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The physiological mechanisms utilized by soil bacteria for acclimation to sudden increases in soil water potential are poorly understood. In this study, we examined the physiological responses of soil isolates of Pseudomonas chlororaphis, P. fluorescens, Bacillus pumulis, and Streptomyces griseus to a sudden increase in solution water potential (dilution). Bacterial isolates were cultured at a low solute water potential (-3.0 MPa) and subjected to rapid water potential increases of 0.5 to 2.0 MPa. The small amount of protein and DNA released by a 2.0 MPa dilution suggests that water potential increases up to 2.0 MPa did not cause significant cell lysis. In response to dilution, intracellular solutes were released...
Soil properties under stands of vegetation dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana) and grass were examined 14 yr after spraying with 2,4-dichlorophenoxy acetic acid (2,4-D) to control sagebrush. Changes in only a few soil chemical properties were found after conversion to grassland. Phosphorus and K were apparently redistributed from depth to the surface 5 cm of soil by grass-dominated vegetation. Conversely, surface concentrations of N were lower under grass vegetation than under undisturbed vegetation. No changes attributable to vegetation conversion were found for total C, Na, Mg, cation exchange capacity, base saturation, pH, bulk density, or potential net N mineralization rates...
A stepwise multiple regression procedure was developed to predict oven-dried bulk density from soil properties using the 1997 USDA-NRCS National Soil Survey Characterization Data. The database includes both subsoil and topsoil samples. An overall regression equation for predicting oven-dried bulk density from soil properties (R2 = 0.45, P < 0.001) was developed using almost 47000 soil samples. Partitioning the database by soil suborders improved regression relationships (R2 = 0.62, P < 0.001). Of the soil properties considered, the stepwise multiple regression analysis indicated that organic C content was the strongest contributor to bulk density prediction. Other significant variables included clay content, water...
The rapid rewetting of a dry soil often yields a pulse in soil CO2 production that persists for 2 to 6 d. This phenomenon is a common occurrence in surface soils, yet the mechanism responsible for producing the CO2 pulse has not been positively identified, We studied the effects of a single drying and rewetting event on soil C pools, to identify which specific C substrates are mineralized to produce the observed pulse in respiration rates. We labeled two soils with C-glucose and measured the enrichment and pool sizes of the released CO2, extractable biomass C, and extractable soil organic matter (SOM-C) throughout a drying and rewetting cycle. After rewetting, respiration rates were 475 to 370% higher than the rates...
Accumulation of nutrients in the surface soil beneath mature pinyon pines (Pinus edulis Engelm.) was compared to nutrient levels in adjacent shrub-dominated areas. With the exception of Cu, concentrations of both macro- and micronutrients ranged from 2 to 20 times higher in the soil beneath 490-year-old trees than in adjacent areas where the length of biotic influence was presumed to be considerably less. Phosphorus concentrations beneath the trees averaged 132 ppm and suggested the presence of octocalcium phosphate. Significantly less clay was found beneath the pinyon trees than in the shrub-dominated openings, an apparent result of eolian material accumulating beneath the pinyon canopy. Regression equations relating...