柠檬酸,葡萄糖和有机质对植物磷素吸收和土壤磷素形态的影响

研究了柠檬酸、葡萄糖和有机质（栎树类凋落物和三叶草茎叶）对几种栽培和野生植物磷素吸收以及高度风化老成土中磷素形态的影响。在未加入无机磷的情况下，连续加入柠檬酸溶液增加了温室盆栽大豆（Ｇｌｙｃｉｎｅｍａｘ（Ｌ．）Ｍｅｒｒ．）和高粱（Ｓｏｒｐｈｕｍｂｉｃｏｌｏｒ）对磷素的吸收。这表明，柠檬酸可以溶解土壤中被铁、铝氧化物固定的磷。当无机磷和柠檬酸溶液同时加入后。由于有机配位体能够阻止土壤对磷素的吸附和固定，植物对磷的吸收总量明显高于仅仅加入无机磷的对照。不论是否加入无机磷，葡萄糖均没有增加植物对磷素的吸收，但却改变了土壤中磷素的形态。该试验的结果还表明，Ｈｅｄｌｄｙ等人提出的土壤磷素分级方法不适于有机质含量很低的酸性土壤。在另一种性质极为相似的酸性土壤中施入粉碎的栎树（Ｑｕｅｒｃｕｓｓｐｐ．）凋落物和三叶草（ＴｒｉｆｏｌｉｕｍＰｒａｔｅｎｓｅ）后，野生商陆（Ｐｈｙｔｏｌａｃｃａａｍｅｒｉｃａｎａ）吸收磷素的能力增强。通过进一步对土壤中的磷素进行化学分级，结果表明，这些有机物质可以改变土壤中磷素存在的形态。本文还就有机质分解过程中的中间产物对土壤磷素有效性的影响机理进行了探讨。

EFFECT OF CITRIC ACID, GLUCOSE AND ORGANIC MATTER ON PLANT P UPTAKE AND SIIL P FRACTIONATIONS IN A HIGHLY WEATHERED ULTISOL

The effect of citric acid and glucose on P uptake by different species of cultivated and wild plants, and P fractionations of the soil was investigated in an acidUltisol. Experiments were conducted in the greenhouse, using continuous additionof citric acid and glucose solutions, and a complete budget study designed to examine the changes of soil phosphorus in various fractions employing a P fractionation procedure. Without inorganic P additions, citric acid increased P uptake bysoybean (Glycine max (L.) Merr.) and sorghum (Sorghum bicolor), indicating that citric acid solubilized the P bound by Al and Fe oxides. The addition of P (20 mg P kg-1 soil)in combination of a continuous addition of eitric acid solution resulted in higher P uptake by soybean and sorghum. The addition of glucose, with and without addition of P,did not change the P uptake by plants. However, the addition of glucose increased tEe organic P in NaOH fraction, and a decrease in inorganic NaOH fractions.A negative microbial P was obtained for all the treatments, especially when glucose was added. This suggests that the method described by Hedley is not suitable for determination of microbial P in very acid soils having little organic matter content. The increase of P uptake by sorghum and a decrease of P in the NaOH fractions in the soil with the addition of inorganic P and citric acid suggests that organic ligands can prevent P from being fixed by soil particles.The addition of oak (Quercus spp.) and red clover (Trifolium pratense) litter to a similar acid soil resulted in a higher P uptake by pokeweed (Phytolacca americana). After a period of 7 months, the resin-P and inorganic bicarbonate P decreased substantially compared with the P at the beginning of experiment. This can be attributable to the P uptake by plant, P taken up by microbial organisms, an increase in organic P, and an increase in HCl fraction. The results also showed that both clover and oak litter did not increase the inorganic P in NaOH fractions.This indieates that products of organic matter decomposition might have prevented the mineralized P from being immobilized by clay particles and Fe- and Al-oxides.An attempt was also made to elucidate the mechanisms involved in the P solubilization by the products of organic matter decomposition, and the resuction of P adsorption by Al- and Fe-compounds in the presence of organic ligands.