Fire effects on litter chemistry and early development of Eucalyptus globulus

Background and aim: Fires affect what happens to litter in ecosystems. Biological and chemical effects of burnt litter on plants are not as of yet fully understood. We aimed to assess the effects of heat-treated leaf litter on germination and seedling root growth of Eucalyptus globulus. Methods: Litter from E. globulus, Acacia dealbata, Pinus pinaster, and Quercus suber was collected in Portugal, on Humic Cambisol, and heated between 25 °C and 600 °C. Those materials were then characterized by: 13C CPMAS NMR spectroscopy, proximate lignin and cellulose, and elemental analyses. Afterwards, they were used as substrate in bioassays with Eucalyptus seeds. Results: Heating changed litter composition (P < 0.05), consistently across species: alkyl C, O-alkyl C, and methoxyl + N-alkyl C decreased more than 50%; and aromatic C increased more than 5-fold. Unheated and lightly heated litters inhibited germination and growth, with maximum inhibition by Quercus and Eucalyptus litters, down to 17% of the control (P < 0.05). Severely charred materials had neutral or stimulatory effects, up to 191% of the control (P < 0.05). These responses were associated with concentrations of dominant C types in litters (P < 0.05). Conclusion: Litter charring, as it occurs during wildfires, is potentially critical for the success of E. globulus’s regeneration from seeds.