Salt Accumulation Can Lead to Salt Injury in Rainy Climates

抄録

Leaf-yellowing is a continuous phenomenon which is apt to go unnoticed. Among it, top leaf-yellowing is often caused by iron deficiency or salt injury. The latter occurs on dry land and in greenhouses. Majuro atoll in the Pacific Ocean is in the tropical wet climate area. The plants show very severer top leaf-yellowing; however, existing studies have found neither Fe deficiency nor salinity in the soil. Here, I succeeded to reproduce the top leaf-yellowing effect through low salinity irrigation water. I planted water spinach (Ipomoea aquatica) in bottomless pots and watered the plants using different amounts of well water containing agriculturally safe levels of salt (Na⁺: 16 mg L^-1). Leaf-yellowing levels, measured by the chlorophyll content in the leaves, were proportional to the Na⁺ concentrations in the potted soil. The accumulation of salt was maximized when the amount of watering was equal to evapotranspiration, whereas further watering washed out the salinity. Sandy carbonatic soil, the majority of Majuro atoll, is considered extremely sensitive to salinity because the Na+ concentrations in the soil were far less than the threshold of US soil Lab. The evidence presented here suggests that salt injury can also occur in wet climates.