Environmental Engineering Reference
In-Depth Information
immobilization in microbial biomass during litter decomposition is often dominant
(
Findlay et al. 2002b
).
This interaction between carbon and other nutrients leads to some important implications
of human-induced changes in element cycling. For example, as CO
2
increases in the atmo-
sphere, plant tissues can become enriched in carbon, and if litter from these plants is avail-
able for decomposition it may require an external nitrogen or phosphorus source to balance
the additional carbon. The converse effect is also plausible—as nitrogen and phosphorus con-
centrations increase there may be a stimulation of decay of previously nutrient-limited
organic carbon pools. Therefore, CO
2
release may be enhanced as an indirect effect of human
fertilization. Greater plant productivity may result from higher CO
2
availability, leading to
increased litter production and accumulation (
Lichter et al. 2008
). In any case there are strong
interactions between carbon compounds undergoing microbial attack and other elements
necessary for biomass production and maintenance. Several components of these interacting
processes are subject to alteration by human-accelerated supply of elements.
While many types of detrital organic matter are nutrient-poor, they all contain nitrogen,
phosphorus, and other biologically relevant elements, and ultimately as the carbon is min-
eralized to CO
2
, the organic forms of nitrogen, phosphorus, and the like are also released
to the environment in simple forms available for uptake by plants and microbes. Unless
the detrital material is permanently stored or recalcitrant, over reasonable timescales any
elements in the original material or associated microbial biomass are eventually returned
to active cycling. Therefore, rates of decay can be the limiting step in completing nutrient
cycles in many ecosystems.
SUMMARY
Processes of decomposition close the cycle begun by primary production by releasing
energy for consumers and returning nutrients such as nitrogen and phosphorus to inor-
ganic forms. Regulation of rates of decay and specific processes causing mass loss both
affect where and when either energy or materials are available for consumption by organ-
isms or assimilation by plants. The basic principles governing the rates and relative impor-
tance of processes are broadly similar across ecosystem types, and for instance the
intrinsic composition of plant litter is almost always an important control on rates of
decomposition. The biochemical composition also influences when (or whether) inorganic
nutrients are released during the decay sequence versus being immobilized in the detri-
tus-microbe complex during some phase of decay.
Particulate detritus and especially dissolved organic carbon move across ecosystem
boundaries and can represent important subsidies to food webs in connected ecosystems.
A wide array of microbes and animals rely on detritus as a food resource and therefore
play a role in influencing rates of decay.
The Future
With the processes of decomposition linked to essentially all elemental cycles and under
the control of biotic and environmental conditions there are a huge number of fruitful
