采用分室（内、外室）培养法，以紫花苜蓿及其耐酸根瘤菌91522为材料，在酸性土壤（pH4.45）中额外补充Al3+至中度铝毒水平，从培养装置根箱外接种，探讨了补充Ca2 、P后，耐酸苜蓿根瘤菌在酸性土壤上的存活、迁移以及群体感应的变化动态。结果表明，补充5 mmol kg-1 Ca2 处理的土壤根瘤菌的数量在97 d种植期内均显著高于对照（Ca0P0，即无Ca2 无P处理），Ca2 5 mmol kg-1 P 0 µmol kg-1处理近根区（距苜蓿植株根1～2 cm）土壤最大根瘤菌数量为同期对照的6.15倍；在此基础上补充P后根瘤菌的数量进一步增加，“Ca2 5 mmol kg-1 P 4 µmol kg-1”处理近根区最大根瘤菌数量为同期对照处理的9.40倍。因此推断Ca2 和P的上述作用存在交互效应。施加Ca2 、P能够显著提高土壤中根瘤菌群体感应物质N-酰基高丝氨酸内酯衍生物（N-acyl-homoserine actones，AHLs）的含量，且Ca2 5 mmol kg-1效果好于Ca2 10 mmol kg-1处理。根瘤菌数量在远根区（距苜蓿植株根6～8 cm）与近根区变化规律一致，即接种1周后根瘤菌数量由远根区向近根区逐渐增加，接种后30 d内达到最高值，之后数量下降并趋于稳定。但近根区根瘤菌数量和AHLs含量均高于远根区，说明宿主根际微环境也能够影响根瘤菌数量和群体感应。初步认为，酸性有铝土壤上补充Ca2 5 mmol kg-1和P 30 µmol kg-1对耐酸根瘤菌的存活、迁移和群体感应有良好的改善效果。该处理最终显著地增强了对酸性土壤极为敏感的苜蓿植株的耐酸铝胁迫能力，较对照显著（p<0.05）改善了酸铝胁迫下苜蓿的植株根鲜重（为对照的4.67倍）、地上部鲜重（3.10倍）、含氮量（2.47倍）和根瘤数（14.74倍）等农艺性状。
Soil acidification has become a serious challenge to farmers in the past decades as a result of acid rain, fertilizer application, climate change, etc. In the year of 2000, about 21% of the arable land soil was defined as acid soil in China. At the same time, about 50% of the agricultural soil the world over has become acid soil. Researchers have been working in fields related to acid soils from the aspect of its biological perspectives in order to remedy and exploit the soil. In the past years the authors have been focusing on the subject of acid tolerance of rhizobium, which may help its legume host, including alfalfa, one of the most sensitive plant to soil acidity, to survive in acid soil. What the authors found in previous studies has shown that acid-tolerant rhizobia improve rhizospheric environment for growth of their legume hosts in acid soil by secreting alkaline substance. Application of a proper amount of calcium (5 mmol kg-1) enhances growth and multiplication of acid-tolerant rhizobia, which leads to better growth of the legume host manifested in significant increase in the concentration of total N in the plant (p<0.05) as compared with CK or Treatment Ca0P0, i.e. no P and Ca addition. At the same time, the quorum sensing of the rhizobia in the rhizosphere improves, too. Addition of phosphorous, as demonstrated in volumes of researches, stimulates root extension and helps the plant stand a number of environmental stresses. Nevertheless so far few papers are available on effect of addition of P and Ca together on growth of rhizobia in acid soil and hence on tolerance of the host plant to acid in soil. To explore the effects, a pot experiment on alfalfa and an acid-tolerant stain of rhizobia, Sinorhizobium meliloti 91522 was carried out using the dual-chamber culture method. In the experiment, the pots were packed with acid soil (pH4.45), which was amended with Al3+ till Al3 toxicity of the soil reached medium in level and each pot was divided into two chambers, i.e. inner and outer chambers. Rhizobia 91522 were inoculated into the soil in the outer chamber, far from the plant in the inner chamber, to test. Results show that within the 97 days after the inoculation the number of rhizobia was all significantly higher in the pots amended with 5 mmol kg-1 Ca2 than in CK. For example, the maximum number of rhizobia in the soil, 1~2 cm from alfalfa root in the pots treated with Ca2 but no P was 615 times that in CK. On such a basis addition of P enhanced the effect of Ca on growth of rhizobia, e.g. the number of rhizobia, increased up to 9.4 times that in CK. Therefore, it could be concluded that interaction existed between Ca and P in the effect. Addition of Ca2 and P also significantly raised the concentration of N-acyl-homoserine actones (AHLs) - the indicator of quorum sensing of rhizobia in the soil under acid and aluminum stresses. For this effect, the addition of 5 mmol kg-1Ca2 worked better than that of 10 mmol kg-1 Ca. The rhizobia in the near root area (1~2 cm from the root) and the far root area (6~8 cm from the root) had similar trends in variation of population during the culturing period, i.e. one week after inoculation, rhizobia spread gradually from the far root zone to the near root zone, peaked in population about 30 days after inoculation, and afterwards the populations of rhizobia in both zones started to decline and level off, However, the population of rhizobia was much bigger in the near root zone than in the far root area all the time except the first two weeks after inoculation, showing that the rhizospheric micro-environment of the host plant is also an important factor affecting the population of rhizobia and quorum sensing. It is tentatively held that addition of 5 mmol kg-1 Ca2 and 30 µmol kg-1 P is an optimal treatment, which helps better survival, migration and quorum sensing of acid-tolerant rhizobia in acid soil under aluminum stress, and hence growth of alfalfa under the aforementioned stresses. The plant in this treatment was 4.67, 3.10, 3.47 and 14.74 times that in CK in root fresh weight, shoot fresh weight, nitrogen concentration and number of nodules, respectively.
张 磊,王晓锋,罗 珍,刘晓燕,吴先勤,付 莉,蔚建军.钙磷对酸铝土壤中苜蓿根瘤菌迁移定殖和群体感应的影响[J].土壤学报,2014,51(5):1120-1131. DOI:10.11766/trxb201312050579 Zhang Lei, Wang Xiaofeng, Luo Zhen, Liu Xiaoyan, Wu Xianqin, Fu Li, Yu Jianjun. Effect of calcium and phosphorous on migration, propagation and quorum sensing of rhizobia in acid soil under aluminum stress[J]. Acta Pedologica Sinica,2014,51(5):1120-1131.复制