Impacts of environmental factors on growth-defense physiological traits of invasive plant Alternanthera philoxeroides

Objective  To explore the impacts of biotic and abiotic factors on the growth-defense physiological traits of invasive plant Alternanthera philoxeroides at large spatial scales, and provide a theoretical basis for dynamic prediction of invaded communities and bio-control under the global environmental change.

Method  We totally set up 72 plots invaded by A. philoxeroides with the area of 10 m×10 m per plot across 21°N−37°N in mainland China (36 terrestrial and 36 aquatic), and measured the nitrogen balance index (NBI), chlorophyll index (Chla), flavonoid index (Flav) and anthocyanin index (Anth) of A. philoxeroides in each plot. We then used the methods of regression analysis and canonical correspondence analysis (CCA) for examining the impacts of geography, climate, nitrogen nutrition, plant diversity and insect occurrence on these four physiological indexes.

Result  Regression analysis and CCA all showed that the Flav had significant positive relationship with latitude and significant negative relationship with rainfall. In regression analysis, the Chla for terrestrial and aquatic A. philoxeroides had significant positive relationship with longitude and nitrate nitrogen content, respectively, while the Anth for aquatic A. philoxeroides had significant negative relationship with latitude but positive relationship with annual mean air temperature. In CCA, the NBI for aquatic A. philoxeroides had strong negative relationships with Pielou evenness index, insect richness and the abundance of Agasicles hygrophila, but had strong positive relationships with Patrick richness index and Shannon-Wiener diversity index, while the Flav for aquatic A. philoxeroides showed the opposite distribution pattern with NBI in CCA ordination chart.

Conclusion  The longitude and nitrogen nutrition mainly affect the physiological growth traits of A. philoxeroides, while the latitude, climate and plant diversity mainly affect its chemical defense traits. Plant diversity and insect occurrence promot the ‘growth-defense’ tradeoff of aquatic A. philoxeroides.