Impacts of invasive weed <i>Chromolaena odorata</i> on growth and development of threatened native tree <i>Aegle marmelos</i> under water stress conditions

Background:The invasive weed Chromolaena odorata has been pronounced in dry habitats in Nepal, where a threatened native tree Aegle marmelos prefers to grow.It is known that the allelochemicals from C. odorata can harm native species differently, however, the impact may depend on environmental factors such as soil moisture in the invaded habitats.This study evaluates how the native tree responds to leaf and root products (leachates) of C. odorata and how water stress influences this interaction.For evaluating these facts, field survey to know the A. marmelos seedling status in C. odorata invaded and uninvaded sites was carried out.The seedlings were also grown in pots by treating the pot soil with C. odorata root and leaf leachates under water-stressed and unstressed conditions.Morphological and biochemical traits (root and shoot length, seedling biomass, leaf and root number, specific leaf area (SLA), photosynthetic pigments and proline) were measured.Results: A significant decrease in A. marmelos seedling population was found within its habitat under the canopy of C. odorata.Root length and biomass of A. marmelos seedlings were decreased by water stress (frequent drought).Addition of C. odorata leaf and root leachates further increased the toxic effects.Similarly, the content of photosynthetic pigments (chlorophylls and carotenoids) was decreased under drought conditions, with C. odorata leachates contributing more to the reduction in chlorophyll amount.The increment of the osmolyte proline in the native seedlings shows the seedlings are experiencing stressful environment.Conclusions: Seedlings of A. marmelos are facing a stressful environment in their habitat invaded by C. odorata.Frequent dryness and exposure of the native seedlings to invasive leachates together can significantly decline the population of threatened native species.Hence, removal of C. odorata from the invaded habitat is recommended before the onset of monsoon season to prevent leaching from its aerial or underground parts to minimize the negative impacts on the growth and development of such a threatened native tree.