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

这项研究的目的是建立一种方法，以确定从深层土壤中获取水分的作物物种或品种。我们集中在自然丰富的土壤和木质部汁液中的水的氢同位素比（dD）。在赞比亚的实地调查中，我们分析了降水和地下水中的dD，发现虽然地下水的dD值在整个实验期间是恒定的，但降水的dD值波动很大。对田间生长的作物的木质部汁液的进一步分析也显示了波动的dD值，表明降水的影响。然而，有显着的差异，在物种之间的dD波动，一个特定的物种的dD值总是更接近地下水相比，其他物种。这一结果反映了物种对地下水的依赖性存在差异。为了解释具体的差异，进行了根的解剖调查。结果表明，对地下水依赖性强的树种通气组织不发育，而对地下水依赖性弱的树种通气组织发育良好。此外，发现作物物种发生水力提升，其是通过植物根系的水运动。这是液压举升在农业领域研究的第一份报告。我们进一步研究了水力提升是否可以通过某些农业实践来增加，并发现遮阳是一种有效的手段。据推测，植物具有较深的根系可以利用作为一个洒水器一样的功能，通过调节水力升降机。

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.