Litter layers

Terrestrial biomass is divided into a number of subreservoirs with different turnover times. Forests contain approximately 90% of all carbon in living matter on land but their NPP is only 60% of the total. About half of the primary production in forests yields twigs, leaves, shrubs, and herbs that only make up 10% of the biomass. Carbon in wood has a turnover time of the order of 50 years, whereas turnover times of carbon in leaves, flowers, fruits, and rootlets are less than a few years. When plant material becomes detached from the living, plant carbon is moved from the phytomass reservoir to litter. "Litter" can either refer to a layer of dead plant material on the soil or all plant materials not attached to a living plant. A litter layer can be a... 

Toxicology and environmental health studies often lack a firm foundation of baseline data, and the NASGLP is a perfect starting point for a baseline data survey. During the field component of the survey, the crews collected two composite samples. One represented the top 5 cm of the soil directly below the litter layer (which will include a lot of the airborne components if they are present), and a second came from the 0-30-cm interval, independent of which soil horizon this may represent. Within this interval (the active layer), most of the interactions between biota and the non-living soil components take place, and thus is the important interval for this type if study. Environment Canada s Biological Methods Division selected one of the northern New Brunswick sites to collect a bulk sample in an attempt to create reference sites across Canada for standardized toxicity test methods. 

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. 

The process of forest litter decomposition is one of the key processes leading to the redistribution of Cs among the ecosystem components. It is affected by two major factors the rate of decomposition, which is dependent on the composition of the litter and the time since the introduction of Cs, which determines the level of decomposition of the uppermost, most heavily contaminated layer. The distribution of i Cs between the separate litter layers is important, since Of and Oh are critical for the roots of many undergrowth plant species (such as V. myrtillus, V. vitis-idaea, V. uUginosu and L. palustre ) and fungal saprotrophs (Clitocybe,... 

Herbs that enjoy dappled shade thrive on the edges of shrubs or by groups of small trees. Add a low-fertility soil improver on an annual basis in order to mimic the leaf litter layer that occurs naturally in woodland areas. Vigorous... 

The decomposition of tree leaves is not entirely confined to the litter layer on the forest floor. Leaves and needles are invaded by bacteria and fungi even as they grow these microorganisms may be either pathogens or saprophytes. ... 

In the San Bernardino Mountains, studies are going on to describe the effects of oxidant injury to ponderosa and Jeffrey pines on the microarthropods and fiingi of the litter layer under trees with various degrees of injury. Initial observations suggested lower population densities of microarthropods in the classes Insecta, Arachnida, and Myriapoda under some severely injured trees. ... 

Disturbance may influence the allelochemlcal environment in various ways. Living biomass is reduced, and fire reduces or eliminates litter and humus layers as well. Hence we should expect the total production of allelochemlcals to be lowered following disturbance. As succession proceeds and total biomass and litter layers rebuild. 

Fauna also influence soil carbon cycling. Bioturbation mixes and aerates soil, physically breaks down litter, creates flow paths for water in soil, and can reduce surface litter stocks and enhance erosion (Bohlen et al., 2004). For example, along a gradient of European earthworm (Lumbricus terrestris) colonization in a deciduous forest of northern Michigan, earthworms are associated with a decrease in litter-layer thickness, apparently mixing some forest floor organic matter into the mineral soil. Thus, fauna can create spatial patterns in SOM stocks. 

Figure 14.10. Principal component analysis of Py-FI mass spectra of (a) cold and (b) hot water extracts from the sequence of organic litter layers Oi-Oe-Oa in a beech stand (Fagus sylvat-ica) obtained before (-pre) and after (-post) aerobic incubation. The arrows indicate changes due to progressive decomposition top-down in the litter profile. Reprinted from Landgraf, D., Leinweber, P, and Makeschin, F. (2006). Cold and hot water extractable organic matter as indicators of litter decomposition in forest soils. Journal of Plant Nutrition and Soil Science 169,76-82, with permission of Wiley-VCH.

Figure 14.15. Depth distribution of summed compound classes in soil profiles under Miscan-thus stands. L and Of describe organic litter layers mainly composed of the Miscanthus residues, Ah the humic mineral topsoil, and Bh an argillic subsoil horizon. Samples were taken in the years 1999 and 2000.

A study of phosphamidon residues (3) in soil which was again made up of the litter layer plus soil to a depth 15 cm showed a rapid loss of the insecticide with the last measurable deposit (level of detection 0.025 ppm) being recorded at 4 days post spray and non-detectable levels after 8 days post spray. This particular study compared the deposits in both coniferous and deciduous areas and similar results were found in each location, thus indicating that litter from coniferous and deciduous trees acted as a common base for the insecticide deposit. 

In the litter-soil sample, the limit of detection was 0.1 ppm. Thus even if aminocarb had reached the litter layer, it was probably not present at levels that could be detected. 

It must be settled whether this approach is sensitive or insensitive towards nonphysiological distributions and amounts of heavy metals, not the least for the sake of biomonitoring. There are data on heavy metal (Zn, Cd, Cu, Pb) accumulation in litter and different soil layers and in plants of some oak woodland next to a metal smelter (Avonmouth near River Severn) in Great Britain (Martin and Bullock 1994). The concentrations in the litter layer are (in xg/kg) Cd 60, Cu about 170, Pb and Zn around 3,000. As usual for these metals except of Zn, where BCF 1 is a normal value, the concentrations of the four metals in photosynthetic organs of oak Quercus robur, other trees and scrubs and the fern Dryopteris are considerably lower than in supporting soils. In this restricted set of metal data, there are pairs of identical soil-leaf BCF only for Quercus robur (Zn, Cd BCF = 0.045) and Dryopteris spp. (Cd, Cu BCF about 0.13) the former corresponds to Ej (L) = -0.28 V, the latter to very similar -0.29 V. 

Fig. 4.1 Organic matter stocks in soil and litter layer under a terra firme forest in San Carlos de Rio Negro, Venezuela (data from Tiessen et al. 1994a).

Salcedo et al. (1991), working in an Atlantic coastal forest in Recife, Brazil, showed that phosphoms from the litter/fermentation layer is cycled back to the vegetation via mycor-rhizae-mediated mechanisms. However, 6l% of the added moved down to the mineral soil, where P in the soil solution is controlled by microbial biomass activity. In contrast. Stark and Jordan (1978), working on a P deficient upland terra firme forest in San Carlos de Rio Negro, Venezuela (Cuevas and Medina 1988), found that nearly 100% of the added 32p was retained in the root mat associated with the litter layer, with less than 0.1% moving down to the surface of the mineral soil. 

Ol — Litter layer Op — Fermentation layer — Humus layer... 

Figure 12 Decomposition dynamics of Spruce needles as indicated by increasing depth in the litter layers (S, L, FI, F2, and Fb). Fb = F layer that has been invaded by white-rot fungi (after Gourbiere, 1982).

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