FACTORS AFFECTING SALT ABSORPTION 



51 



4 6 8 10 



Oxygen pressure. % 



100 



o 



E 



00-1 



3-0 100 



0-6 1-2 1-6 2-5 



Oxygen pressure, % 



Fig. 16. Oxygen pressure and salt absorption 

 a. Relationship between oxygen pressure and the potassium content of 

 excised tomato roots (O — O) and excised rice roots (□ — D) (redrawn from 

 Vlamis and Davis, 1944); b. Relationship between oxygen pressure and 

 phosphate absorption by excised barley roots in solutions of phosphate 

 (1 X 10- 4 M) at pH 4 (redrawn from Hopkins, 1956). 



4. Carbon dioxide and Bicarbonate Ion Concentration 



The dependence of salt absorption in green plants on photo- 

 synthesis has already been mentioned. In the absence of carbon 

 dioxide, uptake of salt is gradually inhibited, as respiratory sub- 

 strates become depleted. 



Dark fixation of carbon dioxide in non-green tissues has an 



