Do foliar endophytes affect grass litter decomposition? A microcosm approach using Lolium multiflorum

Symbiotic infection with fungal endophytes has been shown to decrease herbivory in several temperate grasses. We tested the hypothesis that foliar endophytes of grasses may also affect below-ground processes upon their host death, by altering the litter quality for detritivores or the microenvironment for decomposition. Microcosm–litterbag experiments were used to assess decay rates for litter produced by endophyte ( Neotyphodium sp.) infected vs uninfected Lolium multiflorum plants, and to examine endophyte-mediated effects of prior site occupants on current litter decomposition. We found that litter from endophyte-infected L. multiflorum decomposed more slowly than litter from endophyte-free conspecifics and from a naturally uninfected grass, Bromus unioloides . Furthermore, the endophyte–grass association modified the decomposition environment, so that B. unioloides litter decomposed faster when placed underneath a thick layer of endophyte-free L. multiflorum litter. Litter decay rates increased with the amount of root debris remaining in situ from the previous season, but were not affected by the infection status of prior site occupants. The lower decomposability of litter from infected L. multiflorum plants persisted across a range of microenvironments, as determined by different amounts of above-ground litter and soil moisture conditions. Endophyte infection tended to reduce the N content of decaying litter; however, litter N and C/N ratio mainly accounted for interspecific differences in decomposition. Our results imply that fungal endophytes not only can affect herbivory food chains, but also soil organisms and the ecosystem processes they regulate. This study suggests a novel role for symbiotic foliar endophytes in linking above-ground and below-ground sub-systems.     

An in vitro approach to investigate medicinal chemical synthesis by three herbal plants

Ever since regulatory changes introduced herbals into mainstream supermarkets and pharmacies, there has been an explosion of demand for herbal plants and extracts which can be used to improve human health and well being. Science still lacks a basic mechanistic understanding of how environmental triggers regulate phytochemical accumulation, but this gap can be bridged using in vitro models to examine herbal species responses. For St. John's wort (Hypericum perforatum), uniform in vitro shoot cultures were set up as a parallel to a previously established sand culture system for investigation of physical and chemical environmental factors that control hypericin accumulation. Cytokinin supplementation of shoot culture medium resulted in a proliferation of abundant leaf glands with enhanced levels of hypericin, as compared to controls. Cell cultures of echinacea (Echinacea angustifolia) were established, and hydrophilic pharmacological components (caffeic acid derivatives) were detected. A protocol of rigorous explant pretreatment, and use of newly emerging vegetative shoots permitted establishment of axenic kava (Piper methysticum) callus, which was used to regenerate roots (organogenesis). Kavapyrone synthesis was achieved in both undifferentiated cell cultures and in cultured roots, although at lower levels than found in in vivo root systems. The predominance of kavain and methysticin in both forms of the in vitro cultures was parallel to the relative proportions from kava roots in vivo. The cell and organ cultures of all three herbal medicinals provide advantageous, easily-manipulated models to decipher environmental controls of phytochemical biosynthesis.     

The origin of litter chemical complexity during decomposition

The chemical complexity of decomposing plant litter is a central feature shaping the terrestrial carbon (C) cycle, but explanations of the origin of this complexity remain contentious. Here, we ask: How does litter chemistry change during decomposition, and what roles do decomposers play in these changes? During a long‐term (730 days) litter decomposition experiment, we tracked concurrent changes in decomposer community structure and function and litter chemistry using high‐resolution molecular techniques. Contrary to the current paradigm, we found that the chemistry of different litter types diverged, rather than converged, during decomposition due to the activities of decomposers. Furthermore, the same litter type exposed to different decomposer communities exhibited striking differences in chemistry, even after > 90% mass loss. Our results show that during decomposition, decomposer community characteristics regulate changes in litter chemistry, which could influence the functionality of litter‐derived soil organic matter (SOM) and the turnover and stabilisation of soil C.     

Mixtures with grass litter may hasten shrub litter decomposition after shrub encroachment into mountain grasslands

Aims

Shrub encroachment in mesic grasslands alters the identity and quality of litters entering the system. As litter from shrubs and grasses can differ in their quality, this can lead to differences in litter decomposition by the direct effect of quality, but also to litter interaction during decomposition. The objective of this study was to examine the occurrence of non-additive effects of litter mixtures on the decomposition rates of legume shrub litter (poor in P) or conifer shrub litter (poor in N) and grass litter.

Methods

In addition to single litter type litterbags for the three species, we mixed litters of each pair of possible combinations to determine the influence of each species on mass loss. Litterbags were placed in the field and collected after 1, 6, 8, 12 and 24 months. In each collection, litter of each species remaining in mixed bags was separated, dry weighed and analyzed for C, N and P.

Results

With respect to shrub litter decomposing alone, mass loss of shrub litter when mixed with grass showed a 9–10 % increase in decomposition rate for conifer and a 3 % increase for legume litter. These litter mixture effects varied with time and they were detected after a decomposition period of 1 year in legume litter and of 2 years in conifer litter.

Conclusions

Grass litter hastened conifer and legume litter decomposition in leaf litter mixtures, at least during the first stages of the process. The potential consequences of this result to alter litter accumulation patterns and thus carbon sequestration rates after shrub encroachment into grasslands will depend on whether the observed trends are maintained in the advanced decomposition stages.     

Metabolomics approach to investigate phytotoxic effects of Wedelia trilobata leaves,litter and soil

Although release and accumulation of plant metabolites from plant into soil can influence allelopathy, little information is known about metabolite changes that occur in leaf, litter and soil. In this study, seed germination bioassay tests and metabolomics analysis were performed to investigate the phytotoxic effects and metabolic variations (measured as buckets) in the ethanolic extracts of leaf, leaf litter and soil of Wedelia trilobata. Increasing the ethanolic extracts concentration of all extracts significantly inhibited Lactuca sativa germination rate (GR), shoot height (SH) and root length (RL). Soil exerted the strongest inhibition but contained the lowest number of buckets relative to those of leaf and leaf litter extracts. An overlap overview on the metabolome revealed a poor bucket overlap and redundancy among the leaf, leaf litter and soil extracts. Canonical correspondence analysis concluded that the SH of L. sativa was more sensitive to leaf litter extract and the leaf extract exerted a strong influence on the GR and RL of L. sativa. Multivariate analysis suggested that the metabolome of the leaf, leaf litter and soil differ substantially. Finally, putative identification using MS/MS data demonstrated various plant metabolites with phytotoxic effects that can contribute to the allelopathy of W. trilobata.     

A trait-based approach for modelling microbial litter decomposition

Trait-based models are an emerging tool in ecology with the potential to link community dynamics, environmental responses and ecosystem processes. These models represent complex communities by defining taxa with trait combinations derived from prior distributions that may be constrained by trade-offs. Herein I develop a model that links microbial community composition with physiological and enzymatic traits to predict litter decomposition rates. This approach allows for trade-offs among traits that represent alternative microbial strategies for resource acquisition. The model predicts that optimal strategies depend on the level of enzyme production in the whole community, which determines resource availability and decomposition rates. There is also evidence for facilitation and competition among microbial taxa that co-occur on decomposing litter. These interactions vary with community investment in extracellular enzyme production and the magnitude of trade-offs affecting enzyme biochemical traits. The model accounted for 69% of the variation in decomposition rates of 15 Hawaiian litter types and up to 26% of the variation in enzyme activities. By explicitly representing diversity, trait-based models can predict ecosystem processes based on functional trait distributions in a community. The model developed herein illustrates that traits influencing microbial enzyme production are some of the key controls on litter decomposition rates.     

Phenotypic diversity and litter chemistry affect nutrient dynamics during litter decomposition in a two species mix

We have previously demonstrated that the intraspecific diversity of leaf litter can influence ecosystem functioning during litter decomposition in the field. It is unknown whether the effects of phenotypic diversity persist when litter from an additional species is present. We used laboratory microcosms to determine whether the intraspecific diversity effects of turkey oak leaf litter on nutrient dynamics are confounded by the presence of naturally co-occurring longleaf pine litter. We varied the phenotypic diversity of oak litter (1, 3, and 6 phenotype combinations) in the presence and absence of pine litter and measured fluxes of carbon and nitrogen over a 42-week period. The average soil C:N ratio peaked at intermediate levels of oak phenotypic diversity and the total amount of dissolved organic carbon leached from microcosms decreased (marginally) with increasing oak phenotypic diversity. The soil carbon content, and the total amount of ammonium, nitrate, and dissolved organic carbon leached from microcosms were all influenced by initial litter chemistry. Our results suggest that the effects of phenotypic diversity can persist in the presence of another species, however specific litter chemistries (condensed and hydrolysable tannins, simple phenolics, C:N ratios) are more important than phenotypic litter diversity to most nutrient fluxes during litter decomposition.     

Silicon controls microbial decay and nutrient release of grass litter during aquatic decomposition

The decomposition rate of plant litter is important for the carbon cycle. Element stoichiometry and hardly degradable carbon compounds are main factors controlling the decomposition rate of plant litter. Recent research has linked these factors to silicon availability during plant growth, but no research focused on the effect of silicon on litter decomposition. We therefore conducted a batch experiment to assess the effect of silicon availability to plants on litter degradation, nutrient release and multi elemental stoichiometry. Experiments were conducted in the presence or absence of invertebrate shredders (Gammarus pulex). We show that nutrient content (affected by silicon availability during plant growth) has a strong impact on nutrient turnover, while DOC, N, and Mn were mainly controlled by invertebrate feeding. The carbon turnover during microbial litter decay was strongly influenced by the silicon availability during plant growth, with quicker potential C turnover of litter with higher silicon content. In both Si-rich and Si-poor litter, feeding by invertebrate shredders positively impacted turnover rates, but effects were less pronounced in Si-rich litter. It can be concluded that silicon availability in wetlands dominated by reed plays an important role in carbon sequestration, nutrient cycling, and remobilization during aquatic litter decay.     

Effects of land abandonment on plant litter decomposition in a Montado system: relation to litter chemistry and community functional parameters

Changes in land use and subsequent shifts in vegetation can influence decomposition through changes in litter quality (chemistry and structure) and alterations of soil temperature and moisture. Our aim was to study the effects of land abandonment on litter decomposition in a Mediterranean area of Montado, South Portugal. We tested the hypothesis that decomposition tends to slow down with abandonment, as woody species, richer in lignified structures, replace herbaceous species. We assessed the decomposition of community litter in situ using litterbag technique. To test the influence of local conditions, we simultaneously incubated a standard litter in situ. Our results showed that the shift from herbaceous to shrub-dominated communities lead to decreased decomposition rates. Changes in litter decomposition were primarily driven by changes in litter quality, even though the uneven pattern of litter mass loss over the experiment might reveal an effect from possible differences in microclimate. Shrub litter had higher nutrient content than herbaceous litter, which seemed to favour higher initial decomposition rates, but lower decomposition rate in the longer term. Shrubs also contribute to woody litter, richer in lignin, and secondary compounds that retard decomposition, and may play a role in increasing pools of slowly decomposing organic matter.     

Effects of litter quality and quantity on chemical changes during eucalyptus litter decomposition in subtropical Australia

Plant and Soil - Phosphorus (P) recovery from specific waste streams is necessary to develop environmentally sustainable and efficient fertilizers, achieving maximum productivity with minimum...     

An integrated approach to Phoma systematics

Physiological and morphological characters were recorded from 55 strains of 17 Phoma taxa and one Pyrenochaeta. The results were subjected to numerical analysis and UPGMA dendrograms produced. The full results were compared with TLC profiles of secondary metabolites. Seven distinct clusters were recovered from dendrograms based on full and partial character sets and the grouping of strains within each cluster discussed. The new combination Phoma sambuci-nigrae (Sacc.) Monte, Bridge & Sutton is proposed for P. herbarum f. sambuci-nigrae Sacc.     

Effects of ultraviolet radiation on litter decomposition depend on precipitation and litter chemistry in a shortgrass steppe ecosystem

We examined the effect of altered levels of ultraviolet (UV) radiation (280–400 nm) and different amounts of precipitation on the decomposition rates of litter of contrasting carbon to nitrogen ratio (C : N) in a 3-year field experiment in a shortgrass steppe (SGS) ecosystem. UV radiation was either blocked or passed under clear plastic tents where precipitation was applied to simulate a very dry or very wet year. These treatments minimized or maximized the abiotic component (UV) or the biotic component (biological activity of decomposer organisms) of decomposition to assess potential interactions between the two. Initial litter chemistry varied in response to having been grown under ambient or elevated atmospheric CO₂ concentrations. While precipitation and litter chemistry were the most important drivers in decomposition in this system, UV radiation increased decomposition rates under dry conditions in litter with higher C : N ratios. Exposure to UV radiation slightly increased the amount of holocellulose that was lost from the litter. UV exposure did not affect the decomposition of the lignin fraction. Increased decomposition with UV radiation was accompanied by a decrease in N immobilization over the summer months. These results suggest that the effects of UV radiation on decomposition rates may be primarily abiotic, caused by direct photochemical degradation of the litter. Our results demonstrate that the role of UV radiation in litter decomposition in semiarid systems depends on the aridity of the system and the chemistry of the litter.     

Interactive responses of grass litter decomposition to warming,nitrogen addition and detritivore access in a temperate old field

Plant litter decomposition has been studied extensively in the context of both climate warming and increased atmospheric N deposition. However, much of this research is based on microbial responses, despite the potential for detritivores to contribute substantially to litter breakdown. We measured litter mass-loss responses to the combined effects of warming, N addition and detritivore access in a grass-dominated old field. We concurrently assessed the roles of litter treatment origin vs. microenvironment (direct warming and N-addition effects) to elucidate the mechanisms through which these factors affect decomposition. After 6 weeks, mass loss increased in N-addition plots, and it increased with detritivore access in the absence of warming. After 1 year, warming, N addition, and detritivore access all increased litter mass loss, although the effects of N addition and warming were non-additive in the detritivore-access plots. For the litter-origin experiment, mass loss after 6 weeks increased in litter from N-addition plots and warmed plots, but unlike the overall decomposition response, the N-addition effect was enhanced by detritivore access. Conversely, for the microenvironment experiment, detritivore access only increased mass loss in unfertilized plots. After 1 year, detritivore access increased mass loss in the litter-origin and microenvironment experiments, but there were no warming or N-addition effects. Overall, our results provide support for a substantial role of detritivores in promoting litter mass loss in our system. Moreover, they reveal important interactions between litter origin, microclimate and detritivores in determining decomposition responses to global change.     

An integrated approach to hydropower impact assessment

The submerged aquatic vegetation of 17 Norwegian lakes is described and related to the environmental impacts that result from hydro-electric power (HEP) use of these lakes. Largely based upon physiognomical features, three main community types are discerned. These are denoted as (a) shallow-water, (b) mid-depth, and (c) deep-water community, respectively. The aquatic macrophytes are classified into a plant strategy framework. This classification suggests that these macrophytes frequently exhibit combined traits of the S (stress-tolerating), R (ruderal), and C (competitive) strategies. A plant-strategy index for the lakes is derived from the species classification and related to their HEP use.Broadly, the response features of hydrolake vegetation are: (1) a decline in species richness; (2) the gradual disappearance of the shallow-water and mid-depth communities; (3) a conspicuous absence of vascular submerged macrophytes in storage hydrolakes when lake levels change more than 7 m annually, and; (4) an increased incidence of species possessing plant strategies of the ruderal (R) type. The implications of these results for an environmental impact assessment of hydropower schemes are discussed.     

Soil microbial activities and litter decomposition related to altitude

Summary On a southern slope in the Austrian Central Alps (Hohe Tauern Mountains) at altitudes of 2550 m, 1920 m and 1650 m above sea level, respectively, microbial activities were investigated by measuring the decomposition of litter, the cellulase and xylanase activities, CO₂-evolution and the cell counts of viable non differentiated and cellulolytic bacteria. After one year 46% of litter exposed was decomposed at an altitude of 2550 m, 76% at 1920 m and 86% at 1560 m. Investigations with litter bags of different mesh sizes (25 μm and 1000 μm) revealed that small soil animals (<1 mm) did not significantly influence the decomposition of litter at different altitudes and in different vegetation types. The enzymatic activities and the CO₂-evolution of soils decreased with increasing altitude. Plate counts of bacteria from soils at the alpine zone (2550 m) and the tall grass meadow (1650 m) indicated that in some cases the lower metabolic activities caused by bad climatic conditions were compensated by an increase in cell numbers. This work was supported by the Austrian MaB-Hochgebirgsprogramm, Alpine ?kosysteme