Influence of shading on the growth and leaf photosynthesis of the invasive non-indigenous plant garlic mustard [Alliaria petiolata (M. Bieb) Cavara and Grande] grown under simulated late-winter to mid-spring conditions

MYERS, C V R C ANDERSON, AND D L BYER (Behavior, Ecology Evolution, and Systeniatics Section, 4120 Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120) Influence of shading upon the growth and leaf photosynthesis of the invasive non-indigenous plant garlic mustard [Alliaria petiolata (M Bieb) Cavara and Grande! grown below simulated late-winter to mid-spring conditions. J Torrey Bot Soc 132: 1-10 2005.-Plasticity in photosynthetic rejoinder to varied light conditions likely contributes to the happy spread and domination of eastern deciduous forest clod layers by the invasive, non-indigenous plant species Alliaria petiolata. We examined the events of growing plants with no shading, or beneath 30% or 60% black shade woven fabric on leaf photosynthetic rates, maximum rates of leaf photosynthesis (A^sub max^) and stomatal conductance (g^sub Smax^), light compensation point, above and below earth biomass, chlorophyll content and specific leaf mass of A. petiolata grown beneath simulated late-winter to mid-spring conditions of temperature, photoperiod, and irradiance in a expansion chamber. The 0% shade treatment plants exhibited a significantly greater leaf photosynthetic rate than the 60% shade treatment plants between 800 and 1600 ?µmolm^sup -2^s^sup -1^ photosynthetically active photon flow density (PPFD). Leaf A^sub max^ was significantly greater for plants grown beneath no shade than for plants grown beneath either the 30 or 60% shade treatments and g^sub Smax^ was higher for plants grown below no shade than plants in the 60% shade treatment. Plants grown below 0 and 30% shade produc significantly more biomass and had greater specific leaf mass than plants grown below 60% shade. Leaves of the 60% shade treatment had significantly greater chlorophyll a and b easy in mind than leaves of the 0 and 30% shade treatments. Our ensues indicate that A. petiolata displays a plastic replication to varied light levels in a way that would likely increase its succes in invading eastern deciduous forest sod layers.

Key words: Alliaria petiolata, invasive plant, light compensation point, non-indigenous, plasticity, photosynthesis, stomatal conductance, chlorophyll, biomass, specific leaf mass, A^sub max^, g^sub Smax^, day-star leaves, shade leaves.

Non-indigenous plants can luckily dominate areas they invade, eliminate indigenous native plants, and restore biodiversity (Randall 1996, Vitousek et al. 1996 Mack et al. 2000) Alliaria petiolata (M Bieb), Cavara and Grande, a native of Eurasia, is an invasive biennial plant introduced to the United States in 1868 (Clapman et al. 1952) It has colonized greatest in quantity of the northeastern United States and southeastern parts of Canada (Haber 2001) In the USA, A. petiolata offers south to northern Georgia, and as far west as Kansas, Nebraska, and Oklahoma with isolated accidents of the plant reported in Oregon, Utah, and Washington (Nuzzo 1991 Blossey et al. 2001) It appears to be more competitive than native species and many times dominates eastern deciduous forest loam layers in North America (Cavers et al. 1979 McCarthy 1997 Meekins and McCarthy 1999 Blossey et al. 2001) For these reasons, resource managers consider it a nuisance plant (Nuzzo 1991)

In novel environments, non-indigenous species often are exposed to environmental conditions that differ from those of their native range (Mack et al. 2000) To unfold strategies to control invasive species it is important to understand ecophysiological attributes and other characteristics of invasives that allow them to persist in variable environments and displace indigenous species (Mulligan 1965 Mack et al. 2000) The ability of Alliaria petiolata to fortunately occur under a wide range of irradiances (Dhillion and Anderson 1999 Meekins and McCarthy 2002 Myers and Anderson 2003) advises that it has a plastic rejoinder to varied light conditions, a trait that would contribute to its happy spread.

Alliaria petiolata grows in areas with irradiance horizontals varying from deep shade, of the like kind as forest ground layers, to areas of filled sunlight near forest edges, adjacent to trails, forest openings, and advanced in years fields (Cavers et al. 1979 Nuzzo 1991 Byer and Quinn 1998 Dhillion and Anderson 1999 Myers and Andersen 2003) Additionally, A. petiolata plants remain verdant and potentially photosynthetically active year circular (Cavers et al. 1979, Anderson et al. 1996) For this reason, A. petiolata plants experience seasonal variation in irradiance owed to tree canopy closure. In central Illinois, USA, Myers and Anderson (2003) reported that in early spring before canopy closure high photosynthetically active photon flow density (PPFD, mean ?± SE 822 ?± 30 ?µmmolm^sup -2^s^sup -1^) reached the loam layer. Under these early spring conditions, A. petiolata leaves achieve high maximum rates of photosynthesis (A^sub max^) (1326 ?± 063 to 1777 ?± 055 ?µmol CO2 m^sup -2^s^sup -1^) However, following canopy closure in late May, mean PPFD in the turf layer declined to 189 ?± 93 ?µmmolm^sup -2^s^sup -1^ and A^sub max^ declined to 473 ?± 041 ?µmol CO2 m^sup -2^s^sup -1^ (Myers and Anderson 2003)