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Photosynthesis and Water Vapor Exchange of Pigeonpea Leaves in Response to Water Deficit and Recovery

Dep. of Agronomy, Cornell Univ., Ithaca, NY 14853
Dep. of Plant Science and Biochemistry, Univ. of the West Indies, St. Augustine, Trinidad

^* Corresponding author.

Pigeonpea [Cajanus cajan (L.) Millsp.; cv. UW-10], a crop being developed for use in low-rainfall environments, was studied during development of water stress and recovery after rewatering to determine the treatment effects on photosynthesis and leaf diffusive conductance. Plants were grown in a greenhouse and leaf gas exchange was measured at various photosynthetic photon flux densities during an 8-d period of water stress development and during an 18-d period of recovery following rewatering. Predawn total water potential (~w) declined by 1.0 MPa after 8 d of withholding water, whereas the pressure component of water potential (_p) remained positive due a decrease in the solute component of water potential (_p) from –1.2 to –1.7 MPa. During stress development, decreases in leaf diffusive conductance (g_L) occurred earlier than decreases in photosynthetic CO₂ exchange rate (CER), indicating that a water conservation mechanism was induced. Differences in g_L between unwatered and control plants were first detected at 5 d after withholding water. Differences in CER between control and unwatered plants were not detected until Day 8 of the treatment. As a result of these CER and g_L changes, the CO₂ concentration in the intercellular air space (C_i) decreased during the period from 5 to 8 d after withholding water. After rewatering, CER and gL slowly recovered over an 18-d period. It is concluded that pigeonpea responds to water stress by partially limiting the rate of water loss and maintaining a low CER, and it responds to rewatering by slowly recovering CER and g_L.

Key Words: Transpiration • Water stress • Drought acclimation • Osmotic adjustment • CO₂ exchange rate • Legume • Stomata • Cajanus cajan (L.) Millsp.

Joint contribution from the Dep. of Plant Science and Biochemistry, Univ. of the West Indies; and the Dep. of Agronomy, Cornell Univ. Supported in part by funds from National Science Foundation grant no. INT 8025 899 to T.L. Setter.

Received for publication February 25, 1987.