The Formation Of Aerenchyma And Adventitious Root Of Arundinella Anomala Steud. And Salix Variegata Franch. In Three Gorges Reservoir As Affected By Simulated Flooding

In wetlands, soil flooding initiates a chain of reactions leading to reduced soil oxidation-reduction potential （Eh）. Flood-tolerant plants use several strategies to cope With low soil Eh conditions, such as the development of aerenchyma and adventitious roots. The stress brought on by low O₂ concentrations in flooded soils leads to the formation of aerenchyma in tolerant plant species, a process that can occur in roots, nodules, rhizomes, stems and submerged leaves. Aerenchyma is cortical airspaces which provide a low resistance internal pathway for the movement of O₂ from the shoots to the roots, where it is consumed in respiration and may also re-oxidize the rhizosphere.Aerenchyma can be of two types: schizogenous aerenchyma and lysigenous aerenchyma. Cortical aerenchyma may be formed by a specific process of separation and differential expansion of mature cells （schizogenous aerenchyma） or by death and dissolution of such cells （lysigenous aerenchyma）. Nevertheless, both types of aerenchyma can occur in the same plant and schizogenous aerenchyma may precede the occurrence of lysigenous aerenchyma in the same organ.In this paper, we measured aerenchyma of stem of Arundinella anomala Steud. and Salix variegata Franch., shrubs growing in fluctuating zone of The Three Gorges reservoir suffer periodic flooding, in different flooding environments. Meanwhile we analyzed the formation of adventitious roots about them. In order to ascertain whether phytohormone ethylene and auxin are direct stimuli for aerenchyma formation in flooded plants, we investigated the aerenchyma formation in the stem of A. anomala and S. variegata as affected by addition of ethylene and a-naphthalene acetic acid （a-NAA） under non-flooding conditions.Experiment results are as follows:（1） There were obvious increases in the aerenchyma’s areas of adult A. anomala in continuous flooding treatment and intermittent flooding treatment. Different flooding treatments lead to different changes about the aerenchyma’s formation of A. anomala. Compare with intermittent flooding treatment, the formation of aerenchyma of A. anomala plant is earlier promoted by continuous flooding. There was hardly the formation of aerenchyma of S. variegata plant grew up by 60 d flooding treatment.（2） Following different flooding treatments, the aerenchyma areas of the stem of A. anomala and S. variegata seedlings were all increased. After 5 flooding days, the aerenchyma’s area of stem of A. anomala and S. variegata seedlings in belowground submerged treatment was bigger than the control seedlings. There still have increased in the aerenchyma’s area of stem of A. anomala and S. variegata seedlings submerged with 2m water depth. The seedlings can live in anoxic environment by the aerenchyma formation.（3） In the experiment that the aerenchyma formation in the stem of A. anomala and S. variegata was enhanced when plants were irrigated with either ethylene or a-naphthalene acetic acid. Moreover, the aerenchyma formation in the stem of these two species was strengthened with hormone concentration, in flooding environments, the aerenchyma formation in stem of plants has direct relations to the increase of ethylene and auxin in plants, flooding may not be the direct stimulus for the formation of aerenchyma in plants.（4） adventitious rooting formation of A. anomala was earlier than that of S. variegate. Before 30 d belowground submerged, the number of adventitious rooting of A. anomala was straightly increasing. And after 30 d, the status was turning. After belowground submerged for 20 d, the number of adventitious rooting of A. anomala was more than that of A. anomala plants submerged with 2m water depth. The number of adventitious rooting of S. variegate was increasing in belowground submerged treatment. There was almost not adventitious rooting formation of S. variegate plants submerged with 2 m water depth. So different flooding treatments lead to different adventitious rooting formation of A. anomala and S. variegate.In conclusion, A. anomala and S. variegata can form aerenchyma in order to reduce the resistance of transporting oxygen so that the plants can live in anoxic flooding environment. In flooding condition, the formation of adventitious roots of A. anomala and S. variegata plants was increased. A. anomala and S. variegate have great capacity to living in flooding environment by the formation of aerenchyma and adventitious roots.