Yuqing Sun

Gases and dissolved black carbon (DBC) formed during pyrolysis of nitrogen-rich feedstock would affect atmospheric and aquatic environments. Yet, the mechanisms driving biomass gas evolution and DBC formation are poorly understood. Using thermogravimetric-Fourier transform infrared spectrometry and two-dimensional correlation spectroscopy, we correlated the temperature-dependent primary noncondensable gas release sequence (H₂O → CO₂ → HCN, NH₃ → CH₄ → CO) with specific defunctionalization stages in the order: dehydration, decarboxylation, denitrogenation, demethylation, and decarbonylation. Our results revealed that proteins in feedstock mainly contributed to gas releases, and low-volatile pyrolytic products contributed to DBC. Combining mass difference analysis with Fourier transform ion cyclotron resonance mass spectrometry, we showed that 44-60% of DBC molecular compositions were correlated with primary gas-releasing reactions. Dehydration (-H₂O), with lower reaction energy barrier, contributed to DBC formation most at 350 and 450 °C, whereas decarboxylation (-CO₂) and deamidization (-HCNO) prevailed in contributing to DBC formation at 550 °C. The aromaticity changes of DBC products formed via gas emissions were deduced. Compared to their precursors, dehydration increased DBC aromaticity, while deamidization reduced the aromaticity of DBC products. These insights on pyrolytic byproducts help predict and tune DBC properties via changing gas formed during biochar production, minimizing their negative environmental impacts.

Milk vetch (MV; Astragalus sinicus L.) has been extensively applied in agricultural production, however, its impact on accumulation levels of heavy metals (e.g., Cd) in rice remains poorly understood. This study investigated the effects of MV on rice Cd accumulation, Fe plaque formation, soil properties, and the soil microbial community structure through field experiments. The results showed that MV reduced Cd in grains, roots, stem, and leaves by 49.3%, 73.5%, 60.5%, and 71.5%, respectively. Chemical fertilizer (CF) and MV promoted Fe plaque formation, and MV considerably increased the Fe/Mn ratio in the Fe plaque. More importantly, MV remarkably inhibited Cd transportation from the root Fe plaque to the root by 74.3%. The contents of CaCl 2 -Cd, available phosphorus (AP), and available potassium (AK), as well as the cation exchange capacity (CEC) and urease activity (UA) were significantly reduced in the MV treatment. 16S rDNA high-throughput sequencing was used to determine the community structure of soil microorganisms. Compared with the control, MV increased the diversity and richness of soil microorganisms, increased the relative abundance of anaerobic microorganisms, and significantly increased the relative abundance of Thermodesulfovibrio and Geobacter at the genus level. Through analysis, it was found that the increase of anaerobic microbial abundance was closely related to the decrease of CaCl 2 -Cd. In summary, the application of MV promoted the formation of Fe plaque, inhibited the transport of Cd, increased the abundance of anaerobic microorganisms, decreased the CaCl 2 -Cd content, and finally reduced the Cd content in rice grain.