It was only during the last couple of decades that we began to understand or even appropriately acknowledge the essential role of detritus for within- and between-ecosys-tem cycles of matter and energy. Through the release of nutrients upon decomposition, detritus plays a major role in ecosystem processes by serving as the source for nutrient cycling and provision to primary producers in all biotopes. In many systems, as different as marine kelp forests, sub-tidal seagrass meadows, intertidal salt marshes, and deciduous forests, 80% or more of the annually produced plant biomass is recycled through the detritus pathway rather than consumed by herbivores. In terrestrial habitats, organisms involved in detritus decomposition are responsible for more than 95% of the total community metabolism. In freshwaters, detrital matter, be it dissolved or particulate (see above), greatly exceeds the organic matter present in living microorganisms, plants, or animals.
Worldwide, the annual plant biomass production exceeds animal biomass production by a factor of about 10. Thus, plant detritus is much more important in terms of amount and availability for nutrient release through the action of microorganisms and animals (decomposition: see above) than animal detritus. Accordingly, the ecological significance of vegetal matter decomposition has received a great deal of attention, but the decomposition of animal products (see below) has received relatively little. Among plant detritus, leaf litter may be the most prominent type of detritus in most ecosystems (see above), but depending on the biotope considered needle litter (in boreal forests), monocot litter (in grasslands and wetlands), or algal and angiosperm wrack (in coastal areas) may comprise the detrital pool predominantly or even entirely.
Plant litter of whatever origin (see above) serves as substratum and food source for diverse microorganisms, be it bacteria, yeasts and fungi, microalgae, or protists. Along with the plant litter itself, being of relatively low nutritive value (see above), these microorganisms are ingested by detritus-feeding animals and utilized as readily available and digestible (supplementary) food source (see above). Thus, the digestion of both plant litter and microbial biomass eventually releases nutrients that can be utilized by the vegetation as soon as they are excreted, egested along with fecal masses, or set free upon the death and subsequent decomposition of the detritivore.
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