A putative hybrid of Eucalyptus largiflorens growing on salt- and drought-affected floodplains has reduced specific leaf area and leaf nitrogen

A putative hybrid between Eucalyptus largiflorens F.Muell. and Eucalyptus gracilis F.Muell., called green box, has attracted attention for its ability to grow on the salt- and drought-affected Chowilla floodplain of the Murray River in South Australia. Relationships between carbon isotope discrimination (Δ¹³C) and the ratio of substomatal to ambient CO₂ (ci/ca) indicated that green box was not as water use efficient as E. largiflorens. Specific leaf area of green box and E. gracilis was significantly lower compared with E. largiflorens (38.38 and 36.96 versus 43.71cm ²g^-1). Leaf nitrogen for green box and E. gracilis was significantly lower compared with E. largiflorens (12.66 and 11.35 versus 15.07mgg^-1 dry weight, P=0.004 and 0.001, respectively) and leaf carbon of E. gracilis was significantly higher compared with green box and E. largiflorens (541.75 versus 514.90 and 519.82mgg^-1 dry weight, P=0.002 and 0.011 respectively). There were significantly (P=0.016) more occurrences of elevated ci/ca below a minimum gs in E. gracilis compared with E. largiflorens, with green box being intermediate (means=21.6, 6.8 and 9.4). After 10 years, E. largiflorens trunk circumference had significantly increased (P=0.017) and height had significantly decreased (P=0.026) due to visible dieback. Green box and E. gracilis grew slower, conserving resources, illustrating a useful strategy to consider when choosing plants for revegetation efforts.