Degradability, molecular weight and adsorption properties of dissolved organic carbon and nitrogen leached from different types of decomposing litter

Aims

We characterized dissolved organic matter (DOM) leached during decomposition of deciduous silver birch litter (Betula pendula Roth.), coniferous Norway spruce litter (Picea abies (L.) Karst.) and a mixture of these litters in order to find out whether the properties of DOM would explain the earlier observed signs for higher microbial activity in soil under birch than spruce.

Methods

DOM leached from decomposing litters was collected in a litter-column experiment in the laboratory. Adsorption properties (XAD-8 resin fractionation) and molecular weight as well as the degradability of dissolved organic carbon (DOC) and nitrogen (DON) were measured three times during decomposition: 1) in the early stages, 2) after the mass loss reached 20–30 % and 3) when the mass loss reached 30–40 %.

Results

The leaching of DOC hydrophilic neutrals and bases, regarded easily degradable, decreased during decomposition. The leaching of DOC in hydrophobic acids, regarded refractory, increased from spruce and especially from the mixture litter during decomposition and may be connected to the degree of litter decomposition that was highest for the mixture. Unexpectedly, the degradability of DOC differed only slightly between the litters but the degradability of DON was substantially higher for spruce than birch. Spruce DOM seemed to be more N-rich than birch DOM in the early stages of decomposition and it seemed that labile DON was mobilized earlier from spruce than birch litter.

Conclusions

We conclude that the decomposition degree of litter determines largely the properties of DOM. The observed differences in the properties of DOM sampled during the litter decomposition cannot explain differences in C and N cycling between birch and spruce.     

Microbial communities may modify how litter quality affects potential decomposition rates as tree species migrate

Background and aims

Climate change alters regional plant species distributions, creating new combinations of litter species and soil communities. Biogeographic patterns in microbial communities relate to dissimilarity in microbial community function, meaning novel litters to communities may decompose differently than predicted from their chemical composition. Therefore, the effect of a litter species in the biogeochemical cycle of its current environment may not predict patterns after migration. Under a tree migration sequence we test whether litter quality alone drives litter decomposition, or whether soil communities modify quality effects.

Methods

Litter and soils were sampled across an elevation gradient of different overstory species where lower elevation species are predicted to migrate upslope. We use a common garden, laboratory microcosm design (soil community x litter environment) with single and mixed-species litters.

Results

We find significant litter quality and microbial community effects (P?<?0.001), explaining 47 % of the variation in decomposition for mixed-litters.

Conclusion

Soil community effects are driven by the functional breadth, or historical exposure, of the microbial communities, resulting in lower decomposition of litters inoculated with upslope communities. The litter x soil community interaction suggests that litter decomposition rates in forests of changing tree species composition will be a product of both litter quality and the recipient soil community.     

A closeup study of early beech litter decomposition: potential drivers and microbial interactions on a changing substrate

Aims

Litter decomposition and subsequent nutrient release play a major role in forest carbon and nutrient cycling. To elucidate how soluble or bulk nutrient ratios affect the decomposition process of beech (Fagus sylvatica L.) litter, we conducted a microcosm experiment over an 8 week period. Specifically, we investigated leaf-litter from four Austrian forested sites, which varied in elemental composition (C:N:P ratio). Our aim was to gain a mechanistic understanding of early decomposition processes and to determine microbial community changes.

Methods

We measured initial litter chemistry, microbial activity in terms of respiration (CO₂), litter mass loss, microbial biomass C and N (C_mic and N_mic), non purgeable organic carbon (NPOC), total dissolved nitrogen (TDN), NH₄ ⁺, NO₃ ^- and microbial community composition (phospholipid fatty acids – PLFAs).

Results

At the beginning of the experiment microbial biomass increased and pools of inorganic nitrogen (N) decreased, followed by an increase in fungal PLFAs. Sites higher in NPOC:TDN (C:N of non purgeable organic C and total dissolved N), K and Mn showed higher respiration.

Conclusions

The C:N ratio of the dissolved pool, rather than the quantity of N, was the major driver of decomposition rates. We saw dynamic changes in the microbial community from the beginning through the termination of the experiment.     

Litter decomposition of a pine plantation is affected by species evenness and soil nitrogen availability

Background and aims

Litter decomposition is a key process controlling flows of energy and nutrients in ecosystems. Altered biodiversity and nutrient availability may affect litter decomposition. However, little is known about the response of litter decomposition to co-occurring changes in species evenness and soil nutrient availability.

Methods

We used a microcosm experiment to evaluate the simultaneous effects of species evenness (two levels), identity of the dominant species (three species) and soil N availability (control and N addition) on litter decomposition in a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Northeast China. Mongolian pine needles and senesced aboveground materials of two dominant understory species (Setaria viridis and Artemisia scoparia) were used for incubation.

Results

Litter evenness, dominant species identity and N addition significantly affected species interaction and litter decomposition. Higher level of species evenness increased the decomposition rate of litter mixtures and decreased the incidence of antagonistic effects. A. scoparia-dominated litter mixtures decomposed faster than P. sylvestris var. mongolica- and S. viridis-dominated litter mixtures. Notably, N addition increased decomposition rate of both single-species litters and litter mixtures, and meanwhile altered the incidence and direction of non-additive effects during decomposition of litter mixtures. The presence of understory species litters stimulated the decomposition rate of pine litters irrespective of N addition, whereas the presence of pine litters suppressed the mass loss of A. scoparia litters. Moreover, N addition weakened the promoting effects of understory species litters on decomposition of pine litters.

Conclusions

Pine litter retarded the decomposition of understory species litters whereas its own decomposition was accelerated in mixtures. Nitrogen addition and understory species evenness altered species interaction through species-specific responses in litter mixtures and thus affected litter decomposition in Mongolian pine forests, which could produce a potential influence on ecosystem C budget and nutrient cycling.     

Litter species traits, but not richness, contribute to carbon and nitrogen dynamics in an alpine meadow on the Tibetan Plateau

Aims

Litter, as afterlife of plants, plays an important role in driving belowground decomposition processes. Here we tested effects of litter species identity and diversity on carbon (C) and nitrogen (N) dynamics during litter decomposition in N-limited alpine meadow soil from the Qinghai–Tibet Plateau.

Methods

We incubated litters of four meadow species, a sedge (“S”, Kobresia humilis), a grass (“G”, Elymus nutans), a herb (“H”, Saussurea superba), and a legume (“L”, Oxytropis falcata), in monoculture and in mixture with meadow soil. CO₂ release was measured 21 times during the incubation, and soil available N and microbial biomass C and N were measured before and after the experiment.

Results

The organic C decay rate did not differ much among soils amended with monocultures or mixtures of litter, except in the H, S, L, and S+H treatments, which had much higher decay rates. Potential decomposable C pools were lowest in the control, highest in the L treatment, and intermediate in the S treatment. Mineralized N was completely immobilized by soil microbes in all treatments except the control, S+L, and S+G+L treatments. Litter mixtures had both additive and non-additive effects on CO₂-C emission (mainly antagonistic effects), net N mineralization (mainly synergistic), and microbial biomass C and N (both). Overall, these parameters were not significantly correlated with litter species richness. Similarly, microbial C or N was not significantly correlated with litter N content or C/N. However, cumulative CO₂-C emission and net N mineralization were positively correlated with litter N content and negatively correlated with litter C/N.

Conclusions

Litter N content and C/N rather than litter species richness drove the release of CO₂-C and net available N in this ecosystem. The antagonistic effects of litter mixtures contributed to a modest release of CO₂-C, but their synergistic effects enhanced net available N. We suggest that in alpine meadow communities, balancing species with high and low N contents will benefit soil carbon sequestration and plant competition for available N with soil microbes.     

The effects of the moss layer on the decomposition of intercepted vascular plant litter across a post-fire boreal forest chronosequence

Aims

Feather mosses form a thick ground layer in boreal forests that can intercept incoming litter fall. This interception may influence the decomposition of incoming litter but this has been little explored. We investigated how the moss layer influences decomposition of intercepted litter along a 362-year fire driven forest chronosequence in northern Sweden across which soil fertility declines.

Methods

We placed leaf litter from three plant species into plots in which mosses and dwarf shrubs were either experimentally removed or left intact, at each of ten stands across the chronosequence. After one year we measured litter mass loss, and litter nitrogen and phosphorous.

Results

Litter decomposed consistently faster, and had higher nitrogen and phosphorus, in the presence of mosses and at greater depth in the moss layer. Despite an increase in moss depth across the chronosequence we did not find consistent increases in effects of moss removal on litter decomposition or on litter N or P.

Conclusions

Our findings identify a clear role of the moss layer in boreal forests in promoting the decomposition of intercepted leaf litter, and highlight that this role is relatively consistent across chronosequence stages that vary greatly in productivity and moss depth.     

Nitrogen transfer in litter mixture enhances decomposition rate,temperature sensitivity,and C quality changes

Background and aims

Litter decomposition is a critical process in terrestrial ecosystems and, since in natural conditions plant litter occurs in mixtures, understanding the interactive effects of mixed litter is of great ecological relevance. In this context, we test the hypothesis that N transfer between high quality litter to N-poor substrates are at the base of synergistic interactions, positively affecting litter decay rate, temperature sensitivity, and changes of organic C quality.

Methods

We carried out a manipulative experiment using four organic substrates, encompassing a wide range of biochemical quality (Hedera helix and Quercus ilex leaf litter, cellulose strips and woody sticks), each decomposing either separately or in matched pair mixtures for 360 days. Organic substrates were characterized for mass loss, C and N content and by ¹³C CPMAS NMR to assess biochemical quality changes.

Results

Litter response to mixing was related to the biochemical quality of the components in the mixture: additive when substrates with similarly high (H. helix and Q. ilex) or low (cellulose and wood) N content were paired, but synergistic when substrates with contrasting N content were associated (either of the two leaf litters with either cellulose or wood). Overall, no antagonist effects were observed in this experiment. Interestingly, decomposition of cellulose and wood showed an higher temperature sensitivity, compared to monospecific substrates, when paired with N rich materials. Significant N transfer was found from N rich litter to N poor substrates and ¹³C CPMAS NMR showed rapid changes of C quality of cellulose and wood sticks only when paired with N rich litter.

Conclusions

Our findings support the hypothesis that mixing litters of different quality, with quality expressed in terms of C/N ratio and N content, increases decomposition rate and temperature sensitivity of the lower quality substrates.     

Drivers of spatial variability in urban plant and soil isotopic composition in the Los Angeles basin

Aims

Plant litter decomposition plays an important role in the storage of soil organic matter in terrestrial ecosystems. Conversion of native vegetation to agricultural lands and subsequent land abandonment can lead to shifts in canopy structure, and consequently influence decomposition dynamics by alterations in soil temperature and moisture conditions, solar radiation exposure, and soil erosion patterns. This study was conducted to assess which parameters were more closely related to short-term decomposition dynamics of two predominant Mediterranean leaf litter types.

Methods

Using the litterbag technique, we incubated leaf litter of Pinus halepensis and Rosmarinus officinalis in two Mediterranean land-uses with different degree of vegetation cover (open forest, abandoned agricultural field).

Results

Fresh local litter lost between 20 and 55% of its initial mass throughout the 20-month incubation period. Rosemary litter decomposed faster than pine litter, showing net N immobilization in the early stages of decomposition, in contrast to the net N release exhibited by pine litter. Parameters related to litter quality (N content or C:N) or land-use/site conditions (ash content, an index of soil deposition on litter) were found to explain the cross-site variability in mass loss rates for rosemary and Aleppo pine litter, respectively.

Conclusions

The results from this study suggest that decomposition drivers may differ depending on litter type in this Mediterranean ecosystem. While rosemary litter was degraded mainly by microbial activity, decomposition of pine litter was likely driven primarily by abiotic processes like soil erosion.     

Effects of differential grazing on decomposition rate and nitrogen availability in a productive mountain grassland

Background and aims

Grazing may influence nutrient cycling in several ways. In productive mountain grasslands of central Argentina cattle grazing maintain a mosaic of different vegetation patches: lawns, grazed intensively and dominated by high quality palatable plants, and open and closed tussock grasslands dominated by less palatable species. We investigated if differences in the resources deposited on soil (litter and faeces) were associated with litter decomposition rates and soil nitrogen (N) availability across these vegetation patches.

Methods

We compared the three vegetation patches in terms of litter and faeces quality and decomposability, annual litterfall and faeces deposition rate. We determined decomposition rates of litter and faces in situ and decomposability of the same substrates in a common garden using “litter bags”. We determined soil N availability (with resin bags) in the vegetation patches. Also, we performed a common plant substrates decomposition experiment to assess the effect of soil environment on decomposition process. This technique provides important insights about the soil environmental controls of decomposition (i.e. the sum of soil physicochemical and biological properties, and microclimate), excluding the substrate quality.

Results

The litter quality and faeces deposition rate were higher in grazing lawns, but the total amounts of carbon (C) and nitrogen (N) deposited on soil were higher in tussock grasslands, due to higher litterfall in these patches. The in situ decomposition rates of litter and faeces, and of the two common plant substrates were not clearly related to either grazing pressure, litterfall or litter quality (C, N, P, lignin, cellulose or hemicellulose content). In situ litter decomposition rate and soil ammonium availability were correlated with the decomposition rates of both common plant substrates. This may suggest that difference in local soil environment among patch types is a stronger driver of decomposition rate than quality or quantity of the resource that enter the soil.

Conclusions

Our results show that, although high grazing pressure improves litter quality and increases faeces input, the reduction in biomass caused by herbivores greatly reduces C and N input for the litter decomposition pathway. We did not find an accelerated decomposition rate in grazing lawns as proposed by general models. Our results point to soil environment as a potential important control that could mask the effect of litter quality on field decomposition rates at local scale.     

Interactions between leaf litter and soil organic matter on carbon and nitrogen mineralization in six forest litter-soil systems

Background and aims

Leaf litter decomposes on the surface of soil in natural systems and element transfers between litter and soil are commonly found. However, how litter and soil organic matter (SOM) interact to influence decomposition rate and nitrogen (N) release remains unclear.

Methods

Leaf litter and mineral soil of top 0–5 cm from six forests were incubated separately, or together with litter on soil surface at 25 °C for 346 days. Litter N remaining and soil respiration rate were repeatedly measured during incubation. Litter carbon (C) and mass losses and mineral N concentrations in litter and soil were measured at the end of incubation.

Results

Net N transfer from soil to litter was found in all litters when incubated with soil. Litter incubated with soil lost more C than litter incubated alone after 346 days. For litters with initial C: N ratios lower than 52, net N_min after 346 days was 100 % higher when incubated with soil than when incubated alone. Litter net N_min rate was negatively related to initial C: N ratio when incubated with soil but not when incubated alone. Soil respiration rate and net N_min rate did not differ between soil incubated with litter and soil incubated alone.

Conclusions

We conclude that soils may enhance litter decomposition rate by net N transfer from soil to litter. Our results together with studies on litter mixture decomposition suggest that net N transfer between decomposing organic matter with different N status may be common and may significantly influence decomposition and N release. The low net N_min rate during litter decomposition along with the small size of litter N pool compared to soil N pool suggest that SOM rather than decomposing litter is the major contributor to plant mineral N supply.     

Soil nutrient patchiness and plant genotypes interact on the production potential and decomposition of root and shoot litter: evidence from short-term laboratory experiments with Triticum aestivum

Aims

The purpose of this study was to test the hypotheses that soil nutrient patchiness can differentially benefit the decomposition of root and shoot litters and that this facilitation depends on plant genotypes.

Methods

We grew 15 cultivars (i.e. genotypes) of winter wheat (Triticum aestivum L.) under uniform and patchy soil nutrients, and contrasted their biomass and the subsequent mass, carbon (C) and nitrogen (N) dynamics of their root and shoot litters.

Results

Under equal amounts of nutrients, patchy distribution increased root biomass and had no effects on shoot biomass and C:N ratios of roots and shoots. Roots and shoots decomposed more rapidly in patchy nutrients than in uniform nutrients, and reductions in root and shoot C:N ratios with decomposition were greater in patchy nutrients than uniform nutrients. Soil nutrient patchiness facilitated shoot decomposition more than root decomposition. The changes in C:N ratios with decomposition were correlated with initial C:N ratios of litter, regardless of roots or shoots. Litter potential yield, quality and decomposition were also affected by T. aestivum cultivars and their interactions with nutrient patchiness.

Conclusions

Soil nutrient patchiness can enhance C and N cycling and this effect depends strongly on genotypes of T. aestivum. Soil nutrient heterogeneity in plant communities also can enhance diversity in litter decomposition and associated biochemical and biological dynamics in the soil.     

Higher accumulation capacity of cadmium than zinc by <Emphasis Type="Italic">Arabidopsis halleri ssp. germmifera</Emphasis> in the field using different sowing strategies

Background and Aims

Litter decomposition serves an important role in maintaining nitrogen (N) availability within forest ecosystems. However, the interactive effects of exogenous N, drought, and litter quality and mixing on N immobilization during decomposition remain unclear. The aim of this study was to assess the effects of litter quality, reduced precipitation, N addition, and their interactions on litter mass loss and N immobilization.

Methods

This field study analyzed the effects of N addition and decreased precipitation on the decomposition rates and associated N immobilization of four types of litter: Quercus mongolica (QM), Tilia amurensis (TA), Pinus koraiensis (PK), and a mixture (MIX) of all three. The chemical quality of the MIX was prepared in a 4:3:3 (mass) ratio of PK, TA, and QM litters. Litterbags were placed in an N addition and precipitation manipulation forest field and collected after 92, 154, 365, 457, and 874 days. Decomposing litter residues were characterized for mass loss and N content to assess N immobilization.

Results

The addition of N had no significant effect on litter decomposition under both precipitation conditions, but a reduction in precipitation significantly depressed litter decomposition. The increases in N immobilization with N addition depended on the litter type and decomposition period. Precipitation reduction had significant effects on N immobilization and enhanced the magnitude and duration of N immobilization in decomposing litter, and both of which can be increased by N addition. The results indicate that the litter species is the major regulator that controls mass loss and N immobilization. Furthermore, the MIX treatment did not show non-additive effects on mass loss but did exhibit some weak synergistic effects on N immobilization.

Conclusions

Our results suggest that decomposing litters could help to sequester N depending on the litter identity and water regime in temperate forest ecosystems.

     

Convergence and divergence of nutrient stoichiometry during forest litter decomposition

Background and aims

General theory of forest floor dynamics indicates convergence of properties during detrital decomposition. This study examined the hypothesis that nutrient stoichiometry, i.e. the relative amounts of nutrients, converges during litter decomposition.

Methods

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.) foliar litters that decomposed in their respective forests were analyzed for N, P, Ca, Mg, K, S, Mn, Fe, Zn, and Cu. A novel approach quantified the stoichiometric difference as the angle between nutrient vectors. The approach was also used to synthesize data from 11 previously published studies representing a broad array of litter types and locations.

Results

The stoichiometries of the Douglas-fir and red alder litters converged during the first 2 years of decomposition, but diverged in the subsequent 4 years. This temporal trajectory was explained by two competing sets of processes: stoichiometric convergence occurs when different litters decompose in the same environment, and divergence occurs when the same litter decomposes in different environments. Manganese, Fe, and Ca were important contributors to stoichiometric differences.

Conclusions

Stoichiometric convergence processes often dominate over divergence processes. Consideration of multi-nutrient stoichiometries may enhance the understanding of the functions of litter, including rates of decomposition and relative rates at which nutrients are released.     

Litterfall and litter nutrient dynamics under cocoa ecosystems in lowland humid Ghana

There have been few studies quantifying litterfall, standing litterstock and gross litter decomposition following forest conversion to plantation crops such as cocoa. Additionally, an assessment of changing processes occurring in forest floor litter systems with plantation age is lacking. We investigated litterfall production, standing litter changes and litter decomposition along a chronosequence of shaded cocoa farm fields (secondary forest, 3, 15 and 30-year-old) in the moist semi-deciduous forest belt in the Ashanti Region of Ghana in West Africa over 24 months. Mean annual litterfall production differed significantly among study sites and ranged from 5.0 to 10.4 Mg DM ha^?1. Similarly, standing litter differed significantly between land-use /plot ages. The results showed significant differences in quality between litter from forest and litter from cocoa plantations. Litterfall from forests had higher concentrations of nitrogen and lower concentration of soluble polyphenols and lignin compared to litter from cocoa systems. Monthly decomposition coefficients (k) estimated as $ k = {{\left( {{\text{A}} - \left( {{\text{L}}_1 - {\text{L}}_0 } \right)} \right)} \mathord{\left/ {\vphantom {{\left( {{\text{A}} - \left( {{\text{L}}_1 - {\text{L}}_0 } \right)} \right)} {\left( {{{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} \mathord{\left/ {\vphantom {{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} 2}} \right. } 2}} \right)}}} \right. } {\left( {{{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} \mathord{\left/ {\vphantom {{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} 2}} \right. } 2}} \right)}} $ , where A is litterfall production during the month, L₀ is the standing litterstock at the beginning of the month and L₁ is the standing litterstock at the end of the month. Annual decomposition coefficients (k _L ) were similar in cocoa systems (0.221–0.227) but higher under secondary forests (0.354). Correlations between litter quality parameters and the decomposition coefficient showed nitrogen and lignin concentrations as well as ratios that include nitrogen are the best predictors of decomposition for the litters studied. Our results confirm the hypothesis that decomposition decreases following forest conversion to shaded cocoa systems because of litter quality changes and that decomposition rates correlate to litter quality differences between forest and cocoa ecosystems. The study also showed that standing litter pools and litterfall production in recently converted cocoa plantations are low compared to secondary forests or mature cocoa systems. Management strategies involving the introduction of upper canopy species during plantation development with corresponding replacement of tree mortality with diverse fast growing species will provide high quality and quantity litter resources.     

Environmental controls and the influence of tree species on temporal variation in soil respiration in subtropical China

Background and aims

The knowledge of individual tree species impacts on soil respiration based on rigorous experimental designs is limited, but is crucial to help guide selection of species for reforestation and carbon (C) management purposes.

Methods

We assessed monthly soil respiration and its components, litterfall input, fine root production and mortality under 19-year-old native coniferous Cunninghamia lanceolata and broadleaved Mytilaria laosensis plantations in sub-tropical China.

Results

Total soil respiration from October 2011 to March 2013 was significantly lower under the C. lanceolata than the M. laosensis plantation. The difference in respiration rates derived from fine roots and the litter layer explained much of the variation of total soil respiration between the two tree species. We used an exponential equation and base temperature (10 °C) to normalize soil respiration rate and its components (R₁₀) and determined the correlation between R₁₀ and soil moisture. Although soil moisture had a positive relationship with R₁₀ derived from roots or litter under both C. lanceolata and M. laosensis forests, these positive correlations were masked by negative relationships between soil moisture and R₁₀ derived from root-free soil, which resulted in a neutral correlation between total R₁₀ and soil moisture under C. lanceolata forests. Monthly litterfall input was associated with variation in concurrent total soil respiration rate under the M. laosensis plantation and respiration rate lagging 3 months behind under the C. lanceolata plantation, which may suggest that litterfall input from M. laosensis can more rapidly produce C substrates for microbial respiration than litterfall from C. lanceolata.

Conclusions

This study highlighted that tree species-induced variation in the quality and quantity of fine roots and litterfall can impact not only the soil respiration rate but also the seasonal variation model of forest soil respiration.     

Mixtures with grass litter may hasten shrub litter decomposition after shrub encroachment into mountain grasslands

Aims

Shrub encroachment in mesic grasslands alters the identity and quality of litters entering the system. As litter from shrubs and grasses can differ in their quality, this can lead to differences in litter decomposition by the direct effect of quality, but also to litter interaction during decomposition. The objective of this study was to examine the occurrence of non-additive effects of litter mixtures on the decomposition rates of legume shrub litter (poor in P) or conifer shrub litter (poor in N) and grass litter.

Methods

In addition to single litter type litterbags for the three species, we mixed litters of each pair of possible combinations to determine the influence of each species on mass loss. Litterbags were placed in the field and collected after 1, 6, 8, 12 and 24 months. In each collection, litter of each species remaining in mixed bags was separated, dry weighed and analyzed for C, N and P.

Results

With respect to shrub litter decomposing alone, mass loss of shrub litter when mixed with grass showed a 9–10 % increase in decomposition rate for conifer and a 3 % increase for legume litter. These litter mixture effects varied with time and they were detected after a decomposition period of 1 year in legume litter and of 2 years in conifer litter.

Conclusions

Grass litter hastened conifer and legume litter decomposition in leaf litter mixtures, at least during the first stages of the process. The potential consequences of this result to alter litter accumulation patterns and thus carbon sequestration rates after shrub encroachment into grasslands will depend on whether the observed trends are maintained in the advanced decomposition stages.     

Contribution of 15N-labelled leaf litter to N turnover, nitrous oxide emissions and N sequestration in a beech forest during eleven years

Aims

Decomposition of leaf litterfall plays a major role for nitrogen (N) dynamics in soils. However, little is known as to which extent beech leaf litter contributes to N turnover and nitrous oxide (N₂O) emissions within one decade after litterfall.

Methods

In 1997, we exchanged recently fallen leaf litter by ¹⁵N-labelled litter in a beech stand (Fagus sylvatica) at the Solling, Germany. Measurements were conducted 2–3 and 10–11 years after litter exchange.

Results

Two years after litter exchange, 92 % of added ¹⁵N was recovered in the surface 10 cm of the soil. The labelled N was primarily found in the upper part of the F layer of the moder type humus. Eleven years after litter exchange, 73 % of the added ¹⁵N was lost and the remaining 27 % was mainly recovered in the lower part of the F layer indicating N sequestration. The remaining leaf litter N was subject to measurable N mineralisation (2–3 % of litter N) and N₂O production (0.02 %). Between 0.3 % (eleventh year) and 0.6 % (second year) of total annual N₂O emissions were attributed to beech leaf litter of a single year.

Conclusions

Most of the annual N₂O emissions (1.33–1.54 kg N ha^?1 yr^?1) were probably derived from older soil N pools.     

杉木和香樟酸雨酸解底物的分解格局

采用凋落物分解袋法,选取湘西地区两种人工林优势树种(香樟和杉木)的凋落叶作为分解材料,分析了两种凋落叶经酸解处理后凋落物分解及其微生物活性的变化。结果表明:酸解处理过程会使两种凋落叶损失一定的质量,随着酸解强度的增加质量损失增加,且酸解处理对香樟凋落物质量损失的影响较杉木凋落物大。不同物种凋落物对酸解强度的差异性反应产生了后续分解过程的差异格局:酸雨酸解作用的增强抑制了杉木凋落物分解过程中包括真菌生物量以及纤维素酶与木质素酶在内的微生物活性;而对于香樟凋落物分解过程,微生物活性对酸雨酸解的响应因变量不同、分解期不同而存在差异性。两物种凋落物的总失重率、木质素和纤维素分解率对酸解作用的响应及其在不同分解期的表现也存在差异性:对于杉木凋落物,在分解前期其失重率表现为T1T2T3,而在后期随酸解强度的增大而升高,即T3T2/T1;香樟凋落物在分解的前期(T1T2T3)与后期(T1T2T3)情况则正好与杉木凋落物相反。总之,酸雨酸解凋落物不仅使底物有机组成发生了变化,在一定程度上导致凋落物物理结构紧密程度改变,而且也可能相应地改变了凋落物定殖微生物群落,这些复合影响从不同程度上决定了凋落物分解及其微生物活性对凋落物底物酸解的响应。     

Greater accumulation of litter in spruce (Picea abies) compared to beech (Fagus sylvatica) stands is not a consequence of the inherent recalcitrance of needles

Background and aims

Replacement of beech by spruce is associated with changes in soil acidity, soil structure and humus form, which are commonly ascribed to the recalcitrance of spruce needles. It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.

Methods

Litter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on three nutrient-rich sites and three nutrient-poor sites over a three-year period using the litterbag method (single species and mixed species bags).

Results

Mass loss of beech litter was not higher than mass loss of spruce litter. Mass loss and nutrient release were not affected by litter mixing. Litter decay indicated non-additive patterns, since similar remaining masses under pure beech (47%) and mixed beech-spruce (48%) were significantly lower than under pure spruce stands (67%). Release of the main components of the organic substance (C_org, N_tot, P, S, lignin) and associated K were related to mass loss, while release of other nutrients was not related to mass loss.

Conclusions

In contradiction to the widely held assumption of slow decomposition of spruce needles, we conclude that accumulation of litter in spruce stands is not caused by recalcitrance of spruce needles to decay; rather adverse environmental conditions in spruce stands retard decomposition. Mixed beech-spruce stands appear to be as effective as pure beech stands in counteracting these adverse conditions.     

Combination of nitrogen deposition and ultraviolet-B radiation decreased litter decomposition in subtropical China

Aims

The interactive effects of enhanced nitrogen (N) deposition and ultraviolet-B (UV-B) radiation on litter decomposition are still unknown. The aims are to test whether the interactive effects of the two environmental factors on litter decomposition and nutrient loss are stronger than that of each factor alone.

Methods

Experiment included five treatments: elevated UV-B radiation (UV-B, 10 % enhancement), low N addition (N1, 30 kg N ha^?1 year^?1), high N addition (N2, 60 kg N ha^?1 year^?1), the two combined treatments of the two factors (UV-B+N1 and UV-B+N2), and an unmanipulated control.

Results

The annual decomposition rates under combination of UV-B and N addition significantly decreased compared with that under UV-B and N additions for Pinus massoniana, and did also compared with that under UV-B but did not significantly differ with N additions for Cyclobalanopsis glauca. Negative effects of N additions alone on lignin degradation and P loss were partly offset but negative effect on N loss was further amplified when was combined with UV-B.

Conclusions

The combination of N deposition and UV-B radiation on litter decomposition and nutrient loss was significantly different from that of each factor alone without a general response pattern of decomposition, and was regulated by litter chemistry.