SECTION VI 



OPTIMUM NUTRIENT SOLUTION AND GROWTH 



CONDITIONS FOR THE LABORATORY CULTURE OF 



NUISANCE MACROPHYTES 



Successful laboratory studies of the nutrition and 

 physiology of any plant are facilitated by the avail- 

 ability of a suitable nutrient culture medium and know- 

 ledge of optimum growth conditions. A satisfactory 

 culture medium is one in which essential elements do not 

 become growth limiting during extended culture periods, 

 total salt concentration and concentrations of heavy metals 

 are below toxic levels, and the pH remains within a suit- 

 able range as plants absorb nutrients from the medium. 



Several procedures have been used in formulating nutrient 

 media, including approximation of proportions of the 

 essential elements in soil extracts, determining the amounts 

 of elements taken up from nutrient solutions , and by 

 measuring responses to systematic variations in the con- 

 centrations of individual elements in a medium. 



Relatively little laboratory work has been carried out in 

 which macrophytes have been cultured in synthetic media 

 (Bourn, 1932) . In studies prior to this project, it had 

 been established that macrophytes made reasonably satis- 

 factory growth in a modified Hoaglands solution (Gerloff 

 and Krombholz, 1966), a medium used for many years in 

 laboratory and greenhouse studies with crop plants. The 

 modified Hoagland's medium was used in the studies pre- 

 sented in Section IV of this report. Systematic varia- 

 tions of the concentrations of each essential element in 

 these experiments made it possible to estimate the mini- 

 mum concentration of each element in a culture medium 

 for optimum growth of the macrophytes under study. The 

 formulation of a culture medium based on these optimum 

 concentrations was suggested. In Section VI experiments 

 will be discussed in which this medium was systematically 

 varied to develop a general macrophyte nutrient culture 

 solution. Results also are presented from several studies 

 to determine optimum conditions of temperature and light 

 for macrophytes. 



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