Photosynthesis promotion mechanisms of artificial humic acid depend on plant types: A hydroponic study on C3 and C4 plants.

It is feasible to improve plant photosynthesis to address the global climate goals of carbon neutrality. The application of artificial humic acid (AHA) is a promising approach to promote plant photosynthesis, however, the associated mechanisms for C3 and C4 plants are still unclear. In this study, the real-time chlorophyll synthesis and microscopic physiological changes in plant leave cells with the application of AHA were first revealed using the real-time chlorophyll fluorescence parameters and Non-invasive Micro-test Technique. The transcriptomics suggested that the AHA application up-regulated the genes in photosynthesis, especially related to chlorophyll synthesis and light energy capture, in maize and the genes in photosynthetic vitality and carbohydrate metabolic process in lettuce. Structural equation model suggested that the photodegradable substances and growth hormones in AHA directly contributes to photosynthesis of C4 plants (0.37). AHA indirectly promotes the photosynthesis in the C4 plants by upregulating functional genes (e.g., Mg-CHLI and Chlorophyllase) involved in light capture and transformation (0.96). In contrast, AHA mainly indirectly promotes C3 plants photosynthesis by increasing chlorophyll synthesis, and the Rubisco activity and the ZmRbcS expression in the dark reaction of lettuce (0.55). In addition, Mg2+ transfer and flux in C3 plant leaves was significantly improved by AHA, indirectly contributes to plant photosynthesis (0.24). Finally, the AHA increased the net photosynthetic rate of maize by 46.50 % and that of lettuce by 88.00 %. Application of the nutrients- and hormone-rich AHA improves plant growth and photosynthesis even better than traditional Hoagland solution. The revelation of the different photosynthetic promotion mechanisms on C3 and C4 plant in this work guides the synthesis and efficient application of AHA in green agriculture and will propose the development of AHA technology to against climate change resulting from CO2 emissions in near future.

Nanoscale Iron trioxide catalyzes the synthesis of auxins analogs in artificial humic acids to enhance rice growth.

Humic acids (HAs), kinds of valuable active carbon, are critical for improving soil fertility. However, the majority of soils are poor in HAs, arousing the development of artificial HAs. In this study, two iron-based catalysts (nanoscale iron trioxide (nFe2O3) and FeCl3) were used to catalyze the hydrothermal humification of waste corn straw. With the help of ultra-performance liquid chromatography-mass spectrometry, we proposed the specific humification process with the action of catalysis for the first time, which is of great significance for the design, synthesis and application of artificial HAs in the future. Moreover, the growth-promoting effect and mechanisms of the artificial HAs were determined by rice planting in a greenhouse. Results showed that compared to no catalyst treatment, the FeCl3 and nFe2O3 catalysts increased the decomposition rate of macromolecular biomass by 39 and 14 %, respectively, increasing the yield of artificial HAs. During the humification process, nFe2O3 catalysts benefit the formation of many aromatic structure monomers including furfural and hydroxycaproic acids. These monomers were condensed into growth hormone analogs such as vanillin and methionine sulfoxide and were further built in the artificial HAs. Therefore, the artificial HAs from nFe2O3 catalytic treatment promoted the rice growth the best, showing that the resultant germination rate, root activity, and photosynthetic rate of rice increased by 50, 167, and 72 %, respectively; moreover, the uptake and accumulation of water and nutrient by roots as well as the contents of soluble protein and sugar of rice are also significantly increased. This could be ascribed to the upregulated expression of functional genes including OsRHL1, OsZPT5-07, OsSHR2 and OsDCL. Considering both the economic and environmental benefits, we suggested that the artificial HAs, especially that produced with the action of nFe2O3 catalysis, are promising in alleviating environmental stress from waste biomass and sustainably improving agricultural production.

Characterization of Acid-Aged Biochar and its Ammonium Adsorption in an Aqueous Solution.

According to its characteristics, biochar originating originating from biomass is accepted as a multifunctional carbon material that supports a wide range of applications. With the successfully used in reducing nitrate and adsorbing ammonium, the mechanism of biochar for nitrogen fixation in long-term brought increasing attention. However, there is a lack of analysis of the NH4+-N adsorption capacity of biochar after aging treatments. In this study, four kinds of acid and oxidation treatments were used to simulate biochar aging conditions to determine the adsorption of NH4+-N by biochar under acidic aging conditions. According to the results, acid-aged biochar demonstrated an enhanced maximum NH4+-N adsorption capacity of peanut shell biochar (PBC) from 24.58 to 123.28 mg·g-1 after a H2O2 modification. After the characteristic analysis, the acid aging treatments, unlike normal chemical modification methods, did not significantly change the chemical properties of the biochar, and the functional groups and chemical bonds on the biochar surface were quite similar before and after the acid aging process. The increased NH4+-N sorption ability was mainly related to physical property changes, such as increasing surface area and porosity. During the NH4+ sorption process, the N-containing functional groups on the biochar surface changed from pyrrolic nitrogen to pyridinic nitrogen, which showed that the adsorption on the surface of the aged biochar was mainly chemical adsorption due to the combination of π-π bonds in the sp2 hybrid orbital and a hydrogen bonding effect. Therefore, this research establishes a theoretical basis for the agricultural use of aged biochar.