Cellulase activity on decomposing leaf litter in microcosms

In this paper, we describe cellulase and cellobiose dehydrogenase (CBDH) dynamics in relation to incubation time, mass loss and chemical composition of decomposing deciduous leaf litter. Cellulose disappearance from litter coincided with periods of maximum cellulase activity. CBDH activity peaked later in decomposition after cellulase activity had declined. Enzyme activity patterns differed among litter types when expressed on the basis of decomposition time or cumulative mass loss. The patterns converged when expressed on the basis of chemical composition as indexed by the fraction of cellulose in the lignocellulose complex. We present a three-stage model of decomposition based on temporal changes in cellulase activities and coincident changes in litter chemical composition.     

The effects of a pesticide program on microbial populations from apple leaf litter

The leaf litter microbial community was quantitatively and qualitatively changed when a standard pesticide schedule that comprised an insecticide, a bactericide, and a fungicide was applied to McIntosh apple trees in the summer. Effects were observed for two winters by four indirect assays and three direct methods. Populations were altered qualitatively both years, but the most striking difference was the quantitative impact from year to year. Bacteria, filamentous fungi, and yeasts from treated leaves were reduced 10- to 10 000-fold between November 1976 and April 1977 and did not recover until snow cover had melted in March. Reductions in 1977-1978 were negligible. The marked seasonal difference is attributed to meteorological influences. Fluorescent pseudomonads were among the bacteria depressed by chemicals. Of the 49 genera of fungi and yeasts isolated, Coniothyrium sp., Penicillium spp., Arthrobotrys spp., and Nodulisporium sp. were appreciably reduced, whereas Typhula spp., Pleurophomella sp., Sporobolomyces spp., and Rhodotorula spp. were substantially enhanced by the spray program.     

Connecting litter quality,microbial community and nitrogen transfer mechanisms in decomposing litter mixtures

Synergistic effects on decomposition in litter mixtures have been suggested to be due to the transfer of nitrogen from N‐rich to N‐poor species. However, the dominant pathway and the underlying mechanisms remain to be elucidated. We conducted an experiment to investigate and quantify the control mechanisms for nitrogen transfer between two litter species of contrasting nitrogen status (¹⁵N labeled and unlabeled Fagus sylvatica and Fraxinus excelsior) in presence and absence of micro‐arthropods. We found that ¹⁵N was predominantly transferred actively aboveground by saprotrophic fungi, rather than belowground or passively by leaching. However, litter decomposition remained unaffected by N‐dynamics and was poorly affected by micro‐arthropods, suggesting that synergistic effects in litter mixtures depend on complex environmental interrelationships. Remarkably, more ¹⁵N was transferred from N‐poor beech than N‐rich ash litter. Moreover, the low transfer of ¹⁵N from ash litter was insensitive to destination species whereas the transfer of ¹⁵N from labeled beech litter to unlabeled beech was significantly greater than the amount of ¹⁵N transferred to unlabeled ash suggesting that processes of nitrogen transfer fundamentally differ between litter species of different nitrogen status. Microbial analyses suggest that nitrogen of N‐rich litter is entirely controlled by bacteria that hamper nitrogen capture of microbes in the environment supporting the source‐theory. In contrast, nitrogen of N‐poor fungal dominated litter is less protected and transferable depending on the nitrogen status and the transfer capacity of the microbial community of the co‐occurring litter species supporting the gradient‐theory. Thus, our results challenge the traditional view regarding the role of N‐rich litter in decomposing litter mixtures. We rather suggest that N‐rich litter is only a poor nitrogen source, whereas N‐poor litter, can act as an important nitrogen source in litter mixtures. Consequently both absolute and relative differences in initial litter C/N ratios of co‐occurring litter species need to be considered for understanding nitrogen dynamics in decomposing litter mixtures.     

Nutrient dynamics and lignocellulose degradation in decomposing Quercus serrata leaf litter

The litter mass loss, concentration and mass of some major nutrient elements, degradation of lignin and cellulose in decomposing Quercus serrata Murray leaf litter were monitored for 3 years using the litterbag method. The mobility of elements during the course of the study was in the order of: K > P > C > Mg > Ca > N. Three patterns of nutrient dynamics were observed: (i) concentration increased while mass decreased (N, Mg and Ca); (ii) concentration and nutrient mass decreased (K and C); and (iii) both concentration and mass had fluctuated (P). The C to element ratio tended to increase as the element was released, and decreased as the element was retained. Nitrogen mobility in relation to carbon was characterized by three phases: (i) initial release; (ii) accumulation and (iii) final release. The decay rate (k) calculated from 0–6 months period was overestimated for an average annual rate while those of 0–36 months fit the negative single exponential model (Adj. r² = 0.99) better than shorter periods. For lignin, the concentration had increased then decreased but tended to stabilize after 1 year while the lignin mass had continuously decreased throughout the study period. During the first 9 months, both the concentrations and mass of cellulose had fluctuated but declined thereafter. The amounts of N had initially increased but declined after 1 year; P had fluctuated while K, Ca, Mg and C had decreased throughout the study. N and C/N ratio exerted strong influence on mass loss during the first24 months but the influence of lignin emerged after 24 months.     

Respiration and annual fungal production associated with decomposing leaf litter in two streams

1. We compared fungal biomass, production and microbial respiration associated with decomposing leaves in one softwater stream (Payne Creek) and one hardwater stream (Lindsey Spring Branch). 2. Both streams received similar annual leaf litter fall (478–492 g m^?2), but Lindsey Spring Branch had higher average monthly standing crop of leaf litter (69 ± 24 g m^?2; mean ± SE) than Payne Creek (39 ± 9 g m^?2). 3. Leaves sampled from Lindsey Spring Branch contained a higher mean concentration of fungal biomass (71 ± 11 mg g^?1) than those from Payne Creek (54 ± 8 mg g^?1). Maximum spore concentrations in the water of Lindsay Spring Branch were also higher than those in Payne Creek. These results agreed with litterbag studies of red maple (Acer rubrum) leaves, which decomposed faster (decay rate of 0.014 versus 0.004 day^?1), exhibited higher maximum fungal biomass and had higher rates of fungal sporulation in Lindsey Spring Branch than in Payne Creek. 4. Rates of fungal production and respiration per g leaf were similar in the two streams, although rates of fungal production and respiration per square metre were higher in Lindsey Spring Branch than in Payne Creek because of the differences in leaf litter standing crop. 5. Annual fungal production was 16 ± 6 g m^?2 (mean ± 95% CI) in Payne Creek and 46 ± 25 g m^?2 in Lindsey Spring Branch. Measurements were taken through the autumn of 2 years to obtain an indication of inter‐year variability. Fungal production during October to January of the 2 years varied between 3 and 6 g m^?2 in Payne Creek and 7–27 g m^?2 in Lindsey Spring Branch. 6. Partial organic matter budgets constructed for both streams indicated that 3 ± 1% of leaf litter fall went into fungal production and 7 ± 2% was lost as respiration in Payne Creek. In Lindsey Spring Branch, fungal production accounted for 10 ± 5% of leaf litter fall and microbial respiration for 13 ± 9%.     

Release of plant nutrients from decomposing leaf litter in a South Swedish beech forest

Weight loss and dynamics of plant nutrients (N, P, K, Ca, Mg, S, Fe, Mn, Na, Zn and Cu) in leaf litter were studied in a mature beech forest in South Sweden, using the litter bag technique. An initial decomposition period of about 12 to 18 months was characterized by an absolute net increase of N, P, and S contents in litter, followed by a period of net release of these elements. This development, which was most obvious for N and P, was interpreted as a change from a phase where decomposer activity was limited by the availability of nutrient elements to an energy-limited phase. A net release of nitrogen did not occur until after two years of decomposition, and a transfer of nitrogen and phosphorus between different litter layers is here proposed to work as a retention mechanism.
Potassium and sodium were quickly leached from the litter, while release of magnesium, calcium, and initially also manganese, was more associated to organic matter weight loss. Iron, zinc and copper were all strongly accumulated in the litter material. This is explained by mineral soil admixture for the former element and by atmospheric fall-out in combination with the chemical complex formation character for the latter two elements.
Finally, the importance of the different release processes in the total nutrient recycling of the forest is discussed.     

Aerobic cellulolytic bacterial flora associated with decomposing Phragmites leaf litter in a seawater lake

A litter bag experiment was carried out in a eutrophic seawater lake from autumn to summer in order to determine which bacterial genera play an important role in decomposition of Phragmites communis leaf litter. The count of cellulolytic bacteria and decomposition rate of litter cellulose increased rapidly during the initial month. In contrast, the count of cellulolytic fungi was lowest in this period. Pseudomonas accounted for 65–90% of total isolates of cellulolytic bacteria up to 5 months. These results suggest that Pseudomonas plays an important role in at least the initial decomposition stage of the litter.     

The role of Diplopoda litter grazing activity on recycling processes in a Mediterranean climate

Variation in Diplopoda density and biomass were studied in mediterranean holm oak formations in order to estimate the impact of the feeding activity of these Arthropods. Field and controlled experiments have shown the importance of the litter age and of the nature of leaves on the consumption rate. The consequences of faecal pellet restitution on microbial activity are discussed.     

Interacting effects of leaf litter species and macrofauna on decomposition in different litter environments

The leaf litter environment (single species versus mixed species), and interactions between litter diversity and macrofauna are thought to be important in influencing decomposition rates. However, the role of soil macrofauna in the breakdown of different species of leaf litter is poorly understood. In this study we examine the multiple biotic controls of decomposition – litter quality, soil macrofauna and litter environment and their interactions. The influence of soil macrofauna and litter environment on the decomposition of six deciduous tree species (Fraxinus excelsior L., Acer pseudoplatanus L., Acer campestre L., Corylus avellana L., Quercus robur L., Fagus sylvatica L.) was investigated in a temperate forest, Wytham Woods, Southern England. We used litterbags that selectively excluded macrofauna to assess the relative importance of macrofauna versus microbial, micro and mesofauna decomposition, and placed single species bags in either conspecific single species or mixed species litter environments. The study was designed to separate plant species composition effects on litter decomposition rates, allowing us to evaluate whether mixed species litter environments affect decomposition rates compared to single species litter environments, and if so whether the effects vary among litter species, over time, and with regard to the presence of soil macrofauna. All species had faster rates of decomposition when macrofauna were present, with 22–41% of the total mass loss attributed to macrofauna. Macrofauna were most important for easily decomposable species as soon as the leaves were placed on the ground, but were most important for recalcitrant species after nine months in the field. The mass loss rates did not differ between mixed and single species litter environments, indicating that observed differences between single species and mixed species litterbags in previous field studies are due to the direct contact of neighbouring species inside the litterbag rather than the litter environment in which they are placed.     

The effects of feeding broiler litter on microbial contamination of beef carcasses

Two experiments were conducted to test the effects of feeding broiler litter, either directly in the diet or indirectly through pasture-fertilization, to beef cattle on the incidence of Salmonella typhimurium (S) and Escherichia coli O157:H7 (EC) contamination of carcasses and ground beef. In Experiment 1, beef cows (n = 32) were allotted either ad libitum access to grass hay or a formulated diet (80% deep-stacked broiler litter and 20% corn). In Experiment 2, beef cows (n = 32) were assigned to graze on pastures fertilized with a commercial fertilizer or fresh broiler litter. Cows in Experiment 1 were harvested following a 56-d feeding period; whereas, cows in Experiment 2 were harvested after 5, 10, 20, and 40 d of grazing pastures. All samples of muscle, purge, and ground beef were culture-negative for S and EC, suggesting that beef cattle may consume properly handled deep-stacked broiler litter, or pastures fertilized with fresh litter, without increasing the likelihood of carcass/meat contamination with S and (or) EC.     

The effect of grazing by the detritivore Orchestia grillus on Spartina litter and its associated microbial community

Summary Orchestia grillus efficiently feeds upon microorganisms attached to ingested Spartina alterniflora litter, but does not digest litter itself. Microorganisms respond to Orchestia grazing with increased metabolic activity, reflected in accelerated decomposition of the nitrogen fraction of litter and increased microbial biomass. Increased microbial activity may be partly a function of ammonia excretion and higher diffusion rate due to animal movement, but mainly it is a direct response to grazing. Microbial biomass increases with grazing because the pool of available nitrogen becomes larger. A model postulating interactions between Orchestria, Spartina litter and attached microorganisms is presented.This is contribution no. 180 from the Program in Ecology and Evolution at the State University of New York at Stony Brook     

The direct effects of UV-B radiation on Betula pubescens litter decomposing at four European field sites

A co-ordinated series of field experiments were conducted to consider the effects of elevated UV-B radiation applied directly to decomposing plant litter. Betula pubescens was decomposed under ambient and elevated UV-B (simulating a 15% ozone depletion) using outdoor irradiation facilities at Adventdalen, Norway (78° N), Abisko, Sweden (68° N), Amsterdam, The Netherlands (52° N,) and Patras, Greece (38° N). There was no significant effect of treatment on mass loss for samples collected after 2, 12 and 14 months decomposition at Amsterdam, or after 4 months decomposition at Adventdalen. Significant reductions in the mass loss of litter decomposing under elevated UV-B compared to ambient were found at the other 2 sites. The only effect of treatment on litter chemistry during decomposition was a significant reduction in the N concentration of material at Abisko and a significant increase in C:N at Patras for litter decomposing under elevated UV-B. Significant differences were found in the structure of the fungal community decomposing litter in Sweden, the only site to be tested. These data, and the few published studies of the response of decomposition to UV-B incident on litter suggest that, in the ecosystems and climates that have been studied, such direct effects are typically confined to the initial stages of decomposition, and are rather small in magnitude.     

Season mediates herbivore effects on litter and soil microbial abundance and activity in a semi-arid woodland

Herbivores can directly impact ecosystem function by altering litter quality of an ecosystem or indirectly by shifting the composition of microbial communities that mediate nutrient processes. We examined the effects of tree susceptibility and resistance to herbivory on litter microarthropod and soil microbial communities to test the general hypothesis that herbivore driven changes in litter inputs and soil microclimate will feedback to the microbial community. Our study population consisted of individual piñon pine trees that were either susceptible or resistant to the stem-boring moth (Dioryctria albovittella) and susceptible piñon pine trees from which the moth herbivores have been manually removed since 1982. Moth herbivory increased piñon litter nitrogen concentrations (16%) and decreased canopy precipitation interception (28%), both potentially significant factors influencing litter and soil microbial communities. Our research resulted in three major findings: (1) In spite of an apparent increase in litter quality, herbivory did not change litter microarthropod abundance or species richness. (2) However, susceptibility to herbivores strongly influenced bulk soil microbial communities (i.e., 52% greater abundance beneath herbivore-resistant and herbivore-removal trees than susceptible trees) and alkaline phosphatase activity (i.e., 412% increase beneath susceptible trees relative to other groups). (3) Season had a strong influence on microbial communities (i.e., microbial biomass and alkaline phosphatase activity increased after the summer rains), and their response to herbivore inputs, in this semi-arid ecosystem. Thus, during the dry season plant resistance and susceptibility to a common insect herbivore had little or no observable effects on the belowground organisms and processes we studied, but after the rains, some pronounced effects emerged.     

Species-specific effects of gastropods on leaf litter processing in pond mesocosms

A study of the diet of native brown trout (Salmo trutta) parr and introduced European minnow (Phoxinus phoxinus) in the subalpine lake, Øvre Heimdalsvatn, showed that the two species had considerable dietary overlap, both in the littoral zone and in the outlet of the lake. Chironomidae constituted a substantial proportion of the diet of the two species in both habitats. The results indicated that both zooplankton (Cladocera) and large macroinvertebrates (EPT-species) made up a higher proportion of the minnow diet in the early phase of the minnow establishment (1975–1977) than later, and that the significance of small macroinvertebrates (Chironomidae) as prey has increased during the same period. Dietary analysis of the sympatric brown trout and minnow population in Øvre Heimdalsvatn does not provide a definitive conclusion about the degree of competition between the two species. However, together with the findings in other studies in Øvre Heimdalsvatn that have documented reduced recruitment and individual growth of brown trout, decreased individual growth of minnows and a marked decline in the density of large crustaceans (Lepidurus arcticus and Gammarus lacustris) in the shallow littoral of the lake during the last decades indicates that competitive interactions between the two species are likely. This is probably an example of the competition between two fish species with a high degree of dietary overlap when living in sympatry, most likely caused by absence of alternative prey and alternative habitats due to the high predation risk for both brown trout parr and minnows in deeper parts and in the open waters of the lake.     

Potential effects of leaf litter on water quality in urban watersheds

Leaf litter plays a critical role in regulating ecological functions in headwater forest streams, whereas the effects of leaves on water quality in urbanized streams are not fully understood. This study examined the potential importance of leaf litter for the release and transformations of organic carbon and nutrients in urban streams, and compared the effects with other types of natural organic substrates (periphyton and stream sediment). Nutrients and organic carbon were leached from senescent leaves of 6 tree species in the laboratory with deionized water, and maximal releases, leaching rate constants, composition and bioavailability of the leached dissolved organic carbon (DOC) were determined. Stream substrates (leaf debris, rocks with periphyton, and sediment) were seasonally collected from urban and forest reference streams of the NSF Baltimore Long-term Ecological Research Site and incubated with overlying stream water to estimate areal fluxes of DOC and nitrogen. Leaf litter leaching showed large ranges in maximal releases of DOC (7.0–131 mg g^?1), dissolved organic nitrogen (DON; 0.07–1.39 mg g^?1) and total dissolved phosphorus (TDP; 0.14–0.70 mg g^?1) among tree species. DOC leaching rate constants, carbon to nitrogen ratios, and DOC bioavailability were all correlated with organic matter quality indicated by fluorescence spectroscopy. Results from substrate incubation experiments showed far higher DOC and DON release and nitrate retention with leaf debris than with sediment, or rocks with periphyton. DOC release from leaf debris was positively correlated with stream nitrate retention at residential and urban sites, with the highest values observed during the fall and lowest during the summer. This study suggests the potential importance of leaf litter quantity and quality on fostering DOC and nutrient release and transformations in urban streams. It also suggests that species-specific impacts of leaves should be considered in riparian buffer and stream restoration strategies.     

Irrigation,fertilization and initial substrate quality effects on decomposing Loblolly pine litter chemistry

Changes in carbon chemistry (i.e., carbon compound classes such as aromatics, phenolics, etc.) of loblolly pine (Pinus taeda L.) litter were examined during three years of decomposition under factorial combinations of irrigation and fertilization treatments. Cross polarization magic angle spinning ¹³C nuclear magnetic resonance revealed that total carbon and nutrient concentrations correlated strongly with carbohydrate and O-alkyl carbon concentrations but did not relate well with concentrations of lignin, aromatic and phenolic carbon, or with lignin-related decomposition indices. The best correlations to carbon and nutrient concentrations occurred with the C/N (R²=0.86, P > 0.0001) and alkyl/O-alkyl (R²=0.75, P > 0.0001) decomposition indices. In all situations, the carbon chemistry of the decomposing litter followed the general pattern of accumulation of alkyl and carbonyl carbon with a loss of O-alkyl and methoxy carbon. Only small variations in the aromatic and phenolic carbon concentrations were detected. Since lignin is composed primarily of aromatic and phenolic carbons, the observation that there were only small changes in the aromatic and phenolic carbons of the litter is consistent with the general stability of lignin in these ecosystems. Trends in carbon chemistry during decomposition suggested that fertilization accelerated the decomposition process by about 100% as compared with the control plots. Irrigation also accelerated the decomposition process but to a lower extent (about 62% greater than control plots). Initial litter quality, as defined by the litter C/N, did not have a significant effect on the carbon chemistry of the decomposing litter. This study demonstrated that the decomposition mechanisms were not altered by the treatments but there were important changes in the relative chemistry of the decomposing litter which impacted the rate of decomposition.     

Nutrient release from decomposing leaf litter of Banksia ornata,Dark Island heathland,South Australia

Distinct O₁ and O₂ layers, representing annual litter fall, enabled the sequential loss of biomass and nutrients (phosphorus and nitrogen) to be reconstructed in undisturbed litter layers of Banksia ornata in the Dark Island heathland, South Australia. Apart from an initial loss in biomass and nitrogen, the dry weight and nutrient content of the O₁ layer, exposed to the desiccating influence of the atmosphere, remained relatively constant until covered by the following year's leaf fall. Under the blanket of newly fallen leaves, biomass decomposition proceeded continuously through autumn, winter, spring, into the dry summer season. Even though the biomass of the decomposing leaf (O₂) layer decreased continuously, its nutrient content remained relatively constant until the summer season was reached when total decomposition and nutrient loss occurred. During spring, fine rootlets invaded the decomposing litter layer (O₂) and, together with decomposer fungi, bacteria and soil fauna, maintained the total nutrient content of the decomposing leaf at a constant level. By late spring-early summer shoot growth of the dominant heath species was initiated, inducing the mobilization of the nutrients stored in the decomposing litter layer.     

Fine root growth and nutrient release in decomposing leaf litter in three contrasting vegetation types in central Amazonia

We tested the hypothesis that the growth of fine roots upward into the leaf litter, forming a ‘surface root mat’, found widely in Amazonian forests, is of adaptive value for plants of poor soils because it makes possible more rapid uptake of limiting nutrients. We assessed the effect of invasion by fine roots on the rates of loss of dry mass and nutrient content of leaf litter over 1 year in three plots in each of three contrasting forest types in central Amazonia: the stunted facies of heath forest known as campina (SHF), the taller facies of heath forest known as campinarana (THF), both on spodosols, and the surrounding lowland evergreen rain forest (LERF) on ultisol. Pairs of bags filled with freshly fallen leaves from the trees of Clitoria fairchildiana (Fabaceae) were placed on the litter layer; in order to prevent roots entering the control bag in each pair that bag was lifted from the forest floor and turned over each week, while the treatment bag was left undisturbed. From each plot, four pairs of litter bags were retrieved after 30, 60, 120, 180, 270 and 360 d, and all roots that had grown into the litterbags were carefully removed. The leaves and roots from each bag were oven-dried for nutrient analysis. In no forest type was there a significant difference in the rate of loss of dry matter from the litter between the bags with and without roots. The amounts of roots invading the litter bags increased significantly in the sequence SHF < THF < LERF. In no forest did the presence of roots have a significant effect on the rate of disappearance of N or P from the leaf material, or on the rate of accumulation of Fe and Al. In the SHF there was no significant effect of invasion by roots on the rates of disappearance of Ca, Mg, Mn or Zn, but in the THF, the rates of disappearance of these four elements between 270 and 360 d were significantly greater in the presence of roots. In the LERF the results were similar, but the effects of roots started earlier—the rates of disappearance of Ca and Mg were significantly enhanced between 120 and 360 d. The results from the SHF may be interpreted to suggest that the growth of fine roots (and their fungal associates) upward into leaf litter is unlikely to be explained wholly by their role in the efficient recovery of mineral nutrients.     

Incorporation of carbon from decomposing litter of two pioneer plant species into microbial communities of the detritusphere

For several Staphylococci, such as Staphylococcus aureus, Staphylococcus saprophyticus, and Staphylococcus epidermidis, invasion of eukaryotic cells has been described and this mechanism has been considered an important part of the infection process. The fibrinogen-binding protein (Fbl) of Staphylococcus lugdunensis, a homolog of the clumping factor A of S. aureus, has been described as fibrinogen-binding adhesin and might promote invasion of cells. We therefore characterized several clinical strains of S. lugdunensis in terms of whole cell fibrinogen and fibronectin binding and correlated these results with the invasion of epithelial and endothelial cells by S. lugdunensis. We described for the first time invasion of cells by S. lugdunensis. As invasion of cells by S. lugdunensis was only partly inhibited by cytochalasin D in contrast to a complete inhibition of invasion of cells by S. aureus, further invasion mechanisms are likely to be present in S. lugdunensis. In addition, the Fbl of S. lugdunensis is not involved in the invasion of cells as ruled out by an isogenic fbl mutant.