Effects of waterlogging at different growth stages on the photosynthetic characteristics and grain yield of sorghum (Sorghum bicolor L.).

Various plants, including sorghum (Sorghum bicolor L.), are exposed to waterlogging; however, little is known about the effects of waterlogging at different growth stages on sorghum. A pot experiment was conducted using two sorghum hybrids, Jinuoliang 01 (JN01) and Jinza 31 (JZ31), to investigate the effects of waterlogging at different growth stages on the photosynthesis enzyme activity, chlorophyll content, malondialdehyde (MDA) content, photosynthetic parameters, dry matter accumulation, and grain yield. The experiment was conducted using waterlogging treatments implemented at the five-leaf stage (T1), flowering stage (T2), and filling stage (T3), using standard management (no waterlogging) as a control (CK). The adverse effects of waterlogging on sorghum growth varied with the waterlogging timing, with the maximum impact at T1, followed by T2 and T3. JZ31 was more sensitive to waterlogging compared to JN01. Waterlogged conditions inhibited the photosynthetic enzyme activity and reduced the chlorophyll content and photosynthesis, ultimately lowering the biomass yield and grain yield. The maximum yield loss was observed with the T1 waterlogging treatment; the grain yield of JN01 and JZ31 decreased by 52.01-54.58% and 69.52-71.97%, respectively, compared with CK. Furthermore, the decline in grain yield in T1 was associated with reducing grain number per panicle. These findings indicate that sorghum is sensitive to waterlogging at the five-leaf stage and JZ31 is more sensitive to waterlogging than JN01, which may provide a basis for selecting genotypes and management measures to cope with waterlogging in sorghum.

The leaf-air temperature difference reflects the variation in water status and photosynthesis of sorghum under waterlogged conditions.

Waterlogging stress is one of the most important abiotic stresses limiting sorghum growth and development. Consequently, the responses of sorghum to waterlogging must be monitored and studied. This study investigated changes in the leaf water status, xylem exudation rate, leaf anatomical structure, leaf temperature and photosynthetic performance. Waterlogging-tolerant (Jinuoliang 01, abbreviated JN01) and waterlogging-sensitive (Jinza 31, abbreviated JZ31) sorghum cultivars were planted in pots. The experiment was carried out using a split block design with three replications. Waterlogging stress was imposed at the sorghum five-leaf stage. The leaf free water content (FWC) and relative water content (RWC) decreased under the waterlogged condition. The leaf thickness was thinner under the waterlogged condition, and the main changes occurred in the upper epidermal and mesophyll cells. Gas exchange parameters and the xylem exudation rate were also restrained by waterlogging; however, greater responses of these parameters were observed in JZ31. JZ31 had a higher leaf-air temperature difference (ΔT) than JN01. We found that changes in ΔT were always consistent with changes in the RWC and the gas exchange parameters. ΔT was significantly associated with the leaf RWC, photosynthetic rate (Pn) and transpiration rate (Tr). The results suggest that ΔT may be an indicator reflecting the water status in leaves and can be used to evaluate the tolerance of sorghum to waterlogging.

Magnetically separable and reusable rGO/Fe3O4 nanocomposites for the selective liquid phase oxidation of cyclohexene to 1,2-cyclohexane diol.

A series of magnetically separable rGO/Fe3O4 nanocomposites with various amounts of graphene oxide were successfully prepared by a simple ultrasonication assisted precipitation combined with a solvothermal method and their catalytic activity was evaluated for the selective liquid phase oxidation of cyclohexene using hydrogen peroxide as a green oxidant. The prepared materials were characterized using XRD, FTIR, FESEM, TEM, HRTEM, BET/BJH, XPS and VSM analysis. The presence of well crystallized Fe3O4 as the active iron species was seen in the crystal studies of the nanocomposites. The electron microscopy analysis indicated the fine surface dispersion of spherical Fe3O4 nanoparticles on the thin surface layers of partially-reduced graphene oxide (rGO) nanosheets. The decoration of Fe3O4 nanospheres on thin rGO layers was clearly observable in all of the nanocomposites. The XPS analysis was performed to evaluate the chemical states of the elements present in the samples. The surface area of the nanocomposites was increased significantly by increasing the amount of GO and the pore structures were effectively tuned by the amount of rGO in the nanocomposites. The magnetic saturation values of the nanocomposites were found to be sufficient for their efficient magnetic separation. The catalytic activity results show that the cyclohexene conversion reached 75.3% with a highest 1,2-cyclohexane diol selectivity of 81% over 5% rGO incorporated nanocomposite using H2O2 as the oxidant and acetonitrile as the solvent at 70 °C for 6 h. The reaction conditions were further optimized by changing the variables and a possible reaction mechanism was proposed. The enhanced catalytic activity of the nanocomposites for cyclohexene oxidation could be attributed to the fast accomplishment of the Fe2+/Fe3+ redox cycle in the composites due the sacrificial role of rGO and its synergistic effect with Fe3O4, originating from the conjugated network of π-electrons in its surface structure. The rapid and easy separation of the magnetic nanocomposites from the reaction mixture using an external magnet makes the present catalysts highly efficient for the reaction. Moreover, the catalyst retained its activity for five repeated runs without any drastic drop in the reactant conversion and product selectivity.