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1 Univariate, multivariate, and geostatistical techniques were used to quantify the scale and degree of soil variability around individual perennial sagebrush (Artemisia tridentata ssp. vaseyana) and bluebunch wheatgrass (Pseudoroegneria spicata ssp. spicata) plants. This variability was then compared to that found across the larger sagebrush-steppe site. Samples were taken every metre in a 10-m $\times$ 12-m grid and every 12.5 cm in nine nested 0.5-m $\times$ 0.5-m grids containing at least one Artemisia shrub or Pseudoroegneria tussock (362 total samples). The 11 soil properties measured were organic matter, pH, water content, live root mass, microbial respiration, net N mineralization, nitrification potential,...
(1) Over the 8-year period 1980-87, moderate grazing did not affect the population dynamics of the perennial shrubs Atriplex vesicaria, Maireana astrotricha and Maireana pyramidata. Density of A. vesicaria declined on both grazed and ungrazed transects, but that of Maireana spp. remained almost constant. (2) Turnover rates of A. vesicaria were quite high for both grazed and ungrazed populations, but were extremely low for Maireana spp. (3) Shrub size was the only population parameter significantly affected by grazing. Heights and diameters for both grazed and ungrazed populations declined during dry periods, but this decline was greater for grazed shrubs. After rain, however, grazed shrubs quickly returned to sizes...
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The timing and extent of root growth and development were studied under field conditions in root observation chambers. These chambers were located near small groups of established perennial shrubs. Each of the shrub species, Atriplex confertifolia, Ceratoides lanata, and Artemisia tridentata occur in nearly monospecific stands. The presence of the observation chambers was shown to cause minimal disruption of the soil environment since soil temperatures and water potentials immediately proximate to the observation window were the same as those in the undisturbed soil profile. The season of root growth activity was initiated a few days before active shoot growth in the spring and extended for several months after...
1. Hydraulic redistribution may have important consequences for ecosystem water balance where plant root systems span large gradients in soil water potential. To assess seasonal patterns of hydraulic redistribution, we measured the direction and rate of sap flow in tap-roots, lateral roots and main stems of three mature Prosopis velutina Woot. trees occurring on a floodplain terrace in semiarid south-eastern Arizona, USA. Sap-flow measurements on two of the trees were initiated before the end of the winter dormancy period, prior to leaf flush. 2 Despite the absence of crown transpiration during the dormant season, sap flow was detected in lateral roots and tap-roots of P. velutina. Reverse flow (away from the stem)...
(1) Perturbations were performed on organisms in a below-ground trophic food web in a semi-arid grassland, using five separate biocide treatments to observe changes in trophic structures, interactions, and nutrient cycling. Changes in N mineralization and trophic interactions as predicted on the basis of simple predator-prey microcosm studies were observed following removal of particular groups. (2) Five biocides: streptomycin (bactericide), captan and PCNB (fungicides), carbofuran (insecticide--nematicide), and cygon (acaricide) were applied in situ to soil in cylinders containing predominantly blue grama grass. The response of microbes, fungal grazers, soil inorganic N and plants were followed monthly between...
(1) A field study was conducted in the Mojave Desert to determine the horizontal distribution of two co-dominating species and the degree of interference between individuals of the same species and of different species. (2) Variance/mean analyses indicated that one of the co-dominating species (Larrea tridentata) is regularly distributed and the other (Ambrosia dumosa) is contagiously distributed. (3) The results of a controlled removal experiment showed that water-related interference does occur at this site when water availability is low, and that at present, interference between species is usually more intense than that within a species. These results, together with nearest-neighbour analyses, revealed that regular...
Plants of four Great Basin grass species were grown from seed in two greenhouses at low (340 ? l l-1) and high (680 ? l l-1) CO2 concentration. In all four species, high CO2 promoted mean increases in the number of basal stems, leaf area, specific leaf weight and above-ground dry weight. High CO2 resulted in an increase in CO2 assimilation in two C3 grasses but not in a C4 grass, while all three species showed decreases in stomatal conductance. Mean increases of 60% in aboveground dry weight and 80% in water-use-efficiency are consistent with previously reported high CO2 effects on grasses. No consistent differential effects of high CO2 were observed when comparing annual vs perennial species. Global CO2 enrichment...
(1) The influence of Microtus montanus (Cricetidae) grazing on the population biology of the annual Bromus tectorum and on seedlings of the perennial Agropyron spicatum was investigated using four grazing frequencies (grazed weekly, biweekly, monthly, or once) and ungrazed controls and was initiated at four plant ages (7, 30, 90 and 150 days old) in an unheated glasshouse experiment. (2) In both species, the proportional survival of individuals rose with decreased frequency of grazing and with increased age at initial grazing. (3) The age-by-species interaction for survival showed that B. tectorum increased survival from 17% for plants grazed at 7 days old to 69% for plants grazed at 30 days old or older. For A....
1 We introduce a hydraulic soil-plant model with water uptake from two soil layers; one a pulse-dominated shallow soil layer, the other a deeper soil layer with continuous, but generally less than saturated soil moisture. Water uptake is linked to photosynthetic carbon assimilation through a photosynthesis model for C3 plants. 2 A genetic algorithm is used to identify character suites that maximize photosynthetic carbon gain for plants that experience a particular soil moisture pattern. The character suites include allocation fraction to stem, leaves and shallow root, stem capacitance and stem water storage capacity, maximal leaf conductance and sensitivity of leaf conductance to plant water potential, and a critical...
1. Local population studies have shown that sex allocation among many birds and mammals seems to be partly non-random and in connection to surrounding factors, such as environmental or parental quality. In this scenario, if environmental quality varies in space and time, it is feasible that environmental quality also comes to influence offspring sex ratio on larger geographical scales. 2. Investigating this idea - using nation-wide data sets on size-dimorphic Finnish northern goshawks Accipiter gentilis from 1989 to 1998 - we found that offspring sex ratio is related to spatial and temporal variation in availability of their main prey, woodland grouse species. 3. In a majority of locations (n = 73), broods are large...


    map background search result map search result map Geostatistical Patterns of Soil Heterogeneity Around Individual Perennial Plants Phenology and Dynamics of Root Growth of Three Cool Semi-Desert Shrubs Under Field Conditions Geostatistical Patterns of Soil Heterogeneity Around Individual Perennial Plants Phenology and Dynamics of Root Growth of Three Cool Semi-Desert Shrubs Under Field Conditions