Litter bags

Wilson et al., 1986). The source of detritus will clearly affect the period of refractory decay. For example, the refractory phase of phytodetritus may last for only a few weeks compared to vascular plant detritus which may last for months to years (Valiela, 1995 Opsahl and Benner, 1999). Finally, temperature and size of the decomposing detrital particles also represent parameters affecting decay rate. Early work by Hodson et al. (1983) showed that lignocellulose remineralization rates were enhanced with decreasing particle size due to the higher relative abundance of microbes with an increasing surface-to-volume ratio. To no surprise, litter bag experiments indicate that increases in temperature also increase decay rates due to enhanced microbial activity (Wilson et al., 1986). 

Figure 8.18 Percentage of initial weight of marsh grass (Sarcocornia fructicosa) remaining in litter bags in the Ebre River estuary (Spain) after one year. (Modified from Curdo et al., 2002.)...

Table 17.1. Fungal and bacterial biomass associated with decomposing leaves in streams. All values are maximum biomass estimates from litter bag decomposition studies except the study by Findlay et al. (2002b) where average microbial biomass from randomly collected leaves was estimated...

During the last decades, there have been a number of studies on the degradation of mangrove litter by use of litter-bags (Wafar etal., 1997 Ashton etal., 1999). These have shown rapid initial decomposition followed by low rates and accumulation of refractory compounds. The detritus is often enriched by nitrogen during the decomposition (Wafar etal., 1997 Holmer Olsen, 2002), and recent results also show enrichment with phosphorus (Nielsen Andersen, 2003). 

Under field conditions, the most common method used is the litter bag method. Litter bags with mesh sizes ranging from less than 1 mm to more than 10 mm have been used. Although there are several limitations to this method, investigators have consistently used this method because of its... 

Plant tissues/residues of wheat Triticum aestivum L. Coker 916 or 983 or Southern States 555 ), rye Secale cereale L. Abruzzi ), crimson clover Trifolium incamatum L. Tibbee ), and/or subterranean clover (T. subterranean L. Mount Barker ) were collected from litter bags half buried (i.e., the lower half of the bag was located within the soil) in the field plots (Blum et al. 1991) or from the soil surface (Blum 1997 Lehman and Blum 1997 Staman et al. 2001), freeze-dried, and stored in the dark at room temperature. The freeze-dried plant tissues/residues were ground just before analysis in a Wiley mill (20,40 or 60 mesh screen) and then extracted and analyzed by several different procedures ... 

Fig. 3.8 Phenolic acids extracted from wheat stubble, wheat straw from half buried litter bags, and wheat stubble/soybean (no-till) soil. Phenolic acids isolated and quantified were caffeic acid (CAF), ferulic acid (FER), p-coumaric acid (PCO), p-hydroxybenzoic acid (POH), sinapic acid (SIN), syringic acid (SYR), and vanillic acid (VAN). Becausep-coumaric acid was so high in comparison to other phenolic acids in wheat residues, data are presented twice, once with p-coumaric acid (a) and once without p-coumaric acid (b). Because phenolic acids were so low in the soil they are also presented in (c). The absence of standard error bars for wheat straw and soil indicates that the error bars are too small to be visible. Figures based on data from Blum et al. (1991, 1992). Plenum Publishing Corporation, data used with permission of Springer Science and Business Media...

Mean concentrations of available individual benzoic and cinnamic acid derivatives determined in this Cecil soil were small, less than 4 xg/g soil. The sums of 7 individual phenolic acids (0-2.5 cm soil cores) for wheat stubble tilled under/soybean and fallow/soybean soil samples were 58 and 38%, respectively, of wheat stub-ble/soybean soil samples (100% =12.30 0.58 tig/g). The sum of 7 individual phenolic acids for the 0-2.5 cm core samples was approximately 34% higher than for the 0-10 cm core samples. Plant tissues/residues contained greater individual phenolic acid content than soils. For example wheat stubble contained 258 times and wheat straw from half buried litter bags 65 times the p-coumaric acid of wheat no-till Cecil A soils (4 tig/g soil). 

Figure 92. Radionuclide retention by decaying leaves in litter bags, expressed as logio of (bag count ratio/standard count ratio), as a function of time, (o) Individual measurements ( ) averages for 8-week cycles (—) weight loss plotted on a semi-log scale. The lines were fitted by eye. From Olson and Crossley (1963).

In a different use of a radionuclide tracer, Crossley and Witkamp (1964) studied the effects of naphthalene on arthropods and the breakdown of forest litter. They used white oak leaves (Quercus alba) that had been tagged with Cs by tree-trunk inoculation. The experiment involved placing different amounts of naphthalene flakes on plots of leaf litter. Litter bags containing the tagged leaves were placed on the plots, and the loss of s and the number of arthropods were determined at weekly intervals. The investigators observed a difference between the control and treated plots in the s retention in the litter bags. They commented ... 

New techniques in such studies— radioisotopes, litter bags, use of insecticides, and other experimental approaches—can provide a fresh insight into the ecological problems confronting biologists and agronomists alike. Such experimentation is best approached from a functional viewpoint that is, an over-all consideration of the ecosystem as a dynamic unit, and the soil fauna and soil microflora as parts of that unit... 

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