Aquatic adventitious roots of the wetland plant Meionectes brownii can photosynthesize: Implications for root function during flooding

Abstract

Many wetland plants produce aquatic adventitious roots from submerged stems. Aquatic roots can form chloroplasts, potentially producing endogenous carbon and oxygen. Here, aquatic root photosynthesis was evaluated in the wetland plant Meionectes brownii, which grows extensive stem-borne aquatic roots during submergence. Underwater photosynthetic light and CO2 response curves were determined for aquatic-adapted leaves, stems and aquatic roots of M. brownii. Oxygen microelectrode and 14CO2-uptake experiments determined shoot inputs of O2 and photosynthate into aquatic roots. Aquatic adventitious roots contain a complete photosynthetic pathway. Underwater photosynthetic rates are similar to those of stems, with a maximum net photosynthetic rate (Pmax) of 0.38μmolO2m-2s-1; however, this is c. 30-fold lower than that of aquatic-adapted leaves. Under saturating light with 300mmolm-3 dissolved CO2, aquatic roots fix carbon at 0.016μmol CO2g-1DMs-1. Illuminated aquatic roots do not rely on exogenous inputs of O2. The photosynthetic ability of aquatic roots presumably offers an advantage to submerged M. brownii as aquatic roots, unlike sediment roots, need little O2 and carbohydrate inputs from the shoot when illuminated. © 2010 The Authors. New Phytologist © 2010 New Phytologist Trust.