Department of Plant Sciences

Under strongly acidic soil conditions, low phosphorus nutrition may be a factor that inhibits plant growth. We examined the effects on plant growth of adding a poorly soluble phosphate (AlPO4) under phosphorus-deficient conditions using the high-acidity resistant plants (buckwheat and kenaf) and sensitive plants (sweet basil and red clover). As a result, only buckwheat showed no inhibition of growth despite phosphorus deficiency, but the remaining three species showed reduced growth, with a particularly significant reduction seen in sweet basil. Although the growth inhibition in these species could be reversed by adding AlPO4, the extents were different according to plant species. Sweet basil, whose growth was the most inhibited by phosphorus deficiency, showed the most marked recovery in growth. When the relationship between phosphorus absorption from AlPO4 and the increase in dry weight was investigated, rates of increase in dry weight with phosphorus absorption were the highest in red clover and sweet basil, followed by buckwheat and kenaf. On the other hand, when the amounts of AlPO4 dissolubed by substances secreted from the roots were compared among these plants, AlPO4 solubility was lower in buckwheat and kenaf and higher in red clover and sweet basil. Very high AlPO4 solubility was observed in sweet basil. We conclude that plants with a higher requirement for phosphorus release greater amounts of substances that dissolution otherwise insoluble phosphates such as AlPO4 to ensure their growth.