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Biochemical Effects of Centaurea maculosa on Soil Nutrient Cycles and Plant Communities.
Andrea S. Thorpe1,2, Ragan M. Callaway2, Alecu Diaconu3, Giles C. Thelen2
1Institute for Applied Ecology, 563 SW Jefferson St., Corvallis, Oregon 97333, athorpe@peak.org, office: 541.753.3099
2The University of Montana, Missoula, Montana
3 Institute of Biological Research, Iaşi, Romania
The success of some invasive plants may be due to biochemcials that are novel to the invaded ecosystems. I measured the effects of
Centaurea maculosa (Asteraceae; spotted knapweed) and the root exudate, (±)-catechin, on the soil nitrogen and phosphorus cycles and plant communities. I also compared the strength of many of these effects in the invaded range to those in the native range. 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). In a greenhouse experiment and field study,
C. maculosa tissue contained significantly more phosphorus than several native species. However, in the field, soil phosphate was higher in areas dominated by
C. maculosa than in areas where the species had been removed. Elevated soil phosphate and the resulting phosphorus-efficiency of
C. maculosa appear to beare 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 over 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.
