Autumn olive (Elaeagnus angustifolia) and Amur honeysuckle (Lonicera maackii) have emerged as two important invaders of unmanaged grasslands and open forests in the lower Midwest. Field observations suggest that the species occupy different niches: Elaeagnus has more limited shade tolerance than Lonicera, but more readily colonizes unmanaged grasslands, while Lonicera readily persists under closed forest canopies. This conflicts with published assertions of substantial shade tolerance in Elaeagnus. We examined photosynthetic behavior and allocation patterns for potted individuals grown in outdoor shade houses of 90, 80, 60, 40, and 20% shade.
Results/Conclusions
Photosynthetic light response curves were measured over a range of 0-1600 µmol m-2 s-1 for both species grown in 90 and 20% shade. Although not statistically different, both species appeared to show similar responses when grown under 90% shade, but Elaeagnus showed higher rates at 20% shade. Dark respiration rate, light compensation points, specific leaf area, and chlorophyll contents responded to shade treatment, but didn’t differ between species. Rates of stem growth were significantly higher for Lonicera across the shade gradient. Total, above, and below ground biomass responded to the shade gradient, but did not differ across species. Leaf area g-1 and stem length g-1 were greater in shade, with Elaeagnus far greater than Lonicera overall. Mass allocation to leaves and stems was generally higher in Lonicera.
Differences in photosynthetic behaviors and resource allocation do not seem to explain the habitat differences in the species. With more mass-efficient patterns of leaf area production and stem elongation, Elaeagnus should be more successful in shade.