Microorganisms upon Plant Growth 



251 



Since tlu' soluhlc niatcrials toud to Ic^acli from the soil, this process 

 fax'ors conscr\ation of the nutrients in tlie soil in the absence of a 

 growing crop. 



Under certain conditions, microorganisms reduce various oxidized 



450 



400 



S 350 



w 300 



250 



I 200 



150 



100 



I I Average effects of all plants 



■■■ Average effects of individual plants 



2258,1 _^ 



527.4 ^IL. I 



530.6— ' 

 609 7 — 



m 



Q- u~) ca u<ri— OS 

 Colonies of 

 radiobacter 



Fig. 100. 



Carbon dioxide 

 evolved 



Influence of plants upon the growth and acthities of bacteria in soil 

 (from Starkey). 



substances, hke sulfates and nitrates, to substances which may be 

 to.xic to higher plants or which result in losses of available elements. 

 Microorganisms enter into various associations with plants that 

 are highly important in the growth of the plants. The growth of 

 leguminous plants is directly affected by the symbiotic nodule-form- 

 ing bacteria, making these plants independent of the supply of soil 

 nitrogen. The growth of many trees and other plants depends largely 

 upon the fungi that form mycorrhiza on their roots. This represents 



