Properties and photosynthetic promotion mechanisms of artificial humic acid are feedstock-dependent

Abstract

The artificial humic acids (AHA) approach contributes to achieving the carbon (C) emission peaking and neutrality goal through efficient recycling of waste biomasses and promotion of plant photosynthesis. However, the dependence of their production processes and photosynthetic promotion mechanisms on feedstocks remains unclear. In this study, waste biomasses including camphor leaves (CL), corn stalks (CS), peanut shells (PS), and mixed cyanobacteria (MC) have been respectively converted into artificial humic acids through an environmentally friendly hydrothermal humification approach. The dynamic humification process of different feedstocks and the composition, structural properties, and electron transfer capacity of AHA products were determined. Moreover, the different AHA products were applied to corn to explore their respective photosynthetic promotion mechanisms. High relative contents of lignin and C/N in feedstocks are not conducive to the formation of photodegradable substances and the redox property in AHA. The application of AHA increased the net photosynthetic rate and biomass C of corn by 70–118% and 22–39%, respectively. The AHA produced from higher H/C (0.19) and hemicellulose content (17.09%) in feedstocks (e.g., MC) increased corn photosynthesis by improving light energy capture and conversion efficiency in the PSII process. In contrast, the AHA produced from a higher content of lignin (19.81%) and C/N (7.67) in feedstocks (e.g., CS) increased corn photosynthesis by providing functional enzymes (proteins) and nutrients for leaves. This work provides new insights into the utilization of renewable resources, and the artificial humic acids approach sheds light on environmental sustainability by constructing a closed loop of C in environments. Graphical Abstract: [Figure not available: see fulltext.].