Ecological strategies in a Patagonian arid steppe

Soriano, A.; Sala, Osvaldo E.

doi:10.1007/bf00036131

Cited by 111 publications

(91 citation statements)

References 8 publications

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“…Soils are coarse textured with gravel and stones. Vegetation corresponds to the Occidental floristic district (34) and is dominated by three grass species, Stipa speciosa Trin et Ruprecht, S. humilis Cav., and Poa ligularis Nees ap. Steud, and three shrub species, Mulinum spinosum (Cav.)…”

Section: Methodsmentioning

confidence: 99%

Higher effect of plant species diversity on productivity in natural than artificial ecosystems

Flombaum¹,

Sala

2008

Proc. Natl. Acad. Sci. U.S.A.

137

114

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Current and expected changes in biodiversity have motivated major experiments, which reported a positive relationship between plant species diversity and primary production. As a first step in addressing this relationship, these manipulative experiments controlled as many potential confounding covariables as possible and assembled artificial ecosystems for the purpose of the experiments. As a new step in this endeavor, we asked how plant species richness relates to productivity in a natural ecosystem. Here, we report on an experiment conducted in a natural ecosystem in the Patagonian steppe, in which we assessed the biodiversity effect on primary production. Using a plant species diversity gradient generated by removing species while maintaining constant biomass, we found that aboveground net primary production increased with the number of plant species. We also found that the biodiversity effect was larger in natural than in artificial ecosystems. This result supports previous findings and also suggests that the effect of biodiversity in natural ecosystems may be much larger than currently thought.biodiversity ͉ carbon cycle ͉ ecosystem functioning ͉ Patagonian steppe ͉ resource partitioning H uman activities largely impact the natural rate of change in biodiversity by influencing species invasion, displacement, and extinction rates (1, 2). For this reason, it is crucial to understand the effects of biodiversity change on the functioning of ecosystems and their capacity for providing goods and services (1, 3). The first logical attempt to address the question of the effects of biodiversity on ecosystem functioning with an experimental approach was to create gradients of plant species richness by sowing different numbers of species into homogenized soils (4-6). These experiments with artificial ecosystems showed a positive relationship between plant species richness and productivity (4-8). A further step in our endeavor to assess the effects of biodiversity change on ecosystem functioning requires tackling this issue in natural ecosystems. Observations in natural ecosystems showed inconclusive evidence of the effect of plant species richness on productivity (4, 9-11). Manipulative experiments performed in naturally assembled communities can complement results from synthetic assemblages, which represent early successional stages (12). Here, we report an experiment designed to assess the magnitude of the plant species richness effect on aboveground net primary production (ANPP) in a natural ecosystem in the Patagonian steppe.Our hypotheses were that increased plant species diversity would result in increased ANPP (5,13,14) and that the effect of biodiversity on primary production would be higher in natural than in artificial ecosystems (15). Natural ecosystems should show higher niche partitioning and stronger positive biological interactions among organisms, because species coexisted for longer periods of time and because natural ecosystems have lower frequencies of disturbance (15). Niche partitioning is the use...

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Section: Methodsmentioning

confidence: 99%

Higher effect of plant species diversity on productivity in natural than artificial ecosystems

Flombaum¹,

Sala

2008

Proc. Natl. Acad. Sci. U.S.A.

137

114

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“…Poa populations have experienced significant reductions in over-stocked fields (Perelman, Leon & Bussacca 1997), which have compromised the sustainability of sheep production in this region (Texeira & Paruelo 2006). This C 3 , dioecious bunchgrass is a perennial species approximately 30 cm tall (Soriano & Sala 1983). It is active most of the year, but vegetative growth is limited in winter by low temperatures and in late spring and summer by soil water availability (Soriano & Sala 1983).…”

Section: S P E C I E S D E S C R I P T I O Nmentioning

confidence: 99%

“…This C 3 , dioecious bunchgrass is a perennial species approximately 30 cm tall (Soriano & Sala 1983). It is active most of the year, but vegetative growth is limited in winter by low temperatures and in late spring and summer by soil water availability (Soriano & Sala 1983). Green leaves rapidly expand during spring and flowering occurs in early summer.…”

Section: S P E C I E S D E S C R I P T I O Nmentioning

confidence: 99%

Changes in sex ratios of a dioecious grass with grazing intensity: the interplay between gender traits, neighbour interactions and spatial patterns

2013

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Summary1. Dioecious plants frequently face sex-related resource allocation trade-offs. Differential traits of male and female plants can have important consequences that influence their direct and indirect interactions with neighbours and herbivores. 2. Gender differences in traits have been considered to be inherently linked to sex-biased ratios along environmental stress gradients. However, the mechanisms behind the variation in sex ratios with increasing biotic stress remain elusive. 3. We linked the results of process-based field experiments with fine-scale spatial patterns of naturally established plants (both sexes) at different grazing intensities. We demonstrated that slowgrowing females were better defended against insects and small mammals but were more susceptible than males to competition from neighbours. 4. In large-herbivore exclosures, we found that sex-biased spatial patterns at the microsite scale can be predicted from gender-specific traits, with females more segregated from competitors (unpalatable grasses) than males. Traits related to growth/defence trade-off in females, coupled with their higher competition costs than males, suggest that gender dimorphism in traits can directly influence species interactions and spatial organization. 5. In the presence of large herbivores, female individuals were preferentially browsed despite their larger investment in antiherbivore compounds. The greater distance of females from unpalatable competitors was the main determinant of female-biased consumption by domestic herbivores. Females growing close to neighbours successfully eluded browsing but also faced competition. Scaling up to a population level, population sex ratios drift from female-to male-bias with increasing domestic grazing intensity. 6. Synthesis: The sexual dimorphism in traits of a dioecious bunchgrass results in differential herbivory by natural enemies, differential competitive ability and differential spatial distribution of sexes. Domestic grazers disrupt this balance by shifting species interactions and their spatial organization. Changes in dioecious plant populations towards male-biased sex ratios with grazing intensity could not be predicted solely by gender-specific traits.

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“…Walter's two-layer model (1971Walter's two-layer model ( , 1973) is based on a soil column split into two layers corresponding to the rooting depth of woody and herbaceous plants: (1) an upper-layer from which herbaceous plants can more efficiently extract soil water; and (2) a lower-layer in which only woody plants have roots, and thus the ability to extract water. Although originally conceived for savanna environments, this model has been applied to mixed assemblages of shrubs and grass (for example, Soriano and Sala 1984). Likewise, the pulse-reserve model (Westoby and Bridges unpublished, cited in Noy-Meir 1973), which relates precipitation pulses to the resulting reserves of carbon, has also been widely applied.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Spatial Patterns of Soil Moisture on the Grass and Shrub Responses to a Summer Rainstorm in a Chihuahuan Desert Ecotone

Pockman

Small

2010

Ecosystems

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The cycling of surface water, energy, nutrients, and carbon is different between semiarid grassland and shrubland ecosystems. Although differences are evident when grasslands are compared to shrublands, the processes that contribute to this transition are more challenging to document. We evaluate how surface redistribution of precipitation and plant responses to the resulting infiltration patterns could contribute to the changes that occur during the transition from grassland to shrubland. We measured soil water potential under grasses (Bouteloua eriopoda), shrubs (Larrea tridentata) and bare soil and changes in plant water relations and gas exchange following a 15 mm summer storm in the grasslandshrubland ecotone at the Sevilleta National Wildlife Refuge in central New Mexico USA. Following the storm, soil water potential (W s ) increased to 30 cm depth beneath both grass and shrub canopies, with the greatest change observed in the top 15 cm of the soil. The increase in W s was greater beneath grass canopies than beneath shrub canopies. W s under bare soil increased only to 5 cm depth. The substantial redistribution of rainfall and different rooting depths of the vegetation resulted in high W s throughout most of the rooting volume of the grasses whereas soil moisture was unchanged throughout a large portion of the shrub rooting volume. Consistent with this pattern, predawn water potential (W PD ) of grasses increased more than 5 MPa to greater than -1 MPa whereas W PD of shrubs increased to -2.5 MPa, a change of less than 2 MPa. Transpiration increased roughly linearly with W PD in both grasses and shrubs. In grasses, assimilation was strongly correlated with W PD whereas there was no relationship in shrubs where assimilation showed no significant response to the pulse of soil moisture following the storm. These data show that preferential redistribution of water to grass canopies enhances transpiration and assimilation by grasses following large summer storms. This process may inhibit shrubland expansion at the ecotone during periods without extreme drought.

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Ecological strategies in a Patagonian arid steppe

Cited by 111 publications

References 8 publications

Higher effect of plant species diversity on productivity in natural than artificial ecosystems

Higher effect of plant species diversity on productivity in natural than artificial ecosystems

Changes in sex ratios of a dioecious grass with grazing intensity: the interplay between gender traits, neighbour interactions and spatial patterns

The Influence of Spatial Patterns of Soil Moisture on the Grass and Shrub Responses to a Summer Rainstorm in a Chihuahuan Desert Ecotone

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