Coniferous Litter Research Articles

Relationships between nitrogen, acid-unhydrolyzable residue, and climate among tree foliar litters

Using literature data, we investigated coniferous and broadleaf litter from 58 tree species using a database encompassing concentrations of N and acid-unhydrolyzable residue (AUR) (gravimetric lignin) in newly shed litter, mean annual temperature, and mean annual precipitation. Our aims were to (i) demonstrate any large-scale relationships between concentrations of N and AUR in foliar litter and (ii) determine differences in this respect among litter from Pinus and Quercus. To this end, we had collected foliar litter data for Asia and Europe, forming a climate gradient. Litter from broadleaf and coniferous trees differed significantly in concentrations of N (p < 0.0001, 9.64 versus 5.50 mg/g, respectively) and AUR (p < 0.0001, 219 versus 292 mg/g, respectively). There were highly significant positive linear relationships between concentrations of N and AUR for broadleaf (p < 0.0001) and coniferous litter (p < 0.0001). There were also significant positive relationships for AUR as a function of N concentration for the genera Pinus and Quercus but not within species. That for Scots pine (Pinus sylvestris L.) was negative and that for common oak (Quercus robur L.) not significant.

Mixtures with grass litter may hasten shrub litter decomposition after shrub encroachment into mountain grasslands

Shrub encroachment in mesic grasslands alters the identity and quality of litters entering the system. As litter from shrubs and grasses can differ in their quality, this can lead to differences in litter decomposition by the direct effect of quality, but also to litter interaction during decomposition. The objective of this study was to examine the occurrence of non-additive effects of litter mixtures on the decomposition rates of legume shrub litter (poor in P) or conifer shrub litter (poor in N) and grass litter. In addition to single litter type litterbags for the three species, we mixed litters of each pair of possible combinations to determine the influence of each species on mass loss. Litterbags were placed in the field and collected after 1, 6, 8, 12 and 24 months. In each collection, litter of each species remaining in mixed bags was separated, dry weighed and analyzed for C, N and P. With respect to shrub litter decomposing alone, mass loss of shrub litter when mixed with grass showed a 9–10 % increase in decomposition rate for conifer and a 3 % increase for legume litter. These litter mixture effects varied with time and they were detected after a decomposition period of 1 year in legume litter and of 2 years in conifer litter. Grass litter hastened conifer and legume litter decomposition in leaf litter mixtures, at least during the first stages of the process. The potential consequences of this result to alter litter accumulation patterns and thus carbon sequestration rates after shrub encroachment into grasslands will depend on whether the observed trends are maintained in the advanced decomposition stages.

Responses of soil fauna structure and leaf litter decomposition to effective microorganism treatments in Da Hinggan Mountains, China

Microorganisms are nutritious resources for various soil fauna. Although soil fauna grazing affects microorganism composition and decomposition rate, the responses of soil fauna and leaf litter decomposition to added microorganism is little understood. In this study, in the coniferous and broad-leaved mixed forest of Tahe County in the northern Da Hinggan Mountains, China, three sampling sites (each has an area of 10 m2) were selected. The first two sites were sprinkled with 250 times (EM1) and 1000 times (EM2) diluted effective microorganism (EM) preparations evenly, and the third site was sprinkled with the same volume of water as a control site. The responses of soil fauna structure and leaf litter decomposition to EM treatment were conducted during three years. The results revealed that EM treatment resulted in significant increase of soil organic matter. The number of soil fauna in the EM1 and EM2 sites increased by 12.88% and 2.23% compared to the control site, and among them springtails and mites showed the highest increase. However, the groups of soil fauna in the EM1 and EM2 sites decreased by 6 and 9, respectively. And the changes in the diversity and evenness index were relatively complicated. EM treatment slowed the decomposition of broad-leaved litter, but accelerated the decomposition of coniferous litter. However, the decomposition rate of broad-leaved litter was still higher than that of coniferous litter. The results of this study suggested that the added microorganisms could help individual growth of soil fauna, and this method led to a change in the process of leaf litter decomposition. This paper did not analyze the activity of soil microorganisms, thus it is difficult to clearly explain the complex relationships among litter type, soil fauna and soil microorganisms. Further research on this subject is needed.

Home-field advantage of litter decomposition and nitrogen release in forest ecosystems

Litter decomposition is a major fundamental ecological process that regulates nutrient cycling, thereby affecting net ecosystem carbon (C) storage as well as primary productivity in forest ecosystems. Litter decomposes in its home environment faster than in any other environment. However, evidence for this phenomenon, which is called the home-field advantage (HFA), has not been universal. We provide the first HFA quantification of litter decomposition and nutrient release through meta-analysis of published data in global forest ecosystems. Litter mass loss was 4.2 % faster on average, whereas nitrogen (N) release was 1.7 % lower at the home environment than in another environment. However, no HFA of phosphorus (P) release was observed. Broadleaf litter (4.4 %) had a higher litter mass loss HFA than coniferous litter (1.0 %). The positive HFA of N release was found in the coniferous litter. Mass loss HFA was significantly and negatively correlated with the initial lignin:N litter ratio. The litter decomposition and N release HFAs were obtained when mesh size ranged from 0.15 mm to 2.0 mm. The HFA of litter decomposition increased with decomposition duration during the early decomposition stage. The HFA of N release was well correlated with mass loss, and the greatest HFA was at mass loss less than 20 %. Our results suggest that the litter decomposition and N release HFAs are widespread in forest ecosystems. Furthermore, soil mesofauna is significantly involved in the HFA of litter decomposition.

Analysis of non-cellulosic polysaccharides helps to reveal the history of thick organic surface layers on calcareous Alpine soils

Background and aimsWe investigated the potential of non-cellulosic polysaccharides (NCP) as biomarkers to identify the plant types that dominate present and past litter input into organic surface covers on calcareous Alpine soils and to reveal historic vegetation changes.MethodsAt two sites in the Alps, NCP monomers were quantified in different organs of site-dominating plants, the Oa horizon of four Folic Leptosols, and different sections of thick organic surface layers of four Folic Histosols on calcareous bedrock.ResultsThe dominating plant types at our study sites differ markedly in their NCP composition and (galactose + mannose)/(arabinose + xylose) [GM/AX] ratio (grasses and sedges: 0.2; dicots Fagus and Vaccinium: 0.2–0.6; conifers Abies, Picea, Pinus: 0.7–2.4; mosses: 5). For all except one soil, the NCP signature of the uppermost Oa horizon reflects the present vegetation. For all Histosol O horizons, NCP signatures indicate a dominance of conifer litter throughout their development (up to 1,500 years). Different NCP and GM/AX depth profiles reflect specific patterns of O layer genesis.ConclusionsNCP and GM/AX depth profiles in organic surface covers of soils provide important information about dominating litter sources in the past and can be valuable tools to reveal historic vegetation and/or land use changes.

Interactions of tissue and fertilizer nitrogen on decomposition dynamics of lignin‐rich conifer litter

High tissue nitrogen (N) accelerates decomposition of high‐quality leaf litter in the early phases of mass loss, but the influence of initial tissue N variation on the decomposition of lignin‐rich litter is less resolved. Because environmental changes such as atmospheric N deposition and elevated CO2 can alter tissue N levels within species more rapidly than they alter the species composition of ecosystems, it is important to consider how within‐species variation in tissue N may shape litter decomposition and associated N dynamics. Douglas‐fir (Pseudotsuga menziesii) is a widespread lignin‐rich conifer that dominates forests of high carbon (C) storage across western North America, and displays wide variation in tissue and litter N that reflects landscape variation in soil N. We collected eight unique Douglas‐fir litter sources that spanned a two‐fold range in initial N concentrations (0.67–1.31%) with a narrow range of lignin (29–35%), and examined relationships between initial litter chemistry, decomposition, and N dynamics in both ambient and N fertilized plots at four sites over 3 yr. High initial litter N slowed decomposition rates in both early (0.67 yr) and late (3 yr) stages in unfertilized plots. Applications of N fertilizer to litters accelerated early‐stage decomposition, but slowed late‐stage decomposition, and most strongly affected low‐N litters, which equalized decomposition rates across litters regardless of initial N concentrations. Decomposition of N‐fertilized litters correlated positively with initial litter manganese (Mn) concentrations, with litter Mn variation reflecting faster turnover of canopy foliage in high N sites, producing younger litterfall with high N and low Mn. Although both internal and external N inhibited decomposition at 3 yr, most litters exhibited net N immobilization, with strongest immobilization in low‐N litter and in N‐fertilized plots. Our observation for lignin‐rich litter that high initial N can slow decomposition yet accelerate N release differs from findings where litter quality variation across species promotes coupled C and N release during decomposition. We suggest reevaluation of ecosystem models and projected global change effects to account for a potential decoupling of ecosystem C and N feedbacks through litter decomposition in lignin‐rich conifer forests.

Invertebrate feeding and emergence timing vary among streams along a gradient of riparian forest composition

Summary1. The quality of allochthonous organic matter influences the transfer of energy and nutrients through recipient food webs. We investigated the effects of variation in the composition of riparian forests (deciduous, mixed, coniferous) on the elemental imbalance between basal resources and consumers in streams, on consumer feeding and on potential feedbacks to riparian systems via emergent aquatic insects.2. We tested for differences in elemental stoichiometry (carbon/nitrogen/phosphorus; C/N/P) and stable isotopes (∂13C and ∂15N) between deciduous (red alder, Alnus rubra) and coniferous litter (western hemlock, Tsuga heterophylla) and among abundant stream invertebrates from streams draining different riparian forests (deciduous, mixed, coniferous). We then assessed shredder feeding preferences (of the trichopteran, Lepidostoma unicolor) for litter incubated in streams with these different forest types and quantified differences in emergence of aquatic and semiaquatic insects among streams.3. Both initial (non‐incubated) and stream‐incubated A. rubra litter had lower C/N and C/P and were more depleted in ∂13C and more enriched in ∂15N, than T. heterophylla litter. The stoichiometry of invertebrate tissue did not vary significantly among taxa or with riparian forest composition. A predator (the plecopteran Chloroperlidae) and a collector‐gatherer (the ephemeropteran Paraleptophlebia gregalis) from mixed and coniferous forest streams were more enriched in ∂13C and ∂15N isotopes than those from deciduous streams, suggesting that low availability of palatable, N‐rich A. rubra litter may constrain energy flow and nutrient fluxes up through the food web in systems with little or no A. rubra.4. Consumption of A. rubra litter by L. unicolor was most rapid when the litter had been incubated in streams draining deciduous forests, whereas consumption of T. heterophylla litter was not influenced by the composition of the riparian forest.5. Peak insect emergence from coniferous forest streams occurred 1 month earlier and at 2–3× higher density than from mixed and deciduous‐forest streams, but total biomass of emerging insects throughout the study period was not different between forest types. Assemblages of emerging insects were different between deciduous and coniferous forest streams, and taxon richness and diversity were nearly 2× greater from deciduous than from coniferous forest streams.6. Forest composition influences stream invertebrate feeding and could have reciprocal feedbacks onto riparian systems via altered insect emergence.

New species of Chalara occupying coniferous needles

Chalara is a genus of anamorphic fungi with typical phialidic conidiogenous cells. Species of Chalara live mostly as litter saprotrophs, many of them on coniferous litter. In this study, the morphology and DNA sequences (ITS rDNA, 28S rDNA and EF-1α) of strains of various species of Chalara isolated from coniferous litter needles were compared with those of strains from public collections. The majority of the isolates belonged to the C. longipes. Other strains represent C. piceae-abietis, C. microspora, C. microchona and four hitherto undescribed species. These are introduced here as C. holubovae sp. nov., C. hyalocuspica sp. nov., C. pseudoaffinis sp. nov. and C. recta sp. nov. Chalara recta is most closely related to C. longipes, which was found to be paraphyletic. However, no correlation of molecular data with the morphology was found. Chalara holubovae is specific among the Chalara species in that it has a synanamorph with fusiform conidia. Together with C. hyalocuspica, C. holubovae likely belong to the anamorphic Hyaloscyphaceae. Chalara piceae-abietis is epitypified. Epitypicifation of C. longipes and C. microspora cannot be done due to absence of a convenient specimen. Chalara austriaca may be re-discovered also after a targeted sampling in the locality of the type specimen. The majority of studied species are saprotrophic and colonise litter needles. An endophytic phase in living needles or other parts of a tree was confirmed for the species C. longipes and C. hyalocuspica. C. holubovae has been recorded only as an endophyte.

Breakdown and macroinvertebrate colonization of needle and leaf litter in conifer plantation streams in Shikoku, southwestern Japan

Breakdown and macroinvertebrate colonization of conifer needles (Cryptomeria japonica) and deciduous broadleaves (Euptelea polyandra) were investigated using litter bags in two study sites in streams flowing through a conifer plantation of C. japonica in Shikoku, southwestern Japan (one site with conifer canopy and another with mixed conifer and broadleaved canopy). Breakdown rates and macroinvertebrate densities were compared between litter species (conifer needle vs broadleaf) and between the two sites (conifer vs mixed canopy) to determine (1) whether breakdown rate of broadleaves is higher than conifer needles, (2) whether macroinvertebrates prefer broadleaves to conifer needles, and (3) whether the difference in riparian canopy is reflected in macroinvertebrate abundance. The results indicated that breakdown rates of broadleaves were higher than those of conifer needles, suggesting poorer quality of the latter as food for macroinvertebrates. Differences in macroinvertebrate density between needles and broadleaves were generally consistent with those in breakdown rates: broadleaves tended to have higher densities than needles, suggesting that conifer needles were not preferred by macroinvertebrates. However, total macroinvertebrate density in the conifer site was not significantly different from that in the mixed site, although the dominant shredder taxon differed (conifer site: gammarids; mixed site: lepidostomatids). Although conifer needles are low-quality food for macroinvertebrates, this may offer some advantages. Conifer needles remain on the streambed for longer periods owing to their lower breakdown rates, being a constantly available resource. In addition, accumulations of conifer litter may effectively trap and retain particulate organic matter.

Decomposing capacity of fungi commonly detected in Pinus sylvestris needle litter

Abstract A major part of the fungal community in coniferous litter consists of fungi whose taxonomic position and ecology are unknown. Here, nine isolates from within commonly occurring phylogenetic groups were tested for their ability to decompose Pinus sylvestris needles. In a 1-yr long incubation study, needle mass loss as well as changes in cellulose and lignin content were determined and compared to those caused by two litter basidiomycetes ( Marasmius androsaceus and Mycena epipterygia ) with recognized ability to decompose needles. A basidiomycetous Clavulina / Sistotrema strain appeared to be cellulolytic but not ligninolytic. Chalara longipes and three other strains within Helotiales also decomposed cellulose but not lignin, whereas Mollisia cinerea (also Helotiales) and two Dothideomycetes – Sydowia polyspora and a Mytilinidion sp., seemed unable to cause significant mass loss of cellulose. Lophodermium pinastri (Rhytismatales) readily decomposed cellulose, and also caused considerable loss of lignin.

The Influence of Planting Substrate on Yield of Seven Blueberry Cultivars

To obtain good yields, the highbush blueberry (Vaccinium corymbosum) needs special soil conditions with high organic matter content and optimal pH values, ranging from 4.8 up to 5.5. To create such conditions on an alluvial soil, with low humus content, poorly gleyed, an experiment was organized on the 3rd terrace of the Doamnei River, between 2005-2009 period, at the Research Institute for Fruit Growing Pitesti –Maracineni. The experiment had the following scheme: A Factor - cultivar, with seven graduations: a1- Simultan, a2-Delicia, a3-Lax, a4-Compact, a5-Augusta, a6-Azur a7-Blueray; B Factor - planting substrate, with 3 graduations: b1-5 kg peat+5kg manure; b2= 10 kg coniferous litter; b3= 5kg peat+5 kg manure+40 g sulphur powder; C Factor - experimental year, with 5 graduations (2005-2009). On average, for three planting substrates and the experimental period, Simultan cultivar, except Lax one, registered a significant increase by 14-214% in the number of flower buds per bush, and by 29-213% in number of flower clusters per bush, versus the others 5 studied cultivars. On average, for seven studied cultivars and experimental period the b1 and b3 fertilization treatments showed significant higher values on all studied fruiting indicators, versus b2 fertilization treatment. The treatment b1 registered a significant increase by 7% in number of fruits per bush and a significant decrease by 9% in average berry mass (g) versus b3 treatment. On average, for seven studied cultivars and three planting substrates the number of flower clusters per bush, the number of fruit per bush and berry yield per bush were significantly different from one year to the other over the whole experimental period.

Aboveground litter quality changes may drive soil organic carbon increase after shrub encroachment into mountain grasslands

Shrub encroachment into grasslands is ubiquitous but its impact on soil organic C (SOC) remains unclear. In previous work we had observed that shrub encroachment into mesic mountain grasslands increased SOC content. Here we sought the mechanisms of this increase. To this end, we assessed aboveground and belowground production for a conifer shrub (Juniperus communis L), a legume shrub (Cytisus balansae ssp. europaeus (G. Lopez & Jarvis) Munoz Garmendia) and grass (Festuca eskia Ramond ex DC), together with decomposition rates for both aboveground litter and roots. Belowground C net inputs do not clearly explain SOC increase: grass root production was higher than that of either shrub and the decomposition rate of grass roots was the lowest. Aboveground C net inputs were only slightly greater in shrubs than in grass, but the decomposition rate of litter of both shrubs was much lower than that of grass. The decomposition of conifer litter was N-limited, whereas that of legume shrub litter was P-limited. Thus we conclude that the SOC increases after shrub encroachment into mesic grasslands probably as a result of higher recalcitrance of shrub aboveground litter relative to grass litter.

Humification processes of needle litters on forest floors in Japanese cedar (Cryptomeria japonica) and Hinoki cypress (Chamaecyparis obtusa) plantations in Japan

We quantitatively clarified the early humification processes on Japanese cedar and Hinoki cypress forest floors by using a litterbag experiment and the solid-state 13C CPMAS NMR technique. There was no significant effect on litter mass loss during early humification between both coniferous litters regardless of the shape of their needles. Carbon composition in both litters showed similar trends during early humification. A/O-A as a humification index was low, around 0.6, in both litters throughout the experiment period although 60% of litter mass was lost. Coniferous litter incubated for 3 years might not be well-humified and would be susceptible to physical fragmentation. Carbon mass loss rates in conifers were in the following order: O-alkyl > aliphatic > aromatic > carbonyl carbons, differing with hardwoods. Conifers had concomitantly higher and lower mass loss rates of aliphatic and aromatic carbons than hardwoods. Soil organic carbon (SOC) accumulated in topsoil for conifers had relatively high and low contents of aliphatic and aromatic carbons than that for hardwood. These compositional differences of SOC among forests could be caused by the high and low supply rates of aliphatic and aromatic carbons from litter to topsoil. Consequently, initial litter nature and humification processes can affect the compositional qualities of SOC accumulated in soil.

Leaf litter decomposition—Estimates of global variability based on Yasso07 model

Litter decomposition is an important process in the global carbon cycle. It accounts for most of the heterotrophic soil respiration and results in formation of more stable soil organic carbon (SOC) which is the largest terrestrial carbon stock. Litter decomposition may induce remarkable feedbacks to climate change because it is a climate-dependent process. To investigate the global patterns of litter decomposition, we developed a description of this process and tested the validity of this description using a large set of foliar litter mass loss measurements (nearly 10,000 data points derived from approximately 70,000 litter bags). We applied the Markov chain Monte Carlo method to estimate uncertainty in the parameter values and results of our model called Yasso07. The model appeared globally applicable. It estimated the effects of litter type (plant species) and climate on mass loss with little systematic error over the first 10 decomposition years, using only initial litter chemistry, air temperature and precipitation as input variables. Illustrative of the global variability in litter mass loss rates, our example calculations showed that a typical conifer litter had 68% of its initial mass still remaining after 2 decomposition years in tundra while a deciduous litter had only 15% remaining in the tropics. Uncertainty in these estimates, a direct result of the uncertainty of the parameter values of the model, varied according to the distribution of the litter bag data among climate conditions and ranged from 2% in tundra to 4% in the tropics. This reliability was adequate to use the model and distinguish the effects of even small differences in litter quality or climate conditions on litter decomposition as statistically significant.

Geographical distribution of Scleroconidioma sphagnicola in coniferous forests in Europe and Canada.

The distribution of the dematiaceous microfungus Scleroconidioma sphagnicola in coniferous litter in Europe and Canada was assessed using a culture-dependent approach. Needles of various coniferous species were sampled between May and November of 2008. Twenty needles from each sample were cultivated on 2° malt agar after surface sterilisation with 30 % hydrogen peroxide. The formed mycelia were identified based on their morphology. The identifications were further confirmed by analyses of ITS rDNA. S. sphagnicola was recorded at 8 of the 53 sites. The highest abundance of S. sphagnicola was recorded in mountain areas of the Czech Republic. Further records of S. sphagnicola were acquired from the literature and the GenBank database. S. sphagnicola does not seem to be a ubiquitous coloniser of coniferous litter. However, this study showed that this fungus is found in various regions and the data obtained may serve to make an evaluation of the potential spread of S. sphagnicola.

Sericostoma vittatum (Trichoptera) Larvae Are Able to Use Pine Litter as an Energy Source

AbstractWe tested the effect of conditioning time of Pinus sylvestris litter on food consumption and growth of laboratory‐reared Sericostoma vittatum larvae. In all cases, larval mass was positively correlated with consumption rates but negatively with growth rates and gross production efficiencies. Conditioning time (4, 8 or 30 weeks) had an effect on feeding rates: they were lowest for the least conditioned pine litter, but no effect of conditioning time on growth rates was observed. Contrary to previous reports on conifer litter use by aquatic detritivores, our results indicate that S.vittatum larvae were able to transform the highly refractory pine litter into secondary production even when it was conditioned for only 4 weeks. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Do oribatid mites (Acari: Oribatida) show a higher preference for ubiquitous vs. specialized saprotrophic fungi from pine litter?

Previous studies of oribatid mite feeding preferences for different saprotrophic fungi were limited to ubiquitous fungal species, whereas saprophytes specialized to decompose particular substrates have been neglected. We examined the preference of seven oribatid mite species ( Adoristes ovatus, Eniochthonius minutissimus, Eueremaeus silvestris, Nothrus silvestris, Oppiella subpectinata, Porobelba spinosa and Spatiodamaeus verticillipes) for nine autochthonous saprotrophic fungi from Scots pine litter ( Pinus sylvestris). Among the fungal species offered were specific coniferous litter colonizers ( Allantophomopsis lycopodina, Ceuthospora pinastri, Hormonema dematioides, Scleroconidioma sphagnicola, Verticicladium trifidum, Marasmius androsaceus and Sympodiella acicola) and two ubiquitous species ( Cladosporium herbarum and Oidiodendron griseum). The fungi were inoculated on fragments of pine needles and offered simultaneously and separately to the mites. Our main hypothesis, that oribatid mites (usually occurring in more than one type of ecosystems) would prefer the ubiquitous fungal species rather than those specific to pine litter, was supported only partly. The ubiquitous C. herbarum was highly preferred by all studied mites, but most of them preferred one or more of the specialized fungi with similar intensity. The basidiomycete M. androsaceus along with sterile needles were consistently avoided by all mites in all experiments. Our results do not support the hypothesis, that the “true” fungivorous oribatid mites in traditional sense are more selective fungal feeders than are the “unspecialized” panphytophagous ones. We observed no gradation in preference of fungi for oribatid mites as a group, but rather a discontinuous and dynamic mosaic with particular mites preferring particular fungal species. This heterogeneous mosaic shapes the feeding niches occupied by particular oribatid mite species and probably reduces competition for food source among numerous species coexisting in a given habitat and time.

Dynamics and relationships of Ca, Mg, Fe in litter, soil fauna and soil in Pinus koraiensis-broadleaf mixed forest

The Liangshui Natural Reserve in Heilongjiang Province of China was selected as the study area. The authors collected the samples of forest litter (Tilia amurensis, Fraxinus mandshurica, Pinus koraiensis, Acer mono, Betula costata, and mixed litter), soil in humus horizon (0–5cm) and soil horizon (5–20cm), and soil macrofauna (Oligochaeta, Geophiloporpha and Juliformia) from 2001 to 2002. The role of soil macrofauna in the material cycle was analyzed through comparing the macro-element contents among various parts of the subsystems and using enrichment index (EI). The results indicate that dynamic changes of various litters are very complicated. The contents of Fe in each kind of litter increase firstly, and then decrease in the study period. The changes of macro-element contents are greater in the broad-leaf litter than in the coniferous litter, and the mixed litter is in the middle level, but the differences among them are not significant. The contents of Mg and Fe in humus are higher than those in soil, but the contents of Ca in soil are higher than that in humus. The dynamic changes of macro-element contents in soil and soil fauna are not consistent with those in litter. The diplopod presented obvious enrichment of Ca and Mg (EI>1), but it does not significantly enrich Fe. Earthworm has a stronger enrichment ability of Fe than diplopod and scolopendra, but EI<1. Soil fauna can make great influences on the material cycle of the subsystems.

Soil macrofaunal response to forest conversion from pure coniferous stands into semi-natural montane forests

We studied the response of the macrofauna to forest conversion from pure coniferous stands into semi-natural montane forests in the southern Black Forest (Germany). The investigation was carried out by comparing existing stands that represent the four major stages of the envisaged conversion process. Major results are: (i) environmental parameters indicate a significant alteration of the soil environment, (ii) neither an overall change nor a clear trend in macrofaunal richness and abundance could be established, and (iii) the data for the different taxa suggest specific responses to the conditions of the individual conversion stages. In general, saprophagous taxa seem to be mainly driven by alterations of the resource base (litter quality, microbial parameters) while predatory taxa tend to respond to changes at the consumer level. Associated alterations in the functional structure occurred for macroengineers (earthworms), primary consumers (diplopods, isopods) as well as a wide range of predators. These changes could partly be explained by changes in environmental conditions that did not follow a gradual adjustment during the conversion process. One essential step is the shift from an organic layer composed of low-quality coniferous litter that is dominated by fungi to a litter layer with higher quality food sources. Within this framework, the specific response of the macrofauna is modulated by factors such as differences in structural features of the ground vegetation and availability of woody litter in a stage-specific way. Since the response of the macrofauna depended far less on site conditions than any of the other environmental factors, this invertebrate group may be used as a valuable indicator of the changes associated with different stages of the conversion process. As long as no dramatic change of soil conditions – in particular pH – occurs, however, no fundamental restructuring of the soil community is to be expected.

Assessing sulfate and carbon controls on net methylmercury production in peatlands: An in situ mesocosm approach

Abstract The transformation of atmospherically deposited inorganic Hg to the toxic, organic form methylmercury (MeHg) is of serious ecological concern because MeHg accumulates in aquatic biota, including fish. Research has shown that the Hg methylation reaction is dependent on the availability of SO4 (as an electron acceptor) because SO4-reducing bacteria (SRB) mediate the biotic methylation of Hg. Much less research has investigated the possible organic C limitations to Hg methylation (i.e. from the perspective of the electron donor). Although peatlands are long-term stores of organic C, the C derived from peatland vegetation is of questionable microbial lability. This research investigated how both SO4 and organic C control net MeHg production using a controlled factorial addition design in 44 in situ peatland mesocosms. Two levels of SO4 addition and energetic-equivalent additions (i.e. same number of electrons) of a number of organic C sources were used including glucose, acetate, lactate, coniferous litter leachate, and deciduous litter leachate. This study supports previous research demonstrating the stimulation of MeHg production from SO4 input alone (∼200 pg/L/day). None of the additions of organic C alone resulted in significant MeHg production. The combined addition of SO4 and some organic C sources resulted in considerably more MeHg production (∼500 pg/L/day) than did the addition of SO4 alone, demonstrating that the highest levels of MeHg production can be expected only where fluxes of both SO4 and organic C are delivered concurrently. When compared to a number of pore water samples taken from two nearby peatlands, MeHg concentrations resulting from the combined addition of SO4 and organic C in this study were similar to MeHg “hot spots” found near the upland–peatland interface. The formation of MeHg “hot spots” at the upland–peatland interface may be dependent on concurrent inputs of SO4 and organic C in runoff from the adjacent upland hillslopes.