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.
Factors that inhibit the growth of plants in strongly acidic soils include low pH and aluminum excess. We evaluated two Myrtaceae species (Melaleuca cajuputi and Melaleuca bracteata), which are useful trees in tropical regions due to their resistance to low pH and excessive aluminum, to determine their response characteristics to environmental stresses. The results revealed that M.cajuputi, the growth by the aluminum concentration was not inhibited. However, the root growth of M.bracteata, by the aluminum treatment was inhibited remarkable, and 83.2% inhibited the maximum more than aluminum free. The pH of rhizosphere of both plants has decreased by the BCP plate. However, the pH decrease has decreased as for M. bracteata with high concentration of aluminum, but M.cajuputi is not changed. Next, it was able to be confirmed of aluminum accumulated in the root M.bracteata more than M.cajuputi by hematoxylin and aniline blue dyeing. At the result, it was able to be confirmed of aluminum accumulated in the root M.bracteata more than M.cajuputi. As for M.bracteata, aluminum was absorbed in the inner-cell of the root tissue. On the other hand, M.cajuputi had aluminum only in the surface of the root. We concluded that M.cajuputi was an aluminum tolerance because the mechanism that aluminum doesn't invade the internal tissue of the root was possessed.
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