Plant litter quality influences the contribution of soil fauna to litter decomposition in humid tropical forests, southwestern China

The aim of this field experiment was to quantify the contribution of soil fauna to plant litter decomposition in three forest sites differing in C/N ratio under natural conditions in Xishuangbanna, southwestern China. We conducted a survey of soil fauna communities, the forest floor litter and investigated mass loss of mixed tree species leaf litter for two years in a tropical secondary forest, an evergreen broad-leaf forest and a tropical rain forest. Exclusion treatments of different sized soil fauna from the leaf litter by using varying mesh size litter bags (2 mm and 0.15 mm) were also performed. Mass loss and C and N concentrations in litter bag leaf materials were determined at monthly intervals. We found that: (1) the three forests differed in floor litter biomass and nutrient contents but not in soil fauna richness and abundance; (2) litter mass loss and decomposition rate were slower when soil macrofauna and most of mesofauna were excluded; and (3) greatest soil fauna contribution to plant litter decomposition occurred in the rain forest, where leaf litter C/N ratio was also highest (41.5% contribution: 54.8 C/N ratio), in comparison to 8.69% in the broad-leaf forest and 19.52% in the secondary forest, both with low leaf litter C/N ratios (<32). Our results suggested that, soil fauna played a more pronounced role in the decomposition of mixed leaf litter in tropical rain forest, and significantly bigger effects from fauna were ascribed to the enhancement of N concentration and decrease of C concentration of the initially high C/N ratio litter in this forest site.     

Nutrient Release and Fungal Succession during Decomposition of Crop Residues in a Shifting Cultivation System

Litter decomposition and nutrient‐release patterns of three dominant crop species were studied in a jhum cultivation system in the humid tropics of northeast India. Crop residues showed an exponential weight‐loss pattern with time. The release of nitrogen (N), phosphorus (P), and potassium (K) followed a similar pattern with weight loss, and their mineralization constants were 3.46–20.47, 2.25–18.41, and 3.82–24.70, respectively. The microbial population and fungal diversity in the decomposing litter varied with incubation time and depended mainly on the litter nutrient concentrations. Overall, the foliage residues of Capsicum frutescens and Eleusine coracana with carbon (C)/N < 25 are of good quality, and they decomposed (t₉₉ = 122 and 333 days, respectively) fastest and released 99% of their nutrients (C, N, and K) between 74 and 263 days of incubation. Thus, all the foliage residues, particularly those of Capsicum frutescens and Eleusine coracana, can play a significant role for soil nutrient enrichment in poorly managed jhum cultivation system.     

Introduced slugs and indigenous caterpillars as facilitators of carbon and nutrient mineralisation on a sub-Antarctic island

Indigenous soil macroinvertebrates (moth larvae, weevil larvae, earthworms) are cardinal agents of nutrient release from litter on sub-Antarctic Marion Island (47°S, 38°′E). Their populations are threatened through predation by introduced house mice, which do not prey on an introduced slug Deroceras panormitanum. A microcosm study was carried out to explore whether slugs affect rates of carbon and inorganic nutrient mineralisation from plant litter differently to an indigenous caterpillar (larva of a flightless moth Pringelophaga marioni). Caterpillars stimulated N, Ca, Mg and K mineralisation from plant litter two to five times more than slugs did, whereas the two invertebrate types stimulated C and P mineralisation to the same degree. Consequently, ratios of C:N and N:P released from the litter were different for slugs and caterpillars. Such differences might affect peat nutrient quality and ultimately the peat accumulation-decomposition balance, an important driver of ecological succession. This suggests that slugs cannot simply replace caterpillars without consequences for ecosystem structure and functioning on the island.     

Carbon and nitrogen mineralization dynamics in different soils of the tropics amended with legume residues and contrasting soil moisture contents

Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect, C and N mineralization dynamics in three tropical soils (Af, An₁, and An₂) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 5 mg g⁻¹ dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–135 days. The legume residues markedly enhanced the net cumulative CO₂–C flux and its rate throughout the incubation period. The cumulative CO₂–C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than PP-treated soil samples. After 100 days of incubation, 32–42% of the amended C of residues was recovered as CO₂–C. In one of the three soils (An₁), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly (p < 0.05) greater NH₄⁺–N and NO₃⁻–N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally in both NH₄⁺–N and NO₃⁻–N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period.     

Differential effects of soil properties on leaf nitrogen release

 Identifying the determinants of the N dynamics of plant prunings or litter is important for the efficient management of agroecosystems in order to improve their productivity. The plant materials in these ecosystems are managed as soil surface mulches or are incorporated into the soil. Numerous studies have been conducted to investigate which plant chemical parameter best governs N release. In these studies, different plant materials have been incorporated into a soil with a set of known characteristics. The objective of the present study was to examine the effects of different soil properties on N release from plant leaves, when they were incorporated into soils under non-leaching conditions. A laboratory incubation experiment (for 8 weeks) was carried out with dried and ground leaves of six leguminous plants and wild sunflower, which were mixed with three soils (alfisol; ultisol, udult; ultisol, humult). Leaf cellulose was the major chemical parameter that determined leaf N release in the alfisol and ultisol, udult. In the ultisol, humult, the C/N ratio and hemicellulose concentration were better related to N release. Cellulose was not a good indicator of N release in the ultisol, humult, possibly due to a low soil pH which did not favour the activity of the cellulose-degrading enzymes of microbes active in decomposition. Soil pH determined the specific C source that was used to generate energy for microbial action and N mineralization/immobilization. It also had an effect on the nitrification of the mineralized N. The levels of labile soil C fractions governed the mode or nature of N release (i.e. mineralization or immobilization). The levels of labile leaf C fractions incorporated into the soils governed the extent of N release. The soil N concentration in the decomposable organic matter pool, as compared to the leaf N concentration, determined whether leaf N limited its own release. It is recommended from this study that, in grouping different leaf materials as sources of N, the properties of soils into which they are incorporated should also be considered, in addition to leaf quality in terms of its chemical composition. In future studies, the relationships identified under laboratory conditions in this experiment should be verified under field conditions. Received: 3 December 1997     

Carbon mineralization of tree leaf litter and crop residues from poplar-based agroforestry systems in Northeast China: A laboratory study

Tree leaf litter and crop residues (fine roots and straw) of the two main crops (maize and peanut) collected from temperate poplar-based agroforestry systems in Liaoning Province, China, were used in a laboratory decomposition experiment. The objectives were to assess the decomposition dynamics of individual plant residues of varying quality and to examine whether interactive effects between poplar litter and crop residues exist during decomposition. Rates of residue decomposition were measured as CO₂ production. Peanut roots decomposed faster than the other individual residues due to their high N and P concentrations and low C/N ratio. There were additive effects between poplar litter and crop residues during decomposition, even though significant differences existed in the initial nutrient concentrations of residues. Our results suggest that legume crops can produce high quality residues and thus have the potential to promote nutrient cycling. Therefore, legume crops have an advantage over other crops for intercropping in temperate agroforestry systems from the viewpoint of sustaining soil fertility.     

Tree pruning mulch increases soil C and N in a shaded coffee agroecosystem in Hawaii

Agroforestry can increase the sequestration of carbon (C) in soils of tropical agroecosystems through increased litter and tree pruning inputs. Decomposition of these inputs is a key process in the formation of soil organic matter and in nutrient cycling. Our objectives were to study decay of tree pruning mulch and effects on soil C and N in a shaded coffee agroecosystem in Hawaii. Chipped tree pruning residues (mulch) were added to coffee plots shaded with the Leucaena hybrid KX2 over three years. We measured mulch decomposition and nitrogen loss over one year and changes in soil carbon and nitrogen (N) over two years. Mass loss of mulch was 80% over one year and followed first-order decay dynamics. There was significant loss from all major biochemical components. Net N loss from the mulch was positive throughout the entire period. The C:N and lignin:N ratios of the mulch declined significantly over the decomposition period. Mulch additions significantly increased soil C and N in the top 20 cm by 10.8 and 2.12 Mg ha⁻¹, respectively. In the no-mulch treatment, there was no significant change in soil C or N concentration, but a decline in soil bulk density led to a significant decline in total soil C. Leucaena mulch can provide an important source of organic C and N to coffee agroecosystems and can help sequester C lost as plant biomass during shade tree management.     

Mass loss and nutrient release during litter decay in peatland: The role of microbial adaptability to litter chemistry

In peatlands the reduced decomposition rate of plant litter is the fundamental mechanism making these peat-accumulating ecosystems effective carbon sinks. A better knowledge of litter decomposition and nutrient cycling is thus crucial to improve our predictions of the effects of anthropogenic perturbation on the capacity of peatlands to continue to behave as carbon sinks. We investigated patterns of plant litter decomposition and nutrient release along a minerotrophic-ombrotrophic gradient in a bog on the south-eastern Alps of Italy. We determined mass loss as well as P, N, K, and C release of seven vascular plant species and four moss species after 1 year in both native and transplanted habitats. Hence, differences in litter decay were supposed to reflect the degree of adaptability of microbial communities to litter quality. Polyphenols/nutrient and C/nutrient quotients appeared as the main parameters accounting for decomposition rates of Sphagnum litter. In particular, litter of minerotrophic Sphagnum species decomposed always faster than litter of ombrotrophic Sphagnum species, both in native and transplanted habitats. Decomposition rates of vascular plant litter in native habitats were always higher than the corresponding mass loss rates of Sphagnum litter. Minerotrophic forbs showed the fastest decomposition both in native and transplanted habitats in accordance with low C/P and C/N litter quotients. On the other hand, C/P quotient seems to play a primary role also in controlling decomposition of graminoids. Decomposition of deciduous and evergreen shrubs was negatively related to their high lignin content. Nitrogen release from Sphagnum litter was primarily controlled by C/N quotient, so that minerotrophic Sphagnum litter released more N than ombrotrophic Sphagnum litter. Overall, we observed slower N release from litter of ombrotrophic vascular plant species compared to minerotrophic vascular plant species. No single chemical parameter could predict the variability associated with different functional groups. The release of K was very high compared to all the other nutrients and rather similar between ombrotrophic and minerotrophic litter types. In Sphagnum litter, a higher C/P quotient was associated with a slower P mineralisation, whereas a faster P release from vascular plant litter seems primarily associated with lower C/P and polyphenols/P quotients.     

Effect of earthworm addition on soil nitrogen availability,microbial biomass and litter decomposition in mesocosms

The aim of the study was to determine the effect of adding two tropical earthworm species, Rhinodrilus contortus and Pontoscolex corethrurus, to mesocosms on the availability of mineral N (NH₄ ⁺ and NO₃ ^– concentrations), soil microbial biomass (bio-N), and the decomposition rates of three contrasting leaf litter species, in a glasshouse experiment. The mesocosms were filled with forest soil and covered with a layer of leaf litter differing in nutritional quality: (1) Hevea brasiliensis (C/N=27); (2) Carapa guianensis (C/N=32); (3) Vismia sp., the dominant tree species in the second growth forest (control, C/N= 42); and, (4) a mixture of the former three leaf species, in equal proportions (C/N=34). At the end of the 97-day experiment, the soil mineral N concentrations, bio-N, and leaf litter weight loss were determined. Both earthworm species showed significant effects on the concentrations of soil NO₃ ^– (p<0.01) and NH₄ ⁺ (p<0.05). Bio-N was always greater in the mesocosms with earthworms (especially with R. contortus) and in the mesocosms with leaf litter of H. brasiliensis (6 µg N g^–1 soil), the faster decomposing species, than in the other treatments (0.1–1.6 µg N g^–1). Thus, earthworm activity increased soil mineral-N concentrations, possibly due to the consumption of soil microbial biomass, which can speed turnover and mineralization of microbial tissues. No significant differences in decomposition rate were found between the mesocosms with and without earthworms, suggesting that experiments lasting longer are needed to determine the effect of earthworms on litter decomposition rates.     

De‐eutrophication of a nitrogen‐saturated Scots pine forest by prescribed litter‐raking

Short‐term (<7 years) effects of prescribed litter‐raking on forest‐floor nutrient pools, stand nutrition, and seepage water chemistry were studied in an N‐saturated Scots pine (Pinus sylvestris L.) forest in Southern Germany subject to high atmospheric‐nitrogen deposition. The study was based on a comparison of plots with and without annual prescribed litter raking at three sites with different N‐deposition levels. Prescribed litter‐raking resulted in a considerable reduction of forest‐floor thickness and mass, as well as of forest‐floor C, N, P, K, Mg, and Ca pools. Furthermore, it induced a significant decrease of the foliar N content in current‐year needles of the pines and a more balanced nutritional status of the stand. Particularly on the site subject to the highest N deposition, but to a lesser degree also at the other sites, the mean NO concentration in the subsoil seepage water and the N export into the groundwater were substantially reduced on the litter‐raked plots. The results show that in N‐saturated Scots pine ecosystems prescribed litter‐raking on areas of limited size, which are used as sources of groundwater‐derived drinking water and/or serve as habitat for endangered plant species, is a quick and effective method to achieve a more balanced nutritional status of the trees and to reduce seepage‐water NO concentrations and N export into the groundwater. In terms of sustainable ecosystem nutrient management, the conversion of conifer monocultures into broadleaf‐rich mixed stands is the better, yet less immediately effective method to reduce the seepage‐water N export from conifer forests subject to high atmospheric‐N deposition.     

Contrasting decomposition rates and nutrient release patterns in mixed vs singular species litter in agroforestry systems

Purpose

The rate of litter decomposition can be affected by a suite of factors, including the diversity of litter type in the environment. The effect of mixing different litter types on decomposition rates is increasingly being studied but is still poorly understood. We investigated the effect of mixing either litter material with high nitrogen (N) and phosphorus (P) concentrations or those with low N and P concentrations on litter decomposition and nutrient release in the context of agroforestry systems.

Materials and methods

Poplar leaf litter, wheat straw, peanut leaf, peanut straw, and mixtures of poplar leaf litter-wheat straw, poplar leaf litter-peanut leaf, and poplar leaf litter-peanut straw litter samples were placed in litter bags, and their rates of decomposition and changes in nutrient concentrations were studied for 12 months in poplar-based agroforestry systems at two sites with contrasting soil textures (clay loam vs silt loam).

Results and discussion

Mixing of different litter types increased the decomposition rate of litter, more so for the site with a clay loam soil texture, representing site differences, and in mixtures that included litter with high N and P concentrations (i.e., peanut leaf). The decomposition rate was highest in the peanut leaf that had the highest N and P concentrations among the tested litter materials. Initial N and P immobilization may have occurred in litter of high carbon (C) to N or C to P ratios, with net mineralization occurring in the later stage of the decomposition process. For litter materials with a low C to N or P ratios, net mineralization and nutrient release may occur quickly over the course of the litter decomposition.

Conclusions

Non-additive effects were clearly demonstrated for decomposition rates and nutrient release when different types of litter were mixed, and such effects were moderated by site differences. The implications from this study are that it may be possible to manage plant species composition to affect litter decomposition and nutrient biogeochemistry; mixed species agroforestry systems can be used to enhance nutrient cycling, soil fertility, and site productivity in land-use systems.     

Effects of different quality plant residues on soil carbon accumulation and aggregate formation in a tropical sandy soil in Northeast Thailand as revealed by a 10‐year field experiment

Particulate organic matter (POM) plays important role in soil organic carbon (SOC) retention and soil aggregation. This paper assesses how quality (chemical composition) of four different‐quality organic residues applied annually to a tropical sandy loam soil for 10 years has affected POM pools and the development of soil aggregates. Water‐stable aggregate size distribution (>2, 0·25–2, 0·106–0·25 mm) was determined through wet sieving. Density fractionation was employed to determine POM (light—LF, and heavy—HF fractions, 0·05–1 mm). Tamarind leaf litter showed the highest SOC (<1 mm) accumulation, while rice straw showed the lowest. LF‐C contents had positive correlations with high contents of C and recalcitrant constituents, (i.e. lignin and polyphenols) of the residues. Dipterocarp, a resistant residue, showed the highest LF‐C, followed by the intermediate residues, tamarind, and groundnut, whereas HF was higher in groundnut and tamarind than dipterocarp residues. Rice straw had the lowest LF‐ and HF‐C contents. Tamarind had the highest quantity (51 per cent) of small macroaggregates (0·25–2 mm), while dipterocarp had the most (2·1 per cent) large macroaggregates (>2 mm). Rice straw had the lowest quantities of both macroaggregates. Similar to small‐sized HF (0·05–0·25 mm), small macroaggregates had positive correlation with N and negative correlation with C/N ratios, while large macroaggregates had positive correlations with C and recalcitrant constituents of the residues. Tamarind, with intermediate contents of N and recalcitrant compounds, appears to best promote small macroaggregate formation. Carbon stabilized in small macroaggregates accounted for the tamarind treatment showing the largest SOC accumulation. Copyright © 2010 John Wiley & Sons, Ltd.     

Fate of 15N derived from soil decomposition of abscised leaves and pruning wood from apple (Malus domestica) trees

Abstract

The fate of nitrogen (N) derived from soil incorporating ¹⁵N-labeled apple (Malus domestica) leaves and wood from pruning (hereafter referred to as “pruning wood”) was studied in an 8-month pot experiment. The net mineralization of N was measured as ¹⁵N recovery in perennial ryegrass (Lolium perenne) that was allowed to grow in soils amended with residues < 2 mm in size (litter : soil ratio, w/w, 1:250 for leaves and 1:330 for wood). The immobilization of native soil N as a consequence of residue addition was measured by comparing the amount of total N taken up by ryegrass in residue-amended soil and in control soil. Net immobilization of soil N occurred during the first 2 months after litter addition and was especially high in the soil amended with leaf litter. During the period of soil N immobilization, the amount of soil microbial N was high in the soils treated with both types of residues, while that of mineral N was markedly reduced only in the leaf-litter-amended soil. Net N uptake from the control soil almost stopped after 3 months of plant growth, while ryegrass in the litter-amended soil continued to take up N, indicating a likely release of previously immobilized N. Net mineralization of the ¹⁵N from apple residues was slow during the first 2 months after their incorporation and then increased. In total, 6% (leaves) and 12% (wood) of the N added via residues underwent mineralization, while 67% (leaves) and 85% (wood) were found in the extractable soil N pool (humic and fulvic acids and non-humified fractions). The data indicated that, even if N was incorporated into the soil, apple leaves and pruning wood did not mineralize significant amounts of N in the short term. The evidence suggested that during the decomposition of both types of apple residues the N originally present was incorporated into the stable soil N pool.     

Consumption and release of nitrogen by the harvester termite Anacanthotermes ubachi navas in the northern Negev desert, Israel

The harvester termite, Anacanthotermes ubachi Navas (Hodotermitidea) occurs throughout the desert regions of Israel. This species nests in subsurface galleries where dead plant material, the termite's main food source, and feces are stored. We measured potential net nitrogen (N) mineralization and nitrification and soil respiration in 7-day laboratory incubations of plant litter at different stages of termite processing, termite feces and termite gallery soil (carton) following wetting. Our objectives were (1) to characterize the amount of potential N release from termite-affected plant and soil materials, (2) to evaluate the potential for leaching of N from the galleries and (3) to make a preliminary evaluation of the importance of termites to the carbon (C) and N cycles of the Negev desert. Two distinct phases were seen in the dynamics of inorganic N during the 7 day incubations: (1) release of N following wetting and (2) immobilization of N from day 1 to day 7 of the incubation. The percent of inorganic N produced in 1 day that disappeared by day 7 was significantly higher in the surface and gallery litter in comparison to the feces and the carton. High levels of nitrate (NO₃⁻: 87.5 g N kg⁻¹) compared to ammonium (NH₄⁺: 4.5 g N kg⁻¹) release from the surface and gallery litter samples suggest that there is a potential for leaching of NO₃⁻ from the galleries to surrounding environments. Gallery litter, i.e. litter that had been processed by termites, released significantly less inorganic N and had a higher C:N ratio than surface litter that had not been affected by termite activity. These results suggest that termites actively remove N for their own nutrition, leaving behind litter of lower quality than was produced by plants. Comparison of the C:N ratios of litter and feces suggest that approximately 80% of the C and 65% of the N in the surface and the gallery litter was decomposed and released in the transformation to feces. Given mean annual biomass production in the study site (740 kg ha⁻¹ with 296 kg C ha⁻¹ and 6.6 kg N ha⁻¹), this decomposition represents a release of 237 kg C ha⁻¹ and 4.3 kg N ha⁻¹, supporting the idea that termites function as keystone species in desert ecosystems.     

Recovery of Soil C and N in a Tropical Pasture: Passive and Active Restoration

Soil degradation by deforestation and introduction of exotic grasses is a grave consequence of land‐use change in tropical regions during the last decades. Soil restoration following natural succession (i.e., passive restoration) is slow because of low tree establishment. Introduction of tree plantings by human intervention (i.e., active restoration) results in a promising strategy to accelerate forest succession and soil recovery in tropical region. The present research was carried out to explore the restoration of soil properties after cattle exclusion and of grazing combined with native tree planting introduction (legumes and nonlegumes) in a tropical pasture in Veracruz, southeast Mexico. Results indicate that land‐use changes decreased soil C and N pools in both litter and mineral soil. In addition, soil heterogeneity increased by land‐use changes at both temporal and spatial scales. In the short term, passive succession (i.e., cattle exclusion) favors the recovery of C and N content in labile soil pools, indicated by the increase in litter C and N masses as well as C and N concentrations in soil microbial biomass. Soils under active restoration showed trends to recover the N cycling, such as a greater accumulation of N in litter, in soil total N concentrations, soil microbial biomass N concentrations, rates of net N transformations, and extractable water and microbial biomass C:N ratios mainly under legumes species. Active restoration including legume introduction is a key factor for rapid recovery of soil fertility. Copyright © 2013 John Wiley & Sons, Ltd.     

氮、磷肥对杉木幼苗生物量及养分分配的影响

采用盆栽试验,研究了不同氮、 磷肥对杉木（Cunninghamia lanceolata）幼苗生物量及养分分配的影响。结果表明,供磷可促进杉木幼苗植株和各器官生物量的增加,并影响叶、 茎、 根生物量的分配比例,氮、 磷处理幼苗叶生物量占全株生物量的45% 以上, 施氮反而降低杉木叶、 茎、 根的生物量; 施氮显著增加根和叶的氮含量,而显著降低根和叶的磷含量,对茎的氮、 磷含量没有明显影响; 施磷显著降低叶、 茎、 根的氮含量,叶、 茎、 根的磷含量随供磷水平的增加而逐渐增加。氮磷配施显著影响叶、 茎、 根的氮、 磷含量和氮、 磷累积量。叶片是主要的氮、 磷养分存储器官。氮（或磷）水平的增加可降低杉木幼苗的磷（或氮）利用效率,提高氮（或磷）的利用效率; 氮、 磷肥显著影响杉木幼苗叶、 茎、 根的N/P比。研究结果说明,氮、 磷肥增加了杉木幼苗各器官生物量和氮、 磷含量,影响了幼苗的养分分配和营养平衡。     

Limitless decomposition in leaf litter of Common beech: Patterns,nutrients’ and heavy metal's dynamics

Long-term studies of Common beech litter decomposition are scarce and the relationship of its limit values to nutrients/heavy metals dynamics has not been sufficiently studied. The present study is a rare case in which beech litter decomposes almost entirely and enables analyses of the impacts of nutrients and heavy metals on litter decomposition. The aim of the present paper is to (i) determine a decomposition pattern of leaf litter and estimate the limit values and to (ii) determine the dynamics of the main nutrients and heavy metals (concentration and net amounts, based on ash-free litter) in an unpolluted stand of Common beech.Common beech (Fagus sylvatica L.) leaf litter was incubated in polyester litterbags (1.5 mm mesh size) and 41 samplings were made over a period of 6.5 years until a mass loss of 88.9% was achieved. Carbon (C) plus 12 more nutrients and heavy metals were analyzed.Mass losses of both whole litter and of C were used in order to estimate the limit values as well as to determine significant differences between the two approaches. An asymptotic function gave significant limit values that were close to 100% (p < 0.0001). These results were also supported by a single exponential function (p < 0.0001). The initial increase in concentrations of nutrients was followed by a decrease of N, P, K, Ca, Na and Mn. A similar pattern was observed for some of the heavy metals (Cu, Cd and Fe) while Zn concentrations decreased continuously. A net release (e.g. a decrease in the net amounts) was observed for all nutrients and heavy metals except for Cd. The litter fraction did not leave any stable residues (i.e. limit values were close to 100%), which was at least partly due to the low initial N and very high Mn concentration (20 times higher than in other studies).     

Use of crop residues with alkaline slag to ameliorate soil acidity in an Ultisol

Information regarding the interaction between liming agents and crop residues on soil acidity amelioration is limited. A laboratory incubation study was undertaken to investigate the combined application of alkaline slag (AS, the major component is CaO) and crop residues with different C/N ratios and ash alkalinity content. Incorporation of amendments was effective in reducing soil exchangeable acidity and Al saturation and increasing exchangeable base cations (P < 0.05), but the effect of AS on soil pH adjustment was reduced when added with a high amount of residue with a low C/N ratio. Initial increases in soil pH were attributed to the release of alkalinity from the combined amendments and the mineralization of organic nitrogen (N). During subsequent incubation, the soil pH decreased because of nitrification. Crop residues with a high C/N ratio increased N immobilization and reduced net nitrification, resulting in a slight pH decrease. Crop residues with a low C/N ratio resulted in a sharp decrease in soil pH when applied with low levels of AS because of stimulated soil nitrification, whereas high AS had no consistent effect on net nitrification. Hence, compared to the control (pH = 4.21), a large increase in soil pH occurred, especially when peanut straw was applied at 10 g/kg (pH = 5.16). It is suggested that crop residues with high C/N ratio and also combined with a liming agent such as AS are preferred to ameliorate soil acidity. The liming effect of AS is likely to be negated if added in combination with residues with high N contents.     

Litter decomposition and nitrogen mineralization in newly formed gaps in a Danish beech (Fagus sylvatica) forest

Gap formation is suggested as an alternative forest management approach to avoid extreme changes in the N cycle of forest ecosystems caused by traditional management practises. The present study aimed to investigate the effect of gap formation on N availability in beech litter and mineral soil on sites, which experienced only little soil disturbance during tree harvest. N pools, litter decomposition, and N mineralization rates in mineral soil were studied in two gaps (17 and 30 m in diameter) in a 75-year-old managed European beech (Fagus sylvatica L.) forest in Denmark and related to soil temperature (5 cm depth) and soil moisture (15 cm depth). Investigations were carried out during the first 2 years after gap formation in measurement plots located along the north-south transect running through the centre of each gap and into the surrounding forest.An effect of gap size was found only for soil temperatures and litter mass loss: soil temperatures were significantly increased in the northern part of the large gap during the first year after gap formation, and litter mass loss was significantly higher in the smaller gap. All other parameters investigated revealed no effect of gap size. Nitrification, net mineralization, and soil N concentrations tended to be increased in the gaps. Cumulative rates of net mineralization were two fold higher in the gaps during the growing season (June-October), but a statistically significant increase was found only for soil NH₄-N concentrations during this period. Forest floor parameters (C:N ratios, mass loss, N release) were not significantly modified during the first year after gap formation, neither were the total C content nor the C:N ratio in mineral soil at 0-10 cm depth.     

Decomposition of Emergent Aquatic Plant (Cattail) Litter Under Different Conditions and the Influence on Water Quality

Decomposition of aquatic plant might generate a significant influence on the receiving water body. In this study, decomposition of emergent aquatic plant (cattail) litter was investigated under different conditions to determine the influencing level of the decomposition process on the water quality. Different litter addition rates (0.1, 0.5, 1.0 g L^?1), temperature changes, sediment additions, and kinestates (static and dynamic conditions) were selected as the influencing factors for the decomposition process. The results suggested that the decomposition process could be all accelerated when conducted at a higher litter addition rate, under a cold condition, with sediment addition or on dynamic condition, respectively. Additionally, the maximum ratio of releasing carbon to nitrogen (C/N) was increased when the decomposition process was conducted with a higher litter addition rate, under a cold condition (31.0), with sediment addition (24.6) and on a dynamic condition (28.0), respectively, and the C/N ratios were all higher than that with only 0.5 g L^?1 litter addition (24.5), suggesting that lowering of water temperature, sediment addition, and increasing of oxygen might also enhance the C/N. The high C/N released during the decomposition process implied that the cattail litter might be utilized as the potential organic carbon source for nitrogen removal in the CW system.