Tuesday, August 4, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Background/Question/Methods Amur honeysuckle (Lonicera maackii) is a non-native deciduous shrub introduced from Asia that is rapidly spreading throughout eastern North America. Impacts of Amur honeysuckle in native habitats include reductions in the growth and reproductive success of native trees, shrubs and herbs, and a loss of species diversity. Impacts of Amur honeysuckle to ecosystem function are less well-established, but observations that honeysuckle litter is present for only a brief period after leaf fall suggested that it decomposes quickly. Using leaf litter of bush honeysuckle and two native trees, white ash (Fraxinus americana ) and hickory (Carya spp.), we tested the hypothesis that honeysuckle litter would decay faster than ash and hickory. We further hypothesized that placement of the litter bags beneath honeysuckle shrubs would enhance decomposition of all species, due to the dominant effect of honeysuckle litter in those sites. To test these hypotheses, ten plots were established within a forested area, five dominated by bush honeysuckle shrubs, five without honeysuckle. Eight grams of leaf litter from each of the three species were sealed in mesh bags and placed at the plots and then collected in 0, 1, 3, 6, and 9 month intervals to measure decomposition over time.
Results/Conclusions Honeysuckle had lower initial lignin concentration (6.3%) compared to ash (10.6 %) and hickory (14.5%; P < 0.0001), higher percent nitrogen (honeysuckle 1.8%, ash 0.84%, hickory 1. 23%; P <0.0001), and lower C:N ratio (honeysuckle 30, ash 58, hickory 38; P < 0.0001). Percent carbon also varied among species (P < 0.0001), with honeysuckle (45.1%) having the lowest concentration compared to hickory (45.8%) and ash (48.5%). Phosphorus concentration was higher in honeysuckle litter (1.75 mg g-1; p<0.0001) than in ash (1.26 mg g-1) and hickory (1.15 mg g-1). Honeysuckle litter decomposed much more rapidly than the other two species (P < 0.0001) and followed a simple exponential decay model; after 9 months, honeysuckle litter had only 3 % mass remaining, compared to 51% for both ash and hickory. Contrary to our second hypothesis, location under honeysuckle shrubs slowed the decomposition rate of all leaf litters (P = 0.0003). Vastly shorter residence time for honeysuckle litter compared to two native trees was due at least in part to differences in litter chemistry. Although its leaves decompose much faster than native species, slower decomposition of litter under honeysuckle shrubs confounds the conclusion that this species is accelerating decomposition in invaded forests.
Results/Conclusions Honeysuckle had lower initial lignin concentration (6.3%) compared to ash (10.6 %) and hickory (14.5%; P < 0.0001), higher percent nitrogen (honeysuckle 1.8%, ash 0.84%, hickory 1. 23%; P <0.0001), and lower C:N ratio (honeysuckle 30, ash 58, hickory 38; P < 0.0001). Percent carbon also varied among species (P < 0.0001), with honeysuckle (45.1%) having the lowest concentration compared to hickory (45.8%) and ash (48.5%). Phosphorus concentration was higher in honeysuckle litter (1.75 mg g-1; p<0.0001) than in ash (1.26 mg g-1) and hickory (1.15 mg g-1). Honeysuckle litter decomposed much more rapidly than the other two species (P < 0.0001) and followed a simple exponential decay model; after 9 months, honeysuckle litter had only 3 % mass remaining, compared to 51% for both ash and hickory. Contrary to our second hypothesis, location under honeysuckle shrubs slowed the decomposition rate of all leaf litters (P = 0.0003). Vastly shorter residence time for honeysuckle litter compared to two native trees was due at least in part to differences in litter chemistry. Although its leaves decompose much faster than native species, slower decomposition of litter under honeysuckle shrubs confounds the conclusion that this species is accelerating decomposition in invaded forests.
