Optimization of slow-release fertilizer application improves lotus rhizome quality by affecting the physicochemical properties of starch

To achieve the dual goals of high yield and good quality with low environmental costs, slow-release fertilizer (SRF) has been widely used in lotus cultivation as new type of fertilizer instead of traditional nitrogen fertilizer. However, the optimal amount of SRF and how it would promote lotus rhizome quality remain unclear. This study was designed to investigate the photosynthetic characteristics and the synthesis, accumulation, and physicochemical properties of lotus rhizome starches under six SRF levels (CK, S1, S2, S3, S4, and S5). Compared with CK (0 kg ha–1), the net photosynthetic rate (Pn) and SPAD values of leaves remained at higher levels under SRF treatment. Further research showed that SRF increased the lotus rhizome yield, the contents of amylose, amylopectin, and total starch, and the number of starch granules. Among the six SRF levels, S3 (1 035 kg ha–1) showed the greatest difference from CK and produced the highest levels. With the increasing SRF levels, the peak, hot and final viscosities decreased at first and then increased, but the setback viscosity and pasting temperature increased. In order to interpret these changes at the molecular level, the activities of key enzymes and relative expression levels of starch accumulation related genes were analyzed. Each of these parameters also increased under SRF treatment, especially under the S3 treatment. The results of this study show that SRF, especially S3 (1 035 kg ha–1), is a suitable fertilizer option for lotus planting which can improve lotus rhizome quality by affecting starch accumulations related enzymes and genes. These results will be useful for SRF application to high-quality lotus rhizome production with low environmental costs.