Azolla has been deemed a "super-plant" as it can draw down as much as a tonne of nitrogen per acre per year (0.25 kg/m/yr); this is matched by 6 tonnes per acre of carbon drawdown (1.5 kg/m/yr). Its ability to use atmospheric nitrogen for growth means that the main limit to its growth is usually the availability of phosphorus: carbon, nitrogen and sulphur being three of the key elements of proteins, and phosphorus being required for DNA, RNA and in energy metabolism.  The plant can grow at great speed in favourable conditions – modest warmth and 20 hours of sunlight, both of which were in evidence at the poles during the early Eocene – and can double its biomass over two to three days in such a climate. This rate of growth pushes the plants deep under away from sunlight where death and carbon sequestration occur.