Growth and development of Rumex roots as affected by hypoxic and anoxic conditions

The growth characteristics of three Rumex species were determined under different solution oxygen concentrations in hydroculture. These species all occur in a river foreland ecosystem and they were found to differ in their flood tolerance. The flood-tolerant R. maritimus and R. crispus developed a large num ber of new, aerenchymatous roots within a short period under low solution oxygen concentrations. Biomass production was not affected. In the flood-intolerant R. thyrsiflorus, however, only few slow-growing new roots were developed and biomass production was significantly reduced at solution oxygen concentrations below 2% (v:v). These different responses could be partly explained by a differential aerenchyma formation in new roots of the flood-tolerant species. Aerenchym a can relieve the oxygen stress of the root systems via internal aeration. ITie fast developm ent of new roots of the flood-tolerant R. maritimus and R. crispus after the onset of anaerobiosis coincided with the reduction or cessation of growth of the primary roots. Notwithstanding the cessation of growth, however, primary roots of both species were able to recover following restoration of aerobic conditions after a 13-day anaerobic period. However, the roots of R . thyrsiflorus ceased growing very soon after the onset of anaerobiosis. All had died within 10 days. I he balance between the growth rates of the primary and the newly formed root system are discussed and related to the differential tolerance of the Rumex species to transient flooding.