Plants and the Environment. Limitations to photosynthesis of lettuce grown under tropical conditions: alleviation by root-zone cooling

Author： He J.

Publisher： Oxford University Press

ISSN： 1460-2431

Source： Journal of Experimental Botany, Vol.52, Iss.359, 2001-06, pp. : 1323-1330

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Abstract

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 (g_s), midday leaf relative water content (RWC), and chlorophyll fluorescence ratio F_v/F_m than 20 °C-RZT plants on both sunny and cloudy days. Substantial midday depression of A and g_s occurred on both sunny and cloudy days in both RZT treatments, although F_v/F_m 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 (g_{s sat}) and photosynthetic CO₂ assimilation (A_sat) 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 (P_max), indicating non-stomatal limitation of photosynthesis. Tight temporal coupling of leaf nitrogen content and P_max during both temperature transfers suggested that decreased nutrient status caused this non-stomatal limitation of photosynthesis.