Towards sustainable valorisation of Acacia melanoxylon biomass: Characterization of mature and juvenile plant tissues

In Mediterranean area, Acacia melanoxylon biomass is an abundant waste material from non-native and invasive tree species control actions, requiring suitable disposal. Valorisation of such biomass residues requires its complete characterization to best approach the full potential of each plant material that could suit specific applications. This study compares mature and juvenile A. melanoxylon plant tissues (wood and bark) from two stands in different locations, regarding their chemical characteristics and organic growing media properties, such as mineral content and phytotoxicity effect for Lepidium sativum seeds. Juvenile bark (JB) showed greater total extractives (29%) extracted using solvents of increasing polarity (dichloromethane, ethanol, and water), followed by mature bark (MB) (21%). MB revealed the highest lignin content (>50%) suggesting material resistance to microbial biodegradation in horticultural applications. High barks phenolic content proved to be phytotoxic for cress seeds (null JB root index), although the toxic substances may be removed. After 1 week, ageing effect reduced MB phytototoxicity (root index > 60%) improving seed performance. Bark presented more mineral elements availability than wood. Wood high cellulose (>50%), low extractive (<9%) and moderate total lignin (<30%) contents can be attractive for pulp production, while bark growth medium profile may potentiate its application for horticultural uses. The future research on novel uses of A. melanoxylon plant residues can result in economic benefits that may alleviate management costs.

Keywords: Acacia blackwood; Biomass management; Non-native species; Woody residues.