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1. Soil disturbance by animals affects the availability of water, nutrients, sediment and seeds, which are critical for the maintenance of functional ecosystems. We examined long-lived faunal structures across six vegetation communities in the northern Chihuahuan desert of New Mexico, USA, testing the proposition that disturbances in undesertified grassland differ in magnitude and effect from those in desertified grassland. 2. Vertebrate and invertebrate disturbances totalled 18.9 structures ha−1 across 18 sites. The most common were pits and mounds of American badgers (Taxidea taxus, 32%), nests of the ant Aphaenogaster cockerelli (18.8%) and mounds of kangaroo rats (Dipodomys spectabilis, 31%). 3. Desertification...
1. Plant carbon (C) and nitrogen (N) inputs to soil interact with microbes and abiotic factors like climate and pH to influence soil fertility and plant productivity. Although root exudates and root litter are important factors affecting the cycling of nutrients critical to plant growth, many studies remain focused on effects of above-ground litter inputs. 2. Using two species that co-dominate alpine moist meadows as a model system (the phenolic-rich forb Geum rossii, and the fast-growing grass Deschampsia caespitosa), we asked whether C from G. rossii fine roots could reduce D. caespitosa growth. We hypothesized that root C would indirectly reduce D. caespitosa growth by stimulating soil microbes, thus restricting...
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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,...
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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...
Six study areas along an aridity gradient in Utah were investigated for effects of individual plants on modification of soil chemistry. Measurements were made of the contents of C, N and P and of pH and salinity. In one study area an ungrazed salt desert shrub site was compared with a comparable site with known grazing history. In two study areas, sites that had been tilled and converted from shrub steppe to introduced grass were compared with adjacent untilled soils. At all locations distinct soil chemical patterning was evident in both vertical and horizontal planes. Vertical concentration gradients with surface maxima are greater for C, N and P than for pH or salinity. Horizontal changes in chemical concentrations,...
1 Recent research has demonstrated important linkages between above- and below-ground components of terrestrial ecosystems, but the relationships between aerial parasitic plants, such as dwarf mistletoes, and below-ground organisms, such as mycorrhizal fungi, have not been examined in detail. 2 We examined the relationship between dwarf mistletoe infection, host vigour and the ectomycorrhizal colonization and fungal community composition of pinyon pine (Pinus edulis) using a combination of field observations and glasshouse studies. 3 High levels of dwarf mistletoe infection were not associated with increased mortality or needle loss of infected pinyons, but infected trees had lower shoot growth. 4 Ectomycorrhizal...
1 Although drought frequency and severity are predicted to increase across numerous continental interiors, the consequences of these changes for dominant plants are largely unknown. Over the last decade, the south-western US has experienced six drought years, including the extreme droughts of 1996 and 2002, which led to widespread tree mortality across northern Arizona. 2 We examined the impact of these droughts on the co-dominant tree species of the pinyon?juniper woodland (Pinus edulis and Juniperus monosperma), a major vegetation type in the US. 3 Pinyon mortality following both droughts was 6.5-fold higher than juniper mortality. In addition, large pinyons suffered 2?6-fold greater mortality than small pinyons,...
1. As central place foragers, ants accumulate organic debris near their nests. Consequently, soil nutrient stocks are often enriched near the nest site. We investigated the hypothesis that plant-derived food sources, such as extrafloral nectar (EFN), can encourage soil-dwelling ant colonies to nest near the plant, thereby inadvertently providing the plant with an additional source of mineral nutrients. The study focused on a population of Acacia constricta, a North American shrub bearing EFNs. 2. Several lines of evidence supported the notion that food rewards drew ant nests close to A. constricta plants. Firstly, ant species that visit EFNs nested significantly closer to A. constricta plants than would be expected...
1 Phenolics are an important, biologically reactive component of the carbon (C) pool that moves from plants to soil. Once in soil, phenolics can regulate plant?soil feedbacks because of their influence on soil nitrogen biogeochemistry. 2 Roots are a largely overlooked potential source of below-ground phenolic C. We examined phenolic fluxes from plants to soil in an alpine ecosystem, where phenolics are associated with slow rates of nutrient cycling. Using a phenolic-rich forb (Acomastylis rossii) and a grass with low tissue phenolics (Deschampsia caespitosa), we asked whether leaves, leaf litter or roots are the dominant source of soil phenolics during the growing season. We also determined whether the composition...
1 A 3-year field study examined the physiological and demographic consequences of resource pulse use by an herbaceous, aridland perennial, Cryptantha flava, as well as potential competitive and facilitative interactions with larger shrubs. 2 We applied a pulse of urea and faecal pellets, simulating Mule deer excretions, to plants growing between and under Sagebrush and Rabbitbrush canopies. 3 We hypothesized that C. flava would show strong positive responses to N pulses in open microhabitats, and such plants had approximately 50% increases in leaf N concentrations within days of pulse application, accompanied by increased photosynthetic rates. Over the next year, higher rates of growth and reproduction were found...
1. In order to determine the effect of conspecific adult neighbours and opening size on the process of seedling establishment in Bouteloua gracilis, seeds were added to naturally occurring openings of bare soil, and water was provided up to and beyond the time of adventitious root development of seedlings. Exclusion of roots of neighbours was accomplished using steel tubes sunk in the soil of openings. 2. Adult neighbours affected emergence, survival and performance of seedlings in the whole observed range of opening sizes (10, 20 and 30 cm in diameter). With neighbours present (no root exclusion), seedlings produced few tillers regardless of opening size, and had higher survival only in the 30-cm-diameter openings....
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* 1 Arid ecosystems are a patch mosaic of plants and biological soil crusts that have been described as islands and mantles of fertility, respectively. To determine whether these patches are metabolically linked by a fungal network of dark septate and arbuscular mycorrhizal fungi (AMF), we measured translocation of nitrogen (N) and carbon (C) in a desert grassland using 15N-NO3 and 13C5, 15N-glutamic acid as substrates. * 2 Substrates were applied as point sources to either small patches of biotic crust or to a subset of leaves within a bunch grass tussock. * 3 Both substrates were translocated over approximately 1 m2 areas (approximately 20 patches) at rates up to 100 cm day?1 during a 4-day period following a...
1. There is mounting evidence that leaf litter typically decomposes more rapidly beneath the plant species it derived from than beneath the different plant species, which has been called home-field advantage (HFA). It has been suggested that this HFA results from the local adaptation of soil communities to decompose the litter that they encounter most often, which probably comes from the plant species above them. 2. To test this hypothesis and to investigate how HFA varies over time and in relation to litter quality, we performed the first detailed assessment of HFA in relation to litter decomposition. We monitored decomposition over time in two reciprocal litter transplant experiments involving three high-elevation...
1. Pathogen spillover occurs when disease levels for a given population are driven by transmission from a reservoir species that carries a high pathogen load. Pathogen spillover is widely documented in crop systems, but has been little studied in natural plant communities. 2. The abundant seed production of weedy species may create a scenario where spillover of a generalist seed pathogen onto less abundant seeds of native hosts is possible. The invasive annual weed cheatgrass (Bromus tectorum) is a potential reservoir species for Pyrenophora semeniperda, a multiple-host fungal seed pathogen that naturally occurs in the semi-arid western United States. 3. To investigate potential community-level consequences of spillover...
(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...
1 Resource pulses generally result in a burst of biological activity at multiple scales. For plants, the increased activity is generally considered positive due to an overall up-regulation of physiological activity during the pulse. Longer-term effects remain an understudied aspect of resource pulses. 2 We monitored the short- and long-term effects of nitrogen (N) pulse to the long-lived desert perennial, Cryptantha flava. One group of plants were treated with a one-time application of N in the spring of 1999, a second group received two N pulses (one in the spring of 1999 and one in the spring of 2000), and a third group received ambient N (controls). 3 In the short-term, N-pulse treated plants rapidly increased...
(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) Amplitude in the variation of recruitment, survivorship and fecundity was examined for the introduced annual grass Bromus tectorum in three habitat types in eastern Washington (U.S.A.) for three consecutive generations. A total of 18 143 individuals in populations varying from 364 to 5322 members per site were mapped repeatedly from emergence to death with sufficient frequency to detect multiple constituent cohorts varying in age from fewer than 16 to more than 200 days. (2) Recruitment was usually concentrated in late summer and autumn, but occurred at any time until mid-May of the following year. (3) Most of any population experienced low death risk until June, although some cohorts emerging in late summer...
1 We examined the effects of patch disturbance leading to removal of conspecific neighbours, and of microsite type on the emergence, survival, and performance of seedlings of Bouteloua gracilis at a shortgrass steppe site. Our hypothesis was that the death and/or removal of a full-size B. gracilis plant, would result in increased availability of below-ground resources and thus promote the establishment of conspecific seedlings. 2 In 1990 and 1991, experimental plots were treated to mimic the effects of some common patch disturbance types. Caryopses were then planted into both plant microsites (i.e. located in the hummock formed by adult plants of B. gracilis) and bare soil. Seedlings were watered until they were...
map background search result map search result map Geostatistical Patterns of Soil Heterogeneity Around Individual Perennial Plants Translocation of nitrogen and carbon integrates biotic crust and grass production in desert grassland Phenology and Dynamics of Root Growth of Three Cool Semi-Desert Shrubs Under Field Conditions Geostatistical Patterns of Soil Heterogeneity Around Individual Perennial Plants Translocation of nitrogen and carbon integrates biotic crust and grass production in desert grassland Phenology and Dynamics of Root Growth of Three Cool Semi-Desert Shrubs Under Field Conditions