Effect of drought on water use efficiency, non-structural carbohydrates, and C:N:P stoichiometry in Eucalyptus: A three-year simulated drought experiment in South China

As the global climate changes, droughts are becoming more common. Drought negatively impacts Eucalyptus plantation productivity. However, the mechanisms of drought tolerance in Eucalyptus remain unclear. This study involved a three-year simulated drought to examine the effects of drought on water use efficiency (WUE), non-structural carbohydrates (NSC), and stoichiometric characteristics in Eucalyptus urophylla × E. grandis . Our study demonstrated that drought stress did not affect plant WUE. Water deficit significantly elevated leaf NSC and total soluble sugar (TSS) levels by 25.63 % and 19.12 %, respectively, compared to the control. The impact of short-term drought on NSC and stoichiometric characteristics in the branch was found to be of low significance. The carbon (C), phosphorus (P), and C:nitrogen (N) ratio in the leaf exhibited significant decreases of 18.51 %, 41.77 %, and 21.60 %, respectively. Conversely, the nitrogen, C:P ratio, and N:P ratio in the leaf demonstrated notable increases of 4.43 %, 48.03 %, and 76.57 %, respectively, in response to drought stress. We found intensified phosphorus limitation in plants under short-term drought. Correlations were observed between stochiometric characteristics and non-structural carbohydrates. NSC were observed to be positively associated with carbon isotope ratio (δ 13 C). The level of nitrogen affected the interconversion between starch and TSS. Overall, we observed that Eucalyptus adapted to drought conditions by increasing nitrogen concentration and osmoregulation rather than increasing WUE. This study provides insights into the drought-tolerant mechanisms of WUE, NSC, and C:N:P stoichiometry in Eucalyptus . • A three-year simulated drought experiment by reducing 50 % throughfall was conducted in subtropical Eucalyptus urophylla × E. grandis plantations. • E. urophylla × E. grandis responded to drought by osmoregulation and increasing nitrogen concentration. • Drought exacerbated phosphorus limitation in E. urophylla × E. grandis . • Drought had a limited impact on water use efficiency (δ 13 C) in E. urophylla × E. grandis .