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Shifts in plant community structure in shrub and grass-dominated ecosystems are occurring over large land areas in the western US. It is not clear what effect this vegetative change will have on rates of carbon and nitrogen cycling, and thus long-term ecosystem productivity. To study the effect of different plant species on the decomposability of soil organic substrates and rates of C- and N-cycling, we conducted laboratory incubations of soils from a 15-yr-old experimental plot where big sagebrush (Artemisia tridentata Nutt.) and crested wheatgrass (Agropyron desertorum [Fisch.] Schult.) plants had been planted in a grid pattern. Soil samples collected from beneath crested wheatgrass had significantly greater total...
We report the first simultaneous measurements of ?15N and ?13C of DNA extracted from surface soils. The isotopic composition of DNA differed significantly among nine different soils. The ?13C and ?15N of DNA was correlated with ?13C and ?15N of soil, respectively, suggesting that the isotopic composition of DNA is strongly influenced by the isotopic composition of soil organic matter. However, in all samples DNA was enriched in 13C relative to soil, indicating microorganisms fractionated C during assimilation or preferentially used 13C enriched substrates. Enrichment of DNA in 15N relative to soil was not consistently observed, but there were significant differences between ?15N of DNA and ?15N of soil for three...
The field of soil ecology has relatively few fundamental unifying principles that can be used to explain and predict patterns and processes in belowground ecosystems. Here we propose that a first step towards developing a more comprehensive set of unifying principles in soil ecology is to identify and understand the characteristics shared by a wide range of soils, the common mechanisms driving soil biogeochemical processes, and the biogeochemical constraints imposed on soil biota regardless of soil type. Very often, soil ecologists focus on the differences between soils when, in fact, many soils share a common set of ecological mechanisms that govern biogeochemical processes. Here we explore evidence for the existence...
Soil microbial organisms are central to carbon (C) and nitrogen (N) transformations in soils, yet not much is known about the stable isotope composition of these essential regulators of element cycles. We investigated the relationship between C and N availability and stable C and N isotope composition of soil microbial biomass across a three million year old semiarid substrate age gradient in northern Arizona. The δ15N of soil microbial biomass was on average 7.2‰ higher than that of soil total N for all substrate ages and 1.6‰ higher than that of extractable N, but not significantly different for the youngest and oldest sites. Microbial 15N enrichment relative to soil extractable and total N was low at the...
We investigated the effect of plant residue decomposability and fungal biomass on the dynamics of macroaggregate (250?2000 ?m) formation in a three months' incubation experiment and determined the distribution of residue-derived C and N in the microbial biomass and in aggregate size fractions (250?2000 ?m, 53?250 ?m and <53 ?m) using 13C and 15N data. A silty loam soil (sieved <250 ?m) was incubated with and without addition of 15N labelled maize leaves (C/N = 27.4) and roots (C/N = 86.4). Each treatment was carried out with and without fungicide application. The addition of maize residues enhanced soil respiration and microbial biomass C and N and resulted in increased macroaggregate formation with a higher and...
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Changes in nutrient inputs due to aboveground herbivory may influence the litter and soil microbial community responsible for processes such as decomposition. The mesophyll-feeding scale insect (Matsucoccus acalyptus) found near Sunset Crater National Monument in northern Arizona, USA significantly increases pi�on (Pinus edulis) needle litter nitrogen (N) and phosphorus (P) concentrations by 50%, as well as litter inputs to soil by 21%. Because increases in needle litter quality and quantity of this magnitude should affect the microbial communities responsible for decomposition, we tested the hypothesis that insect herbivory causes a shift in soil microbial and litter microarthropod function. Four major findings...
Soil organic matter (SOM) biomarker methods were utilized in this study to investigate the responses of fungi and bacteria to freeze–thaw cycles (FTCs) and to examine freeze–thaw-induced changes in SOM composition and substrate availability. Unamended, grass-amended, and lignin-amended soil samples were subject to 10 laboratory FTCs. Three SOM fractions (free lipids, bound lipids, and lignin-derived phenols) with distinct composition, stability and source were examined with chemolysis and biomarker Gas Chromatography/Mass Spectrometry methods and the soil microbial community composition was monitored by phospholipid fatty acid (PLFA) analysis. Soil microbial respiration was also measured before and during freezing...
Recent research suggests that micronutrients such as Mn may limit growth of slow-growing biological soil crusts (BSCs) in some of the drylands of the world. These soil surface communities contribute strongly to arid ecosystem function and are easily degraded, creating a need for new restoration tools. The possibility that Mn fertilization could be used as a restoration tool for BSCs has not been tested previously. We used microcosms in a controlled greenhouse setting to investigate the hypothesis that Mn may limit photosynthesis and consequently growth in Collema tenax, a dominant N-fixing lichen found in BSCs worldwide. We found no evidence to support our hypothesis; furthermore, addition of other nutrients (primarily...
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Dryland ecosystems have long been considered to have a highly heterogeneous distribution of nutrients and soil biota, with greater concentrations of both in soils under plants relative to interspace soils. We examined the distribution of soil resources in two plant communities (dominated by either the shrub Coleogyne ramosissima or the grass Stipa hymenoides) at two locations. Interspace soils were covered either by early successional biological soil crusts (BSCs) or by later successional BSCs (dominated by nitrogen (N)-fixing cyanobacteria and lichens). For each of the 8 plant type??crust type??locations, we sampled the stem, dripline, and 3 interspace distances around each of 3 plants. Soil analyses revealed that...
Archaea are common and abundant members of biological soil crust communities across large-scale biogeographic provinces of arid North America. Regardless of microbial community development, archaeal populations averaged 2 � 107 16S rRNA gene copies per gram of soil, representing around 5% of the prokaryotic (total calculated bacterial and archaeal) numbers assessed by quantitative-PCR. In contrast, archaeal diversity, determined by denaturing gradient gel electrophoresis fingerprinting and clone libraries of 16S rRNA genes, was very restricted. Only six different phylotypes (all Crenarchaea) were detected, three of which were very dominant. Some phylotypes were widespread, while others were typical of Southern desert...
We report the first simultaneous measurements of ?15N and ?13C of DNA extracted from surface soils. The isotopic composition of DNA differed significantly among nine different soils. The ?13C and ?15N of DNA was correlated with ?13C and ?15N of soil, respectively, suggesting that the isotopic composition of DNA is strongly influenced by the isotopic composition of soil organic matter. However, in all samples DNA was enriched in 13C relative to soil, indicating microorganisms fractionated C during assimilation or preferentially used 13C enriched substrates. Enrichment of DNA in 15N relative to soil was not consistently observed, but there were significant differences between ?15N of DNA and ?15N of soil for three...
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Carbon capture and storage (CSS) technology has the potential to inadvertently release large quantities of CO2 through geologic substrates and into surrounding soils and ecosystems. Such a disturbance has the potential to not only alter the structure and function of plant and animal communities, but also soils, soil microbial communities, and the biogeochemical processes they mediate. At Mammoth Mountain, we assessed the soil microbial community response to CO2 disturbance (derived from volcanic ‘cold’ CO2) that resulted in localized tree kill; soil CO2 concentrations in our study area ranged from 0.6% to 60%. Our objectives were to examine how microbial communities and their activities are restructured by extreme...
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Tropical rain forests are known for their high biological diversity, but the effects of plant diversity on important ecosystem processes in this biome remain unclear. Interspecies differences in both the demand for nutrients and in foliar and litter nutrient concentrations could drive variations in both the pool sizes and fluxes of important belowground resources, yet our understanding of the effects and importance of aboveground heterogeneity on belowground biogeochemistry is poor, especially in the species-rich forests of the wet tropics. To investigate the effects of individual tree species on belowground biogeochemical processes, we used both field and laboratory studies to examine how carbon (C), nitrogen (N),...
In arid ecosystems, abiotic processes facilitate the physical and chemical degradation of plant litter to the extent that decomposition models that use climatic and litter composition variables as surrogates for microbial activity are not predictive. The purpose of this study was to estimate the potential contribution of photodegradation to the decomposition of plant litters that varies in architecture and chemical composition. Litter of Pinus edulis, Juniperus monosperma and Populus deltoides were exposed to ambient and attenuated sunlight, with and without supplemental water additions, at a riparian forest site along the Middle Rio Grande (New Mexico, USA). Mass loss, elemental composition, and microbial extracellular...
Although freeze–thaw cycles can alter soil physical properties and microbial activity, their overall impact on soil functioning remains unclear. This review addresses the effects of freeze–thaw cycles on soil physical properties, microorganisms, carbon and nutrient dynamics, trace gas losses and higher organisms associated with soil. I discuss how the controlled manipulation of freeze–thaw cycles has varied widely among studies and propose that, despite their value in demonstrating the mechanisms of freeze–thaw action in soils, many studies of soil freeze–thaw cycles have used cycle amplitudes, freezing rates and minimum temperatures that are not relevant to temperature changes across much of the soil...
Although freeze?thaw cycles can alter soil physical properties and microbial activity, their overall impact on soil functioning remains unclear. This review addresses the effects of freeze?thaw cycles on soil physical properties, microorganisms, carbon and nutrient dynamics, trace gas losses and higher organisms associated with soil. I discuss how the controlled manipulation of freeze?thaw cycles has varied widely among studies and propose that, despite their value in demonstrating the mechanisms of freeze?thaw action in soils, many studies of soil freeze?thaw cycles have used cycle amplitudes, freezing rates and minimum temperatures that are not relevant to temperature changes across much of the soil profile in...
Soil organic matter (SOM) biomarker methods were utilized in this study to investigate the responses of fungi and bacteria to freeze?thaw cycles (FTCs) and to examine freeze?thaw-induced changes in SOM composition and substrate availability. Unamended, grass-amended, and lignin-amended soil samples were subject to 10 laboratory FTCs. Three SOM fractions (free lipids, bound lipids, and lignin-derived phenols) with distinct composition, stability and source were examined with chemolysis and biomarker Gas Chromatography/Mass Spectrometry methods and the soil microbial community composition was monitored by phospholipid fatty acid (PLFA) analysis. Soil microbial respiration was also measured before and during freezing...
Plant detritus is an important source of labile C that drives soil microbial growth and regulates the balance of N mineralization and immobilization. In semiarid ecosystems, timing of plant detrital inputs may be especially important in regulating microbial C and N cycling because of the relatively short window of time when moisture is available. Low soil moisture in early-summer may inhibit microbial colonization of recently released detritus, resulting in C-limitations to microbial growth, and this may explain the NO3? accumulation commonly observed in semiarid, arid, and Mediterranean ecosystems. We examined linkages between soil C availability and gross N cycling rates during summer in three common semiarid...
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Species losses and additions can disrupt the relationship between resident species and the structure and functioning of ecosystems. Persistent human-trampling, on the other hand, can have similar effects through the disruption of biocrusts on surface soils of semiarid systems, affecting soil stability and fixation of carbon and nitrogen. Here, we tested the interactive and synergistic impacts of the exclusion of native mammalian herbivores and the effects of introduced lagomorphs in a semiarid thorn scrub ecosystem, where soils were subjected to two different trampling intensities (i.e., trampled and non-trampled). We postulated that because of their differential habitat use and fossorial activities, with respect...
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Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic...
map background search result map search result map Impacts of herbivorous insects on decomposer communities during the early stages of primary succession in a semi-arid woodland Effects of canopy tree species on belowground biogeochemistry in a lowland wet tropical forest Impacts of herbivorous insects on decomposer communities during the early stages of primary succession in a semi-arid woodland Effects of canopy tree species on belowground biogeochemistry in a lowland wet tropical forest