Oak Litter Research Articles

Plant canopy effects on litter accumulation and soil microbial biomass in two temperate forests

The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha−1) compared to oak stands (15.7t ha−1). Canopy leaf area was also significantly larger in mixed stands (1.96m2 m−2) than in oak stands (1.73m2 m−2). Soil organic carbon (Corg) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (Cmic), nitrogen (Nmic), and total soil nitrogen (Ntot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean Corg/Ntot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as Cmic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.

Effects of nitrogen availability on microbial activities, densities and functional diversities involved in the degradation of a Mediterranean evergreen oak litter ( Quercus ilex L.)

The effect of available nitrogen N ((NH 4) 2S0 4) amendments on various microbial variables in three different layers (OhLn, OhLv, OhLf) of a Mediterranean litter profile under an evergreen oak forest ( Quercus ilex L.) were studied. Since Mediterranean litters are generally N limiting, the goal of the study was to understand how low (0.1 and 1%) and high (5 and 10%) N amendments impact specific biological variables such as hyphal length, community-level-catabolic-profiles (CLCPs) in ECO and FF Biolog™ plates, basal respiration, enzymatic activities (i.e. alkaline phosphatases (AlP), laccases, peroxidases and cellulases), and laccase and cellulase isoforms from three different litter layers. Results indicated that the effects of N amendments occurred over very short incubation time (3 d), and varied depending on N concentration and litter organic matter (OM) quality (i.e. depth). Thus, it appeared that the more active layer was the intermediate (OhLv) layer, which probably contained the most labile and available C pools. As a consequence, OhLv was also the layer showing globally the more intensive microbial responses following low N amendments. Indeed, in this layer, low N supplies caused several marked increases in enzymes activities (i.e. laccases, cellulases and alkaline phosphatases), hyphal length and isoenzyme patterns, suggesting a microbial reallocation of C to biomass and enzyme production. On the contrary, high N supplies resulted in adverse effects on almost all the variables, suggesting repression or cytotoxic phenomena.

LONG‐TERM BURNING INTERACTS WITH HERBIVORY TO SLOW DECOMPOSITION

Fires can generate spatial variation in trophic interactions such as insect herbivory. If trophic interactions mediated by fire influence nutrient cycling, they could feed back on the more immediate consequences of fire on nutrient dynamics. Here we consider herbivore-induced effects on oak litter quality and decomposition within a long-term manipulation of fire frequency in central Minnesota, USA. We focused on bur oak (Quercus macrocarpa) trees, which are common across the fire frequency gradient and are often heavily infested with either lace bugs (Corythuca arcuata) or aphids (Hoplochaithropsus quercicola). We used targeted exclusion to test for herbivore-specific effects on litter chemistry and subsequent decomposition rates. Lace bug exclusion led to lower lignin concentrations in litterfall and subsequently accelerated decomposition. In contrast, aphid exclusion had no effect on litterfall chemistry or on decomposition rate, despite heavy infestation levels. Effects of lace bug herbivory on litterfall chemistry and decomposition were similar in burned and unburned areas. However, lace bug herbivory was much more common in burned than in unburned areas, whereas aphid herbivory was more common in unburned areas. These results suggest that frequent fires promote oak-herbivore interactions that decelerate decomposition. This effect should amplify other influences of fire that slow nitrogen cycling.

Characterization of a Mediterranean litter by13C CPMAS NMR: relationships between litter depth, enzyme activities and temperature

SummaryOrganic matter mineralization of forest litter is catalysed by the action of different extracellular enzymes produced by microorganisms. Coupling enzyme activities with data on the general macromolecular structure of organic matter, provided by cross‐polarization magic angle spinning13C nuclear magnetic resonance (13C CPMAS NMR), allows researchers new insights into organic matter degradation processes. In this paper, the effect of the temperature of incubation on the degradation processes was evaluated in three distinct layers (OhLn, OhLv and OhLf) of an evergreen oak litter (Quercus ilexL.), located in the Mediterranean area of south‐eastern France. We studied degradation phenomena by a combination of13C CPMAS NMR and microbiological analysis. In order to determine the microbial activity of litter layers, three enzyme activities (laccase, cellulase and butyrate esterase) were measured in a 6‐month mesocosm study. Results showed an increase in the alkyl C toO‐alkyl‐C ratio and an increase of the phenolic C and carboxyl C regions, indicating a preferential degradation of polysaccharides. The aromaticity also increased with litter depth and degradation, and humification processes were more elevated at 30°C.anovashowed significant effects (P< 0.001) of increased temperature, depth and time of degradation on microbiological variables. Further information is needed about the variations in temperature and temperature‐litter response and soil functions to link fundamental understanding of carbon stabilization, climate change and global C cycling.

Non‐enzymatic hydrolysis of fluorescein diacetate (FDA) in a Mediterranean oak (Quercus ilex L.) litter

SummaryWe show the presence of interfering substances when the total microbial activity in litter samples is measured with fluorescein diacetate (FDA), and we propose some methodological modifications to avoid such interference. Three distinct litter layers (the OhLn, the OhLv and the OhLf) of evergreen oak (Quercus ilex L.) were characterized by 13C CPMAS NMR and the spectra show that the recalcitrant aromatic and phenolic compounds increase with the degree of degradation of litter. A wide range of sources of interference in the hydrolysis of FDA was found. To understand the origin of this interference, sterilized litter materials (i.e. γ‐irradiated or autoclaved) and a wide range of organic substances (i.e. amino acids, glucose, sorbitol and organic humic acids) were investigated. Insignificant differences on the FDA hydrolysis activity (FDA activity) were found in the γ‐irradiated and non‐irradiated OhLn litter, indicating that γ‐irradiation does not destroy enzymes. Conversely, after heat‐sterilization of litter, samples showed FDA activity corresponding to 60, 34.8 and 30.8% (in the OhLn, the OhLv and the OhLf layers, respectively) of that of control litters. This indicates the presence of non‐enzymatic interfering substances in the FDA assays. As the humification and litter depth increased, hydrolysis of FDA due to interferences decreased, indicating degradation and/or chelation of interfering substances. We hypothesize that lysine, arginine, histidine and cysteine are mainly responsible for the hydrolysis of FDA. We suggest that the use of phosphate buffer (50 mm, pH 7.0) with incubation < 30 minutes, in combination with a temperature between 30 and 40°C, produces insignificant interference in the determination of the final FDA activity in litter samples.

Grass and oak litter exert different effects on seedling emergence of herbaceous perennials from grasslands and woodlands

Summary The effects of litter on seedling emergence (e.g. during succession from grassland to woodland) may not only depend on litter amount and environmental conditions but may also be related to litter types. We tested the effect of litter types, litter cover and soil moisture on the emergence of four congeneric pairs of grassland and woodland species. We carried out a controlled pot experiment (Experiment I) using litter and species from two habitats (grassland vs. woodland), three levels of litter cover (low, medium, high) and two levels of water‐addition (leading to constantly humid or intermittently dry substrate). Amounts of litter were adjusted to result in the same relative light reduction for both litter types. Consequently, we applied 2 g, 4 g and 8 g of grassland litter and 0.5 g, 1 g and 2 g of woodland (oak) litter per pot. To separate the shade effect of litter from its mechanical plus chemical effects we exposed additional pots with seeds of the same species to deep shade conditions (Experiment II) corresponding to 4 g and 1 g of grass and oak litter, respectively. Under intermittently dry conditions both litter types increased seedling emergence. In addition, we found a significant interaction between litter type and species origin: seedling emergence of woodland species was significantly lower from beneath grass litter than from beneath oak litter, whereas grassland species emerged equally well from beneath both litter types. Compared with seed germination under a shade cloth, seedling emergence of woodland species from beneath grass litter was reduced by 44%. Litter significantly affected soil humidity and the amplitude of diurnal temperature fluctuations. Differential effects of litter types on woodland and grassland species are probably related to litter structure. Synthesis. Our experimental data present evidence that ecosystem specific litter effects slow down succession from grassland to woodland and that the effect size is controlled by the litter amount present and the environmental conditions.

Evaluation of stream ecological integrity using litter decomposition and benthic invertebrates

Biomonitoring programs to access the ecological integrity of freshwaters tend to rely exclusively on structural parameters. Here we evaluated stream ecological integrity using (a) benthic macroinvertebrate derived metrics and a biotic index as measures of structural integrity and (b) oak litter decomposition and associated fungal sporulation rates as measures of functional integrity. The study was done at four sites (S1, S2, S3 and S4) along a downstream increasing phosphorus and habitat degradation gradient in a small stream. The biotic index, invertebrate metrics, invertebrate and fungal communities' structure and sporulation rates discriminated upstream and downstream sites. Decomposition rates classified sites S4 and S2 as having a compromised ecosystem functioning. Although both functional and structural approaches gave the same results for the most impacted site (S4), they were complementary for moderately impacted sites (S2 and S3), and we therefore support the need for incorporating functional measures in evaluations of stream ecological integrity.

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

AbstractWhen 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.

Impact of deciduous tree species on litterfall quality, decomposition rates and nutrient circulation in pine stands

This study is focused on the decomposition rates and chemical composition in pure pine ( Pinus taeda L.) and mixed pine-deciduous litter. Litter bags contained either 100% loblolly pine needles or 80% loblolly pine needles and 20% leaves of one of five deciduous species: yellow poplar ( Liriodendron tulipifera L.), elm ( Ulmus americana L.), sweetgum ( Liquidambar styraciflua L.), water oak ( Quercus nigra L.) or red oak ( Q. falcata L.) were incubated in a loblolly pine stand in Auburn, AL. Decomposition rates and changes in carbon (C), nitrogen (N) and phosphorus (P) concentration and content were measured during one year of incubation. Mixed litter had higher initial ash and N concentrations, increased decomposition rates, and narrow C:N ratio compared to a pure pine litter. Small amounts of yellow poplar, sweetgum and water oak litter significantly increased initial P concentration in mixed litter. Decomposition rates were highest in elm–pine mix, followed by mixes with red oak and yellow poplar. Pine–elm mix had the highest N and P accumulation-release rates, allowing us to conclude that elm would cause the greatest N and P cycling increase in pine stands. Deciduous species, particularly elm, red oak and yellow poplar, may be considered as an ameliorative species to increase nutrient circulation in pine stands.

Growth and mycorrhizal community structure of Pinus sylvestris seedlings following the addition of forest litter.

We report the effects of pine and oak litter on species composition and diversity of mycorrhizal fungi colonizing 2-year-old Pinus sylvestris L. seedlings grown in a bare-root nursery in Lithuania. A layer of pine or oak litter was placed on the surface of the nursery bed soil to mimic natural litter cover. Oak litter amendment appeared to be most favorable for seedling survival, with a 73% survival rate, in contrast to the untreated mineral bed soil (44%). The concentrations of total N, P, K, Ca, and Mg were higher in oak growth medium than in pine growth medium. Relative to the control (pH 6.1), the pH was lower in pine growth medium (5.8) and higher in oak growth medium (6.3). There were also twofold and threefold increases in the C content of growth medium with the addition of pine and oak litter, respectively. Among seven mycorrhizal morphotypes, eight different mycorrhizal taxa were identified: Suillus luteus, Suillus variegatus, Wilcoxina mikolae, a Tuber sp., a Tomentella sp., Cenococcum geophilum, Amphinema byssoides, and one unidentified ectomycorrhizal symbiont. Forest litter addition affected the relative abundance of mycorrhizal symbionts more than their overall representation. This was more pronounced for pine litter than for oak litter, with 40% and 25% increases in the abundance of suilloid mycorrhizae, respectively. Our findings provide preliminary evidence that changes in the supply of organic matter through litter manipulation may have far-reaching effects on the chemistry of soil, thus influencing the growth and survival of Scots pine seedlings and their mycorrhizal communities.

Dynamics of phosphatase activities in a cork oak litter ( Quercus suber L.) following sewage sludge application

As part of a study of the processes involved in litter biodegradation following sewage sludge (SS) addition, the variations over 14 months of phosphatase activities in a cork oak litter ( Quercus suber L.) were investigated. A field experimental design was carried out using the litter-bag method on both a fertilized plot receiving SS applications (twice 1.5 T ha - 1 ) and a control plot. Acid (APH) and alkaline (BPH) phosphatases were measured, along with several biotic and abiotic variables potentially involved in the regulation of these enzymes. These included moisture, temperature, pH, water-extractable inorganic P ( P W ) , culturable heterotrophic bacteria and fungi. Sludge addition had significant effects on all the variables measured. Indeed, sludge increased significantly BPH activities, available P W , microbial densities (i.e. bacteria and fungi) and pH in the fertilized plot. In contrast, APH activities decreased significantly following sludge addition. As a consequence, the BPH/APH ratio increased markedly and immediately in the fertilized plot, but only after the 1st amendment. Following the 1st preconditioning SS amendment, the 2nd fertilization had fewer effects on biological variables, because of summer dryness. The different properties examined varied significantly with incubation time, and most were significantly related to the seasonal patterns of litter moisture in this Mediterranean forest ecosystem. Hence, sewage sludge application modified the intensity of microbial responses to environmental factors, but biological patterns regulating P turn-over were maintained.

Stimulation of leaf litter decomposition and associated fungi and invertebrates by moderate eutrophication: implications for stream assessment

Summary1. We investigated the effect of moderate eutrophication on leaf litter decomposition and associated invertebrates in five reference and five eutrophied streams in central Portugal. Fungal parameters and litter N and P dynamics were followed in one pair of streams. Benthic invertebrate parameters that are considered useful in bioassessment were estimated in all streams. Finally, we evaluated the utility of decomposition as a tool to assess stream ecosystem functional integrity.2. Decomposition of alder and oak leaves in coarse mesh bags was on average 2.3–2.7× faster in eutrophied than in reference streams. This was attributed to stimulation of fungal activity (fungal biomass accrual and sporulation of aquatic hyphomycetes) by dissolved nutrients. These effects were more pronounced for oak litter (lower quality substrate) than alder. N content of leaf litter did not differ between stream types, while P accrual was higher in the eutrophied than in the reference stream. Total invertebrate abundances and richness associated with oak litter, but not with alder, were higher in eutrophied streams.3. We found only positive correlations between stream nutrients (DIN and SRP) and leaf litter decomposition rates in both fine and coarse mesh bags, associated sporulation rates of aquatic hyphomycetes and, in some cases, total invertebrate abundances and richness.4. Some metrics based on benthic invertebrate community data (e.g. % shredders, % shredder taxa) were significantly lower in eutrophied than in reference streams, whereas the IBMWP index that is specifically designed for the Iberian peninsula classified all 10 streams in the highest possible class as having ‘very good’ ecological conditions.5. Leaf litter decomposition was sufficiently sensitive to respond to low levels of eutrophication and could be a useful functional measure to complement assessment programmes based on structural parameters.

Spatial Patchiness of Litter, Nutrients and Macroinvertebrates during Secondary Succession in a Tropical Montane Cloud Forest in Mexico

We test the hypothesis that secondary succession in Tropical Montane Cloud Forest (TMCF) in Mexico is accompanied by an increase in the spatial structuring of litter resources, soil nutrient concentrations and the soil macroinvertebrate community at a within-plot scale (5–25 m). This increased spatial structuring is expected because secondary succession in these forests is associated with an increase in the diversity of trees that dominate the canopy. If each tree species generates a particular soil environment under its canopy, then under a diverse tree community, soil properties will be spatially very heterogeneous. Tree censuses and grid sampling were performed in four successional stages of a secondary chronosequence of TMCF. Variography was used to analyse spatial patterns in continuous variables such as nutrient concentrations, while Spatial Analysis by Distance Indices (SADIE) was applied to determine patchiness in the distribution of soil macroinvertebrate taxa. Secondary succession was found to be accompanied by the predicted increase in the spatial structuring of litter resources and the macroinvertebrate community at the within-plot scale. Spatial patterns in the macroinvertebrate community only became evident for all taxa in the oldest forest (100 years old). Patches with low Ca and Mg concentrations in early successional soils were associated with patches where pine litter was most abundant while those with low P concentrations in late successional stages were associated with patches where oak litter was most abundant. Results suggest that anthropogenic disturbance aboveground promotes a more homogeneous resource environment in the surface soil, which compared to older forests, sustains a less diverse and less spatially structured macroinvertebrate community.

Site of leaf origin affects how mixed litter decomposes

Recent studies have demonstrated that mass loss, nutrient dynamics, and decomposer associations in leaf litter from a given plant species can differ when leaves of that species decay alone compared to when they decay mixed with other species’ leaves. Results of litter-mix experiments have been variable, however, making predictions of decomposition in mixtures difficult. It is not known, for example, whether interactions among litter types in litter mixes are similar across sites, even for litter mixtures containing the same plant species. To address this issue, we used reciprocal transplants of litter in compartmentalized litterbags to study decomposition of equal-mass litter mixtures of sugar maple ( Acer saccharum Marshall) and red oak ( Quercus rubra L.) at four forest sites in northwestern Connecticut. These species differ significantly in litter quality. Red oak always has higher lignin concentrations than maple, and here C:N is lower in oak leaves and litter, a pattern often observed when oak coexists with maple. Overall, we observed less mass loss and lower N accumulation in sugar maple and red oak litter mixtures than we predicted from observed dynamics in single-species litterbags. Whether these differences were significant or not depended on the site of origin of the leaves ( P<0.02), but there was no significant interaction between sites of decay and the differences in observed and predicted decomposition ( P>0.2) . Mixing of leaf litter types could have significant impacts on nutrient cycling in forests, but the extent of the impacts can vary among sites and depends on the origin of mixed leaves even when the species composition of mixes is constant.

Patterns Of Litter Disappearance In A Northern Hardwood Forest Invaded By Exotic Earthworms

A field study was conducted to evaluate the effects of exotic earthworm invasions on the rates of leaf litter disappearance in a northern hardwood forest in southcentral New York, USA. Specifically, we assessed whether differences in litter quality and the species composition of exotic earthworm communities affected leaf litter disappearance rates. Two forest sites with contrasting communities of exotic earthworms were selected, and disappearance rates of sugar maple and red oak litter were estimated in litter boxes in adjacent earthworm-free, transition, and earthworm-invaded plots within each site. After 540 days in the field, 1.7-3 times more litter remained in the reference plots than in the earthworm-invaded plots. In the earthworm-invaded plots, rates of disappearance of sugar maple litter were higher than for oak litter during the first year, but by the end of the experiment, the amount of sugar maple and oak litter remaining in the earthworm-invaded plots was identical within each site. The composition of the earthworm communities significantly affected the patterns of litter disappearance. In the site dominated by the anecic earthworm Lumbricus terrestris and the endogeic Aporrectodea tuberculata, the percentage of litter remaining after 540 days (approximately 17%) was significantly less than at the site dominated by L. rubellus and Octolasion tyrtaeum (approximately 27%). This difference may be attributed to the differences in feeding behavior of the two litter-feeding species: L. terrestris buries entire leaves in vertical burrows, whereas L. rubellus usually feeds on litter at the soil surface, leaving behind leaf petioles and veins. Our results showed that earthworms not only accelerate litter disappearance rates, but also may reduce the differences in decomposition rates that result from different litter qualities at later stages of decay. Similarly, our results indicate that earthworm effects on decomposition vary with earthworm community composition. Furthermore, because earthworm invasion can involve a predictable shift in community structure along invasion fronts or through time, the community dynamics of invasion are important in predicting the spatial and temporal effects of earthworm invasion on litter decomposition, especially at later stages of decay.

Mineralization of forest litter nutrients by heat and combustion

Temperature dependant mineralization dynamics during fire of litter species characteristic of the New Jersey pine barrens was determined. Senescent leaf material of pitch pine ( Pinus rigida), white oak ( Quercus alba) and black huckleberry ( Gaylusssacia baccata) were collected at the time of abscission; sorted, ground and oven-dried at 70 °C. Replicate samples were then heated for 2 h at: 70, 100, 200, 300, 400, and 550 °C. Mass loss and total nitrogen and total phosphorus concentration of the heated material were determined. Additional samples of the residual material were extracted with deionized water, and the filtrate was assayed for the anions: NO 3 − , PO 4 − 3 , SO 4 − 2 ; and cations: NH 4 + , K +, Mg ++, and Ca ++. By heating leaf litter over a range of temperatures, to simulate the heterogeneous nature of forest litter burning, we identified patterns of nutrient mineralization characteristic of specific temperatures, some of which were common to all three litter species and others unique to individual species. In general, it appears that black huckleberry leaf litter was the most nutrient rich and the most labile. In huckleberry litter, there was a large reserve of soluble nitrogen, sulfur, phosphate, calcium and magnesium that became available upon heating to 200 °C. Pitch pine litter was the most nutrient poor, and the rates of nutrient mineralization were also generally the lowest of the three species studied. White oak litter nutrient concentration and rates of mineralization along the temperature gradient were intermediate. For all three litter species examined organic and inorganic nitrogen losses due to volatilization were >99% upon heating to 550 °C, and soluble magnesium concentrations declined significantly at temperatures of 300 °C, despite having a volatilization temperature greater than 1100 °C. Under the temperature range employed, heating of leaf litter resulted in little volatilization loss of phosphorus; however, the amount of soluble phosphate phosphorus was much lower in all three litter types at temperatures of 300 °C and above. With increasing temperatures, inorganic phosphate ions presumably became bound to cations in the ash, forming insoluble metal phosphates. The dramatic increase of the ratio of total phosphorus to soluble inorganic phosphate at higher temperatures, the loss of soluble magnesium above 300 °C, and the near complete loss of nitrogen at 550 °C suggests that after intense fires availability of these minerals may be dramatically reduced.

The effect of mixing ground leaf litters to soil on the development of pitch pine ectomycorrhizal and soil arthropod communities in natural soil microcosm systems

The addition of leaf litter to soil influences both the nutrients and polyphenols of soil. It is likely that contrasting nutrient and polyphenolic composition of different plant litters may affect plant growth, mycorrhizal and soil arthropod communities. We report results from a microcosm experiment of effects of incorporation of three single leaf litter species and a mixture of all three on pitch pine seedling growth, their ectomycorrhizal community and soil arthropod community. The three litter species (pine, oak and huckleberry) represent co-dominant species within the New Jersey pine barrens ecosystem. We show that the leaf litters have different composition of nutrients and polyphenols, with rooting matrix containing pine litter having lower inorganic nitrogen content (1.6 μg g −1) than oak (19.9 μg g −1) and huckleberry (4.4 μg g −1), but oak litter having the highest extractable phosphorus (13.3 cf. 0–0.08 μg g −1) and total phenol content and lowest condensed tannin content. These differences were imparted to rooting matrix of homogenized humic (Oa) layer of pine barrens soil to which milled leaf litter was added and used in the microcosms. Pitch pine seedlings grew significantly better in un-amended rooting matrix (0.33±0.02 g) than any of the litter treatments (0.15±0.02–0.17±0.01 g) and tissue P concentrations tracked phosphate concentrations in the rooting matrix. Total P accumulation into plant tissue was higher in oak than control, attributable to a significantly higher ( P<0.05) accumulation in roots (3.3±0.19 mg g −1) compared to other species (1.1±0.04–2.3±0.08 mg g −1). No relationship was seen between tissue N concentration and soil N, but seedlings growing in huckleberry litter amended soil accumulated less N than control. The effect of leaf litters on the ectomycorrhizal community composition were determined by PCA (first two axes accounted for 81% of the variance) and stepwise multiple regression analysis. These analyses showed that huckleberry leaf litter had a significant impact on mycorrhizal community composition with morphotypes Cg and DB being more abundant in the presence of huckleberry litter (178±13 cf. 68±15–106±15 for Cg and 141±11 cf. 88±23–111±18 for DB) and its influence of elevating nitrate nitrogen, organic nitrogen, total phenols and protein precipitation content of the rooting matrix. Mycorrhizal morphotypes BS and SB were significantly more abundant in the community where these soil factors were low in the absence of leaf litter addition. Total ectomycorrhizal abundance was negatively related to hydrolysable tannin concentration in the rooting matrix ( r 2=0.132, P<0.05). There was no influence of leaf litter type on mite density (dominated by non-burrowing phthiracarids), but collembolan density (dominated by Folsomia spp) showed a greater than threefold reduction in population density in the presence of leaf litter ( F=6.47, P<0.05). Collembolan density was positively correlated with mycorrhizal morphotypes GS and SB ( P<0.05) and negatively related to morphotypes DB ( P<0.05) and soil extractable NH 4–N ( P<0.05), suggesting a possible selection of fungal species in their diet and a relationship between collembola and nitrification.

Leaf litter decomposition in a chaparral ecosystem, Southern California

Decomposition losses from leaves of three evergreen chaparral species, scrub oak ( Quercus dumosa), ceanothus ( Ceanothus crassifolius), and manzanita ( Arctostaphylos glauca), were quantified over a 2-y field exposure using litterbags. Changes in ash-free dry mass, C, and N were monitored at 2- to 6-month intervals at four replicate sites composed of patches of these three chaparral species. Three proximate C fractions were extracted from fresh and decomposing litter samples: polar and non-polar extractives (EXT), acid-solubles (ACID), and acid-insolubles (KLIG). The chemical structure of fresh and decomposed litter was additionally characterized using high-resolution solid-state 13C NMR spectroscopy, while morphological properties were examined by scanning electron microscopy (SEM). After 2 y, the litters had lost between 20.7%±1.2 ( Ceanothus) and 35.2%±6.8 ( Quercus) of their original ash-free dry mass. The manzanita decomposed at a significantly faster rate than the other two litter types during the first few months of field exposure. Yet, after 2 y, mass loss was greater for the oak. Differences in decomposition rates could not be accounted for based on a single litter quality index. Fresh manzanita exhibited a significantly higher N content, which could explain its initially faster decay rate. Fresh oak litter, on the other hand, had a relatively high ACID and O-alkyl C ( O-ALK) content, which may have been responsible for its decay pattern. Fresh ceanothus contained a relatively low KLIG content, yet it decomposed more slowly than the two other species. The solid-state 13C NMR spectra of the ceanothus litter had two peaks characteristic of proanthocyanidins, which likely contributed to the recalcitrance of this litter type. SEM revealed that ceanothus leaf surfaces were left nearly unchanged after field exposure. In comparison, the oak and manzanita leaf surfaces were pitted and covered by microbial growth to the point of being unrecognizable. Taken together, our results indicate that a combination of biological, physical and chemical factors need to be examined to clarify the different decomposition rates and patterns of these three chaparral species.

Do woodlice and earthworms interact synergistically in leaf litter decomposition?

SummaryIn laboratory microcosms, we investigated the influence of diversity of both leaf litter and detritivores on decomposition processes. Either woodlice or earthworms, or a combination of woodlice and earthworms, fed on leaf litter of either oak or alder, or oak and alder for 8 weeks. Mass loss of leaf litter, soil microbial respiration and soil nutrient concentrations were determined every 2 weeks.For four out of seven decomposition parameters, the joint effects of woodlice and earthworms were stronger than the sum of single‐species effects when they had fed on alder litter. When feeding on oak litter, however, woodlice and earthworms together revealed lower decomposition rates than predicted from their single effects. Joint effects of detritivores on decomposition of mixed litter were always lower than predicted from the sum of their effects.In mixed‐litter assays, we obtained intermediate values of decomposition parameters, indicating that doubling the species richness of leaf litter from one to two species did not promote decomposition processes. Effects of mixing litter were, thus, mostly additive; essentially only when earthworms fed on mixed litter we observed, mostly positive, non‐additive effects of diverse litter.Our findings provide evidence for a potential effect on ecosystem functioning through joint action of detritivores even at low species diversity, while litter diversity seems to be less significant. On high‐quality litter, isopods and earthworms are not functionally redundant but act synergistically on litter decomposition. The effects of detritivore diversity on ecosystem processes, however, are context‐specific and depend on the quality and diversity of the available food sources, and on species‐specific characteristics of the detritivores.

Phenotypic variation in oak litter influences short- and long-term nutrient cycling through litter chemistry

The influence of intraspecific variation on ecosystem functioning is relatively unknown. We investigated the effects of litter phenotype on carbon and nitrogen fluxes in the litter and soil, and on microarthropod and bacterial populations over a 3-year period. Different litter phenotypes significantly affected carbon and nitrogen fluxes. Short- and long-term fluxes within single phenotype treatments were significantly, but unpredictably, different from a mixed phenotype treatment. Fluxes were associated with variation in litter chemistry which has a significant genetic component. We found no effects of phenotype identity on soil bacterial or microarthropod communities. However, persistent litter phenotype effects upon carbon and nitrogen fluxes support our previous suggestion that losses in genetic diversity may influence ecosystem processes.