TY - JOUR

T1 - Crassulacean acid metabolism enhances underwater photosynthesis and diminishes photorespiration in the aquatic plant Isoetes australis

AU - Pedersen, Ole

AU - Rich, S.M.

AU - Pulido Pérez, Cristina

AU - Cawthray, G.R.

AU - Colmer, T.D.

PY - 2011

Y1 - 2011

N2 - Underwater photosynthesis by aquatic plants is often limited by low availabilityof CO2, and photorespiration can be high. Some aquatic plants utilize crassulaceanacid metabolism (CAM) photosynthesis. The benefits of CAM for increased underwaterphotosynthesis and suppression of photorespiration were evaluated forIsoetes australis, a submerged plant that inhabits shallow temporary rock pools.• Leaves high or low in malate were evaluated for underwater net photosynthesisand apparent photorespiration at a range of CO2 and O2 concentrations.• CAM activity was indicated by 9.7-fold higher leaf malate at dawn, comparedwith at dusk, and also by changes in the titratable acidity (lmol H+ equivalents) ofleaves. Leaves high in malate showed not only higher underwater net photosynthesisat low external CO2 concentrations but also lower apparent photorespiration.Suppression by CAM of apparent photorespiration was evident at arange of O2 concentrations, including values below air equilibrium. At a high O2concentration of 2.2-fold the atmospheric equilibrium concentration, net photosynthesiswas reduced substantially and, although it remained positive in leavescontaining high malate concentrations, it became negative in those low in malate.• CAM in aquatic plants enables higher rates of underwater net photosynthesisover large O2 and CO2 concentration ranges in floodwaters, via increased CO2 fixationand suppression of photorespiration.

AB - Underwater photosynthesis by aquatic plants is often limited by low availabilityof CO2, and photorespiration can be high. Some aquatic plants utilize crassulaceanacid metabolism (CAM) photosynthesis. The benefits of CAM for increased underwaterphotosynthesis and suppression of photorespiration were evaluated forIsoetes australis, a submerged plant that inhabits shallow temporary rock pools.• Leaves high or low in malate were evaluated for underwater net photosynthesisand apparent photorespiration at a range of CO2 and O2 concentrations.• CAM activity was indicated by 9.7-fold higher leaf malate at dawn, comparedwith at dusk, and also by changes in the titratable acidity (lmol H+ equivalents) ofleaves. Leaves high in malate showed not only higher underwater net photosynthesisat low external CO2 concentrations but also lower apparent photorespiration.Suppression by CAM of apparent photorespiration was evident at arange of O2 concentrations, including values below air equilibrium. At a high O2concentration of 2.2-fold the atmospheric equilibrium concentration, net photosynthesiswas reduced substantially and, although it remained positive in leavescontaining high malate concentrations, it became negative in those low in malate.• CAM in aquatic plants enables higher rates of underwater net photosynthesisover large O2 and CO2 concentration ranges in floodwaters, via increased CO2 fixationand suppression of photorespiration.

U2 - 10.1111/j.1469-8137.2010.03522.x

DO - 10.1111/j.1469-8137.2010.03522.x

M3 - Journal article

VL - 190

SP - 332

EP - 339

JO - New Phytologist

JF - New Phytologist

SN - 0028-646X

IS - 2

ER -