02615nas a2200301   4500008004100000245014000041210006900181260001200250300001600262490000700278520164500285653001501930653001801945653000801963653001101971653002101982653001702003653002602020653001502046653003002061653002202091653001902113100001702132700001502149700001502164700001702179856011702196       2011                        eng d00aIn situ O 2 dynamics in submerged Isoetes australis: Varied leaf gas permeability influences underwater photosynthesis and internal O 20 aIn situ O 2 dynamics in submerged Isoetes australis Varied leaf   c2011///  a4691 - 47000 v623 aA unique type of vernal pool are those formed on granite outcrops, as the substrate prevents percolation so that water accumulates in depressions when precipitation exceeds evaporation. The O 2 dynamics of small, shallow vernal pools with dense populations of Isoetes australis were studied in situ, and the potential importance of the achlorophyllous leaf bases to underwater net photosynthesis (PN) and radial O 2 loss to sediments is highlighted. O 2 microelectrodes were used in situ to monitor pO 2 in leaves, shallow sediments, and water in four vernal pools. The role of the achlorophyllous leaf bases in gas exchange was evaluated in laboratory studies of underwater PN, loss of tissue water, radial O 2 loss, and light microscopy. Tissue and sediment pO 2 showed large diurnal amplitudes and internal O 2 was more similar to sediment pO 2 than water pO 2. In early afternoon, sediment pO 2 was often higher than tissue pO 2 and although sediment O 2 declined substantially during the night, it did not become anoxic. The achlorophyllous leaf bases were 34% of the surface area of the shoots, and enhanced by 2.5-fold rates of underwater PN by the green portions, presumably by increasing the surface area for CO 2 entry. In addition, these leaf bases would contribute to loss of O 2 to the surrounding sediments. Numerous species of isoetids, seagrasses, and rosette-forming wetland plants have a large proportion of the leaf buried in sediments and this study indicates that the white achlorophyllous leaf bases may act as an important area of entry for CO 2, or exit for O 2, with the surrounding sediment. © 2011 The Author(s).10aAerenchyma10aaquatic plant10aCAM10amalate10aphotorespiration10asediment O 210asubmergence tolerance10atissue O 210aunderwater photosynthesis10avernal rock pools10awetland plants1 aPedersen, O.1 aPulido, C.1 aRich, S.M.1 aColmer, T.D.  uhttp://www.scopus.com/inward/record.url?eid=2-s2.0-80052891489&partnerID=40&md5=2632d744a43a2ba980f6aec51cf382b6