Abstract:

In the context of increasing anthropogenic activities, nutrient enrichment and physical disturbances are among the most important environmental factors influencing biological invasions. On the other hand, clonal growth and vegetative propagation are considered important life history traits promoting the invasiveness of plants in high-resource and disturbed habitats. Alternanthera philoxeroides, endemic to South America, is an amphibious clonal weed invading areas worldwide. It is widely distributed in warm-temperate and subtropical regions, and tends to invade nutrient-rich and disturbed habitats such as riparian zones, wetlands, and arable areas. Throughout its introduced range, A. philoxeroides rarely produces viable seeds and reproduces mainly by vegetative propagation via storage roots and stems. Therefore, formation of storage roots, sprouting of root buds, and growth of new ramets are crucial characteristics in the life history of A. philoxeroides. We conducted three container experiments to examine the responses of vegetative propagation characteristics of A. philoxeroides to two factors—nutrient addition and physical disturbance (two types of physical disturbance: fragmentation and burial of storage roots). Nutrient addition increased total biomass and mean length of storage roots 1.5-fold, and biomass allocation to storage roots by 15% (i.e., vegetative reproductive allocation). Number of root buds increased by approximately 15 sprouts per g (dry mass) of storage root. Burial depth had no effect on number of sprouts per root fragment. Neither storage root size nor burial depth affected main stem length or mean relative growth rate of ramets. Our results suggest that adaptation of vegetative propagation characteristics to nutrient enrichment and physical disturbances may enable localA. philoxeroides populations to grow rapidly, and contribute greatly to the persistence of metapopulations at the watershed scale.

Key words: biological invasion, biomass allocation, clonal growth, exotic invasive plant, nutrient enrichment, physical disturbance, root bud, vegetative propagule bank