The Impact of CO2 Enrichment on Water Relations in Maranthes corymbosa and Eucalyptus tetrodonta

Abstract

Seeds of Maranthes corymbosa Blume and Eucalyptus tetrodonta F.Muell were sown under ambient or CO2 enriched conditions (two replicate tents per treatment) in tropical Australia and allowed to grow, rooted in the ground, for 20 months. For both species, periodic measurements of leaf water potential, stomatal conductance and leaf temperature were made on four replicate leaves on each of four replicate trees within each tent. Measurements were made in November (M. corymbosa) and June (E. tetrodonta). At the same time, atmospheric wet and dry bulb temperatures were recorded and hence leaf-to-air vapour presure difference (LAVPD) calculated. Measurements of pre-dawn leaf water potential were also made on E. tetrodonta. Leaves were also taken to the laboratory, rehydrated to full turgor and pressure-volume analyses undertaken. For M. corymbosa, leaf water potential was lower throughout the day for control leaves compared to leaves growing in CO2 enriched air. Similarly, pre dawn leaf water potential was lower for control E. tetrodonta trees than for trees grown with CO2 enrichment. However, mid-morning and mid-afternoon values of leaf water potential for E. tetrodonta were slightly lower for plants growing in CO2 enriched air compared to control plants. In both species, stomatal conductance was consistently lower for trees grown in CO2 enriched air than for controls. Whole plant hydraulic conductivity of both species was significantly lower for trees grown in CO2 enriched air than for control trees. For both species, maximum turgor and bulk volumetric elastic modulus increased and osmotic potential at zero turgor decreased for trees grown in CO2 enriched air.

Tropical forest responses to increasing atmospheric CO2: current knowledge and opportunities for future research

“…This could lead to a reduction in soil water depletion due to reduced canopy-scale transpiration, which could sustain transpiration, and therefore photosynthesis, for a longer time between rain events (Morgan et al 2004;Keel et al 2007;Leuzinger and Körner 2007;Holtum and Winter 2010;Leuzinger and Körner 2010;Macinnis-Ng et al 2011). Such water savings could also facilitate microbial activity and nutrient provision, and enable turgor pressure in meristem tissues to remain above the critical threshold required for cell expansion (Boyer 1968;Eamus et al 1995), thereby facilitating growth. Second, elevated c a could increase the NSC pool, which, in turn, could be used to sustain plant metabolism for longer periods following stomatal closure and cessation of A in response to drought, according to the carbon-centric perspective (Sala et al 2012).…”

Changes in root growth and relationships between plant organs and root hydraulic traits in American elm (Ulmus americana L.) and red oak (Quercus rubra L.) seedlings due to elevated CO2 level

“…At the same time, total plant biomass in these species significantly increased by 27%-67% (Eamus et al, 1995;Lee and Jarvis, 1996;Kinney and Lindroth, 1997;Curtis and Wang, 1998;Tomlinson and Anderson, 1998;Huxman et al, 1999;Thomas et al, 1999;Hattenschwiler, 2001;Tognetti et al, 2002;Rey and Jarvis, 2003). However, it is unclear whether plant organs or root hydraulic conductance initially responds to elevated levels of CO 2 and how plant organ development interacts with the conductance when a species acclimatizes to the increase in CO 2 .…”

“…Many studies have shown that after 4 months to 4.5 years of exposure to high levels of CO 2 , root hydraulic conductance decreased in the seedlings of Maranthes corymbosa and Eucalyptus tetrodonta (Eamus et al, 1995), Helianthus annuus (Huxman et al, 1999), Erica arborea, Myrtus communis and Juniperus communis , Fagus sylvatica, Abies alba, Acer pseudoplatanus, Quercus robur, Taxus baccata (Hattenschwiler, 2001) and in Betula pendula saplings (Rey and Jarvis, 2002), but increased in Salix sagitta seedlings (Johnson et al, 2002). At the same time, total plant biomass in these species significantly increased by 27%-67% (Eamus et al, 1995;Lee and Jarvis, 1996;Kinney and Lindroth, 1997;Curtis and Wang, 1998;Tomlinson and Anderson, 1998;Huxman et al, 1999;Thomas et al, 1999;Hattenschwiler, 2001;Tognetti et al, 2002;Rey and Jarvis, 2003).…”

MAESPA: a model to study interactions between water limitation, environmental drivers and vegetation function at tree and stand levels, with an example application to [CO<sub>2</sub>] × drought interactions

“…We test the impact of acclimation of two leaf physiology parameters, k L and f . A number of studies have found decreases in the leaf-specific hydraulic conductance (k L ) in plants grown in eC a (Atkinson and Taylor, 1996;Eamus et al, 1995;Eguchi et al, 2008;Heath et al, 1997), with reductions in a wide range of 10-100 %. Berryman et al (1994) found a higher sensitivity of g s to decreasing water content of excised leaves in Maranthes corymbosa, which can be interpreted as a less negative f in the Tuzet model (Eq.…”

“…A simple prediction for this interaction is that the C a response will be higher under soil drought for two reasons: firstly, lower leaflevel water use under eC a (Eamus, 1991;Medlyn et al, 2001) leads to higher soil water content, which helps plants avoid soil water deficits; and secondly, lower intercellular CO 2 concentration (C i ) during drought enhances the C a response because of the non-linear response of photosynthetic rate to C i (Grossman-Clarke et al, 2001;McMurtrie et al, 2008). While both mechanisms have been confirmed in a number of crop and grassland studies (e.g.…”