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

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

Photodegradation of plant litter in the Sonoran Desert varies by litter type and age

Predicting litter decay rates in arid systems has proved elusive and sunlight (photodegradation) is a potentially important but poorly understood driver of litter decay in these systems. We placed three litter types (Cynodon dactylon, Larrea tridentata leaves, and L. tridentata twigs) in envelopes whose tops either transmitted all solar radiation, filtered UV-B, filtered all UV, or filtered all UV and visible solar radiation, on the soil surface of the Sonoran Desert and assessed mass loss over 14 months. Regardless of treatment, final mass loss was greatest in C. dactylon litter and least in L. tridentata twig litter, consistent with initial litter characteristics of presumed litter quality; C. dactylon had the lowest lignin concentration and lignin:N, and the highest cellulose:lignin and area:mass. Compared to litter in sunlight, excluding solar UV, or UV-B, slowed mass loss of all 3 litter types, and UV-B appeared more effective than UV-A in photodegradation. The relative contribution of UV photodegradation to mass loss increased with litter age. After 14 months, litter exposed to solar UV lost 1.2 (C. dactylon), 1.3 (L. tridentata twigs) and 1.4 (L. tridentata leaves) times as much mass as litter not exposed to UV radiation. The relative contribution of UV photodegradation to mass loss increased with the initial C:N ratio of litter, but was not related to initial lignin concentration or optical properties (i.e. UV and visible absorbance and transmittance) of litter. Within all litter type by treatment combinations, there was a strong positive correlation between litter mass loss and ash concentration. In some cases, a discontinuity in this relationship was detected, suggesting a threshold ash concentration, above which further mass loss was negligible. We expected these thresholds to be most prevalent in sunlight, because soil films could prevent sunlight from reaching litter and thereby minimize photodegradation. Contrary to expectations, thresholds were more common in shade or UV filter treatments, suggesting that reductions in photodegradation attributable to soil films were not typically responsible. The effect of shading, which likely enhanced microbial degradation via higher relative humidity due to lower temperatures, depended on litter type and time. Compared to litter in sunlight, mass loss of shaded litter was greater over the initial 3 months in all litter types, illustrating that microbial degradation in shade was greater than photodegradation in sunlight. These differences in mass loss between shaded and sunlit litter increased over the 14 month experiment in L. tridentata twigs, declined in L. tridentata leaves, and disappeared within 6 months in C. dactylon, illustrating that the timing of this shift in the dominance of photodegradation versus microbial degradation was highly dependent on litter type. In a second experiment, we reduced microclimate differences among sun and shade treatments, pre-sterilized litter to reduce microbial degradation, and examined the mass loss of young and old and L. tridentata leaf litter after 53 days outdoors. Consistent with our first experiment, mass loss attributable to photodegradation was greater in old than young litter. Unsterilized litter exposed to sunlight (UV and visible) lost 1.3 (young) and 1.5 (old) times as much mass as shaded litter. Pre-sterilized litter exposed to sunlight lost 11.4 (young litter) and 45.9 (old litter) times as much mass as shaded litter. These large differences in pre-sterilized litter were the result of the very small mass loss of shaded litter (≤0.2%), together with modest losses of sunlit litter (<5%). Taken together, our findings suggest that as litter aged, microbial degradation became a weaker driver of mass loss, while photodegradation became stronger.     

森林凋落物分解研究进展

 森林凋落物分解是森林生态系统养分生物循环的重要环节,而分解过程中所释放的CO2是全球碳素收支的重要组分,开展森林凋落物分解研究是充分认识森林生态系统结构和功能的基础。研究认为:凋落物分解的预测指标可分为3类,即环境指标(如实际蒸散量)、凋落物物理质量(如叶抗张强度)和化学质量指标(如C/N比、木质素/N比和C/P比等);凋落物分解过程中养分释放机制极其复杂,养分动态模式主要有淋溶—释放、淋溶—富集—释放和富集—释放3种,并因凋落物种类、分解阶段和元素本身性质的不同而异;凋落物混合分解并非单一树种分解的简单叠加,因树种组成和比例不同,基质的化学组成会发生变化,从而影响分解者的多样性、丰富度和生理活性,进而直接和间接地影响其分解速率;凋落物混合分解中可能存在无效应、促进效应和抑制效应;现有的研究结果显示,凋落物混合分解的适宜比例应与群落中不同树种的种群比例相一致;CO2浓度升高不仅影响凋落物的化学性质,而且与分解环境中土壤的生物活性密切相关,但CO2浓度升高并不改变凋落物质量与分解速率之间的关系;越来越多的研究显示,CO2浓度升高的环境下,植物群落的物种组成会产生变化,这种变化对养分循环速率的影响远大于单纯大气CO2浓度变化的影响。     

Interactions between litter quality, decomposition and soil fertility: a laboratory study

Leaf litters from beech (Fagus sylvatica L.) and oak (Quercus robur L.) trees were collected from mixed, deciduous woodlands growing on three soil types that varied in mineral nutrient concentrations and N mineralisation potential. Litter quality, including %N, %Mn, %P, acid detergent fibre, cellulose, Klason lignin, phenylpropanoid constituents of lignin, hexose and pentose sugar (mainly from hemicelluloses) varied within species according to soil type. However, oak and beech showed the opposite responses to soil nutrient status for most of these variables. The litters were incubated in the laboratory for 12 months (at 18 °C and constant moisture) on beds of forest floor material from two soils of contrasting high nutrient material (HNM) or low nutrient material (LNM) nutrient status to investigate litter quality and substrate interactions. At 4, 8 and 12 months there were significant differences in mass losses from oak and beech litters from all sites, and for each litter type exposed to the HNM and LMN soils. At 12 months mean mass losses were higher for HNM treatment (38.7% oak, 27.8% beech) than for the LNM treatment (30.6% oak, 25.5% beech). However, the beech and oak litters from the different sites consistently responded in opposite ways on the same soil treatment reflecting site-related effects on litter quality. Initial concentration of Klason lignin was the best predictor for mass losses from litter species and litter types. Intra-specific variation in rates of litter decomposition of beech and oak litters from different sites, and differences in their interactions with the two forest floor materials, illustrate the complexities of proximate controls on decomposition that are often masked in system-level studies.     

Effects of tree species and topography on soil chemistry, litter quality, and decomposition in Northeast Turkey

Leaf litters from beech (Fagus orientalis Lipsky.) and oak (Quercus robur L.), and needle litters from fir (Abies nordmanniana Spach.) and pine (Pinus sylvestris L.) trees were collected from north-facing site and south-facing site and at three slope positions (top, middle and bottom) on each aspect that varied in soil chemical characteristics (soil pH, cation exchange capacity and base saturation). The litters were analysed for initial total carbon, nitrogen, acid detergent fibre, lignin and cellulose concentrations. Nitrogen, acid detergent fibre and lignin concentrations and carbon:nitrogen and lignin:nitrogen ratios varied significantly within and between species according to soil chemical characteristics on aspects and slope positions. Litter decomposition was studied in the field using the litterbag technique. The litters were placed on two aspects and at three slopes on each aspect in October 2001, and were sampled every 6-month for 2 years. The main effects of aspect, species and slope position on decomposition rates were all statistically significant. Oak leaf litter showed highest decomposition rates, followed by pine, fir and beech litter, and the litters placed on north-facing site decomposed faster than those on the south-facing site. The litters placed at the top slope position decomposed slower than at those at either the bottom or middle positions. Initial lignin concentrations explained most of the variation in decomposition rates between species, and within species for the aspects and the slope positions, but the explained variance showed differences between aspects and slope positions. This result illustrates the important point that litter quality may define the potential rates of microbial decomposition but these are significantly influenced by the biotic and abiotic environment in which decomposition takes place.     

Decomposition of tree leaf litter and crop residues from ginkgo agroforestry systems in Eastern China: an in situ study

Purpose

Litter decomposition is a crucial biogeochemical process linking nutrient cycling and carbon (C) storage in ecosystems, but few studies have investigated this process in agroforestry systems, where tree leaf litter is mixed with intercrop residues.

Materials and methods

A 360-day in situ litter bag decomposition experiment was conducted in three ginkgo (Ginkgo biloba L.) plantation systems (a ginkgo-corn (Zea mays L.)-wheat (Triticum aestivum L.) system, ginkgo-rape (Brassica napus L.)-soybean (Glycine max (L.) Merr.) system, and pure ginkgo system).

Results and discussion

Ginkgo leaves decomposed fastest in the ginkgo-corn-wheat system, followed by the ginkgo-soybean-rape system, and the pure ginkgo system. Among all litter species, corn leaves and a ginkgo-corn mixture in the ginkgo-corn-wheat system decomposed fastest and wheat straw most slowly. The Olson’s litter exponential decay model showed the same results; approximately 9 months and slightly less than 27 months was required to decompose 50 and 95% of the litter, respectively. Compared to single-species litter, mixed litters accelerated litter decomposition, except for the ginkgo-wheat mixture. Litter nitrogen (N) loss varied dramatically among litter species during the 360-day in situ incubation.

Conclusions

The agroforestry system, litter quality, and mixed effects play important roles in litter decomposition. The Ca content, organic carbon, and living vegetation should be taken into account when studying litter decomposition in agroforestry. Analysis during the litter decomposition process clearly indicated that litter N loss changes dramatically.

     

Direct and indirect effects of nitrogen deposition on litter decomposition

Elevated nitrogen (N) deposition can affect litter decomposition directly, by raising soil N availability and the quantity and quality of litter inputs, and indirectly by altering plant community composition. We investigated the importance of these controls on litter decomposition using litter bags placed in annual herb based microcosm ecosystems that had been subject to two rates of N deposition (which raised soil inorganic N availability and stimulated litter inputs) and two planting regimes, namely the plant species compositions of low and high N deposition environments. In each microcosm, we harvested litter bags of 10 annual plant species, over an 8-week period, to determine mass loss from decomposition. Our data showed that species differed greatly in their decomposability, but that these differences were unlikely to affect decomposition at the ecosystem level because there was no correlation between a species’ decomposability and its response to N deposition (measured as population seed production under high N, relative to low N, deposition). Litter mass loss was ～2% greater in high N deposition microcosms. Using a comprehensive set of measurements of the microcosm soil environments, we found that the most statistically likely explanation for this effect was increased soil enzyme activity (cellobiosidase, β-glucosidase and β-xylosidase), which appears to have occurred in response to a combination of raised soil inorganic N availability and stimulated litter inputs. Our data indicate that direct effects of N deposition on litter input and soil N availability significantly affected decomposition but indirect effects did not. We argue that indirect effects of changes to plant species composition could be stronger in natural ecosystems, which often contain a greater diversity of plant functional types than those considered here.     

Litter decomposition in fynbos vegetation,South Africa

The Western Cape of South Africa is characterized by the hyperdiverse vegetation of the Fynbos biome. Typical fynbos vegetation is a fire-adapted sclerophyllous Mediterranean-type ecosystem on poor, sandy or stony soils. It is characterized by plants with low nutrient content producing slowly decomposing litter. Fire is recognized as a major factor for carbon and nutrient cycling in this vegetation type. However, knowledge of biological decomposition processes in this biome is limited. We used litter-bags to measure mass loss and changes in chemical composition in litter from three species representing characteristic taxa in fynbos, a Protea exima hybrid, Erica multumbellifera, and Restio multiflorus, during approximately 180 days. In addition, we used a standard litter of a species with high nutrient content, Galenia africana, and a mixture of Protea and Erica. We compare our results with a previous study from renosterveld including the geophyte Watsonia borbonica, which occurs in both vegetation types and occurs commonly in the study area. We found that decomposition rate among the true fynbos plant species P. exima, E. multumbellifera, R. multiflorus and W. borbonica varied almost eight-fold. Litter decomposition was strongly correlated to litter stoichiometry, i.e. C/N and C/P-ratios. Most litters accumulated one or several nutrients during the study period. The mixture of litters decomposed faster than expected from the results of each litter separately. Our study indicates that biological decomposition may be more important for carbon and nutrient cycling in fynbos than previously thought. These results are in accordance with recent studies showing large variation in plant litter quality within vegetation types and biomes. Such large variation in litter quality and decomposition rate suggests that some generalisations about ecosystem processes in the fynbos may need reevaluation.     

土壤微生物群落结构对凋落物组成变化的响应

凋落物分解是陆地生态系统养分循环的关键过程,明确凋落物多样性如何影响土壤微生物群落构成和多度,继而潜在地改变凋落物分解的微生物学机制有助于认识生物多样性和森林生态系统功能的关系。通过小盆模拟试验,应用磷脂脂肪酸谱图的方法研究了我国南方红壤丘陵区典型物种马尾松和湿地松的凋落物分别与白栎和青冈的凋落物混合,与单一针叶凋落物分解时相比,针阔混合凋落物分解过程中土壤微生物群落结构的变化,结果显示:(1)针阔混合凋落物分解时土壤微生物群落磷脂脂肪酸(Phospholipidfatty acids,PLFA)总量低于单一针叶处理,细菌和放线菌的相对多度高于单一针叶处理,真菌则相反,群落真菌/细菌低于单一针叶处理,土壤微生物生物量的差异主要来自于真菌;(2)主成分分析表明:针阔混合凋落物分解与单一针叶凋落物分解的土壤微生物群落结构差异显著,两个时期(分解9个月和18个月)主成分一分别可以解释65.74%和89.63%的变异,第一主成分主要包括18∶2ω6,9、18∶1ω9c、17∶0和10Me18∶0等磷脂脂肪酸;(3)土壤微生物群落结构受凋落物初始C/N和木质素/N调控,土壤微生物群落细菌的相对多度与凋落物初始C/N和木质素/N显著负相关,真菌则与凋落物初始C/N和木质素/N显著正相关,群落真菌/细菌与凋落物初始C/N和木质素/N显著正相关。针阔凋落物混合分解通过改变凋落物C/N和木质素/N,提供了对分解者更为有利的微环境。     

Decomposition of black locust and black pine leaf litter in two coeval forest stands on Mount Vesuvius and dynamics of organic components assessed through proximate analysis and NMR spectroscopy

Litter quality is an important determinant of soil organic matter formation. Changes of organic components were investigated along decomposition of black locust (Robinia pseudoacacia L.) leaf litter and black pine (Pinus nigra Arn.) needle litter in the native adjacent coeval forest stands. To this purpose, data from proximate analyses were compared with those from CPMAS ¹³C NMR. Newly shed leaf litter of black locust had significantly higher concentrations of ADSS (acid detergent soluble substances) as well as lower concentrations of cellulose and AUR (acid unhydrolyzable residues that include lignin) and higher AUR-to-Cellulose ratio than that of black pine. The ¹³C CPMAS NMR spectra of newly shed leaf litter of black locust and black pine revealed that O-Alkyl-C components (including cellulose and hemicelluloses) accounted, respectively, for 53.8% and 61.4% of the total area of the spectra. All other C fractions were relatively more abundant in black locust than in black pine. Within individual sampling periods, relationships between residual litter mass and concentrations of ADSS, cellulose and AUR were examined, as were relationships between residual litter C and NMR fractions. Four periods were defined based on the slopes of the decomposition curve, with the length of period I defined by the start of a net decrease of AUR. Proximate analyses and NMR data showed changes in chemical composition over the decomposition process, as well as changes in decay rates of the residues, following different paths in the two litters. ADSS decayed faster in black locust litter; in contrast cellulose and AUR decayed faster in that of black pine. AUR concentration increased in both litters during decomposition; however, compared to black pine, the remaining litter of black locust was richer in AUR, despite the lower initial concentration, and had a higher AUR-to-Cellulose ratio. Phenol-C and Aryl-C decayed faster in black locust litter, while Alkyl-C decayed faster in that of black pine. In both litters, mass loss in periods was negatively correlated to concentration of AUR at the start of the periods. C loss in periods was negatively correlated to the concentration at the start of the periods of MC-to-PC (an index of lignin content) in black locust litter and positively correlated to Alkyl-C and O-Alkyl-C in that of black pine. Phenol-C, O-Alkyl-C and Aryl-C were the most decomposable C fractions in black locust. O-Alkyl-C and Alkyl-C were the most decomposable C fractions in black pine. Limit value was lower in black pine than in black locust. Consequently the different pattern of litter decomposition can affect the size of C sequestration in the forest floor and the quality of accumulated organic carbon.     

The arthropods associated with the decomposition of some common grass and weed species in the soil

The arthropod fauna associated with the decomposition of herbage of various species on the surface of the soil was studied. Litter of Rumex, Urtica, Ranunculus, Senecio and Lolium disappeared rapidly at first and thereafter at a slower rate. Dactylis disappeared more slowly than the other litters over the first 6$\text{1}\text{2}$ months but its rate of disappearance thereafter was greater than that of the other species. There were quantitative and qualitative differences between the microarthropod communities associated with the various litters. Highest populations of microarthropods were recorded from Dactylis. Dactylis and Lolium were the most similar in the species composition of their faunas. Changes occurred in the relative abundance of various arthropod groups and species during the course of decomposition in all litters.     

Decomposition of Alder,Ash, and Poplar Litter in a Mediterranean Riverine Area

Abstract

Litter decomposition dynamics of three Mediterranean riverine species [Alnus glutinosa (L.) Gaertn, Fraxinus angustifolia Vahl., and Populus x hybrida] was studied in a 2‐year experiment in the province of Guadalajara (Spain) using the litterbag technique. Decay rates of the litter were estimated by fitting a single exponential model to the litter decomposition data. At the end of the experiment (after 485 days), the remaining litter necromass varied in the following order: Populus x hybrida>Alnus glutinosa>Fraxinus angustifolia. Litter of the three species was fast degraded; ash litter was almost totally degraded at the end of the experiment. Alder had the highest concentrations of total nitrogen and ammonium in litter, and its pattern of degradation and release to the system was different to the other two litters. This could influence the soil nutrient contents in each system as was indicated by the soil nutrient values.     

Effects of nitrogen addition and litter properties on litter decomposition and enzyme activities of individual fungi

Litter decomposition is an important process of C and N cycling in the soil. Variation in the response of litter decomposition to nitrogen (N) addition (positive, negative or neutral) has been observed in many field studies. However, mechanism about variability in individual fungal species response to N addition has not yet been well demonstrated in the literature. Therefore, the objective of this study was to investigate the effects of N addition and litter chemistry properties on litter decomposition and enzyme activities of individual fungi. Three fungal species (Penicillium, Aspergillus, and Trichoderma) were isolated from a subtropical mixed forest soil. An incubation experiment was conducted using the individual fungi with two types of litter (leaf of Pinus massoniana and needle of Cryptocarya chinensis) and different N addition levels (0, 50 and 100 for N-deficient treatments, and 500 and 1000 μg N for N-excessive treatments). Cumulative CO₂-C, enzyme activities, and lignin and cellulose loss were measured during the incubation period of 60 days. Litter decomposition and enzyme activities significantly varied with the fungal species, while the N addition and litter types greatly affected fungal enzyme activities. The N treatments significantly increased lignin-rich needle decomposition by lignocellulose decomposers (Penicillium and Aspergillus) but did not affect their leaf decomposition. On the contrary, The N treatments stimulated leaf decomposition by cellulolytic species (Trichoderma) but did not affect its needle decomposition. Correlation analysis showed that lignin in the litter was the key component to affect litter decomposition. Activities of N-acetyl-β-glucosaminidase and phenol oxidase were both positively correlated to litter decomposition. The fungi (Penicillium and Aspergillus) with higher production of N-acetyl-β-glucosaminidase showed higher litter decomposition ability. The low N addition levels stimulated Penicillium and Aspergillus litter decomposition, but they still required more N source (e.g., litter N source) to support decomposition. Depressed fungal litter N uptake (lower N-acetyl-β-glucosaminidase activities) only occurred at the highest N addition level. Litter decomposition of Trichoderma depended more on external N and its litter decomposition capability was the lowest among the three species.     

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.     

Nonadditive effects of litter mixtures on decomposition and correlation with initial litter N and P concentrations in grassland plant species of northern China

We studied the occurrence of nonadditive effects of litter mixtures on the decomposition (the deviation of decomposition rate of litter mixtures from the expected values based on the arithmetic means of individual litter types) of litters from three plant species (i.e., Stipa krylovii Roshev., Artemisia frigida Willd., and Allium bidentatum Fisch. ex Prokh. & Ikonn.-Gal.) endemic to the grassland ecosystems of Inner Mongolia, northern China and the possible role of initial litter N and P on such effects. We mixed litters of the same plant species that differed in N and P concentrations (four gradients for each species) in litterbags and measured mass losses of these paired mixtures after 30 and 80 days under field conditions. We found the occurrence of positive, nonadditive effects of litter mixtures and showed that the magnitude of the nonadditive effects were related to the relative difference in the initial litter N and P concentrations of the paired litters.     

Differential response of ectomycorrhizal and saprotrophic fungal mycelium from coniferous forest soils to selected monoterpenes

The mycelia of saprotrophic (SP) and ectomycorrhizal (ECM) fungi occur throughout the upper soil horizons in coniferous forests and could therefore be exposed to high concentrations of monoterpenes occurring in the needle litter of some tree species.Monoterpenes are mycotoxic and could potentially affect fungi that are exposed to them in the litter layers. In order to investigate whether monoterpenes typical of coniferous litters could influence fungal communities, we analysed the monoterpene content of freshly fallen needles of Pinus sylvestris, Picea abies and Picea sitchensis. The most abundant monoterpenes were found to be α-pinene, β-pinene and 3-carene. We evaluated the effects of these three monoterpene vapours on the biomass production of 23 SP isolates and 16 ECM isolates. Overall, 75% of ECM isolates and 26% of SP isolates were significantly inhibited by at least one of the monoterpene treatments and both intra- and inter-specific variations in response were observed.Monoterpene concentrations are highest in surface litters. The differential effects on fungal taxa may influence the spatial and temporal distribution of fungal community composition, indirectly affecting decomposition and nutrient cycling, the fundamental ecosystem processes in which fungi have a key role in coniferous forest soils.     

Litter decomposition and nutrient release in relation to atmospheric deposition of S and N in a dry tropical region

Temporal and spatial variations in litterfall, leaf litter decomposition and nutrient release were quantified along an air pollution gradient around an industrial area in a dry tropical region of India. Significant differences were found in litterfall between the sites. Litter decomposition rates also significantly varied among the study sites. Litter decomposition was faster at sites away from the industrial region with coal-fired power plants. The concentrations of N and P increased, whereas that of Ca and SO₄-S decreased in decomposing litter over time. The nutrient release pattern was also modified by atmospheric deposition. Concentrations of SO₂ and NO₂ were negatively correlated with relative mass loss. Turnover time of nutrients, except SO₄-S in decomposing litter was maximal at the site receiving highest atmospheric depositions. The study documents that industrial emissions significantly modified nutrient cycling in adjacent terrestrial ecosystems.     

Carbon and nitrogen transfer in leaf litter mixtures

The decomposition rate of litter mixtures can differ from that expected on the basis of the decomposition rate of the individual components. This difference may be linked to nitrogen (N) transfer from high-N to low-N components. Transfer of N is probably also associated with transfer of C, but the extent and direction of this C transfer are unknown. This study examined transfer and loss in laboratory microcosms of C and N from two mixed litter species (Scots pine, Pinus sylvestris L. and maize, Zea mays L.), which have natural isotopic differences in ¹³C. Half the material was ¹⁵N-labelled and the plants were fertilised or unfertilised. Substantial bidirectional transfer of C and N occurred between the litters, with net transfer of C from pine to maize litter and net transfer of N from high-N to low-N litter. Mixtures of fertilised and unfertilised plant litter showed higher than expected C losses and net transfer of N. Mixtures with litters from the same fertilisation treatment had small or insignificant net transfer of N and their C losses did not differ from values estimated using the decomposition rates of the pure litters.     

Carbon and nitrogen turnover in response to warming and nitrogen addition during early stages of forest litter decomposition—an incubation experiment

Purpose

Little is known about the interactive effects of temperature, nitrogen (N) supply, litter quality, and decomposition time on the turnover of carbon (C) and N of forest litter. The objective of this study was to investigate the interactive effects of warming, N addition and tree species on the turnover of C and N during the early decomposition stage of litters in a temperate forest.

Materials and methods

A 12-week laboratory incubation experiment was carried out. The leaf litters including two types of broadleaf litters (Quercus mongolica and Tilia amurensis), a needle litter (Pinus koraiensis), and a mixed litter of them were collected from a broad-leaved Korean pine mixed forest ecosystem in northeastern China in September 2009. Nine treatments were conducted using three temperatures (15, 25, and 35 °C) combined with three doses of N addition (equal to 0, 75, and 150 kg?·?ha^?1?a^?1, respectively, as NH₄NO₃).

Results and discussion

After 12 weeks of incubation, the mass loss ranged between 12 and 35 %. The broadleaf litters had greater mass loss and cumulative CO₂–C emission than the needle litter. Temperature and N availability interacted to affect litter mass loss and decomposition rate. The dissolved organic carbon (DOC) and nitrogen (DON) concentrations in litter leachate varied widely with litter types. DOC increased significantly with increased temperature but decreased significantly with increased N availability. DON increased significantly with increased N availability but showed a higher level at the moderate decomposition temperature. The amounts of CO₂ and N₂O emission were significantly higher at 25 °C than those at 15 and 35 °C, and were significantly increased by the N addition.

Conclusions

The present study indicated relatively intricate temperature and N addition effects on C and N cycling during early stages of litter decomposition, implying that future increases in temperature and N deposition will directly affect C and N cycling in broad-leaved Korean pine mixed forest ecosystem, and may indirectly influence the ecosystem composition, productivity, and functioning in NE China. It is, therefore, important to understand the interactive effects of biotic and abiotic factors on litter decomposition in field conditions in order to assess and predict future ecosystem responses to environmental changes in NE China.     

Litter decomposition in peatlands is promoted by mixed plants

Purpose

The carbon sink function of peatlands is primarily driven by a higher production than decomposition of the litter Sphagnum mosses. The observed increase of vascular plants in peatlands could alter the decomposition rate and the carbon (C) cycle through a litter mixing effect, which is still poorly studied. Here, we examine the litter mixing effect of a peat moss (Sphagnum fallax) and two vascular plants (Pinus uncinata and Eriophorum vaginatum) in the field and laboratory-based experiment.

Materials and methods

During the laboratory incubation, mass loss, CO₂ production, and dissolved organic carbon concentration were periodically monitored during 51 days. The collected data were then processed in a C dynamics model. The calculated enzymatic activity was correlated to the measured β-glucosidase activity in the litter. In the field experiment, mass loss and CO₂ production from litter bags were annually measured for 3 years.

Results and discussion

Both laboratory and field experiments clearly show that the litter mixture, i.e., Sphagnum-Pinus-Eriophorum, had a synergistic effect on decomposition by enhancing the mass loss. Such enhanced mass loss increased the water extractable C and CO₂ production in the litter mixture during the laboratory experiment. The synergistic effect was mainly controlled by the Sphagnum-Eriophorum mixture that significantly enhanced both mass loss and CO₂ production. Although the β-glucosidase activity is often considered as a major driver of decomposition, mixing the litters did not cause any increase of the activity of this exo-enzyme in the laboratory experiment suggesting that other enzymes can play an important role in the observed effect.

Conclusions

Mixing litters of graminoid and Sphagnum species led to a synergistic effect on litter decomposition. In a context of vegetation dynamics in response to environmental change, such a mixing effect could alter the C dynamics at a larger scale. Identifying the key mechanisms responsible for the synergistic effect on litter decomposition, with a specific focus on the enzymatic activities, is crucial to better predict the capacity of peatlands to act as C sinks.