The enhanced functional traits contribute to the successful invasion of Amaranthus palmeri in salinity environments: a comparison with its congeners

Different performance in functional traits between plants can help ecologists to find alien plants successful invasion mechanisms in salinity environments. A pot experiment was conducted to compare 10 functional traits between invasive species Amaranthus palmeri and its co-occuring congener Amaranthus tricolor. Plants grown in the monoculture and co-cultivation types were subjected to four concentrations of NaCl: 0 mM (CK), 75 mM (LS), 150 mM (MS), 200 mM (HS). In monoculture, salinity significantly promoted the growth of A. tricolor. While A. palmeri’s performance decreased due to salinity stress except maximum root length (MRL). In co-cultivation, leaf functional traits of A. tricolor in LS and MS and leaf number (LN), plant height (PH) and biomass (TB) in HS significantly increased. LN and TB of A. palmeri under MS and HS and leaf shape traits, specific leaf area (SLA) and root: shoot ratio (R/S) under LS markedly increased. Almost all functional traits (especially LN, PH, MRL and TB) of A. palmeri were dramatically higher than A. tricolor under co-cultivation, but SLA and R/S relationships were contrary. Functional traits of A. palmeri under co-cultivation were higher than it under monoculture except R/S and leaf shape index (LSI). Moreover, most relative interaction index and relative biomass values of A. palmeri were also higher than A. tricolor in same cultivation types, but phenotypic plasticity index patterns were opposite. Overall, A. palmeri outperforms congeners owing to the enhanced functional traits (superior LN, PH, MRL, TB and lower R/S) related to resource absorption and interception in salt environments.