Morphophysiological responses of Alnus subcordata (L.) seedlings to permanent flooding and partial submersion

Alnus subcordata (L.), the Caucasian alder, is a pioneer riparian tree native in riparian zones and wetlands of the Middle East region of Asia. In the Hyrcanian forest of North Iran, one of the most valuable forest communities in this world region, the use of this species through afforestation practices is being considered to restore the forest cover in extensive wetland areas that have been recently altered by a significant increase in the duration of their waterlogged conditions. To assess restorers, the morphophysiological responses to flooding stress of A. subcordata were investigated during a 120-day exsitu experiment. Fortyeight one yearold seedlings were subjected to three flooding treatments: 1) unflooded; 2) permanently flooded (i.e., 3 cm of flooding depth); and 3) partially submersed (i.e., 15 cm of flooding depth). Although survival of seedlings at the end of the experiment was almost complete, plants subjected to the two flooding stress treatments had a significantly lower growth. Other responses to flooding included the formation of hypertrophied lenticels and adventitious roots and a surprising higher allocation of biomass in roots. However, free proline concentration in leaves and roots was not affected by flooding. Overall, the results showed that A. subcordata is able to withstand long periods of waterlogged conditions by readjusting some morphological and physiological parameters.