Leaf Expansion, Stomatal Conductance, and Transpiration of Vegetable Amaranth (Amaranthus sp.) in Response to Soil Drying

By Fulai Liu, H. Stützel. 2002

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This study was designed to quantify the responses of leaf expansion, stomatal conductance, and transpiration of four genotypes of vegetable amaranth (Amaranthus tricolor L. (Hin Choi), A. tricolor L. (Co. 2), A. blitum L. (WS80-192), and A. cruentus L. (RRC 1027)) to soil drying. Two greenhouse experiments were conducted during 1999 and 2000. Soil water status was expressed as the fraction of transpirable soil water (FTSW). Leaf expansion rates, stomatal conductances, and transpiration rates of the stressed plants were determined relative to those of nonstressed plants, and expressed as relative leaf expansion (RLE), relative stomatal conductance (RSC), and relative transpiration (RT), respectively. The rate of soil water extraction differed among genotypes, with RRC 1027 depleting soil water fastest and Hin Choi slowest. Whereas in 1999 all genotypes were equally efficient in soil water use, RRC 1027 extracted a greater volume of transpirable soil water than the other genotypes in 2000. The responses of RLE, RSC, and RT to FTSW were well described by linear-plateau models which allowed calculation of soil-water thresholds for leaf expansion (CL), stomatal conductance (CS), and transpiration (CT). Values for CL were higher than for CS and CT. CL was similar for the four genotypes in each year, whereas, CS and CT differed among genotypes. CS and CT was lowest for Hin Choi and highest for WS80-192. Differences of CL, CS, and CT between the two experiments might have been due to the different soils used in the experiments and the different evaporative demands during the drought cycles. Under drought stress, the reduction of transpiration of vegetable amaranth was due mainly to reduction of stomatal conductance, not to reduction of leaf expansion. The relative reduction of dry weight caused by drought stress was positively correlated with CS or CT across the four genotypes. Variation in CS and CT among amaranth genotypes revealed different responses to drought stress, which could make them suitable for different drought situations. Amaranths (Amaranthus L. sp.) are protein-rich, annual, herba- ceous dicotyledoneous plants of worldwide distribution (Martin and Telek, 1979). Their use as vegetables in tropical agriculture has been well documented (Martin and Ruberte, 1975). Like many C4 crops, amaranths flourish in warm, humid, sunny environments and have lower rates of water loss and greater water use efficiency than C3 plants, especially in dry conditions (Field and Mooney, 1986; Sage and Pearcy, 1987). Therefore, amaranth has often been described as a drought tolerant crop (Myers, 1996; Whitehead and Singh, 1992). However, no quantitative information is available about the re- sponses of leaf expansion, stomatal conductance, and transpiration of these species to soil water deficits. Also, little is known about possible genotypic differences in these traits and their relations to plant performance under drought stress. Therefore, the objectives of this study were to quantify sensitivity of leaf area expansion, stomatal conductance, and transpiration among four genotypes of vegetable amaranth to soil drying and to evaluate the importance of these responses for crop performance during soil drying.

Subfields: Global and Planetary Change, Plant Science

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