Silicate fertilization potentiates the nodule formation and symbiotic nitrogen fixation in soybean1

ABSTRACT The application of silicon (Si) to the soil can increase the grain yield of the soybean crop by improving the nitrogen biological fixation, due to its beneficial effect on the Bradyrhizobium-soybean symbiosis. This study aimed to investigate the effect of fertilization with calcium and magnesium silicate on plant growth, root nodulation and nitrogen (N) uptake, in two soybean cultivars [BRS 1074 IPRO (transgenic) and BRS-MG 800A (conventional)], under greenhouse conditions. The application of silicate significantly increased the number of root nodules only for the BRS-MG 800A, while the positive effects of the silicate addition on nodule size, chlorophyll level and leaf N concentration were observed in both cultivars. The soybean cultivars show distinct responses to the silicate application, with respect to growth and dry matter yield, being the BRS 1074 IPRO more responsive than the BRS-MG 800A. Therefore, Si may induce the formation of root nodules in soybean plants and lead to significant increases in the nitrogen biological fixation and plant growth. These results highlight that Si is not only involved in the improvement of plant growth, but it can be also considered a crucial element to improve the symbiotic performance of soybean plants. However, the physiological basis of how and where silicate exerts its influence on nodulation and nitrogen biological fixation still remains unknown.

摘要 硅（silicon, Si）施用于土壤可通过提升氮（nitrogen, N）生物固氮能力提高大豆籽粒产量，因其对慢生根瘤菌-大豆共生体系（Bradyrhizobium-soybean symbiosis）具有有益效应。本研究旨在探究温室条件下，钙镁硅酸盐施肥对两个大豆品种[转基因品种BRS 1074 IPRO与常规品种BRS-MG 800A]的植株生长、根瘤结瘤（root nodulation）及氮吸收的影响。仅对BRS-MG 800A品种而言，硅酸盐施用可显著提升其根瘤数量；而在两个品种中，硅酸盐添加均对根瘤尺寸、叶绿素水平（chlorophyll level）及叶片氮浓度产生积极影响。就植株生长与干物质产量（dry matter yield）而言，两个大豆品种对硅酸盐施用的响应存在显著差异，其中BRS 1074 IPRO的响应程度高于BRS-MG 800A。由此可见，硅可诱导大豆植株根瘤的形成，并显著提升其氮生物固氮能力与植株生长水平。本研究结果表明，硅不仅可促进植株生长，还可作为提升大豆植株共生性能（symbiotic performance）的关键元素。然而，硅酸盐如何、在何处对根瘤结瘤及氮生物固氮发挥作用的生理基础（physiological basis）仍未明确。