Metabolic network plasticity underpins Eucalyptus water use efficiency under drought

Abstract

Several Eucalyptus species are grown worldwide primarily for fiber production, while also playing a crucial role in forest ecosystem health within their natural environment. Although various chemical and physiological traits have been identified as contributors to water-deficit (WD) acclimation, the role of metabolism-mediated mechanisms in Eucalyptus WD responses remains unclear. Here, we performed a comprehensive characterization integrating metabolomic and physiological analyses of 14 Eucalyptus species subjected to well-watered (WW) and WD conditions. Our results showed that different Eucalyptus species employ different strategies to enhance water use efficiency (WUE) in response to WD. A total of 53 metabolites were significantly altered by WD in at least one species. Principal component analyses indicate that E. cloeziana and E. stenostona were the most metabolically responsive species to WD. Notably, these species exhibited highest increases in WUE following WD imposition, which was also closely associated to constating network properties - higher network density in E. cloeziana and network heterogeneity in E. stenostona - but specially with the highest number of hub-like nodes. Overall, WUE was positively correlated with both network density and the number of hub-like nodes in in metabolic networks under WD. Moreover, WD triggered the emergence of new hubs associated with the tricarboxylic acid (TCA) cycle and the related pathways. Our findings highlight that the Eucalyptus metabolic responses to WD are species-specific, but metabolic network plasticity - defined as the ability to modify network topology and density - plays a key role in regulating WUE under WD.