Subsequent Decomposition Rates Research Articles

Photo-exposure affects subsequent peat litter decomposition

Exposure to sunshine is known to play a role in litter decomposition in some semi-arid areas. The aim of this study was to find out if it also plays a role in higher latitude environments in peat litter decomposition and could contribute to an explanation to the patchy nature of peat litter decomposition.Peat litter from 5 microenvironments (top of slope, bottom of slope, ridge, ryam and hollow) and put out and exposed to the sun or shaded over a summer in Western Siberia, 26km west of the town of Khanty-Mansiysk. Afterwards the peat litter was incubated in the laboratory - at field capacity or submerged in peat water - and CO2 and methane emission measured. Chemical composition of exposed and control peat litter was also investigated using stepwise extraction.The results indicate that exposure to sunlight does increase subsequent decomposition rate in most peat litters when incubated at field capacity, but the difference between the treatments levelled off at the end of the 2weeks incubation in most peat litter types. The total extra carbon loss was calculated to be up to about 2mg C m−2 over a season. When incubated submerged previous photo-exposure had less effect on CO2 evolution then when incubated at field capacity. No methane emission was recorded in any treatment. Some differences in chemical composition between exposed and shaded peat litters were found that could help explain the differences in subsequent decomposition rate. The results indicate that photodegradation could play a role in peat litter decomposition at higher latitudes when peat is disturbed and exposed to sunshine. However, the effect of photo-exposure in these areas is much smaller than observed in semi-arid areas at lower latitudes.

Shelters of leaf-tying herbivores decompose faster than leaves damaged by free-living insects: Implications for nutrient turnover in polluted habitats

Leaf-eating insects can influence decomposition processes by modifying quality of leaf litter, and this impact can be especially pronounced in habitats where leaf-eating insects reach high densities, for example in heavily polluted areas. We hypothesized that the decomposition rate is faster for shelters of leaf-tying larvae than for leaves damaged by free-living insects, in particular due to the accumulation of larval frass within shelters. We exposed litter bags containing samples of three different compositions (shelters built by moth larvae, leaves damaged by free-living insects and intact leaves of mountain birch, Betula pubescens ssp. czerepanovii) for one year at two heavily polluted sites near the nickel-copper smelter at Monchegorsk in north-western Russia and at two unpolluted sites. The decomposition rate of leaves damaged by free-living insects was 91% of that of undamaged leaves, whereas the mass loss of leaves composing shelters did not differ of that of undamaged leaves. These differences between leaves damaged by different guilds of herbivorous insects were uniform across the study sites, although the decomposition rate in polluted sites was reduced to 77% of that in unpolluted sites. Addition of larval frass to undamaged leaves had no effect on the subsequent decomposition rate. Therefore we suggest that damaged leaves tied by shelter-building larvae decompose faster than untied damaged leaves due to a looser physical structure of the litter, which creates favourable conditions for detritivores and soil decomposers. Thus, while leaf damage by insects per se reduces litter quality and its decomposition rate, structuring of litter by leaf-tying insects counterbalances these negative effects. We conclude that leaf-tying larvae, in contrast to free-living defoliators, do not impose negative effects on nutrient turnover rate even at their high densities, which are frequently observed in heavily polluted sites.

Seasonal variations in the availability of labile substrate confound the temperature dependence of organic matter decomposition

In empirically deriving the temperature dependence of organic matter decomposition, changing substrate availability can confound the derivation of any inferred intrinsic temperature dependence. In essence, when conditions are favourable for rapid decomposition, that fast rate can deplete the pool of available substrate leading to reduced subsequent decomposition rates. This is a potential problem under any experimental or observational setting. Its potential effect for measurements under seasonally varying temperatures is investigated here in a modelling study.Soil organic matter continuously loses carbon through decomposition which is generally replenished through new litter influx from senescing plant leaves, roots or other carbon sources. The CenW/CENTURY model was used to investigate to what extent inclusion of varying substrate supply within a realistic modelling framework modified the derived temperature dependence of organic matter decomposition. The model was run with different lignin to nitrogen ratios of fresh litter, and with litter either being generated continuously at a constant rate, or with litter fall being restricted to autumn.In systems with recalcitrant litter, as might be produced by conifers or eucalypts, the confounding effect of changing substrate supply was only slight. In systems with more labile litter, however, such as that produced by nutrient-rich grasslands, the confounding effect of varying substrate availability substantially weakened the derived temperature dependence. This effect was even more pronounced in systems with litter fall restricted to the autumn months. Reported temperature dependencies inferred from measurements with seasonally varying temperatures have shown weaker temperature dependencies than those inferred from laboratory incubation. The direction and magnitude of the confounding effect of changing substrate supply modelled here was consistent with the difference in temperature response observed in these different systems. It thus helps to reconcile these different reported temperature dependencies.

Effects of Ips typographus (L.) damage on litter quality and decomposition rates of Oriental Spruce [Picea Orientalis (L.) Link.] in Hatila Valley National Park, Turkey

This study investigated the effects of Ips typographus (L.) damage on initial litter quality parameters and subsequent decomposition rates of oriental spruce tree species [Picea orientalis (L.) Link]. The needle litter was collected from highly damaged, moderately damaged and control stands on two aspects (north and south) and two slope position (top and bottom) on each aspect. The litter was analyzed for initial total carbon, lignin and nutrient (nitrogen, phosphorus, potassium, calcium, magnesium and manganese) concentrations. The variability in nitrogen and calcium concentrations and ratios of C:N, lignin:N and lignin:Ca was significantly affected by the insect damaged levels. While nitrogen concentrations in needle litter increased with increasing insect damage (and consequently the ratios of C:N and lignin:N decreased), calcium concentrations decreased (and consequently the ratio of lignin:Ca increased). Aspect and slope positions explained most of the variability in carbon, lignin, phosphorus, potassium, magnesium and manganese concentrations and lignin:P ratio between all studied stands. Litter decomposition was studied in the field using the litterbag technique. The litter from highly damaged stands showed highest decomposition rates followed by moderately damaged and control stands. The mass loss rates were significantly positively correlated with initial nitrogen concentration and negatively with C:N and lignin:N ratios. The effects of microclimate resulting from canopy damage on litter decomposition was also examined at the same time using standard litter with the same litter quality parameters, but they showed no significant differences among the insect damage levels indicating that alteration of the litter quality parameters produced by I. typographus damage played a more important role than altered microclimate in controlling needle litter decomposition rates. However, changes in microclimate factors due to topography influenced decomposition rates.

LONG‐TERM BURNING INTERACTS WITH HERBIVORY TO SLOW DECOMPOSITION

Fires can generate spatial variation in trophic interactions such as insect herbivory. If trophic interactions mediated by fire influence nutrient cycling, they could feed back on the more immediate consequences of fire on nutrient dynamics. Here we consider herbivore-induced effects on oak litter quality and decomposition within a long-term manipulation of fire frequency in central Minnesota, USA. We focused on bur oak (Quercus macrocarpa) trees, which are common across the fire frequency gradient and are often heavily infested with either lace bugs (Corythuca arcuata) or aphids (Hoplochaithropsus quercicola). We used targeted exclusion to test for herbivore-specific effects on litter chemistry and subsequent decomposition rates. Lace bug exclusion led to lower lignin concentrations in litterfall and subsequently accelerated decomposition. In contrast, aphid exclusion had no effect on litterfall chemistry or on decomposition rate, despite heavy infestation levels. Effects of lace bug herbivory on litterfall chemistry and decomposition were similar in burned and unburned areas. However, lace bug herbivory was much more common in burned than in unburned areas, whereas aphid herbivory was more common in unburned areas. These results suggest that frequent fires promote oak-herbivore interactions that decelerate decomposition. This effect should amplify other influences of fire that slow nitrogen cycling.

Short‐Term Disappearance of Foliar Litter in Three Species Before and After a Hurricane1

ABSTRACTLitter disappearance was examined before (1989) and after (1990) Hurricane Hugo in the Luquillo Experimental Forest, Puerto Rico using mesh litterbags containing abscised Cyrilla racemiflont or Dacryodes excelsa leaves or fresh Prestoea montana leaves. Biomass and nitrogen dynamics were compared among: (i) species; (ii) mid‐ and high elevation forest types; (iii) riparian and upland sites; and (iv) pre‐ and post‐hurricane disturbed environments. Biomass disappearance was compared using multiple regression and negative exponential models in which the slopes were estimates of the decomposition rates subsequent to apparent leaching losses and the y‐intercepts were indices of initial mass losses (leaching). Cyrilla racemiflora leaves with low nitrogen (0.39%) and high lignin (22.1%) content decayed at a low rate and immobilized available nitrogen. Dacryodes excelsa leaves had moderate nitrogen (0.67%) and lignin (16.6%) content, decayed at moderate rates, and maintained the initial nitrogen mass. Prestoea montana foliage had high nitrogen (1.76%) and moderate lignin (16.7%) content and rapidly lost both mass and nitrogen. There were no significant differences in litter disappearance and nitrogen dynamics among forest types and slope positions. Initial mass loss of C. racemiflora leaves was lower in 1990 but the subsequent decomposition rate did not change. Initial mass losses and the overall decomposition rates were lower in 1990 than in 1989 for Dacryodes excelsa. Dacryodes excelsa and C. racemiflora litter immobilized nitrogen in 1990 but released 10‐15 percent of their initial nitrogen in 1989, whereas P. montana released nitrogen in both years (25‐40%). Observed differences in litter disappearance rates between years may have been due to differences in the timing of precipitation. Foliar litter inputs during post‐hurricane recovery of vegetation in Puerto Rico may serve to immobilize and conserve site nitrogen.

Soil CO2 evolution in Florida slash pine plantations. II. Importance of root respiration

Respiration of live roots was the single largest contributor to soil CO2 evolution in two mature slash pine (Pinuselliottii) plantations. Root respiration accounted for 51% of soil CO2 evolution at the 9-year-old plantation and 62% at the 29-year-old plantation. Additional estimates, calculated from data recorded from two small trenched plot sites at the 29-year-old plantation and based on possible variations in initial root biomass and subsequent decomposition rates, also averaged 62% of soil CO2 evolution. Specific root respiration averaged 0.40 g•g−1•year−1, varying from 0.34 to 1.70 g•g−1•year−1. Plots with larger proportions of fine roots had faster soil CO2 evolution rates.

The utilization of ZnSO 4 decomposition in thermochemical hydrogen cycles

We find that the ZnSO 4 decomposition reaction can be used as the high temperature step in a number of thermochemical cycles. It is especially applicable as a substitute for the H 2SO 4 decomposition step in H 2SO 4 based cycles, and significantly improves the efficiency of such cycles. In this study, we have taken an initial look at the effects of heat-up rate on the decomposition of ZnSO 4 as it is heated through an α-β transition at 1015 K. We find that a rapid heat-up of fine ZnSO 4 particulates through this transition leads to fracturing of the ZnSO 4 crystallites and significantly enhances its subsequent decomposition rate at ∼1043 K. We also find evidence for an autocatalytic decomposition process in fine ZnSO 4 particulates with either rapid or slow heat-up rates. We believe that a combination of (1) fracturing of the crystallites and (2) surface catalysis by ZnO to equilibrate the SO 3/SO 2/O 2 gaseous products contributes to the observed autocatalytic behaviour.

Decomposition of nitrous oxide on nickel oxide catalyst at low temperatures and pressures

The catalytic decomposition of nitrous oxide at the surface of nickel oxide has been investigated in the pressure range 0.05 to 1 torr between 22 and 140 °C. Except during the initial 10 to 20 min of reaction, the reaction is strictly first order, but the logarithm of the specific rate constant decreases linearly with increase of the logarithm of the initial pressure of nitrous oxide. This decrease is a result of the poisoning of the catalyst by the irreversible adsorption of oxygen on about 0.05 % of the surface sites during the reaction, and not by adsorption of gaseous oxygen, one of the products of decomposition. With the aid of a flow technique and differential pressure measurements before and after the removal of gas phase oxygen produced by the N2O decomposition, the rate of oxygen uptake by the catalyst during the initial stages has been measured and found to depend exponentially on the extent of its adsorption; and the amount absorbed at the pseudo-steady state (when first order kinetics first become valid) has been evaluated. Virtually all the kinetic results may be interpreted in terms of the two reactions: N2O (a) → N2(g) + O (a), O (a) + N2O (g) → N2(g) + O2(g), both of which proceed at an essentially uniform group of sites and on which the activation energies are controlled by the total number of oxygen adatoms on these sites. Supplementary studies of the adsorption of gaseous oxygen both at low and high temperatures, and of nitrous oxide at low temperatures, and the effect of high temperature presorbed oxygen on the subsequent decomposition rate of nitrous oxide are also reported. The low overall activation energy of 3 kcal/mole found experimentally for this reaction is also shown to be a direct consequence of the mechanism proposed.