Mixed Litter Research Articles

Diversidade de organismos zoospóricos heterotróficos do Parque Estadual das Fontes do Ipiranga, São Paulo, SP, Brasil: novas citações

Visando o levantamento dos organismos zoospóricos heterotróficos pertencentes aos filos Blastocladiomycota, Chytridiomycota e Oomycota do Córrego Pirarungaua, situado no Parque Estadual das Fontes do Ipiranga (PEFI), São Paulo, SP, Brasil, foram coletadas amostras de água e folhedo misto, no período de junho/2011 a abril/2012. No laboratório, as amostras foram transferidas para placas-de-petri esterilizadas e tratadas pelo método de iscagem múltipla com substratos celulósicos, queratinosos e quitinosos. Foram identificados 42 táxons, sendo 27 deles ao nível específico. Sete espécies são novas citações para o Parque Estadual das Fontes do Ipiranga: Cladochytrium setigerum Karling, Diplophlyctis intestina (Schenk) J. Schröt, Myzocytiopsis humana (Karling) M.W. Dick, Nowakowskiella elongata Karling, Nowakowskiella multispora Karling, Plectospira myriandra Drechsler e Pythium graminicola Subramanian, as quais são descritas, comentadas e ilustradas. Myzocytiopsis humana é mencionada pela primeira vez no Brasil.

The importance of native and exotic plant identity and dominance on decomposition patterns in mountain woodlands of central Argentina

Exotic species can have a strong influence on ecosystem processes, especially when exotic invaders differ from natives in key morpho-functional features. We explored whether exotic species, especially those forming monospecific patches in Chaco montane woodlands, differ from natives in leaf attributes and decomposability. We then evaluated how exotic monospecific patches in that region alter litter decomposability, by weighting leaf trait values and decomposability by species abundance in the communities. In general, native and exotic species from Córdoba Chaco montane woodlands did not differ in leaf attributes (specific leaf area, leaf toughness, and leaf water content), or decomposability. Because of similar trait values and decomposability, we expected to find no differences in litter decomposability between plots dominated by exotic species and those of Native woodland. However, individual species decomposability weighted by species abundance in the communities showed that litter from exotic monospecific plots had slower decomposition than native ones. This pattern was confirmed by the higher decomposability and higher quality of the naturally mixed litter collected from native plots, compared to those collected from exotic plots. Despite the general similarities between most native and exotic species inhabiting Chaco montane woodlands, the overwhelming dominance of some exotic invaders in monospecific stands (and the consequent weight of their attributes on the litter each woodland produces) might be driving differences in decomposition patterns between woodland types. Our results indicate that when estimating the impact of exotic species on ecosystem processes, we should include their relative abundance in the community, as well as the relevance of the traits influencing those processes. Otherwise, we may draw erroneous conclusions.

Combined effects of multifactor climate change and land-use on decomposition in temperate grassland

Climate change is likely to alter decomposition rates through direct effects on soil biotic activity and indirect effects on litter quality with possible impacts on the global carbon budget and nutrient cycling. Currently, there is a need to study the combined effects of climatic drivers and agricultural practises on decomposition.In an in situ litter bag experiment, we studied the effects of rainfall variability (including drought combined with heavy rain pulses as well as regular irrigation) interacting with winter warming and increased winter precipitation and with changes in cutting frequency, on decomposition in a temperate grassland. Litter bags contained mixed and species-specific litter of all different climate and land-use manipulations and were placed within the plots of litter origin. Moreover, we aimed to disentangle the causes of changes in decomposition by investigating two further approaches: Firstly, we studied the effects of changes in leaf chemicals as a result of the manipulations by removing litter from the experiment that has been pre-exposed to the manipulations before placing it on an untreated standard plot outside the experiment. Secondly, we assessed the effects of changes in soil faunal activity by investigating the decomposition of standard material under differing rainfall variability.As a result, decomposition was reduced when litter bags were exposed to drought for six weeks within an 11 months period. Neither additional winter rain nor winter warming had an effect on decomposition, likely because winter warming reduced snow cover and increased variability of surface temperatures. Climate manipulations did not change litter quality. Furthermore, decomposition on the untreated standard plot was not affected by the climate manipulations that the litter was previously exposed to. Thus, reduced decomposition under extreme rainfall variability and drought may mainly be caused by a decrease in soil biotic activity, as indicated by reduced decomposition of standard material during drought.More frequent cutting strongly stimulated decomposition, however, this stimulating effect was absent under extreme rainfall variability including drought. The stimulation of decomposition under more frequent cutting was attributed to changes in litter quality, namely a decrease in C/N ratio. Accordingly, litter from more frequently cut communities decomposed faster on the untreated control plot outside the experiment.Projected increases in drought frequency and increased rainfall variability under climate change may inhibit decomposition and alter nutrient and carbon cycling along with soil quality. Especially decomposition in frequently cut grassland appears vulnerable towards drought.

No evidence for adaptive sex ratio variation in the cooperatively breeding meerkat, Suricata suricatta

Where a maternal trait influences the fitness of sons or daughters, mothers would be expected to bias the sex ratio towards the sex whose fitness they are more able to increment. In many polygynous species, maternal characteristics affect the fitness of sons more than that of daughters, but, in meerkats, variance in female reproductive success exceeds variance in male reproductive success and maternal rank affects the success of daughters more than sons. Dominant females would therefore be expected to produce an excess of daughters, a reversal of the hypothesis' usual predictions. In a long-term data set, despite a strong effect of maternal rank on daughters' success, we found no indication that dominant females produce female-biased litters. Offspring sex ratios did not deviate significantly from equality, and were also unaffected by maternal mass, age or number of previous litters produced in the same season. We suggest that potential advantages to both mother and offspring of producing and developing in mixed litters may result in the adaptive maintenance of an equal offspring sex ratio.

凋落物和增温联合作用对峨眉冷杉幼苗抗氧化特征的影响

Abies fabri(Mast.) Craib is an endemic and dominant species in typical subalpine dark coniferous forests,which mainly distributed in mountain regions of Western Sichuan,China.Due to the great sensitivity of the regeneration capacity to the climate change,it becomes the one of typical forest for studying effects of climate change on terrestrial ecosystem on eastern Tibetan Plateau.To asses how Abies Fabri seedlings may respond and adapt to future climate changes,we investigated the effects of temperature elevation and litter addition on the antioxidative responses of A.fabri seedlings.Temperature elevation was created by the combined use of open top chamber(OTCs) and electrical bar,and litter was artificially added in different types.Thus,four treatments were performed in this study: 1) litter A + temperature elevation T(A-T);2) litter B + temperature elevation T(B-T);3) litter A + the ambient temperature T0(A-T0);4) litter B + the ambient temperature T0(B-T0).A stands for the mixed litter by seventy-five percentage of A.fabri woodly litter(Woodly,W)and twenty-five percentage of Azalea viburnum shrub litter(Shrub,S);and B,the mixed litter by fifty-five percentage of A.fabri woodly litter(Woodly,W)and forty-five percentage of Azalea viburnum shrub litter(Shrub,S).The results showed that: 1) under the ambient temperature,the electrical conductivity,the malondialdehyde(MDA) and proline content,and the rate of superoxide anion radical(O-2) of A.fabri seedlings is higher under litter A than litter B;the soluble sugar and starch contents,the superoxide dismutase(SOD),ascorbate peroxidase(APX),catalase(CAT) activity of A.fabri seedlings is lower under litter A than litter B.These results suggested that litter B will be helpful to the growth of A.fabri seedlings;2) temperature elevation markedly increased the proline content and hydrogen peroxide(H2O2) of A.fabri under litter A.However,under litter B temperature elevation significantly decreased the content of malondialdehyde(MDA),free proline,soluble sugar and starch contents,and increased rate of superoxide anion radical(O-2).Obviously,the oxidative damage of A.fabri seedlings suffering from temperature elevation is lower under litter B than under litter A;3) the interaction of litter and temperature elevation reduced the soluble sugar and starch contents of A.fabri seedlings.The electrical conductivity,the malondialdehyde and proline content of A.fabri seedlings in B-T treatment is lower than the A-T treatment;the peroxidase(POD),ascorbate peroxidase(APX),glutathione(GR) and catalase(CAT) activity of A.fabri seedlings is higher in B-T treatment than in A-T treatments.These present results suggested that litter B with lower needles proportion will be helpful to A.fabri seedlings to future climate warming.

围封对内蒙古大针茅草地土壤碳矿化及其激发效应的影响

土壤呼吸及其控制机理是全球变化研究的重点之一,其中土壤呼吸的温度敏感性和激发效应是近年来的研究热点。以长期围封的大针茅草地(Fenced grassland, FG)和自由放牧草地(Grazing grassland, GG)为对象,通过不同温度(5、10、15、20、25℃和30℃)和添加混合凋落物的室内培养途径,探讨了长期围封对草地碳矿化(或土壤微生物呼吸)的温度敏感性和激发效应的影响。实验结果表明:在培养42 d内,长期围封的大针茅草地的土壤碳矿化累积量高于自由放牧草地;土壤碳矿化量随温度的升高而升高,围封对大针茅草地土壤碳矿化的温度敏感性的影响不显著,<em>Q</em>₁₀值介于1.1-1.9之间。添加混合凋落物使土壤碳矿化表现出了明显的激发效应,且自由放牧草地的激发效应高于长期封育草地;在培养的前7 d,土壤激发效应随着培养温度升高而增强,激发效应最高值达6.38;但在整个培养期(42 d)土壤激发效应15℃为最大。从长远角度看,中间温度更有利于土壤激发效应以及土壤碳矿化。在相同的有机物质输入状况下,长期围封大针茅草地的激发效应更低,可能是大针茅草地在长期围封状况下仍然具有碳固持效应的重要机制之一。;In recent decades, the carbon (C) cycle and soil respiration of terrestrial ecosystems have been become hot topics for the global climate change, and research focused on the temperature sensitivity and priming effects of soil microbial respiration (or soil C mineralization) has increased rapidly since 2000. In this study, we focused on long-term fenced <em>Stipa grandis</em> grassland (FG) and grazing <em>Stipa grandis</em> grassland (GG) in Inner Mongolia, China, investigating the impact of land-use change on the temperature sensitivity and the priming effects of soil microbial respiration by incubating soils in the laboratory under a temperature gradient (5, 10, 15, 20, 25 and 30℃) and with substrate addition (mixed litter). The incubation experiment was continued for 6 weeks, and the rates of soil C mineralization were measured throughout using our newly developed equipment. The results showed that the amount of soil C mineralization was higher in GG than that in FG duration the 6-weeks incubation. The rates of soil C mineralization increased significantly with increasing incubation temperature for both GG and FG (temperature coefficient (<em>Q</em>₁₀) values ranged from 1.1 to 1.9), however, the <em>Q</em>₁₀ values for GG and FG were not significantly different. After mixed-litter addition, the rates of soil C mineralization not only in GG but also in FG increased significantly, and showed the apparent priming effects of C mineralization. Compared with long-term fenced grassland (FG), grazing grassland (GG) had higher priming effects, which even after only 7 d were 6.38 times higher. Moreover, the priming effects increased with increasing incubation temperature in the first week, although these effects were the highest at 15℃ duration the 42 d of incubation. These findings suggest that, on a longer time scale, medium temperatures should promote soil C mineralization. On the whole, long-term grazing exclusion depressed the priming effect of soil microbial respiration and resulted in less C emission under the same mixed litter input. This is probably one of the mechanisms underlying the capacity of long-term fenced grasslands to sequester CO₂ in Inner Mongolia.

Comparison of growth performance and agonistic interaction in weaned piglets of different weight classes from farrowing systems with group or single housing

The present study was designed to analyze the growth performance, behavioral patterns and intensity of injuries of weaned pigs (26 days) during a rearing period of 6 weeks. The farrowing system (group housing (GH) v. single housing (SH)) and the post-weaning regrouping weight class (light, medium, heavy) were considered as the main factors. A number of 120 GH-pigs and 120 SH-pigs were kept in three batches (20 pens, 12 pigs each). The GH- and SH-pigs were divided by weight into three groups: light (5 to ⩽7 kg), medium (>7 to ⩽9 kg) and heavy (>9 to ⩽12 kg), with two pigs of six different litters in each pen. The pigs were weighed individually at weaning (week 1) and during rearing (weeks 2, 3 and 7). The feed conversion ratio (FCR) was calculated between weeks 1 and 7. The duration and number of fights (NF) per pen and hour were determined by continuous sampling (40 h after weaning). Lesions of the integument were scored into four classes (none, minor, medium, severe) and recorded at weaning and 48 h afterwards. The farrowing system had no effect on the weights in week 1 (GH: 7.8 kg v. SH: 7.7 kg; week as linear, quadratic regression nested within housing systems) or in week 7 (GH: 29.4 kg v. SH: 28.6 kg). The body weights were influenced significantly by the weaning weight class (light: 11.7 kg (s.e.m.: 0.30), medium: 14.8 kg (s.e.m.: 0.22), heavy: 17.3 kg (s.e.m.: 0.26)). The FCR of the GH-pigs was 1.64 (s.e.m.: 0.03) and 1.58 (s.e.m.: 0.03) for SH-pigs. A reduced agonistic behavior of the GH-pigs was observed with 2.1 fights per pen and hour (s.e.m.: 0.07) v. the SH-pigs with 4.6 fights per pen and hour (s.e.m.: 0.05). The fight duration of the GH-pigs with 10.3 s per pen and hour (s.e.m.: 1.07) was significantly lower in comparison to the SH-pigs with 18.8 s per pen and hour (s.e.m.: 1.06). The SH-pigs had more new skin lesions at the shoulders than the GH-pigs 48 h after weaning (P < 0.05). In conclusion, early mixing of unacquainted litters during lactation had no influence on their growth performance during rearing but reduced agonistic behavior and lesion score difference during the first 2 days after weaning. No significant interaction between the farrowing system and weaning weight class was detected with regard to growth performance and NF.

The influence of litter mixing on decomposition and soil fauna assemblages in a Pinus koraiensis mixed broad-leaved forest of the Changbai Mountains, China

Although much research aiming to determine in what ways aboveground systems may affect belowground processes and communities has been conducted, the effects of litter mixing on decomposition processes and decomposer communities remain controversial. In this study, a litter mixing experiment was conducted using litterbags in a Pinus koraiensis mixed broad-leaved forest of the Changbai Mountains, in which the treatments consisted of litter monocultures of each of four canopy tree species, namely P. koraiensis, Fraxinus mandshurica, Tilia amurensis and Acer mono, as well as mixtures of two and four different species. It was found that the different litter species decomposed in monoculture at different rates. The litter mixing had idiosyncratic effects on the decomposition, which depended on the field incubation time and composition species. Litter species identity was an important determinant of abundances and diversity of soil fauna, while litter mixing had weak or no significant effects on the soil fauna communities. The study results also showed that soil fauna has an important influence on litter decomposition; however, the extent of the relationship between decomposition and soil fauna was not stronger in the litter mixtures than in the monocultures. It is concluded that litter mixing had effects on decomposition, with relatively minor effects on soil fauna communities in comparison to the effects of litter species identity.

Earthworms, litter and soil carbon in a northern hardwood forest

The important role of soil carbon (C) in the global C cycle has stimulated interest in better understanding the mechanisms regulating soil C storage and its stabilization. Exotic earthworm invasion of northern forest soils in North America can affect soil C pools, and we examined their effects on these mechanisms by adding 13C labeled leaf litter to adjacent northern hardwood forests with and without earthworms. Two types of labeled litter were produced, one with the 13C more concentrated in structural (S) components and the other in non-structural (NS) components, to evaluate the role of biochemical differences in soil C stabilization. Earthworm invasions have reduced soil C storage in the upper 20 cm of the soil profile by 37 %, mostly by eliminating surface organic horizons. Despite rapid mixing of litter into mineral soil and its incorporation into aggregates, mineral soil C has not increased in the presence of earthworms. Incorporation of litter C into soil and microbial biomass was not affected by biochemical differences between S versus NS labeled litter although NS litter C was assimilated more readily into earthworm biomass and S litter C into fungal hyphae. Apparently, the net effect of earthworm mixing of litter and forest floor C into mineral soil, plus stabilization of that C in aggregates, is counterbalanced by earthworm bioturbation and possible priming effects. Our results support recent arguments that biochemical recalcitrance is not a major contributor to the stabilization of soil C.

Carbon and nitrogen transfer in leaf litter mixtures

The decomposition rate of litter mixtures can differ from that expected on the basis of the decomposition rate of the individual components. This difference may be linked to nitrogen (N) transfer from high-N to low-N components. Transfer of N is probably also associated with transfer of C, but the extent and direction of this C transfer are unknown. This study examined transfer and loss in laboratory microcosms of C and N from two mixed litter species (Scots pine, Pinus sylvestris L. and maize, Zea mays L.), which have natural isotopic differences in 13C. Half the material was 15N-labelled and the plants were fertilised or unfertilised. Substantial bidirectional transfer of C and N occurred between the litters, with net transfer of C from pine to maize litter and net transfer of N from high-N to low-N litter. Mixtures of fertilised and unfertilised plant litter showed higher than expected C losses and net transfer of N. Mixtures with litters from the same fertilisation treatment had small or insignificant net transfer of N and their C losses did not differ from values estimated using the decomposition rates of the pure litters.

Effect of mixing piglets affected by Escherichia coli diarrhea on growth and welfare responses

Objective: To evaluate the effects of mixing piglets prior to weaning on growth and behavioral and physiological stress markers during the preweaning and postweaning periods in the face of an outbreak of Escherichia coli diarrhea. Materials and methods: Twenty-four sows and their litters from two adjacent rooms (A and B, 12 litters per room), and six focal piglets (three males and three females) from each litter were included. In Room B, E coli diarrhea occurred Day 12 after birth. On Day 18, the partitions between pairs of neighboring pens were removed for 12 litters, allowing piglets access to two adjoining crate areas (forming six mixed litters). Pigs were weaned on Day 28. Growth performance, behavioral stress markers, and physiological stress markers (neutrophil:lymphocyte ratio and acute phase proteins [APPs]) were measured from birth to Day 58. Results: When colibacillosis occurred in Room B, there was a detrimental effect on growth performance, especially highlighted when piglets were mixed prior to weaning. Concentrations of APPs 2 days after weaning were higher in Room B. Mixed piglets spent more time fighting immediately after mixing; however, after weaning, mixed piglets spent less time fighting than the controls. Implications: Mixing piglets affected by E coli diarrhea may have a detrimental effect on growth rate. Animals with colibacillosis may have higher APP concentrations. After weaning, pigs mixed pre-weaning spend less time fighting than controls, which might help them cope with the stress of weaning.

Non-additive effect of species diversity and temperature sensitivity of mixed litter decomposition in the alpine meadow on Tibetan Plateau

Few studies of the effects of litter diversity on the temperature sensitivity of mixed litter mass loss (MLML) are available. We tested the hypothesis that high litter diversity would reduce the magnitude of effects of climate and environmental change on MLML with 0.5/1 mm litter bags and sampling once after 1 yr of decomposition, using 51 combinations of litter mixtures from 25 dominant species at 3200 and 3800 m elevations on the Tibetan Plateau. Generally, our study supported our hypothesis. High temperature (i.e. lower elevation) reduced the dependency of MLML and non-additive effects on species richness. Species composition significantly affected MLML and its Q10 (i.e. the ratio of litter mass loss rate at a temperature T1 that is 10 °C lower than a temperature T2) when species richness was less than 8. Shrubs significantly decreased the Q10 of MLML when the species richness of litter mixture was less than 4. These findings suggest that the influence of future warming on MLML may depend on the balance between the magnitude of the impacts of climate change on shrub invasion and loss of species diversity in alpine region.

Mass loss and nutrient dynamics during litter decomposition under three mixing treatments in a typical steppe in Inner Mongolia

Mixing effects during litter decomposition could occur between two or more different litter species because of the potential nutrient transfer. However, evidence of mixing effects is variable and the underlying mechanisms remain unclear. Using a three-year decomposition experiment, we aim to examine for the effects of litter mixing and position on decomposition rates and nitrogen (N) and phosphorus (P) dynamics. We studied litter decomposition of Stipa krylovii (Sk) and Astragalus galactites (Ag), two dominant species with contrasting litter quality, in a typical steppe of northern China in both single decomposition and three mixing treatments. The three mixing treatments included thorough mixing (Sk-Ag), Ag over Sk (Ag/Sk), and Sk over Ag (Sk/Ag). Both the Sk-Ag and the Sk/Ag mixture had negative mixing effects on the mass loss of the litter mixture, while the Ag/Sk mixture had a neutral mixing effect. The percent mass loss was higher when the litter species was placed at the top (25.0 and 51.9 % of mass remaining for Ag and Sk, respectively) than at the bottom (38.3 and 61.8 % of mass remaining for Ag and Sk, respectively). The Sk/Ag mixture had negative effects on the release of N while all three mixing treatments had positive effects on the release of P. Our results indicate that: (1) mixing treatments can induce different mixing effects; (2) environmental factors likely play an important role in controlling the mixing effect; and (3) litter-mixtures have different non-additive effects on N and P, which may further increase the heterogeneity of N and P availability as the two litter species may fall differentially in terms of space and time.

Tree Species Effect on Litter Decomposition and Nutrient Release in Mediterranean Oak Forests Changes Over Time

Tree species can affect the decomposition process through the quality of their leaf fall and through the species-specific conditions that they generate in their environment. We compared the relative importance of these effects in a 2-year experiment. Litterbags containing leaf litter of the winter-deciduous Quercus canariensis, the evergreen Q. suber and mixed litter were incubated beneath distinct plant covers. We measured litter carbon loss, 9 macro- and micronutrients and 18 soil chemical, physical and biological parameters of the incubation environment. Tree species affected decay dynamics through their litter quality and, to a lesser extent, through the induced environmental conditions. The deciduous litter showed a faster initial decomposition but left a larger fraction of slow decomposable biomass compared with the perennial litter; in contrast the deciduous environment impeded early decomposition while promoting further carbon loss in the latter decay stages. The interaction of these effects led to a negative litter–environment interaction contradicting the home-field advantage hypothesis. Leaf litter N, Ca and Mn as well as soil N, P and soil moisture were the best predictors for decomposition rates. Litter N and Ca exerted counteractive effects in early versus late decay stages; Mn was the best predictor for the decomposition limit value, that is, the fraction of slowly decomposable biomass at the later stage of decomposition; P and soil moisture showed a constant and positive relation with carbon loss. The deciduous oak litter had a higher initial nutrient content and released its nutrients faster and in a higher proportion than the perennial oak litter, significantly increasing soil fertility beneath its canopy. Our findings provide further insights into the factors that control the early and late stages of the decomposition process and reveal potential mechanisms underlying tree species influence on litter decay rate, carbon accumulation and nutrient cycling.

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

Summary1. 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.

Leaf traits and litter flammability: evidence for non‐additive mixture effects in a temperate forest

Summary1. Although it is recognized that plant species vary in their flammability, we currently lack a mechanistic understanding of how plant traits influence fire and how litter mixtures behave in a fire. As modified fire regimes and climate change shift the species composition of communities, a mechanistic perspective is especially important to understand and predict fire in potentially novel plant communities. This work addresses three questions: (i) How do eight species common in Sierra Nevada mixed‐conifer forest differ in their litter flammability? (ii) What leaf traits are associated with various flammability components? and (iii) Do individual species measurements predict multi‐species combinations, or are there non‐additive effects?2. Leaf litter was collected in Sequoia and Kings Canyon National Parks, California, from eight dominant tree species in mixed‐conifer forest. Controlled flammability tests were performed on reconstructed monospecific litter beds and on mixed litter beds, using litter from three species. We tested for non‐additive effects in multi‐species mixtures using the weighted mean of single‐species measures for each flammability component as a null expectation for each mixture; departures from this null indicated non‐additive effects.3. Most flammability components fell within two major axes of variation, one relating to total heat release and another to fire intensity. The eight species differed significantly in all flammability components, with large‐leaved species creating litter that burned with higher intensity.4. Non‐additive species mixture effects are common in this system. Flammability tends to be driven by the most flammable component of the mixture.5. Synthesis. We have demonstrated positive non‐additive effects in mixtures of leaf litter. The most flammable constituent species of a mixture has disproportionate effects on the fire environment faced by the entire community. This could potentially influence community assembly and alter the selective environment faced by co‐occurring species.

Warming effects on the early decomposition of three litter types, Eastern Tibetan Plateau, China

Temperature and litter quality are two of the key factors controlling litter decomposition. Predicted global warming and vegetation succession will therefore have profound impacts. This study was conducted to assess effects of experimental warming on litter decomposition and nutrient dynamics of two contrasting tree species (red birch,Betula albosinensisBurk., and dragon spruce,Picea asperataMast.) and a mixture of the two with the heating cable method in the eastern Tibetan Plateau of China. This treatment raised surface soil temperature by 3.2°C and resulted in a 5.2% decline in soil moisture 10 cm below the soil surface. The water content of dragon spruce, red birch and mixed litter was decreased by 18, 11 and 13%, respectively. Marked differences between the two species in the decomposition rates and nutrient remaining percentages were detected. Moreover, we found positive, non‐additive effects of litter mixture. Experimental warming did not affect mass loss and nutrient release of dragon spruce litter but significantly increased mass loss and affected nutrient release of red birch and mixed litter during the early decomposition period. Overall, inter‐specific (red birch and dragon spruce) differences in decomposability were substantially larger than warming‐induced responses. Thus, a warming‐induced community succession towards dragon spruce forests in the Tibetan Plateau region could have a greater impact on early litter decomposition than warming itself.

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 aimsReplacement 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.MethodsLitter 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).ResultsMass 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 (Corg, Ntot, P, S, lignin) and associated K were related to mass loss, while release of other nutrients was not related to mass loss.ConclusionsIn 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.

How does litter quality affect the community of soil protists (testate amoebae) of tropical montane rainforests?

Litter quality and diversity are major factors structuring decomposer communities. However, little is known on the relationship between litter quality and the community structure of soil protists in tropical forests. We analyzed the diversity, density, and community structure of a major group of soil protists of tropical montane rainforests, that is, testate amoebae. Litterbags containing pure and mixed litter of two abundant tree species at the study sites (Graffenrieda emarginata and Purdiaea nutans) differing in nitrogen concentrations were exposed in the field for 12months. The density and diversity of testate amoebae were higher in the nitrogen-rich Graffenrieda litter suggesting that nitrogen functions as an important driving factor for soil protist communities. No additive effects of litter mixing were found, rather density of testate amoebae was reduced in litter mixtures as compared to litterbags with Graffenrieda litter only. However, adding of high-quality litter to low-quality litter markedly improved habitat quality, as evaluated by the increase in diversity and density of testate amoebae. The results suggest that local factors, such as litter quality, function as major forces shaping the structure and density of decomposer microfauna that likely feed back to decomposition processes.

Investigating diversity dependence of tropical forest litter decomposition: experiments and observations from Central Africa

AbstractQuestionsMixed litter may decompose at different rates to single‐species litter, leading to differences in ecosystem functioning and decomposition. Studies of the effects of different litter species and combinations are rare in tropical forests and absent from African forests. Therefore we investigated: (1) Are there differences in litter decomposition in two forest types differing in tree diversity; and (2) is litter decomposition diversity‐dependent?LocationOld‐growth moist evergreen tropical forest Dja Faunal Reserve, southeast Cameroon.MethodsWe calculate decomposition rates (leaf litter fall/leaf litter standing crop) along a tree diversity gradient in two forest types (naturally occurring low‐diversity monodominant and adjacent higher‐diversity mixed forest). Both forests experience the same climate on the same soil type; the former is dominated by a single species, Gilbertiodendron dewevrei (De Wild.) J. Léonard, probably due to lack of a long‐term disturbance and has similar edaphic factors. Decomposition experiments were conducted in both forest types using single and mixed species litter bags of standard high‐quality (bay leaves; Laurus nobilis L.) and low‐quality (G. dewevrei) litter over 9 months.ResultsThe estimated decomposition rate in mixed forest was four times faster than in monodominant forest, and not significantly correlated with local quadrat‐scale tree species diversity. The litter bag experiment showed that decomposition of high‐quality leaves was faster than low‐quality leaves (k values: 2.0 yr−1 vs 0.6 yr−1). Decay rates for each single species litter type were not significantly different in both forest types. However, G. dewevrei litter in mixed bags decomposed faster than in single‐species bags in mixed forest, suggesting an impact of litter mixing on decomposition. In addition, bay litter in mixed bags decomposed faster in mixed than in monodominant forests across the three study sites.ConclusionThe observed difference in litter decomposition rate between low‐diversity monodominant and adjacent high‐diversity forest is more likely due to dominance of low‐quality G. dewevrei litter, rather than low‐diversity of the litter itself.