Figures 30 and 31 present the cumulative ammonium and nitrate up- 

 take during the 11th and 17th day after transfer. The ambient concen- 

 trations were allowed to sink to relatively low levels by the 11th day 

 and were then replenished. Substantial nitrate uptake occurred, and 

 both ammonium and nitrate uptake were restricted (ZD"- percent and 33 per- 

 cent, respectively) by aeration. Hence, failure of the nitrate-treated 

 plants to grow as well as those treated with ammonium under these con- 

 ditions was not a result of an inability to absorb nitrate. 



f . Discussion . Forced aeration of the root system was clearly 

 detrimental to plant growth under the conditions used in these experi- 

 ments. During early growth the effects of aeration were more severe, 

 especially when nitrate was the sole nitrogen source, than when aera- 

 tion was imposed after the plants had developed vigorously under non- 

 aerated conditions. Even in the latter case where growth rates were 

 not restricted by aeration, there was a differential effect on root 

 and shoot growth, with aeration promoting the former at the apparent 

 expense of the latter. Both ammonium and nitrate uptake were slightly 

 restricted by forced aeration during short-term experiments [Figs. 26 

 and 29) . With nitrate, there was a marked restriction in nitrate re- 

 ductase activity (Tables 11 and 14) and probably in translocation of 

 the nitrogen absorbed as nitrate (Table 13) . Soluble protein was 

 restricted by aeration after 6 weeks' growth with ammonium as well as 

 with nitrate (Table 11) suggesting an impact on nitrogen assimilation 

 for both. However, aside from the effect on ammonium uptake, the pre- 

 sent ^^N data (Table 13) do not indicate how this effect might come 

 about . 



Nitrate nitrogen was not a suitable sole source of nitrogen even 

 under nonaerated conditions. Total nitrogen concentrations and solu- 

 ble protein (Table 11) were generally lower in nitrate-treated plants 

 (Table 12). Nitrate reductase activity and nitrate uptake (Figs. 26 

 and 29) could be induced by exposure to nitrate (Table 14) . Presence 

 of ammonium in the ambient medium severely lowered nitrate reductase, 

 especially in the root tissue (Table 11). The extent resulting from 

 depressed nitrate uptake is unknown. Low nitrate accumulation and low 

 nitrate reductase in the shoots (Table 11) imply an inability to 

 translocate nitrate, which is in agreement with the low total N 

 translocation (Table 13) . 



Tentatively, it is concluded that the inability to utilize nitrate 

 effectively is partially a result of a low uptake capability. How- 

 ever, the plants do have the ability to generate nitrate uptake cap- 

 acity (Fig. 31) and still not grow as effectively as with ammonium 

 (Table 15) . A further ineffectiveness in their nitrate assimilation 

 pathway seems indicated. 



2. Field Studies . 



This aspect of marsh establishment and development is of interest 

 for several reasons. One is that adequate nutrient supply is 



60 



