Mild abiotic stresses have different effects on chlorophyll fluorescence parameters in leaves of young woody and herbaceous invasive plants.
The effects of abiotic stresses (high and chilling temperatures, and drought) on woody (Acer negundo L., Fraxinus pennsylvanica Marsh.), and herbaceous [Conysa canadensis L., Echinocystis lobata (Michx.) Torr. et Gray] invasive plants have been assessed by establishing chlorophyll fluorescence (ChlF) indexes for the leaves of seedlings. Our data indicate that the four invasive plants have different mechanisms in place to change ChlF in response to high or low temperature, or drought. In particular, we noted that photochemical quenching of ChlF was depressed (except for F. pennsylvanica during chilling) while non-photochemical quenching of ChlF was activated in woody plants (except for drought) in response to these stresses. This effect, which was related to the inhibition of PSII activity, allowed for partial reduction of the quinone pool. In contrast, enhanced PSII activity and suppressed non-photochemical quenching in the leaves of C. canadensis was observed in response only to high temperature stress. This may have resulted from an increase in the oxidation of the quinone pool, which helps to activate electron transport between the two photosystems. In addition, both herbaceous plants displayed high tolerance to drought when compared to F. pennsylvanica, a woody plant. These differences in the response of the photosynthetic apparatus to stresses may lie in differences in the adaptive ability of invasive species to secondary habitats.