AOBPreview originally published online on June 15, 2007
Annals of Botany 2007 100(2):335-345; doi:10.1093/aob/mcm113
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Leaf Water Relations and Net Gas Exchange Responses of Salinized Carrizo Citrange Seedlings during Drought Stress and Recovery
1 University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
2 Departament of Citriculture, IMIDA, 30150 La Alberca, Murcia, Spain
3 Centro de Edafologia y Biologia Aplicada del Segura, CSIC, Campus Universitario de Espinardo, 30100, Murcia, Spain
* For correspondence. E-mail JMSN{at}ufl.edu
Received: 22 January 2007 Returned for revision: 19 February 2007 Accepted: 27 April 2007 Published electronically: 15 June 2007
Background and Aims: Since salinity and drought stress can occur together, an assessment was made of their interacting effects on leaf water relations, osmotic adjustment and net gas exchange in seedlings of the relatively chloride-sensitive Carrizo citrange, Citrus sinensis x Poncirus trifoliata.
Methods: Plants were fertilized with nutrient solution with or without additional 100 mM NaCl (salt and no-salt treatments). After 7 d, half of the plants were drought stressed by withholding irrigation water for 10 d. Thus, there were four treatments: salinized and non-salinized plants under drought-stress or well-watered conditions. After the drought period, plants from all stressed treatments were re-watered with nutrient solution without salt for 8 d to study recovery. Leaf water relations, gas exchange parameters, chlorophyll fluorescence, proline, quaternary ammonium compounds and leaf and root concentrations of Cl– and Na+ were measured.
Key Results: Salinity increased leaf Cl– and Na+ concentrations and decreased osmotic potential (
) such that leaf relative water content (RWC) was maintained during drought stress. However, in non-salinized drought-stressed plants, osmotic adjustment did not occur and RWC decreased. The salinity-induced osmotic adjustment was not related to any accumulation of proline, quaternary ammonium compounds or soluble sugars. Net CO2 assimilation rate (ACO2) was reduced in leaves from all stressed treatments but the mechanisms were different. In non-salinized drought-stressed plants, lower ACO2 was related to low RWC, whereas in salinized plants decreased ACO2 was related to high levels of leaf Cl– and Na+. ACO2 recovered after irrigation in all the treatments except in previously salinized drought-stressed leaves which had lower RWC and less chlorophyll but maintained high levels of Cl–, Na+ and quaternary ammonium compounds after recovery. High leaf levels of Cl– and Na+ after recovery apparently came from the roots.
Conclusions: Plants preconditioned by salinity stress maintained a better leaf water status during drought stress due to osmotic adjustment and the accumulation of Cl– and Na+. However, high levels of salt ions impeded recovery of leaf water status and photosynthesis after re-irrigation with non-saline water.
Key words: Carrizo citrange, citrus, Cl–, Na+, salt stress, drought stress, proline, carbohydrates
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