Sun Qing Bin, Shen Ren Fang, Zhao Xue Qiang, Chen Rong Fu, Dong Xiao Ying
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Ann Bot. 2008 Nov;102(5):795-804. doi: 10.1093/aob/mcn166. Epub 2008 Aug 29.
Aluminium (Al) toxicity and phosphorus (P) deficiency often co-exist in acidic soils and limit crop production worldwide. Lespedeza bicolor is a leguminous forage species that grows very well in infertile, acidic soils. The objective of this study was to investigate the effects of Al and P interactions on growth of Lespedeza and the distributions of Al and P in two different Al-resistant species, and to explore whether P can ameliorate the toxic effect of Al in the two species.
Two species, Lespedeza bicolor and L. cuneata, were grown for 30 d with alternate Al and P treatments in a hydroponics system. Harvested roots were examined using a root-system scanner, and the contents of Al, P and other nutrient elements in the plants were determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Haematoxylin staining was used to observe the distribution of Al in the roots of seedlings. After pre-culture with or without P application, organic acids in the exudates of roots exposed to Al were held in an anion-exchange resin, eluted with 2 m HCl and then analysed using high-performance liquid chromatography (HPLC).
Lespedeza bicolor exhibited a stronger Al resistance than did L. cuneata; Al exclusion mechanisms may mainly be responsible for resistance. P application alleviated the toxic effect of Al on root growth in L. bicolor, while no obvious effects were observed in L. cuneata. Much less Al was accumulated in roots of L. bicolor than in L. cuneata after P application, and the P contents in both roots and shoots increased much more for L. bicolor than for L. cuneata. Lespedeza bicolor showed a higher P/Al ratio in roots and shoots than did L. cuneata. P application decreased the Al accumulation in root tips of L. bicolor but not in L. cuneata. The amount of Al-induced organic acid (citrate and malate) exudation from roots pre-cultured with P was much less than from roots without P application; no malate and citrate exudation was detected in L. cuneata.
P enhanced Al resistance in the Al-resistant L. bicolor species but not in the Al-sensitive L. cuneata under relatively high Al stress, although P in L. cuneata might also possess an alleviative potential. Enhancement of Al resistance by P in the resistant species might be associated with its more efficient P accumulation and translocation to shoots and greater Al exclusion from root tips after P application, but not with an increased exudation of organic acids from roots.
铝（Al）毒性和磷（P）缺乏在酸性土壤中常常同时存在，限制了全球农作物产量。二色胡枝子是一种豆科牧草，在贫瘠的酸性土壤中生长良好。本研究的目的是调查Al和P相互作用对二色胡枝子生长以及两种不同耐Al品种中Al和P分布的影响，并探讨P是否能减轻两种植物中Al的毒性作用。
在水培系统中，对二色胡枝子和楔叶胡枝子这两个品种进行Al和P交替处理，培养30天。收获的根系用根系扫描仪进行检测，植物中Al、P和其他营养元素的含量用感应耦合等离子体原子发射光谱法（ICP-AES）测定。苏木精染色用于观察幼苗根系中Al的分布。在有或无P处理的预培养后，将暴露于Al的根系分泌物中的有机酸保留在阴离子交换树脂中，用2m HCl洗脱，然后用高效液相色谱法（HPLC）分析。
二色胡枝子比楔叶胡枝子表现出更强的耐Al性；Al排斥机制可能是耐Al性的主要原因。施P减轻了Al对二色胡枝子根系生长的毒性作用，而在楔叶胡枝子中未观察到明显影响。施P后，二色胡枝子根系中积累的Al比楔叶胡枝子少得多，二色胡枝子根系和地上部的P含量增加幅度均比楔叶胡枝子大得多。二色胡枝子根系和地上部的P/Al比值高于楔叶胡枝子。施P降低了二色胡枝子根尖中Al的积累，但对楔叶胡枝子没有影响。用P预培养的根系中，Al诱导的有机酸（柠檬酸和苹果酸）分泌量比未施P的根系少得多；在楔叶胡枝子中未检测到苹果酸和柠檬酸的分泌。
在相对较高的Al胁迫下，P增强了耐Al品种二色胡枝子的耐Al性，但对Al敏感品种楔叶胡枝子没有增强作用，尽管楔叶胡枝子中的P可能也具有缓解潜力。P对耐Al品种耐Al性的增强可能与其更有效地积累P并向地上部转运以及施P后根尖对Al的排斥作用增强有关，而与根系有机酸分泌增加无关。
