The main purpose of this article is to explore the mechanism of action of carbon-based materials in the anaerobic digestion (AD) production of medium-chain carboxylic acids (MCCA). Currently, there are various methods to increase production, but there is no review on how carbon-based materials improve MCCA. This paper first introduced the chain elongation (CE) technology, focusing on the factors affecting the production of MCCA by AD, such as pH, temperature, the ratio of electron donor (ED) to an electron acceptor (EA), substrate type, and other related factors. This article introduces the preparation and characteristics of carbon-based materials, as well as the effect and mechanism of adding carbon-based materials to AD acid production. Finally, the shortcomings of the current research were pointed out, and future research directions were prospected, aiming to provide a reference for improving the efficiency of AD of MCCA using carbon-based materials.
Inappropriate organic fertilizer application may cause serious environmental risks, especially nitrogen (N) and phosphorus (P) losses. To achieve a win–win for high yield and environmental protection in organic agriculture, it was essential to demonstrate the relationship between the organic fertilizer input, rice yields, and risks of N and P losses. Based on a rice and green manure cropping rotation field experiment in the Yangtze River Delta of China, the effects of organic fertilization rates on the dynamics of surface water N and P concentrations and rice grain yields were determined. The results showed that the N (total N, ammonium-nitrogen, nitrate-nitrogen) and P (total P and dissolved P) concentrations in surface water immediately and greatly reached the highest values 1 day after basal fertilization and topdressing fertilization. Then, the N and P concentrations sharply decreased and were maintained at a relatively low level. The initial 3 and 7 days after organic fertilization were the high-risk periods for controlling N and P runoff losses. The surface water N and P concentrations had a positive correlation with the organic fertilization rate in high-risk periods. Besides, the effects of organic fertilization on surface water P concentrations existed longer than those of N concentrations. The rice grain yields increased with the increase in organic fertilization rates, but high organic fertilizer input (>225 kg N per hectare) did not increase the grain yield. Meanwhile, the high organic fertilizer input had the highest risks for N and P losses. Therefore, in organic rice farming, organic fertilization rates with 150~200 kg N per hectare are the optimal organic fertilizer input, with relatively high grain yields and low N and P losses.
Selenium (Se) is involved in the growth and development of plants. More importantly, Se from plant foods is a primary source of Se intake for humans and animals. Improving the Se content in vegetables through biofortification is an effective way to solve the hidden hunger induced by Se deficiency. This study demonstrated the effect of different exogenous Se application concentrations on the growth, antioxidative capacity, and nutritional quality of purple lettuce (Lactuca sativa var. crispa L. “Purple Rome”) at the seedling stage. The low Se application concentration (≤8 μM) significantly promoted the lettuce seedling growth. Conversely, the high Se application concentration (16 μM) inhibited the seedling growth and overproduced the reactive oxygen species in lettuce root tips, which caused oxidative damage to membrane lipids and cell death. Furthermore, the enzyme activities and gene expression of the antioxidant enzymes, superoxide dismutase-peroxidase, and catalase, were significantly increased under exogenous Se application. The exogenous Se application significantly increased the accumulation of nutrients in purple lettuce at the seedling stage. Remarkably, the exogenous Se application concentrations were significantly positively related to the Se and anthocyanin contents. The gene expression levels of chalcone synthase were positively correlated with the anthocyanin contents under exogenous Se application. This study contributes to the role of Se in lettuce growth and provides a reference for producing high-quality purple lettuce rich in Se and anthocyanins.
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