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SOIL WATER POTENTIAL AFFECTS CROP GROWTH RATE OF WHEAT TROUGH CHANGES IN LEAF AREA, NOT  PHOTOSYNTHESIS.   H.-T. Wang¹, O. Monje² and G.W. Stutte². ¹BioServe Space Technologies, Boulder, CO ²Dynamac Corporation, Kennedy Space Center, FL.

Plant growth conditions must be optimized for use in advanced life support systems during space flight. Wheat cv. Apogee was grown at three soil water potentials (y_s): –0.5 kPa, -0.3 kPa, and –0.1 kPa for 24 days. Measurements of leaf area and dry mass were made at 5, 9, 14 and 18 DAP and used to determine the leaf area index (LAI), net assimilation rate (NAR), and crop growth rate (CGR). y_s did not have a significant effect on plant development until after 9 DAP, at which time growth was affected by y_s. Plants grown at –0.1 kPa exhibited the largest CGR and LAI and had the greatest biomass, suggesting that –0.1 kPa was the optimal y_s. These results are in contrast to those observed with Superdwarf wheat. Growth analysis indicated that changes in CGR were due to changes in leaf area, rather than changes in photosynthesis. There was no significant difference between chlorophyll fluorescence measurements: Fv/Fm, qN and qP of plants grown at different y_s, which further indicated that y_s had little effect on photosynthesis. Slight differences in starch content of plants grown at different y_s were observed. This study provided baseline data characterizing the effect of y_s on wheat growth for the PESTO experiment. 

(This work was supported in part by NASA’s Fundamental Biology Program (NCC-0034) and Spaceflight and Life Sciences Training Program.)