Synergistic Effects of Water Management and Silicon Foliar Spraying on the Uptake and Transport Efficiency of Cadmium in Rice (Oryza sativa L.)

Comparing the Effects of Lime Soil and Yellow Soil on Cadmium Accumulation in Rice during Grain-Filling and Maturation Periods

The karst area has become a high-risk area for Cadmium (Cd) exposure. Interestingly, the high levels of Cd in soils do not result in an excessive bioaccumulation of Cd in rice. Carbonate rock dissolution ions (CRIs) could limit the accumulation and translocation of Cd in rice. CRIs can become a major bottleneck in the remediation and management of farmlands in karst areas. However, there is limited research on the effects of CRIs in soils on Cd accumulation in rice. The karst area of lime soil (LS) and the non-karst areas of yellow soil (YS) were collected, and an external Cd was added to conduct rice cultivation experiments. Cd and CRIs (Ca2+, Mg2+, CO32-/HCO3-, and OH-) in the rice-soil system were investigated from the grain-filling to maturity periods. The results showed that CRIs of LS were significantly higher than that of YS in different treatments. CRIs of LS were 2.05 mg·kg-1 for Ca2+, 0.90 mg·kg-1 for Mg2+, and 42.29 mg·kg-1 for CO32- in LS. CRIs could influence DTPA Cd, resulting in DTPA Cd of LS being lower than that of YS. DTPA Cd of YS was one to three times larger than that of YS. Cd content in different parts of rice in YS was higher than that of LS. Cd in rice grains of YS was one to six times larger than that of LS. The uptake of Cd from the soil during Filling III was critical in determining rice Cd accumulation. CRIs in the soil could affect Cd accumulation in rice. Ca2+ and Mg2+ had significant negative effects on Cd accumulation of rice at maturity and filling, respectively. CO32-/HCO3- and OH- had significant negative effects on DTPA Cd in soil.

Effect of common horsetail extract on growth characteristics, essential oil yield and chemical compositions of basil (Ocimum basilicum L.)

To investigate the effect of horsetail extract containing high silicon on morphological traits, growth, content, and compositions of essential oil of sweet basil (Ocimum basilicum L.) an experiment turned into carried out in the shape of a randomized complete block design with three replications. Foliar treatment of horsetail extract with zero, 0.5, 1, and 2% concentrations was applied on 6-8 leaf plants. The assessed traits include plant height, number of leaves per plant, number of sub-branches, leaf area index, plant fresh weight, plant dry weight, total anthocyanin, the content of total phenol and total flavonoid, antioxidant activity, essential oil content, and compounds were measured. The findings demonstrated that the increase of silicon-containing horsetail extract enhanced the improved increase in growth and phytochemical trait values. The use of horsetail extract in the 2% treatment increased plant height, the number of leaves per plant, the number of sub-branches, leaf area index, fresh weight, and dry weight of the plant by 49.79, 45.61, 91.09, 99.78, 52.78 and 109.25%, respectively, compared to the control. The highest content of total phenol (2.12 mg GAE/g DW), total flavonoid (1.73 mg RE/g DW), total anthocyanin (0.83 mg C3G/g DW), and antioxidant activity (184.3 µg/ml) was observed in the 2% extract treatment. The content of essential oil increased with increasing the concentration of horsetail extract, so the highest amount of essential oil was obtained at the concentration of 2%, which increased by 134.78% compared to the control. By using GC-MS, the essential oil was analyzed. The main components of the essential oil include methyl eugenol (12.93-25.93%), eugenol (17.63-27.51%), 1,8-cineole (15.63-20.84%), linalool (8.31-19.63%) and (Z)-caryophyllene (6.02-14.93%). Increasing the concentration of horsetail extract increased the compounds of eugenol, 1,8-cineole, and linalool in essential oil compared to the control, but decreased the compounds of methyl eugenol and (Z)-caryophyllene. Foliar spraying of horsetail extract, which contains high amounts of silicon, as a stimulant and biological fertilizer, can be a beneficial ingredient in increasing the yield and production of medicinal plants, especially in organic essential oil production.

Ameliorating Effects of Graphene Oxide on Cadmium Accumulation and Eco-Physiological Characteristics in a Greening Hyperaccumulator (Lonicera japonica Thunb.)

Graphene oxide (GO), as a novel carbon-based nanomaterial (CBN), has been widely applied to every respect of social life due to its unique composite properties. The widespread use of GO inevitably promotes its interaction with heavy metal cadmium (Cd), and influences its functional behavior. However, little information is available on the effects of GO on greening hyperaccumulators under co-occurring Cd. In this study, we chose a typical greening hyperaccumulator (Lonicera japonica Thunb.) to show the effect of GO on Cd accumulation, growth, net photosynthesis rate (Pn), carbon sequestration and oxygen release functions of the plant under Cd stress. The different GO-Cd treatments were set up by (0, 10, 50 and 100 mg L-1) GO and (0, 5 and 25 mg L-1) Cd in solution culture. The maximum rate of Cd accumulation in the roots and shoots of the plant were increased by 10 mg L-1 GO (exposed to 5 mg L-1 Cd), indicating that low-concentration GO (10 mg L-1) combined with low-concentration Cd (5 mg L-1) might stimulate the absorption of Cd by L. japonica. Under GO treatments without Cd, the dry weight of root and shoot biomass, Pn value, carbon sequestration per unit leaf area and oxygen release per unit leaf area all increased in various degrees, especially under 10 mg L-1 GO, were 20.67%, 12.04%, 35% and 28.73% higher than the control. Under GO-Cd treatments, it is observed that the cooperation of low-concentration GO (10 mg L-1) and low-concentration Cd (5 mg L-1) could significantly stimulate Cd accumulation, growth, photosynthesis, carbon sequestration and oxygen release functions of the plant. These results indicated that suitable concentrations of GO could significantly alleviate the effects of Cd on L. japonica, which is helpful for expanding the phytoremediation application of greening hyperaccumulators faced with coexistence with environment of nanomaterials and heavy metals.

Mitigation effects of foliar supply of different sulfur forms on uptake, translocation and grain accumulation of Cd and As by paddy rice on basis of liming

Co-contamination of Cd and As in strongly acidic paddy soil has posed great challenges for remediation practice due to their distinct properties. Liming is a necessary but inadequate measure for normal growth of paddy rice and for Cd and As remediation in strongly acidic paddy soils rich in iron minerals. A greenhouse rice pot cultivation experiment was conducted to explore the efficiency and mechanisms of how foliar supply of different sulfur forms (K2S, K2SO4) could further mediate the uptake, translocation and grain accumulation of Cd and As by paddy rice on basis of liming. Results showed that compared to liming alone (CK), co-application of liming and foliar supply of K2S (L + FK2S) significantly reduced contents of Cd and As in brown rice by 44.4 % and 24.7 %, respectively. Contrastingly, co-application of liming and foliar supply of K2SO4 (L + FK2SO4) decreased Cd content of brown rice by 55.5 %, but had no effect on As content. Foliar supply of K2S and K2SO4 dramatically facilitated Cd upward transfer from roots to shoots by enhancing root Cd transfer from cell wall into trophoplast. On the other hand, both sulfur forms remarkably elevated sulfur contents in leaves and significantly inhibited Cd translocation from leaves to grain by enhancing vacuolar sequestration of Cd in leaves. Compared to CK and L + FK2SO4 treatment, it was by enhancing glutathione synthesis, cell wall deposition in roots and vacuolar sequestration of As in leaves that L + FK2S showed greater inhibiting effects on transfer of As from roots, stems and leaves to grain. Foliar supply of either sulfate or sulfide could efficiently decrease grain Cd of paddy rice, but only foliar supply of sulfide is effective in reducing grain As.

Effects of Cadmium Stress on Carbon Sequestration and Oxygen Release Characteristics in A Landscaping Hyperaccumulator-Lonicera japonica Thunb

The carbon sequestration and oxygen release of landscape plants are dominant ecological service functions, which can play an important role in reducing greenhouse gases, improving the urban heat island effect and achieving carbon peaking and carbon neutrality. In the present study, we are choosing Lonicera japonica Thunb. as a model plant to show the effects of Cd stress on growth, photosynthesis, carbon sequestration and oxygen release characteristics. Under 5 mg kg^-1 of Cd treatment, the dry weight of roots and shoots biomass and the net photosynthetic rate (P_N) in L. japonica had a significant increase, and with the increase in Cd treatment concentration, the dry weight of roots and shoots biomass and P_N in the plant began to decrease. When the Cd treatment concentration was up to 125 mg kg^-1, the dry weight of root and shoots biomass and P_N in the plant decreased by 5.29%, 1.94% and 2.06%, and they had no significant decrease compared with the control, indicating that the plant still had a good ability for growth and photoenergy utilization even under high concentrations of Cd stress. The carbon sequestration and oxygen release functions in terms of diurnal assimilation amounts (P), carbon sequestration per unit leaf area (W_CO2), oxygen release per unit leaf area (W_O2), carbon sequestration per unit land area (P_CO2) and oxygen release per unit land area (P_O2) in L. japonica had a similar change trend with the photosynthesis responses under different concentrations of Cd treatments, which indicated that L. japonica as a landscaping Cd-hyperaccumulator, has a good ability for carbon sequestration and oxygen release even under high concentrations of Cd stress. The present study will provide a useful guideline for effectively developing the ecological service functions of landscaping hyperaccumulators under urban Cd-contaminated environment.