Decomposition Of Plant Detritus Research Articles

Organic-matter flow in kelp forest

Ecology and Climate![Figure][1] Laminaria ochroleuca is moving north as the climate warms. PHOTO: AGE FOTOSTOCK/ALAMY STOCK PHOTO As the global climate warms, there are shifts in the geographical distribution of organisms, which can be accompanied by changes in ecosystem functioning. Pessarrodona et al. have been investigating the ecosystem consequences of the climate-driven arrival of warm-temperate kelp forest communities to the northwestern coastlines of Europe. Cycling of organic matter in the ecosystem—through kelp growth, herbivory, and decomposition—was faster in the new communities relative to cycling in native cold-temperate kelp communities. Notably, decomposition of plant detritus occurred 6.5 times faster. The continued northward expansion of warm-temperate kelp can be expected to lead to shifts in the flow of organic matter through these ecosystems and to further changes in associated communities of consumer organisms. J. Ecol. 10.1111/1365-2745.13053 (2018). [1]: pending:yes

Warming enhances sedimentation and decomposition of organic carbon in shallow macrophyte-dominated systems with zero net effect on carbon burial.

Temperatures have been rising throughout recent decades and are predicted to rise further in the coming century. Global warming affects carbon cycling in freshwater ecosystems, which both emit and bury substantial amounts of carbon on a global scale. Currently, most studies focus on the effect of warming on overall carbon emissions from freshwater ecosystems, while net effects on carbon budgets may strongly depend on burial in sediments. Here, we tested whether year-round warming increases the production, sedimentation, or decomposition of particulate organic carbon and eventually alters the carbon burial in a typical shallow freshwater system. We performed an indoor experiment in eight mesocosms dominated by the common submerged aquatic plant Myriophyllum spicatum testing two temperature treatments: a temperate seasonal temperature control and a warmed (+4°C) treatment (n=4). During a full experimental year, the carbon stock in plant biomass, dissolved organic carbon in the water column, sedimented organic matter, and decomposition of plant detritus were measured. Our results showed that year-round warming nearly doubled the final carbon stock in plant biomass from 6.9±1.1g C in the control treatment to 12.8±0.6g C (mean±SE), mainly due to a prolonged growing season in autumn. DOC concentrations did not differ between the treatments, but organic carbon sedimentation increased by 60% from 96±9.6 to 152±16gCm-2 yaer-1 (mean±SE) from control to warm treatments. Enhanced decomposition of plant detritus in the warm treatment, however, compensated for the increased sedimentation. As a result, net carbon burial was 40±5.7gCm-2 year-1 in both temperature treatments when fluxes were combined into a carbon budget model. These results indicate that warming can increase the turnover of organic carbon in shallow macrophyte-dominated systems, while not necessarily affecting net carbon burial on a system scale.

Macrofauna in Mediterranean and Black Sea transitional aquatic ecosystems: A comparative study of the benthic populations sampled by box corer and leaf bags

This study compares the ethic macrofauna sampled with a box corer and the leaf bag technique, widely used to study plant detritus decomposition processes. The study was carried out in 10 transitional aquatic ecosystems located in the Mediterranean and the Black Sea, covering a wide salinity range.A total of 171 taxa were sampled, 49 only in the sediment samples, 50 only in the leaf bags and 72 common to both. The macroinvertebrate assemblages sampled by the two techniques were different in terms of taxonomic and functional composition; annelids characterized mainly the corer samples, whereas arthropods were a dominant component in the leaf bags. Concerning functional groups, collectors and shredders were dominant respectively in the corer and the leaf bag samples. The taxonomic and the functional dominant composition also varied in relation to water salinity, mainly in the corer samples but less in the leaf bags. The sediment and leaf bag assemblages were significantly different at the scale of the lagoon and in most of the sampling sites. Primary biological variables and diversity indices showed a common trend with both sampling devices across the salinity gradient, but were also highly variable within each lagoon. The results indicated that the assemblages inhabiting the superficial sediment and colonizing litter detritus in transitional waters were distinct, but also highlighted the heterogeneity among these ecosystems.

The role of the seagrass <i>Posidonia oceanica</i> in the cycling of trace elements

Abstract. The aim of this study was to investigate the role of the seagrass Posidonia oceanica on the cycling of a wide set of trace elements (Ag, As, Ba, Bi, Cd, Co, Cr, Cs, Cu, Fe, Ga, Li, Mn, Ni, Pb, Rb, Sr, Tl, V and Zn). We measured the concentration of these trace elements in different compartments of P. oceanica (leaves, rhizomes, roots and epiphytes) in a non-polluted seagrass meadow representative of the Mediterranean and calculated the annual budget from a mass balance. We provide novel data on accumulation dynamics of many trace elements in P. oceanica compartments and demonstrate that trace element accumulation patterns are mainly determined by plant compartment rather than by temporal variability. Epiphytes were the compartment, which showed the greatest concentrations for most trace elements. Thus, they constitute a key compartment when estimating trace element transfer to higher trophic levels by P. oceanica. Trace element translocation in P. oceanica seemed to be low and acropetal in most cases. Zn, Cd, Sr and Rb were the trace elements that showed the highest release rate through decomposition of plant detritus, while Cs, Tl and Bi showed the lowest. P. oceanica acts as a sink of potentially toxic trace elements (Ni, Cr, As and Ag), which can be sequestered, decreasing their bioavailability. P. oceanica may have a relevant role in the cycling of trace elements in the Mediterranean.

Including the effects of water stress on decomposition in the Carbon Budget Model of the Canadian Forest Sector CBM-CFS3

Decomposition of plant detritus and humified organic matter in terrestrial ecosystems is a primary source of atmospheric carbon dioxide (CO 2), yet the dynamics of decomposition are not well understood, particularly their response to climate change. The Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) presently includes a sub-model to simulate the decomposition of dead organic matter carbon pools using base decay rates modified by temperature quotients. In this study, representation of litter decomposition was improved in the CBM-CFS3 by reducing decay rates under limited moisture conditions. Water stress effects were determined from comparisons of model predictions with data from a 12-year national litterbag decomposition study—the Canadian Intersite Decomposition Experiment (CIDET). Several simple water-stress modifiers based on precipitation and potential evapotranspiration were tested, and parameters were simultaneously fit by minimizing the least-squared error. The best-fitting formulation used the annual average of the ratio of monthly precipitation to monthly potential evapotranspiration, and increased the explained variance by 8%. Water-stress modifiers were applied to decay rates to predict carbon stocks at 516 ground plots from a national soil plot database. The addition of the water-stress modifier modestly increased litter and humified organic matter carbon stocks at dry locations and decreased these carbon stocks at non-water-stressed locations. The new ability to lower decay rates of certain dead organic matter pools under limited moisture conditions in the CBM-CFS3 has the potential to reduce bias in carbon flux predictions for those regions and for future climate change scenarios where moisture limits decomposition processes.

Environmental factors affecting Phragmites australis litter decomposition in Mediterranean and Black Sea transitional waters

1. Leaf litter decomposition rates in aquatic ecosystems are known to be related to many abiotic and biotic factors. 2. Field experiments were carried out during spring 2005 in 16 ecosystems, each with four sampling sites, using the litter bag technique to investigate the influence of abiotic factors on patterns of reed litter breakdown in different physiographic, hydrological and physico-chemical gradients occurring in transitional water ecosystems in the Eastern Mediterranean and Black Sea. 3. Significant differences in leaf litter decomposition were observed among the studied ecosystems along univariate gradients of tidal range, water temperature, salinity and sinuosity index. 4. Overall, 71% of variance in the litter breakdown rate was explained by the hydrological, physico-chemical and physiographic components. Specifically, tidal range, salinity and sinuosity index are among the key factors in the most commonly used typological schemes for classifying transitional water ecosystems (i.e. Confinement Concept and Venice System), due to their influence on abundance and distribution of benthic macroinvertebrates and other guilds. 5. The patterns observed at the regional scale of the study suggest that certain key abiotic factors are likely to play a major role as drivers of plant detritus decomposition processes, through their influence on the overall metabolism of microorganisms and benthic macroinvertebrates. 6. These observations have implications for the identification of reference conditions for transitional water ecosystems in the studied area, on which all processes of classification and conservation of their ecological status are based.

Isolation of fungal cellobiohydrolase I genes from sporocarps and forest soils by PCR.

Cellulose is the major component of plant biomass, and microbial cellulose utilization is a key step in the decomposition of plant detritus. Despite this, little is known about the diversity of cellulolytic microbial communities in soil. Fungi are well known for their cellulolytic activity and mediate key functions during the decomposition of plant detritus in terrestrial ecosystems. We developed new oligonucleotide primers for fungal exocellulase genes (cellobiohydrolase, cbhI) and used these to isolate distinct cbhI homologues from four species of litter-decomposing basidiomycete fungi (Clitocybe nuda, Clitocybe gibba, Clitopilus prunulus, and Chlorophyllum molybdites) and two species of ascomycete fungi (Xylaria polymorpha and Sarcoscypha occidentalis). Evidence for cbhI gene families was found in three of the four basidiomycete species. Additionally, we isolated and cloned cbhI genes from the forest floor and mineral soil of two upland forests in northern lower Michigan, one dominated by oak (Quercus velutina, Q. alba) and the other dominated by sugar maple (Acer saccharum) and American basswood (Tilia americana). Phylogenetic analysis demonstrated that cellobiohydrolase genes recovered from the floor of both forests tended to cluster with Xylaria or in one of two unidentified groups, whereas cellobiohydrolase genes recovered from soil tended to cluster with Trichoderma, Alternaria, Eurotiales, and basidiomycete sequences. The ability to amplify a key fungal gene involved in plant litter decomposition has the potential to unlock the identity and dynamics of the cellulolytic fungal community in situ.

Ecosystem processes: litter breakdown patterns in Mediterranean and Black Sea transitional waters

1 - Leaf litter decomposition rates, in aquatic ecosystems, are known to be related to many different abiotic and biotic factors. 2 - Here, we focus on the influence of abiotic factors, searching for patterns of reed litter decay rates on gradient of physiographic, hydrological and physico-chemical components of transitional water ecosystems. 3 - Field experiments were carried out in 16 water ecosystems in the Eastern Mediterranean and Black Sea in spring 2005. 4 - Significant differences of leaf litter decomposition were observed among ecosystems along univariate gradient of tidal range, index of sinuosity, water temperature and salinity. At least 71% of variance in the litter breakdown rate was explained by the considered abiotic factors. 5 - It is concluded that, at the macro-ecological scale of study, some key abiotic factors, such as tidal range and salinity, are suggested to play a major role as drivers of plant detritus decomposition processes. 6 - The relevance of the described abiotic drivers as descriptor of the most commonly used classification schemes for transitional water ecosystems (i.e., Confinement and Venice System classifications), is a further support to their role as environmental forcing factors.

Effects of invertebrate patch use behaviour and detritus quality on reed leaf decomposition in aquatic systems: A modelling approach

We present a mechanistic model of reed leaf decomposition in a Mediterranean coastal lagoon (Lake Alimini Grande, Puglia, Italy). The aim is to assess the importance of the heterogeneity of leaf detritus and the rules governing patch colonisation by benthic macroinvertebrates to detritus decomposition. We thus propose two versions of a model where the effects of the behavioural choices of invertebrate consumers on detritus mass loss are tested. The models reproduce the functioning of the detritus-based system by simulating the mechanisms regulating the patch use of the two major biotic agents of decomposition, i.e. heterotrophic microflora and macroinvertebrates. Specifically, the microflora are assumed to remain in the patch until leaf decomposition is complete, while the macroinvertebrates move in and out of the patch according to patch attractiveness. The veracity of the simulated decomposition patterns and rates was tested using Phragmites australis leaves in Lake Alimini Grande. In a simulated leaf detritus decomposition model, mass loss takes place according to a negative exponential model. The comparison between observed and simulated data shows that the heterogeneous detritus model provides the best description of reed leaf decomposition. Decomposition rates are also affected by the behavioural characteristics of invertebrate consumers, since they are directly related to invertebrate abundance and inversely to a resource threshold value. The results indicate that the behaviour of detritivore invertebrates influences ecosystem-level processes of plant detritus decomposition.

Summer drought disturbance on plant detritus decomposition processes in three River Tirso (Sardinia, Italy) sub-basins

Here, we study the variation patterns of detritus decomposition along a river continuum in a Mediterranean type river basin, and the influence of summer drought disturbance on this pattern. The study was carried out in three 4th order sub-basins (hereafter referred to as Assolo, Laconi and Olzai) of the river Tirso basin (Sardinia, ITALY), with one study site per stream order in each sub-basin (4 stream orders × 3 sub-basins = 12 study sites). The three sub-basins were selected according to their exposure to summer drought, Assolo being the most exposed and Laconi the least exposed. Reed (Phragmites australis (Cav.) Steudel) detritus decomposition was studied during the fall and spring periods, utilising the leaf packs technique with 3 sampling dates and 8 replicate packs per sample in each period. At all sites, the stream width was recorded fortnightly for one year. Overall, the reed leaf packs underwent rapid decomposition in the river Tirso basin (k=0.0193 d−1), but very high variation was observed among leaf pack decomposition rates (C.V. = 112.7%). Seasons, sub-basins, and stream orders accounted for 88% of the total variance observed (Three Way ANOVA). The decomposition rate was significantly higher in spring than in fall, in the Laconi sub-basin than in the Olzai and Assolo sub-basins, and in 4th order streams than in 2nd and 3rd. Decomposition rates were also higher at relatively undisturbed sites than at the study sites exposed to complete summer desiccation (e.g., 2nd, 3rd, 4th in the Olzai sub-basin; 1st, 2nd, 3rd in the Assolo sub-basin). The strongest effects of summer drought disturbance occurred at the lowest order stream branches (i.e., 1st and 2nd order) suggesting that the resilience of detritus decomposition processes to the disturbance arising from Mediterranean type climates increases with stream order.

DECOMPOSITION IN PELAGIC MARINE ECOSYSTEMS

SUMMARY During the decomposition of plant detritus, complex microbial successions develop which are dominated in the early stages by a number of distinct bacterial morphotypes. The microheterotrophic community rapidly becomes heterogenous and may include cyanobacteria, fungi, yeasts and bactivorous protozoans. Microheterotrophs in the marine environment may have a biomass comparable to that of all other heterotrophs and their significance as a resource to higher trophic orders, and in the regeneration of nutrients, particularly nitrogen, that support ‘regenerated’ primary production, has aroused both attention and controversy. Soluble low molecular weight substrates (dissolved organic matter, or DOM) are for the most part rapidly turned over and readily taken up with a high growth efficiency by bacteria although detrital particulate organic material (POM) is turned over slowly and utilized with a low growth efficiency, owing to the structural complexity of the detritus. The presence of appropriate substra...

The role of mycorrhizae in plant ecology

The effects of vesicular–arbuscular mycorrhizae (VAM) and ectomycorrhizae (ECM) on plant ecology are considered, with emphasis on four areas. The first of these is mycotrophy in wild plants. We suggest that many natives have lower nutrient demands than crop plants and may therefore be less responsive to mycorrhizal infection. Pot experiments must be interpreted with caution because their outcome is strongly influenced by such factors as soil type and pot size. The second topic is the role of mycorrhizae in competition. Mycorrhizae have been shown to figure in plant–plant competition for limited resources. Several lines of indirect evidence suggest that mycorrhizae are involved in allelopathic interactions between plants. Mycorrhizae could aid in competition between plants and microorganisms. Mycorrhizal roots are sometimes found in humus layers of the forest floor. It has been postulated that mycorrhizal fungi influence the decomposition of plant detritus. The most important role of mycorrhizal roots in the organic layer may be, in many cases, a close physical association with the most nutrient-rich microsites of the heterogeneous soil volume. The ability to allocate absorbing tissue to localized organic matter zones has been documented for roots of forest trees and for hyphae of VAM fungi. The advantageous physical placement may result in greater nutrient acquisition for the plant than would occur if root and hyphal distribution were random. Third, the occurrence of mycorrhizae in natural communities has not frequently been documented in ways that show the abundance of infection in the whole community. Future surveys in natural ecosystems should include a measure of the relative abundance of the major plant species in the community. The final topic is carbon allocation to the symbiosis. We suggest that estimates for VAM from a few percent to ~50% of gross photosynthesis can be reconciled to some extent by considering the dynamic processes of root and mycelial turnover.

Effects of nutrient enrichment on the colonization and decomposition of plant detritus by the microbiota of an arctic lake

The effects of nitrogen and phosphorus enrichment on the colonization and decomposition of plant litter (Carex) by the microbiota of Toolik Lake, Alaska, were studied in microcosms. Added phosphorus resulted in a fourfold (p ≤ 0.01) increase in the levels of ATP associated with the microbiota on fresh litter, while nitrogen-plus-phosphorus enrichments resulted in a twofold increase in the ATP associated with the microbiota of fresh (p ≤ 0.01) or partially degraded (p ≤ 0.05) litter compared with controls. Neither nitrogen nor phosphorus enrichments, alone or together, significantly altered the observed weight loss of either fresh or partially degraded litter, although additional phosphorus was immobilized by the litter microbiota when available. Subsequent experiments demonstrated that the increase in ATP resulting from nutrient enrichment occurred when the microcosms were incubated in daylight but not in the dark, suggesting that nutrient enrichment primarily stimulated the photosynthetic component of the detrital community.