Developing an understanding of traits linked to invasiveness is critical for conservation and restoration efforts. Two traits hypothesized to increase invasiveness are higher allocation to sexual reproduction and greater phenotypic plasticity. While some evidence exists supporting these hypotheses, biomass allocation measures are typically not adjusted for changes in proportional allocation due to size. We accounted for size using an allometric approach to test these hypotheses, comparing three closely related taxa of cattails: the native (Typha latifolia), an exotic invasive (T. angustifolia), and their hybrid (T. x. glauca), which is an even more aggressive invader. We examined sexual reproductive allocation and phenotypic plasticity in reproductive allocation along a nitrogen gradient because invasiveness of the hybrid in particular increases with nitrogen availability. We expected sexual reproductive allocation to increase with nitrogen due to increased availability of resources, although the strong clonal growth of cattails may lead to the reverse result. We measured reproductive allocation in stems from experimental wetland mesocosms at low (0 – 6 g/m2/year), medium (9 – 21 g/m2/year), and high (27 – 45 g/m2/year) levels of nitrogen addition. We then conducted non-linear least squares regression to determine changes in allocation coefficients among taxa, nutrient levels, and their interaction.
Results/Conclusions
The native was least successful in the experimental mesocosms, perhaps due to competition from the invasive taxa, resulting in too small a sample size for statistical analysis. Both invasive taxa were plastic in their reproductive allocation, but contrary to our hypothesis, they allocated less to sexual reproduction at higher nutrient levels. Additionally, contrary to our hypotheses, the more invasive T. x glauca allocated less to reproduction and was less plastic than the less invasive T. angustifolia, although they only differed significantly in allocation at low nutrient levels. Further, T. x glauca had a lower probability of flowering at a given biomass. Thus, our results are the opposite of those found for some invasive-native comparisons. This contrast may be due to our use of an allometric approach or may be because the success of invasive cattails is associated with clonal growth rather than sexual reproduction, especially at high nutrients. We conclude that that further investigation of the relationship of clonal traits to invasiveness is warranted.