Sodium concentration in the plants at the first sampling date (ANa) 

 is positively related to height as it was to yield. The concentration is 

 significantly higher in samples from the tall-height zone (Tab. 32). 



Magnesium concentration in the plant tissue at the first (AMg) and 

 second (BMg) sampling dates are in the regression equation. However, 

 there is no relationship of magnesium with height apparent from the sim- 

 ple correlations (Tab. 27) or the means (Tab. 32). This variable may 

 have entered the regression equation due to its relationship with other 

 variables. 



The iron concentration in the plant tissue at the first sampling date 

 (AFe) is positively correlated with height. The difference is greater 

 between locations than between height zones. This difference is probably 

 because finer sediments occur at the locations where taller plants are 

 found, and these sites would be expected to contain more iron (associated 

 with clay) than the sandy sites. 



Nitrogen concentration at the first sampling date (AN) was positively 

 correlated with height, while nitrogen concentration at the third sampling 

 date (CN) was negatively correlated with height. A probable explanation 

 for this is that plant-available nitrogen is scarce in the marsh environ- 

 ment. At the first sampling date, high nitrogen concentrations in the 

 plant are indicative of a high potential for growth. At maturity, the 

 nitrogen concentration is lowest in plants which have achieved maximum 

 growth due to dilution in the greater amount of plant tissue. 



Calcium concentration at the third sampling date (CCa) probably enters 

 the regression equation because of its relationship to other variables 

 since no relationship with height is apparent from the means (Tab. 32) or 

 the simple correlation with height (Tab. 27). 



Phosphorus concentration at the second sampling time (BP) was posi- 

 tively correlated with plant height. This indicates that where greater 

 amounts of phosphorus are available for growth, greater heights are 

 attained. 



The concentration of manganese at the second sampling time (BMn) 

 appears to be negatively related to height according to the regression 

 coefficient (Tab. 30). However, the simple correlation shows a positive 

 relationship of BMn to height. This is an example of sign reversal of 

 b-values when there is correlation between variables in the model. This 

 positive relationship of manganese concentration to height is opposite of 

 the relationship with yield. 



f . Predicting Standing Crop of Mineral Nutrients from Dry Weight . 

 It is of interest to know the quantities of nutrients conveyed to estu- 

 arine food chains by S. alterniflora (Williams and Murdoch, 1969). From 

 the data in this study, standing crop of nutrients contained in the 

 aboveground part of mature S. alterniflora stands can be calculated 

 (Tab. 33). The data used were three 0.25-square meter samples clipped 



120 



