Enhanced adaptability of Sesbania rostrata to Pb/Zn tailings via stem nodulation

Sesbania rostrata is wellknown for its stem nodulation, but the roles of stem nodulation in root nodulation and adaptation of S. rostrata to Pb/Zn-enriched tailings environment has been poorly understood. We investigated the effects of inoculating （with stem nodule treatment） and non-inoculating （without stem nodule treatment） Azorhizobium caulinodans on the growth, root nodulation, and N fixation of S. rostrata grown on three different types of soil substrata： Pb/Zn tailings, garden soil amended tailings, and garden soil. The results showed that plant height, stem basal diameter, biomass, chlorophyll content, nitrogen content and N-accumulation per plant were 2.3%-4.9%, 2.2%-7.7%, 27.8%-72.2%, 17.1%-23.5%, 12.3%-34.2%, and 43.1%-131.2%, respectively, higher in treatments with stem nodule than those without stem nodule for the same soil substrate. With respect to soil substrata, all measurements had consistently higher values in tailings than in amended tailings and garden soil, indicating that the poorer the soil condition, the greater the contribution of stem nodule. In contrast, the number and fresh weight of root nodules on plants without stem nodule were 6.9-11.6 times and 5.8-29.0 times higher than those with stem nodule, respectively, especially with respect to the plants grew on Pb/Zn tailings. In general, stem nodulation favored plant growth and nitrogen fixation of S. rostrata, but suppressed root nodulation. With the ability of stem and root nodulation, S. rostrata can be used as a pioneer plant species for remediation of Pb/Zn tailings.

Responses of Sesbania rostrata and S. cannabina to Pb, Zn, Cu and Cd toxi-cities

Responses of Sesbania rostrata and S. cannabina to Pb, Zn, Cu and Cd toxicities were assessed by a seed-suspending seedbed(SSS) approach. The results showed that the SSS approach was suitable for testing the tolerance of a plant to the stress of toxic metals. The endpoints include seed germination success, straightened radicle and hypocotyl of the seedlings from the seeds. The measurements could be done easily and accurately. It was found that the elongation of radicle was the most sensitive indicator to the stress of heavy metals among the endpoints. When exposure to lower or medium concentrations of Pb, Zn, and Cd, the development of the lateral roots were favorable. Species of S. rostrata was more tolerant than S. cannabina to the heavy metals, especially to Zn and Cd. The ED 50 of Pb, Zn, Cu and Cd were 32.90, 5.32, 4.40 and 12.00 μg/ml for S. rostrata, respectively, and they were 30.11, 2.87, 4.05 and 4.94 μg/ml respectively for S. cannabina.

多花黑麦草在酸化铅锌尾矿上的定植和生长

铅锌矿尾矿上设置长喙田菁压青和不压青处理 ,在此基础上研究多花黑麦草的萌发、生长和重金属积累情况 .结果表明 ,种植长喙田菁改善了尾矿理化性状 ,尤其是提高了有机质、全N、有效态磷和K的含量 .尾矿的强酸性环境 (pH <3)是影响黑麦草在其上定植的主要因素 .施用石灰可暂时改善尾矿酸度 ,但实验结束时尾矿酸度几乎完全恢复原状 .因此 ,施用石灰可能只对种子发芽产生作用 .大多数情况下多花黑麦草能在尾矿上萌发、生长和定植 ,并产生较大的生物量 (DM 1.4～ 3.2t·km-2 ) ,表现出对酸性尾矿环境的一定的适应性 .与未栽培长喙田菁的对照相比 ,栽培长喙田菁处理以及栽培长喙田菁并压青处理分别使多花黑麦草的生物量提高了 4 .8%～ 39.5 %和 7.7%～ 139.5 % ,其中压青处理又比不压青处理提高了 2 .7%～ 75 .8% .“长喙田菁 多花黑麦草”植被系列是一个成功的铅锌矿尾矿废弃地复垦的先锋阶段 .

茎瘤对长喙田菁在铅锌尾矿环境适应中的意义 Ⅱ.茎瘤对长喙田菁固氮和积累重金属的影响

探讨茎瘤对长喙田菁 (Sesbaniarostrata)在铅锌矿尾矿、客土和纯土环境中结瘤、固氮和积累重金属的影响。结果表明 :保留茎瘤使长喙田菁全株植物氮含量和单株植物氮积累量分别比去除茎瘤处理提高了 12 .4%～34 .0 %和 43.3%～ 131.4%,且环境愈恶劣 ,这种作用愈为显著。同时 ,保留茎瘤处理显著抑制了长喙田菁根瘤的生长 ,同样表现出环境愈恶劣 ,抑制作用愈显著的趋势。因此 ,在尾矿环境胁迫下 ,长喙田菁更趋向于选择茎瘤作为固氮途径。由此可见 ,茎瘤对生长在铅锌尾矿环境中的长喙田菁获得氮素及支持其生长有着特别重要的作用。此外 ,茎瘤使长喙田菁体内重金属含量略有下降 ,但下降幅度很小 ;铅、锌、铜、镉等 4种重金属均在根部含量最高 ,远大于茎和叶 ,茎和叶之间差异不显著 ,均表现为随栽培介质中重金属含量的增加而提高的趋势 ;长喙田菁对 4种重金属积累量为锌 >铅 >铜 >镉。研究结果再次证明了长喙田菁具有很强的在重金属污染环境中进行生物固氮的能力。

茎瘤对长喙田菁在铅锌尾矿环境适应中的意义 Ⅰ.茎瘤对长喙田菁生长发育的影响

通过设置保留茎瘤和去除茎瘤处理 ,研究长喙田菁 (Sesbaniarostrata)在铅锌尾矿、客土和纯土环境中的生长发育情况。结果表明 :保留茎瘤使长喙田菁的株高、地上部生物量、地下部生物量、全株生物量和叶绿素含量分别比去除茎瘤处理提高了 2 4 %～ 4 8%、2 7 4 %～ 6 7 9%、2 8 5 %～ 99 3%、2 7 6 %～ 72 3%和 17 0 %～ 2 3 4 %,这种作用在纯尾矿处理组最为显著 ,客土处理组次之 ,即环境愈恶劣 ,茎瘤这种作用愈显著 ,证明了茎瘤对长喙田菁适应铅锌尾矿环境有积极的贡献。

营养杯对长喙田菁在铅锌尾矿上的生长、固氮和重金属积累的影响

设置移栽时营养杯的有无及其大小作试验,研究长喙田菁在乐昌铅锌矿强酸化尾矿上的生长、固氮和积累重金属情况。结果表明,强酸性(pH<3)是限制植物定植的主要因素,在pH=5-7情况下,长喙田菁能在该尾矿库中定植、生长和固氮,表现出良好的适应性。未带营养杯移栽的长喙田菁在尾矿上生长84d,其株高117cm、茎基部直径1.35cm、单株生物量(干物质)20.2g、单位面积生物量(干物质)2828kghm-2、氮素积累量40kghm-2;带营养杯移栽的上述各指标分别达到140-144cm、1.59-1.68cm、36.6-38.8g、5124-5432kghm-2和77-107kghm-2,均显著高于未带营养杯处理的。长喙田菁根部铅、锌、铜、镉含量均最高,其次为茎,叶中最低;长喙田菁的4种重金属积累量为锌(186-221mgkg-1)>铅(96-145mgkg-1)>铜(17-30mgkg-1)>镉(3-4mgkg-1)。带营养杯移栽能有效提高长喙田菁的产量和氮积累量,且明显降低其体内的重金属含量。试验证明长喙田菁是较理想的铅锌矿尾矿废弃地植被重建的先锋植物。

重金属胁迫对长喙田菁茎瘤豆血红蛋白和叶绿素含量的影响

盆栽试验种植长喙田菁 ,栽培介质分别为纯铅锌尾矿 (T)、改性铅锌尾矿 (ST )和纯土壤 (S) ,对各处理长喙田菁茎瘤的豆血红蛋白和叶绿素含量进行分析。结果表明 ,T、ST组的茎瘤数量分别为S组的 5 5 %和 89% ,茎瘤生物量则分别为S组的 6 6 %和 90 % ,但各实验组长喙田菁茎瘤的豆血红蛋白和叶绿素含量无显著性差异 ,暗示尾矿环境对茎瘤的固氮活性可能无显著影响。