Phosphorus in plant physiology P content of plants Approximately 0.2%of plant dry weight is P Plants require a relatively large amount of P. The phosphate concentration in the cytosol is maintained at fairly constant concentrations in the 5 to 8 mol/ms regardless of the external phosphate concentration except under severe P deficiency. By contrast is the vacuolar phosphate concentrationP content of plants • Approximately 0.2% of plant dry weight is P • Plants require a relatively large amount of P. The phosphate concentration in the cytosol is maintained at fairly constant concentrations in the 5 to 8 mol/m3 regardless of the external phosphate concentration except under severe P deficiency. By contrast is the vacuolar phosphate concentration. Phosphorus in plant physiology