The beneficial effect of silicon to reduce the nitrate content of sorghum

Sorghum [<i>Sorghum bicolor</i> (L.) Moench] is one of the major fodder crops. Sufficient nitrogen (N) supply is essential for a good yield and forage quality. However, N excess may cause nitrate accumulation in the plant, which can be toxic to ruminant livestock animals. Silicon (Si) application reportedly enhances the utilization of N and reduces the nitrate content in plants. However, our knowledge regarding the interaction between Si and N in sorghum is still limited. Hence, this study investigated the possibility of nitrate content reduction by Si application in sorghum. We analyzed the nitrate content in the shoots of 6-week-old hydroponically grown plants with or without Si application. The analysis was also conducted with plants at the heading stage (13-week-old) receiving higher N supply. The dry matter production was not affected by Si application in either experiment. The assimilated N was slightly decreased by Si application in 6-week-old plants, but not in plants at the heading stage. The nitrate content was reduced by Si application in both experiments. The effect of Si application on the N metabolism was confirmed by a modulated expression of the genes for N transport and assimilation, in which an upregulation of the cytokinin signal transduction pathway might be involved. The <i>in vitro</i> digestibility was not significantly affected by Si application. These findings suggest that Si application benefits fodder sorghum production by reducing nitrate content without compromising the biomass yield and quality, although further study with plants grown under more practical conditions is necessary.

高粱（*Sorghum bicolor* (L.) Moench）是主要饲用作物之一。充足的氮（N）供应对获得良好产量与饲用品质至关重要。然而，过量施氮会导致植株体内硝酸盐积累，该物质对反刍家畜具有毒性。已有研究证实，施用硅（Si）可提升植物对氮的利用率并降低植株硝酸盐含量。但目前学界关于高粱中硅与氮的互作机制仍所知有限。因此，本研究探讨了通过施用硅降低高粱硝酸盐含量的可行性。我们分别分析了两组水培种植植株的地上部硝酸盐含量：一组为6周龄植株，分别施以硅与不施硅处理；另一组为处于抽穗期（13周龄）且供应高氮水平的植株。两项试验中，施硅均未对干物质产量产生影响。6周龄植株经施硅处理后，同化氮水平略有下降，但抽穗期植株未出现该变化。两项试验中，施硅均显著降低了植株硝酸盐含量。通过对氮转运与同化相关基因的表达调控分析，证实了施硅对氮代谢的调控作用，其中细胞分裂素信号转导通路的上调可能参与其中。体外消化率未受施硅的显著影响。上述研究结果表明，施用硅可在不牺牲生物量产量与品质的前提下，通过降低硝酸盐含量助力饲用高粱生产，但仍需在更贴近实际生产的种植条件下开展进一步研究。