Biodegradable hydrogel microspheres from paper waste as a substrate for ex vitro adventitious rooting of Eucalyptus grandis x E. urophylla clonal plants

The use of hydrogels as support for plant rooting has been extensively studied. However, mineral substrates remain the most common choice despite their limitations in availability, cost, and environmental impact. In the context of plant biotechnology and sustainable clonal propagation systems, this study evaluated biodegradable hydrogel microspheres composed of cellulose microfibrils (CMF) and nanofibrils (CNF), derived from waste paper, as an alternative substrate for the ex vitro adventitious rooting and acclimatisation of Eucalyptus urophylla x E. grandis (urograndis eucalypt) clonal plants. The microspheres were subjected to alkaline pre-treatments: (1) sodium hydroxide (NaOH); (2) NaOH + hydrogen peroxide (Bleached); (3) calcium silicate (CaSiO₃); (4) magnesium silicate (MgSiO₃), and characterised using Fourier transform infrared spectroscopy (FTIR). Clonal plants' performance was assessed through morphological traits and the Dickson Quality Index (DQI). Following 30 days of observation, the Bleached, CaSiO₃, and MgSiO₃ treatments performed similarly to those of the vermiculite control in terms of rooting, vigour, and the absence of contamination. Following 90 days, favourable outcomes were maintained concerning height, stem diameter, and DQI. Notably, MgSiO₃-treated microspheres promoted greater leaf and shoot development, while Bleached microspheres enhanced leaf area. In contrast, NaOH-treated samples led to contamination and reduced performance. These findings demonstrate that CMF/CNF-based hydrogel microspheres, particularly those treated with MgSiO₃, represent a sustainable biotechnological innovation and effective alternative substrate for the large-scale clonal propagation of urograndis eucalypt.