How do allometric growth patterns and resource strategies of an invasive hydrophyte differ between island and mainland habitats?

For plants, leaves and fine roots are essential for resource acquisition. Investigating their economic spectrum and allometric growth helps to understand invasion mechanisms. This study compared 12 leaf and root traits and 4 environmental factors of an invasive hydrophyte ( Eichhornia crassipes ) between island and mainland in China. Results showed significant differences in all functional traits between the two habitats except root average diameter (RAD). (1) Compared to E. crassipes in the mainland habitat, those in the island habitat exhibited significantly higher values of leaf perimeter (LP: 32.42 ± 1.11 cm, 1.07 times), specific leaf area (SLA: 29.66 ± 2.50 cm²·g⁻¹, 1.35 times), specific root area (SRA: 1163.94 ± 129.11 cm²·g⁻¹, 1.69 times), and specific root length (SRL: 5164.07 ± 599.59 cm·g⁻¹, 1.43 times). In contrast, leaf dry matter content (LDMC: 0.11 ± 0.01, 0.79 times), leaf tissue density (LTD: 0.10 ± 0.02 g·cm⁻³), root dry matter content (RDMC: 0.06 ± 0.01, 0.80 times), and root tissue density (RTD: 0.05 ± 0.01 g·cm⁻³, 0.51 times) were significantly lower. (2) Positive correlations existed between LT and RAD, LDMC and LTD, LTD and RTD, RDMC and RTD. Negative correlations were found between SLA and LDMC, SRA and RDMC, SRA and RTD. (3) Positive allometric growth relationships were observed between LT and RAD, LDMC and LTD in mainland. (4) In both environments, increasing pH and water temperature significantly boosted acquisitive traits (SLA, SRL, SRA) and reduced conservative traits (LTD, RDMC, RTD). Water salt content had opposite effects. In summary, E. crassipes , a severe invasive hydrophyte on both island and the mainland, adopts a relatively acquisitive strategy on island, shifting to a relatively conservative one upon mainland invasion.