Skip to main content
Advanced Search

Filters: Tags: Biology and Fertility of Soils (X)

12 results (308ms)   

View Results as: JSON ATOM CSV
thumbnail
Various biotic and abiotic components of soil ecology differed significantly across an area whereHalogeton glomeratus is invading a native winterfat, [ Krascheninnikovia (= Ceratoides) lanata] community. Nutrient levels were significantly different among the native, ecotone, and exotic-derived soils. NO3, P, K, and Na all increased as the cover of halogeton increased. Only Ca was highest in the winterfat area. A principal components analysis, conducted separately for water-soluble and exchangeable cations, revealed clear separation between halogeton- and winterfat-derived soils. The diversity of soil bacteria was highest in the exotic, intermediate in the ecotone, and lowest in the native community. Although further...
Freeze–thaw cycles can promote soil N losses as a result of microbial and root cell lysis; however, minimal freeze–thaw effects have typically been observed in studies that have imposed moderate temperature cycles. We conducted laboratory incubations on surface soil (top 3 cm) collected in a temperate old field from late fall through mid-winter to examine how variation in freeze–thaw amplitude, number, timing of collection, and freezing rate altered soil extractable N. We varied freeze–thaw amplitude by imposing minimum cycle temperatures of 0, −1, −2, −5, and −10°C for a series of either one or two cycles and held control samples constant at 3°C. We also examined the effects of freezing rates of 1, 3, and 30°C...
Freeze–thaw cycles can promote soil N losses as a result of microbial and root cell lysis; however, minimal freeze–thaw effects have typically been observed in studies that have imposed moderate temperature cycles. We conducted laboratory incubations on surface soil (top 3 cm) collected in a temperate old field from late fall through mid-winter to examine how variation in freeze–thaw amplitude, number, timing of collection, and freezing rate altered soil extractable N. We varied freeze–thaw amplitude by imposing minimum cycle temperatures of 0, −1, −2, −5, and −10°C for a series of either one or two cycles and held control samples constant at 3°C. We also examined the effects of freezing rates...
Cyanobacterial-lichen soil crusts can be a dominant source of nitrogen for cold-desert ecosystems. Effects of surface disturbance from footprints, bike and vehicle tracks on the nitrogenase activity in these crusts was investigated. Surface disturbances reduced nitrogenase activity by 30?100%. Crusts dominated by the cyanobacterium Microcoleus vaginatus on sandy soils were the most susceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichen Collema tenax was present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of nitrogenase activity reduction were affected by the degree of soil disruption and whether sites were...
thumbnail
The sensitivity of creeping bentgrass (Agrostis palustris Huds.) to the extreme heat found in the southeastern United States has led to the development of new greens-management methods. The purpose of this study was to examine the effects of subsurface aeration and growth regulator applications on soil microbial communities and mycorrhizal colonization rates in a creeping bentgrass putting green. Two cultivars (Crenshaw and Penncross), a growth regulator (trinexapacethyl), and subsurface aeration were evaluated in cool and warm seasons. Total bacterial counts were higher in whole (unsieved) soils than in sieved soils, indicating a richer rhizosphere soil environment. Mycorrhizal infection rates were higher in trinexapac-ethyl...
Although drying of soil has increased fertility in laboratory-based experiments, a direct link between longer-scale weather conditions associated with drought and soil fertility has not been documented at the field scale. Soil from a semiarid grassland on the Sevilleta National Wildlife Refuge (NWR) that was collected over a 10-year period had the highest levels of potentially mineralizable nitrogen (PMN, a measure of potential soil fertility) during drought periods in 1989 and 1995. Whereas previous soil collections on the Sevilleta NWR were made for different reasons, soils were collected in June 2002 near the peak of a regional-scale drought to test the hypothesis that potential soil fertility increased with...
Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus, but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in...
thumbnail
Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus, but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in...
thumbnail
Biological soil crusts (biocrusts) are critical components of arid and semi-arid ecosystems that contribute significantly to carbon (C) and nitrogen (N) fixation, water retention, soil stability, and seedling recruitment. While dry-land ecosystems face a number of environmental changes, our understanding of how biocrusts may respond to such perturbation remains notably poor. To determine the effect that elevated CO2 may have on biocrust composition, cover, and function, we measured percent soil surface cover, effective quantum yield, and pigment concentrations of naturally occurring biocrusts growing in ambient and elevated CO2 at the desert study site in Nevada, USA, from spring 2005 through spring 2007. During...
thumbnail
The types and amounts of carbon (C) and nitrogen (N) inputs, as well as irrigation management are likely to influence gaseous emissions and microbial ecology of agricultural soil. Carbon dioxide (CO2) and nitrous oxide (N2O) efflux, with and without acetylene inhibition, inorganic N, and microbial biomass C were measured after irrigation or simulated rainfall in two agricultural fields under tomatoes (Lycopersicon esculentum). The two fields, located in the California Central Valley, had either a history of high organic matter (OM) inputs ("organic" management) or one of low OM and inorganic fertilizer inputs ("conventional" management). In microcosms, where short-term microbial responses to wetting and drying were...
Irrigation and rain-out shelters were used to simulate precipitation patterns of wet and dry years in the northern Chihuahuan Desert. Irrigation provided approximately double the long-term average monthly precipitation. Rain was excluded during the wet season, July-October, to simulate a dry year. N net mineralization in laboratory incubations was undectable at calculated water potentials less than -1 MPa. Witb increasing moisture, mineralization gradually rose to the highest observed rates near field capacity. There was no mineralization maximum at moisture contents below field capacity. Irrigation significantly increased the water potential and rainfall exclusion reduced water potentials to less than-8 MPa. The...
thumbnail
CyanobacteriaMichen soil crusts can be a dominant source of nitrogen for cold-desert ecosystems. Effects of surface disturbance from footprints, bike and vehicle tracks on the nitrogenase activity in these crusts was investigated. Surface disturbances reduced nitrogenase activity by 30-100%. Crusts dominated by the cyanobacterium Microcoleus vaginatus on sandy soils were the most susceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichen Collema tenax was present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of nitrogenase activity reduction were affected by the degree of soil disruption and whether sites were dominated...