The physiological responses of salinity stressed tomato plants to mycorrhizal infection and variation in rhizosphere carbon dioxide concentration

[摘要] ENGLISH ABSTRACT: This investigation was undertaken to determine whether elevated concentrations of dissolved inorganiccarbon (DIC) supplied to plant roots could improve plant growth and alleviate the effects of salinity stresson tomato plants infected with arbuscular mycorrhizae. Lycopersicon esculentum cv. FI44 seedlings weregrown in hydroponic culture (pH 5.8) with 0 and 75 mM NaCI and with or without infection with thefungus Glomus mosseae. The root solution was aerated with ambient CO2 (360 ppm) or elevated CO2 ( 5000 ppm) concentrations. The arbuscular and hypha I components of mycorrhizal infection as well as thepercentages total infection were decreased or increased according to the variation in seasons. The plant dryweight of mycorrhizal plants was increased by 30% compared to non-mycorrhizal plants at elevatedconcentrations of CO2, while the dry weight was decreased by 68% at ambient CO2 concentrations.Elevated CO2 also stimulated the growth of the mycorrhizal fungus. Elevated CO2 increased the plant dryweight and stimulated fungal growth of mycorrhizal plants possibly by the provision of carbon due to theincorporation of HCO)- by PEPc. Plant roots supplied with elevated concentrations of CO2 had a decreasedCO2 release rate compared to roots at ambient CO2. This decrease in CO2 release rate at elevated CO2 wasdue to the increased incorporation of HC03- by PEPc activity. Under conditions of salinity stress plants hada higher ratio of N03-: reduced N in the xylem sap compared to plants supplied with 0 mM NaCI. Undersalinity stress conditions, more N03- was transported in the xylem stream possibly because of theproduction of more organic acids instead of amino acids due to low P conditions under which the plantswere grown. The N03· uptake rate of plants increased at elevated concentrations of CO2 in the absence ofsalinity because the HCO)- could be used for the production of amino acids. In the presence of salinity,carbon was possibly used for the production of organic acids that diverted carbon away from the synthesisof amino acids. It was concluded that mycorrhizas were beneficial for plant growth under conditions ofsalinity stress provided that there was an additional source of carbon. Arbuscular mycorrhizal infection didnot improve the nutrient uptake of hydroponically grown plants.

[发布机构] Stellenbosch University