Consumption of Leaf Litter by Lumbricus terrestris (Oligochaeta) on a Michigan Woodland Floodplain

Abstract

The consumption rate of leaf litter by Lumbricus terrestris (Oligochaeta) was studied from April through May 1981, on a Michigan woodland floodplain. Feeding chambers containing earthworms and leaf litter, which excluded soil microfauna, were placed on the floodplain. After 4 weeks, earthworms consumed leaves equivalent in amount to 93.87o of the total annual leaf fall. The mean consumption rate was 11.0 mg dry weight leaves g-1 live weight earthworms d-1 for a 4-week period with a maximum rate of 14.3 mg. The consumption rate of leaf litter by L. terrestris reported herein was similar to rates reported in other studies. INTRODUCTION Few studies have been conducted on the role of soil macroinvertebrates in leaf litter breakdown in wetland areas, particularly floodplains. It has been hypothesized that a woodland floodplain may serve as a temporary storage area for detritus such as leaf litter before it enters the stream or river (Merritt and Lawson, 1979; Cummins, 1980). In a Michigan woodland floodplain, Merritt and Lawson (1979) found that several groups of macroinvertebrates were involved in leaf litter breakdown (e.g., Gastropoda, Isopoda, Insecta, Diplopoda); however, earthworms appeared to be the most important group. The importance of earthworms in leaf litter degradation is welldocumented for several types of forest and agricultural lands (Kurcheva, 1960; Raw, 1962; Edwards and Heath, 1963; Van Rhee, 1963; Satchell, 1967; Edwards and Lofty, 1972; Lofty, 1974); however, less is known about their importance in floodplain soils. The objective of this study was to determine the rate at which Lumbricus terrestris (Linn.) consumed leaf litter in a Michigan woodland floodplain. MATERIALS AND METHODS Research was conducted on a point bar of the Augusta Creek floodplain located in the W. K. Kellogg Research Forest (Kalamazoo Co.), southwestern Michigan. At this location, Augusta Creek is a third-order channel (ca. 10 m width, 0.7 m depth). The floodplain is heavily forested and contains numerous species. Some of the major tree and shrub species are black ash (Fraxinus nigra Marsh.), green ash (F. pennsylvania Marsh.), basswood (Tilia americana L.), dogwood (Cornus spp.) and black cherry (Prunus serotina Ehrh.). The dominant lowland herbaceous vegetation consists of jewelweed (Impatiens capensis Meerb.), wood nettle (Laporta canadensis (L.) Wedd.), running strawberry (Euonymus obovatus Nutt.), skunk cabbage (Symplocarpus foetidus (L.) Nutt.) and iris sp. The soil of the point bar is poorly drained Adrian muck (Terric Medisaprist) which has high soil moisture and organic content most of the year. Green ash leaves were collected from the ground in early spring, air-dried and weighed in 10-g packs. A 3 m2 experimental plot, dominated by skunk cabbage, was chosen for its homogenous composition. In each of six rows, six holes were dug (27 cm apart, 18 cm deep) in the plot. The excavated soil was hand-sorted to remove large debris and steam heated to 55 C for 30 min to eliminate soil fauna. Thirty-six perforated plastic feeding chambers (22 cm high x 20 cm diam), each lined with 50 ,tm