February 24 th, Jeffrey M Warren, Ph.D. Environmental Sciences Division Oak Ridge National Laboratory. Climate change Plant water relations

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1 Terrestrial Water Relations & Climate Change Outline Jeffrey M Warren, Ph.D. Environmental Sciences Division Oak Ridge National Laboratory Climate change Plant water relations ORNL elevated CO 2 study general results water dynamics secondary impacts February 24 th,

2 (C) 2008 Scripps CO 2 Program 2

3 RF Keeling Scripps CO 2 Program AR4 Synthesis Report. Climate Change IPCC 3

4 AR4 Synthesis Report. Climate Change IPCC AR4 Synthesis Report. Climate Change IPCC 4

5 IPCC Fourth Assessment Report Climate change...very likely that heat waves will be more intense, more frequent and longer lasting in a future warmer climate...precipitation intensity is projected to increase...longer periods between rainfall events...drying of the mid-continental areas during summer, indicating a greater risk of droughts Increased atmospheric CO 2 plant fertilizer effect increase leaf level water use efficiency Increased air and soil Temperature optimum for photosynthesis increase in rate of respiration Altered timing and magnitude of Precipitation impact productivity species interactions 5

6 Terrestrial Water Relations & Climate Change Terrestrial Water Relations & Climate Change Soil Root Root Stem Leaf Xylem 6

7 Terrestrial Water Relations & Climate Change Soil-Plant-Atmosphere (SPA) Continuum Atmosphere Plant Ecosystem Water Flux Soil Taiz & Zeiger Plant Physiology 7

8 Impacts of Climate Change on SPA Ponderosa Pine Atmosphere Plant CO 2 Temperature Precipitation ptake CO 2 up Leaf water loss Soil Increased water availability in and uptake from the soil results in increased carbon gain. Hubbard et al

9 Ecosystem Water Dynamics are critical for: belowground processes nutrient turnover signaling linkages between roots and shoots production foliage, fruit, wood, seedling establishment quality structural/chemical characteristics multi-trophic trophic level species interactions site water/heat flux hydrology, climate change How does increasing CO 2 effect forest processes and water dynamics? 9

10 ORNL FACE Sweetgum plantation Uses Free-Air CO 2 Enrichment (FACE) CO 2 exposure (550 ppm) started in 1998 Quantify carbon, nitrogen and hydrological cycles Quantify physiological and ecological dynamics Use results to inform models 10

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12 RESULTS Altered C partitioning through time Ne et primary production (g m -2 year -1 ) Leaves Wood Fine roots 300 Greater production 200 under 100 elevated CO Year Iversen et al. 12

13 RESULTS NPP, N uptake decline through time RESULTS Shift in NPP x N relationship elevated CO 2 filled circles ambient CO 2 open circles elevated CO 2 filled circles ambient CO 2 open circles Norby, Warren, Iversen et al. Norby, Warren, Iversen et al. 13

14 RESULTS ORNL FACE after 11 years Increase in net primary production Atmosphere ORNL FACE SPA water dynamics Increase in N uptake, decrease in N availability Increase in fine root production, deeper in the soil Increase in soil C Plant Reduction in water use Soil 14

15 Xylem sap flow using Granier s thermal dissipation technique Soil water content with frequency domain capacitance Xylem sap flow with thermal dissipation probes 15

16 Leaf water flux assessed with porometer or IRGA Xylem sap flow using Granier s thermal dissipation technique Tr ranspiration (mm m day -1 ) 4 E CO2 A CO Day of Year Daily transpiration during

17 Deep soil water extraction reduced Elevated CO 2 trees use 25-45% less water Soil Water (m 3 m -3 ) cm soil depth 0-20 cm soil depth E CO2 20 A CO2 EA E:A residual water Day of Year E:A res sidual Eleva ated:ambient Sap flow Day of Year 17

18 Elevated CO 2 reduces water use, and increases outflow (runoff) by ~80 mm year 2007 Precip Extreme VPD T max 50 Drought 5 40 Precipitation (mm) VPD T max (deg C) Day of Year 0 Biome-BGC modeling 18

19 Why do elevated CO 2 trees use progressively less water during drought? Elevated CO 2 Increased leaf loss Elevate ed:ambient Sap flow Extreme Drought Day of Year 2007 Extreme E CO2 litter Drought A CO2 litter ** Day of Year Leaf Litter (g m -2 ) 19

20 Elevated CO 2 decreased water use but increased leaf loss? Drought + elevated CO 2 increases loss of leaves A CO2 sapflow ratio E CO2 : sapflow E litter A litter ** Leaf Litter (g m -2 ) But increased root biomass, deeper in soil Reduced soil water extraction less water stress? Reduced Transpiration reduces latent heat loss excessive leaf temperatures? Day of Year 20

21 Elevated CO 2 Reduced stomatal conductance Elevated CO 2 Increased leaf temperature 50 g c (mmol m -2 s -1 ) 140 A CO2 0.8 E:A = DOY 120 E CO E CO2 :A CO Day of Year af (E CO2 - A CO2 ) ( C) ΔT lea Day of Year T leaf ECO2 ( C) 21

22 Drought + elevated CO 2 increases loss of leaves Elevated CO 2 Reduced C uptake But increased root biomass, deeper in soil Reduced soil water extraction less water stress? Reduced Transpiration reduces latent heat loss excessive leaf temperatures? - Maybe Reduced Transpiration reduces C uptake carbon starvation? GP PP (g C m -2 d -1 ) 25 E CO A CO2 CO2 E CO2 :A C Day of Year 22

23 Drought + elevated CO 2 increases loss of leaves Xylem water transport through roots, stem, leaves under tension But increased root biomass, deeper in soil Reduced soil water extraction less water stress? -vessel elements in Angiosperms (left) -tracheids in conifers (below, Douglas-fir) Reduced Transpiration reduces latent heat loss excessive leaf temperatures? - Maybe Reduced Transpiration reduces C uptake carbon starvation? - Maybe High Temperature increases Vapor Pressure Deficit differential loss of hydraulic conductivity? 23

24 Loss of Xylem Conductivity Air seeding hypothesis through bordered pits Double ended pressure chamber to induce embolism Embolized Air Functional Water 0 MPa -1 MPa -2 MPa 24

25 Volume, mass or pressure based measurement of conductivity vity (%) K ss of conductiv los elevated CO 2 ambient CO 2 branch xylem ψ (applied pressure; MPa) 25

26 100 um 1 mm R5 Ambient CO2 26

27 Drought + elevated CO 2 increases loss of leaves Elevated CO 2 induced leaf loss due to thermal damage, carbon balance or loss of hydraulic conductivity But increased root biomass, deeper in soil Reduced soil water extraction less water stress? Reduced Transpiration reduces latent heat loss excessive leaf temperatures? - Maybe Enhanced sensitivity to stress may Enhanced sensitivity to stress may reduce the potential benefits of elevated CO 2 to forest carbon uptake Reduced Transpiration reduces C uptake carbon starvation? - Maybe High Temperature increases Vapor Pressure Deficit differential loss of hydraulic conductivity? Yes Increased sensitivity to embolism increased xylem cell size 27

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30 Recent Collaborators ORNL - R. Norby, S. Wullschleger, C. Iversen, J. Childs H. Bilheux, J. Horita, D. Weston, P. Thornton University of Tennessee - E. Perfect, J. Franklin, N. Labbe, A. Sahadevan, T. Feild, D. Chatelet, A. Classen University of Tennessee collaboration Sap flow, sapwood area Wood chemical, physical & mechanical properties 30