Seasonal effect of the exotic invasive plant Solidago gigantea on soil pH and P fractions

Invasions by alien plants can alter biogeochemical cycles in recipient ecosystems. We test if Early Goldenrod ( Solidago gigantea ) alters P fractions. To that end, we compare invaded plots and adjacent, uninvaded resident vegetation for specific fractions of organic and inorganic P, phosphomonoesterase (PME) activity in topsoil, and immobilization of P in above‐ and belowground organs and in soil microbial biomass. Invaded plots had lower soil pH and 20%–30% higher labile P fractions (resin‐P i , bicarb‐P i , NaOH‐Pi), and the difference was consistent across seasons. There was no difference in microbial P. Alkaline‐PME activity was 30% lower in topsoil of invaded plots. Annual P uptake in aboveground phytomass was not markedly higher in Solidago. In contrast, P in belowground organs steadily increased in autumn in invaded plots, due to both increased biomass and increased P concentrations. This indicated higher net P immobilization in Solidago , far in excess of both resorption from senescing shoots and P requirements for aboveground biomass in subsequent year. Higher turnover rates of P in belowground organs and mobilization of sparingly soluble P forms through rhizosphere acidification may be involved in the observed differences in soil P status between invaded and uninvaded plots.