Nutrient enrichment triggers contrasting sexual reproductive responses in native and invasive plants in a saltmarsh

The effect of nutrient enrichment on the size differences between invasive and native plants has been widely documented, but the effect on their reproductive differences is less clear. We hypothesized that, under nutrient enrichment, the positive size-dependent response (increase as a consequence of the increased plant size) should dominate for invasive species, while the plastic response (decrease resulting from an altered reproductive allometric trajectory) should be stronger for noninvasive native species, resulting in an increase in the invasive species' reproductive advantage. In a 2-year control experiment, we studied the effects of nutrient enrichment on the growth and reproduction (both sexual and clonal) of the dominant native and invasive plants from the low-marshes of Yangtze estuary in their respective monocultures and mixtures. Here we show that, nutrient enrichment generally reduced the reproduction of the native plant but increased that of the invasive plant. The disparity in reproductive responses between the two species can be attributed to the overriding effect of negative plastic response in the native plant, compared to the positive size-dependent response observed in the invasive plant. This study proposes that nutrient enrichment can confer the invasive plant an advantage in reproduction due to its difference in both size-dependent and plastic responses from the native competitor, demonstrating an overlooked pathway that nutrient enrichment hasten biological invasions.