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Journal of Experimental Botany, Vol. 52, No. 359, pp. 1323-1330, June 1, 2001
© 2001 Oxford University Press

Original Papers

Limitations to photosynthesis of lettuce grown under tropical conditions: alleviation by root-zone cooling

J. He1,3, S.K. Lee1 and I.C. Dodd2

1 Natural Sciences Academic Group, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616
2 Department of Botany, The University of Queensland, St Lucia 4072, Australia

Aerial parts of lettuce plants were grown under natural tropical fluctuating ambient temperatures, but with their roots exposed to two different root-zone temperatures (RZTs): a constant 20 °C-RZT and a fluctuating ambient (A-) RZT from 23–40 °C. Plants grown at A-RZT showed lower photosynthetic CO2 assimilation (A), stomatal conductance (gs), midday leaf relative water content (RWC), and chlorophyll fluorescence ratio Fv/Fm than 20 °C-RZT plants on both sunny and cloudy days. Substantial midday depression of A and gs occurred on both sunny and cloudy days in both RZT treatments, although Fv/Fm did not vary diurnally on cloudy days. Reciprocal temperature transfer experiments investigated the occurrence and possible causes of stomatal and non-stomatal limitations of photosynthesis. For both temperature transfers, light-saturated stomatal conductance (gs sat) and photosynthetic CO2 assimilation (Asat) were highly correlated with each other and with midday RWC, suggesting that A was limited by water stress-mediated stomatal closure. However, prolonged growth at A-RZT reduced light- and CO2-saturated photosynthetic O2 evolution (Pmax), indicating non-stomatal limitation of photosynthesis. Tight temporal coupling of leaf nitrogen content and Pmax during both temperature transfers suggested that decreased nutrient status caused this non-stomatal limitation of photosynthesis.

Key words: Lactuca sativa L., root-zone temperature, photosynthetic CO2 assimilation, stomatal conductance, relative water content.


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L Qin, J He, S. Lee, and I. Dodd
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J. Exp. Bot., August 28, 2007; (2007) erm156v1.
[Abstract] [Full Text] [PDF]


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