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Titolo:
Stable isotopes in ecosystem science: Structure, function and dynamics of a subtropical Savanna
Autore:
Boutton, TW; Archer, SR; Midwood, AJ;
Indirizzi:
Texas A&M Univ, Dept Rangeland Ecol & Management, College Stn, TX 77843 USA Texas A&M Univ College Stn TX USA 77843 gement, College Stn, TX 77843 USA Macaulay Land Use Res Inst, Aberdeen AB15 8QH, Scotland Macaulay Land Use Res Inst Aberdeen Scotland AB15 8QH AB15 8QH, Scotland
Titolo Testata:
RAPID COMMUNICATIONS IN MASS SPECTROMETRY
fascicolo: 13, volume: 13, anno: 1999,
pagine: 1263 - 1277
SICI:
0951-4198(1999)13:13<1263:SIIESS>2.0.ZU;2-R
Fonte:
ISI
Lingua:
ENG
Soggetto:
SOIL ORGANIC-MATTER; C-13 NATURAL ABUNDANCE; TERM FIELD EXPERIMENTS; AFRICAN HUMID SAVANNA; PROSOPIS-GLANDULOSA; WATER RELATIONS; VEGETATION CHANGE; CARBON ISOTOPES; WOODY-PLANTS; SOUTH TEXAS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
107
Recensione:
Indirizzi per estratti:
Indirizzo: Boutton, TW Texas A&M Univ, Dept Rangeland Ecol & Management, College Stn,TX 77843 USA Texas A&M Univ College Stn TX USA 77843 ege Stn, TX 77843 USA
Citazione:
T.W. Boutton et al., "Stable isotopes in ecosystem science: Structure, function and dynamics of a subtropical Savanna", RAP C MASS, 13(13), 1999, pp. 1263-1277

Abstract

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 beenutilized to document changes in ecosystem structure and function using a case study from a subtropical savanna ecosystem. Specifically, we demonstrate that: (1) delta(13)C values of soil organic carbon record a vegetation change in this ecosystem from C-4 grassland to C-3 woodland during the past 40-120 years, and (2) delta(2)H and delta(18)O 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(13)C values of plants and soils indicate that areas now dominated by C-3 subtropical thorn woodland were once C-4 grasslands. delta(13)C values of current organicmatter inputs from wooded landscape elements in this region are characteristic of C-3 plants (-28 to -25 parts per thousand), while those of the associated soil organic carbon are higher and range from -20 to -15 parts per thousand. Approximately 50-90% of soil carbon beneath the present C-3 woodlands is derived from C-4 grasses. A strong memory of the C-4 grasslands thatonce dominated this region is retained by delta(13)C values of organic carbon associated with fine and coarse clay fractions. When delta(13)C values are evaluated in conjunction with C-14 measurements of that same soil carbon, it appears that grassland-to-woodland conversion occurred largely withinthe 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 explorers. Concurrent changes in soil delta(13)C 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 C-4 grassland and the present C-3 woody vegetation. Present day woodlands have hydrologic characteristics fundamentally different from those ofthe 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(18)O and delta(2)H 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 reachof 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 this subtropical savanna. Stable isotopes provided direct, spatially explicit evidence for dramatic changes in ecosystem physiognomy and demonstrated some functional consequences for the hydrologic cycle. Furthermore, grassland-to-woodland conversion has been geographically extensive in the worlds' drylands, suggesting that these ecosystem-level changes in vegetation structure, carbon cycling, and hydrology may have implications for regional/global biogeochemistry and climate. Copyright (C) 1999 John Wiley & Sons, Ltd.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 30/11/20 alle ore 16:54:25