JXB Advance Access originally published online on May 14, 2009
Journal of Experimental Botany 2009 60(8):2325-2339; doi:10.1093/jxb/erp123
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This article appears in the following Journal of Experimental Botany issue: Special Issue: Mesophyll conductance to CO2: mechanisms, modelling, and ecological implications [View the issue table of contents]
Responses of gm to Single Environmental Factors |
Leaf gas exchange, carbon isotope discrimination, and grain yield in contrasting rice genotypes subjected to water deficits during the reproductive stage
1Institute of Agro-Environmental and Forest Biology, National Research Council, Via Salaria km 29.300, I-00015 Monterotondo Scalo (RM), Italy
2Department of Forest Sciences and Resources, University of Tuscia, Via S. Camillo De Lellis s.n.c., I-01100, Viterbo, Italy
3Crop and Environmental Sciences Division, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines
* To whom correspondence should be addressed. E-mail: mauro.centritto{at}ibaf.cnr.it
Genotypic variations in leaf gas exchange and yield were analysed in five upland-adapted and three lowland rice cultivars subjected to a differential soil moisture gradient, varying from well-watered to severely water-stressed conditions. A reduction in the amount of water applied resulted in a significant decrease in leaf gas exchange and, subsequently, in above-ground dry mass and grain yield, that varied among genotypes and distance from the line source. The comparison between the variable J and the 
values in recently synthesized sugars methods, yielded congruent estimations of mesophyll conductance (gm), confirming the reliability of these two techniques. Our data demonstrate that gm is a major determinant of photosynthesis (A), because rice genotypes with inherently higher gm were capable of keeping higher A in stressed conditions. Furthermore, A, gs, and gm of water-stressed genotypes rapidly recovered to the well-watered values upon the relief of water stress, indicating that drought did not cause any lasting metabolic limitation to photosynthesis. The comparisons between the A/Ci and corresponding A/Cc curves, measured in the genotypes that showed intrinsically higher and lower instantaneous A, confirmed this finding. Moreover, the effect of drought stress on grain yield was correlated with the effects on both A and total diffusional limitations to photosynthesis. Overall, these data indicate that genotypes which showed higher photosynthesis and conductances were also generally more productive across the entire soil moisture gradient. The analysis of revealed a substantial variation of water use efficiency among the genotypes, both on the long-term (leaf pellet analysis) and short-term scale (leaf soluble sugars analysis).
Key words: Carbon isotope discrimination, drought stress, mesophyll conductance, Oryza sativa, photosynthesis, rice, water-use efficiency
Received 26 January 2009; Revised 23 March 2009 Accepted 24 March 2009