Drought stress effects on gas exchange and water relations of the invasive weed Chromolaena odorata

In this study, the effects of drought stress on gas exchange and water relations of the invasive weed Chromolaena odorata were investigated. Drought stress was induced in potted plants by withholding water. The responses of drought stressed plants (DS) were then compared to well-watered (WW) controls. Measurements of diurnal gas exchange and chlorophyll fluorescence parameters were taken initially and every two days after water was withheld to day 10. Maximum CO2 uptake in WW plants ranged from 10.5 to 12.8 μmol m−2 s−1 while in the DS treatment values decreased from 9.3 μmol m−2 s−1 on day 0 to 3.95 μmol m−2 s−1 on day 10. Trends in diurnal leaf conductance and transpiration in DS and WW plants were similar to those for CO2 uptake. In WW plants, maximum quantum yield (Fv/Fm) of Photosystem II (PS II) was high, while in the DS treatment, it decreased significantly from day 2 to day 10. Leaf water potential (Ψ) was high in WW plants and significantly lower in DS plants. Water use efficiency (WUE) and proline concentrations were low in WW plants and increased significantly with drought stress. The photosynthetic rates in C. odorata suggest a high capacity for light utilization and water absorption and transport to leaves. Early stomatal closure and significant reductions in stomatal conductance suggest that C. odorata may be considered as a drought-avoider species which is sensitive to water deficit and responds by rapid wilting and leaf abscission. Our study provides empirical evidence for links between plant functional traits and the ecological success of an important invasive species.