Effects of collembolan grazing on fungal colonization of leaf litter

After a detailed field study of the leaf litter biota of an aspen poplar forest at the time of snow melt, and the confirmation of selective fungal feeding by field-collected specimens of Onychiurus subtenuis Folsom, an attempt was made to assess the effects of this selective feeding on the colonization of leaf litter by two common species of litter fungi. Simple microcosms held under controlled laboratory conditions were used in this study.The results showed that relatively low rates of selective grazing by the Collembola had potentially important effects on the competitive colonizing ability of the individual fungal species studied.     

Effects of collembolan grazing on nutrient release and respiration of a leaf litter inhabiting fungus

An attempt was made to assess the effect of grazing by Onychiurus subtenuis Folsom on nutrient release from and respiration of a sterile dark fungus using simple microcosms held under controlled laboratory conditions.The results showed that the fungus was very efficient in taking up all available soluble NO₃^? and PO₄^2? and that collembolan grazing had no effects in releasing these nutrients during the 10 day experiment. Significant increase in respiration of litter colonized by the fungus was observed following collembolan grazing, but this increase was attributed to the activity of bacteria and fungi tracked into the leaf litter systems by the Collembola.     

Carbon and nitrogen dynamics of decomposing leaf litter in a tropical hill evergreen forest

This study was carried out in a tropical hill evergreen forest in northern Thailand. Two tree species Castanopsis accuminatissima and Schima wallichii were the dominant species in the study plot. Decomposition processes of these two species were studied using a litter bag method to evaluate the roles of these species in the nutrient cycling in this hill evergreen forest. The decomposition rates (k) were 0.99–1.05 and 0.55–0.61 in C. accuminatissima and S. wallichii, respectively. In this monsoon forest, the relationship between the onset of rain and the accumulation and decomposition of litter is an important mechanism for linking climate and availability of plant nutrient. Weight loss for both species showed a similar pattern shaped by the seasonal availability of water. However, the nitrogen dynamics were apparently different in the two species. During the rainy season, C. accuminatissima released nitrogen during the decomposition processes, while S. wallichii nitrogen was immobilized in the leaf litter over the rainy season. C. accuminatissima released nitrogen, subsequently available for uptake by trees, while S. wallichii accumulated nitrogen over 15 months and so their roles are important for the retention of nutrients in the hill evergreen forest ecosystem. Thus the two species have different functions in the nutrient dynamics in the forest floor.     

Tree species effects on microbial respiration from decomposing leaf and fine root litter

Tree species have an impact on decomposition processes of woody litter, but the effects of different tree species on microbial heterotrophic respiration derived from decomposing litter are still unclear. Here we used leaf and fine root litter of six tree species differing in chemical and morphological traits in a temperate forest and elucidated the effects of tree species on the relationships between litter-derived microbial respiration rates and decomposition rates and morphological traits, including specific leaf area (cm² g⁻¹) and specific root length (m g⁻¹) of litter at the same site. Litterbags set in forest soil were sequentially collected five times over the course of 18 months. During litter decomposition, microbial respiration from leaf and fine root litter differed among the six tree species. Temporal changes in the remaining mass and morphology (specific leaf area and specific root length) were observed, and the magnitude of these changes differed among species. Positive correlations were observed between respiration and mass loss or morphology across species. These results revealed that litter mass loss and morphological dynamics during decomposition jointly enhanced microbial respiration, and these carbon-based litter traits explained species differences in decomposition of leaves and fine roots. In conclusion, tree species influenced the magnitude and direction of microbial respiration during leaf/fine root litter decomposition. Tree species also affected the relationship between microbial respiration and litter decomposition through direct effects of litter traits and indirect effects mediated by regulation of heterotroph requirements.     

Succession of collembolan communities during decomposition of leaf and root litter: Effects of litter type and position

Little is known about the collembolan community involved in the decomposition of fine root (≤2.0 mm in diameter) litter, which is largely different from leaves in both litter quality and position. The collembolan communities involved in root and leaf litter decomposition were compared in a litterbag experiment in a coniferous forest of Chamaecyparis obtusa. A two-factor experiment (litter type × litter position) was conducted to evaluate the relative effects of litter quality and position. Litterbags of roots and leaves were each placed at two positions (on the soil surface and in the soil), and were collected at seven different times over three years. Abundance and biomass of Collembola involved in root decomposition in the soil were higher than those involved in leaf decomposition on the soil surface, and the collembolan community composition largely differed between these two types of litterbag. Differences between root and leaf decomposition were mainly caused by litter position, but effects of litter type were also detected at species-level. Species that preferred roots were abundant at an early stage of litter decomposition in the soil. Because the early stage of decomposition in the soil is naturally achieved only by root litter initially deposited in the soil, root litter may function as an essential resource for certain species. The results of this study indicate that root litter contributes to collembolan community organization as a spatially and qualitatively different resource than leaf litter. This also suggests that root litter is decomposed via different soil faunal processes than leaf litter.     

Fungal biomass and nitrogen in decomposing scots pine needle litter

The development of fungal biomass and increase of amounts of N was studied in decomposing pine needle litter for about 3 yr. After a relatively rapid increase of the amount of mycelium the fungal biomass became rather constant after about 2 yr. The absolute amount of N in the needles increased between the 4th and the 16th months and this increase was correlated to the increase of fungal biomass in the needles.     

Microbial activity and leaching during initial oak leaf litter decomposition

The decomposition of oak leaf litter was studied by means of a litterbag experiment in an oak forest in the Netherlands. The contribution of microbial activity and leaching to weight loss and element dynamics during the first 6 weeks of decomposition was investigated by means of frequent respiration measurements and extractions of the litter and by a qualitative comparison of throughfall and litter percolation water chemistry. The oak-leaf litter lost 9.3% of its initial dry weight during the first 6 weeks. In total, 90% of this observed weight loss was explained by the processes studied. About 5.9% (64% of the total) of this weight loss was attributed to microbial tespiration and 0.5% (5%) to the loss of inorganic solutes. Leaching of dissolved organic compounds was estimated to account for 2.0% (21%). The results indicated a fast leaching of K and Cl out of the fresh litter during the first 2 weeks, while Mg, Fe, Mn, Si, ortho P, and dissolved organic N were released at a much lower rate. At the same time, small amounts of H⁺, NH _inf4 ^sup+ and NO _inf3 ^sup- were retained in the litter.     

Carbon and nitrogen transfer in leaf litter mixtures

The decomposition rate of litter mixtures can differ from that expected on the basis of the decomposition rate of the individual components. This difference may be linked to nitrogen (N) transfer from high-N to low-N components. Transfer of N is probably also associated with transfer of C, but the extent and direction of this C transfer are unknown. This study examined transfer and loss in laboratory microcosms of C and N from two mixed litter species (Scots pine, Pinus sylvestris L. and maize, Zea mays L.), which have natural isotopic differences in ¹³C. Half the material was ¹⁵N-labelled and the plants were fertilised or unfertilised. Substantial bidirectional transfer of C and N occurred between the litters, with net transfer of C from pine to maize litter and net transfer of N from high-N to low-N litter. Mixtures of fertilised and unfertilised plant litter showed higher than expected C losses and net transfer of N. Mixtures with litters from the same fertilisation treatment had small or insignificant net transfer of N and their C losses did not differ from values estimated using the decomposition rates of the pure litters.     

Nitrogen dynamics of decomposing hardwood leaf litter in a central himalayan forest

The N dynamics in four decomposing broadleaf litter species of a mixed broadleaf forest in Central Himalaya was followed for a period of 578 days. The C:N ratio above which net immobilization and below which net mineralization took place, differed among species. Once the nitrogen release phase started, the release was in proportion to the weight loss.     

Impact of excreted nitrogen by grazing cattle on nitrate leaching

Abstract. At De Marke experimental farm, data on water and nitrogen flows in the unsaturated zone were gathered on two grazed pastures on sandy soils during the years 1991 to 1994. These provided a basis for calibration and validation of simulation models. The different levels of nitrate-N concentrations of the two plots could largely be explained by differences in crop uptake and simulated denitrification as influenced by different groundwater levels. The irregular distribution of excreta was taken into account by a simulation study quantifying the variability of nitrate-N concentrations under a grazed field. The resulting distribution of simulated nitrate-N concentrations explained the average and peak values of the measured concentrations. Temporal variability of weather was used to assess the nitrate leaching risk under urine patches deposited in either July or September. At site A the probability of exceeding the EC-directive by drinking water (11.3 mg/1 nitrate-N) under a urination deposited in either July or September was respectively 10 and 25%. The average field concentration at this site will hardly ever be a high risk for the environment under the current farm management. At site B the EC-directive will be exceeded under any urine patch in almost 100% of the years, affecting the field average concentration. In field B careful grazing management would result in less nitrate leaching, but the environmental goals would not be reached.     

Nutrient changes in decomposing beech leaf litter assessed using a solution flux approach

The decomposition of beech (Fagus sylvatiea L.) leaf litter was examined in lysimeters. The experiment allowed comparison of data from mass changes of bioelements in leaf litter and the solution flux balance of through fall input and lysimeter output over a two-year period (1983 and 1984). The annual C loss from the leaf litter was 19%. Na and K concentrations in this leaf litter decreased in the first year and remained constant in the second, while those of Ca and Mg showed no significant changes. N and S amounts per ha increased during the first year by about 7 kg N ha^?1 and 0.5 kg S ha^?1. Ash, Fe, Mn and Al amounts per ha increased to 470, 130 and 240% of their initial levels. These net increases in the first year of decomposition are discussed. The mean annual water and element input by through fall during the experiment corresponded approximately to the long-term average. Thirty to 40 mm more water was evaporated from the litter layer in the drier year (1983) than in 1984. Total N, NO, Na and C1 flux rates of through fall inputs and lysimeter outputs were equal. NH, input rates were greater and organic N smaller than the output rates of the lysimeters. Water balance data indicated that the lysimeter output of K, Mg, Ca and SO, exceeded through fall input. Probable reasons for these differences are discussed.     

Origin of the nitrogen assimilated by soil fauna living in decomposing beech litter

We investigated the nitrogen source for main taxa of soil fauna in two beech forests of contrasted humus type using ¹⁵N-labelled beech litter and ¹⁵N analysis of soil fauna. ¹⁵N-labelled beech litter was deposited on the topsoil in December 2000 in four stands of different ages at Leinefelde (Germany) with mull humus and in one mature stand at Sorø (Denmark) with moder humus. The fate of the tracer isotope was measured in litter and soil, as well as in the soil fauna, and for each taxa, we calculated the proportion of N in the animal derived from the labelled substrate. Of the original N contained in the litter, 20-41% was lost after 9 months at Leinefelde, and only 10% at Sorø. This loss was counterbalanced by the incorporation of 24-31% external N at Leinefelde, and 31% at Sorø, partly originating from fungal colonisation of the added litter. The proportion of N assimilated from the labelled litter by the different soil animals varied in relation to their mobility and feeding preferences. Large and mobile soil animals, especially predators, derived on average less ¹⁵N because they were also able to feed outside the labelled litter boxes. Detritivores assimilated at most 15% of their nitrogen content at Leinefelde and 11% at Sorø from the decomposing labelled litter. The most labelled taxa at Leinefelde were small fungivorous and coprophagous species, mainly isotomid Collembola such as Isotomiella and Folsomia. At Sorø, best labelled taxa were saprophagous species such as Enchytraeidae, Glomeridae and Phthiracaroidea. These low rates of ¹⁵N assimilation indicate that fresh litter is not directly the main N source for soil animals. The results obtained suggest that soil fauna fed preferentially upon microorganisms colonising the litter at Leinefelde (mull) and from litter itself at Sorø (moder).     

Nutrient release from decomposing leaf litter of temperate deciduous forest trees along a gradient of increasing tree species diversity

In the litter of six deciduous tree species (Fagus sylvatica, Tilia spp., Fraxinus excelsior, Carpinus betulus, Acer pseudoplatanus and Acer platanoides) and in stand-specific litter mixtures, we compared mass loss and nutrient release across diversity levels along a gradient of decreasing proportion of Fagus in stands with similar environmental and physical soil conditions. The litterbag studies ran over 22 months. The decomposition rate constants (k) of the temperate forest species ranged from k = 0.5 for Fagus to k = 1.5-2 for all other tree species. In Fagus, k was closely negatively correlated with the thickness of the litter layer and positively correlated with soil pH and isopod abundance. k was significantly higher in the mixed species stands (except for Carpinus and Fraxinus) and was positively correlated with earthworm abundance. Over the whole incubation time, nutrient amount and release rates of N, P, K, Ca and Mg as well as C-related ratios showed significant differences between tree species but no consistent differences among the diversity levels. Initial C-related nutrient ratios of the leaf litter and abundance of mesofauna and macrofauna were correlated with the length of time lag before nutrient release. We conclude that the mere number of tree species is not the main driver of nutrient release and decomposition processes, but that key groups of the decomposer fauna as well as the characteristic traits of the individual tree species are decisive.     

Stabilisation of soil organic matter in invertebrate faecal pellets through leaf litter grazing

Soils were amended with either leaf litter or faeces from pill millipedes fed on the leaf litter, then incubated at 20 °C for 130 days whilst monitoring the respiration rates. Significantly more CO₂ was respired from soil containing leaf litter than that amended with an equivalent weight of faecal matter, whilst the unamended soil exhibited a respiration rate similar to soil amended with faecal material. Consideration of these findings with recently observed differences in biochemical compositions of litter and faeces suggests that processing of plant litter by detritivores leads to more stabilised forms of organic matter by removal of biochemical components essential to the nutrient requirements of the invertebrate and the soil microbial biomass.     

The initial lignin:nitrogen ratio of litter from above and below ground sources strongly and negatively influenced decay rates of slowly decomposing litter carbon pools

Understanding the interactions between the initial biochemical composition and subsequent decomposition of plant litter will improve our understanding of its influence on microbial substrate use to explain the flow of organic matter between soil carbon pools. We determined the effects of land use (cultivation/native woodland/native pasture), litter type (above and below ground) and their interaction on the initial biochemical composition (carbon, nitrogen, water soluble carbon, lignin, tannin and cellulose) and decomposition of litter. Litter decomposition was studied as the mineralization of C from litter by microbial respiration and was measured as CO₂–C production during 105 d of laboratory incubation with soil. A two-pool model was used to quantify C mineralization kinetics. For all litter types, the active C pool decay rate constants ranged from 0.072 d⁻¹ to 0.805 d⁻¹ which represented relatively short half-lives of between 1 and 10 days, implying that this pool contained compounds that were rapidly mineralized by microbes during the initial stages of incubation. Conversely, the decay rate constants for the slow C pool varied widely between litter types within and among land uses ranging from 0.002 d⁻¹ and 0.019 d⁻¹ representing half-lives of between 37 and 446 days. In all litter types, the initial lignin:N ratio strongly and negatively influenced the decay rate of the slow C pool which implied that the interaction between these two litter quality variables had important controls over the decomposition of the litter slow C pool. We interpret our results to suggest that where the flow of C from the active pool to the slow pool is largely driven by microbial activity in soil, the rate of transfer of C will be largely controlled by the quality of litter under different land-use systems and particularly the initial lignin:N ratio of the litter. Compared with native pastures and cultivation, above and below ground litter from native woodland was characterized by higher lignin:N ratio and more slowly decomposing slow C pools which implies that litter is likely to persist in soils, however based on the sandy nature of the soils in this study, it is likely to lack protection from microbial degradation in the long term.     

Soil characteristics determine soil carbon and nitrogen availability during leaf litter decomposition regardless of litter quality

Climate and litter quality have been identified as major drivers of litter decomposition, but our knowledge of how soil characteristics (e.g. microbial community and chemical properties) determine carbon (C) and nitrogen (N) availability derived from the decomposition of litter of different qualities is still scarce. We conducted a microcosm experiment to evaluate how soils with contrasting microbial communities and soil properties (denoted Soils A and B hereafter, where Soil B has higher bacterial and fungal abundance, fungal:bacterial ratio, and organic C than Soil A) determine the availability of soil C (carbohydrates, proteins, amino acids and phenols) and N (dissolved organic and inorganic N, microbial biomass N and available N) during the decomposition of litter of contrasting quality (C:N ratios ranging from 20 to 102). We also evaluated the relative importance of soil characteristics and litter quality as drivers of C and N inputs to the soil during this process. Overall, higher soil C and N availability after litter decomposition was found in Soil B than in Soil A. Soil characteristics had a higher positive effect on soil C and N contents than litter quality during litter decomposition. We also found that changes in N availability and organic matter quality registered after litter decomposition, linked to different soil characteristics, were able to promote dissimilarities in the potential mineralization rates. In conclusion, our study provides evidence that soil characteristics (e.g. microbial communities and chemical properties) can be more important than litter quality in determining soil C and equally important for N availability during the decomposition of leaf litter.     

Nitrogen and cation mobilization by soil fauna feeding on leaf litter and soil organic matter from deciduous woodlands

Decomposing oak litter was incubated in laboratory microcosms and the effects of adding a variety of soil animals upon nitrogen and cation release were monitored. Various groups of macrofauna caused a marked increase in ammonium release with smaller increases in calcium, potassium and sodium leaching. Microfauna also had significant but much less marked effects upon nitrogen and cation release.The effects of different grazing intensities of the millipede Glomeris marginata on a variety of forest organic substrates show that the animals amplified existing patterns of nutrient release.     

Temporal dynamics of microbial communities on decomposing leaf litter of 10 plant species in relation to decomposition rate

Few empirical studies have examined how microbial communities on decomposing litters change in relation to litter chemistry or how microbial community composition is related to the rate of decomposition. We examined the relationships among microbial community composition, litter chemistry, and decomposition rates in a common garden experiment of the decomposition of leaf litters of 10 plant species. Microbial community composition, as measured by phospholipid fatty acids (PLFA), and 7 litter chemistry variables (%N, C:N, four carbon fractions, and lignin:N) were examined at 1, 2, and 8 months into decomposition. Both microbial and litter chemistry variables were reduced to a single axis each through nonmetric multidimensional scaling (NMS) to examine the relationship between microbes, litter chemistry, and decomposition rates. Although microbial communities were separated according initial litter chemistry and lability, individual measures of litter chemistry had limited ability to predict microbial community composition during decomposition. Decomposition rate constants were explained by litter chemistry of initial, 1-, 2- and, 8-month old litters (60–72% of the variance), and by microbial community composition at the 8-month collection date (67%). The results suggest that initial litter chemistry determines the rate of decomposition and microbial community composition early in decomposition while the composition of the microbial community plays a more important role in determining decomposition rate later in decomposition.     

Evidence that straw does not increase the mobilization of N from decomposing salal (Gaultheria shallon Pursh.) leaf litter

We tested whether straw could induce higher N release from decomposing salal leaf litter, which ostensibly interferes with mineralization of N. We mixed forest floor material from two forest types with ¹⁵N-enriched salal leaf litter, and incubated the mixtures 3 years with and without straw amendments. The amounts of N, as well as the relative amounts of ¹⁵N, extracted in five fractions were, respectively, 29-93 and 25-82% lower in straw-amended forest floor. Results suggest that straw diverted microbial decomposition activity away from the more recalcitrant litter fractions. Previous reports of higher mineral-N availability in straw-amended forest floors are best explained by a fertilizer effect of straw as opposed to a ‘priming effect’.     

Effect of nitrogen inputs to cereals on nitrate leaching from sandy soils

Abstract. The effect of nitrogen fertilizer inputs to cereal crops on nitrate leaching after harvest was tested on 21 experiments on sandy soils in England. At small nitrogen fertilizer rates leaching increased very little with increasing inputs, while at high rates more than half of any additional nitrogen could be accounted for as increase in nitrate leached. In many cases the response fitted two straight lines. Nitrogen offtake in grain also fitted two straight lines, with a form which complemented the leaching response. The gradient averaged 0.52 kg N in grain for every additional 1kg N applied below the break point, but only 0.05 kg/kg above. The break points were generally close to or above the economic optimum N input. The effect of inputs on leaching could he quantitatively related to nitrogen offtake in grain, assuming a constant ratio of nitrogen in grain to total nitrogen uptake. The results show that fields receiving N inputs in excess of the economic optimum cause a disproportionately large nitrate loss. However because of uncertainty in predicting the break point in advance, modest further reduction in leaching will occur by reducing inputs to somewhat below the expected economic optimum.