Integrative physiological, biochemical, and metabolomic analyses reveal complex drought and zinc stress tolerance in a novel Miscanthus hybrid

Stresses caused by drought and heavy metals (HMs) adversely affect the establishment and yield potential of <i>Miscanthus</i> plants. These stresses are particularly acute on lower quality 'contaminated and marginal-lands' less suitable for food production. In our prior research assessing drought and zinc stress tolerance across seven novel <i>Miscanthus</i> hybrids, a <i>M. sacchariflorus</i> × <i>M. sinensis</i> hybrid 'GRC10' exhibited superior stress tolerance and biomass production. This study investigated the effects of drought (D), zinc (Zn) stress, and their combination (D + Zn) on stress tolerance in the <i>Miscanthus</i> GRC10 using untargeted metabolomics to uncover stress tolerance mechanisms. Synchronous measurements of growth parameters, leaf gas exchange parameters, the maximum quantum yield of photosystem II (Fv/Fm), performance index (PI-ABS), antioxidant enzyme activity, proline, and malondialdehyde (MDA) production were made to elucidate associations. Both D, Zn, and combination (D + Zn) stress induced a broad metabolic reprogramming of secondary metabolism and hormone synthesis pathways. Fatty acid derivatives, nitrogen-containing compounds, hormone/signal-related compounds (jasmonate), and secondary metabolites (phenylpropanoids, N-containing compounds, and terpenes) showed significant (<i>p</i> < 0.05) abundance changes in response to D, Zn, and its combination D + Zn stress. Drought, Zn, and combination D + Zn stress treatments increased proline accumulation (<i>p</i> < 0.0001), antioxidant enzyme activities (<i>p</i> < 0.05), including superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), and decreased levels of MDA. Overall, these responses indicate that the <i>Miscanthus</i> GRC10 hybrid displays a complex response to drought and Zn stresses that confers growth resilience in Zn-contaminated and drought-prone lands.