Search Results - (Author, Cooperation:B. A. Hungate)

2014-04-26

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Atmosphere/*chemistry ; *Carbon Cycle ; Carbon Dioxide/*chemistry ; Climate Change ; Soil/*chemistry

2012-06-09

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; *Biodiversity ; Ecology ; *Ecosystem ; *Extinction, Biological ; Models, Biological

2011-07-15

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Atmosphere/*chemistry ; Carbon Dioxide/*analysis/metabolism ; Ecosystem ; Gases/*analysis ; Global Warming/statistics & numerical data ; *Greenhouse Effect/statistics & numerical data ; Methane/*analysis ; Nitrous Oxide/*analysis ; Oryza/growth & development ; Soil/analysis/*chemistry ; Wetlands

2018-04-03

The American Society for Microbiology (ASM)

0099-2240

1098-5336

Biology

2018-08-23

American Association for the Advancement of Science (AAAS)

2375-2548

Natural Sciences in General

1365-2486

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Energy, Environment Protection, Nuclear Power Engineering

Geography

Elevated atmospheric carbon dioxide (Ca) usually reduces stomatal conductance, but the effects on plant transpiration in the field are not well understood. Using constant-power sap flow gauges, we measured transpiration from Quercus myrtifolia Willd., the dominant species of the Florida scrub-oak ecosystem, which had been exposed in situ to elevated Ca (350 µmol mol−1 above ambient) in open-top chambers since May 1996. Elevated Ca reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively. Temporarily reversing the Ca treatments showed that at least part of the reduction in transpiration was an immediate, reversible response to elevated Ca. However, there was also an apparent indirect effect of Ca on transpiration: when transpiration in all plants was measured under common Ca, transpiration in elevated Ca-grown plants was lower than that in plants grown in normal ambient Ca. Results from measurements of stomatal conductance (gs), leaf area index (LAI), canopy light interception and correlation between light and gs indicated that the direct, reversible Ca effect on transpiration was due to changes in gs caused by Ca, and the indirect effect was caused mainly by greater self-shading resulting from enhanced LAI, not from stomatal acclimation. By reducing light penetration through the canopy, the enhanced self-shading at elevated Ca decreased stomatal conductance and transpiration of leaves at the middle and bottom of canopy. This self-shading mechanism is likely to be important in ecosystems where LAI increases in response to elevated Ca.

Electronic Resource

1365-2486

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Energy, Environment Protection, Nuclear Power Engineering

Geography

Leaf conductance often decreases in response to elevated atmospheric CO2 concentration (Ca) potentially leading to changes in hydrology. We describe the hydrological responses of Florida scrub oak to elevated Ca during an eight-month period two years after Ca manipulation began. Whole-chamber gas exchange measurements revealed a consistent reduction in evapotranspiration in response to elevated Ca, despite an increase in leaf area index (LAI). Elevated Ca also increased surface soil water content, but xylem water deuterium measurements show that the dominant oaks in this system take up most of their water from the water table (which occurs at a depth of 1.5–3 m), suggesting that the water savings in elevated Ca in this system are primarily manifested as reduced water uptake at depth. Extrapolating these results to larger areas requires considering a number of processes that operate on scales beyond these accessible in this field experiment. Nevertheless, these results demonstrate the potential for reduced evapotranspiration and associated changes in hydrology in ecosystems dominated by woody vegetation in response to elevated Ca.

Electronic Resource

1432-1939

Key words Elevated CO2 ; Soil food web ; Community structure ; Nematodes ; Protozoa

Springer Online Journal Archives 1860-2000

Biology

Abstract  We measured soil bacteria, fungi, protozoa, nematodes, and biological activity in serpentine and sandstone annual grasslands after 4 years of exposure to elevated atmospheric CO2. Measurements were made during the early part of the season, when plants were in vegetative growth, and later in the season, when plants were approaching their maximum biomass. In general, under ambient CO2, bacterial biomass, total protozoan numbers, and numbers of bactivorous nematodes were similar in the two grasslands. Active and total fungal biomasses were higher on the more productive sandstone grassland compared to the serpentine. However, serpentine soils contained nearly twice the number of fungivorous nematodes compared to the sandstone, perhaps explaining the lower standing crop of fungal biomass in the serpentine and suggesting higher rates of energy flow through the fungal-based soil food web. Furthermore, root biomass in the surface soils of these grasslands is comparable, but the serpentine contains 6 times more phytophagous nematodes compared to the sandstone, indicating greater below-ground grazing pressure on plants in stressful serpentine soils. Elevated CO2 increased the biomass of active fungi and the numbers of flagellates in both grasslands during the early part of the season and increased the number of phytophagous nematodes in the serpentine. Elevated CO2 had no effect on the total numbers of bactivorous or fungivorous nematodes, but decreased the diversity of the nematode assemblage in the serpentine at both sampling dates. Excepting this reduction in nematode diversity, the effects of elevated CO2 disappeared later in the season as plants approached their maximum biomass. Elevated CO2 had no effect on total and active bacterial biomass, total fungal biomass, or the total numbers of amoebae and ciliates in either grassland during either sampling period. However, soil metabolic activity was higher in the sandstone grassland in the early season under elevated CO2, and elevated CO2 altered the patterns of use of individual carbon substrates in both grasslands at this time. Rates of substrate use were also significantly higher in the sandstone, indicating increased bacterial metabolic activity. These changes in soil microbiota are likely due to an increase in the flux of carbon from roots to soil in elevated CO2, as has been previously reported for these grasslands. Results presented here suggest that some of the carbon distributed below ground in response to elevated CO2 affects the soil microbial food web, but that these effects may be more pronounced during the early part of the growing season.

Electronic Resource

1432-1939

Key words N mineralization ; Elevated CO2 ; Annual grasslands ; Soil moisture

Springer Online Journal Archives 1860-2000

Biology

Abstract  Nitrogen (N) limits plant growth in many terrestrial ecosystems, potentially constraining terrestrial ecosystem response to elevated CO2. In this study, elevated CO2 stimulated gross N mineralization and plant N uptake in two annual grasslands. In contrast to other studies that have invoked increased C input to soil as the mechanism altering soil N cycling in response to elevated CO2, increased soil moisture, due to decreased plant transpiration in elevated CO2, best explains the changes we observed. This study suggests that atmospheric CO2 concentration may influence ecosystem biogeochemistry through plant control of soil moisture.

Electronic Resource