The role of bacteria in pH increase of nettle water

The investigation was designed to elucidate and explain the pH increase observed when a water extract of stinging nettle,Urtica dioica, was supplied to plants grown in sand or peat culture. The pH, bacterial number, organic acid content, and NH ₄ ⁺ and NO ₃ ^– content were determined in aerated nettle water, sterilised (UV-treated) nettle water and nutrient solution at intervals during 48 h. The pH increase was closely linked to increase in aerobic bacteria and the simultaneous decrease in organic acids and NH ₄ ⁺ concentration in the media. Consequently, the pH rise in nettle water is due to consumption of organic acids by bacteria and the accompanying shift of the acid-base equilibrium towards a more basic state.