Waterlogging tolerance of Bidens pilosa translates to increased competitiveness compared to native Bidens biternata.
Background and aims: Waterlogging is a common natural disturbance that has negative impacts on dry-land plant species. However, few studies have focused on how waterlogging influences the invasiveness of non-native plant species on dry lands. Bidens pilosa is an invasive dry-land plant of the Asteraceae family that causes serious damage to biodiversity and agricultural production in southern China. To date, it remains unclear how waterlogging affects the competitiveness and growth of B. pilosa. The goal of this study is to determine whether waterlogging promotes the competitiveness of invasive B. pilosa. Methods: The growth and physiological responses of invasive B. pilosa and native B. biternata and the competition effects between them were studied after 0 (control), 5, 10, 15, and 20 days of waterlogging stress (wherein the water level was maintained at the soil surface level). Results: After short-term waterlogging stress, the competitive balance index of invasive B. pilosa significantly increased, indicating that short-term waterlogging on dry lands could significantly improve the competitiveness of invasive B. pilosa. Invasive B. pilosa maintained more rapid adventitious root generating capacity and higher root dehydrogenase activity under waterlogging conditions than native B. biternata, which allowed B. pilosa to adapt to the anoxic conditions much more rapidly. The smaller reductions in net photosynthetic rate, actual quantum yield of photosystem II and relative growth rate in B. pilosa than in B. biternata showed that invasive B. pilosa had stronger tolerance to waterlogging than native B. biternata. Conclusion: Our results indicate that invasive B. pilosa has stronger tolerance to waterlogging than native B. biternata and that short-term waterlogging on dry lands can significantly improve the competitiveness of invasive B. pilosa. Short-term waterlogging on dry lands caused by extreme precipitation during the rainy season is expected to promote the invasive potential of exotic B. pilosa.