Sas L, Rengel Z, Tang C
Soil Science and Plant Nutrition, The University of Western Australia, 35 Stirling Hwy, WA6009, Crawley, Australia
Plant Sci. 2001 May;160(6):1191-1198. doi: 10.1016/s0168-9452(01)00373-9.
In symbiotically-grown legumes, rhizosphere acidification may be caused by a high cation/anion uptake ratio and the excretion of organic acids, the relative importance of the two processes depending on the phosphorus nutritional status of the plants. The present study examined the effect of P deficiency on extrusions of H(+) and organic acid anions (OA(-)) in relation to uptake of excess cations in N(2)-fixing white lupin (cv. Kiev Mutant). Plants were grown for 49 days in nutrient solutions treated with 1, 5 or 25 mmol P m(-3) Na(2)HPO(4) in a phytotron room. The increased formation of cluster roots occurred prior to a decrease in plant growth in response to P deficiency. The number of cluster roots was negatively correlated with tissue P concentrations below 2.0 g kg(-1) in shoots and 3 g kg(-1) in roots. Cluster roots generally had higher concentrations of Mg, Ca, N, Cu, Fe, and Mn but lower concentrations of K than non-cluster roots. Extrusion of protons and OA(-) (90% citrate and 10% malate) from roots was highly dependent on P supply. The amounts of H(+) extruded per unit root biomass decreased with time during the experiment. On the equimolar basis, H(+) extrusion by P-deficient plants (grown at 1 and 5 mmol P m(-3)) were, on average, 2-3-fold greater than OA(-) exudation. The excess cation content in plants was generally the highest at 1 mmol P m(-3) and decreased with increasing P supply. The ratio of H(+) release to excess cation uptake increased with decreasing P supply. The results suggest that increased exudation of OA(-) due to P deficiency is associated with H(+) extrusion but contributes only a part of total acidification.
在共生生长的豆科植物中，根际酸化可能是由于高阳离子/阴离子吸收比以及有机酸的分泌，这两个过程的相对重要性取决于植物的磷营养状况。本研究考察了缺磷对固氮白羽扇豆（品种：基辅突变体）中H⁺和有机酸阴离子（OA⁻）分泌以及过量阳离子吸收的影响。植物在人工气候室中，于添加了1、5或25 mmol P m⁻³ Na₂HPO₄的营养液中培养49天。在因缺磷导致植物生长下降之前，簇生根的形成就已增加。簇生根的数量与地上部组织磷浓度低于2.0 g kg⁻¹以及根部组织磷浓度低于3 g kg⁻¹呈负相关。与非簇生根相比，簇生根通常具有较高的镁、钙、氮、铜、铁和锰浓度，但钾浓度较低。根中质子和OA⁻（90%为柠檬酸和10%为苹果酸）的分泌高度依赖于磷供应。在实验过程中，单位根生物量挤出的H⁺量随时间减少。在等摩尔基础上，缺磷植物（在1和5 mmol P m⁻³下生长）挤出的H⁺平均比OA⁻渗出量大2 - 3倍。植物中的过量阳离子含量通常在1 mmol P m⁻³时最高，并随磷供应增加而降低。H⁺释放与过量阳离子吸收的比率随磷供应减少而增加。结果表明，缺磷导致的OA⁻分泌增加与H⁺挤出有关，但仅占总酸化的一部分。
