Kirk G J D, Bajita J B
International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines.
New Phytol. 1995 Sep;131(1):129-137. doi: 10.1111/j.1469-8137.1995.tb03062.x.
Rice plants (Oryza sathiva L., cv. IR34) were grown with their roots sandwiched between cylinders of an anaerobic low-Zn Mollisol. After periods of root-soil contact of up to 12 d (total plant age c. 28 d) the profiles of different Zn fractions, reduced and oxidized Fe, and pH in the soil near the root plane' were determined. The concentration of easily plant-extractable Zn in the soil (measured by extraction in I M KCl) was negligible, and so it was necessary for the plants to induce changes in the soil to solubilize Zn. After 6 d, there was a substantial accumulation of Zn associated with organic matter and amorphous ferric hydroxide within 4-5 mm of the root plane. Over the next 6 d, the accumulation continued but there was a substantial depletion of the accumulated fractions within 2 mm of the root plane. The zones of accumulation and depletion coincided with zones of Fe(III) accumulation and soil acidification in which the pH decreased from the bulk soil value of 7.3 by over 0.2 pH units; i.e. a two-fold increase in H concentration, The acidification was the result of H released from the roots to balance excess intake of cations over anions, and H generated in the oxidation of Fe(H) by root-released O . At the high pH and CO., pressure of the experimental soil (7.3 and c. 0.9 kPa. respectively), soil acidity diffusion is fast and consequently the pH drop at the root surface was small. The rate of Fe oxidation peaked before 6 d, but the acidification and Zn accumulation continued beyond 6 d unabated. It is concluded that Fe oxidation released Zn from highly insoluble fractions, and that this Zn was re-adsorbed on Fe(OH) and on organic matter in forms that were acid-soluble and therefore accessible to the plants.
水稻植株（Oryza sathiva L.，品种IR34）种植时，其根系夹在厌氧低锌软土的圆柱之间。在根系与土壤接触长达12天（植株总龄约28天）后，测定根平面附近土壤中不同锌组分、还原态和氧化态铁以及pH的分布情况。土壤中易于被植物提取的锌浓度（通过1M KCl提取测定）可忽略不计，因此植物有必要诱导土壤发生变化以溶解锌。6天后，在根平面4 - 5毫米范围内，与有机物和无定形氢氧化铁相关的锌大量积累。在接下来的6天里，积累仍在继续，但在根平面2毫米范围内积累的组分大量减少。积累和减少的区域与铁（III）积累和土壤酸化区域重合，其中pH从土体土壤值7.3下降超过0.2个pH单位；即H⁺浓度增加了两倍。酸化是根系释放H⁺以平衡阳离子过量吸收阴离子的结果，以及根系释放的O₂将Fe（II）氧化产生H⁺的结果。在实验土壤的高pH和CO₂压力（分别为7.3和约0.9 kPa）下，土壤酸度扩散很快，因此根表面的pH下降很小。铁氧化速率在6天前达到峰值，但酸化和锌积累在6天后仍持续且未减弱。得出的结论是，铁氧化从高度不溶性组分中释放出锌，并且这种锌以酸溶性形式重新吸附在Fe（OH）₃和有机物上，因此植物可以吸收。
