Substrate litter

Particulate organic matter LF — 2-18% of organic C, 1-16% of total N SSF - 20 45% of organic C and 13-40% of total N Partially decomposed plant litter isolated by density fractionation (LF) or sieving (SSF). Substrate and centre for soil microbial activity, short-term reservoir of nutrients, food source for earthworms and other soil fauna and focci for formation of water stable aggregates. 

Hg concentrations in forest soils, mosses and fungal fruiting bodies are variable, and are influenced by many factors, such as the extent of forest-based capture of atmospheric Hg deposition, transmission of Hg from the forest canopy to the litter layer whether covered with mosses or not, and type of moss and soil layer conditions and configurations. Within the fungal fruiting bodies, further alternation of the Hg cycle occurs on account of mycelia substrate preferences and Hg allocation to stalk and caps, according to developmental stage. 

Fixation of molecular nitrogen, N2, to ammonia in forest ecosystems can occur on and/or in a variety of forest substrates including plant canopy and stems, epiphitic plants compartments, wood, litter, soil and roots. A recent review of the magnitude of N inputs to forest ecosystems indicates that non-symbiotic fixation ranges from < 1 to 5 kg/ha/yr and symbiotic fixation ranges from about 10 to 160 kg/ha/yr in early successional ecosystems where N2-fixing species are present. 

The DOC/enzyme/microbe interaction (DEMI) model divides bacterioplankton into two functional guilds, opportunists and decomposers, and DOC into two pools, labile and recalcitrant. In the context of the model, labile DOC is defined as directly assimilable monomers (saccharides, amino acids, and organic acids) and readily hydrolyzed polymers (polysaccharides, proteins, and nucleic acids). Because these substrates turn over rapidly, thus are unlikely to be transported far, most of the carbon in this pool will be autochthonous lysates and exudates, or allochthonous leachates from storms or seasonal litter fall. Recalcitrant DOC is defined as humic substances created by oxidative reactions among proteins, polysaccharides, hydrocarbons, and phenolic molecules. For inland waters, recalcitrant DOC is largely of allochthonous origin. 

Moore,T. R., Bubier, J. L., and Bledzki, L. (2007). Litter decomposition in temperate peatland ecosystems The effect of substrate and site. Ecosystems 10(6), 949-963. 

In all the studies referred to, the presence of the insecticide is determined by chemical means. The major concern is the biological effect of the material on the ecosystem. In a classical study, Yule (19) determined DDT residues in forest soils and litter using GLC and TLC techniques. Bioassays using Drosophila spp insects were then done on these samples and the mortality equivalent in terms of ug of DDT was determined. The mortality equivalent level of DDT was 50 to 250 times lower than the chemical analysis level. Thus, although the insecticide may be present in the substrate for a period of time extending... 

In genetically altered mdrlajb (—j—) knockout mice without P-gp/ both transplacental transport of P-gp substrates and the incidence of fetal malformations increase (93). Transplacental transport of the P-gp substrates/ digoxhi/ saquinavir and paclitaxel/ was increased 2.4-/ 7-, and 16-fold/ respectively/ in the knockout mice compared to transport in the wild-type animals. In another murine study/ mdrlajh (—j—) fetuses were susceptible to cleft palate malformation induced by prenatal exposure to a photoisomer of avermectin Bla/ whereas their wild-type litter mates were protected from the teratogen (87). 

In experiments designed to test these controls on decomposition, researchers often find that not all of these factors are equally important in aU ecosystems. Heneghan et al. (1999) comparing a single substrate between a temperate and two tropical sites found that soil fauna are not important in controlling decomposition in the temperate forest, but soil fauna are important and could explain the differences between the two tropical sites. In a three-factorial experiment (climate, litter quality, and biota), Gonzalez and Seastedt (2001) found that climate and litter quality had dominant effects at a temperate and dry tropical site, while all three factors were important in the wet tropical site. 

Figure 32 Graphical depiction of the response of litter decomposition rate to changes in climate and edaphic factors that favor decomposition ( environmental quality ), (a) Theoretical response that substrate a decomposes faster than substrate b under all conditions (b) The observed response of pine needles and aspen leaf litter mass loss to changing conditions, (after Taylor and Parkinson, 1988a).

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