Litter Decay Rates Research Articles

Effects of Calcium on the Rate and Extent of Litter Decomposition in a Northern Hardwood Forest

Cross-site syntheses of litter decomposition studies have shown that litter calcium (Ca) concentration may have a role in controlling the extent of decomposition of tree foliage. We used an ongoing watershed CaSiO3 addition experiment at the Hubbard Brook Experimental Forest in New Hampshire, USA, to test the hypotheses that increased Ca in litter would have no effect on the initial rates of litter decay but would increase the extent or completeness (limit value) of foliar litter decomposition. We tested these hypotheses with a 6-year litter decomposition experiment using foliar litter of four tree species that are prominent at this site and in the Northern Hardwood forest type of North America: sugar maple (Acer saccharum Marsh), American beech (Fagus grandifolia Ehrh.), yellow birch (Betula alleghaniensis Britt.), and white ash (Fraxinus americana L.). The experiment used a reciprocal transplant design with the Ca-treated watershed and a control site providing two sources of litter and two placement sites. The litter from the Ca-treated site was 10–92% higher in Ca concentration, depending on species, than the litter from the control site. After about 3 years of decomposition, the Ca concentrations in the litter reflected the placement of the litter (that is, the site in which it was incubated) rather than the source of the litter. The source of the litter had no significant effect on measures of initial decomposition rate, cumulative mass loss (6 years), or limit value. However, the placement of the litter had a highly significant effect on extent of decomposition. Some litter types responded more than others; in particular, beech litter placed in the Ca-treated site had a significantly higher limit value, indicating more complete decomposition, and maple litter in the Ca-treated site had a marginally higher limit value. These results indicate that Ca may influence the extent of litter decomposition, but it is the Ca at the incubation site rather than the initial litter Ca that matters most. The results also suggest that loss of Ca from the soil due to decades of acid deposition at this site may have impeded late-stage litter decomposition, possibly leading to greater soil C storage, especially in forest stands with a substantial component of beech. Likewise, de-acidification may lead to a reduction in soil C.

Decay rates of leaf litters from arbuscular mycorrhizal trees are more sensitive to soil effects than litters from ectomycorrhizal trees

SummaryWhile it is well established that leaf litter decomposition is controlled by climate and substrate quality at broad spatial scales, conceptual frameworks that consider how local‐scale factors affect litter decay in heterogeneous landscapes are generally lacking.A critical challenge in disentangling the relative impacts of and interactions among local‐scale factors is that these factors frequently covary due to feedbacks between plant and soil communities. For example, forest plots dominated by trees that associate with ectomycorrhizal (ECM) fungi often differ from those dominated by trees that associate with arbuscular mycorrhizal (AM) fungi in terms of their litter quality, microbial community structure and inorganic nutrient availability. Here, we evaluate the extent to which such factors alter leaf litter decomposition rates.To characterize variations in decomposition rates, we compared decay rates of high‐quality litter (maple;AM) and low‐quality litter (oak;ECM) across forest plots representing a gradient in litter matrix quality and nitrogen (N) availability driven by the relative proportions ofAMandECMtrees in each plot. In experiment two, we added litter from twoAMand threeECMtree species to forest plots with either a high‐quality litter matrix and high N availability (i.e.AM‐dominated plots) or a low‐quality litter matrix and low N availability (i.e.ECM‐dominated plots). In both experiments, we found thatAMlitter decomposed more rapidly thanECMlitter, and this effect was enhanced inAM‐dominated plots.Then, to separate the contributions of litter matrix effects from N availability effects, we added N fertilizer to a subset of plots from experiment two. Nitrogen addition increased decay rates of high‐quality litter across all sites, but had no effect on low‐quality litter, suggesting that low N availability, not litter matrix quality, constrains decomposition of high‐quality litters. Hence, N availability appears to alter litter decomposition patterns independently of litter matrix properties.Synthesis. Our results indicate that shifts in the relative abundance ofECM‐ andAM‐associated trees in a plot or stand have the potential to affect litter decay rates through both changes in litter quality as well as through alterations of the local‐scale soil environment.

Changes in litter quality caused by simulated nitrogen deposition reinforce the N‐induced suppression of litter decay

Rates of nitrogen (N) deposition are increasing in industrialized and rapidly developing nations. Simulated N deposition suppresses plant litter decay rates, in particular for low quality (high lignin) litter. Litter quality is a primary driver of litter decomposition; however, it is not clear how changes in litter quality caused by long‐term ecosystem exposure to chronic N additions interact with altered soil N‐availability to influence litter decay dynamics. To document the effects of simulated N deposition on litter quality, we conducted a meta‐analysis of available litter nutrient data from simulated N deposition experiments in temperate forests. To directly test whether changes in litter quality caused by N deposition affect decay rates, we also conducted a reciprocal litterbag study in an existing N addition experiment, where a northern hardwood forest has been exposed to simulated N deposition for more than 20 years. The experiment enabled us to disentangle the effects of N additions, litter quality, and their interactions on litter decay dynamics. We measured litter mass loss and extracellular enzyme activities after one and two years of decomposition. The meta‐analysis demonstrated that simulated N deposition causes decreases of leaf Al, B, Ca, Mg, Mn, P, and Zn concentrations, and increased leaf N concentrations. Moreover, higher cumulative amounts of simulated N deposition result in greater decreases of leaf Ca and Mn concentrations. In the field experiment, litter originally collected from N‐enriched plots exhibited similar N‐induced nutrient changes as observed in our meta‐analysis and also had lower lignolytic enzyme activities and decay rates than litter collected from control plots. The decreased litter decay rates observed with simulated N deposition were a result of the combined effects of the N fertilization itself and the historical effects of N deposition on tree litter chemistry. The data suggest that changes in litter quality caused directly by long‐term N enrichment reinforce the negative effects of simulated N deposition on litter decay, particularly for high lignin species. The slowed decay associated with changes in litter quality caused by N enrichment itself may partly explain the accumulation of organic matter previously observed at ours and at other simulated N deposition experiments.

Mangrove associates versus true mangroves: a comparative analysis of leaf litter decomposition in Sundarban

Mangrove species are broadly classified as ‘true mangroves’ and ‘mangrove associates’. We hypothesized that the leaf litter decomposition rates of true mangroves differ significantly from the mangrove associates under the same ecological and bio-climatic conditions. In order to test this hypothesis, the leaf litter decay rates of 24 true mangrove species and 10 mangrove associates along with the concomitant carbon and nitrogen dynamics of the litters were studied in the tropical mangrove forest of Sundarban by means of litter bags. The decomposition was monitored for six consecutive weeks in the pre-monsoon, monsoon and post-monsoon season. All the species in general went through a rapid decay phase in the first 2 weeks, however, the rate substantially decreased in the following 4 weeks. Most of the species studied had significant seasonal variability (p < 0.05) in the decay rate. Species-specific decay was highest throughout the monsoon and least during the post-monsoon season. The mean dry weight composition (i.e. percentage of dry weight of the leaf litters remaining at the end of weekly intervals) of the true mangroves was 10–12 % higher than the mangrove associates throughout the sampling period. The mean decay constants (K in week−1) of the true mangroves were 0.15 ± 0.05, 0.20 ± 0.06 and 0.16 ± 0.05 in the pre-monsoon, monsoon and post-monsoon season respectively. The mangrove associates had significantly higher decay constants in the respective seasons that followed the order 0.23 ± 0.09, 0.25 ± 0.06 and 0.24 ± 0.09. As a consequence, the computed mean half-life period of the true mangrove litters (32 ± 11 days) was much higher than the mangrove associates (23 ± 11 days). This showed that collectively the leaf litters of mangrove associates degraded at a much faster rate than the true mangroves throughout the annual cycle and thus our hypothesis was justified.

Decomposition of Suaeda salsa and Phragmites australis in the degraded wetland of Shaohai: Species and tissue difference implications on ecosystem restoration

Litter decomposition plays a key role in the recovery of wetlands, as it regulates the rate of soil organic matter (SOM) retention, fuels soil biota, and provides critical nutrients for plant growth. In natural plant succession, plant biological processes (especially litter decomposition) and soil chemistry can drive each other; therefore, the relationship between plant and soil can be used to restore the degraded wetlands without any side effect on the ecosystem. However, how litter decomposition influences soil chemistry and wetland restoration across species and tissues is not clear. We conducted a field litterbag study on decomposition of leaves, stems, roots, and fine roots of <i>Suaeda salsa</i> (<i>S. salsa</i>) and <i>Phragmites australis</i> (<i>P. australis</i>) in a degraded wetland of Shaohai in Qingdao near the Jiaozhou Bay, China. Results showed that litter decomposition is species and tissue specific. <i>S. salsa</i> had a higher decay rate and a larger amount of net nitrogen (N) release than <i>P. australis</i>, but the pattern was only limited in leaf litter; in stems and roots, the decomposition pattern was opposite. Leaf litter had a larger decay rate and amount of net N release than other tissues. Litter decay rates are positively related with initial N concentrations under low lignin concentrations (acid-insoluble carbon (C) fractions, “low” is &lt; 35%), confirming the interactive effect of lignin and N concentrations on litter decay rates. Litter N release pattern is controlled by the decomposition of N-rich C fractions. After 202 days of decomposition, <i>S. salsa</i> (especially stems and roots) contributed less SOM and N than <i>P. australis</i>, but <i>S. salsa</i> (especially leaves) released more N than <i>P. australis</i>, suggesting that <i>S. salsa</i> (especially its leaf) had an advantage to supply short-term N, while <i>P. australis</i> had an advantage to supply long-term N. Therefore, litter decomposition of <i>S. salsa</i> can be suggested for restoring degraded coastal wetlands because it can supply both short-term nutrients and long-term nutrients for new species settlement. Our study gave a further understanding of litter decomposition and suggested litter decomposition as the criterion to select plant species for the restoration of degraded wetlands, but long-term study should be continued to test the conclusion.

Climate change may reduce litter decomposition while enhancing the contribution of photodegradation in dry perennial Mediterranean grasslands

Understanding how the interactions between solar UV radiation and climate will affect leaf litter decomposition is fundamental to predict how soil and ecosystem biogeochemical cycles will respond to ongoing climate change. We carried out a manipulative experiment to investigate how UV radiation and its interaction with increased temperature (3 °C on average) and a ∼35% reduction in precipitation affect the decomposition of “standing” and “on the ground” litter of Stipa tenacissima, a dominant species in semiarid Mediterranean grasslands. UV radiation was manipulated using specially designed screens that either passed or blocked 90% of the UV radiation. All climate change manipulation treatments decreased litter decomposition compared to the control treatment. In particular, litter decay rates were reduced by a 34%, 43% and 62% in the rainfall reduction (RE), warming (W), and the combination of warming and rainfall reduction (WRE) treatments, respectively, compared to the control treatment. Across climate manipulation treatments, higher decay rates were observed in litter exposed to UV radiation than in litter non-exposed to UV radiation, and in litter placed on the ground than in standing litter. However, significant interactions were found between climate manipulation and UV exposure or position treatments. In the control and RE treatments, litter on the ground decomposed 25% faster than standing litter. In the W and WRE treatments, litter decomposition rates increased by 29% when exposed to UV radiation despite lower overall decay rates were observed in these treatments. Overall, lignin losses were parallelled by increases in soluble cell materials, particularly when litter was exposed to UV radiation. Our results indicate that predicted climate change scenarios will likely reduce leaf litter decomposition rates, while enhancing the relative contribution of photodegradation to overall litter decomposition in dry perennial Mediterranean grasslands.

Influence of manganese on decomposition of common beech (Fagus sylvatica L.) leaf litter during field incubation

Litter decomposition is of crucial importance for sustainable production in forest ecosystems with pedoclimatic conditions and nutrients being the main factors controlling litter decomposition. In particular, manganese (Mn) could accelerate decomposition of litter in the lignin-dominated (late) stage. Correlations between Mn concentration and litter decay rate were previously reported and explained by the role of Mn2+ in lignin degradation as a cofactor of the enzyme manganese peroxidase. However, the role of Mn in litter decay has been little experimentally tested yet. This study aims to assess the increased decomposition rate of common beech (Fagus sylvatica L.) leaf litter experimentally enriched in Mn (0.9–17.0 mg g−1) using a litterbag experiment (500 days of in situ incubation). Mass loss and acid unhydrolyzable residue, Mn, carbon (C), and dissolved organic carbon were determined in remaining materials and litter leachates. Our results showed a positive influence of Mn on litter and C decay and on the release of hydrophobic dissolved organic C. We explained these results by an enhanced ligninolysis leading to an increase in dissolved polyphenolic compounds.

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

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

Leaf litter breakdown and benthic invertebrate colonization affected by seasonal drought in headwater lotic systems of Andean Patagonia

We aimed to establish the effect of seasonal drought on leaf litter breakdown and invertebrate communities. Differences in breakdown rates of Nothofagus pumilio were experimentally compared using the litter bag method (coarse and fine mesh size bags) in two first-order streams, one intermittent and one perennial, during two different hydrological periods. Colonizing fauna found in coarse mesh bags was quantified, identified and compared with benthic biota from the same streams. Leaf litter decay rates in low flow conditions revealed that breakdown was principally a consequence of microbial action in the intermittent stream. In contrast, breakdown in high flow conditions was caused by invertebrate feeding in both streams. Collector–gatherers constituted most of the abundance and biomass in bags from the intermittent stream, due to their rapid benthic recolonization. Shredders peaked at approximately 50% remaining leaf litter mass in both streams only during high flow, which coincided with general models of detritus breakdown in streams. Considering global warming scenarios, with drought and water temperature increases expected for many regions of the world, these studies on the consequences for the biota and ecological processes of small streams will allow the prediction of negative effects on such vulnerable ecosystems.

Leaf litter species identity alters the structure of pond communities

The input of leaf litter resources is a major driver of ecosystem processes in terrestrial and freshwater habitats. Although variation exists in the quantity and composition of litter inputs due to natural and anthropogenic causes, few studies have examined how such variation influences the structure and composition of aquatic food webs. Using outdoor mesocosms, we examined the bottom–up effects of 10 chemically distinct tree litter species on microbial, algal, invertebrate and vertebrate fauna found in temperate ponds. We hypothesized that individual litter species, which differ in their traits, would differentially and predictably affect abiotic and biotic elements of pond communities. We further hypothesized that the presence of leaf litter, regardless of species, would elevate resource supply and increase the biomass of community members. Finally, we hypothesized that a mixture of litter species would have non-additive effects on community responses. We followed the system for > 4 months and measured > 30 abiotic and biotic responses related to primary and secondary production. The different species of leaf litter had major effects on abiotic and biotic responses, including phytoplankton, periphyton, zooplankton, snails, amphipods and tadpoles. Most biological responses were negatively associated with soluble carbon content of litter, or litter decay rate. Other litter traits, including phenolic concentrations and litter C:N were of secondary importance but did exhibit both positive and negative associations with several responses. The absence of litter had pervasive effects on abiotic attributes, but did not promote substantial changes in organism biomass. Most responses to the litter mixture were additive. Our results suggest that changes in temperate forest composition can strongly affect pond communities.

Urbanization effects on leaf litter decomposition, foliar nutrient dynamics and aboveground net primary productivity in the subtropics

Urbanization can alter nutrient cycling. This research evaluated how urbanization affected nutrient dynamics in the subtropics. We established 17–0.04 ha plots in five different land cover types—slash pine (Pinus elliottii) plantations (n = 3), rural natural pine forests (n = 3), rural natural oak forests (n = 4), urban pine forests (n = 3) and urban oak forests (n = 4) in the Florida panhandle, a subtropical region that has experienced rapid urbanization. On each plot, we measured the decomposition of mixed species foliar litter, the nutrient release patterns in decomposing litter, foliar litter quality, and forest floor temperatures. Aboveground net primary productivity and soil carbon and nitrogen contents were also measured to characterize the carbon and nitrogen stocks and fluxes in the urban and rural sites. Litter decay rates, liter quality indices and nutrient release patterns in decomposing litter did not differ among urban and rural forests despite differences in forest floor temperatures between urban and rural sites. Urban forest floor temperatures are on average warmer by 0.63 °C in the winter (p = 0.005) and tend to have a more narrow temperature range than those of the rural forested sites. Foliar mass was measured over an 82 week period that was characterized by drought, which may have masked an urbanization effect. Urban forest land covers had higher aboveground net primary productivity and foliar productivity compared to rural land covers. This increased input of foliar carbon is not reflected in statistically different forest floor or surface soil (0–7.5 cm) carbon contents between urban and rural sites. Understanding how drought interacts with other drivers of change in urban systems may be a necessary component of city specific ecological knowledge.

Signature wood modifications reveal decomposer community history.

Correlating plant litter decay rates with initial tissue traits (e.g. C, N contents) is common practice, but in woody litter, predictive relationships are often weak. Variability in predicting wood decomposition is partially due to territorial competition among fungal decomposers that, in turn, have a range of nutritional strategies (rot types) and consequences on residues. Given this biotic influence, researchers are increasingly using culture-independent tools in an attempt to link variability more directly to decomposer groups. Our goal was to complement these tools by using certain wood modifications as ‘signatures’ that provide more functional information about decomposer dominance than density loss. Specifically, we used dilute alkali solubility (DAS; higher for brown rot) and lignin:density loss (L:D; higher for white rot) to infer rot type (binary) and fungal nutritional mode (gradient), respectively. We first determined strength of pattern among 29 fungi of known rot type by correlating DAS and L:D with mass loss in birch and pine. Having shown robust relationships for both techniques above a density loss threshold, we then demonstrated and resolved two issues relevant to species consortia and field trials, 1) spatial patchiness creating gravimetric bias (density bias), and 2) brown rot imprints prior or subsequent to white rot replacement (legacy effects). Finally, we field-tested our methods in a New Zealand Pinus radiata plantation in a paired-plot comparison. Overall, results validate these low-cost techniques that measure the collective histories of decomposer dominance in wood. The L:D measure also showed clear potential in classifying ‘rot type’ along a spectrum rather than as a traditional binary type (brown versus white rot), as it places the nutritional strategies of wood-degrading fungi on a scale (L:D=0-5, in this case). These information-rich measures of consequence can provide insight into their biological causes, strengthening the links between traits, structure, and function during wood decomposition.

Linking tree species identity to anaerobic microbial activity in a forested wetland soil via leaf litter decomposition and leaf carbon fractions

Our aim was to examine the linkage between tree species and anaerobic microbial activity in a forested wetland. If plant species have a unique influence on soil microorganisms, then knowing plant species identity has tremendous potential to predict rates of microbial activity belowground. We expected the linkage to occur via leaf litter decay rate and differences in leaf litter carbon (C) fractions. We used leaf litter from 10 tree species (angiosperm and gymnosperm, deciduous and evergreen) and soil from a forested wetland in New York State. We quantified leaf litter decay on the soil surface and correlated variation in rates with leaf mass per area (LMA) and several C fractions. We extracted water-soluble compounds from green leaves and leaf litter and tested their ability to fuel anaerobic carbon dioxide (CO2) production and methane (CH4) production. We also added leaf litter directly to soil to examine how the residue might influence anaerobic microbial activity. Leaf decay rates exhibited a negative linear relationship with LMA. Variations in rates of soil methane (CH4) production were species specific and greater with gymnosperms (mean = 8.6 μmol g−1 d−1) than angiosperms (mean = 3.7 μmol g−1 d−1). Rates of anaerobic CO2 production were less affected by plant species. Pectin and hemicellulose in leaf litter was particularly conducive to anaerobic decomposition and CH4 production. The influence of plant species on soil microbial activity will become clearer when we can better quantify leaf C fractions and understand the decomposability of each fraction in relationship to others.

Tropical wetlands: A missing link in the global carbon cycle?

Tropical wetlands are not included in Earth system models, despite being an important source of methane (CH4) and contributing a large fraction of carbon dioxide (CO2) emissions from land use, land use change, and forestry in the tropics. This review identifies a remarkable lack of data on the carbon balance and gas fluxes from undisturbed tropical wetlands, which limits the ability of global change models to make accurate predictions about future climate. We show that the available data on in situ carbon gas fluxes in undisturbed forested tropical wetlands indicate marked spatial and temporal variability in CO2 and CH4 emissions, with exceptionally large fluxes in Southeast Asia and the Neotropics. By upscaling short-term measurements, we calculate that approximately 90 ± 77 Tg CH4 year−1 and 4540 ± 1480 Tg CO2 year−1 are released from tropical wetlands globally. CH4 fluxes are greater from mineral than organic soils, whereas CO2 fluxes do not differ between soil types. The high CO2 and CH4 emissions are mirrored by high rates of net primary productivity and litter decay. Net ecosystem productivity was estimated to be greater in peat-forming wetlands than on mineral soils, but the available data are insufficient to construct reliable carbon balances or estimate gas fluxes at regional scales. We conclude that there is an urgent need for systematic data on carbon dynamics in tropical wetlands to provide a robust understanding of how they differ from well-studied northern wetlands and allow incorporation of tropical wetlands into global climate change models.

Opposing effects of substrate quality and site factors on forest floor turnover rates: an example from the tropics

In boreal-to-cool temperate regions, there is a consistent relationship between litter quality, litter decay rates in litterbags and forest floor turnover rates across different tree functional types such as conifers and deciduous trees. This is partly due to the synergistic relationship between substrate quality and site conditions (understorey temperatures)incontrollingforestfloordynamics.Thatis,specieswithhigherlightpenetrationhavehigherunderstorey temperatureand litterof higher qualitycomparedwith species withlower light penetration. Thefindings of our studyin Sarawak werepartlyconsistent withthistrend,with substrate quality, microbial respiration and mass loss rates of the litter in litterbags being higher for pioneer species from a young secondary forest (YSF) than for climax species from a primary forest (PF). However, the microbial respiration in the forest floor and its turnover ratewerelowerintheYSFwithlowerforestfloorwatercontentthanthoseinthePF.Thisdiscrepancywasexplained bytheopposingrelationshipbetweensubstratequalityandsiteconditions(forestfloormoisture).Thatis,intheYSF, thefavourableeffectsofsubstratequalityondecompositionwereoverriddenbytheunfavourableeffectsofforest floor moisture and the reverse was the case in the PF. It was concluded that the relationship between substrate quality and site factors (synergistic vs. opposing) in controlling decomposition is macroclimate dependent and that the power of substrate quality for predicting forest floor dynamics is lower in the tropics than that in boreal-to-cool temperate regions.

Long-term litter decay in Canadian forests and the influence of soil microbial community and soil chemistry

Long-term rates of litter decay have been shown to be primarily influenced by temperature, moisture and litter quality. However, while decomposition is a biological process, the relative importance of microbial communities and other soil chemistry factors is not well understood. Our analysis examined long-term litter decay parameters, microbial community composition via phospholipid fatty acid (PLFA) analysis, and soil organic horizon chemistry at 14 upland forested sites. Data were collected as part of the Canadian Intersite Decomposition Experiment (CIDET), a 12-year national litter decomposition experiment. Residual errors from a two-pool exponential decay model with decay rates modified by mean annual air temperature and moisture stress were compared to PLFA marker groups and chemistry variables. Residual errors were not well explained by soil PLFA marker group abundance or concentration, soil pH, nor soil C:N ratios. The best predictor of residual error was soil carbon percent (%C), with higher %C associated with slower than predicted decomposition.

An invasive species may be better than none: invasive signal and native noble crayfish have similar community effects

Summary Human activities have resulted in the decline of native crayfish and promoted the spread of invasive crayfish species in European fresh waters, threatening ecosystem structure and functioning. We compared effects of native noble crayfish (Astacus astacus), invasive signal crayfish (Pacifastacus leniusculus) and of the absence of crayfish on leaf litter breakdown and invertebrate prey density and biomass in stream ecosystems. In microcosm experiments, invertebrate shredder density was significantly reduced by crayfish presence but similarly affected by the two crayfish species. While crayfish did not directly influence leaf litter breakdown, their presence reduced litter decay rates through predation on invertebrate shredders (i.e. trophic cascade). These effects were again similar between native and invasive crayfish but differed among shredder prey species. Field experiments confirmed that leaf litter breakdown was significantly reduced by crayfish. Although total invertebrate density was not affected by crayfish predation, species‐specific effects were observed (e.g. Limnephilidae [Trichoptera] densities were reduced in the presence of crayfish) but did not differ between native and invasive species. Our results show that crayfish can have strong, but species‐specific, effects on invertebrate prey and indirect effects on leaf litter breakdown. Contrary to previous findings and popular belief, results also indicate that native noble crayfish and invasive signal crayfish have similar effects on stream communities. Hence, from a management perspective, it may be preferable to have invasive crayfish than no crayfish when impairment results in unsuitable habitats for native species.

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

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. 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. 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. 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.

Global relationship of wood and leaf litter decomposability: the role of functional traits within and across plant organs

AbstractAimRecent meta‐analyses have revealed that plant traits and their phylogenetic history influence decay rates of dead wood and leaf litter, but it remains unknown if decay rates of wood and litter covary over a wide range of tree species and across ecosystems. We evaluated the relationships between species‐specific wood and leaf litter decomposability, as well as between wood and leaf traits that control their respective decomposability.LocationGlobal.MethodsWe compiled data on rates of wood and leaf litter decomposition for 324 and 635 tree species, respectively, and data on six functional traits for both organs. We used hierarchical Bayesian meta‐analysis to estimate, for the first time, species‐specific values for wood and leaf litter decomposability standardized to reference conditions (k*woodandk*leaf) across the globe. With these data, we evaluated the relationships: (1) between wood and leaf traits, (2) between eachk* and the selected traits within and across organs, and (3) between wood and leafk*.ResultsAcross all speciesk*woodandk*leafwere positively correlated, phylogenetically clustered and correlated with plant functional traits within and across organs.k* of both organs was usually better described as a function of within‐ and cross‐organ traits, than of within‐organ traits alone. When analysed for angiosperms and gymnosperms separately, wood and leafk* were no longer significantly correlated, but eachk* was still significantly correlated to the functional traits.Main conclusionsWe demonstrate important relationships among wood and leaf litter decomposability as after‐life effects of traits from the living plants. These functional traits influence the decomposability of senesced tissue which could potentially lead to alterations in the rates of biogeochemical cycling, depending on the phylogenetic structure of the species pool. These results provide crucial information for a better representation of decomposition rates in dynamic global vegetation models.

Litter decomposition along a primary post-mining chronosequence

The aim of this study was to describe the decomposition of litter along a successive series of sites developed at a post-mining overburden deposit over 12, 21 and 45 years, representing the early, mid and late stages of succession. Litter decomposition was largely dependent on the initial composition of the litters. The tree litter of the mid and late stages decomposed faster than the grass litter of the early stage, with 64, 60 and 35 % of mass lost over 2 years, respectively. The contents of hot-water-soluble C and N, which were the best predictors of litter decay rates, were relatively stable over time in all litters. Neither the nutrient content nor the plant biopolymer composition exhibited convergence during decay, indicating that the litter-derived soil organic matter most likely carries a legacy of the original vegetation. In contrast to the litter chemistry, the development of the microbial community was largely specific to the decay stage and consistent among the litters, showing decreasing fungal dominance in time. Extracellular enzymes were found to be of limited value in the prediction of litter decay rates, chemical transformation or microbial community composition.