Density-dependent responses of reproductive allocation to elevated atmospheric CO2 in Phytolacca americana

Abstract

• This study was conducted to determine whether elevated CO2 alters patterns of plant reproduction, and whether density affects population- and individual-level responses to elevated CO2. • Phytolacca americana was grown in a glasshouse at three population densities under ambient and elevated CO2 environments, and harvested at both vegetative and seed mature stages. • CO2 did not affect the observed or estimated minimum size required for reproduction. At the population-level, elevated CO2 increased the total and above-ground biomass at both harvests. Density decreased both measurements at the second harvest. At the individual-level, elevated CO2 increased reproductive mass but decreased seed size, and the responses of reproductive allocation were density-dependent. Net photosynthesis at saturating light (Pmax) increased under elevated CO2, but decreased with density, with a CO2 x density interaction. • These results indicate that CO2 advances timing of flowering by changing growth rate rather than modifying minimum size required for reproduction, while density modifies the responses of reproductive allocations to elevated CO2 in P. americana.