Plants were germinated and grown for 6 weeks under conditions des- 

 cribed for experiment 4. A series of plants was selected for a 17-day 

 uptake period utilizing the treatments described for experiment 4. 

 Plants were not deprived of nitrogen before the uptake period but were 

 transferred directly from the ammonium pretreatment (Table 1) solutions 

 to the labeled treatment solutions. At this stage, the shoots and 

 roots averaged 3.21 and 1.04 grams fresh weight per plant and all 

 plants were green and healthy. The uptake solutions contained either 

 4-mM ammonium or 4-mM nitrate labeled with 9o-percent ^^N and contained 

 all other nutrients as given in Table 1. Aeration and nonaeration 

 treatments were used. Four plants were placed in a pot containing 880 

 milliliters of the appropriate uptake solution. The ammonium or ni- 

 trate concentration in the uptake solution was then monitored at var- 

 ious time intervals (correcting for water loss) throughout the 17-day 

 period. 



At the end of the 17 days, plants were harvested and separated into 

 insoluble and soluble fractions for -^^N analyses. Although the data 

 from this experiment have not been completely analyzed yet some signi- 

 ficant observations are available. The gain in fresh weight in 17 days 

 was significantly greater with ammonium treatments as compared to ni- 

 trate treatments (Table 16) . No significant differences in total 

 weight were noted for aeration versus nonaeration with either nitrogen 

 source. However, aeration did affect the relative distribution of 

 fresh weight gain between shoots and roots. With aeration, greater 

 root weight relative to shoot weight resulted as compared to nonaera- 

 tion (Table 16) . No noticeable effects were observed with respect to 

 leaf yellowing as was observed with nitrate cultures or aeration in 

 young seedlings. Thus, the ammonium culture promoted greater fresh 

 weight production than the nitrate even after the 6-week growth stage; 

 it did so even when the nitrate treatment did not induce the severe 

 chlorotic symptoms observed when nitrate was supplied early in growth. 



Table 16. Experiment 5. Growth of shoots and roots in 17 days as 

 influenced by nitrogen source and aeration. Plants were 

 grown for 6 weeks with ammonium and without aeration, at 

 which time shoot and root fresh weight averaged 3.21 and 

 1.04 grams per plant. 





Final 



Weight 



Increase in 17 Days 



Treatment 



(Grams Per Plant) 



(Grams Per Plant) 



(17 days) 



Shoots 



Roots 



Shoots 



Roots 



Total 















Ammonium 



5.65 



1.86 



2.43 



0.82 



3.25 



Ammonium + Aeration 



5,07 



2.62 



1.86 



1.58 



3.44 



Nitrate 



4.60 



1.69 



1.19 



0.65 



1.84 



Nitrate + Aeration 



4.26 



2.12 



1.05 



1.08 



2.13 















59 



