Sulfate Transport Processes Under Drought Stress: Interaction with Mycorrhization and Elevated pCO2 in Young Pedunculate Oak (Quercus robur L.) Trees
Drought stress mediated changes in sulfate transport processes, i.e. sulfate uptake and xylem loading of sulfate in the roots, and its dependency on mycorrhization and pCO2 were analyzed in young pedunculate oak (Quercus robur L.) trees. Withdrawal of water supply caused strong negative values of pre-dawn shoot water potential, indicating severe water stress. Elevated pCO2, but not mycorrhization transiently improved the water status of the trees. Sulfate uptake was largely independent from pre-dawn shoot water potential irrespective of mycorrhization and pCO2. In contrast, xylem loading of sulfate decreased with decreasing shoot water potential. Mycorrhization and – to a lesser extent – also elevated pCO2 improved xylem loading under drought stress. As a consequence, also relative xylem loading, i.e. the % amount of the sulfate taken up that was loaded into the xylem, was slightly improved. The positive effect of mycorrhization on xylem loading of sulfate under drought stress is surprising, since plants were inoculated with the ectomycorrhizal fungus Laccaria laccata that is not supposed to enter the vascular bundle of the root. Therefore, signaling by the fungus across the bundle sheath has to be assumed.
KeywordsDrought Stress Mycorrhizal Root Quercus Robur Elevated pCO2 Sulfate Uptake
Financial support by the commission of the EU under contract no. EC EV5V-CT92-0093 and by the State of Baden-Württemberg is gratefully acknowledged.
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