Tuesday, August 7, 2007

PS 30-89: Gas exchange and carbon allocation patterns in invasive Alliaria petiolata and co-occurring native species

Laurel J. Anderson and Lushani C. Nanayakkara. Ohio Wesleyan University

Alliaria petiolata (garlic mustard) invades undisturbed forests and can displace native plants.  This biennial overwinters as a rosette, and maintains high photosynthetic rates as it grows a flowering stalk under the leafless forest canopy in early spring.  In this four year study, we hypothesized that A. petiolata’s ability to capitalize on spring light availability may contribute to its success as an invader, and that A. petiolata maintains higher photosynthetic rates than native species, both when the canopy is leafless and at other times of year.  We compared photosynthetic rates in A. petiolata to those of native perennial (Geum vernum, Viola striata) and biennial (Hydrophyllum appendiculatum) species that also overwinter as rosettes and form spring flowering stalks.  Photosynthesis was measured using the LI-6400 IRGA system every three to six weeks in two forests in Ohio from March 2004 through May 2006.  In early spring, A. petiolata rosettes had higher photosynthetic rates than V. striata (P. < 0.05) and similar rates to G. vernum and H. appendiculatum.  In summer and fall, H. appendiculatum, G. vernum and V. striata had similar or significantly higher photosynthetic rates than A. petiolata (P < 0.05).  Therefore, other factors related to carbon gain and allocation may be more important than photosynthetic rate in giving A. petiolata an advantage over native plants, in addition to its known allelopathic effects.  We measured shoot biomass allocation in flowering stalks collected for the four species in June 2006 and found that A. petiolata invests a significantly greater percentage of aboveground biomass in seed production than the native species (P < 0.05).  Earlier leaf production in A. petiolata may also prolong this species’ spring carbon gain period relative to the natives.  Measurements of leaf nitrogen content, leaf construction cost, and A-Ci curve analyses are currently underway for all four species.

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