Later Stages Of Decomposition Research Articles

The decomposition process and nutrient release of invasive plant litter regulated by nutrient enrichment and water level change.

Wetlands are vulnerable to plant invasions and the decomposition of invasive plant litter could make impacts on the ecosystem services of wetlands including nutrient cycle and carbon sequestration. However, few studies have explored the effects of nutrient enrichment and water level change on the decomposition of invasive plant litter. In this study, we conducted a control experiment using the litterbag method to compare the decomposition rates and nutrient release in the litter of an invasive plant Alternanthera philoxeroides in three water levels and two nutrient enrichment treatments. This study found that the water level change and nutrient enrichment showed significant effects on the litter decomposition and nutrient dynamic of A. philoxeroides. The increase of water level significantly reduced the decomposition rate and nutrient release of litter in the nutrient control treatment, whereas no clear relationship was observed in the nutrient enrichment treatment, indicating that the effect of water level change on litter decomposition might be affected by nutrient enrichment. At the late stage of decomposition, the increase of phosphorus (P) concentration and the decrease of the ratio of carbon to P suggested that the decomposition of invasive plant litter was limited by P. Our results suggest that controlling P enrichment in water bodies is essential for the management of invasive plant and carbon sequestration of wetlands. In addition, the new index we proposed could provide a basis for quantifying the impact of invasive plant litter decomposition on carbon cycle in wetlands.

Decay stages of wood and associated fungal communities characterise diversity\u2013decomposition relationships

The biodiversity–ecosystem function relationship is a central topic in ecology. Fungi are the dominant decomposers of organic plant material in terrestrial ecosystems and display tremendous species diversity. However, little is known about the fungal diversity–decomposition relationship. We evaluated fungal community assemblies and substrate quality in different stages of wood decay to assess the relationships between fungal species richness and weight loss of wood substrate under laboratory conditions. Wood-inhabiting fungal communities in the early and late stages of pine log decomposition were used as a model. Colonisation with certain species prior to inoculation with other species resulted in four-fold differences in fungal species richness and up to tenfold differences in the rate of wood substrate decomposition in both early- and late-decaying fungal communities. Differences in wood substrate quality had a significant impact on species richness and weight loss of wood and the relationships between the two, which were negative or neutral. Late communities showed significantly negative species richness–decay relationships in wood at all decay stages, whereas negative relationships in early communities were significant only in the intermediate decay stage. Our results suggest that changes in fungal communities and wood quality during wood decomposition affect the fungal diversity–decomposition relationship.

Root presence modifies the long‐term decomposition dynamics of fungal necromass and the associated microbial communities in a boreal forest

Recent studies have highlighted that dead fungal mycelium represents an important fraction of soil carbon (C) and nitrogen (N) inputs and stocks. Consequently, identifying the microbial communities and the ecological factors that govern the decomposition of fungal necromass will provide critical insight into how fungal organic matter (OM) affects forest soil C and nutrient cycles. Here, we examined the microbial communities colonising fungal necromass during a multiyear decomposition experiment in a boreal forest, which included incubation bags with different mesh sizes to manipulate both plant root and microbial decomposer group access. Necromass-associated bacterial and fungal communities were taxonomically and functionally rich throughout the 30months of incubation, with increasing abundances of oligotrophic bacteria and root-associated fungi (i.e., ectomycorrhizal, ericoid mycorrhizal and endophytic fungi) in the late stages of decomposition in the mesh bags to which they had access. Necromass-associated β-glucosidase activity was highest at 6months, while leucine aminopeptidase peptidase was highest at 18months. Based on an asymptotic decomposition model, root presence was associated with an initial faster rate of fungal necromass decomposition, but resulted in higher amounts of fungal necromass retained at later sampling times. Collectively, these results indicate that microbial community composition and enzyme activities on decomposing fungal necromass remain dynamic years after initial input, and that roots and their associated fungal symbionts result in the slowing of microbial necromass turnover with time.

Co-incorporating leguminous green manure and rice straw drives the synergistic release of carbon and nitrogen, increases hydrolase activities, and changes the composition of main microbial groups

Rice straw (RS) was incorporated into paddy soil together with leguminous green manure (e.g., Chinese milk vetch, Astragalus sinicus L., MV) in a mesocosm-scale experiment and the enzyme activity and composition of main microbial groups were measured. Mixing MV and RS caused a synergistic release of residual C and N, leading to a low C/N ratio at the middle and late decomposition stages of the mixture and shortening the time to complete decomposition. Furthermore, the highest abundances of Gram-negative (G−) bacteria and fungi and the highest activities of α- and β-glucosidase, β-cellobiosidase, β-xylosidase, N-acetyl-glucosaminidase, and acid phosphomonoesterase were observed in the residue mixture, especially at the middle and late stages of the experiment. The residue decomposition rate was positively correlated with residual N and mineral N concentrations. Most hydrolases and both oxidase (phenol oxidase and peroxidase) activities, and G− bacterial (especially 18:1 ω5c, Photobacterium) abundance explained the decomposition of mixing residues. In conclusion, co-incorporation of MV and RS could stimulate their decomposition by retaining a relatively low C/N ratio, enhancing G− bacterial abundance and hydrolase activities. Introducing leguminous green manures in paddy fields may be an effective way to accelerate the decomposition of rice straw.

Forest Microhabitat Affects Succession of Fungal Communities on Decomposing Fine Tree Roots.

Belowground litter derived from tree roots has been shown as a principal source of soil organic matter in coniferous forests. Fate of tree root necromass depends on fungal communities developing on the decaying roots. Local environmental conditions which affect composition of tree root mycobiome may also influence fungal communities developing on decaying tree roots. Here, we assessed fungal communities associated with decaying roots of Picea abies decomposing in three microhabitats: soil with no vegetation, soil with ericoid shrubs cover, and P. abies deadwood, for a 2-year period. Forest microhabitat showed stronger effect on structuring fungal communities associated with decaying roots compared to living roots. Some ericoid mycorrhizal fungi showed higher relative abundance on decaying roots in soils under ericoid shrub cover, while saprotrophic fungi had higher relative abundance in roots decomposing inside deadwood. Regardless of the studied microhabitat, we observed decline of ectomycorrhizal fungi and increase of endophytic fungi during root decomposition. Interestingly, we found substantially more fungal taxa with unknown ecology in late stages of root decomposition, indicating that highly decomposed roots may represent so far overlooked niche for soil fungi. Our study shows the importance of microhabitats on the fate of the decomposing spruce roots.

Decomposition of different crop straws and variation in straw-associated microbial communities in a peach orchard, China

Crop residue is a major source of soil organic matter; therefore, application of crop straw to soil contributes to the sustainable development of organic agriculture. To better understand the transformation of crop straw in orchard soils, we investigated the relationship between the characteristics of straw decomposition and functional diversity of associated microbial communities in a long-term peach orchard, China. Mesh bags, each containing 30 g of corn or bean straw, were buried at a soil depth of 20 cm in a 12-year-old peach orchard for 360 d (October 2011–October 2012). Three treatments were applied, i.e., fresh corn straw, fresh corn straw with nitrogen fertilizer (urea, 10.34 g/kg), and fresh bean straw. Changes in straw residual rate, straw water content and soil conditions were monitored after treatment. The functional diversity of straw-associated microbial communities was analyzed by the Biolog-Eco microplate assay. During the decomposition process, straw residual rates did not vary considerably from 10 d (30.4%–45.4%) to 360 d (19.0%–30.3%). Irrespective of nitrogen addition, corn straw decomposed faster than bean straw. Corn straw with nitrogen fertilizer yielded the highest average well color development (AWCD) values (1.11–1.67), followed by corn straw (1.14–1.68) and bean straw (1.18–1.62). Although the AWCD values did not differ significantly among the three treatments, substantial differences occurred across various time periods of the decomposition process (P<0.01). In terms of carbon source utilization, the dominant microbial groups fed mainly on saccharides. Hard-to-decompose substances gradually accumulated in the middle and late stages of straw decomposition. Of the six categories of carbon sources tested, the utilization rate of aromatics was the lowest with corn straw, whereas that of polymers was the lowest with bean straw. Among different treatments, straw residual rate was negatively correlated to soil available phosphorous, soil available potassium and soil temperature (P<0.05), but not to soil water content. In some cases (corn straw with or without nitrogen fertilizer), straw residual rate was negatively correlated to straw water content, amino acid utilization and carboxylic acid utilization, and positively correlated with microbial species richness and evenness (P<0.05). Microbial community associated with corn and bean straw decomposition in soil was respectively dominated by aromatic- and polymer-metabolizing groups during the middle and late stages of this process, which could reduce the stability of microbial community structure and decrease the rate of straw decomposition in fruit tree orchard.

Five-year study on the effects of warming and plant litter quality on litter decomposition rate in a Tibetan alpine grassland

The decomposition of plant litter is a key link in global C budgets and provides strong feedback to changes in climate and biogeochemical cycles. However, the combined effects of global warming and plant litter quality on the rate of plant litter decomposition and nutrient dynamics in alpine ecosystems are still poorly understood. We conducted a warming experiment to investigate the effects of litter quality and temperature on decomposition rates and variations in nutrients of four common herbaceous plants (low-quality litter species Stipa purpurea and Carex moorcroftii and high-quality litter species Astragalus confertus and Leontopodium nanum) during 2011–2016. During the initial stages of decomposition, warming had no significant effect on the mass loss of plant litter for low-quality litter species, but in the later stages of decomposition, it had a negative effect on the mass loss across all species (P < 0.05). Litter quality was the best predictor of N and P release/immobilisation during the decomposition of aboveground plant litter. Low-quality litter had the highest immobilisation of N at about 80% of the initial remaining mass; nutrients were then released in the following stages of decomposition. However, the fraction of initial P decreased with the mass remaining during the initial and later phases of decomposition, but a short period of P immobilisation occurred in the middle phase of decomposition. For high-quality litter, the fraction of initial N and P decreased with the mass remaining during the whole decomposition process. Warming had a marginal influence on the N and P dynamics throughout the decomposition process. Our study showed that the decay of plant litter was strongly suppressed by warming climate and that the N and P dynamics on the investigated Tibetan grassland were mainly regulated by litter quality, providing valuable insights into the biogeochemical cycles of nutrients in alpine ecosystems.

Synergistic effects: a common theme in mixed-species litter decomposition.

Litter decomposition plays a key role in nutrient cycling across ecosystems, yet to date, we lack a comprehensive understanding of the nonadditive decomposition effects in leaf litter mixing experiments. To fill that gap, we compiled 69 individual studies with the aim to perform two meta-analyses on nonadditive effects. We show that a significant synergistic effect (faster decomposition in mixtures than expected) occurs at a global scale, with an average increase of 3-5% in litter mixtures. In particular, low-quality litter in mixtures shows a significant synergistic effect, while additive effects are observed for high-quality species. Additionally, synergistic effects turn into antagonistic effects when soil fauna are absent or litter is in very late stages of decomposition (near-humus). In contrast to temperate and tropical areas, studies in boreal regions show significant antagonistic effects. Our two meta-analyses provide a systematic evaluation of nonadditive effects in mixed litter decomposition studies and show that litter quality alters the effects of litter mixing. Our results indicate that nutrient transfer, soil fauna and inhibitory secondary compounds can influence mixing effects. We also highlight that synergistic and antagonistic effects occur concurrently, and the final litter mixing effect results from the interplay between them.

Quality dependence of litter decomposition and its carbon, nitrogen and phosphorus release under simulated acid rain treatments.

Litter decomposition is of utmost importance to elemental cycling in terrestrial ecosystems, with litter quality being frequently considered to predominantly control litter decomposition. However, how acid rain (AR) would affect litter decomposition and its elements release remains inconclusive, although AR has widely occurred in Europe, North America, and East Asia. This study was conducted to observe leaf litter decomposition and release of carbon (C), nitrogen (N), and phosphorus (P) of three crops (maize, rice, and soybean) under simulated AR treatments. Results showed that the accumulated mass loss during decomposition was significantly different among species, supporting the view of litter quality predominantly controlling decomposition. Specifically, quality dependence of litter decomposition was observed in the late stage of decomposition, while mass loss of litters was comparable in the first month among species. With decomposition, the litter C/N ratio significantly increased for the three species while the C/P and N/P ratios significantly decreased or tended to decrease, suggesting that litter N was releasedpreferentially over C and P. However, AR treatments did not significantly affect litter decomposition and its elements release in our investigation period. Moreover, litter P content appeared to strongly affect the release of C, N, and P during litter decomposition, and such P dependence could to some extentbe alleviated by AR treatments. Our results suggest that AR may change the quality dependence of litter decomposition and further studies are needed to illustrate its potential mechanisms.

Nitrogen Additions Retard Nutrient Release from Two Contrasting Foliar Litters in a Subtropical Forest, Southwest China

Litter decomposition plays a critical role in regulating biogeochemical cycles in terrestrial ecosystems and is profoundly impacted by increasing atmospheric nitrogen (N) deposition. Here, a N manipulation experiment was conducted to explore the effects of N additions (0 kg N ha−1 yr−1, 20 kg N ha−1 yr−1 and 40 kg N ha−1 yr−1) on decay rates and nutrients release of two contrasting species, the evergreen and nutrient-poor Michelia wilsonii and the deciduous and nutrient-rich Camptotheca acuminata, using a litterbag approach at the western edge of the Sichuan Basin of China. The decay rate and the mineralization of N and phosphorus (P) was faster in nutrient-rich C. acuminata litter than in nutrient-poor M. wilsonii litter, regardless of N regimes. N additions tended to decrease the decay constant (k value) in M. wilsonii litter, but had no effect on C. acuminata litter. N additions had no significant effects on carbon (C) release of both litter types. N additions showed negative effects on N and P release of M. wilsonii litter, particularly in the late decomposition stage. Moreover, for C. acuminata litter, N additions did not affect N release, but retarded P release in the late stage. N additions did not affect the C:N ratio in both litter types. However, N additions—especially high-N addition treatments—tended to reduce C:P and N:P ratios in both species. The effect of N addition on N and P remaining was stronger in M. wilsonii litter than in C. acuminata litter. The results of this study indicate that N additions retarded the nutrients release of two foliar litters. Thus, rising N deposition might favor the retention of N and P via litter decomposition in this specific area experiencing significant N deposition.

Patterns and mechanisms for larval aggregation in carrion beetle Necrodes littoralis (Coleoptera: Silphidae)

Carrion is a patchy, nutrient-rich and frequently bulky resource that hosts a complex community of competing organisms. Several insect species have specialized to use carrion for breeding, revealing a specific suite of behavioural adaptations. Larvae of carrion insects regularly aggregate while feeding, frequently forming spectacular larval masses. Here we analysed patterns and mechanisms of collective feeding by larvae of the communally breeding carrion beetle Necrodes littoralis. Using results of laboratory behavioural assays and findings from previous field experiments using pig carcasses we found that: (1) under field conditions N. littoralis larval aggregations were prevalent on large carcasses, during late decomposition stages; (2) under laboratory conditions larvae of all instars, when present on meat, formed stable aggregations; (3) larvae consistently responded to thermal characteristics of a feeding environment, aggregating in the hottest place and following changes in the heat source location, which suggests thermal cues are important for their aggregation; and (4) ground-deposited chemical cues elicited a minor response by the third-instar larvae, which indicates these cues are less important for the aggregation of larval N. littoralis. These findings highlight the prevalence of communal feeding among necrophagous insect larvae, revealing the interspecific and intraspecific diversity of patterns and mechanisms for larval aggregation on carrion.

Analysis of microbial utilization of rice straw in paddy soil using a DNA‐SIP approach

AbstractConsidering the close connection between soil microorganisms with carbon (C) cycling, the aim of this study was to identify the specific bacterial and fungal microbes that assimilate 13C from incorporated rice straw and explore their dynamics and characteristics during straw decomposition in paddy soil. Soil microcosms based on 12/13C‐labeled rice straw were incubated with the determination of CO2 production at 1, 3, 7, 14, 28, 56 and 90 days after straw incorporation. Meanwhile, the targeted soil bacterial and fungal communities were characterized using a DNA‐based stable isotope probing (DNA‐SIP) approach combined with Illumina MiSeq sequencing. Rice straw decomposed rapidly in the first 2 weeks, coupled with a large turnover of soil native organic matter. During this process, Actinobacteria including the orders Streptomycetales, Caternulisporales and Corynebacteriales dominated the community utilizing rice straw‐derived C with a succession from Streptomyces, to Kitasatospora, to Catenulispora. At Days 56 to 90, the dominant orders assimilating rice straw‐derived 13C were Micrococcales, Sphingobacteriia, Gammaproteobacteria from phyla Actinobacteria, Bacteroidetes and Proteobacteria, respectively. The fungal orders Onygenales, Capnodiales, Sordariales and Pleosporales showed stronger ability of 13C utilization at late decomposition stage. Taken together, along with stimulation of soil organic matter mineralization after rice straw addition, dynamics of 13C‐assimilating bacterial and fungal groups with various characteristics were identified.

Coarse Woody Debris as Microhabitats of Soil Macrofauna in Polluted Areas

We built a map of the distribution of earthworm abundance in coniferous forests in the area affected by long-term emissions from the Middle Ural Copper Smelter. It is established that a “lumbricide desert” of about 65 km2 without earthworms in the forest litter and soil mineral horizons has been formed near the smelter due to extremely high concentrations of heavy metals. However, we have also found that earthworms (only Dendrodrilus rubidus tenuis) inhabit logs of the late stages of decomposition in this area. Their abundance is comparable to that in the soil of unpolluted (background) areas; single individuals (including cocoons) were also found in the soil directly under the logs. Gastropods, which are absent in standard soil samples in this area, were also recorded in these logs (five species). We suppose that the presence of such “survival microsites” may serve as a mechanism of recolonization of polluted areas by groups sensitive to pollution after the reduction of emissions, followed by a decrease in soil toxicity.

The optical properties in alkali-soluble fractions extracted from newly shed litters in a subalpine forest

Humification of plant detritus is an important pathway for soil organic matter formation. The long-standing studies considered that humification proceeds at very late stages of litter decomposition, while the degree of humification in newly shed litters before decomposition remains unclear. In this study, we aimed to explore the degree of humification and conjugate structures of humic substances in newly shed litters, and their variations between litter types with different chemical components and between seasons with different environmental conditions. In this study, we collected fresh foliar (evergreen vs. deciduous and tree vs. shrub), twig, flower, and fruit litters by litter traps in a subalpine forest on the eastern Tibetan Plateau monthly from April to November 2016. The humification degrees of these newly shed litters were evaluated by the optical properties (i.e., ΔlogK, E4/E6, and A600/C) of the alkaline-extracted humic acid-like solutions. E4/E6 and ΔlogK are often used to evaluate the degree of humification, and these values were also used to classify the maturity levels of humic substances. We found that the ΔlogK, E4/E6, and A600/C values varied greatly among seasons with a higher degree of humification observed in August than in the other months for foliar litter. Compared with other litter components, foliar litter exhibited higher ΔlogK, E4/E6, and A600/C values, indicating that fresh foliar litter had a lower degree of humification than the other litters. Twig litter had more stable and abundant precursors of soil organic matter with a higher degree of humification. Moreover, higher degrees of humification with lower ΔlogK and E4/E6 values were observed in evergreen and tree litter species than in deciduous and shrub species, indicating that deciduous and shrub species retained strong abilities to sequester carbon (C). The degree of humification in newly shed litters was strongly affected by chemical components. Twig litter had more stable and abundant precursors of soil organic matter with high degree of humification. Deciduous species and shrub species retained strong abilities to sequester C in cold biomes. Additionally, the humic substances in newly shed litters were very young (type Rp), as assessed by the ΔlogK and A600/C values according to the Kumada’s classification, implying that these humic substances might have faster turnover times but strongly contribute to soil organic matter formation in this subalpine forest.

Microbial communities associated with decomposing deadwood of downy birch in a natural forest in Khibiny Mountains (Kola Peninsula, Russian Federation)

Deadwood plays an important role in the forest ecosystems, providing nutrients and habitat for a wide range of organisms, preventing soil erosion, and improving carbon storage. Microorganisms are primary agents in wood decomposition. The aim of the present research is to describe the changes in diversity, structure and abundance of microbial communities over downy birch lying deadwood decomposition in a boreal forest under natural conditions. This study also included investigations on the potential involvement of deadwood in climate change.The decomposition of deadwood was visually assessed using a five-class system. The microbial community diversity and composition were assessed with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. Real time PCR was used to evaluate the absolute and relative microbial abundance. The potential involvement of deadwood in climate change was assessed by in situ-measuring of the carbon dioxide (CO2) emissions from downy birch lying deadwood and from soil.The results obtained indicate that deadwood represents a substrate whose physico-chemical and microbiological property change with time. Higher diversity of fungi, bacteria, and archaea were recorded in the decay class 5. Conversely, actinobacteria showed the lowest values of diversity in decay class 5. We observed a succession of dominant microbial taxa over the decomposition progress. Overall, the abundance of each microbial group increases with the advance of decomposition. Among the estimated physico-chemical properties, nitrogen content, that increased with decay, and pH were the most important candidate drivers of microbial community composition and abundance. CO2 emissions were recorded higher in the decay class 5 and in soil of plots with the highest amount of lying deadwood.Bacteria dominated the microbial community and may play a more important role in the late stages of wood decomposition conversely to fungi and actinobacteria that are assumed to be primary involved in early stages of wood colonization. Archaea are shown to be an integral and dynamic component of decaying wood biota. The presence of large amounts of deadwood may affect greenhouse gas (GHG) emissions, especially in the event of an increase in temperatures that could reduce the carbon (C) sink capacity of the boreal forests.

Linking microbial community structure to carbon substrate chemistry in soils following aboveground and belowground litter additions

Plant aboveground litter (AL) and belowground litter (BL) differ in their carbon (C) chemistry, which can substantially affect soil microbial communities through litter inputs. Few studies, however, have compared how AL and BL additions to the soil change C substrate chemistry, microbial communities and their relationships during various decomposition stages. We tracked concurrent changes in C substrate chemistry and microbial communities with AL and BL addition to bare soil based on a 412-day laboratory incubation experiment. Carbon substrate chemistry was measured by solid-state 13C nuclear magnetic resonance (NMR), and the microbial community was measured by quantitative real-time polymerase chain reaction (qPCR) and high-throughput sequencing. We found that AL addition strongly increased the gene copy number of both bacterial and fungal communities in the early stage of decomposition (the first 72 days) but had no effect on their gene copy number in the late stage of decomposition (after 72 days). The bacterial community composition in bare soil and soil with AL addition diverged, while the fungal community composition converged from the early to the late stage. BL addition, in contrast, did not strongly change the gene copy number or composition of bacterial and fungal communities in either the early or late stages. Labile C (e.g., O-alkyl-C), whose content increased significantly with AL addition but not with BL addition, was the key C substrate affecting microbial communities throughout the whole incubation period. Our findings demonstrate that the effects of labile C on soil decomposition can persist for a long time. The responses of bacterial and fungal communities to labile C inputs differ in various decomposition stages, which is important for predicting soil and litter decomposition processes, and thereby soil carbon sequestration.

Wood Decay Characteristics and Interspecific Interactions Control Bacterial Community Succession in Populus grandidentata (Bigtooth Aspen).

Few studies have investigated bacterial community succession and the role of bacterial decomposition over a continuum of wood decay. Here, we identified how (i) the diversity and abundance of bacteria changed along a chronosequence of decay in Populus grandidentata (bigtooth aspen); (ii) bacterial community succession was dependent on the physical and chemical characteristics of the wood; (iii) interspecific bacterial interactions may mediate community structure. Four hundred and fifty-nine taxa were identified through Illumina sequencing of 16S rRNA amplicons from samples taken along a continuum of decay, representing standing dead trees, downed wood, and soil. Community diversity increased as decomposition progressed, peaking in the most decomposed trees. While a small proportion of taxa displayed a significant pattern in regards to decay status of the host log, many bacterial taxa followed a stochastic distribution. Changes in the water availability and chemical composition of standing dead and downed trees and soil were strongly coupled with shifts in bacterial communities. Nitrogen was a major driver of succession and nitrogen-fixing taxa of the order Rhizobiales were abundant early in decomposition. Recently downed logs shared 65% of their bacterial abundance with the microbiomes of standing dead trees while only sharing 16% with soil. As decay proceeds, bacterial communities appear to respond less to shifting resource availability and more to interspecific bacterial interactions – we report an increase in both the proportion (+9.3%) and the intensity (+62.3%) of interspecific interactions in later stages of decomposition, suggesting the emergence of a more complex community structure as wood decay progresses.

Carbon and Nitrogen Responses in Litterfall and Litter Decomposition in Red Pine (Pinus densiflora S. et Z.) Stands Disturbed by Pine Wilt Disease

Research Highlight: Forest disturbance by insects or disease can have a significant influence on nutrient return by litterfall and decomposition, but information regarding disturbance gradients is scarce. This study demonstrated that the disturbance intensity caused by pine wilt disease greatly altered the quality and quantity of carbon (C) and nitrogen (N) in litterfall components and decomposition processes. Background and Objectives: This study was conducted to evaluate the C and N status of litterfall and litter decomposition processes in a natural red pine (Pinus densiflora S. et Z.) stand disturbed by pine wilt disease in southern Korea. Nine red pine plots with varying degrees of disturbance caused by pine wilt disease were established based on differences in the stand basal area. Litterfall and the decomposition of needle litter and branches under different degrees of disturbance were measured for three years. Results: There was a significant correlation (p &lt; 0.05) between disturbance intensity and the C and N concentration of litterfall components depending on the time of sampling. The annual C and N inputs through litterfall components decreased linearly with decreasing disturbance intensities. The decomposition rates of branches were higher in slightly disturbed plots compared with severely disturbed plots for the late stage of branch decomposition, whereas the decomposition rates of needle litter were not affected by the disturbance intensity of pine wilt disease. Carbon and N concentrations from needle litter and branches were not linearly related to the intensities of disturbance, except for the initial stage (one year) of needle litter decomposition. Conclusions: The results indicated that the incidence of pine wilt disease was a major cause of C and N loss through litterfall and decomposition processes in pine wilt disease disturbed stands, but the magnitude of loss depended on the severity of the disease disturbance.

Decomposition of Spartina alterniflora and concomitant metal release dynamics in a tidal environment

The decomposition of salt marsh plants is affected by the variation of physiochemical factors caused by the change of tide level. In the present study, plant tissues of Spartina alterniflora from controlled metal exposure experiments were subjected to a field decomposition trial at different tidal levels in a tidal flat of Chongming Island, Shanghai. The contents of the metals and Pb stable isotope ratios of the plant litter and the adjacent sediment were followed. The mass loss rate of the root and leaf litters of S. alterniflora decreased with the increase of burial time. Leaf had the highest decomposition rate (0.009 day−1 to 0.020 day−1) compared to that of the roots (0.004 day−1 to 0.005 day−1) and stems (0.002 day−1 to 0.006 day−1). Leaf had the highest decomposition rate possibly due to the significantly lower C/N ratio (16.0–44.6) compared to that of the roots (32.8–88.9) and stems (43.7–120.9). The mass loss rate of the roots and leaves of S. alterniflora was higher in the high tidal marsh than that in the low tidal marsh, especially at the late stages of decomposition. The concentrations of metals in leaf litter of S. alterniflora increased, whereas the pools of metals in most of the plant litters decreased significantly with the increasing of the decomposition time. The ratios of 207Pb/206Pb and 208Pb/206Pb in the root litters decreased significantly in the first 290 days of decomposition and then increased significantly at Day 350, while the Pb isotope ratios in adjacent sediment showed no significant changes. Fast mass loss of plant litters induced the significant decrease in metals' pools at early stages of decomposition, and release of the plant tissue Pb was greatly inhibited due to the slowed mass loss at the late stages of decomposition.

First evidences that the ectomycorrhizal fungus Paxillus involutus mobilizes nitrogen and carbon from saprotrophic fungus necromass

Fungal succession in rotting wood shows a surprising abundance of ectomycorrhizal (EM) fungi during the late decomposition stages. To better understand the links between EM fungi and saprotrophic fungi, we investigated the potential capacities of the EM fungus Paxillus involutus to mobilize nutrients from necromass of Postia placenta, a wood rot fungus, and to transfer these elements to its host tree. In this aim, we used pure cultures of P. involutus in the presence of labelled Postia necromass (15 N/13 C) as nutrient source, and a monoxenic mycorrhized pine experiment composed of labelled Postia necromass and P. involutus culture in interaction with pine seedlings. The isotopic labelling was measured in both experiments. In pure culture, P. involutus was able to mobilize N, but C as well, from the Postia necromass. In the symbiotic interaction experiment, we measured high 15 N enrichments in all plant and fungal compartments. Interestingly, 13 C remains mainly in the mycelium and mycorrhizas, demonstrating that the EM fungus transferred essentially N from the necromass to the tree. These observations reveal that fungal organic matter could represent a significant N source for EM fungi and trees, but also a C source for mycorrhizal fungi, including in symbiotic lifestyle.