot exposures. Colonization did not improve plant growth of B. thunbergii plants and most died under production conditions. An insulated chamber, utilizing heated and cooled air was developed for experimental control of supra-optimal root zone temperature. The optimal operating temperatures were between 20 and 50°C ±0.2. Water relations of B. thunbergii, B. microphylla, and P. tobira, uncolonized and colonized plants, during induced high temperature root stress were studied in a glasshouse. Predawn xylem water potential initially increased in response to high medium temperatures, and decreased over time. Stomatal conductance and evapotranspiration were reduced initially in response to high medium temperatures. This reduction continued incremently over time. Root damage occurred, as indicated by reductions in stomatal conductance, at 40°C for B. thunbergii and P. tobira and at 45°C for B. microphylla . Colonization increased stomatal conductance and evapotranspiration at ambient medium temperatures. Colonization mediated some of the response to high medium temperatures by maintaining lower initial xylem water potentials of B. thunbergii and P . tobira...