Later Stages Of Decomposition Research Articles

Immobilization of heavy metals during aquatic and terrestrial litter decomposition in an alpine forest

Plant litter decomposition is an important pathway of heavy metal cycling in forested soil and watershed ecosystems globally, but is so far an overlooked aspects in the existing literature. To investigate the temporal dynamics of heavy metals in decomposing litter, we conducted a two-year field experiment using litterbag method across aquatic and terrestrial ecosystems in an alpine forest on the eastern Tibetan Plateau. Using multigroup comparisons of structural equation modeling with different litter mass-loss intervals, we assessed the direct and indirect effects of several biotic and abiotic factors on the release rates of lead (Pb), cadmium (Cd), and chromium (Cr). Results suggested that both the concentrations and amounts of Pb, Cd, and Cr increased during litter decomposition regardless of ecosystem type and litter species, showing an immobilization pattern. The release rates of Pb, Cd, or Cr shared a common hierarchy of drivers across aquatic and terrestrial ecosystems, with environmental factors and initial litter quality having both direct and indirect effects, and the effects of initial litter quality gained importance in the late decomposition stages. However, litter chemical dynamics and microbial diversity index have significant effects on release rates throughout the decomposition process. Our results are useful for better understanding heavy metal fluxes in aquatic and terrestrial ecosystems, and for predicting anthropogenic heavy metal pollution impacts on ecosystems. In addition, our results indicated that not only spatial but also temporal variability should be taken into consideration when addressing heavy metal dynamics accompanying litter decomposition process.

Thermal degradation kinetics of flame-retardant glass-fiber-reinforced polyamide 6T composites based on bridged DOPO derivatives

A novel phosphaphenanthrene oxide, based on bridged 9,10-dihrdro-9-oxa-10-phosphaphenamhrene-10-oxide (DOPO) derivatives (PN-DOPO), was synthesized and incorporated into glass-fiber-reinforced polyamide 6T (GFPA6T) composites. Moreover, a commercial product of aluminum diethyl-phosphinate (OP1230) was introduced as a comparison to examine the effects on the flame-retardant properties and thermal stabilities of GFPA6T. UL-94 test and cone calorimetry results displayed that PN-DOPO showed better flame retardancy of GFPA6T than OP1230. Scanning electronic microscopy results of the char residues after UL-94 test indicated that PN-DOPO promoted a compact char formation. More importantly, the activation energies and the kinetic parameters of the decomposition process were calculated through the Kissinger–Akahira–Sunose (K–A–S) and Flynn–Wall–Ozawa (F–W–O) methods, and the thermal degradation mechanism was studied with the Coats–Redfern method based on thermogravimetric analysis at multiple heating rates. The results demonstrated that the E values of GFPA6T/PN-DOPO at the early decomposition and the late decomposition are higher than those of GFPA6T and GFPA6T/OP1230, especially in the late decomposition stage. The fact indicates that the higher E value and more dense carbonization protection layer contribute to the superior flame retardancy of PN-DOPO for GFPA6T.

Temporal dynamics of phosphorus during aquatic and terrestrial litter decomposition in an alpine forest

Plant litter decomposition in forested soil and watershed is an important source of phosphorus (P) for plants in forest ecosystems. Understanding P dynamics during litter decomposition in forested aquatic and terrestrial ecosystems will be of great importance for better understanding nutrient cycling across forest landscape. However, despite massive studies addressing litter decomposition have been carried out, generalizations across aquatic and terrestrial ecosystems regarding the temporal dynamics of P loss during litter decomposition remain elusive. We conducted a two-year field experiment using litterbag method in both aquatic (streams and riparian zones) and terrestrial (forest floors) ecosystems in an alpine forest on the eastern Tibetan Plateau. By using multigroup comparisons of structural equation modeling (SEM) method with different litter mass-loss intervals, we explicitly assessed the direct and indirect effects of several biotic and abiotic drivers on P loss across different decomposition stages. The results suggested that (1) P concentration in decomposing litter showed similar patterns of early increase and later decrease across different species and ecosystems types; (2) P loss shared a common hierarchy of drivers across different ecosystems types, with litter chemical dynamics mainly having direct effects but environment and initial litter quality having both direct and indirect effects; (3) when assessing at the temporal scale, the effects of initial litter quality appeared to increase in late decomposition stages, while litter chemical dynamics showed consistent significant effects almost in all decomposition stages across aquatic and terrestrial ecosystems; (4) microbial diversity showed significant effects on P loss, but its effects were lower compared with other drivers. Our results highlight the importance of including spatiotemporal variations and indicate the possibility of integrating aquatic and terrestrial decomposition into a common framework for future construction of models that account for the temporal dynamics of P in decomposing litter.

Contrasting effects of ectomycorrhizal fungi on early and late stage decomposition in a boreal forest.

Symbiotic ectomycorrhizal fungi have received increasing attention as regulators of below-ground organic matter storage. They are proposed to promote organic matter accumulation by suppressing saprotrophs, but have also been suggested to play an active role in decomposition themselves. Here we show that exclusion of tree roots and associated ectomycorrhizal fungi in a boreal forest increased decomposition of surface litter by 11% by alleviating nitrogen limitation of saprotrophs-a "Gadgil effect". At the same time, root exclusion decreased Mn-peroxidase activity in the deeper mor layer by 91%. Our results show that ectomycorrhizal fungi may hamper short-term litter decomposition, but also support a crucial role of ectomycorrhizal fungi in driving long-term organic matter oxidation. These observations stress the importance of ectomycorrhizal fungi in regulation of below-ground organic matter accumulation. By different mechanisms they may either hamper or stimulate decomposition, depending upon stage of decomposition and location in the soil profile.

Integrating chemical, biological and soil fauna variables during beech leaf litter decay: A partial least squares approach for a comprehensive view of the decomposition process

Litter decomposition is an ecosystem process that is regulated by a multitude of factors and by their complex interactions. Current decomposition paradigms do not always offer a coherent view of the process because it can be hardly understood without a thorough analysis of interacting factors. Thus, there is a need to further understand the mechanics of litter decay with a comprehensive approach, especially in temperate forest ecosystems where decomposition plays a crucial role in regulating them as source or sink of CO2. Therefore, the aim of this work was to identify the interactions between chemical, biological and soil fauna variables in order to discern driving variables and the changes in their interactions during long-time (1300 days) beech leaf litter decomposition. In order to investigate patterns of variation and co-variation within and between datasets, we used Two-block Partial Least Squares, helping us to interpret the decomposition process with a systemic approach. Our key findings showed that the decomposition process of beech litter in two Mediterranean forests was driven by litter quality at the beginning and in the later stages of decomposition, while edaphic and climatic factors were implied in the central steps, with a dramatic change of scenario around 2.5 years. Simultaneous and interacting changes in chemical variables, extracellular enzyme activities, and soil fauna were shown, with a significant role of lignocellulosic components and enzymes involved in their degradation, Mn residual weight, and abundance of Collembola.

Assessing the temporal dynamics of aquatic and terrestrial litter decomposition in an alpine forest

Abstract Litter decomposition supplies nutrients and energy within and among aquatic and terrestrial ecosystems. It is driven by several biotic and abiotic factors, the relative importance of which may change during litter decay. However, to date, very few studies have addressed the temporal dynamics of such factors across aquatic and terrestrial ecosystems, which limits our understanding of litter decomposition process. To assess the temporal dynamics of major abiotic and biotic litter decomposition drivers, we conducted a 2‐year field experiment to evaluate the losses of foliar litter carbon (C) and nitrogen (N) in alpine streams, riparian zones and forest floors. Environmental (soil, water and climatic) factors were continuously monitored, and incubated plant litter was sampled over time to assess temporal changes in litter chemistry and microbial diversity. We analysed sequential litter decomposition stages based on mass‐loss intervals and used structural equation modelling to disentangle the relative importance of each biotic and abiotic driver. Our results suggested that across the aquatic and terrestrial ecosystems, litter C and N loss was generally controlled by a common hierarchy of drivers: (a) Environment and initial litter quality regulated C and N loss via both direct and indirect effects, and their total effects were mainly significant in the early and late decomposition stages, respectively; (b) changes in litter chemistry significantly influenced litter decomposition throughout the decomposition process, mainly via direct effects; and (c) microbial diversity per se showed minimal effects on litter C and N loss. The identified common hierarchy of biotic and abiotic drivers and their direct and indirect effects on C and N loss at different decomposition stages across aquatic and terrestrial ecosystems indicates the possibility of integrating aquatic and terrestrial decomposition into a single framework for future construction of models accounting for temporal dynamics of litter decomposition. A plain language summary is available for this article.

Nitrogen enrichment regulates straw decomposition and its associated microbial community in a double-rice cropping system

Litter bag method was conducted to investigate the decomposition characteristics of rice straw (6000 kg ha−1) and its associated microbial community under different nitrogen (N) addition rates (0, 90, 180 and 270 kg N ha−1) under double-rice rotation. Generally, straw mass reduction and nutrient release of rice straw were faster in early stage of decomposition (0−14 days after decomposition), when easily-utilized carbohydrates and amines were the preferential substrates for involved decomposers. Straw-associated N-acetyl-glucosamidase and L-leucine aminopeptidase activities, which were higher under 180 and 270 kg N ha−1 addition, showed more activities in the early stage of decomposition. Gram-positive bacteria were the quantitatively predominant microorganisms, while fungi and actinomycetes played a key role in decomposing recalcitrant compounds in late decomposition stage. Straw residue at middle decomposition stage was associated with greater cbhI and GH48 abundance and was followed by stronger β-glucosidase, β-cellobiohydrolase and β-xylosidase activities. Although enzyme activities and cellulolytic gene abundances were enhanced by 180 and 270 kg N ha−1 application, microbial communities and metabolic capability associated with rice straw were grouped by sampling time rather than specific fertilizer treatments. Thus, we recommended 180 kg N ha−1 application should be the economical rate for the current 6000 kg ha−1 rice straw returning.

Fungal community structure of fallen pine and oak wood at different stages of decomposition in the Qinling Mountains, China

Historically, intense forest hazards have resulted in an increase in the quantity of fallen wood in the Qinling Mountains. Fallen wood has a decisive influence on the nutrient cycling, carbon budget and ecosystem biodiversity of forests, and fungi are essential for the decomposition of fallen wood. Moreover, decaying dead wood alters fungal communities. The development of high-throughput sequencing methods has facilitated the ongoing investigation of relevant molecular forest ecosystems with a focus on fungal communities. In this study, fallen wood and its associated fungal communities were compared at different stages of decomposition to evaluate relative species abundance and species diversity. The physical and chemical factors that alter fungal communities were also compared by performing correspondence analysis according to host tree species across all stages of decomposition. Tree species were the major source of differences in fungal community diversity at all decomposition stages, and fungal communities achieved the highest levels of diversity at the intermediate and late decomposition stages. Interactions between various physical and chemical factors and fungal communities shared the same regulatory mechanisms, and there was no tree species-specific influence. Improving our knowledge of wood-inhabiting fungal communities is crucial for forest ecosystem conservation.

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.

The role of bicarbonate anions in methotrexate degradation via UV/TiO2: Mechanisms, reactivity and increased toxicity

Bicarbonate anion (HCO3−) is a major constituent in wastewater and natural water matrices, and the aim of this study was to investigate its roles in the degradation of the antineoplastic agent methotrexate via UV/TiO2. A comprehensive investigation of reaction mechanisms was performed by conducting scavenger experiments and substructure reactivity and Microtox® toxicity tests. In the presence of HCO3−, the methotrexate degradation rate substantially increased, indicating the involvement of CO3−. The estimated second-order rate constants of methotrexate with CO3− and OH were 1.4 × 107 M−1 s−1 and 8.7 × 109 M−1 s−1, respectively. Both the valence hole (hvb+) and OH resulted in the generation of CO3−. Initial transformation pathways of methotrexate were proposed, including the addition of atomic oxygen, hydroxylation, deamination, CC cleavage and CN cleavage. CN cleavage at the aniline moiety (the N(13) position) is the primary decomposition pathway, leading to an aminopterin yield of 43%. CO3− preferentially reacted with the 4-aminobenzamide (ABZ) moiety and generated toxic byproducts during the later stages of decomposition, which was not observed in the UV/TiO2 system. The reactivity of the three methotrexate substructures decreased in the following order in the presence of HCO3−: ABZ ≫ DHP ≫ LG∼0; however, without HCO3−, the following order was observed: ABZ ∼ DHP > LG. The results of this work suggest that the increase in toxicity induced by the presence of HCO3− likely occurs in many other OH-based advanced oxidation processes in wastewater containing pharmaceutical cocktails with ABZ moieties.

Sugar cane straw left in the field during harvest: decomposition dynamics and composition changes

The understanding of sugar cane straw decomposition dynamics is essential for defining a sustainable rate of straw removal for bioenergy production without jeopardising soil functioning and other ecosystem services. Thus, we conducted a field study in south-east Brazil over 360 days to evaluate sugar cane straw decomposition and changes in its composition as affected by increasing initial straw amounts and management practices. The sugar cane straw amounts tested were: (1) 3.5 Mg ha–1 (i.e. 75% removal); (2) 7.0 Mg ha–1 (i.e. 50% removal); (3) 14.0 Mg ha–1 (i.e. no removal); and (4) 21.0 Mg ha–1 (i.e. no removal plus 50% of the extra straw left on the field). In addition, two management practices were studied for the reference straw amount (14 Mg ha–1), namely straw incorporation into the soil and irrigation with vinasse. The findings showed that dry mass (DM) loss increased logarithmically as a function of the initial amount left on the soil surface. An exponential curve efficiently described straw DM and C losses, in which more readily decomposable compounds are preferably consumed, leaving compounds that are more recalcitrant in the late stages of decomposition. After 1 year of decomposition, net straw C and N losses reached approximately 70% and 23% respectively for the highest initial straw amounts. Straw incorporation in the soil significantly accelerated the decomposition process (i.e. 86% DM loss after 1 year) compared with maintenance of straw on the soil surface (65% DM loss after 1 year), whereas irrigation with vinasse had little effect on decomposition (60% DM loss after 1 year). We conclude that straw decomposition data are an essential starting point for a better understanding of the environmental effects caused by straw removal and other management practices in sugar cane fields. This information can be used in models and integrated assessments towards a more sustainable sugar cane straw management for bioenergy production.

Litter mixture dominated by leaf litter of the invasive species, Flaveria bidentis, accelerates decomposition and favors nitrogen release.

In natural ecosystems, invasive plant litter is often mixed with that of native species, yet few studies have examined the decomposition dynamics of such mixtures, especially across different degrees of invasion. We conducted a 1-year litterbag experiment using leaf litters from the invasive species Flaveria bidentis (L.) and the dominant co-occurring native species, Setaria viridis (L.). Litters were allowed to decompose either separately or together at different ratios in a mothproof screen house. The mass loss of all litter mixtures was non-additive, and the direction and strength of effects varied with species ratio and decomposition stage. During the initial stages of decomposition, all mixtures had a neutral effect on the mass loss; however, at later stages of decomposition, mixtures containing more invasive litter had synergistic effects on mass loss. Importantly, an increase in F. bidentis litter with a lower C:N ratio in mixtures led to greater net release of N over time. These results highlight the importance of trait dissimilarity in determining the decomposition rates of litter mixtures and suggest that F. bidentis could further synchronize N release from litter as an invasion proceeds, potentially creating a positive feedback linked through invasion as the invader outcompetes the natives for nutrients. Our findings also demonstrate the importance of species composition as well as the identity of dominant species when considering how changes in plant community structure influence plant invasion.

Life in leaf litter: novel insights into community dynamics of bacteria and fungi during litter decomposition

Microorganisms play a crucial role in the biological decomposition of plant litter in terrestrial ecosystems. Due to the permanently changing litter quality during decomposition, studies of both fungi and bacteria at a fine taxonomic resolution are required during the whole process. Here we investigated microbial community succession in decomposing leaf litter of temperate beech forest using pyrotag sequencing of the bacterial 16S and the fungal internal transcribed spacer (ITS) rRNA genes. Our results reveal that both communities underwent rapid changes. Proteobacteria, Actinobacteria and Bacteroidetes dominated over the entire study period, but their taxonomic composition and abundances changed markedly among sampling dates. The fungal community also changed dynamically as decomposition progressed, with ascomycete fungi being increasingly replaced by basidiomycetes. We found a consistent and highly significant correlation between bacterial richness and fungal richness (R=0.76, P<0.001) and community structure (RM antel =0.85, P<0.001), providing evidence of coupled dynamics in the fungal and bacterial communities. A network analysis highlighted nonrandom co-occurrences among bacterial and fungal taxa as well as a shift in the cross-kingdom co-occurrence pattern of their communities from the early to the later stages of decomposition. During this process, macronutrients, micronutrients, C:N ratio and pH were significantly correlated with the fungal and bacterial communities, while bacterial richness positively correlated with three hydrolytic enzymes important for C, N and P acquisition. Overall, we provide evidence that the complex litter decay is the result of a dynamic cross-kingdom functional succession.

Microbial crop residue decomposition dynamics in organic and conventionally managed soils

Agricultural practices can influence soil microbial communities, which are the primary regulators of soil carbon and nutrient cycling processes. Differences in microbial community composition have the potential to affect the fate of carbon and nutrients during decomposition and may therefore influence the retention of C and provisioning of crop nutrients in agroecosystems. Long term management-induced shifts in microbial communities and resource availability may interact to affect the microbial utilization of fresh inputs of crop residues in the short term, with lasting impacts on soil C accrual and fertility. The objective of this study was to investigate whether long-term organic and conventional management resulted in differences in microbial residue decomposition. Soils under conventional and organic management planted with annual crops or with a mix of annual crops and three years of perennial alfalfa were collected from a long-term (19 y) field study in Saskatchewan, Canada and were incubated in the laboratory with and without 13C-labelled barley residues for 98d. We measured extracellular enzyme activities (EEAs) and the incorporation of crop residue-derived C within major microbial groups (fungi, actinobacteria, and Gram positive and negative bacteria) during decomposition. Total PLFA biomass and EEAs were highest in soils from the conventional-annual system, similar between the conventional and organic perennial systems, and similar or lowest in the organic-annual system. Crop residue additions alleviated these differences; that is, in residue-amended soils total PLFA biomass, EEAs, and the abundance of the fungal biomarker increased in the organic systems compared to the unamended soils to become similar to the conventional systems. In contrast, residue additions induced small or no changes in biomass and EEAs in the conventional-annual soils. Using 13C-PLFA-SIP we showed that the general pattern of microbial succession during decomposition was similar among soils, but that fungi and especially actinobacteria were relatively more dominant in organic compared to conventionally managed soils during early and later stages of decomposition, respectively. Thus, shifts in the decomposer community composition were greater in soils originating from organic management, possibly as a result of larger changes in resource availability during the incubation that advanced the rate of microbial succession. This may reinforce long term differences in SOC quality and nutrient availability between management regimes. Organically-managed cropping systems are particularly reliant on biological cycling of organic nutrients to support crop growth. This work reinforces the importance of adequate crop residue returns for maintaining soil function, particularly where external organic amendments are not applied to balance nutrients exported as crop products.

Volatile Organic Compounds of Decaying Piglet Cadavers Perceived by Nicrophorus vespilloides.

In the necrophagous burying beetle Nicrophorus vespilloides (Coleoptera: Silphidae), cadaver preference appears to depend on cadaver size and on the maturity of the beetle. We previously showed that newly emerged females with immature ovaries prefer later stages of decomposition of large cadavers. Our present aim is the determination of specific chemical compounds involved in the discrimination of cadaveric odor bouquets and the recognition of specific stages of decomposition. We used headspace samples of maggot-infested piglet cadavers at various decomposition stages and performed gas chromatography coupled with electroantennography (GC-EAD) to record 45 EAD-active compounds. Using GC coupled with mass spectrometry, we identified 13 of the EAD-active compounds. The headspace of the fresh decomposition stage was characterized mainly by high relative amounts of trimethylpyrazine. High relative amounts of dimethyl trisulfide were characteristic of bloated, post-bloating, and advanced decay stages. The advanced decay and dry remains stages were dominated by high relative amounts of phenol. Statistically, this compound had the highest impact on discrimination between the fresh decomposition stage, which is important for mature burying beetles for reproduction, and the advanced decay stage, which is nutritionally more attractive for newly emerged beetles. Phenol might, therefore, function as a key substance for newly emerged female burying beetles, so that they can locate suitable cadavers for feeding to maturation.

CAUSES OF DEATH IN CHILDREN AND ADOLESCENTS ACCORDING TO THE MATERIAL OF THE INSTITUTE OF FORENSIC MEDICINE IN NIŠ FOR THE PERIOD 2003-2012

This paper examines the causes of death in children and adolescents for a ten-year period (2003-2012) according to data from the autopsy records of the Institute of Forensic Medicine in Nis. The causes of death (natural or violent) were analyzed in relation to sex, age, season, and environment (rural and urban areas), socio-economic and living conditions, and the number of children in the family. The results obtained were statistically analyzed, plotted and discussed in relation to data from the literature available. Regarding the autopsy cases of children and adolescents (194), 106 (54.63%) were the cases of violent causes of death and 87 were the cases (44.84%) of natural causes of death, while in one case the cause of death could not be determined due to late-stage decomposition alterations of the corpse. The most common natural causes of death were asphyxia, immaturity of the fetus and acute pneumonia. Most common causes of violent death were contusion of the brain, destruction of the brain and brainstem, polytrauma, and bleeding. Acta Medica Medianae 2016;55(2):65-70.

Understanding the effectiveness of litter from tropical dry forests for the restoration of degraded lands

Ecological restoration of degraded lands is of great importance for sustainable development of environment. In order to determine the biological potential of species to aid soil restoration, it is necessary to evaluate litter production, its temporal variation, their rate of decomposition and nutrient release. In this study therefore, we examined patterns of litter fall production, quality of litter, and decomposition pattern of selected multipurpose tree species, viz., Shorea robusta, Tectona grandis, Hardwickia binnata, Butea monosperma and dry mix trees in the dry tropical deciduous forest of vindhyan highland, India. Average litter fall was 4.76±1.21Mgha−1yr−1 and varied significantly among species as follows dry mix>S. robusta>T. grandis>B. monosperma>H. binnata. Leaf litter comprised of the highest fraction in all the species. In the litter bag experiment, mass loss and mineralization rate were significantly different among the species and were assumed to be effected by the initial chemical composition of the litter. Similar release of carbon and nitrogen was studied at monthly interval in the same litter bags. Annual relative mass loss was evidently higher in the dry mix trees, H. binnata and B. monosperma followed by T. grandis and S. robusta. Nitrogen percentage increased significantly as decomposition progressed for all the species and a decrease was observed at the later stages of decomposition. The carbon percentage during decomposition showed a significant decrease throughout the study. Species with higher initial concentration of nitrogen and comparatively lower initial lignin, lignin:N and C:N ratio litter decomposed at faster rate than the other selected species, viz., (dry mix>H. binnata>B. monosperma>T. grandis>S. robusta). Mass loss showed significant positive correlation with N mineralization rate. Carbon, lignin, lignin:N and C:N showed significant negative correlations with decay rate. The study recommended that for biological restoration of soil mix plantation would be the most appropriate. While H. binnata and B. monosperma individually shows the better results for the rapid recovery of degraded lands as their rate of litter decomposition is relatively faster than T. grandis and S. robusta. Although, T. grandis and S. robusta species shows higher litter production but their release of nutrient is slow in to the soil. The faster decomposition increases the more release of nutrient in to the soil and thus increases the rate of organic matter turnover and enhances nutrient cycling.

Leaf litter C and N cycling from a deciduous permanent crop

ABSTRACTOur understanding of leaf litter carbon (C) and nitrogen (N) cycling and its effects on N management of deciduous permanent crops is limited. In a 30-day laboratory incubation, we compared soil respiration and changes in mineral N [ammonium (NH4+-N) + nitrate (NO3–-N)], microbial biomass nitrogen (MBN), total organic carbon (TOC) and total non-extractable organic nitrogen (TON) between a control soil at 15N natural abundance (δ15N = 1.08‰) without leaf litter and a treatment with the same soil, but with almond (Prunus dulcis (Mill.) D.A. Webb) leaf litter that was also enriched in 15N (δ15N = 213‰). Furthermore, a two-end member isotope mixing model was used to identify the source of N in mineral N, MBN and TON pools as either soil or leaf litter. Over 30 d, control and treatment TOC pools decreased while the TON pool increased for the treatment and decreased for the control. Greater soil respiration and significantly lower (p < 0.05) mineral N from 3 to 15 d and significantly greater MBN from 10 to 30 d were observed for the treatment compared to the control. After 30 d, soil-sourced mineral N was significantly greater for the treatment compared to the control. Combined mineral N and MBN pools derived from leaf litter followed a positive linear trend (R2 = 0.75) at a rate of 1.39 μg N g−1 soil day−1. These results suggest early-stage decomposition of leaf litter leads to N immobilization followed by greater N mineralization during later stages of decomposition. Direct observations of leaf litter C and N cycling assists with quantifying soil N retention and availability in orchard N budgets.

The effect of Jatropha curcas L. leaf litter decomposition on soil carbon and nitrogen status and bacterial community structure (Senegal)

The cultivation of Jatropha curcas L. as a biodiesel feedstock has been encouraged in Senegal to reduce dependence on fossil fuels and mitigate the effects of climate change. J. curcasis is a poisonous plant which sheds its leaves during the dry season. Although the leaves are toxic for animals, they can help to recycle soil organic matter. This study set out to determine the effect of the decomposition dynamics of green and senescent J. curcas leaves on the soil C and N contents and on the structure of the bacterial community. Leaf litter decomposition was studied for 4 months by laboratory incubation and samples were taken at the start of incubation and at 3, 28, 56, 90 and 120 days. Green leaves had a higher N content, higher concentrations of water soluble compounds and hemicelluloses, but a lower C:N ratio and lignin content than senescent leaves regardless of the cultivar. The cultivar, the type of litter and the interaction between them, all had a significant effect on the soil N content (p<0.0001, R2=0.995) and C:N ratio (p<0.0001, R2=0.998). However, the cultivar was the only factor that affected the leaf C content (p<0.05, R2=0.624). The initial N content explained the N-NH4+ mineralization at the start of decomposition and the initial lignin content explained the N-NH4+ mineralization at later stages of decomposition. The recalcitrant C content in the green leaves was estimated as being between 70.01 and 73.33% of the total C content and between 72 and 77.33% in senescent leaves. This suggests that Jatropha litter may contribute significantly to soil C sequestration. The results indicate that the soil had higher bacterial diversity in the later stages of litter decomposition, for both types of litter and all cultivars. Key words: Jatropha curcas L., leaf litter, nitrogen mineralization, carbon mineralization, bacterial community, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE), Senegal.

Exogenous nutrients and carbon resource change the responses of soil organic matter decomposition and nitrogen immobilization to nitrogen deposition.

It is unclear whether exogenous nutrients and carbon (C) additions alter substrate immobilization to deposited nitrogen (N) during decomposition. In this study, we used laboratory microcosm experiments and 15N isotope tracer techniques with five different treatments including N addition, N+non-N nutrients addition, N+C addition, N+non-N nutrients+C addition and control, to investigate the coupling effects of non-N nutrients, C addition and N deposition on forest floor decomposition in subtropical China. The results indicated that N deposition inhibited soil organic matter and litter decomposition by 66% and 38%, respectively. Soil immobilized 15N following N addition was lowest among treatments. Litter 15N immobilized following N addition was significantly higher and lower than that of combined treatments during the early and late decomposition stage, respectively. Both soil and litter extractable mineral N were lower in combined treatments than in N addition treatment. Since soil N immobilization and litter N release were respectively enhanced and inhibited with elevated non-N nutrient and C resources, it can be speculated that the N leaching due to N deposition decreases with increasing nutrient and C resources. This study should advance our understanding of how forests responds the elevated N deposition.