Leaching

Abstract

The decomposition of autumn-shed leaves has traditionally been subdivided into three more or less distinct phases: leaching, microbial colonization and invertebrate feeding (Petersen & Cummins 1974, Gessner et al. 1999). Leaching is defined as the abiotic removal of soluble substances, among them phenolics, carbohydrates and amino acids (for analyses of these compounds, see Chapters 10, 11 and 14). It is largely completed within the first 24-48 h after immersion in water, and results in a loss of up to 30% of the original mass, depending on leaf species. Gessner & Schwoerbel (1989) showed that no such rapid leaching loss can be observed when fresh, rather than pre-dried, alder and willow leaves are used. Fungal colonization proceeded more slowly on fresh than on pre-dried alder and willow leaves (Bärlocher 1991, Chergui & Pattee 1992), dynamics of chemical leaf constituents differed between fresh and pre-dried leaves during subsequent decomposition (Gessner 1991), but no effects on invertebrate colonization have been observed (Chergui & Pattee 1993, Gessner & Dobson 1993). In a survey of 27 leaf species, drying significantly changed the magnitude of leaching in a majority of cases (Taylor & Bärlocher 1996), although the direction of change was variable among species with drying actually decreasing leaching in several cases. Some representative data are listed in Table 5.1.