Water acquisition in rainfed lowland rice evaluated through the isotope analysis of xylem water

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The aim of the research was to establish a methodology to identify crop species or varieties that acquire water from deeper soil layers. We have focused on the natural abundance of hydrogen isotope ratio (dD) in water of both soil and xylem sap. In the field investigation at Zambia, we have analyzed dD in precipitation and the groundwater, and found that while the groundwater had a constant dD values through the experimental period the precipitation showed a heavy fluctuation in dD values. Further analysis of the xylem sap of crops grown in the field has shown also the fluctuated dD values, suggesting the effect of the precipitation. However, there were significant differences in the dD fluctuation between species; a particular species had dD values always closer to the groundwater comparing with other species. The results imply the species differences in the dependency on the groundwater as water source. To explain the specific differences, the anatomical investigations of the roots were conducted. As a result, it was found that the species with high dependency on the groundwater did not develop aerenchyma at all but the species with low dependency developed well. Moreover, it was found that a crop species occurs hydraulic lift that is a water movement through a plant root system. This was the first report of hydraulic lift in agricultural field study. We have further examined if hydraulic lift can increase with certain agricultural practices, and found that shading is an effective means. It is assumed that plants with deeper root system may be utilized as a sprinkler-like function by regulating hydraulic lift.