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1

Digitale Medien

PLANT COMPETITION UNDERGROUND (1997)

Casper, Brenda B. ; Jackson, Robert B.

Palo Alto, Calif. : Annual Reviews

Annual Review of Ecology, Evolution, and Systematics 28 (1997), S. 545-570

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ISSN: 0066-4162

Quelle: Annual Reviews Electronic Back Volume Collection 1932-2001ff

Thema: Biologie

Notizen: Abstract Belowground competition occurs when plants decrease the growth, survival, or fecundity of neighbors by reducing available soil resources. Competition belowground can be stronger and involve many more neighbors than aboveground competition. Physiological ecologists and population or community ecologists have traditionally studied belowground competition from different perspectives. Physiologically based studies often measure resource uptake without determining the integrated consequences for plant performance, while population or community level studies examine plant performance but fail to identify the resource intermediary or mechanism. Belowground competitive ability is correlated with such attributes as root density, surface area, and plasticity either in root growth or in the properties of enzymes involved in nutrient uptake. Unlike competition for light, in which larger plants have a disproportionate advantage by shading smaller ones, competition for soil resources is apparently more symmetric. Belowground competition often decreases with increases in nutrient levels, but it is premature to generalize about the relative importance of above- and belowground competition across resource gradients. Although shoot and root competition are often assumed to have additive effects on plant growth, some studies provide evidence to the contrary, and potential interactions between the two forms of competition should be considered in future investigations. Other research recommendations include the simultaneous study of root and shoot gaps, since their closures may not occur simultaneously, and improved estimates of the belowground neighborhood. Only by combining the tools and perspectives from physiological ecology and population and community biology can we fully understand how soil characteristics, neighborhood structure, and global climate change influence or are influenced by plant competition belowground.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1146/annurev.ecolsys.28.1.545

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Digitale Medien

Root production and demography in a california annual grassland under elevated atmospheric carbon dioxide (2002)

Higgins, Paul A. T. ; Jackson, Robert B. ; Des Rosiers, Julia M. ; [weitere]

Oxford, UK : Blackwell Science Ltd

Global change biology 8 (2002), S. 0

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ISSN: 1365-2486

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie , Energietechnik , Geographie

Notizen: This study examined root production and turnover in a California grassland during the third year of a long-term experiment with ambient (LO) and twice-ambient atmospheric CO2 (HI), using harvests, ingrowth cores, and minirhizotrons. Based on one-time harvest data, root biomass was 32% greater in the HI treatment, comparable to the stimulation of aboveground production during the study year. However, the 30–70% increase in photosynthesis under elevated CO2 for the dominant species in our system is considerably larger than the combined increase in above and belowground biomass. One possible explanation is, increased root turnover, which could be a sink for the additional fixed carbon. Cumulative root production in ingrowth cores from both treatments harvested at four dates was 2–3 times that in the single harvested cores, suggesting substantial root turnover within the growing season. Minirhizotron data confirmed this result, demonstrating that production and mortality occurred simultaneously through much of the season. As a result, cumulative root production was 54%, 47% and 44% greater than peak standing root length for the no chamber (X), LO, and HI plots, respectively. Elevated CO2, however, had little effect on rates of turnover (i.e. rates of turnover were equal in the LO and HI plots throughout most of the year) and cumulative root production was unaffected by treatment. Elevated CO2 increased monthly production of new root length (59%) only at the end of the season (April–June) when root growth had largely ceased in the LO plots but continued in the HI plots. This end-of-season increase in production coincided with an 18% greater soil moisture content in the HI plots previously described. Total standing root length was not affected by CO2 treatment. Root mortality was unaffected by elevated CO2 in all months except April, in which plants grown in the HI plots had higher mortality rates. Together, these results demonstrate that root turnover is considerable in the grassland community and easily missed by destructive soil coring. However, increased fine root turnover under elevated CO2 is apparently not a major sink for extra photosynthate in this system.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00514.x

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Digitale Medien

Gas exchange and photosynthetic acclimation over subambient to elevated CO2 in a C3–C4 grassland (2001)

Anderson, Laurel J. ; Maherali, Hafiz ; Johnson, Hyrum B. ; [weitere]

Oxford, UK : Blackwell Science Ltd

Global change biology 7 (2001), S. 0

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ISSN: 1365-2486

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie , Energietechnik , Geographie

Notizen: Atmospheric CO2 (Ca) has risen dramatically since preglacial times and is projected to double in the next century. As part of a 4-year study, we examined leaf gas exchange and photosynthetic acclimation in C3 and C4 plants using unique chambers that maintained a continuous Ca gradient from 200 to 550 µmol mol−1 in a natural grassland. Our goals were to characterize linear, nonlinear and threshold responses to increasing Ca from past to future Ca levels. Photosynthesis (A), stomatal conductance (gs), leaf water-use efficiency (A/gs) and leaf N content were measured in three common species: Bothriochloa ischaemum, a C4 perennial grass, Bromus japonicus, a C3 annual grass, and Solanum dimidiatum, a C3 perennial forb. Assimilation responses to internal CO2 concentrations (A/Ci curves) and photosynthetically active radiation (A/PAR curves) were also assessed, and acclimation parameters estimated from these data. Photosynthesis increased linearly with Ca in all species (P 〈 0.05). S. dimidiatum and B. ischaemum had greater carboxylation rates for Rubisco and PEP carboxylase, respectively, at subambient than superambient Ca (P 〈 0.05). To our knowledge, this is the first published evidence of A up-regulation at subambient Ca in the field. No species showed down-regulation at superambient Ca. Stomatal conductance generally showed curvilinear decreases with Ca in the perennial species (P 〈 0.05), with steeper declines over subambient Ca than superambient, suggesting that plant water relations have already changed significantly with past Ca increases. Resource-use efficiency (A/gs and A/leaf N) in all species increased linearly with Ca. As both C3 and C4 plants had significant responses in A, gs, A/gs and A/leaf N to Ca enrichment, future Ca increases in this grassland may not favour C3 species as much as originally thought. Non-linear responses and acclimation to low Ca should be incorporated into mechanistic models to better predict the effects of past and present rising Ca on grassland ecosystems.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1354-1013.2001.00438.x

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4

Digitale Medien

Groundwater use and salinization with grassland afforestation (2004)

Jobbágy, Esteban G. ; Jackson, Robert B.

Oxford, UK : Blackwell Science Ltd

Global change biology 10 (2004), S. 0

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ISSN: 1365-2486

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie , Energietechnik , Geographie

Notizen: Vegetation changes, particularly transitions between tree- and grass-dominated states, can alter ecosystem water balances and soluble salt fluxes. Here we outline a general predictive framework for understanding salinization of afforested grasslands based on biophysical, hydrologic, and edaphic factors. We tested this framework in 20 paired grassland and adjacent afforested plots across ten sites in the Argentine Pampas. Rapid salinization of groundwater and soils in afforested plots was associated with increased evapotranspiration and groundwater consumption by trees, with maximum salinization occurring on intermediately textured soils. Afforested plots (10–100 ha in size) showed 4–19-fold increases in groundwater salinity on silty upland soils but 〈twofold increases on clay loess soils and sand dunes. Two years of salinity and groundwater measurements at a 40 ha Eucalyptus camaldulensis plantation revealed that the plantation reduced groundwater recharge, underwent groundwater discharge on 〉50% of the days, and depressed the water table 38 cm on average compared to the adjacent grassland. Soil cores and vertical electrical soundings indicated that ≈6 kg m−2 of salts accumulated close to the water table and suggested that salinization resulted from the exclusion of fresh groundwater solutes by tree roots. Groundwater use with afforestation in the Pampas and in other regions around the world can enhance primary production and provide a tool for flood control. However, our framework and experimental data also suggest that afforestation can compromise the quality of soils and water resources in predictable ways based on water use, climate, and soil texture.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-2486.2004.00806.x

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5

Digitale Medien

Ecosystem carbon loss with woody plant invasion of grasslands (2002)

Banner, Jay L. ; Jobbágy, Esteban G. ; Pockman, William T. ; [weitere]

[s.l.] : Macmillian Magazines Ltd.

Nature 418 (2002), S. 623-626

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ISSN: 1476-4687

Quelle: Nature Archives 1869 - 2009

Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik

Notizen: [Auszug] The invasion of woody vegetation into deserts, grasslands and savannas is generally thought to lead to an increase in the amount of carbon stored in those ecosystems. For this reason, shrub and forest expansion (for example, into grasslands) is also suggested to be a substantial, if uncertain, ...

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1038/nature00910

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6

Digitale Medien

Nonlinear grassland responses to past and future atmospheric CO 2 (2002)

Polley, H. Wayne ; Johnson, Hyrum B. ; Anderson, Laurel J. ; [weitere]

[s.l.] : Macmillian Magazines Ltd.

Nature 417 (2002), S. 279-282

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ISSN: 1476-4687

Quelle: Nature Archives 1869 - 2009

Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik

Notizen: [Auszug] Carbon sequestration in soil organic matter may moderate increases in atmospheric CO2 concentrations (Ca) as Ca increases to more than 500 µmol mol-1 this century from interglacial levels of less than ...

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1038/417279a

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7

Digitale Medien

The fate of carbon in grasslands under carbon dioxide enrichment (1997)

Holland, Elisabeth A. ; Jackson, Robert B. ; Chapin, F. Stuart ; [weitere]

[s.l.] : Macmillan Magazines Ltd.

Nature 388 (1997), S. 576-579

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ISSN: 1476-4687

Quelle: Nature Archives 1869 - 2009

Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik

Notizen: [Auszug] The concentration of carbon dioxide (CO2) in the Earth's atmosphere is rising rapidly, with the potential to alter many ecosystem processes. Elevated CO2 often stimulates photosynthesis, creating the possibility that the terrestrial biosphere will sequester carbon in ...

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1038/388576a0

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8

Digitale Medien

Elevated CO2 increases belowground respiration in California grasslands (1996)

Luo, Yiqi ; Jackson, Robert B. ; Field, Christopher B. ; [weitere]

Springer

Oecologia 108 (1996), S. 130-137

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ISSN: 1432-1939

Schlagwort(e): Carbon cycle ; Ecosystem ; Global change ; Respiration

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract This study was designed to identify potential effects of elevated CO2 on belowground respiration (the sum of root and heterotrophic respiration) in field and microcosm ecosystems and on the annual carbon budget. We made three sets of respiration measurements in two CO2 treatments, i.e., (1) monthly in the sandstone grassland and in microcosms from November 1993 to June 1994; (2) at the annual peak of live biomass (March and April) in the serpentine and sandstone grasslands in 1993 and 1994; and (3) at peak biomass in the microcosms with monocultures of seven species in 1993. To help understand ecosystem carbon cycling, we also made supplementary measurements of belowground respiration monthly in sandstone and serpentine grasslands located within 500 m of the CO2 experiment site. The seasonal average respiration rate in the sandstone grassland was 2.12 μmol m-2 s-1 in elevated CO2, which was 42% higher than the 1.49 μmol m-2 s-1 measured in ambient CO2 (P=0.007). Studies of seven individual species in the microcosms indicated that respiration was positively correlated with plant biomass and increased, on average, by 70% with CO2. Monthly measurements revealed a strong seasonality in belowground respiration, being low (0–0.5 μmol CO2 m-2 s-1 in the two grasslands adjacent to the CO2 site) in the summer dry season and high (2–4 μmol CO2 m-2 s-1 in the sandstone grassland and 2–7 μmol CO2 m-2 s-1 in the microcosms) during the growing season from the onset of fall rains in November to early spring in April and May. Estimated annual carbon effluxes from the soil were 323 and 440 g C m-2 year-1 for the sandstone grasslands in ambient and elevated CO2. That CO2-stimulated increase in annual soil carbon efflux is more than twice as big as the increase in aboveground net primary productivity (NPPa) and approximately 60% of NPPa in this grassland in the current CO2 environment. The results of this study suggest that below-ground respiration can dissipate most of the increase in photosynthesis stimulated by elevated CO2.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00333224

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9

Digitale Medien

Detecting changes in soil carbon in CO2 enrichment experiments (1995)

Hungate, Bruce A. ; Jackson, Robert B. ; Field, Christopher B. ; [weitere]

Springer

Plant and soil 187 (1995), S. 135-145

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ISSN: 1573-5036

Schlagwort(e): annual grassland ; carbon-13 ; carbon dioxide ; carbon storage ; serpentine soil ; soil carbon ; statistical power

Quelle: Springer Online Journal Archives 1860-2000

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Abstract After four growing seasons, elevated CO2 did not significantly alter surface soil C pools in two intact annual grasslands. However, soil C pools in these systems are large compared to the likely changes caused by elevated CO2. We calculated statistical power to detect changes in soil C, using an approach applicable to all elevated CO2 experiments. The distinctive isotopic signature of the fossil-fuel-derived CO2 added to the elevated CO2 treatment provides a C tracer to determine the rate of incorporation of newly-fixed C into soil. This rate constrains the size of the possible effect of eievated CO2 on soil C. Even after four years of treatment, statistical power to detect plausible changes in soil C under elevated CO2 is quite low. Analysis of other elevated CO2 experiments in the literature indicates that either CO2 does not affect soil C content, or that reported CO2 effects on soil C are too large to be a simple consequence of increased plant carbon inputs, suggesting that other mechanisms are involved, or that the differences are due to chance. Determining the effects of elevated CO2 on total soil C and long-term C storage requires more powerful experimental techniques or experiments of longer duration.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00017086

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