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.     

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.     

Nutrient release from decomposing leaf mulches of karité (Vitellaria paradoxa) and néré (Parkia biglobosa) under semi-arid conditions in Burkina Faso, West Africa

Information on decomposition and nutrient release from leaf litter of trees in agroforestry parkland systems in Sub-Saharan Africa is scarce despite the significant role of these trees on soil fertility improvement and maintenance. Decomposition and nutrient release patterns from pruned leaves of the two most common species of parklands of the semi-arid zone of West Africa: Vitellaria paradoxa C.F. Gaertn (known locally as karité) and Parkia biglobosa (Jacq.) Benth. (known locally as néré), were investigated by a litter-tube study in Burkina Faso. Litter quality, methods of leaf exposure to the soil and combination with fertilizers were the factors studied. Leaves of néré had a higher nutrient content (C, N, P, Ca) and contained more ash and lignin than leaves of karité. Karité leaves had a greater content of K, cellulose and polyphenols. The pruned leaves of karité and néré showed two distinct decomposition patterns. Néré leaves decomposed more rapidly, with less than 32% of the initial weight remaining after the rainy season (4 months) while karité leaves decomposed more slowly with 43% of the leaf litter remaining after the rainy season. Addition of urea and compost did not significantly affect the rate of decomposition. Significant interaction was observed between species and method of leaf exposure for the first sampling date. Leaf litter of néré buried in soil gave the highest weight loss (34% of the initial mass in 1 month) compared with exposed leaf litter of néré and karité, and buried leaf litter of karité. Except for N, nutrient release patterns were similar for both species but the nutrient release rates were higher for néré leaves compared with karité leaves. N was immobilised in karité leaves most likely due to low N and high phenolic content. The rate of nutrient release from karité leaves followed the general trend K>P>N.     

Indirect effects of N and S deposition on a Norway spruce ecosystem. An update of findings within the Skogaby project

In this paper we try to interpret results from different investigations where an ecosystem with Norway spruce was manipulated with increased N and S deposition via the soil system. The site, in Skogaby in Southwest Sweden, had 1989–93 an annual deposition of 9 kg NH₄-N; 7 kg NO₃-N and 20 kg SO₄-S ha^–1. The stand was treated during 6 years with 100 kg N and 114 kg S ha^– y^–1 in the form of ammonium sulphate (NS treatment). The stand reacted with increased above ground production of 31% after 3 years of treatment. The uptake above ground of N was 155 kg ha^–1 higher than in the control. Those trends were even stronger after 6 years of treatment. There were no decreases in the uptake of P, K, Ca or Mg (but for B) after 3 or 6 years of NS-treatment. Needle macro nutrient concentrations in relation to N decreased for several nutrients due to dilution effects. As result of the NS treatment pH increased markedly in the litter layer, and less, but significantly, in the humus layer. A decrease in pH value by about 0.3 units was found in the rest of the soil profile down to 50 cm. Dry mass of needle litter fall and litter layer both increased as a result of 6 years of NS-treatment. After three years of treatment 77–80% of all living fine roots in both control and NS treatment were found in the humus layer and the upper 10 cm of the mineral soil. The amount of living fine roots in the humus layer of NS-treated trees decreased to about one third of the control, and the amount of dead fine roots increased by 150% compared with untreated trees after 6 years of treatment. It is argued that the decreased amount of living and increased amount of dead fine roots not necessarily are indications of decreased root vitality. It can also be explained by increased root turnover rate and decreased decomposition rates of N rich new and old fine root litter. No inorganic N was leached from the control plots whereas the NS treated plots started to leach NO₃ the second year of treatment. During 1989–1993 a total of 44 kg NO₃-N and 30 kg NH₄-N per ha was lost from the system which means that 88% of the N supplied was retained by the ecosystem. At first SO₄ was adsorbed in the soil, but after five years of treatment the output was almost equal to the input.     

C-NMR analysis of decomposing litter and fine roots in the semi-arid Mulga Lands of southern Queensland

Plant litter and fine roots are important carbon (C) inputs to soil and a direct source of CO₂ to the atmosphere. Solid-state carbon-13 nuclear magnetic resonance (¹³C-NMR) spectroscopy was used to investigate the nature of C changes during decomposition of plant litter and fine roots of mulga (Acacia aneura F. Muell. Ex. Benth.), wheat (Triticum aestivum L.), lucerne (Medicago sativa) and buffel grass (Cenchrus ciliaris) over an 18-month period. Alkyl C was closely associated with total N concentrations in all litter materials during decay and as alkyl C increased so did total N, indicating an increase in refractory biomacromolecules. Mulga phyllodes had the greatest alkyl C concentration of all litter and fine root materials, and also exhibited the NMR peaks assigned to tannins that may slow or hinder decomposition rates and nitrification. Mulga litter and fine roots decomposed slower than all other litter materials and the soil under mulga had the highest soil C concentration, indicating slower CO₂ release. The alkyl C-to-O-alkyl C ratio is generally used as an index of the extent of decomposition, but is not useful for the decay of woody components. Of all the NMR ratios studied that may indicate the extent of decomposition, the carbohydrate C-to-methoxyl C ratio proved to have the strongest and most consistent relationship with decay time, fraction of mass remaining and total C, even though increases in alkyl C were observed with decreases in carbohydrate C.     

Non-additive effects vary with the number of component residues and their mixing proportions during residue mixture decomposition: A microcosm study

Poplar leaf litter and crop residues (leaves and stems) of two main crops (soybean and maize) collected from semiarid agroforestry systems of Northeast China were used in our microcosm study. The aims were to examine whether non-additive effects (synergistic or antagonistic) between poplar leaf litter and crop residues exist during decomposition and to identify the influence of residue mixing proportion on the incidence of non-additive effects of residue mixture for the same plant residues. We determined residue decomposition rate by measuring mass loss and N release. Synergistic effects between poplar leaf litter and crop residues were more common than additive effects in terms of mass loss and N release. Moreover, the interactive effects between tree leaf litter and crop residues on decomposition varied with the number of component residues and their mixing proportion. Three-residue mixtures produced synergistic effects on mass loss and N release, although two-residue mixtures showed an additive effect in some cases. In addition, as compared with equal proportion, mixing residues with unequal proportion increased the incidence of non-additive effects during decomposition of residue mixture. These findings highlight that residue decomposition dynamics in ecosystems should be assessed on the basis of plant residue mixtures and their mixing proportions, which may help us better understand nutrient dynamics and guide our decisions on nutrient management.     

Plant litter quality influences the contribution of soil fauna to litter decomposition in humid tropical forests, southwestern China

The aim of this field experiment was to quantify the contribution of soil fauna to plant litter decomposition in three forest sites differing in C/N ratio under natural conditions in Xishuangbanna, southwestern China. We conducted a survey of soil fauna communities, the forest floor litter and investigated mass loss of mixed tree species leaf litter for two years in a tropical secondary forest, an evergreen broad-leaf forest and a tropical rain forest. Exclusion treatments of different sized soil fauna from the leaf litter by using varying mesh size litter bags (2 mm and 0.15 mm) were also performed. Mass loss and C and N concentrations in litter bag leaf materials were determined at monthly intervals. We found that: (1) the three forests differed in floor litter biomass and nutrient contents but not in soil fauna richness and abundance; (2) litter mass loss and decomposition rate were slower when soil macrofauna and most of mesofauna were excluded; and (3) greatest soil fauna contribution to plant litter decomposition occurred in the rain forest, where leaf litter C/N ratio was also highest (41.5% contribution: 54.8 C/N ratio), in comparison to 8.69% in the broad-leaf forest and 19.52% in the secondary forest, both with low leaf litter C/N ratios (<32). Our results suggested that, soil fauna played a more pronounced role in the decomposition of mixed leaf litter in tropical rain forest, and significantly bigger effects from fauna were ascribed to the enhancement of N concentration and decrease of C concentration of the initially high C/N ratio litter in this forest site.     

Scots pine litter decomposition along drainage succession and soil nutrient gradients in peatland forests, and the effects of inter-annual weather variation

Peatlands form a large carbon (C) pool but their C sink is labile and susceptible to changes in climate and land-use. Some pristine peatlands are forested, and others have the potential: the amount of arboreal vegetation is likely to increase if soil water levels are lowered as a consequence of climate change. On those sites tree litter dynamics may be crucial for the C balance. We studied the decomposition of Scots pine (Pinus sylvestris L.) needle and root litter in boreal peatland sites representing gradients in drainage succession (succession following water level drawdown caused by forest drainage) and soil nutrient level during several years of varying weather conditions. Neither gradient had an unambiguous effect on litter mass loss. Mass loss over 2 years was faster in undrained versus drained sites for both needle litter, incubated in the moss layer, and fine root litter, incubated in 0-10 cm peat layer, suggesting moisture stress in the surface layers of the drained sites limited decomposition. Differences among the drained sites were not consistent. Among years, mass loss correlated positively with precipitation variables, and mostly negatively or not at all with temperature sum. We concluded that a long-term water level drawdown in peatlands does not necessarily enhance decay of fresh organic matter. Instead, the drained site may turn into a ‘large hummock-system’ where several factors, including litter quality, relative moisture deficiency, higher acidity, lower substrate temperature, and in deeper layers also oxygen deficiency, may interact to constrain organic matter decomposition. Further, the decomposition rates may not vary systematically among sites of different soil nutrient levels following water level drawdown. Our results emphasize the importance of annual weather variations on decomposition rates, and demonstrate that single-period incubation studies incorporate an indeterminable amount of temporal variation.     

Tree roots in canopy soils of old European beech trees—An ecological reassessment of a forgotten phenomenon

The formation of adventitious roots in humus accumulations in tree canopies is widely acknowledged from tropical and temperate rainforests, while the occurrence of those canopy roots in temperate tree species under mesic climates has been largely disregarded for ca. 100 years. Moreover, almost nothing is yet known of the ecological growth conditions or the structure or morphology of such canopy root systems. This study reports on the occurrence of tree fine roots in crown humus pockets of old European beech (Fagus sylvatica L.) trees. The aim was to compare these canopy roots with the fine roots in the terrestrial organic layer soil in terms of fine root biomass density, root morphological traits, ectomycorrhizal colonisation and chemical composition of the root tissue, and to relate these root traits to the chemical properties of the respective soils. Fine root biomass density in crown humus pockets was ca. 7 times higher than in the terrestrial organic layer, even though soil chemical properties of both rooting media were similar. Fine roots in the canopy differed from terrestrial fine roots by lower specific root tip abundance, specific root length, and specific root surface area, all of which points to a longer lifespan of the fine roots in the canopy. Moreover, canopy roots revealed a lower percentage of root tips colonised by ectomycorrhizal fungi than terrestrial roots (87% vs. 93%). Chemical composition of the root tissue in canopy and terrestrial soils was similar for most elements, but canopy roots showed lower P, Fe, and Al concentrations and a higher N/P ratio than terrestrial roots. Root P concentrations of both canopy and terrestrial fine roots were closely related to soil P concentration, but not to soil C/P or N/P ratios. On the other hand, tissue N of canopy roots, but not of terrestrial roots, revealed a clear dependence on soil N and C/N values, suggesting a more limited N availability in the canopy soil compared to the terrestrial organic layer. However, the overall small differences in soil chemical properties between canopy and terrestrial organic layer soil cannot explain the markedly higher volumetric root density in the crown humus and the differences in ecomorphological traits between canopy and terrestrial soil. Instead, it is speculated that these differences are more likely a result of temporarily high water availability in crown humus pockets due to high water flow along the surface of branches to the central crown parts of the beech trees.     

Nitrogen transfer between high- and low-quality leaves on a nutrient-poor Oxisol determined by N enrichment

It has been proposed that the C/N ratio, or quality, of litter or mulch mixtures affects N release. Although total N release from these mixtures and the effects on soil N are relatively well understood, a mechanistic understanding of the interactions between litter species with respect to their N release is still lacking. This study examines decomposition and N dynamics in mixtures of high-quality leguminous mulch, gliricidia [Gliricidia sepium (Jacq.) Kunth. ex Walp.] with a C/N ratio of 13, and low-quality cupuaçu [Theobroma grandiflorum (Wild. ex Spring) Schumann] litter with a C/N ratio of 42, which occur in combination in agroforestry systems. Ratios of 100:0, 80:20, 50:50, 20:80, 0:100 of fresh ¹⁵N-enriched gliricidia leaves and senescent cupuaçu leaves, totaling the same dry weight of 6.64 t ha⁻¹, were applied to an Oxisol and sampled at 6, 14, 38, and 96 days after application. After more than 40% of the N in the gliricidia leaves had been released and the microbial biomass N reached its peak, a significant increase in available soil N occurred at day 14, which was more pronounced with greater amounts of gliricidia in the leaf mixture. However, relative to the N applied in the leaf mixture, there was no significant difference in available soil N with greater proportions of gliricidia. Total N release from the mixtures corresponded to the total N applied by gliricidia. Until day 38, cupuaçu C mineralization was significantly faster in the presence of the highest proportion of gliricidia compared to lower proportions. This faster C mineralization of more than 0.5% per day, however, did not increase total C loss or N release from cupuaçu leaves after 96 days. The use of ¹⁵N tracers identified an N transfer from gliricidia leaves and the soil to cupuaçu leaves and consequently, a lower N release from gliricidia to the soil in the presence of cupuaçu leaves. Though we expected that available N in the soil would also decrease with greater amounts of cupuaçu litter in the mixture, our results indicated an additive effect of the two species on N release and soil mineral N, with gross interactions between them canceling net interactive effects. Therefore, N release of leaf mixtures behaved as predicted from a calculated sum of individual release patterns, in spite of a transfer of N from the high- to the low-quality leaves.     

Leaf litterfall and decomposition of different above- and belowground parts of birch (Betula ermanii) trees and dwarf bamboo (Sasa kurilensis) shrubs in a young secondary forest in Northern Japan

In many Japanese forests, the forest understory is largely dominated by dwarf bamboo (Sasa) species, which compete with overstory vegetation for soil nutrients. We studied the rate of leaf litterfall, and decomposition and mineralization of carbon (C) and nitrogen (N) from various components (leaf, root, wood, and rhizome) of overstory and understory vegetation in a young Betula ermanii forest from 2002 to 2004. Total litterfall was 377 g m⁻² year⁻¹, of which the overstory vegetation contributed about two thirds. A litter decomposition experiment conducted for 770 days indicated that mass loss of different litter components varied significantly, except for Sasa kurilensis wood and rhizome. Relative decomposition rates were significantly greater in the first growth period (June to October) than the dormant period (November to May) in most cases. Rainfall was the most important abiotic variable, explaining 75–80% of the variability in mass loss rates. Concentrations of ethanol soluble substances and N were significantly positively correlated (r=0.77 to 0.97, P<0.05) with mass loss at an early stage (41 days). The ratios of lignin/N and C/N were found to be negatively correlated with mass loss rates at all stages of litter decomposition. C stock loss was similar to that of mass loss, whereas N stock loss was slower, except for S. kurilensis fine root litter. The evergreen understory species S. kurilensis exhibited greater N use efficiency than B. ermanii, suggesting better competitive ability that might favor the production of a high biomass and invasion under tree species like B. ermanii.     

Decomposition and substrate quality of leaf litters and fine roots from three exotic plantations and a native forest in the southwestern highlands of Ethiopia

Substrate quality and decomposition (measured as CO₂ release in laboratory microcosms) of fresh leaf litter and fine roots of Cupressus lusitanica, Pinus patula, Eucalyptus grandis and native forest trees were studied. Changes in litter chemistry in each forest stand were analysed by comparing fresh leaf litter (collected from trees) and decomposed litter from the forest floor. Elemental concentrations, proximate fractions including monomeric sugars, and cross polarisation magic-angle spinning (CPMAS) ¹³C NMR spectra were analysed in leaf litters, decomposed litter and fine roots. Leaf litters and fine roots varied in their initial substrate chemistry with Ca concentration in leaf litters being higher than that in fine roots. In each stand, fine roots had a higher acid unhydrolysable residue (AUR) (except for the Pinus stand), higher holocellulose concentration and lower concentration of water-soluble extractives (WSE) and dichloromethane extractives (NPE) than fresh leaf litter. Likewise, ¹³C NMR spectra of fine roots showed lower alkyl and carboxyl C, and higher phenolic (except P. patula), aromatic and O-alkyl C proportions than leaf litters. Compared with fresh leaf litter, decomposed litter had lower concentrations of potassium, holocellulose, WSE, NPE, arabinose and galactose, similar or higher concentrations of Mg, Ca, S and P, and higher concentrations of N and AUR. CPMAS ¹³C NMR spectra of decomposed litter showed a higher relative increase in signal intensity due to methoxyl C, aromatic C, phenolic C and carboxylic C compared with alkyl C. In a microcosm decomposition study, the proportion of initial C remaining in leaf litter and fine roots significantly fitted an exponential regression model. The decomposition constants (k) ranged between 0.0013 and 0.0030 d⁻¹ for leaf litters and 0.0010-0.0017 d⁻¹ for fine roots. In leaf litters there was a positive correlation between the k value and the initial Ca concentration, and in fine roots there was an analogous positive correlation with initial WSE. Leaf litters decomposed in the order Cupressus>native forest>Eucalyptus∼Pinus, and fine roots in the order Pinus>native forest>Cupressus∼Eucalyptus. In each stand the fine root decomposition was significantly lower than the leaf litter decomposition, except for the P. patula stand where the order was reversed.     

Rhododendron thickets alter N cycling and soil extracellular enzyme activities in southern Appalachian hardwood forests

Rhododendron maximum L., a spreading understory shrub, inhibits overstory regeneration and alters forest community structure in southern Appalachian hardwood forests. Using paired plots and reciprocal litter transplants in forests with and without R. maximum cover, we examined the influence of R. maximum on litter mass and quality, N cycling and soil extracellular enzymes. Standing stocks of soil organic matter, soil N, leaf litter mass and fine root biomass were greater in forests with R. maximum than those without. Tannin extracts from R. maximum foliage, and leaf litter and fine roots collected under R. maximum had a relatively high capacity to precipitate protein compared to extracts from trees. Across the growing season, soil inorganic N availability was generally lower under R. maximum, mostly due to reduced NO₃⁻ availability. Our data suggest that R. maximum litter alters N cycling through the formation of recalcitrant polyphenol–organic N complexes. Soil extracellular enzymes indicate the potential processing rates of organic substrates. Between forest types, polyphenol oxidase activity was greatest in R. maximum O horizons, regardless of litter type, suggesting that the local microbial community can better degrade and access protein–tannin-complexed N. Protease activity did not differ between forest types, but was greater on R. maximum leaf litter than hardwood leaf litter. The alteration of the N cycle via the formation of polyphenol–organic N complexes may contribute to hardwood seedling suppression, while the enzymatic release of these complexes by ericoid mycorrhizal fungi may increase N acquisition for R. maximum and contribute to its expansion in southern Appalachian forests.     

Early-stage decomposition of maize litter at different positions in a semi-arid cropland

ABSTRACT

Litter decomposition plays a crucial role in controlling carbon (C) cycling and nutrient turnover in agroecosystems. In this study, the litterbag method was used to investigate the mass loss and nitrogen (N) dynamics of maize litters (culms, leaves and sheaths) at aerial, surficial and belowground positions in the initial 191 d of decomposition. For any tissue, the decomposition rates in the air and on the soil surface were similar, but both were less than the decomposition rates below the ground. The sheaths always decomposed at a lower rate than the other two tissues at any position. During decomposition, the N concentrations for all tissues decreased at both the aerial and the surficial positions but increased for belowground leaves and sheaths in the last months. For the N amount, these three tissues generally exhibited a net N release during the experiment irrespective of the position. Overall, position plays a crucial role in controlling early-stage litter decomposition in croplands, and this role will be modified by litter quality. Therefore, further studies on litter decomposition should fully consider the litter position to comprehensively evaluate the biogeochemical cycles in agroecosystems.     

Amounts of carbon mineralised and leached as DOC during decomposition of Norway spruce needles and fine roots

Changes in climate or forest management practices leading to increased litter production will most likely cause increased leaching rates of dissolved organic carbon (DOC) from the O horizon. The rhizosphere is often assumed to have a large carbon flux associated with root turnover and exudation. However, little has been done to quantify the amount of DOC originating from root litter. We studied decomposition of fine root and needle litter of Norway spruce (Picea abies) through a combined incubation and leaching experiment in the laboratory using five different litter types: fresh needle litter, aged needles from the litter layer, fresh and dead roots from mineral soil samples, and seven-year-old roots from a previous litterbag study. After respiration measurements, the samples were percolated with artificial throughfall water and DOC and UV absorbance were measured in the leachate. Mineralisation of dissolved organic matter in the leachate and sorption of DOC to ferrihydrite were determined as a measure of DOC ability to be stabilised by iron (hydr)oxide surfaces.The mineralisation rate and DOC production rate of root samples were always lower than that of needle samples. However, root and needle derived dissolved organic matter (DOM) were similar in terms of aromaticity, as indicated by their specific UV absorbance, and ability to be sorbed by ferrihydrite. For seven-year-old roots, a significantly higher fraction of carbon was lost as DOC (30%) than for younger roots (20%). Furthermore, DOM from old roots bound more strongly to ferrihydrite and is mineralised at a lower rate than DOC from younger roots, suggesting that roots at late stages of decomposition, although a small fraction of total litter, significantly contribute to carbon build-up in mineral soils. The slower decomposition rate of roots compared with needles must be taken into account when modelling litter decomposition.     

Mass loss and nutrient release during litter decay in peatland: The role of microbial adaptability to litter chemistry

In peatlands the reduced decomposition rate of plant litter is the fundamental mechanism making these peat-accumulating ecosystems effective carbon sinks. A better knowledge of litter decomposition and nutrient cycling is thus crucial to improve our predictions of the effects of anthropogenic perturbation on the capacity of peatlands to continue to behave as carbon sinks. We investigated patterns of plant litter decomposition and nutrient release along a minerotrophic-ombrotrophic gradient in a bog on the south-eastern Alps of Italy. We determined mass loss as well as P, N, K, and C release of seven vascular plant species and four moss species after 1 year in both native and transplanted habitats. Hence, differences in litter decay were supposed to reflect the degree of adaptability of microbial communities to litter quality. Polyphenols/nutrient and C/nutrient quotients appeared as the main parameters accounting for decomposition rates of Sphagnum litter. In particular, litter of minerotrophic Sphagnum species decomposed always faster than litter of ombrotrophic Sphagnum species, both in native and transplanted habitats. Decomposition rates of vascular plant litter in native habitats were always higher than the corresponding mass loss rates of Sphagnum litter. Minerotrophic forbs showed the fastest decomposition both in native and transplanted habitats in accordance with low C/P and C/N litter quotients. On the other hand, C/P quotient seems to play a primary role also in controlling decomposition of graminoids. Decomposition of deciduous and evergreen shrubs was negatively related to their high lignin content. Nitrogen release from Sphagnum litter was primarily controlled by C/N quotient, so that minerotrophic Sphagnum litter released more N than ombrotrophic Sphagnum litter. Overall, we observed slower N release from litter of ombrotrophic vascular plant species compared to minerotrophic vascular plant species. No single chemical parameter could predict the variability associated with different functional groups. The release of K was very high compared to all the other nutrients and rather similar between ombrotrophic and minerotrophic litter types. In Sphagnum litter, a higher C/P quotient was associated with a slower P mineralisation, whereas a faster P release from vascular plant litter seems primarily associated with lower C/P and polyphenols/P quotients.     

Decomposition of fine roots of Pinus kesiya and turnover of organic matter, N and P of coarse and fine pine roots and herbaceous roots and rhizomes in subtropical pine forest stands of different ages

Organic matter accumulation, N and P concentrations of fine (<2 mm diameter) and coarse (2-10 mm) roots of Pinus kesiya and fine roots and rhizomes of ground vegetation, and decomposition of P. kesiya fine roots (<2 mm diameter) were studied in 6-, 15- and 23-year-old P. kesiya forest stands at Shillong, the capital of Meghalaya, India. The mean annual dry weight of P. kesiya fine roots did not vary significantly between the stands, but the coarse root mass increased significantly from the 6- to 23-year-old stand. However, herbaceous fine roots and rhizomes showed a reverse trend. Live roots (biomass) showed a higher N and P concentration than the necromass (dead root mass). Nutrient concentrations were greater in the fine roots compared to coarse roots. N and P accumulation was maximum in the 6-year-old stand and minimum in the 15-year-old stand. P. kesiya fine roots decomposed in a three-phased manner in all the stands. The first phase, lasting about 30 days, was characterised by a slow rate of weight loss. This was followed by a rapid phase of weight loss up to 90 days, with an average weight loss of 7.7 mg day^-1, and the third phase showed a slow decay pattern (1.2 mg day^-1). The weight loss pattern showed a strong seasonal trend; a faster rate of decay in the warm-humid period and a slow rate of decay in the dry-cold period. Nitrogen and P concentration in the decomposing root litter showed a marked decrease and/or increase during decomposition. The study reveals that in the 6-year-old pine stand the roots of herbaceous plants play a more significant role in maintaining the organic matter, N and P status of the soil, while in the older stands pine roots assumed greater significance.     

Accumulation and solubility of metals during leaf litter decomposition in non-polluted and polluted soil

The decomposition of alder ( Alnus glutinosa ) and poplar ( Populus tremula ) leaf litter placed in direct contact with non-polluted and metal-polluted soil was investigated over 25 months in a controlled model-ecosystem experiment using the litterbag method. In addition to mass loss, we monitored the total and soluble concentrations of carbon, Cu, Zn, Cd and Pb. Leaves from trees grown on polluted soil had larger initial Zn, Cd and dissolved organic carbon concentrations. Neither the origin of the leaves (from trees grown on non-polluted or polluted soil) nor the placement of the leaves in polluted or unpolluted soil affected the decomposition process. Total metal contents increased in leaves placed on polluted soil over time. The solubility of metals in the leaf litter decreased over time, indicating that leaves acted as a temporary pool for metals from the soil in direct contact with the leaves. The sorbed metals were strongly bound in the litter even after two years of decomposition. The strong binding and thus reduced bioavailability of the metals provides an explanation for why they had no observable effects on litter decomposition.     

Site of leaf origin affects how mixed litter decomposes

Recent studies have demonstrated that mass loss, nutrient dynamics, and decomposer associations in leaf litter from a given plant species can differ when leaves of that species decay alone compared to when they decay mixed with other species’ leaves. Results of litter-mix experiments have been variable, however, making predictions of decomposition in mixtures difficult. It is not known, for example, whether interactions among litter types in litter mixes are similar across sites, even for litter mixtures containing the same plant species. To address this issue, we used reciprocal transplants of litter in compartmentalized litterbags to study decomposition of equal-mass litter mixtures of sugar maple (Acer saccharum Marshall) and red oak (Quercus rubra L.) at four forest sites in northwestern Connecticut. These species differ significantly in litter quality. Red oak always has higher lignin concentrations than maple, and here C:N is lower in oak leaves and litter, a pattern often observed when oak coexists with maple. Overall, we observed less mass loss and lower N accumulation in sugar maple and red oak litter mixtures than we predicted from observed dynamics in single-species litterbags. Whether these differences were significant or not depended on the site of origin of the leaves (P<0.02), but there was no significant interaction between sites of decay and the differences in observed and predicted decomposition (P>0.2) . Mixing of leaf litter types could have significant impacts on nutrient cycling in forests, but the extent of the impacts can vary among sites and depends on the origin of mixed leaves even when the species composition of mixes is constant.     

A microcosm study on the respiration and weight loss in birch litter and raw humus as influenced by soil fauna

Summary The effect of diverse soil fauna (Collembola, Acari, Enchytraeidae, Nematoda) on decomposition of dead organic matter was studied in microcosms containing (1) birch leaf litter, (2) raw humus of coniferous forest and (3) litter on humus. Total respiration (CO₂ evolution) was monitored weekly, and mass loss, length of fungal hyphae (total and metabolically active) and survival of animal populations were checked at the end of weeks 12 and 21–22 from the start of experiment. Animal populations established themselves well during the incubation. At the end of the experiment some replicates containing litter had microarthropod densities of up to 500 specimens per microcosm, corresponding to a field population of 200 000 m^–2. The soil animals had a positive influence on total respiration in all substrates. By the end of experiment 32.0%, 22.6% and 14.6% more CO₂ had evolved in the presence of animals in litter, litter + humus and humus alone, respectively. There was clear trend towards a higher mass loss in the presence of animals, though it was significant in litter only. Our results showed that a diverse soil animal community enhances the activity of soil microbes, and may thereby accelerate decomposition in raw coniferous forest soil.