How hydrothermal carbonization aqueous phase (AHL) derived from brown seaweed affects the germination and growth of Phaseolus vulgaris cv. ‘borlotto’ (Fabaceae)

Over the past 20 years, climate change has had a significant negative impact on agricultural productivity, and this trend is expected to continue with the forecasted increase in population growth and food requirements. To address this issue, it is urgent to find ways to limit climate change-induced loss of crop yield and promote sustainable agriculture. One potential solution is the use of macroalgae as plant fertilizer and biostimulant. Macroalgae thriving in dystrophic environments produce huge biomass that can cause several problems, including the displacement of native species, changes in ecosystem functioning, and negative impacts on human activities such as fishing and tourism. As a result, there is growing interested in finding ways to manage and exploit this abundant biomass. Hydrothermal carbonization (HTC) is a thermo-chemical process that can convert wet biomass into a carbonaceous solid fraction (hydrochar) and a liquid phase (aqueous HTC liquid or AHL) without requiring an energy-intensive drying step. While hydrochar has been studied, little is known about the potential of AHL. This study aimed to investigate the effects of AHL from different HTC temperature extraction (180, 240 and 300 °C) on the productivity of Phaseolus vulgaris cv. ‘Borlotto’ (common bean) plants. The use of AHL resulted in increase of the biomass of the whole plant. Depending on temperature of the process, treated samples showed either higher shoot or root biomass. The higher plant biomass values observed in AHL-treated samples were due to higher rates of photosynthesis and water use efficiency, which were related to higher stomatal density. These findings strongly support the idea of reusing AHL solutions in agriculture, especially those derived from seaweed feedstock, as a mean of resource management and promoting a circular green economy.