02477nas a2200277   4500008004100000245013900041210006900180260001200249300001400261490000800275520153700283653003901820653001301859653001601872653002101888653002601909653003001935653001601965653001801981100001701999700001502016700001502031700001902046700001702065856011702082       2011                        eng d00aCrassulacean acid metabolism enhances underwater photosynthesis and diminishes photorespiration in the aquatic plant Isoetes australis0 aCrassulacean acid metabolism enhances underwater photosynthesis   c2011///  a332 - 3390 v1903 aUnderwater photosynthesis by aquatic plants is often limited by low availability of CO 2, and photorespiration can be high. Some aquatic plants utilize crassulacean acid metabolism (CAM) photosynthesis. The benefits of CAM for increased underwater photosynthesis and suppression of photorespiration were evaluated for Isoetes australis, a submerged plant that inhabits shallow temporary rock pools. Leaves high or low in malate were evaluated for underwater net photosynthesis and apparent photorespiration at a range of CO 2 and O 2 concentrations. CAM activity was indicated by 9.7-fold higher leaf malate at dawn, compared with at dusk, and also by changes in the titratable acidity (μmol H + equivalents) of leaves. Leaves high in malate showed not only higher underwater net photosynthesis at low external CO 2 concentrations but also lower apparent photorespiration. Suppression by CAM of apparent photorespiration was evident at a range of O 2 concentrations, including values below air equilibrium. At a high O 2 concentration of 2.2-fold the atmospheric equilibrium concentration, net photosynthesis was reduced substantially and, although it remained positive in leaves containing high malate concentrations, it became negative in those low in malate. CAM in aquatic plants enables higher rates of underwater net photosynthesis over large O 2 and CO 2 concentration ranges in floodwaters, via increased CO 2 fixation and suppression of photorespiration. © 2010 The Authors. New Phytologist © 2010 New Phytologist Trust.10aCrassulacean acid metabolism (CAM)10aIsoetids10aLeaf malate10aphotorespiration10asubmergence tolerance10aunderwater photosynthesis10aVernal pool10aWetland plant1 aPedersen, O.1 aRich, S.M.1 aPulido, C.1 aCawthray, G.R.1 aColmer, T.D.  uhttp://www.scopus.com/inward/record.url?eid=2-s2.0-79953053245&partnerID=40&md5=c2507c2a16ac2dc7fa92a276d5376677