Composition of speciose leaf litter alters stream detritivore growth, feeding activity and leaf breakdown

Leaf litter derived from riparian trees can control secondary production of detritivores in forested streams. Species-rich assemblages of leaf litter reflect riparian plant species richness and represent a heterogeneous resource for stream consumers. Such variation in resource quality may alter consumer growth and thus the feedback on leaf breakdown rate via changes in feeding activity. To assess the consequences of this type of resource heterogeneity on both consumer growth and subsequent litter breakdown, we performed a laboratory experiment where we offered a leaf-shredding stream detritivore (the stonefly Tallaperla maria, Peltoperlidae) ten treatments of either single- or mixed-species leaf litter. We measured consumer growth rate, breakdown rate and feeding activity both with and without consumers for each treatment and showed that all three variables responded to speciose leaf litter. However, the number of leaf species was not responsible for these results, but leaf species composition explained the apparent non-additive effects. T. maria growth responded both positively and negatively to litter composition, and growth on mixed-litter could not always be predicted by averaging estimates of growth in single-species treatments. Furthermore, breakdown and feeding rates in mixed litter treatments could not always be predicted from estimates of single-species rates. Given that species richness and composition of senesced leaves in streams reflects riparian plant species richness, in-stream secondary production of detritivores and organic matter dynamics may be related to species loss of trees in the riparian zone. Loss of key species may be more critical to maintaining such processes than species richness per se.     

Mixed leaf litter effects on decomposition rates and soil microarthropod communities in an oak–pine stand in Japan

Rates of decomposition, and soil faunal abundance and diversity associated with single-species and mixed-species litters were studied in a litter bag experiment in an oak–pine forest. We used two canopy species of leaf litter, pine and oak, and one shrub species, Sasa, and compared decomposition rates, and soil microarthropod abundance and community structure of oribatid mites in the litter bags. Mass loss of single species decreased in the order: oak > pine > Sasa. While the total mass loss rates of mixed litter were intermediate between those of the constituent species, enhancement of mass loss from the three-species mixture and from mixed slow-decomposing litters (pine and Sasa) was observed. Faunal abundance in litter bags was higher in mixed-species litter than in those with single-species litter, and species richness of oribatid mites was also higher in the three-species mixed litter. Faunal abundance in single-species litter bags was not correlated with mass loss, although enhancement of mass loss in mixed litter bags corresponded with higher microarthropod abundance. Habitat heterogeneity in mixed litter bags seemed to be responsible for the more abundant soil microarthropod community.     

天童国家森林公园常见植物凋落叶分解的研究

 选择天童地区常绿阔叶林及其退化群落常见植物种为对象,着重探讨分解速率和基质营养含量以及比表面积(Specific Leaf Area, SLA)的关系,并试图通过单独分解试验和混合分解试验的比较,从物种、功能群角度探讨凋落叶多样性和分解这一生态系统过程的关系,为深入研究常绿阔叶林常见植物种的营养策略、群落养分循环等奠定基础,也为植被恢复、森林生态系统管理提供理论依据。结果表明：所有凋落叶随时间进程失重率增大,但失重率并不与时间呈线性相关;凋落叶分解后N、P均发生了变化,大多数凋落叶在分解初期N、P均发生了积累,营养元素的释放和富集与凋落叶初始营养状况无明显的相关性。凋落叶的年分解系数与凋落叶中的初始N含量有较高的相关性,而与初始P含量则无显著的相关性;凋落叶的分解速率与成熟叶的面积无相关性,而与其SLA有很强的相关性。通过模型分析,天童地区大多数常见树种凋落叶分解95%需1～4年,平均是2.54年;分解率最高的物种为山鸡椒(Litsea cubeba),其值为6.280,最低的为黄丹木姜子(Litsea elongata),其值为0.558。凋落物混合对分解有很大的影响,虽在初期对分解有阻碍作用,但长期是促进的。若不考虑功能群差异,则可得出多样性的增加有利于分解的结论。功能群数目的增加在凋落物分解前期对分解起促进作用,但这种作用随分解的进展逐渐减小。混合物种的特性往往是决定分解过程的最重要的因素。     

Ecosystem consequences of selective feeding of an insect herbivore: palatability–decomposability relationship revisited

1. The relationship between leaf palatability and litter decomposability is critical to understanding the effects of selective feeding by herbivores on decomposition processes, and several studies have reported that there is a positive relationship between them. 2. However, palatability is not always positively correlated with decomposability, because of species‐specific feeding adaptation of herbivores to host plants. Moreover, the effects of selective feeding by herbivores on soil decomposition processes should be understood in terms of the inputs of leaf litter and excrement. 3. The present study examined the relationships between leaf palatability and the decomposability of litter and frass, using Lymantria dispar Linnaeus and 15 temperate deciduous tree species. 4. Larvae of L. dispar exhibited a clear feeding preference, and subsequently the excreted frass mass differed among tree species. Litter and frass decomposability also differed among tree species, and frass was more rapidly decomposed than litter. There were no positive or negative correlations between palatability and decomposability of litter and frass. 5. These results indicate that L. dispar larvae may accelerate the decomposition process in temperate deciduous forests through selective feeding on plants with relatively low litter decomposability and the production of frass with higher decomposability than the litter.     

Fungi are involved in the effects of litter mixtures on consumption by shredders

1. Decomposition of litter mixtures in both terrestrial and aquatic ecosystems often shows non‐additive diversity effects on decomposition rate, generally interpreted in streams as a result of the feeding activity of macroinvertebrates. The extent to which fungal assemblages on mixed litter may influence consumption by macroinvertebrates remains unknown. 2. We assessed the effect of litter mixing on all possible three‐species combinations drawn from four tree species (Alnus glutinosa, Betula pendula, Juglans regia and Quercus robur) on both fungal assemblages and the rate of litter consumption by a common shredder, Gammarus fossarum. After a 9‐week inoculation in a stream, batches of leaf discs were taken from all leaf species within litter mixture combinations. Ergosterol, an indicator of fungal biomass, and the composition of fungal assemblages, assessed from the conidia released, were determined, and incubated litter offered to G. fossarum in a laboratory‐feeding experiment. 3. Mixing leaf litter species enhanced both the Simpson’s index of the fungal assemblage and the consumption of litter by G. fossarum, but had no clear effect on mycelial biomass. Specifically, consumption rates of J. regia were consistently higher for mixed‐species litter packs than for single‐species litter. In contrast, the consumption rates of B. pendula were not affected by litter mixing, because of the occurrence of both positive and negative litter‐mixing effects in different litter species combinations that counteracted each other. 4. In some litter combinations, the greater development of some fungal species (e.g. Clavariopsis aquatica) as shown by higher sporulation rates coincided with increased leaf consumption, which may have resulted from feeding preferences by G. fossarum for these fungi. 5. Where litter mixture effects on decomposition rate are mediated via shredder feeding, this could be due to indirect effects of the fungal assemblage.     

Do ectomycorrhizas alter leaf-litter decomposition in monodominant tropical forests of Guyana?

This work tested the hypothesis that ectomycorrhizas (EM) of Dicymbe corymbosa alter leaf-litter decomposition and residual litter quality in tropical forests of Guyana. Mass loss of leaf litter in litter bags was determined on three occasions, in two experiments, during a 12-month period. Paired root-exclusion plots were located randomly within a D. corymbosa forest. Both D. corymbosa and mixed-species leaf litters were reciprocally transplanted into their respective forest types. Elemental analysis was performed on the residual D. corymbosa leaf litter after 1 yr. Leaf litter mass loss in the D. corymbosa forest was not influenced by EM, despite high EM colonization. Elemental analysis of D. corymbosa leaf litter residues demonstrated reduced calcium levels in the presence of EM, which were negatively correlated with EM rootlet-colonizing mass. The lack of EM effect on the litter decomposition rate, coupled with high EM colonization, suggests an important but indirect role in mineral nutrient acquisition. Lowered Ca concentration in leaf litter exposed to EM may suggest a high Ca demand by the ectotroph system.     

Review of mixed forest litter decomposition researches

The litter plays an important role in forest ecosystems. Decomposition of mixed leaf litters has recently become an active research area because it mimics the natural state of leaf litters in most of forests. Many studies reported effects of mixing litters on their decomposition, ranging from positive, negative to neutral. In this paper decomposition mechanisms of mixed litters concluded by researchers were summarized. Firstly, plant litter quality had been recognized as an important factor to affect decomposition rate. Some studies showed a positive significant correlation between initial N, P concentration and non-additive effect in litter mixture decomposition. Secondly, it has been suggested that litter mixture could increase abundance and diversity of fauna and microbial decomposers, especially fungi. Thirdly, compared with single litter decomposition, the nutrient exchange between different litter species is often considered as one of main non-additive effects observed in litter mixture. Some results showed that the active transport of nutrients by fungal hyphae derived positive effect on the decomposition of litter mixture. The multiple factors such as, leaf litter species, investigation method and plot, were also analyzed. In conclusion, it is necessary to enhance a further research on factors in mixed litter decomposition and an interaction between various factors due to the complex relationship. We are looking forward to using these theories of mixed litter decomposition to direct practical forest management.     

Review of mixed forest litter decomposition researches

The litter plays an important role in forest ecosystems. Decomposition of mixed leaf litters has recently become an active research area because it mimics the natural state of leaf litters in most of forests. Many studies reported effects of mixing litters on their decomposition, ranging from positive, negative to neutral. In this paper decomposition mechanisms of mixed litters concluded by researchers were summarized. Firstly, plant litter quality had been recognized as an important factor to affect decomposition rate. Some studies showed a positive significant correlation between initial N, P concentration and non-additive effect in litter mixture decomposition. Secondly, it has been suggested that litter mixture could increase abundance and diversity of fauna and microbial decomposers, especially fungi. Thirdly, compared with single litter decomposition, the nutrient exchange between different litter species is often considered as one of main non-additive effects observed in litter mixture. Some results showed that the active transport of nutrients by fungal hyphae derived positive effect on the decomposition of litter mixture. The multiple factors such as, leaf litter species, investigation method and plot, were also analyzed. In conclusion, it is necessary to enhance a further research on factors in mixed litter decomposition and an interaction between various factors due to the complex relationship. We are looking forward to using these theories of mixed litter decomposition to direct practical forest management.     

Mixing effects on litter decomposition rates in a young tree diversity experiment

Litter decomposition is an essential process for biogeochemical cycling and for the formation of new soil organic matter. Mixing litter from different tree species has been reported to increase litter decomposition rates through synergistic effects. We assessed the decomposition rates of leaf litter from five tree species in a recently established tree diversity experiment on a post-agriculture site in Belgium. We used 20 different leaf litter compositions with diversity levels ranging from 1 up to 4 species. Litter mass loss in litterbags was assessed 10, 20, 25, 35, and 60 weeks after installation in the field. We found that litter decomposition rates were higher for high-quality litters, i.e., with high nitrogen content and low lignin content. The decomposition rates of mixed litter were more affected by the identity of the litter species within the mixture than by the diversity of the litter per se, but the variability in litter decomposition rates decreased as the litter diversity increased. Among the 15 different mixed litter compositions in our study, only three litter combinations showed synergistic effects. Our study suggests that admixing tree species with high-quality litter in post-agricultural plantations helps in increasing the mixture's early-stage litter decomposition rate.     

Palatability, decomposition and insect herbivory: patterns in a successional old-field plant community

We tested the hypothesis that selective feeding by insect herbivores in an old‐field plant community induces a shift of community structure towards less palatable plant species with lower leaf and litter tissue quality and may therefore affect nutrient cycling. Leaf palatability of 20 herbaceous plant species which are common during the early successional stages of an old‐field plant community was assayed using the generalist herbivores Deroceras reticulatum (Mollusca: Agriolomacidae) and Acheta domesticus (Ensifera: Gryllidae). Palatability was positively correlated with nitrogen content, specific leaf area and water content of leaves and negatively correlated with leaf carbon content and leaf C/N‐ratio. Specific decomposition rates were assessed in a litter bag experiment. Decomposition was positively correlated with nitrogen content of litter, specific leaf area and water content of living leaves and negatively correlated with leaf C/N‐ratio. When using phylogentically independent contrasts the correlations between palatability and decomposition versus leaf and litter traits remained significant (except for specific leaf area) and may therefore reflect functional relationships. As palatability and decomposition show similar correlations to leaf and litter traits, the correlation between leaf palatability and litter decomposition rate was also significant, and this held even in a phylogenetically controlled analysis. This correlation highlights the possible effects of invertebrate herbivory on resource dynamics. In a two‐year experiment we reduced the density of above‐ground and below‐ground insect herbivores in an early successional old‐field community in a two‐factorial design by insecticide application. The palatability ranking of plants showed no relationship with the specific change of cover abundance of plants due to the reduction of above‐ or below‐ground herbivory. Thus, changes in the dominance structure as well as potentially associated changes in the resource dynamics are not the result of differences in palatability between plant species. This highlights fundamental differences between the effects of insect herbivory on ecosystems and published results from vertebrate‐grazing systems.     

Higher temperature reduces the effects of litter quality on decomposition by aquatic fungi

1. We investigated the effects of riparian plant diversity (species number and identity) and temperature on microbially mediated leaf decomposition by assessing fungal biodiversity, fungal reproduction and leaf mass loss. 2. Leaves of five riparian plant species were first immersed in a stream to allow microbial colonisation and were then exposed, alone or in all possible combinations, at 16 or 24 °C in laboratory microcosms. 3. Fungal biodiversity was reduced by temperature but was not affected by litter diversity. Temperature altered fungal community composition with species of warmer climate, such as Lunulospora curvula, becoming dominant. 4. Fungal reproduction was affected by litter diversity, but not by temperature. Fungal reproduction in leaf mixtures did not differ or was lower than that expected from the weighted sum of fungal sporulation on individual leaf species. At the higher temperature, the negative effect of litter diversity on fungal reproduction decreased with the number of leaf species. 5. Leaf mass loss was affected by the identity of leaf mixtures (i.e. litter quality), but not by leaf species number. This was mainly explained by the negative correlation between leaf decomposition and initial lignin concentration of leaves. 6. At 24 °C, the negative effects of lignin on microbially mediated leaf decomposition diminished, suggesting that higher temperatures may weaken the effects of litter quality on plant litter decomposition in streams. 7. The reduction in the negative effects of lignin at the higher temperature resulted in an increased microbially mediated litter decomposition, which may favour invertebrate‐mediated litter decomposition leading to a depletion of litter stocks in streams.     

Mound-building behaviour of a keystone bioturbator alters rates of leaf litter decomposition and movement in urban reserves

Bioturbation, the disturbance of soil and litter by digging animals plays an important role for a variety of species and ecological processes in many ecosystems. The majority of studies globally on the ecosystem engineering effects of digging vertebrates have focussed on mammals, with birds, reptiles and amphibians remaining comparatively understudied. The loss of ecosystem engineers is a key conservation challenge, and the return of these species is increasingly seen as a priority for habitat restoration; yet this concept is highly novel when we consider urban ecosystems. The Australian brush-turkey (Alectura lathami), historically a rainforest bird and now common in urban ecosystems, displaces significant quantities of soil and leaf litter through its foraging and nest-building behaviour and has previously been described as an ecosystem engineer. Here, we tested the effect of brush-turkey nest building on the decomposition rate of leaf litter, an important ecosystem process. We placed mesh bags of dried Angophora costata and Lantana camara leaves at increasing distances from brush-turkey incubation mounds. We predicted that leaf litter closer to the nest would break down faster during the brush-turkey breeding season due to increased turnover associated with nest mound maintenance. We found slower leaf litter decomposition in the breeding than the non-breeding season, but a relatively greater rate of decomposition closer to the mound in the breeding season. Our results show a seasonal difference in the spatial pattern of leaf litter decomposition and movement; we interpret that brush-turkey mound-building behaviour was the key driver. The ecosystem services provided by brush-turkeys are of particular interest for future research as this species is naturally recolonizing areas where it has been absent for decades, including urban areas. The effect of this species on ecosystem processes including nutrient cycling, seedbank stimulation and reduced fuel loads warrants further investigation.     

Causes and consequences of monodominance in tropical lowland forests

Tropical canopy dominance in lowland, well-drained forests by one plant species is a long-standing conundrum in tropical biology. Research now shows that dominance is not the result of one trait or mechanism. We suggest that the striking dominance of Gilbertiodendron dewevrei in the Ituri Forest of northeastern Congo is the result of a number of traits in adult trees that significantly modify the understory environment, making it difficult for other species to regenerate there. Adults cast deep shade that reduces light levels in the understory of the Gilbertiodendron forest to levels significantly lower than in the mixed-species forest. Moreover, the monodominant forest has deep leaf litter that could inhibit the establishment of small-seeded species, and the leaf litter is slow to decompose, potentially causing the low availability of nitrogen. We expect that juveniles of Gilbertiodendron may have an advantage in this environment over other species. In general, it appears that all tropical monodominant species share a similar suite of traits.     

Litter mixing significantly affects decomposition in the Hulun Buir meadow steppe of Inner Mongolia,China

Aims We explored the decomposition rates of single- and mixed-species litter, the litter-mixing effect and the effect of component litters in a mixture on decomposition.Methods In a litter bag experiment, shoot litters from two dominant grasses (Leymus chinensis and Stipa baicalensis) and one legume (Melissitus ruthenica) were decomposed separately and as a mixture from May 2010 to September 2011 in the Hulun Buir meadow steppe of Inner Mongolia, China. We separated the litter mixture into its individual component litters (i.e. the different single-species litters) and analyzed the changes in litter mass remaining and litter nitrogen (N) remaining during single- and mixed-species litter decomposition.Important findings (i) Litter mixing had significant positive effects on litter decomposition. The litter-mixing effect was strongest for the mixture of S. baicalensis and L. chinensis litters, followed by the mixture of S. baicalensis and M. ruthenica litters. (ii) Single-species component litters decomposed faster in the mixtures than separately (positive effect), but these effects were not significant for legume species M. ruthenica litter. Relative to single-species litter decomposition, the decomposition rates of the two grass (S. baicalensis and L. chinensis) litters significantly increased when they were mixed with each other or with M. ruthenica litter. (iii) For each species litter type, the percentage of litter N remaining during decomposition (N R) differed between the single-species litter and mixed litter treatments. The N R of S. baicalensis litter was higher when it was decomposed in the mixture than in isolation. However, the N R of L. chinensis litter was lowest in its mixture with M. ruthenica among the treatments. Regardless of its decomposition in the mixture or in isolation, the N R of M. ruthenica litter varied little among treatments. There was a significant positive relationship between the N R and percentage of initial litter mass remaining in both the single litter and mixed litter treatments. These results suggest that N transfer may happen among component litters in mixture and further affect the decomposition.     

Litter quality, stream characteristics and litter diversity influence decomposition rates and macroinvertebrates

1. We examined the relative importance of litter quality and stream characteristics in determining decomposition rate and the macroinvertebrate assemblage living on autumn‐shed leaves. 2. We compared the decomposition rates of five native riparian tree species (Populus fremontii, Alnus oblongifolia, Platanus wrightii, Fraxinus velutina and Quercus gambelii) across three south‐western streams in the Verde River catchment (Arizona, U.S.A.). We also compared the decomposition of three‐ and five‐species mixtures to that of single species to test whether plant species diversity affects rate. 3. Decomposition rate was affected by both litter quality and stream. However, litter quality accounted for most of the variation in decomposition rates. The relative importance of litter quality decreased through time, explaining 97% of the variation in the first week but only 45% by week 8. We also found that leaf mixtures decomposed more quickly than expected, when all the species included were highly labile or when the stream environment led to relatively fast decomposition. 4. In contrast to decomposition rate, differences in the invertebrate assemblage were more pronounced across streams than across leaf litter species within a stream. We also found significant differences between the invertebrate assemblage colonising leaf mixtures compared with that colonising pure species litter, indicating non‐additive properties of litter diversity on stream invertebrates. 5. This study shows that leaf litter diversity has the capacity to affect in‐stream decomposition rates and stream invertebrates, but that these effects depend on both litter quality and stream characteristics.     

陆地生态系统混合凋落物分解研究进展

凋落物分解在陆地生态系统养分循环与能量流动中具有重要作用,是碳、氮及其他重要矿质养分在生态系统生命组分间循环与平衡的核心生态过程。自然生态系统中,植物群落大多具有较高的物种丰富度和多样性,其混合凋落物在分解过程中也更有可能发生养分传递、化学抑制等种间互作,形成多样化的分解生境,多样性较高的分解者类群以及复杂的级联效应分解,这些因素和过程均对研究混合凋落物分解过程、揭示其内在机制形成了极大的挑战。从构成混合凋落物物种丰富度和多样性对分解生境、分解者多样性及其营养级联效应的影响等方面,综合阐述混合凋落物对陆地生态系统凋落物分解的影响,探讨生物多样性在凋落物分解中的作用。通过综述近些年的研究发现,有超过60%的混合凋落物对其分解速率的影响存在正向或负向的效应。养分含量有差异的凋落物混合分解过程中,分解者优先利用高质量凋落物,使低质量的凋落物反而具有了较高的养分有效性,引起低质量凋落物分解加快并最终使混合凋落物整体分解速率加快;而凋落物物种丰富度对土壤动物群落总多度有轻微的影响或几乎没有影响,但是对线虫和大型土壤动物的群落组成和多样性有显著影响,并随着分解阶段呈现一定动态变化;混合凋落物改变土壤微生物生存的理化环境,为微生物提供更多丰富的分解底物和养分,优化微生物种群数量和群落结构及其分泌酶的活性,并进一步促进了混合凋落物的分解。这些基于植物-土壤-分解者系统的动态分解过程的研究,表明混合凋落物分解作用不只是经由凋落物自身质量的改变,更会通过逐级影响分解者多样性水平而进一步改变分解速率和养分释放动态,说明生物多样性确实在一定程度上调控凋落物分解及其养分释放过程。     

Assessing the influence of wildfire on leaf decomposition and macroinvertebrate communities in boreal streams using mixed-species leaf packs

1. We investigated how compositional differences in riparian leaf litter derived from burned and undisturbed forests influenced leaf breakdown and macroinvertebrate communities using experimental mixed-species leaf packs in boreal headwater streams. Leaf pack mixtures simulating leaf litter from dominant riparian woody-stem species in burned and undisturbed riparian zones were incubated in two references and two fire-disturbed streams for 5 weeks prior to measuring temperature-corrected breakdown rates and macroinvertebrate community composition, richness, and functional metrics associated with decomposers such as shredder abundance and % shredders.
2. Leaf litter breakdown rates were higher and had greater variability in streams bordered by reference riparian forests than in streams where riparian forests had been burned during a wildfire. Streams bordered by fire disturbance showed significant effects of litter mixture on decomposition rates, observed as significantly higher decomposition rates of a fire-simulated leaf mixture compared to all other mixtures.
3. Variation among sites was higher than variation among litter mixtures, especially for macroinvertebrate community composition. In general, fire-simulated leaf mixtures had greater shredder abundances and proportions, but lower overall macroinvertebrate abundance; however, the shredder abundance trend was not consistent across all leaf mixtures at each stream.
4. These results show that disturbance-driven riparian forest condition and resulting composition of leaf subsidies to streams can influence aquatic invertebrate community composition and their function as decomposers. Therefore, if one of the primary goals of modern forest management is to emulate natural disturbance patterns, boreal forest managers should adapt silvicultural practices to promote leaf litter input that would arise post-fire, thereby supporting stream invertebrate communities and their function.

     

Macroinvertebrate identity mediates the effects of litter quality and microbial conditioning on leaf litter recycling in temperate streams

Plant litter decomposition is an essential ecosystem function that contributes to carbon and nutrient cycling in streams. Aquatic shredders, mainly macroinvertebrates, can affect this process in various ways; they consume leaf litter, breaking it down into fragments and creating suitable habitats or resources for other organisms through the production of fine particulate organic matter (FPOM). However, measures of litter‐feeding traits across a wide range of aquatic macroinvertebrates are still rare. Here, we assessed the contributions of 11 species of freshwater macroinvertebrates to litter decomposition, by measuring consumption rate, FPOM production, and assimilation rate of highly decomposable (Alnus glutinosa) or poorly decomposable (Quercus robur) leaf litter types. In general, an increase in the quality of litter improved the litter consumption rate, and fungal conditioning of the leaf litter increased both the litter consumption rate and FPOM production. Macroinvertebrates specializing in leaf litter consumption also appeared to be the most sensitive to shifts in litter quality and the conditioning process. Contrary to expectations, the conditioning process did not increase the assimilation of low‐quality litter. There was a strong correlation between the relative consumption rate (RCR) of the two litter types, and the relative FPOM production (RFP) was strongly correlated to the RCR. These findings suggest a consistent relationship between RCR and macroinvertebrate identity that is not affected by litter quality, and that the RFP could be inferred from the RCR. The varying responses of the macroinvertebrate feeding traits to litter quality and the conditioning process suggest that the replacement of a shredder invertebrate species by another species could have major consequences for the decomposition process and the detritus‐based food web in streams. Further studies onto the importance of invertebrate identity and the effects of litter quality in a variety of freshwater ecosystems are needed to understand the whole ecosystem functioning and to predict its response to environmental changes.     

Decomposition and nitrogen release from the foliage litter of fir (Abies sachalinensis) and oak (Quercus crispula) under different forest canopies in Hokkaido, Japan

When two tree species co-occur, decomposition and nitrogen (N) release from the foliage litter depend on two factors: the forest floor conditions under each canopy type and the species composition of the litter. We conducted an experiment using fir and oak to answer several questions regarding decomposition beneath canopies of the two species and the effects of litter species composition on decomposition. We compared the rates of decomposition and N release from three different litters (fir needle, oak leaf, and a mixture of the two) in 1-mm-mesh litterbags on the forest floor under three different canopies (a 40-year-old fir plantation, large oak trees, and mixed fir and oak trees) in Hokkaido, Japan, over a 2-year period. Beneath each of these canopy types, the litter decomposition rate and percentage of N remaining in the litterbags containing a mixture of fir and oak litter were not significantly different from the expected values calculated for litterbags containing litter from a single tree species. Oak leaf litter decomposed significantly faster than fir needle litter beneath each canopy type. The litter decomposition rate was significantly higher beneath the fir canopy than under the oak canopy, and was intermediate under the mixed canopy of fir and oak. No net N release, that is, a decrease in the total N compared to the original amount, was detected from fir litter under each canopy type or from oak leaf litter beneath the oak canopy. N increased over the original amount in the fir litter beneath the oak canopy and the mixed canopy of fir and oak, but N was released from the oak litter under the fir canopy and the mixed canopy of fir and oak. These results suggest that oak leaf litter blown onto fir forest floor enhances nutrient cycling, and this might be a positive effect of a mixed stand of conifer and broad-leaved trees.     

Plant palatability to leaf‐cutter ants (Atta laevigata) and litter decomposability in a Neotropical woodland savanna

Although leaf‐cutter ants have been recognized as the dominant herbivore in many Neotropical ecosystems, their role in nutrient cycling remains poorly understood. Here we evaluated the relationship between plant palatability to leaf‐cutter ants and litter decomposability. Our rationale was that if preference and decomposability are related, and if ant consumption changes the abundance of litter with different quality, then ant herbivory could affect litter decomposition by affecting the quality of litter entering the soil. The study was conducted in a woodland savanna (cerrado denso) area in Minas Gerais, Brazil. We compared the decomposition rate of litter produced by trees whose fresh leaves have different degrees of palatability to the leaf‐cutter ant Atta laevigata. Our experiments did not indicate the existence of a significant relationship between leaf palatability to A. laevigata and leaf‐litter decomposability. Although the litter mixture composed of highly palatable plant species showed, initially, a faster decay rate than the mixture of poorly palatable species, this difference was no longer visible after about 6 months. Results were consistent regardless of whether litter invertebrates were excluded or not from litter bags. Similarly, experiments comparing the decomposition rate of litter from pairs of related plant species also showed no association between plant palatability and decomposition. Decomposition rate of the more palatable species was faster, slower or similar to that of the less palatable species depending upon the particular pair of species being compared. We suggest that the traits that mostly influence the decomposition rate of litter produced by cerrado trees may not be the same as those that influence plant palatability to leaf‐cutter ants. Atta laevigata select leaves of different species based – at least in part – on their nitrogen content, but N content was a poor predictor of the decomposition rates of the species we studied.