Muhammad Saif Ullah

Allelopathy has garnered considerable attention, but the effects of different allelochemicals on invasive plants remain unclear. This study addressed the knowledge gap surrounding allelopathy and its impact on native and invasive plant species. We focused on the impact of caffeic acid and its derivatives on the growth and competitiveness of the native Lantana indica and the invasive plant Solidago canadensis. We selected three allelochemicals, caffeic acid, methyl caffeic acid, and ethyl caffeic acid, for evaluation at two concentrations (0.1 mM and 1.0 mM). Three planting methods were employed: (1) a single species of S. canadensis, (2) a single species of L. indica, and (3) a combination of S. canadensis and L. indica. In addition, a control group was also included. Results revealed that high concentrations (1 mM) of methyl caffeate (MC) and ethyl caffeate (EC) significantly reduced seed germination rate, seed germination index, and seed germination speed index of L. indica compared to a low concentration (0.1 mM). Plant height, stem diameter, biomass, and root length in the control group (CK) of S. canadensis were significantly higher than those in the treated groups. However, with increasing allelochemical concentration, L. indica’s relative competitiveness gradually decreased. These findings provide insights into the concentration-dependent effects of allelopathic compounds on the growth of L. indica and S. canadensis. By analyzing how these allelochemicals influence the growth and competitiveness of native and invasive plants, the study sheds light on the dynamics of allelochemical interactions between these species. This knowledge can be pivotal for understanding plant competition dynamics in ecosystems and could inform strategies to control invasive species or promote native plant growth.

Plant invasions can affect soil properties in the invaded habitat by altering the biotic and abiotic nature of soils through positive or negative plant–soil feedback. Litter decomposition from many invasive species enhanced soil nutrients, thereby decreasing native plant diversity and leading to further plant invasions. Here, we examined the impact of litter decomposition from an invasive plant (Sphagneticola trilobata) in a range of soils at varying depths on growth and physiology of its native congener (Sphagneticola calendulacea). We added litter from S. trilobata to each soil type at different depths (0, 2, 4 and 6 cm). Plants of S. calendulacea were grown in each treatment, and morphological and physiological parameters were measured at the end of the growing period. All soils treated with litter displayed increases in soil nutrients at depths of 2 and 4 cm; while most growth traits, leaf chlorophyll and leaf nitrogen of S. calendulacea decreased at the same soil depths. Therefore, litter decomposition from invasive S. trilobata resulted in a positive plant–soil feedback for soil nutrients, and a negative plant–soil feedback for growth in native S. calendulacea. Our findings also suggest that the effects of litter decomposition from an invasive plant on soils and native species can vary significantly depending on the soil depth at which the litter is deposited. Future studies should focus on plant–soil feedback for more native and invasive species in invaded habitats, and the effects of invasive litter in more soil types and at greater soil depths.