ELEVATED CO2 INFLUENCES SALT TOLERANCE OF RICE

Authors: Wilson, Clyde; Liu, Xuan; Zeng, Linghe

Submitted to: Proceedings of the International Salinity Forum
Publication Type: Proceedings
Publication Acceptance Date: 4/11/2005
Publication Date: 4/25/2005
Citation: Wilson, C., Liu, X., Zeng, L. 2005. Elevated CO2 influences salt tolerance of rice. In: Proceedings of the International Salinity Forum, Managing Saline Soils and Water: Science, Technology, and Soil Issues. April 25-27, 2005. Riverside, CA pp:481-484.

Interpretive Summary: Due to increases in global population, world agriculture must produce a greater yield per unit land area than ever before. The Food and Agriculture Organization (FAO) has estimated that as much as 50% of the increase in global food production in the latter half of the twentieth century is attributable to the expansion of irrigation. Some have estimated that 20 to 30 million hectacres are affected seriously affected by salt. At present, more agricultural land is not being irrigated due to salinity problems than there is new land coming under irrigation. Another concern is that high-quality water needed for irrigated agriculture is becoming increasingly scarce due to changing environmental standards and rising demands from urban areas. Unlike most toxins or herbicides, salinity has no specific cellular target in plants. Thus, most of the early work on salinity focused on the manifestations of salt-stress. The mechanisms, to large extent, remain unknown. Early work suggested that sugar levels did not limit growth of plants in saline environments. However, further studies demonstrated elevated CO2 levels could enhance partially reverse growth reduction brought about by salt stress. This reversal if brought about mainly by increased tiller formation. Our work demonstrates that a salt-sensitive grass, rice, grown under saline conditions responds to elevated CO2 levels the same way as tolerant wheat. These results are important in light of the recent findings that the gene content and gene order is highly conserved among different grass genomes. Since rice and wheat seem to respond similarly to that elevated CO2 levels, the use of elevated CO2 levels may be a useful tool to identify useful salt-tolerant traits. Thus, once plant breeders map a useful trait in wheat, they could use that information to search for the similar genes in rice.

Technical Abstract: Salt-sensitive rice plants (cultivar 'M202') were grown in SPAR chambers at 350 ppm and 800 ppm CO2. Plants were grown in buckets filled with sand and Yoshida nutrient solution. For salt treatments, NaCl and CaCl2 were added (5:1 on a molar basis) to the Yoshida solution to achieve salinities of EC 3.9 and 6.5. The Yoshida solution without adding salts (EC = 0.9) was used as the control. Salinity significantly (P=0.05) reduced leaf area, leaf dry weight, stem dry weight, root dry weight, and tiller number for both 350-ppm and 800-ppm grown plants. Elevated-CO2 treatment partly overcame these reductions. Under salt stress, the 800-ppm grown plants had significantly higher leaf area, leaf dry weight, stem dry weight, root dry weight, and tiller numbers compared to the 350-ppm-grown salt-stressed plants. Despite continued growth at elevated CO2, the 800-ppm plants displayed a higher net photosynthetic rate compared to 350 ppm plants which may account for the increases described. However, elevated CO2 significantly (P=0.05) reduced leaf stomatal conductance and leaf transpiration rate of the salt-stressed rice relative to 350 ppm controls. Thus, it is also possible that elevated CO2 partially ameliorated salinity stress by reducing the salt load. A morphological component for the partial alleviation of salinity stress with elevated CO2 might be tillering. The physiological basis of the partial alleviation of salinity stress at the elevated CO2 is still unknown.