Water relations between shrubs and grasses in semi-arid Argentina

Peláez, D.V.; Distel, Roberto Alejandro; Bóo, Roberto M.; Elı́a, Omar R.; Mayor, M.D.

doi:10.1006/jare.1994.1046

Cited by 63 publications

(45 citation statements)

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“…These values for xylem water were comparable with those for soil water in the upper 0.5 m of the profile, indicating that this is where grasses acquire the majority of their soil water. These results are in agreement with prior studies at this site 86 and other savanna sites [93][94][95][96][97][98] which indicate that water uptake by savanna grasses is confined largely to the upper 0.5-1.0 m of the soil.…”

Section: Ecosystem Structure and Hydrologic Function: Root Distributisupporting

confidence: 94%

Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical savanna

Boutton

Archer

Midwood³

1999

Rapid Commun. Mass Spectrom.

140

104

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Stable isotopes are often utilized as intrinsic tracers to study the effects of human land uses on the structural and functional characteristics of ecosystems. Here, we illustrate how stable isotopes of H, C, and O have been utilized to document changes in ecosystem structure and function using a case study from a subtropical savanna ecosystem. Specifically, we demonstrate that: (1) delta 13C values of soil organic carbon record a vegetation change in this ecosystem from C4 grassland to C3 woodland during the past 40-120 years, and (2) delta 2H and delta 18O of plant and soil water reveal changes in ecosystem hydrology that accompanied this grassland-to-woodland transition. In the Rio Grande Plains of North America, delta 13C values of plants and soils indicate that areas now dominated by C3 subtropical thorn woodland were once C4 grasslands. delta 13C values of current organic matter inputs from wooded landscape elements in this region are characteristic of C3 plants (-28 to -25/1000), while those of the associated soil organic carbon are higher and range from -20 to -15/1000. Approximately 50-90% of soil carbon beneath the present C3 woodlands is derived from C4 grasses. A strong memory of the C4 grasslands that once dominated this region is retained by delta 13C values of organic carbon associated with fine and coarse clay fractions. When delta 13C values are evaluated in conjunction with 14C measurements of that same soil carbon, it appears that grassland-to-woodland conversion occurred largely within the past 40-120 years, coincident with the intensification of livestock grazing and reductions in fire frequency. These conclusions substantiate those based on demographic characteristics of the dominant tree species, historical aerial photography, and accounts of early settlers and explores. Concurrent changes in soil delta 13C values and organic carbon content over the past 90 years also indicate that wooded landscape elements are behaving as sinks for atmospheric CO2 by sequestering carbon derived from both the previous C4 grassland and the present C3 woody vegetation. Present day woodlands have hydrologic characteristics fundamentally different from those of the original grasslands. Compared to plants in remnant grasslands, tree and shrub species in the woodlands are rooted more deeply and have significantly greater root biomass and density than grasslands. delta 18O and delta 2H values of plant and soil water confirm that grassland species acquire soil water primarily from the upper 0.5 m of the soil profile. In contrast, trees and shrubs utilize soil water from throughout the upper 4 m of the profile. Thus, soil water that formerly may have infiltrated beyond the reach of the grassland roots and contributed to local groundwater recharge or other hydrologic fluxes may now be captured and transpired by the recently formed woodland plant communities. The natural abundances of stable isotopes revealed fundamental information regarding the impacts of human land use activities on the structure and function of th...

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Section: Ecosystem Structure and Hydrologic Function: Root Distributisupporting

confidence: 94%

Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical savanna

Boutton

Archer

Midwood³

1999

Rapid Commun. Mass Spectrom.

140

104

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“…1 in evaluating water acquisition and resource partitioning by different plant FTs include comparing plant and soil water potentials and/or measuring stable isotopes of hydrogen and/or oxygen in plant and soil water (Ehleringer et al 1999). For example, Montaña et al (1995) and Peláez et al (1994) measured water potentials of co-occurring grasses and shrubs in the Chihuahuan Desert in Mexico and in semi-arid Argentina, respectively. They suggest that some shrubs and grasses may utilize the same water source, but their data also suggest that the shrubs Prosopis glandulosa and P. caldenia access deeper water than co-occurring grasses and shallow-rooted shrubs.…”

Section: Methodsological Issuesmentioning

confidence: 99%

“…For example, two species growing side-byside and accessing the same water source, with respect to spatial position, can avoid competition for water by being active during different times of the year (e.g., Cable 1969;Golluscio et al 1998;Nobel and Zhang 1997;Peláez et al 1994;Reynolds et al 2000;Roupsard et al 1999). Within a community, different phenologies affect the temporal dynamics of species-specific leaf area indices, which in turn determines which species use, and how much, seasonal precipitation (Schwinning et al 2002).…”

Section: Plant Phenologymentioning

confidence: 99%

Plant responses to precipitation in desert ecosystems: integrating functional types, pulses, thresholds, and delays

2004

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The 'two-layer' and 'pulse-reserve' hypotheses were developed 30 years ago and continue to serve as the standard for many experiments and modeling studies that examine relationships between primary productivity and rainfall variability in aridlands. The two-layer hypothesis considers two important plant functional types (FTs) and predicts that woody and herbaceous plants are able to co-exist in savannas because they utilize water from different soil layers (or depths). The pulse-reserve model addresses the response of individual plants to precipitation and predicts that there are 'biologically important' rain events that stimulate plant growth and reproduction. These pulses of precipitation may play a key role in long-term plant function and survival (as compared to seasonal or annual rainfall totals as per the two-layer model). In this paper, we re-evaluate these paradigms in terms of their generality, strengths, and limitations. We suggest that while seasonality and resource partitioning (key to the two-layer model) and biologically important precipitation events (key to the pulse-reserve model) are critical to understanding plant responses to precipitation in aridlands, both paradigms have significant limitations. Neither account for plasticity in rooting habits of woody plants, potential delayed responses of plants to rainfall, explicit precipitation thresholds, or vagaries in plant phenology. To address these limitations, we integrate the ideas of precipitation thresholds and plant delays, resource partitioning, and plant FT strategies into a simple 'threshold-delay' model. The model contains six basic parameters that capture the nonlinear nature of plant responses to pulse precipitation. We review the literature within the context of our threshold-delay model to: (i) develop testable hypotheses about how different plant FTs respond to pulses; (ii) identify weaknesses in the current state-of-knowledge; and (iii) suggest future research directions that will provide insight into how the timing, frequency, and magnitude of rainfall in deserts affect plants, plant communities, and ecosystems.

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“…Models based on the 'Walter hypothesis' -4-have been widely applied in literature (Walker et al, 1981, Walker and Noy-Meir, 1982, Eagleson and Segarra, 1985, van Langevelde et al, 2003. Some experiments and observations have supported 'Walter hypothesis' (Knoop and Walker, 1985, Sala et al, 1989, Pelaez et al, 1994 but many others have cast doubts on the existence of vertical rooting niche separation (Scholes and Walker, 1993, Belsky, 1990, Le Roux et al, 1995, Mordelet et al, 1997, Smit and Rethman, 2000, Hipondoka et al, 2003.…”

Section: What Is Special About the Savanna Environment That Allows Trmentioning

confidence: 99%

Tree–grass co-existence in savanna: Interactions of rain and fire

Accatino

Michele

Vezzoli

et al. 2010

Journal of Theoretical Biology

116

105

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The mechanisms permitting the co-existence of tree and grass in savannas have been a source of contention for many years. The two main classes of explanations involve either competition for resources, or differential sensitivity to disturbances. Published models focus principally on one or the other of these mechanisms. Here we introduce a simple ecohydrologic model of savanna vegetation involving both competition for water, and differential sensitivity of trees and grasses to fire disturbances. We show how the coexistence of trees and grasses in savannas can be simultaneously controlled by rainfall and fire, and how the relative importance of the two factors distinguishes between dry and moist savannas. The stability map allows to predict the changes in vegetation structure along gradients of rainfall and fire disturbances realistically, and to clarify the distinction between climate-and disturbance-dependent ecosystems.

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Water relations between shrubs and grasses in semi-arid Argentina

Cited by 63 publications

References 0 publications

Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical savanna

Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical savanna

Plant responses to precipitation in desert ecosystems: integrating functional types, pulses, thresholds, and delays

Tree–grass co-existence in savanna: Interactions of rain and fire

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