Dr. Ansari, 1. Root nodules occur on the roots of the plants that associate with symbiotic nitrogen fixing bacteria. Under N-limiting conditions, the symbiotic relationship is more stronger because due to lack of soil N,  leguminous plants prefer to fix atmospheric N. Therefore you may get reverse trend i.e more soil N ,less symbiotic N fixation.

In the second situation 2. Nitrate reductase are molybdoenzymes that reduce nitrate to nitrite. This reaction is critical for the production of protein in most crop plants as nitrate is the predominant source of nitrogen in fertilized soils. Therefore, less soil N means less nitrate reductase activity due to availability of less nitrate in the soil.

3. In the third situation more soil N increases soil beta glucosidase activities. So, they are directly correlated.

I am giving the logical views, hope it will satisfy you. 

Thank you Dr. Tarafdar

You have well tried to obviate my confusion. In addition, in the 3rd points i.e. correlation between N and beta glucosidase. You did not explain the reason. Please explain and suggest me some quality research papers of all the aspects for further study  

Beta glucosidase participates in the final stage of cellulose decomposition. It is a digestive enzymes for cellubiose/triose mineralization. It catalyzes the enzymatic hydrolysis of various polysaccharides and beta-glucosides. It is a driving force in the decomposition of carbohydrates in soils. It has been reported that beta-glucosidase activities are markedly affected by temperature, moisture, nutrient availability (including N) and other soil parameters (Bandick and Dick, 1999; Knight and Dick, 2004).