Biochemical effects of Centaurea maculosa on soil nutrient cycles and plant communities

The success of some invasive plants may be because of biochemcials that are novel to the invaded ecosystems. Plants, herbivores, and soil microbes native to invaded communities may lack a coevolutionary-based response to biochemical traits of the invader. In addition, these biochemicals may also alter abiotic components of soil nutrient cycles.; I tested for effects of Centaurea maculosa and the root exudate, (+/-)-catechin, on the soil nitrogen and phosphorus cycles and plant communities. Most importantly, I also compared the strength of many of these effects in the invaded range to those in the native range. My research provides evidence that C. maculosa has strong, biochemical effects on soil nutrient cycling, at least partially due to exudation of the polyphenol, (+/-)-catechin. Nitrification in soils from part of the invaded range of C. maculosa (Montana) was strongly reduced by both C. maculosa and application of (+/-)-catechin. In contrast, there were very weak effects on nitrification in soils from part of the native range of C. maculosa (Romania). A different study found that C. maculosa also has strong effects on the soil phosphorus cycle. In a greenhouse experiment and field study, I found that Centaurea maculosa was more phosphorus efficient than many native species, even when phosphorus was extremely limiting. However, in the field study, soil phosphate was elevated in C. maculosa rhizospheres. I suggest that elevated soil phosphate and the resulting phosphorus-efficiency of C. maculosa are due to the exudation of (+/-)-catechin, a strong chelator for the metals that bind phosphorus in many of the soils invaded by C. maculosa. Finally, in a series of studies repeated for two years, I found that when tested in situ, (+/-)-catechin had strong allelopathic effects on the growth of several plant species in Montana, but very weak effects on species in Romania. Thus, C. maculosa appears to alter not just the aboveground plant community, but also fundamental ecosystem properties. These effects may persist long after the removal of the invasive species. Furthermore, biogeographic comparisons suggest that coevolution plays an important role in both plant community interactions and plant-soil interactions.