Effect of atmospheric concentration of water vapour and CO2 in determining transpiration-photosynthesis relationships of cotton leaves

✍ Scribed by J.F Bierhuizen; R.O Slatyer

• Publisher: Elsevier Science
• Year: 1965
• Weight: 685 KB
• Volume: 2
• Category: Article
• ISSN: 0002-1571
• DOI: 10.1016/0002-1571(65)90012-9

✦ Synopsis

Transpiration (E) and apparent photosynthesis (A) relationships of cotton leaves were examined under a range of light intensities (1,000-6,000 fc.), CO2 concentrations (0.02-0.2~ CO2), air temperatures (30-40°C), relative humidities (40-80~o) and windspeeds (0.6-3.1 cm/sec).

The ratio E/A (g of water transpired per gram carbohydrate produced) was observed to increase linearly with leaf-air vapour pressure difference, values ranging from about 100-500 as Ae increased from about 5 to 25 mm Hg, and to decrease with increasing light intensity and decreasing windspeed. With other conditions held constant, the ratio declined rapidly as COs concentration was increased, approaching minimum values of less than 100 when CO s was no longer limiting photosynthesis.

Under conditions of CO2 limitation, the leaf-air water-vapour pressure (Ae) and CO s concentration (Av) differences and the diffusive resistances in the water vapour (Zr), and CO~ (Zr') pathways adequately accounted for variation in observed values of E/A and enabled reasonable predictions of E/A to be made of any given Ae or Av.

Under natural conditions, the small amount of variability expected in (Zr'/Zr) and Av for any one crop suggests that, as a first approximation, variability in E/A from region to region is due largely to variability in Ae. This proposition is well supported by data from a number of crops in different climatic zones.