RESUMEN
With large forested urban areas, the city of Edmonton, Alberta, Canada, faces high annual costs of replacing trees injured by deicing salts that are commonly used for winter road maintenance. Ectomycorrhizal fungi form symbiotic associations with tree roots that allow trees to tolerate the detrimental effects of polluted soils. Here, we examined mycorrhizal colonization of Pinus contorta by germinating seeds in soils collected from different locations: (1) two urban areas within the city of Edmonton, and (2) an intact pine forest just outside Edmonton. We then tested the responses of seedlings to 0-, 60-, and 90-mM NaCl. Our results showed lower abundance and diversity of ectomycorrhizal fungi in seedlings colonized with the urban soils compared to those from the pine forest soil. However, when subsequently exposed to NaCl treatments, only seedlings inoculated with one of the urban soils containing fungi from the genera Tuber, Suillus, and Wilcoxina, showed reduced shoot Na accumulation and higher growth rates. Our results indicate that local ectomycorrhizal fungi that are adapted to challenging urban sites may offer a potential suitable source for inoculum for conifer trees designated for plating in polluted urban environments.
Asunto(s)
Hongos/fisiología , Micorrizas/fisiología , Pinus/microbiología , Estrés Salino , Cloruro de Sodio/metabolismo , Biodiversidad , Hongos/clasificación , Hongos/genética , Hongos/aislamiento & purificación , Micorrizas/clasificación , Micorrizas/genética , Micorrizas/aislamiento & purificación , Pinus/fisiología , Plantones/microbiología , Plantones/fisiología , Árboles/microbiología , Árboles/fisiologíaRESUMEN
Growth and physiological parameters were examined in rat root ( Raf.) plants grown under controlled environment conditions in hydroponics and subjected to different pH and salinity treatments to determine whether these environmental factors may contribute to poor establishment of in oil sands constructed wetlands. When plants were subjected to a root zone pH ranging from 6.0 to 9.5, the plants that were growing at pH 7.0 showed the highest relative growth rates and chlorophyll concentrations compared with lower and higher pH levels. The greatest inhibition of growth occurred at pH ranging from 8.0 to 9.5. High pH also triggered significant reductions in tissue concentrations of N, P, and microelements, whereas the concentrations of Mg increased at pH >8. When NaCl (25, 50, and 100 mmol L) was added to the nutrient solution at pH 7.0 and 8.5, higher mortality and greater tissue concentrations of Na and Cl were measured in plants growing at pH 8.5 compared with pH 7.0. The results show that plants growing at the optimum pH of 7.0 can better tolerate salinity compared with plants exposed to high root zone pH. Both pH and salinity may present important environmental constraints to growth and establishment of plants in oil sands constructed wetlands.
RESUMEN
BACKGROUND: Flooding reduces supply of oxygen to the roots affecting plant water uptake. Some flooding-tolerant tree species including tamarack (Larix laricina (Du Roi) K. Koch) produce adventitious roots in response to flooding. These roots were reported to have higher hydraulic conductivity under flooding conditions compared with non-adventitious roots. In the present study, we examined structural and functional modifications in adventitious roots of tamarack seedlings to explain their flooding tolerance. RESULTS: Seedlings were subjected to the flooding treatment for six months, which resulted in an almost complete disintegration of the existing root system and its replacement with adventitious roots. We compared gas exchange parameters and water relations of flooded plants with the plants growing in well-drained soil and examined the root structures and root water transport properties. Although flooded seedlings had lower needle chlorophyll concentrations, their stomatal conductance, net photosynthesis rates and shoot water potentials were similar to non-flooded plants, indicative of flooding tolerance. Flooded adventitious roots had higher activation energy and a higher ratio of apoplastic to cell-to-cell water flow compared with non-flooded control roots as determined with the 1-hydroxypirene 3,6,8-trisulfonic acid apoplastic tracer dye. The adventitious roots in flooded plants also exhibited retarded xylem and endodermal development and accumulated numerous starch grains in the cortex. Microscopic examination of root sections treated with the PIP1 and PIP2 antibodies revealed high immunoreactivity in the cortex of non-flooded roots, as compared with flooded roots. CONCLUSIONS: Structural modifications of adventitious roots suggest increased contribution of apoplastic bypass to water flow. The reduced dependence of roots on the hypoxia-sensitive aquaporin-mediated water transport is likely among the main mechanisms allowing tamarack seedlings to maintain water balance and gas exchange under flooding conditions.