title: Limitations to photosynthesis of lettuce grown under tropical conditions: alleviation by root-zone cooling.
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 degrees C-RZT and a fluctuating ambient (A-) RZT from 23-40 degrees 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 degrees 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 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 (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 (Pmax), 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.
authors: Natural Sciences Academic Group, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616. jhe@nie.edu.sg
authors: J
authors: J
authors: He
authors: S K
authors: SK
authors: Lee
authors: I C
authors: IC
authors: Dodd
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D005453:Fluorescence; D018545:Lactuca / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D009997:Osmotic Pressure; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D018517:Plant Roots / Q000502:physiology*; D018520:Plant Shoots / Q000502:physiology / Q000528:radiation effects; D013696:Temperature; D014329:Tropical Climate; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D009584:Nitrogen; D010100:Oxygen