Geology topics

D.A. Neher

Publications and source records attributed to D.A. Neher.

4 recordsLinked to original sources

USGS2009

Impact of biological soil crusts and desert plants on soil microfaunal community composition

Carbon and nitrogen are supplied by a variety of sources in the desert food web; both vascular and non-vascular plants and cyanobacteria supply carbon, and cyanobacteria and plant-associated rhizosphere bacteria are sources of biological nitrogen fixation. The objective of this study was to compare the relative influence of vascular plants and biological soil crusts on desert soil nematode and protozoan abundance and community composition. In the first experiment, biological soil crusts were removed by physical trampling. Treatments with crust removed had fewer nematodes and a greater relative ratio of bacterivores to microphytophages than treatments with intact crust. However, protozoa composition was similar with or without the presence of crusts. In a second experiment, nematode community composition was characterized along a spatial gradient away from stems of grasses or shrubs. Although nematodes generally occurred in increasing abundance nearer to plant stems, some genera (such as the enrichment-type Panagrolaimus) increased disproportionately more than others (such as the stress-tolerant Acromoldavicus). We propose that the impact of biological soil crusts and desert plants on soil microfauna, as reflected in the community composition of microbivorous nematodes, is a combination of carbon input, microclimate amelioration, and altered soil hydrology. ?? Springer Science + Business Media B.V. 2009.

Plant and Soil↗

USGS2007

Soil nematode communities are ecologically more mature beneath late- than early-successional stage biological soil crusts

Biological soil crusts are key mediators of carbon and nitrogen inputs for arid land soils and often represent a dominant portion of the soil surface cover in arid lands. Free-living soil nematode communities reflect their environment and have been used as biological indicators of soil condition. In this study, we test the hypothesis that nematode communities are successionally more mature beneath well-developed, late-successional stage crusts than immature, early-successional stage crusts. We identified and enumerated nematodes by genus from beneath early- and late-stage crusts from both the Colorado Plateau, Utah (cool, winter rain desert) and Chihuahuan Desert, New Mexico (hot, summer rain desert) at 0-10 and 10-30 cm depths. As hypothesized, nematode abundance, richness, diversity, and successional maturity were greater beneath well-developed crusts than immature crusts. The mechanism of this aboveground-belowground link between biological soil crusts and nematode community composition is likely the increased food, habitat, nutrient inputs, moisture retention, and/or environmental stability provided by late-successional crusts. Canonical correspondence analysis of nematode genera demonstrated that nematode community composition differed greatly between geographic locations that contrast in temperature, precipitation, and soil texture. We found unique assemblages of genera among combinations of location and crust type that reveal a gap in scientific knowledge regarding empirically derived characterization of dominant nematode genera in deserts soils and their functional role in a crust-associated food web. ?? 2006 Elsevier B.V. All rights reserved.

Applied Soil Ecology↗

USGS2007

Heterogeneity of soil nutrients and subsurface biota in a dryland ecosystem

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 only available potassium (Kav) and ammonium concentrations were consistently greater under plants (7 of 8 sites and 6 of 8 sites, respectively). Nitrate and iron (Fe) were greater under plants at 4 sites, while all other nutrients were greater under plants at less than 50% of the sites. In contrast, calcium, copper, clay, phosphorus (P), and zinc were often greater in the interspace than under the plants. Soil microbial biomass was always greater under the plant compared to the interspace. The community composition of N-fixing bacteria was highly variable, with no distinguishable patterns among microsites. Bacterivorous nematodes and rotifers were consistently more abundant under plants (8 and 7 sites, respectively), and fungivorous and omnivorous nematodes were greater under plants at 5 of the 8 sites. Abundance of other soil biota was greater under plants at less than 50% of the sites, but highly correlated with the availability of N, P, Kav, and Fe. Unlike other ecosystems, the soil biota was only infrequently correlated with organic matter. Lack of plant-driven heterogeneity in soils of this ecosystem is likely due to (1) interspace soils covered with BSCs, (2) little incorporation of above-ground plant litter into soils, and/or (3) root deployment patterns. ?? 2007 Elsevier Ltd. All rights reserved.

Soil Biology and Biochemistry↗

USGS2006

Effects of altered temperature and precipitation on desert protozoa associated with biological soil crusts

Biological soil crusts are diverse assemblages of bacteria, cyanobacteria, algae, fungi, lichens, and mosses that cover much of arid land soils. The objective of this study was to quantify protozoa associated with biological soil crusts and test the response of protozoa to increased temperature and precipitation as is predicted by some global climate models. Protozoa were more abundant when associated with cyanobacteria/lichen crusts than with cyanobacteria crusts alone. Amoebae, flagellates, and ciliates originating from the Colorado Plateau desert (cool desert, primarily winter precipitation) declined 50-, 10-, and 100-fold, respectively, when moved in field mesocosms to the Chihuahuan Desert (hot desert, primarily summer rain). However, this was not observed in protozoa collected from the Chihuahuan Desert and moved to the Sonoran desert (hot desert, also summer rain, but warmer than Chihuahuan Desert). Protozoa in culture began to encyst at 37??C. Cysts survived the upper end of daily temperatures (37-55??C), and could be stimulated to excyst if temperatures were reduced to 15??C or lower. Results from this study suggest that cool desert protozoa are influenced negatively by increased summer precipitation during excessive summer temperatures, and that desert protozoa may be adapted to a specific desert's temperature and precipitation regime. ?? 2006 by the International Society of Protistologists.

Journal of Eukaryotic Microbiology↗