We conducted field experiments to test the general hypothesis that the com- position of decomposer communities and their trophic interactions can influence patterns of plant litter decomposition and nitrogen dynamics in ecosystems. Conventional (CT) and no-tillage (NT) agroecosystems were used to test this idea because of their structural sim- plicity and known differences in their functional properties. Biocides were applied to ex- perimentally exclude bacteria, saprophytic fungi, and microarthropods in field exclosures. Abundances of decomposer organisms (bacteria, fungi, protozoa, nematodes, microar- thropods), decomposition rates, and nitrogen fluxes were quantified in surface and buried litterbags (Secale cereale litter) placed in both NT and CT systems. Measurements of in situ soil respiration rates were made concurrently. The abundance and biomass of all microbial and faunal groups were greater on buried than surface litter. The mesofauna contributed more to the total heterotrophic C in buried litter from CT (6-22%) than in surface litter from NT (0.4-1/1%). Buried litter decay rates (1.4-1.7%/d) were -2.5 times faster than rates for surface litter (0.5-O.7%/d). Ratios of fungal to bacterial biomass and fungivore to bacterivore biomass on NT surface litter generally increased over the study period resulting in ratios that were 2.7 and 2.2 times greater, respectively, than those of CT buried litter by the end of the summer. The exclusion experiments showed that fungi had a somewhat greater influence on the decomposition of surface litter from NT while bacteria were more important in the de- composition of buried litter from CT. The fungicide and bactericide reduced decomposition rates of NT surface litter by 36 and 25% of controls, respectively, while in CT buried litter they were reduced by 21 and 35% of controls, respectively. Microarthropods were more important in mobilizing surface litter nitrogen by grazing on fungi than in contributing to litter mass loss. Where fungivorous microarthropods were experimentally excluded, there was less than a 5% reduction in mass loss from litter of both NT and CT, but fungi- fungivore interactions were important in regulating litter N dynamics in NT surface litter. As fungal densities increased following the exclusion of microarthropods on NT surface litter, there was 25% greater N retention as compared to the control after 56 d of decay. Saprophytic fungi were responsible for as much as 86% of the net N immobilized (1.81 g /m2) in surface litter by the end of the study when densities of fungivorous microarthropods were low. Although bacteria were important in regulating buried litter decomposition rates and the population dynamics of bacterivorous fauna, their influence on buried litter N dynamics remains less clear. The larger microbial biomass and greater contribution of a bacterivorous fauna on buried litter is consistent with the greater carbon losses and lower carbon assimilation in CT than NT agroecosystems. In summary, our results suggest that litter placement can strongly influence the com- position of decomposer communities and that the resulting trophic relationships are im- portant to determining the rates and timing of plant litter decomposition and N dynamics. Furthermore, cross placement studies suggest that the decomposer communities within each tillage system, while not discrete, are adapted to the native litter placements in each.

Microbial and Faunal Interactions and Effects on Litter Nitrogen and Decomposition in Agroecosystems

Coweeta is one of the oldest continuously operating laboratories of its type in the world. For the first time, a complete review and summary of more than 50 years study of the hydrological and ecological responses of baseline and managed Southern Appalachian hardwood forests at Coweeta is now supplied by this volume. The long-term research approach represents a continuum of theory, experimentation and application using watersheds as landscape units of investigation. Thus, the information encompasses a wide range of interpretations and interests. In addition to in-depth analyses of terrestrial and stream processes, the breadth of coverage includes historical perspectives and relevance of ecosystem science to management needs. In a broader sense, the Coweeta research effort is considered from a perspective of national and international forest hydrology and ecology programs.

Forest hydrology and ecology at Coweeta.

Over the past four decades ecosystem scientists have stressed that biotic and abiotic system components must be studied in concert. This philosophy maintains that an ecosystem is a harmonious interplay between organisms and their environment and possesses cybernetic properties that " . . . make possible the orderly cycle of life" ( 84). Although some researchers have emphasized that organisms and their behavior are the building blocks of an ecosystem (5 8, 105), most ecosystem research has been process rather than entity oriented (93). Functional groups, the basic units of an ecosystem model, have usually been defined by broad taxonomic relationships even though criteria that describe roles in a system would be more suitable. Once there is a clear understanding of what roles organisms have, studies can be· directed at how organisms interact to generate ecosystem dynamics.

Arthropod regulation of micro- and mesobiota in below-ground detrital food webs

Biodiversity and carbon (C) cycling have been the focus of much research in recent decades, partly because both change as a result of anthropogenic activities that are likely to continue. Soils are extremely species-rich and store approximately 80% of global terrestrial C. Soil organisms play a key role in C dynamics and a loss of species through global changes could influence global C dynamics. Here, we synthesize findings from published studies that have manipulated soil species richness and measured the response in terms of ecosystem functions related to C cycling (such as decomposition, respiration and the abundance or biomass of decomposer biota) to evaluate the impact of biodiversity loss on C dynamics. We grouped studies where one or more biotic groups had been manipulated to include a richness of 10 species in order to reflect 'low' and 'high' extents of diversity manipulations. There was a positive relationship between species richness and C cycling in 77-100% of low-diversity experiments, even when the richness of just one biotic group was manipulated, whereas positive relationships occurred less frequently in studies with greater richness (35-64%). Moreover, when positive relationships were observed, these often indicated functional redundancy at low extents of diversity or that community composition had a stronger influence on C cycling than did species richness. Initial reductions in soil species richness resulting from global changes are unlikely to alter C dynamics significantly unless particularly influential species are lost. However, changes in community composition, and the loss of species with an ability to facilitate specialized soil processes related to C cycling, as a result of global changes, may have larger impacts on C dynamics.

Soil biodiversity and carbon cycling: A review and synthesis of studies examining diversity-function relationships

Publisher Summary This chapter illustrates detritus-based food webs responding to various disturbance regimes occurring in conventionally tilled (CT) and non-tilled (NT) systems. The detritus food web is based largely in the soil system, and is important in regulating nutrient cycling and energy flow, it is reasonable to expect that this food web may be a viable and meaningful indicator of disturbance exerted by tillage and alternative weed management strategies. The principal differences in disturbance regimes involve cultivation, herbicide application, residue management and manipulation of weed levels, therefore, emphasis is placed on these factors. The chapter also reviews the results of previous studies, determines how different components of the detritus food web respond to the disturbances relative to each other, and examines the consequences of these disturbances for overall food web structure. Furthermore, while disturbances in CT systems may exert predictable negative effects on most groups of soil organisms, the responses of species assemblages are less predictable. Individual taxonomic species are undoubtedly a more sensitive indicator of ecosystem disturbance than are entire functional groups, and is therefore a more appropriate unit for biomonitoring purposes.

Impacts of Disturbance on Detritus Food Webs in Agro-Ecosystems of Contrasting Tillage and Weed Management Practices

The fungi Mycena galopus (Pers. ex Fr.) Kummer and Marasmius androsaceus (L. ex Fr.) Fr. produced over 99% of the fruit bodies on a site under Picea sitchensis Carr. In the laboratory M. androsaceus colonized litter from both the L and F 1 horizons more than twice as fast as M. galopus , but in the field its distribution was restricted to the L horizon whereas M. galopus occurred in the F 1 horizon. The collembolan Onychiurus latus Gisin, the most abundant mycophagous arthropod at the field site which consistently had basidiomycete hyphae in its gut, was found throughout the autumn in the litter horizons in densities up to 600 m −2 . This collembolan showed a marked preference for the mycelium of M. androsaceus rather than that of M. galopus in both laboratory and field tests. These results suggest that selective grazing by O. latus may be an important factor in determining the vertical distribution of these two fungi in the field.

Interaction between two decomposer basidiomycetes and a collembolan under Sitka spruce: Distribution, abundance and selective grazing

The hypothesis that selective grazing by Onychiurus latus Gisin altered the outcome of competition between two basidiomycetes, Mycena galopus (Pers. ex Fr.) Kummer and Marasmius androsaceus (L. ex Fr.) Fr. on Sitka spruce litter was tested. Without grazing M. androsaceus had the higher colonizing ability of litter in the laboratory whereas with grazing the position was reversed. Field exclusion experiments also suggested that higher densities of O. latus resulted in a reduction in the activity of M. androsaceus and an increase in that of M. galopus and vice versa. It is suggested that selective grazing may be an important factor determining the field distribution of these fungi, since M. androsaceus , the preferred food source, was restricted to the L litter horizon where the density of O. latus was not high enough to alter the outcome of competition whereas M. galopus predominated in the F 1 horizon. The rate of decomposition of Sitka spruce litter in the laboratory caused by M. androsaceus (17% dry weight loss over 6 months at 11°C) increased by 4–14% in the presence of grazing by O. latus whereas that of M. galopus (11.5%) decreased by 12–16%.

Interaction between two decomposer basidiomycetes and a collembolan under Sitka spruce: Grazing and its potential effects on fungal distribution and litter decomposition

Kathryn Newell

Papers

Interaction between two decomposer basidiomycetes and a collembolan under Sitka spruce: Distribution, abundance and selective grazing

Interaction between two decomposer basidiomycetes and a collembolan under Sitka spruce: Grazing and its potential effects on fungal distribution and litter decomposition

414 What was the impact of the first part of the SARS-CoV-2 pandemic on routine childhood MMR uptake in Morecambe Bay?