Humic substances stimulate initial growth and reduce arsenic stress in Corymbia citriodora seedlings

The use of arsenic (As) tolerant plants and those with a well-developed root system have shown great relevance in phytoremediation campaigns. Corymbia citriodora presents these characteristics that can be enhanced by humic substances (HS) from organic matter. The objective of the present study was to determine if HS extracted from vermicompost can modify the root system architecture, stimulate growth, increase robustness and relieve stress promoted by As in C. citriodora seedlings. Two preliminary tests were carried out to obtain the best concentration-response for HS and the toxic As concentration. Subsequently, an experiment was carried out in nursery pots with nutrient solution and four treatments: Control, HS, As and As + HS. HS alleviated the reduced growth caused by As with regards to dry mass, root collar diameter and height of the aerial part. The Dickson quality index (DQI) was reduced by the action of As and this negative affect was mitigated by HS. Our results show the positive effect of the HS in alleviating As abiotic stress in C. citriodora seedlings, demonstrating its potential to mitigate the toxicity of this chemical element.