Decomposition of Subtropical Fruit Tree Leaf Litter at Nelspruit,South Africa

There is limited information about the decomposition of leaf litter from subtropical fruit trees despite their potential for managing soil fertility. The aim of this study was to quantify the effect of quality on decomposition and nutrient-release patterns from leaf litter of avocado, litchi, and mango trees in South Africa. The litterbag technique was used for investigation. The decomposition results over 2 years indicated significant differences in mass loss among the tree species with low rapid loss for litchi (57.3 percent). The annual decomposition rate constant (k) decreased in the order mango (0.82) > avocado (0.76) > litchi (0.69). The concentrations of phosphorus, potassium, manganese, and polyphenols in all species decreased while nitrogen, sulfur, and calcium concentrations increased with time. The nutrient-release pattern of the leaf litter from the three species varied considerably due to different quality characteristics. This had an influence on litter decomposition and thus its management.     

Decomposition and Nutrient Release from Litter Fall in the Semi‐arid Tropics of Sudan

In Sudan, tree plantations remain the first choice and are widely used in protecting arable lands from sand movement. Decomposition and nutrient changes from leaves of some agroforestry trees (Eucalyptus microtheca, Ficus spp., and Leucaena leucocephala) and litter fall from guava (Psidium guajava) and mango (Magnifera indica) were monitored (in a 12‐week litter‐bag experiment). Rate of dry‐matter weight loss from guava (0.098 wk^?1) was significantly (P < 0.01) faster than from mango residues (0.04 wk^?1). Corresponding values for Leucaena, Eucalyptus, and Ficus were 0.0533, 0.0524, and 0.0438 wk^?1, respectively. In general, micronutrients tend to accummulate during a decomposition period. Potassium (K) was the only element found to be consistently lost by leaching very rapidly from all litters. Nitrogen (N) was released at a significantly (P < 0.03) higher rate from Leucaena (0.0558 wk^?1) compared to Ficus (0.0399 wk^?1) and Eucalyptus (0.0301 wk^?1). Mobility of nutrients from the litters was in the order of K > phosphorus (P) = N > calcium (Ca) > magnesium (Mg). It is concluded that ficus and mango leaves are suitable for improving quality of arid soils through buildup of soil organic matter and supplying easily released organic sulfur (S) (environmentally sound management practice) whereas litter from guava is suitable for temporary nutrient correction. Mixing of guava and mango residues may slow fast decomposition of the former.     

Influence of elevated UV-B radiation on leaf litter chemistry and subsequent decomposition in humid subtropical China

Purpose

Exposure to elevated ultraviolet B (UV-B) radiation during plant growth may influence plant tissue chemistry and subsequent decomposition. We conducted a 22-month decomposition experiment to evaluate the effects of UV-B radiation on litter chemistry and subsequent decomposition in humid subtropical forest systems.

Materials and methods

Leaf litters were derived from five native tree species, including Cunninghamia lanceolata, Cinnamomum camphora, Schima superba, Cyclobalanopsis glauca, and Elaeocarpus sylvestris, which grew under ambient and elevated UV-B radiation treatments for 1 year.

Result and discussion

UV-B treatment significantly altered the original C, N, P, K, and lignin content and ratios of C/N, lignin/N, and C/P of leaf litter of five species but just slightly accelerated decomposition at variable degree from 2 % to 13 %. Statistical analyses showed litter species, but not UV-B treatment, had significant effect on decomposition. Only initial lignin content was significantly related to the decay rate. Abundant precipitation and warm temperature in subtropical China maybe weaken or even mask the importance of litter chemistry change resulted from UV-B radiation to decomposition especially in early decomposition stage.

Conclusions

Exposure to supplemental UV-B level induced significant changes of the initial leaf litter chemistry but did not accelerate significantly subsequent decomposition of each species in humid subtropical areas of China at least in the early phase. The interspecific differences in litter chemistry of the five species showed greater effect on decomposition than elevated UV-B radiation at the early decomposition stage.     

Litter quality and its potential effect on decay rates of materials from Canadian forests

Decomposition is influenced by a wide array of factors including macroclimate, microclimate, soil biota, soil nutrients, substrate piece size and substrate quality. To separate the influence of some of these factors a 10-year study, the Canadian Intersite Decomposition Experiment, was established in 1992 to measure the decay of 11 standard litter types on a range of forest types at 21 sites across Canada. As part of the study we analysed the initial elemental contents (N, P, S, K, Ca, Mg) and carbon (C) fractions (extractables, cellulose, hemicellulose, lignin) by¹³C NMR and wet chemical proximate analysis in a total of 37 primarily foliar litter types representative of the range of species found at the different CIDET sites. Litter types especially non-conifer species varied greatly in their qualities. Principal component analyses showed that the litter types could be distinguished by the elemental macronutrient contents through the ratio of N+P+K:S, by proximate chemical analyses through the ratio of water soluble:acid fractions, and by NMR through the ratio of O-alkyl:alkyl C. Litter quality data was used in three simple models of litter decay to predict how the mass loss of the different litter types could vary. Two models using a linear or single exponential decay equation and litter lignin and N content predicted a 2–5 fold difference in total mass loss for the different litter types. A third model using a summed exponential decay equation for three chemical fractions and a ligno-cellulose index predicted that for all but one litter type, variation in mass loss between types would be less than a 20%.     

甘肃省兴隆山森林主要树种凋落叶分解速率与初始质量的关系

[目的]开展凋落叶分解速率研究,探讨凋落叶分解速率与初始质量的关系,为甘肃省兴隆山森林生态系统物质循环研究提供依据。[方法]采用凋落物分解袋法,以兴隆山青杄、山杨和白桦3种主要树种的凋落叶为研究对象,进行凋落叶分解速率及凋落叶初始质量的研究,明确凋落叶分解速率与初始质量的关系。[结果]青杄中龄林针叶分解速率为0.16,95%分解期为19.08a;青杄近熟林针叶分解速率为0.13,95%分解期为23.70a;山杨和白桦凋落叶分解速率均为0.11,95%分解期分别为28.57a和27.27a;山杨和白桦凋落叶分解速率明显要小于青杄针叶,这很可能是凋落叶分解主场效应和分解袋孔径较小所致。凋落叶分解速率与氮含量呈显著线性正相关,与木质素含量、碳/氮值、木质素/氮值和钾含量呈显著线性负相关,特别是与木质素含量、氮含量和木质素/氮值,相关系数均达0.700 0以上;钾含量、木质素含量、木质素/氮、碳/磷和纤维素含量是影响兴隆山森林凋落叶分解速率的重要指标。[结论]木质素/氮值是影响凋落叶分解速率的关键质量指标,凋落叶初始木质素/氮值越高,分解速率越低。     

Leaf decomposition in two semi-evergreen tropical forests: influence of litter quality

Decomposition processes in tropical semi-evergreen forests are still poorly understood. The influence of soil properties and litter quality on decomposition rate was studied in two semi-evergreen forests of Guadeloupe, a forest plantation and a secondary forest, located on different soils. Leaf litter of four tree species was enclosed in litterbags for a 14-month period. Non-linear correlations were calculated between mass loss and the concentration of major leaf components (soluble C, N, lignin, cellulose, tannins, total soluble phenols) in order to determine the best predictor of leaf litter decomposition. Soil physico-chemical properties and ratios between some of the above-mentioned litter quality parameters were also examined as mass loss predictors. In addition, non-linear correlations were calculated between mass loss and litter quality parameters, at successive periods. Litter quality was the main determinant of litter decomposition in the studied forests. Several litter quality parameters were correlated with leaf disappearance, varying according to stages of decomposition. Between 1 month and 2.5 months, the mass loss was correlated negatively with the initial phenol content and with initial lignin:N and (lignin+phenol):N ratios. From 2.5 to 5.5 months, the mass loss was correlated negatively with the initial phenol content and positively with the initial cellulose content. At later stages of decomposition (9-14 months), the mass loss was correlated negatively with the initial tannin content. Differences in soil characteristics and fauna did not seem to be enough to affect decomposition.     

Leaf litter C and N cycling from a deciduous permanent crop

Our 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.     

Rainforest litter quality and chemical controls on leaf decomposition with near‐infrared spectrometry

Plant‐litter chemical quality is an important driver of many ecosystem processes, however, what actually constitutes high‐ or low‐quality litter (chemical potential for fast and slow decomposition, respectively) is often interpreted by the indices available. Here, near‐infrared spectroscopy (NIRS) was used to explore leaf‐litter chemical quality and the controls on decomposition in the tropical rainforest region of north Queensland Australia. Leaf‐litter samples from litterfall collections and litterbag studies were used. NIRS was used to calibrate the chemical compositions of the material (N, P, C, Mg, Ca, acid detergent fiber, acid detergent lignin, α‐cellulose, and total phenolics) from a smaller sample set covering the spectral range in the full set of samples. Calibrations were compared for both separate (local) and combined models, for litterbags, and litterfall. Coefficients of determination (r²) in the local models ranged from 0.88 (litterbag Mg) to 0.99 (litterfall N), with residual prediction deviation ratios > 3 for all constituents except Mg (≈ 2.5). Mass loss in the litterbags was strongly related to the NIR spectra, with model r²'s of 0.75 (in situ leaves) and 0.76 (common control leaf). In situ decomposability was determined from modeling the initial NIR spectra prior to decomposition with litterbag exponential‐decay rates (model r² of 0.81, n = 85 initial samples). A best subset model including litter‐quality, climate, and soil variables predicted decay better than the NIR decomposability model (r² = 0.87). For litter quality alone the NIR model predicted decay rate better than all of the best predictive litter–chemical quality indices. The decomposability model was used to predict in situ decomposability in the litterfall samples. The chemical variables explaining NIR decomposability for litterfall were initial P, C, and phenolics (linear model r² = 0.80, n = 2471). NIRS is a holistic technique that is just as, if not more accurate, than litter–chemical quality indices, when predicting decomposition and decomposability, shown here in a regional field study.     

Lignin and cellulose degradation and nitrogen dynamics during decomposition of three leaf litter species in a Mediterranean ecosystem

Cellulose and lignin degradation dynamics was monitored during the leaf litter decomposition of three typical species of the Mediterranean area, Cistus incanus L., Myrtus communis L. and Quercus ilex L., using the litter bag method. Total N and its distribution among lignin, cellulose and acid-detergent-soluble fractions were measured and related to the overall decay process. The litter organic substance of Cistus and Myrtus decomposed more rapidly than that of Quercus. The decay constants were 0.47 year⁻¹, 0.75 year⁻¹ and 0.30 year⁻¹ for Cistus, Myrtus and Quercus, respectively. Lignin and cellulose contents were different as were their relative amounts (34 and 18%, 15 and 37%, 37 and 39% of the overall litter organic matter before exposure, for Cistus, Myrtus and Quercus, respectively). Lignin began to decrease after 6 and 8 months of exposure in Cistus and Myrtus, respectively, while it did not change significantly during the entire study period in Quercus. The holocellulose, in contrast, began to decompose in Cistus after 1 year, while in Quercus and Myrtus immediately. Nitrogen was strongly immobilized in all the litters in the early period of decay. Its release began after the first year in Cistus and Myrtus and after 2 years of decomposition in Quercus. These litters still contained about 60, 20 and 90% of the initial nitrogen at the end of the experiment (3 years). Prior to litter exposure nitrogen associated with the lignin fraction was 65, 54 and 37% in Cistus, Myrtus and Quercus, while that associated with the cellulose fraction was 30, 24 and 28%. Although most of the nitrogen was not lost from litters, its distribution among the litter components changed significantly during decomposition. In Cistus and Myrtus the nitrogen associated with lignin began to decrease just 4 months after exposure. In Quercus this process was slowed and after 3 years of decomposition 8% of the nitrogen remained associated with lignin or lignin-like substances. The nitrogen associated with cellulose or cellulose-like substances, in contrast, began to decrease from the beginning of cellulose decomposition in all three species. At the end of the study period most of the nitrogen was not associated to the lignocellulose fraction but to the acid-detergent-soluble substance (87, 88 and 84% of the remaining litter nitrogen).     

The initial lignin:nitrogen ratio of litter from above and below ground sources strongly and negatively influenced decay rates of slowly decomposing litter carbon pools

Understanding the interactions between the initial biochemical composition and subsequent decomposition of plant litter will improve our understanding of its influence on microbial substrate use to explain the flow of organic matter between soil carbon pools. We determined the effects of land use (cultivation/native woodland/native pasture), litter type (above and below ground) and their interaction on the initial biochemical composition (carbon, nitrogen, water soluble carbon, lignin, tannin and cellulose) and decomposition of litter. Litter decomposition was studied as the mineralization of C from litter by microbial respiration and was measured as CO₂–C production during 105 d of laboratory incubation with soil. A two-pool model was used to quantify C mineralization kinetics. For all litter types, the active C pool decay rate constants ranged from 0.072 d⁻¹ to 0.805 d⁻¹ which represented relatively short half-lives of between 1 and 10 days, implying that this pool contained compounds that were rapidly mineralized by microbes during the initial stages of incubation. Conversely, the decay rate constants for the slow C pool varied widely between litter types within and among land uses ranging from 0.002 d⁻¹ and 0.019 d⁻¹ representing half-lives of between 37 and 446 days. In all litter types, the initial lignin:N ratio strongly and negatively influenced the decay rate of the slow C pool which implied that the interaction between these two litter quality variables had important controls over the decomposition of the litter slow C pool. We interpret our results to suggest that where the flow of C from the active pool to the slow pool is largely driven by microbial activity in soil, the rate of transfer of C will be largely controlled by the quality of litter under different land-use systems and particularly the initial lignin:N ratio of the litter. Compared with native pastures and cultivation, above and below ground litter from native woodland was characterized by higher lignin:N ratio and more slowly decomposing slow C pools which implies that litter is likely to persist in soils, however based on the sandy nature of the soils in this study, it is likely to lack protection from microbial degradation in the long term.     

Standardization of Litchi Leaf Nutrient Composition for Tissue Analysis in Sub Tropics of India

ABSTRACT

Variation in leaf nutrient composition with leaf age and position of leaflets was assessed for ‘Calcuttia’ and ‘Dehradun’ litchi cultivars under loam to sandy loam soils of north India. Leaf samples were collected from first to sixth pair of leaflets starting from the apex of terminal shoots to downward positions during December to May at monthly intervals at two locations for three successive years. The leaves were analyzed for N, P, K, Ca, Mg, Fe, Zn, Cu and Mn concentrations. In both litchi cultivars, leaf N, P, Zn and Cu contents remained more in young leaves; whereas, leaf Ca, Mg, Mn and Fe contents were observed higher in older leaves. Leaf K concentration exhibited inconsistent patterns; however, leaf K concentration in pair of leaflets on the shoot declined basipetal, being maximum in upper pair of leaflets and minimum in lower pair of leaflets. Levels of macro and micronutrients exhibited a degree of stability at second and third pair of leaflets when sampled during February–March. Leaf compositions differed significantly during active vegetative growth, flowering, and fruit development. The results revealed that 4–5 months old leaves from autumn flush at second and third pair of leaflets from the apex of terminal litchi shoots at the advent of panicle initiation (February–March) should be collected to assess the nutritional concentrations of litchi orchards under North India conditions.     

Partitioning of carbon and nitrogen during decomposition of 13C15N‐labeled beech and ash leaf litter

The aim of this study was to determine the influence of leaf‐litter type (i.e., European beech—Fagus sylvatica L. and European ash—Fraxinus excelsior L.) and leaf‐litter mixture on the partitioning of leaf‐litter C and N between the O horizon, the topsoil, the soil microbial biomass, and the CO₂ emission during decomposition. In a mature beech stand of Hainich National Park, Thuringia, Germany, undisturbed soil cores (?? 24 cm) were transferred to plastic cylinders and the original leaf litter was either replaced by ¹³C¹⁵N‐labeled beech or ash leaf litter, or leaf‐litter‐mixture treatments in which only one of the two leaf‐litter types was labeled. Leaf‐litter‐derived CO₂‐C flux was measured every second week over a period of one year. Partitioning of leaf‐litter C and N to the soil and microbial biomass was measured 5 and 10 months after the start of the experiment. Ash leaf litter decomposed faster than beech leaf litter. The decomposition rate was negatively related to initial leaf‐litter lignin and positively to initial Ca concentrations. The mixture of both leaf‐litter types led to enhanced decomposition of ash leaf litter. However, it did not affect beech leaf‐litter decomposition. After 5 and 10 months of in situ incubation, recoveries of leaf‐litter‐derived C and N in the O horizon (7%–20% and 9%–35%, respectively) were higher than in the mineral soil (1%–5% and 3%–8%, respectively) showing no leaf‐litter‐type or leaf‐litter‐mixture effect. Partitioning of leaf‐litter‐derived C and N to microbial biomass in the upper mineral soil (< 1% of total leaf‐litter C and 2%–3% of total leaf‐litter N) did not differ between beech and ash. The results show that short‐term partitioning of leaf‐litter C and N to the soil after 10 months was similar for ash and beech leaf litter under standardized field conditions, even though mineralization was faster for ash leaf litter than for beech leaf litter.     

Nutrient release from decomposing leaf mulches of karité (Vitellaria paradoxa) and néré (Parkia biglobosa) under semi-arid conditions in Burkina Faso, West Africa

Information on decomposition and nutrient release from leaf litter of trees in agroforestry parkland systems in Sub-Saharan Africa is scarce despite the significant role of these trees on soil fertility improvement and maintenance. Decomposition and nutrient release patterns from pruned leaves of the two most common species of parklands of the semi-arid zone of West Africa: Vitellaria paradoxa C.F. Gaertn (known locally as karité) and Parkia biglobosa (Jacq.) Benth. (known locally as néré), were investigated by a litter-tube study in Burkina Faso. Litter quality, methods of leaf exposure to the soil and combination with fertilizers were the factors studied. Leaves of néré had a higher nutrient content (C, N, P, Ca) and contained more ash and lignin than leaves of karité. Karité leaves had a greater content of K, cellulose and polyphenols. The pruned leaves of karité and néré showed two distinct decomposition patterns. Néré leaves decomposed more rapidly, with less than 32% of the initial weight remaining after the rainy season (4 months) while karité leaves decomposed more slowly with 43% of the leaf litter remaining after the rainy season. Addition of urea and compost did not significantly affect the rate of decomposition. Significant interaction was observed between species and method of leaf exposure for the first sampling date. Leaf litter of néré buried in soil gave the highest weight loss (34% of the initial mass in 1 month) compared with exposed leaf litter of néré and karité, and buried leaf litter of karité. Except for N, nutrient release patterns were similar for both species but the nutrient release rates were higher for néré leaves compared with karité leaves. N was immobilised in karité leaves most likely due to low N and high phenolic content. The rate of nutrient release from karité leaves followed the general trend K>P>N.     

Microbial activity and quality changes during decomposition of Quercus ilex leaf litter in three Mediterranean woods

Changes in enzyme activities during litter decomposition provide diagnostic information on the dynamics of decay and functional microbial succession. Here we report a comparative study of enzyme activities involved in the breakdown of major plant components and of other key parameters (microbial respiration, fungal biomass, N, lignin and cellulose contents) in homogeneous leaf litter of Quercus ilex L. incubated in three evergreen oak woods in Southern Italy (Campania), differing for chemical and physical soil characteristics and microclimatic conditions. The results showed that the litter mass loss rates were similar in the three wood sites. Independently of the incubation sites, cellulase, xylanase and peroxydase activities showed seasonal variations with maximum and minimum levels in wet and dry periods, respectively, and this pattern closely matched microbial respiration. Activities of α- and β-amylase, instead, were high at the beginning of incubation and quickly decreased with decomposition progress because their substrate was rapidly depleted. Laccase activity, in contrast, was low at the beginning of incubation but after 6 months it increased significantly. The increase of laccase activity was correlated to an increase in fungal biomass, probably reflecting a major shift in the litter microbial community. As concerns quality changes, N and lignin content did not significantly change during decay. The cellulosic component started being degraded after about 6 months in the litter incubated in two of the three wood sites and from the start of decomposition in the third site. Apart from minor differences in the levels of certain enzyme activities, the data showed that the functional microbial succession involved in the decomposition of Q. ilex leaf litter did not change appreciably in response to differences in soil and microclimatic conditions in the incubation sites.     

Decomposition of sun and shade leaves from three deciduous tree species,as affected by their chemical composition

Freshly fallen leaf litter from sweet chestnut (Castanea sativa Mill), oak (Quercus robur L.) and beech (Fagus sylvatica L.) trees were classified into sun, intermediate and shade leaf types and analysed for N, acid detergent fibre, holocellulose, and lignin. In addition, the sugar constituents of structural polysaccharides (mainly from hemicelluloses) were determined after trifluoracetic acid (TFA) hydrolysis, and the phenylpropanoid (PPD) derivatives of lignin after alkaline CuO oxidation. The litters were decomposed in laboratory microcosms for 2 years. Decomposition rates were initially rapid and then plateaued, but differences in mass losses for the leaf litter categories, and between the three species, were significant at 6, 12, 18 and 24 months. Mean mass losses after 24 months were 49.6% for chestnut, 40.4% for oak and 26.3% for beech. Mean losses for chestnut, oak and beech litter categories were 48.6%, 38.2% and 24.6%, respectively, for sun leaves, and 51.0%, 44.5% and 28.5%, respectively, for shade leaves. Initial lignin concentrations showed a negative correlation with mass losses over the first 6 months but initial acid detergent fibre was a better predictor of decomposition rates after 24 months. Within species, however, total extractable sugars and PPD concentrations reflected differences in decomposition rates between the different categories of leaf types. The analysis for specific carbohydrates and lignin derivatives improved the resolution of litter quality characterisation but did not explain the observed patterns of decomposition in long-term laboratory incubations. It is suggested that these may be affected by influence of the culture conditions on the composition of fungal communities.     

Degradation of hemicellulose, cellulose and lignin in decomposing spruce needle litter in relation to N

Decomposing needles from a Norway spruce forest in southern Sweden were studied for 559 days under laboratory conditions. Falling needles were collected in control (Co) plots and plots that had received 100 kg N ha⁻¹ yr⁻¹ as (NH₄)₂SO₄ for 9 years under field conditions. One of the aims was to determine whether the previously documented low decomposition rate of the N fertilized (NS) needles could be explained by a lower degradation degree of lignin. The lignin content was studied using the alkaline CuO oxidation method, the Klason lignin method and CPMAS ¹³C NMR spectroscopy. The amounts of cellulose and hemicellulose were also determined.The fertilized needle litters initially decomposed faster than the unfertilized, but later this reaction reversed, so that at the end the mass loss was 45% initial C in the control and 35% initial C in NS. Klason lignin decreased with time in both treatments and overall, the change of Klason lignin mirrored the litter mass loss. No major difference as regards the decomposition of hemicellulose occurred between the treatments, whereas significantly lower concentrations of cellulose were found in NS needles throughout the incubation. The CuO derived compounds (VSC) were somewhat lower in NS needles throughout the decomposition time. Initially, VSC increased slightly in both treatments, which contradicts the Klason lignin data. There was a weak positive relationship (p>0.05) between VSC and Klason lignin. Both vanillyls compounds (V) and cinnamyl compounds (Ci) increased slightly during decomposition, whereas syringyl compounds (S) vanished entirely. The lignin degradation degree, i.e. the acid-to-aldehyde ratio of the vanillyl compounds expressed as (Ac/Al)_v, showed no significant effect of treatment. The ¹³C NMR analyses of the combined samples showed increased content of aromatic C with increasing decomposition time. The carbohydrate content (O-alkyl C) was lower in the fertilized needle litter throughout the incubation time. The alkyl C content tended to increase with decomposition time and N fertilization. The alkyl C/O-alkyl C ratios increased in both treatments during the incubation. The NMR results were not tested statistically.In conclusion, no major difference concerning lignin degradation could be found between the unfertilized and N fertilized needle litter. Thus, the study contradicts the hypothesis that higher amounts of N reduce lignin degradation. The reduced biological activity is probably due to direct N effects on the microorganisms and their decomposing ability.     

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.     

Chronic N deposition does not apparently alter the biochemical composition of forest floor and soil organic matter

Future rates of atmospheric N deposition have the potential to slow litter decay and increase the accumulation of soil organic matter by repressing the activity of lignolytic soil microorganisms. We investigated the relationship between soil biochemical characteristics and enzymatic responses in a series of sugar maple (Acer saccharum)-dominated forests that have been subjected to 16 yrs of chronic N deposition (ambient + 3 g NO₃⁻–N m⁻² yr⁻¹), in which litter decay has slowed and soil organic matter has accumulated in sandy spodosols. Cupric-oxide-extractable lignin-derived phenols were quantified to determine the presence, source, and relative oxidation state of lignin-like compounds under ambient and experimental N deposition. Pools of respired C and mineralized N, along with rate constants for these processes, were used to quantify biochemically labile substrate pools during a 16-week laboratory incubation. Extracellular enzymes mediating cellulose and lignin metabolism also were measured under ambient and experimental N deposition, and these values were compared with proxies for the relative oxidation of lignin in forest floor and surface mineral soil. Chronic N deposition had no influence on the pools or rate constants for respired C and mineralized N. Moreover, neither the total amount of extractable lignin (forest floor, P = 0.260; mineral soil, P = 0.479), nor the relative degree of lignin oxidation in the forest floor or mineral soil (forest floor P = 0.680; mineral soil P = 0.934) was influenced by experimental N deposition. Given their biochemical attributes, lignin-derived molecules in forest floor and mineral soil appear to originate from fine roots, rather than leaf litter. Under none of the studied circumstances was the presence or relative oxidation of lignin correlated with the activity of cellulolytic and lignolytic extracellular enzymes. Although chronic atmospheric N deposition has slowed litter decay and increased organic matter in our experiment, it had little effect on biochemical composition of lignin-derived molecules in forest floor and surface mineral soil suggesting organic matter has accumulated by other means. Moreover, the specific dynamics of lignin phenol decay is decoupled from short-term organic matter accumulation under chronic N deposition in this ecosystem.     

Leaf litter decomposition in the pure and mixed plantations of <Emphasis Type="Italic">Cunninghamia lanceolata</Emphasis> and <Emphasis Type="Italic">Michelia macclurei</Emphasis> in subtropical China

Leaf litter decomposition of Cunninghamia lanceolata, Michelia macclurei, and their mixture in the corresponding stands in subtropical China was studied using the litterbag method. The objective was to assess the influence of native evergreen broadleaved species on leaf litter decomposition. The hypotheses were: (1) M. macclurei leaf litter with lower C/N ratio and higher initial N concentration decomposed faster than C. lanceolata litter, (2) decomposition rates in litter mixtures could be predicted from single-species decay rates, and (3) litters decomposed more rapidly at the site that contained the same species as in the litterbag. The mass loss of leaf litter was positively correlated with initial N concentration and negatively correlated with C/N ratio. The decomposition rate of M. macclurei leaf litter was significantly higher than that of C. lanceolata needle litter in the pure C. lanceolata stand. Contrary to what would be predicted, the litter mixture decomposed more slowly than expected based on the results from component species decomposing alone. There was no significant difference in litter decomposition rate between different habitats.     

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.