Answer:
a. Photosynthetic rate does not depend on the amount of available nitrogen
Step-by-step explanation:
Options are "A) Photosynthetic rate does not depend on the amount of available nitrogen B) Photosynthetic rate is positively correlated with the amount of available nitrogen C) The amount of available nitrogen is positively correlated with the photosynthetic rate D) The amount of available nitrogen does not depend on the photosynthetic rate"
Null Hypothesis is the hypothesis of no difference so apt null hypothesis would be that there is no relation between the photosynthetic rate and the amount of available nitrogen