Computer Science
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997adspr..20.1869c&link_type=abstract
Advances in Space Research, Volume 20, Issue 10, p. 1869-1877.
Computer Science
5
Scientific paper
A 34-day functional test was conducted in Johnson Space Center's Variable Pressure Growth Chamber (VPGC) to determine responses of a wheat stand to reduced pressure (70 kPa) and modified partial pressures of carbon dioxide and oxygen. Reduced pressure episodes were generally six to seven hours in duration, were conducted at reduced ppO_2 (14.7 kPa), and were interrupted with longer durations of ambient pressure (101 kPa). Daily measurements of stand net photosynthesis (Pn) and dark respiration (DR) were made at both pressures using a ppCO_2 of 121 Pa. Corrections derived from leakage tests were applied to reduced pressure measurements. Rates of Pn at reduced pressure averaged over the complete test were 14.6 % higher than at ambient pressure, but rates of DR were unaffected. Further reductions in ppO_2 were achieved with a molecular sieve and were used to determine if Pn was enhanced by lowered O_2 or by lowered pressure. Decreased ppO_2 resulted in enhanced rates of Pn, regardless of pressure, but the actual response was dependent on the ratio of ppO_2/ppCO_2. Over the range of ppO_2/ppCO_2 of 80 to 200, the rate of Pn declined linearly. Rate of DR was unaffected over the same range and by dissolved O_2 levels down to 3.1 ppm, suggesting that normal rhizosphere and canopy respiration occur at atmospheric ppO_2 levels as low as 11 kPa. Partial separation of effects attributable to oxygen and those related to reduced pressure (e.g. enhanced diffusion of CO_2) was achieved from analysis of a CO_2 drawdown experiment. Results will be used for design and implementation of studies involving complete crop growth tests at reduced pressure.
Barta D. J.
Corey Kenneth A.
Henninger Donald L.
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