Patch structure and dynamics in a Patagonian arid steppe

Soriano, A.; Sala, Osvaldo E.; Perelman, Susana B.

doi:10.1007/bf00040332

Cited by 109 publications

(132 citation statements)

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“…Presence of shrubs may account for high soil NH 4 þ concentrations due to high inputs of organic matter in soil (Charley and West, 1975;Schlesinger et al, 1996). Shrub islands not only have high primary production (Soriano et al, 1994) but also trap a large fraction of windblown organic material, which may be produced in other microenvironments, all of which provide organic matter with carbon and nitrogen substrate for microbial growth and nitrogen mineralization. The bare-soil microenvironment had the lowest ammonium concentrations and a high nitrate/ammonium ratio, associated with the absence of vegetative cover (Table 2 and Fig.…”

Section: Resultsmentioning

confidence: 99%

Controls on nitrification in a water-limited ecosystem: experimental inhibition of ammonia-oxidising bacteria in the Patagonian steppe

López

Austin

Sala

et al. 2003

Soil Biology and Biochemistry

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We studied controls on nitrification in an undisturbed water-limited ecosystem by inhibiting autotrophic nitrifying bacteria in soils with varying levels of vegetative cover. The activity of nitrifying bacteria was disrupted using nitrapyrin, 2-chloro-6-(trichloromethyl)-pyridine, under field conditions in three microenvironments (underneath shrubs, next to grasses and in bare soil). Ammonia-oxidising bacteria were detected by PCR analysis of DNA in soils. The inhibition of nitrification changed the concentrations of NO 3 2 and NH 4 þ in the soil, while the microenvironment was most important in determining the response of bacteria to the inhibitor. Nitrapyrin application resulted in a significant ðp , 0:05Þ reduction in soil NO 3 2 concentration (39%) and a significant increase ðp , 0:001Þ in soil NH 4 þ concentration (41%). Untreated bare-soil microenvironments had the lowest concentrations of NH 4 þ (1.57 mg/g of dry soil) and NO 3 2 (0.49 mg/g of dry soil) when compared to the other microenvironments, and showed the highest impacts of nitrification inhibition. For example, NH 4 þ concentrations increased 288%and NO 3 2 concentrations decreased 60% in inhibited bare-soil microenvironments. In contrast, untreated microenvironments underneath shrubs had the highest levels of NH 4 þ (10.01 mg/g of dry soil) and NO 3 2 (0.69 mg/g of dry soil), but showed no significant effects of inhibition of nitrification on soil nitrogen concentrations. q

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Section: Resultsmentioning

confidence: 99%

Controls on nitrification in a water-limited ecosystem: experimental inhibition of ammonia-oxidising bacteria in the Patagonian steppe

López

Austin

Sala

et al. 2003

Soil Biology and Biochemistry

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“…In the Patagonian steppe, there are highly vegetated patches (e.g. shrubs with tussock grasses) embedded in a low cover matrix (Soriano et al 1994;Cipriotti and Aguiar 2005a, b). In paddocks subjected to grazing, palatable species tend to grow associated to non-palatable species that provide refuge to avoid herbivores (Oesterheld and Oyarzábal 2004;Aguiar 2005b, Graff et al 2007).…”

Section: Discussionmentioning

confidence: 99%

Herbivory resistance traits in populations of Poa ligularis subjected to historically different sheep grazing pressure in Patagonia

Rotundo

Aguiar

2007

Plant Ecol

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Seeding selected populations with high grazing resistance may foster recovery of plant populations threatened by overgrazing. Resistance to grazing depends on grazing avoidance (escape from grazers) and grazing tolerance (ability to growth after defoliation). Many studies of grazing tolerance defoliate plants at a fixed height instead of removing the same proportion of biomass and therefore confound tolerance with avoidance. For this reason, the information on evolution of tolerance to defoliation at the intraspecific level is remarkably scarce despite the abundance of papers published that evaluate responses to defoliation. The estimation of the cost of tolerance is also troublesome because current methods usually include spurious correlations due to correlation between variables that share common terms. The objectives of this paper were to assess the intraspecific variation in tolerance and in traits associated with avoidance and growth in populations with different sheep grazing histories. We also estimated the percentage of biomass removed when the defoliation treatment was imposed at fixed height in order to separate tolerance and avoidance. Finally, we estimated the cost of tolerance using a new method proposed for spurious correlations. Results of a greenhouse experiment indicated no difference in tolerance among the three compared populations. However, the populations from overgrazed fields had more prostrate growth form, higher specific leaf area, and higher tillering rate (when no defoliated) than populations from exclosures. We confirmed that fixed height defoliation would have removed a higher proportion of shoot biomass from taller than from shorter individual plants, confounding grazing tolerance and avoidance. Regarding the cost of tolerance, we found no differences from a null model of no cost, indicating that the evolution (or future breeding) of more tolerant genotypes would not be constrained by this cost.

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“…In the case of grasses, 20 0.2 ϫ 5 m plots were randomly located and harvested. This plot shape was used because it reduces sampling variance by encompassing a large proportion of the community heterogeneity (see Soriano et al 1994). Grass biomass was divided into three categories (green, recent dead, and old dead) and then was oven-dried and weighed.…”

Section: Methodsmentioning

confidence: 99%

Controls of Grass and Shrub Aboveground Production in the Patagonian Steppe

Jobbágy¹,

Sala²

2000

Ecological Applications

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Abstract. We studied the temporal dynamics of aboveground net primary production (ANPP) and senescence in a semiarid steppe representative of the Occidental District of Patagonia. We focused on the association of ANPP and senescence with climatic fluctuations at annual and seasonal scales. We estimated annual ANPP based on biomass harvests of grasses and shrubs (the dominant functional groups) at the peak of the growing season (January). The ANPP and senescence of grasses alone were also estimated for several periods within each year.The mean annual ANPP of the studied community for 10 years was 56 g·m Ϫ2 ·yr Ϫ1 , and the coefficient of variation was 26%. Grass and shrub mean annual ANPP had similar levels. Annual shrub production was associated with cumulative precipitation for the whole year, whereas annual grass production was not associated with precipitation. The average seasonal dynamics of grass ANPP showed its peak during spring, and there was no grass production during late summer and early fall. The peak green biomass of grass was achieved in early summer. Average senescence rates were more constant throughout the year, except for winter, when senescence was almost interrupted. Winter grass ANPP was positively associated with fall temperature, spring grass ANPP was positively related to winter precipitation, and summer grass ANPP was positively related to spring precipitation. Grass senescence during spring was negatively related to precipitation in the same season.Our results highlight the importance of separating functional types in productivity studies. The differential effect of precipitation on grass and shrub ANPP masked the association when these functional groups were pooled. ANPP association with climatic variables in the Occidental District of the Patagonian steppe shifted from precipitation alone to precipitation and temperature when the temporal scale of analysis changed from annual to seasonal.

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Patch structure and dynamics in a Patagonian arid steppe

Cited by 109 publications

References 19 publications

Controls on nitrification in a water-limited ecosystem: experimental inhibition of ammonia-oxidising bacteria in the Patagonian steppe

Controls on nitrification in a water-limited ecosystem: experimental inhibition of ammonia-oxidising bacteria in the Patagonian steppe

Herbivory resistance traits in populations of Poa ligularis subjected to historically different sheep grazing pressure in Patagonia

Controls of Grass and Shrub Aboveground Production in the Patagonian Steppe

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