The reservoir pool for gaseous cycles of matter is
Atmosphere
Hydrosphere
Both $(a) $ and $(b)$
Lithosphere
Concentration of nitrogen remains constant by
The agent/s which make/s free atmospheric nitrogen available to plants is/are
Natural reservoir of phosphorous.
Full form of $GNP$
Phosphorus is major constituent of
$(1)$ Biological membranes
$(2)$ Nucleic acid
$(3)$ Cellular energy transfer system
$(4)$ Protein synthesis