illustrating a three-trophic food chain (
producers-herbivores-carnivores) linked to
decomposers. The movement of
mineral nutrients through the food chain, into the mineral nutrient pool, and back into the
trophic system illustrates ecological recycling. The movement of energy, in contrast, is unidirectional and noncyclic. An example of ecological recycling occurs in the
enzymatic digestion of
cellulose. "Cellulose, one of the most abundant organic compounds on Earth, is the major
polysaccharide in plants where it is part of the cell walls. Cellulose-degrading enzymes participate in the natural,
ecological recycling of plant material." Different ecosystems can vary in their recycling rates of litter, which creates a complex feedback on factors such as the competitive dominance of certain plant species. Different rates and patterns of ecological recycling leaves a legacy of environmental effects with implications for the future evolution of ecosystems. Ecological recycling is common in organic farming, where nutrient management is
fundamentally different compared to agri-business styles of
soil management. Organic farms that employ ecosystem recycling to a greater extent support more species (increased levels of biodiversity) and have a different
food web structure. Organic agricultural ecosystems rely on the services of biodiversity for the recycling of nutrients through soils instead of relying on the supplementation of
synthetic fertilizers. The model for ecological recycling agriculture adheres to the following principals: • Protection of biodiversity. • Use of renewable energy. • Recycling of plant nutrients. Where produce from an organic farm leaves the farm gate for the market the system becomes an open cycle and nutrients may need to be replaced through alternative methods.
Influence of Trophic Interactions on Nutrient Cycling in Freshwater Systems Trophic interactions also play a crucial role in regulating nutrient cycling, especially in freshwater systems. They not only alter how nutrients, such as
nitrogen (N) and
phosphorus (P), are distributed and the rate at which they are recycled in these systems, but also can determine which species are most dominant by doing so . Predators can indirectly influence nutrient availability through top-down control of
herbivores, thereby affecting
primary production and nutrient uptake . One of the more important mechanisms linking
foodwebs to nutrient cycling is the trophic relationship of
planktovorous fish,
zooplankton, and
phytoplankton . When zooplankton populations are high, they consume phytoplankton at a greater rate, thereby limiting the incorporation of nitrogen and phosphorus into organic matter . As a consequence, inorganic forms of nitrogen, such as ammonium (NH₄⁺) and dissolved phosphorus in the form of phosphate (PO₄³⁻), are kept at a higher concentration in the water column . Under these conditions, organisms such as
nitrogen-fixing cyanobacteria will be less competitive since inorganic nitrogen is already abundant, favoring species that depend on direct uptake of ammonium or
nitrate . Meanwhile, increased inorganic phosphorus in the water favors those plankton species that are more efficient at uptaking this limiting nutrient . If fewer predators are feeding on zooplankton in the system, species such as
Daphnia will have a competitive advantage because of their larger size and higher phosphorus requirement for growth. In contrast, if the zooplankton population is regulated by an increase in planktovorous fish numbers, phytoplankton can more easily proliferate and assimilate large amounts of nitrogen and phosphorus into their biomass, reducing the availability of these nutrients in their bioavailable forms . Consumers such as zooplankton and fish also excrete ammonium as a waste product and phosphate during metabolic processes . These can be directly taken in by primary producers, making this consumer-driven internal cycling of nutrients another important source of the redistribution of nutrients in freshwater systems .
Ecosystem engineers that cycles nutrients through the layers of the oceanic water column. Whales can migrate to great depths to feed on bottom fish (such as
sand lance Ammodytes spp.) and surface to feed on
krill and
plankton at shallower levels. The whale pump enhances growth and productivity in other parts of the ecosystem. The persistent legacy of environmental feedback that is left behind by or as an extension of the ecological actions of organisms is known as
niche construction or ecosystem engineering. Many species leave an effect even after their death, such as coral skeletons or the extensive habitat modifications to a wetland by a beaver, whose components are recycled and re-used by descendants and other species living under a different selective regime through the feedback and agency of these legacy effects. Ecosystem engineers can influence nutrient cycling efficiency rates through their actions. taken from
Charles Darwin's publication on the movement of organic matter in soils through the ecological activities of worms.
Earthworms, for example, passively and mechanically alter the nature of soil environments. The bodies of dead worms passively contribute mineral nutrients to the soil. The worms also mechanically modify the physical structure of the soil as they crawl about (
bioturbation) and digest on the
molds of organic matter they pull from the
soil litter. These activities transport nutrients into the
mineral layers of soil. Worms discard wastes that create
worm castings containing undigested materials where bacteria and other decomposers gain access to the nutrients. The earthworm is employed in this process and the production of the ecosystem depends on their capability to create feedback loops in the recycling process.
Shellfish are also ecosystem engineers because they: 1) Filter suspended particles from the water column; 2) Remove excess nutrients from coastal bays through
denitrification; 3) Serve as natural coastal buffers, absorbing wave energy and reducing erosion from boat wakes, sea level rise and storms; 4) Provide nursery habitat for fish that are valuable to coastal economies.
Fungi contribute to
nutrient cycling and nutritionally rearrange patches of
ecosystem creating
niches for other organisms. In that way,
fungi growing on
dead wood allow
xylophages to grow and develop, and in turn, affect dead wood, contributing to wood
decomposition and
nutrient cycling in the
forest floor. ==History==