Aerenchyma formation and porosity in root of a mangrove plant, Sonneratia alba (Lythraceae)

Abstract

Aerenchyma gas spaces are important for plants that grow in flooded and anaerobic sites or habitats, because these gas spaces provide an internal pathway for oxygen transport. The objective of this study is to characterize the development of aerenchyma gas spaces and observe the porosity in roots of Sonneratia alba. Tissue at different developmental stages was collected from four root types, i.e. cable root, pneumatophore, feeding root and anchor root, of S. alba. In S. alba, gas space is schizogenously produced in all root types, and increases in volume from the root meristem to mature root tissues. The aerenchyma formation takes place immediately, or 3-5 mm behind the root apex. At first, cortical cells are relatively round in cross sections (near the root apex); they then become two kinds of cells, rounded and armed, which combine together, forming intercellular spaces behind the root apex. The average dimensions of cortical cells increased more than 1.3 times in the vertical direction and over 3.3 times in the horizontal direction. At maturity, aerenchyma gas spaces are long tuberous structures without diaphragms and with numerous small pores on the lateral walls. Within the aerenchyma, many sclereids grow intrusively. Root porosity in all root types ranged from 0-60%. Pneumatophores and cable roots had the highest aerenchyma area (50-60%).

Aerenchyma tissue development and gas-pathway structure in root of Avicennia marina (Forsk.) Vierh.

“…This type of schizogenous aerenchyma formation was observed in all four Avicennia marina root types. The same condition has been observed in some wetland plants, such as Sagittaria lancifolia, Thalia geniculata, and Pontederia cordata (Longstreth and Borkhsenious 2000), Filipendula ulmaria and Caltha palustris (Smirnoff and Crawford 1983), as well as in another mangrove plant, S. alba (Purnobasuki and Suzuki 2004), with a similar root system to A. marina.…”

Combined effects of simulated tidal sea-level rise and salinity on seedlings of a mangrove species, Kandelia candel (L.) Druce

“…The fourth type of experiment simulates different tidal flooding events, where sealevel rise results in both deep flooding level and long flooding duration. Prolonged tidal flooding enhances anaerobic conditions in soils and may become stressful to mangroves (Hovenden et al, 1995;Purnobasuki & Suzuki, 2004;Chen et al, 2005). During a flood event, oxygen concentrations in the soil can be reduced rapidly by as much as 28% after 6 h of flooding and as much as 72% after 20 h (Skelton & Allaway, 1996).…”

Emission of CO2 and CH4 to the atmosphere by sediments and open waters in two Tanzanian mangrove forests

“…Transport of gases is then largely limited to diffusion across the horizontal sediment -water interface. Open lenticels during air exposure allow for rapid diffusion of CO 2 from the air-filled aerenchyma tissue of roots to the atmosphere (Purnobasuki & Suzuki 2004, 2005. The CO 2 is generated by root respiration (Kitaya et al 2002, Lovelock et al 2006 or derived from microheterotrophic production in the surrounding deep sediments via transport across the root epidermis (Scholander et al 1955).…”