Geology topics

R. L. Sinsabaugh

Publications and source records attributed to R. L. Sinsabaugh.

4 recordsLinked to original sources

USGS2014

A multiscale, hierarchical model of pulse dynamics in arid-land ecosystems

Ecological processes in arid lands are often described by the pulse-reserve paradigm, in which rain events drive biological activity until moisture is depleted, leaving a reserve. This paradigm is frequently applied to processes stimulated by one or a few precipitation events within a growing season. Here we expand the original framework in time and space and include other pulses that interact with rainfall. This new hierarchical pulse-dynamics framework integrates space and time through pulse-driven exchanges, interactions, transitions, and transfers that occur across individual to multiple pulses extending from micro to watershed scales. Climate change will likely alter the size, frequency, and intensity of precipitation pulses in the future, and arid-land ecosystems are known to be highly sensitive to climate variability. Thus, a more comprehensive understanding of arid-land pulse dynamics is needed to determine how these ecosystems will respond to, and be shaped by, increased climate variability.

Annual Review of Ecology, Evolution, and Systemati↗

USGS2007

Molecular analysis of fungal communities and laccase genes in decomposing litter reveals differences among forest types but no impact of nitrogen deposition

The fungal community of the forest floor was examined as the cause of previously reported increases in soil organic matter due to experimental N deposition in ecosystems producing predominantly high-lignin litter, and the opposite response in ecosystems producing low-lignin litter. The mechanism proposed to explain this phenomenon was that white-rot basidiomycetes are more important in the degradation of high-lignin litter than of low-lignin litter, and that their activity is suppressed by N deposition. We found that forest floor mass in the low-lignin sugar-maple dominated system decreased in October due to experimental N deposition, whereas forest floor mass of high-lignin oak-dominated ecosystems was unaffected by N deposition. Increased relative abundance of basidiomycetes in high-lignin forest floor was confirmed by denaturing gradient gel electrophoresis (DGGE) and sequencing. Abundance of basidiomycete laccase genes, encoding an enzyme used by white-rot basidiomycetes in the degradation of lignin, was 5-10 times greater in high-lignin forest floor than in low-lignin forest floor. While the differences between the fungal communities in different ecosystems were consistent with the proposed mechanism, no significant effects of N deposition were detected on DGGE profiles, laccase gene abundance, laccase length heterogeneity profiles, or phenol oxidase activity. Our observations indicate that the previously detected accumulation of soil organic matter in the high-lignin system may be driven by effects of N deposition on organisms in the mineral soil, rather than on organisms residing in the forest floor. However, studies of in situ gene expression and temporal and spatial variability within forest floor communities will be necessary to further relate the ecosystem dynamics of organic carbon to microbial communities and atmospheric N deposition. ?? 2007 The Authors; Journal compilation ?? 2007 Society for Applied Microbiology and Blackwell Publishing Ltd.

Environmental Microbiology↗

USGS2003

Metabolic and structural response of hyporheic microbial communities to variations in supply of dissolved organic matter

Hyporheic sediment bacterial communities were exposed to dissolved organic matter (DOM) from a variety of sources to assess the interdependence of bacterial metabolism and community composition. Experiments ranged from small-scale core perfusions with defined compounds (glucose, bovine serum albumin) to mesocosms receiving natural leaf leachate or water from different streams. Response variables included bacterial production, oxygen consumption, extracellular enzyme activity, and community similarity as manifest by changes in banding patterns of randomly amplified polymorphic DNA (RAPD). All DOM manipulations generated responses in at least one metabolic variable. Additions of both labile and recalcitrant materials increased either oxygen consumption, production, or both depending on background DOM. Enzyme activities were affected by both types of carbon addition with largest effects from the labile mixture. Cluster analysis of RAPD data showed strong divergence of communities exposed to labile versus recalcitrant DOM. Additions of leaf leachate to mesocosms representing hyporheic flow-paths caused increases in oxygen consumption and some enzyme activities with weaker effects on production. Community structure yeas strongly affected; samples from the leachate-amended mesocosms clustered separately from the control samples. In mesocosms receiving water from streams ranging in DOC (0.5-4.5 mg L -1 ), there were significant differences in bacterial growth, oxygen consumption, and enzyme activities. RAPD analysis showed strongest clustering of samples by stream type with more subtle effects of position along the flowpaths. Responses in community metabolism were always accompanied by shifts in community composition, suggesting carbon supply affects both functional and structural attributes of hyporheic bacterial communities .

Limnology and Oceanography↗

USGS2002

Allocation of extracellular enzymatic activity in relation to litter composition, N deposition, and mass loss

Decomposition of plant material is a complex process that requires interaction among a diversity of microorganisms whose presence and activity is subject to regulation by a wide range of environmental factors. Analysis of extracellular enzyme activity (EEA) provides a way to relate the functional organization of microdecomposer communities to environmental variables. In this study, we examined EEA in relation to litter composition and nitrogen deposition. Mesh bags containing senescent leaves of Quercus borealis (red oak), Acer rubrum (red maple) and Cornus florida (flowering dogwood) were placed on forest floor plots in southeastern New York. One-third of the plots were sprayed monthly with distilled water. The other plots were sprayed monthly with NH4NO3 solution at dose rates equivalent to 2 or 8 g N m-2 y-1. Mass loss, litter composition, fungal mass, and the activities of eight enzymes were measured on 13 dates for each litter type. Dogwood was followed for one year, maple for two, oak for three, For each litter type and treatment, enzymatic turnover activities were calculated from regressions of LN (%mass remaining) vs. cumulative activity. The decomposition of dogwood litter was more efficient than that of maple and oak. Maple litter had the lowest fungal mass and required the most enzymatic work to decompose, even though its mass loss rate was twice that of oak. Across litter types, N amendment reduced apparent enzymatic efficiencies and shifted EEA away from N acquisition and toward P acquisition, and away from polyphenol oxidation and toward polysaccharide hydrolysis. The effect of these shifts on decomposition rate varied with litter composition: dogwood was stimulated, oak was inhibited and maple showed mixed effects. The results show that relatively small shifts in the activity of one or two critical enzymes can significantly alter decomposition rates.

Biogeochemistry↗