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Effect of Water Stress on Photosynthesis and Transpiration of Flag Leaves and Spikes of Barley and Wheat 1
Author(s) -
Johnson R. R.,
Frey N. M.,
Moss Dale N.
Publication year - 1974
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1974.0011183x001400050035x
Subject(s) - transpiration , photosynthesis , flag (linear algebra) , hordeum vulgare , biology , water stress , agronomy , horticulture , botany , poaceae , mathematics , pure mathematics , algebra over a field
‘Dickson’ barley ( Hordeum vulgare L.) and ‘Era’ wheat ( Triticum aestivum L.) were grown in a growth chamber in 25‐cm diameter ✕ 29‐cm deep plastic pots. Starting 7 days after the spike emerged from the flag leaf sheath, water was withheld for up to 7 days, during which time flag leaf water potentals fell as low as −33 bars. Rates of net photosynthesis and transpiration of both flag leaves and awned spikes decreased linearly with decreasing flag leaf water potential. Net photosynthesis reached zero in the flag leaves and spikes of each species when the leaf water potentials reached −31 to −33 bars. Flag leaf transpiration reached zero at −28 bars in both barley and wheat, and linear regression equations predicted that spike transpiration would reach zero at −39 and −31 bars in barley and wheat, respectively. Barley spikes possessed a greater amount of awn tissue and had higher net photosynthetic and transpiration rates than did wheat spikes. A significant linear relationship existed between ribulose 1,5‐diphosphate (RudP) carboxylase activity and flag leaf water potential for flag leaves and awns of both varieties. Photosynthetic rates decreased to zero at −33 bars while substantial RudP carboxylase activity remained in all tissues. If in vivo RudP carboxylase activities are comparable to the in vitro rates measured, this enzyme did not likely limit photosynthesis at low water potentials. The rapid and severe stress imposed in this growth chamber experment similarly affected the potosynthetic process of both awned spikes and flag leaves of wheat and barley. The time course of the development of severe stress in plants growing in the field may be quite different, however, than for potted plants. Thus, if awned spikes have an advantage in drought situations in the field, it is probably related to their recovery or survival capability and not to differences in the way water stress affects photosynthesis in awns compared to leaves.