Root Litter Decomposition Research Articles

Succession of soil microarthropod communities during the aboveground and belowground litter decomposition processes

The process of litter decomposition is driven by interactions among climate, litter quality, and decomposers. However, information about the soil animal community involved in fine-root litter decomposition remains limited. We compared the composition of the soil microarthropods involved in leaf and root decomposition in field experiments using litterbags. To evaluate the relative effects of litter type and initial litter position, we set up a two-factor experiment (litter type × litter position). Litterbags containing either roots or leaves were placed at two positions (either on the soil surface or buried within the soil) and were collected to follow the succession of microarthropods in the decomposing litter for three years. We found different successional patterns of soil microarthropods between the natural processes of leaf and root litter decomposition (i.e. leaves on the soil surface and roots buried within the soil), which were caused by taxonomy-specific responses to both litter quality and litter position. Prostigmata were clearly affected by the stage of litter decomposition; they were initial colonisers of decomposition in all litterbag treatments. The abundances of other taxa were more determined by litter position; however, Oribatida showed a preference for later stages of decomposition, while Collembola and Mesostigmata were strongly determined by water content related to litter position. Although litter quality was not the primary factor controlling their distribution, the ratio of Oribatida to Collembola gradually increased during the decomposition process in the belowground litterbags. Our results indicate that Oribatida are primarily involved in root litter decomposition process, particularly in the late stages of decomposition under natural conditions.

Decomposition rates of fine roots from three herbaceous perennial species: combined effect of root mixture composition and living plant community

Aims In most ecosystems, plant roots from different species decompose in mixtures and in the presence of living roots; however much root decomposition research has focused on how roots of individual species or artificial mixtures decompose in the absence of living plants. We thus examined two poorly studied components of root litter decomposition: 1) whether decomposition of root mixtures can be predicted from the sum of the decomposition rates of each component species and 2) how living plants influence rates of root decomposition.

Molecular fate of root and shoot litter on incorporation and decomposition in earthworm casts

Roots and shoots have contrasting molecular composition and decomposition rate in soils and the mechanisms regulating these rates are still debated. Earthworms have a strong influence on litter decomposition and their feces (casts) are complex and dynamic organo-mineral structures. This study aimed at monitoring the incorporation and decomposition of root and shoot litter in earthworm casts at the molecular scale. Casts were collected from a mesocosm experiment, 2, 4, 8, 24 and 54weeks after the addition of root or shoot litter to the soil surface. Molecular characterization was achieved for litter and casts using pyrolysis gas chromatography-mass spectrometry after in situ tetramethylammonium hydroxide derivatization (TMAH-Py-GC-MS). To maximize understanding of the processes occurring in casts, the study used principal components analysis and specific molecular dynamics monitoring. The fate of root litter in casts was reflected principally in aromatic compound dynamics, while aliphatic compound evolution enabled monitoring of shoot litter fate in casts. Earthworms rapidly incorporated both roots and shoots into casts, resulting in a phase dominated by litter incorporation up to two months of the experiment. After two months, the decomposition of shoot and root (to a lesser extent) litter incorporated into casts was the dominant process. Two pools of lignin-derived compounds were identified, one originating from undecomposed litter (mainly non-oxidized) and one resulting from litter decomposition (more oxidized). Moreover, the significant contribution of aliphatic compounds, such as ω-hydroxyalkanoic and n-alkanedioic acids, by the end of the experiment and in control samples suggested that compounds with a greater degree of oxidation could be preferentially preserved in earthworms casts on a longer term.

How do microbial communities in top- and subsoil respond to root litter addition under field conditions?

Contrasting microbial community composition and activity at different soil depths may affect root litter decomposition. These effects have up to now been investigated mainly in laboratory studies, which may not be able to take into account complex in situ conditions. Our study aimed to analyze the composition and activity of microbial communities after addition of 13C labeled wheat root litter to a loamy soil under grassland at 30, 60 and 90 cm depths, during a three-year field experiment. We investigated the dynamics of bacterial and fungal abundances and community structures by DNA genotyping and pyrosequencing of 16S and 18S rDNAs. The genetic structures of bacterial and fungal communities were evaluated by automated ribosomal intergenetic spacer analysis. The functions of these communities were analysed by determination of extracellular enzyme activities and viable microbial communities involved in 13C labeled organic matter decomposition studied by 13C PLFAs.The abundance of fungal and bacterial communities (16S and 18S rDNAs and PLFA) and the potential activities of enzymes involved in the C- and N-cycles were significantly higher at the top 30 cm compared with deeper soil throughout the experiment. Both were stimulated by fresh litter input. A trend to decreasing bacterial and fungal richness was noted after root litter addition at 30 cm, while richness of bacteria at 90 cm and those of fungi at 60 and 90 cm increased. Moreover, root litter addition caused a reduction of the Shannon Weaver Diversity index and a shift in microbial community structure at all three depths, which was more pronounced for bacteria at 30 and 60 cm and for fungi at 90 cm. The changes during litter degradation resulted in similar dynamics of most enzyme activities at all depths. Chitinase activity was enhanced after 29 months compared to initial conditions indicating the availability of high amounts of microbial detritus. The degrading microbial community as assessed by 13C PLFA showed similar temporal dynamics at all three depths. Fungal contribution to this community decreased during later stages of litter degradation, while the contribution of Gram+ bacteria increased. We conclude that litter addition led to convergence of microbial communities of top- and subsoil through stimulation of copiotrophic populations. Soil microbial community structures are thus connected with the amount of fresh litter input. Enzyme activities and 13C PLFA reflect to some extent the changes occurring during degradation, i.e. exhaustion of fresh plant material and accumulation of detritus.

Fire affects root decomposition, soil food web structure, and carbon flow in tallgrass prairie

Abstract. Root litter decomposition is a major component of carbon (C) cycling in grasslands, where it provides energy and nutrients for soil microbes and fauna. This is especially important in grasslands where fire is common and removes aboveground litter accumulation. In this study, we investigated whether fire affects root decomposition and C flow through the belowground food web. In a greenhouse experiment, we applied 13C-enriched big bluestem (Andropogon gerardii) root litter to intact tallgrass prairie soil cores collected from annually burned (AB) and infrequently burned (IB) treatments at the Konza Prairie Long Term Ecological Research (LTER) site. Incorporation of 13C into microbial phospholipid fatty acids and nematode trophic groups was measured on six occasions during a 180-day decomposition study to determine how C was translocated through the soil food web. Results showed significantly different soil communities between treatments and higher microbial abundance for IB. Root decomposition occurred rapidly and was significantly greater for AB. Microbes and their nematode consumers immediately assimilated root litter C in both treatments. Root litter C was preferentially incorporated in a few groups of microbes and nematodes, but depended on burn treatment: fungi, Gram-negative bacteria, Gram-positive bacteria, and fungivore nematodes for AB and only omnivore nematodes for IB. The overall microbial pool of root-litter-derived C significantly increased over time but was not significantly different between burn treatments. The nematode pool of root-litter-derived C also significantly increased over time, and was significantly higher for the AB treatment at 35 and 90 days after litter addition. In conclusion, the C flow from root litter to microbes to nematodes is not only measurable but also significant, indicating that higher nematode trophic levels are critical components of C flow during root decomposition, which, in turn, is significantly affected by fire. Not only does fire affect the soil community and root decomposition, but the lower microbial abundance, greater root turnover, and the increased incorporation of root litter C by microbes and nematodes for AB suggests that annual burning increases root-litter-derived C flow through the soil food web of the tallgrass prairie.

Disentangling the Litter Quality and Soil Microbial Contribution to Leaf and Fine Root Litter Decomposition Responses to Reduced Rainfall

Climate change-induced rainfall reductions in Mediterranean forests negatively affect the decomposition of plant litter through decreased soil moisture. However, the indirect effects of reduced precipitation on litter decomposition through changes in litter quality and soil microbial communities are poorly studied. This is especially the case for fine root litter, which contributes importantly to forests plant biomass. Here we analyzed the effects of long-term (11 years) rainfall exclusion (29% reduction) on leaf and fine root litter quality, soil microbial biomass, and microbial community-level physiological profiles in a Mediterranean holm oak forest. Additionally, we reciprocally transplanted soils and litter among the control and reduced rainfall treatments in the laboratory, and analyzed litter decomposition and its responses to a simulated extreme drought event. The decreased soil microbial biomass and altered physiological profiles with reduced rainfall promoted lower fine root—but not leaf—litter decomposition. Both leaf and root litter, from the reduced rainfall treatment, decomposed faster than those from the control treatment. The impact of the extreme drought event on fine root litter decomposition was higher in soils from the control treatment compared to soils subjected to long-term rainfall exclusion. Our results suggest contrasting mechanisms driving drought indirect effects on above-(for example, changes in litter quality) and belowground (for example, shifts in soil microbial community) litter decomposition, even within a single tree species. Quantifying the contribution of these mechanisms relative to the direct soil moisture-effect is critical for an accurate integration of litter decomposition into ecosystem carbon dynamics in Mediterranean forests under climate change.

Plant species control and soil faunal involvement in the processes of above‐ and below‐ground litter decomposition

Among the factors determining litter decomposition rates, the role of soil fauna as decomposers still remains unclear, especially for how they are involved in decomposing below‐ground root litter compared to their relatively‐known contributions to decomposing above‐ground leaf litter. We conducted a litterbag experiment using two sizes of meshes and pursued the leaf and root decomposition of six major tree species in a Japanese temperate forest over 411‐days to test the interactive effects of soil mesofauna and litter quality addressed based on two features (litter types and species) on the process. Moreover, given a possible correlation between litter traits of the leaves and roots, we examined whether soil mesofauna alters the relationship between leaf and root decomposition across species. We found that the effects of plant species identity was stronger than that of soil mesofauna for determining the litter mass loss rate and the microbial respiration rate in both above‐ground and below‐ground decomposition. In addition, we found a significant positive correlation between leaf and root litter decomposition processes, regardless of the involvement soil mesofauna. On the other hand, the presence of soil mesofauna increased microbial respiration rates in the early stage of leaf decomposition; however, soil mesofauna did not affect root microbial respiration rates during the experiment. Such differential involvement of mesofauna in the leaf and root litter decomposition may drive the general patterns of faster and slower decomposition of plant leaves and roots in the soil, respectively.

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.

Size-dependent morphological and chemical property of fine root litter decomposition

To estimate cause-and-effect relationships of decomposition rates of fine root litter up to 2 mm in diameter, we explored the relationships between mass loss rates and substrate litter properties with respect to chemical and morphological dynamics. Mass loss, nitrogen (N) concentration, specific root area (SRA), root tissue density (RTD), and their remaining proportions were measured for initial and residual fine roots of two diameter classes (<0.5 and 0.5–2 mm) of Quercus serrata and Ilex pedunculosa in a temperate forest. Litterbags were sequentially collected after 1 month of decomposition and then every 3 months for 27 months. N concentration dynamics during decomposition showed a significant interaction between species and diameter, and there was a greater convergence between diameter classes for Q. serrata than for I. pedunculosa. The remaining area and volume of the two diameters changed during decomposition in both species, but the degree of change was somewhat different between the species. The remaining surface area and volume in I. pedunculosa roots showed greater differences between diameter classes compared with Q. serrata roots. Remaining mass was positively correlated with the remaining C concentration and surface area and was negatively correlated with the remaining tissue volume and N concentration, according to principal component analysis analysis. Differences in morphological and chemical properties between diameter sizes of two species could indicate differences in decomposition processes. Estimates of fine root decomposition rates are best obtained by a combination of biological and physicochemical species-specific processes.

No depth-dependence of fine root litter decomposition in temperate beech forest soils

Subsoil organic carbon (OC) tends to be older and is presumed to be more stable than topsoil OC, but the reasons for this are not yet resolved. One hypothesis is that decomposition rates decrease with increasing soil depth. We tested whether decomposition rates of beech fine root litter varied with depth for a range of soils using a litterbag experiment in German beech forest plots. In three study regions (Schorfheide-Chorin, Hainich-Dün and Schwäbische-Alb), we buried 432 litterbags containing 0.5 g of standardized beech root material (fine roots with a similar chemical composition collected from 2 year old Fagus sylvatica L. saplings, root diameter < 2 mm) at three different soil depths (5, 20 and 35 cm). The decomposition rates as well as the changes in the carbon (C) and nitrogen (N) concentrations of the decomposing fine root litter were determined at a 6 months interval during a 2 years field experiment. The amount of root litter remaining after 2 years of field incubation differed between the study regions (76 ± 2 % in Schorfheide-Chorin, 85 ± 2 % in Schwäbische-Alb, and 88 ± 2 % in Hainich-Dün) but did not vary with soil depth. Our results indicate that the initial fine root decomposition rates are more influenced by regional scale differences in environmental conditions including climate and soil parent material, than by changes in microbial activities with soil depth. Moreover, they suggest that a similar potential to decompose new resources in the form of root litter exists in both surface and deep soils.

Intercropping affects the rate of decomposition of soil organic matter and root litter

Aims Intercropping increases aboveground and belowground crop productivity, suggesting potential for carbon sequestration. Here we determined whether intercropping affects decomposition of soil organic matter (SOM) and root litter. Methods We measured in the laboratory and the field the breakdown of SOM, root litter of maize, wheat, or faba bean, litter mixtures, and a standard substrate (compost) in soils from a long term intercropping experiment. Results Soil organic matter from intercrop plots decomposed faster than SOM from monocrop plots, but compost decomposed at similar rates in different soils. Faster SOM decomposition was associated with lower soil C:N ratio. Root litter mixtures of maize and wheat decomposed as expected from single litters, but litter mixture of maize and faba bean decomposed faster than expected, both in the laboratory and in the field. Root litter decomposed slowly in maize/wheat intercrop soil compared to the two monocropped soils in the laboratory, but the effect was absent in the field. Conclusions Intercropping increases SOM decomposition, presumably through reduced SOM recalcitrance resulting from lower C:N ratio, higher litter input and better N retention. Depending on the crop combination, also non-additive effects of root litter mixing can enhance organic matter decomposition in intercropping soils.

Temperature sensitivity of microbial respiration of fine root litter in a temperate broad-leaved forest.

The microbial decomposition respiration of plant litter generates a major CO2 efflux from terrestrial ecosystems that plays a critical role in the regulation of carbon cycling on regional and global scales. However, the respiration from root litter decomposition and its sensitivity to temperature changes are unclear in current models of carbon turnover in forest soils. Thus, we examined seasonal changes in the temperature sensitivity and decomposition rates of fine root litter of two diameter classes (0–0.5 and 0.5–2.0 mm) of Quercus serrata and Ilex pedunculosa in a deciduous broad-leaved forest. During the study period, fine root litter of both diameter classes and species decreased approximately exponentially over time. The Q 10 values of microbial respiration rates of root litter for the two classes were 1.59–3.31 and 1.28–6.27 for Q. serrata and 1.36–6.31 and 1.65–5.86 for I. pedunculosa. A significant difference in Q 10 was observed between the diameter classes, indicating that root diameter represents the initial substrate quality, which may determine the magnitude of Q 10 value of microbial respiration. Changes in these Q 10 values were related to seasonal soil temperature patterns; the values were higher in winter than in summer. Moreover, seasonal variations in Q 10 were larger during the 2-year decomposition period than the 1-year period. These results showed that the Q 10 values of fine root litter of 0–0.5 and 0.5–2.0 mm have been shown to increase with lower temperatures and with the higher recalcitrance pool of the decomposed substrate during 2 years of decomposition. Thus, the temperature sensitivity of microbial respiration in root litter showed distinct patterns according to the decay period and season because of the temperature acclimation and adaptation of the microbial decomposer communities in root litter.

Validating tree litter decomposition in the Yasso07 carbon model

Up-to-date and accurate information of ecosystem state and functioning becomes ever more critical for decision-making and policy. For complex ecosystems such as forests, these demands can in some cases not be met by field observations only, especially at larger scales. Additionally, methodological requirements include comparability and transparency. To satisfy these needs, models can provide an important supplement or alternative.We examined the validity of the litter decomposition and soil carbon model Yasso07 in Swiss forests based on data on observed decomposition of (i) foliage and fine root litter from sites along a climatic and altitudinal gradient and (ii) of 588 dead trees from 394 plots of the Swiss National Forest Inventory. Our objectives were to (i) examine the effect of the application of three different published Yasso07 parameter sets on simulated decay rate; (ii) analyze the accuracy of Yasso07 for reproducing observed decomposition of litter and dead wood in Swiss forests; and (iii) evaluate the suitability of Yasso07 for regional and national scale applications in Swiss forests.From the three examined parameter sets, the set was identified which resulted in the best agreement between Yasso07 results and observed decomposition. No significant differences were found between simulated and observed remaining C in foliage and fine root litter after 10 years and in lying dead trees after 14–21 years. The model overestimated the decomposition of standing dead trees. We concluded that Yasso07 can provide accurate information on temporal changes in C stocks in litter and deadwood in Swiss forests in a transparent manner that is valid for, e.g., reporting purposes under the UNFCCC and the Kyoto Protocol.

Decomposition of aboveground and root litter for three desert herbs: mass loss and dynamics of mineral nutrients

Litter decomposition is an important process in terrestrial C and N cycling, but it is still unclear which factors are controlling litter decomposition and nutrient release in arid and semiarid environments. Litterbag experiment was carried out to evaluate the mass loss and nutrient dynamics of aboveground and belowground litter of three desert plants with different life form (ephemeral herbs and perennials). The decomposition rates of Erodium oxyrrhynchum and Eremurus inderiensis (ephemeral herbs) were faster than that of Seriphidium santolinum (perennial) after 2 years. The content of neutral soluble detergent positively correlated with mass loss and was responsible for the faster rates in the primary decomposition phase. Additionally, differences in mass loss and N release between aboveground and belowground litter depended on litter type. Decomposition of the aboveground litter was mainly affected by initial nutrient content and C component of litter, whereas root decomposition was primarily determined by the content of recalcitrant compounds of litter. Only stem generally exhibited N accumulation, whereas there was no relationship between the initial N content and net N immobilization during decomposition of leaf and root litter. Our results suggest that the decomposition rate and nutrient release in temperate desert are closely linked to initial nutrients and C contents of litters, and decomposition of desert litters depended on plant life form.

Response of microbial respiration from fine root litter decomposition to root water content in a temperate broad-leaved forest

Microbial respiration from plant litter decomposition is sensitive to soil water status; however, its response to water status remains ambiguous, particularly in the litter of fine roots. We investigated the effect of fine-root water content on microbial respiration after 468 days of decomposition in forest soil for two diameter classes (0-0.5 and 0.5-2 mm) of Quercus serrata and Ilex pedunculosa in central Japan. Direct measurement of microbial respiration from root litter resulted in a range of 0.015-3.52 nmol CO2 g −1 s −1 . Microbial respiration in both diameter classes and species decreased linearly with decreasing root water content. These changing patterns of microbial respiration did not differ significantly between the diameter classes of either species, indicating that microbial respiration was regulated by the moisture of root litter, and not by characteristics associated with diameter class or species. In contrast, the carbon to nitrogen ratio and mass loss of the root litter differed significantly between diameter classes in both species. These findings suggest that along with chemical and morphological properties of fine root litter, the changes in root water content should also be considered as a viable factor in microbial activity variations. Drying-wetting cycles of fine roots could lead to sensitive responses of microorganisms during the short term, leading to variation in the decomposition rate of fine root litter over the long term. This study provided insight into the potential impact of microbial physiological performance on heterotrophic respiration and fine root decomposition under the varying root water content.

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.

Effects of external and internal nutrient supplies on decomposition of wild rice, Zizania palustris

We examined effects of external supplies of nitrogen (N) and phosphorus (P) from the environment and internal supplies of N and P from within litter tissue on wild rice shoot and root litter decomposition and N and P dynamics. To investigate the effects of external supplies, wild rice shoot and root litterbags were decayed in mesocosms in the field over 115 days with either added N or P or a control in ambient conditions. To investigate the effects of the internal nutrient supply, wild rice plants were grown with added N, P, both N and P, or no supplemental nutrient, to produce enriched litters, which were then decayed for 168 days under controlled temperature in the laboratory. Both external and internal N and P supplies affected shoot litter decay more than decay of root litter. Increased external P supply significantly increased the rate of wild rice shoot decay and P mineralization but adding N had no effect on decay rates through time. Neither adding N nor P influenced root decay. Enrichment of P internally in the litter through fertilization increased the concentration of P (0.16%) and water-soluble compounds (28.7% WS) in shoot litter compared to control shoot litter (0.11% P, 19.8% WS), which likely caused the significant increase in shoot decay rates, particularly in the labile pool. In contrast, N enrichment not only increased plant growth but also increased lignin concentrations (7.5%) compared to control shoot litter (2.7% lignin) for added structural support. This significantly inhibited decay and nearly doubled the amount of mass remaining after 168 days (42.1% OM) when compared to control shoots (22.4% OM). Increased lignin likely overrides a concomitant increase in nitrogen concentration in shoot litter and appears to control wild rice decomposition. Lignin and phosphorus appear to play a key role in driving wild rice decay through the effects on litter quality.

Impact of the plant community composition on labile soil organic carbon, soil microbial activity and community structure in semi-natural grassland ecosystems of different productivity

The main objective was to describe the effects of plant litter on SOC and on soil microbial activity and structure in extensively managed grasslands in Central Germany that vary in biomass production and plant community composition. The decomposition of shoot and root litter was studied in an incubation experiment. Labile C and N were isolated by hot water extraction (CHWE, NHWE), while functional groups of microbes were identified by PLFA analysis and microbial activity was measured using a set of soil exo-enzymes. The plant community composition, particulary legume species affected SOC dynamics and below-ground microbial processes, especially via roots. This was reflected in about 20% lower decomposition of root litter in low productivity grassland soil. The CHWE soil pool was found to be a key driver of the below-ground food web, controlling soil microbial processes. Below-ground responses appear to be related to the presence of legume species, which affected the microbial communities, as well as the ratio between fungal and bacterial biomass and patterns of soil enzyme activity. Low productivity fungal-dominated grasslands with slow C turnover rates may play an important role in SOC accumulation. The approach used here is of particular importance, since associated biological and biochemical processes are fundamental to ecosystem functioning.

Collembola species composition and diversity effects on ecosystem functioning vary with plant functional group identity

The relationship between decomposer diversity and ecosystem functioning is little understood although soils accommodate a significant proportion of worldwide biodiversity. Collembola are among the most abundant and diverse decomposers and are known to modify plant growth. We examined the effects of Collembola species diversity (one, two and three species belonging to different life history groups) and composition on litter decomposition and the performance of plant communities (above- and belowground productivity) of different functional groups (grasses, forbs and legumes). Collembola densities did not increase with diversity indicating niche overlap. Generally, Collembola species composition was a better predictor for ecosystem functioning than Collembola species number with the impacts of Collembola diversity and composition on ecosystem functioning strongly depending on plant functional group identity. Non-linear effects of Collembola diversity on litter decomposition and plant productivity suggest pronounced and context dependent species interactions and feeding habits. Net surface litter decomposition was decreased by Collembola, whereas root litter decomposition was at maximum in the highest Collembola diversity treatment. Forbs benefitted most from the presence of three Collembola species. Similarly, Collembola diversity influenced root depth distribution in a plant functional group specific way: while grass root biomass decreased with increasing Collembola diversity in the upper and lower soil layer, legume root biomass increased particularly in the lower soil layer. Idiosyncratic and context dependent effects of Collembola diversity and composition even in rather simple assemblages of one to three species suggest that changes in Collembola diversity may have unpredictable consequences for ecosystem functioning. The finding that changes in Collembola performance did not directly translate to alterations in ecosystem functioning indicates that response traits do not necessarily conform to effect traits. Distinct plant functional group specific impacts of Collembola diversity on root depth distribution are likely to modify plant competition in complex plant communities and add a novel mechanism how decomposers may affect plant community assembly.

Content and composition of natural organic matter in water of Lake Pitkjärv and mire feeding Kuke River (Estonia)

The seasonal and spatial changes of content and composition of dissolved organic carbon in water flowing out from bog were studied. Water was sampled from the Kuke River flowing out from Koigi Bog (eastern Saaremaa, Estonia) and in comparison the water samples from the bog lake (Lake Pitkjärv) were analyzed regularly during 18 months. Absorptions of water samples were measured at 250, 254, 285, 365 and 436 nm on UV–Vis spectrophotometer and pH, conductivity and concentration of dissolved organic carbon (DOC) were measured. Specific ultraviolet absorptions (SUVA) and the ratios of absorptions were calculated to characterize the nature of dissolved organic carbons. The significant changes of the concentration of DOC were determined in water sampled from the Kuke River during the dry days, but it was much steadier during rest sampling time. Analysis of water from the Lake Pitkjärv showed relatively high content of macromolecular organic compounds rich in aromatics (SUVA254 = 4.58 L mg−1 m−1), whereas water samples from the Kuke River contained predominantly more homogeneous low-molecular-weight materials poor in aromatics (SUVA254 = 2.96 L mg−1 m−1). Calculated values of SUVA285 confirmed that organic carbon in river water can be also originated from the decomposition of root litter. The values of ratio of UVA250/A365 for water samples from Kuke River indicated the fulvic nature of DOC as conformed by the SUVA254 and SUVA285 values. The values of A254/A436 for river were higher than 14 indicating that the organic matter in water from lake and river contained lots of UV absorbing functional groups.