Search Results - (Author, Cooperation:G. J. Collatz)

2014-11-21

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Agriculture/*methods/*statistics & numerical data ; Atmosphere/*chemistry ; Biomass ; Biota ; *Carbon Cycle ; Carbon Dioxide/*analysis/metabolism ; Climate Change/statistics & numerical data ; Crops, Agricultural/growth & development/metabolism ; Efficiency ; Factor Analysis, Statistical ; Geography ; Hawaii ; *Seasons

2011-11-15

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2012-09-01

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 Dioxide/*analysis ; *Climate Change

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract. A new model of photosynthesis published recently in this journal (H. Farazdaghi & G. E. Edwards, Plant, Cell and Environment (1988) 11, 789–798; 799–809) clams to have a more complete mechanistic basis than currently used models based on the paper of G. D. Farquhar, S. von Caemmerer & J. A. Berry (Planta (1980) 149, 78–90). In this paper, we examine the validity of the new kinetic expression for the rate of CO2 fixation by Rubisco, and the derivation of an equation for photosynthetic CO2 assimilation as a function of light intensity and CO2 concentration presented in the new model. In addition, we compare measured response curve of photosynthesis to CO2 and light with simulated curves using alternative models. We conclude that the new model is mechanistically misleading and, empirically, overestimates the extent to which light and CO2 co-limit the rate of photosynthesis under most physiological conditions.

Electronic Resource

1365-2486

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Energy, Environment Protection, Nuclear Power Engineering

Geography

Human modification of the landscape potentially affects exchanges of energy and water between the terrestrial biosphere and the atmosphere. This study develops a possible scenario for land cover in the year 2050 based on results from the IMAGE 2 (Integrated Model to Assess the Greenhouse Effect) model, which projects land-cover changes in response to demographic and economic activity. We use the land-cover scenario as a surface boundary condition in a biophysically-based land-surface model coupled to a general circulation model for a 15-years simulation with prescribed sea surface temperature and compare with a control run using current land cover. To assess the sensitivity of climate to anthropogenic land-cover change relative to the sensitivity to decadal-scale interannual variations in vegetation density, we also carry out two additional simulations using observed normalized difference vegetation index (NDVI) from relatively low (1982–83) and high (1989–90) years to describe the seasonal phenology of the vegetation.In the past several centuries, large-scale land-cover change occurred primarily in temperate latitudes through conversion of forests and grassland to highly productive cropland and pasture. Several studies in the literature indicate that past changes in surface climate resulting from this conversion had a cooling effect owing to changes in vegetation morphology (increased albedo). In contrast, this study indicates that future land-cover change, likely to occur predominantly in the tropics and subtropics, has a warming effect governed by physiological rather than morphological mechanisms. The physiological mechanism is to reduce carbon assimilation and consequently latent relative to sensible heat flux resulting in surface temperature increases up to 2 °C and drier hydrologic conditions in locations where land cover was altered in the experiment. In addition, in contrast to an observed decrease in diurnal temperature range (DTR) over land expected with greenhouse warming, results here suggest that future land-cover conversion in tropics could increase the DTR resulting from decreased evaporative cooling during the daytime. For grid cells with altered land cover, the sensitivity of surface temperature to future anthropogenic land-cover change is generally within the range induced by decadal-scale interannual variability in vegetation density in temperate latitudes but up to 1.5 °C warmer in the tropics.

Electronic Resource

1432-2048

Gas exchange ; Oxygen inhibition ; Photorespiration ; Photosynthesis ; Simmondsia ; Water stress

Springer Online Journal Archives 1860-2000

Biology

Abstract The response of net photosynthesis and apparent light respiration to changes in [O2], light intensity, and drought stress was determined by analysis of net photosynthetic CO2 response curves. Low [O2] treatment resulted in a large reduction in the rate of photorespiratory CO2 evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating [CO2]. These results indicate that [CO2], [O2] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO2 uptake decreased in low [O2] and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO2 compensation point or the [CO2] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.

Electronic Resource