摘要
水稻、小麦根系H^+的分泌量随供磷水平的降低而增加,并存在明显的昼夜变化。在自然光照下H^+分泌量随光强度增加而增多,同时强光比黑暗时H^+分泌对磷供应水平更为敏感。磷供应不足还诱导水稻根系柠檬酸分泌量增加,而苹果酸则差异不明显。难溶性磷的溶解率与根系H^+和柠檬酸分泌所导致的根际pH下降有密切联系。因此,在有效磷不足的条件下可明显提高稻、麦根际土壤中难溶性磷的利用率,其中丰产型小麦和粳稻品种对土壤中磷利用的根际效应更为显著。
This paper deals with pH change under different phosphorus levels and the mechanism of sparingly soluble phosphate utilization by rice and wheat. The effects of roots system on medium pH were related to the levels of phosphate supplied. Medium pH declined obviously, as the level of phosphate supplied decreased. Under P deficiency stress, more protons were extruded by roots. However, there was a distinct difference in H^+-extrusion rate among the various plant species and cultivars. Baofeng 7228 extruded more H^+ than Zhengying No. 1 in wheat, and hybrid rice had higher H^+-extrusion rate than its parents. The remarkable drop of rhizosphere pH occurred in the root zone approximately 4cm above the root tip under P deficiency stress. Furthermore, it was observed that the proton efflux by roots was proportional to light intensity, and had a diurnal change. The maximum rate appeared between 3: 00 P. M. to 7: 00 P. M. The main organic acids extruded by roots were malic and citric acids. There was a marked inverse relation between P levels and citric acid efflux, the amount of citric acid extruded by rice roots increasing distinctly under P deficiency. And the extent of solubilization of rock phosphate was negatively proportional to rhizosphere pH value. A decrease of rhizosphere pH promoted the utilization of sparingly soluble phosphate extractable with 1 mol/L HC1 in soil. Japonica rice had higher ability to use sparingly soluble phosphorus than indica rice. Therefore, it is concluded that phosphorus availability to plants depends on root system character, extent of acidification of soil in the rhizosphere and extrusion of specific organic acids.
基金
国家自然科学基金
关键词
水稻
小麦
根际
H^+分泌
供磷水平
phosphate supply
rhizosphere
H^+-extrusion
organic acid
insoluble phosphorus
