Environmental Controls on Foliar Respiration in Arctic Plants ! Mary Heskel ! ! Dissertation Defense 4.26.13 !
Foliar respiration and the terrestrial carbon cycle ! • Foliar respiratory release ≈ 1/2 photosynthetic uptake (Poorter et al. 1990; Atkin et al. 2007) ! ! • Provides energy and C skeletons in all tissues at all times ! ! • Promotes efficient Trumbore 2006 ! photosynthesis (Kromer 1995; Hoefnagel et al. 1998) ! Photosynthesis ( A ) ! ! ! ! !!!!!!!! ! Photorespiration ! • Global foliar respiratory CO 2 CO 2 ! ! release >> fossil fuel ! ! emissions (Canadell et al. 2007) ! ! Respiration ( R ) ! !
Environmental controls on respiration ! Photosynthe*c!uptake! Respiratory!release! Environmentally sensitive ! - Temperature* ! - Nutrient availability ! - Seasonality and phenology ! - Canopy position ! - LIGHT ! Currently no mechanistic model for foliar R. ! ! Models based on temperature, N, % of photosynthetic C gain, or multiple processes. !
• Arctic soils and vegetation store ~1/3 global terrestrial carbon (Gorham 1991; Ping et al. 2008; Tarnocai et al. 2009) ! ! • Arctic warming ~ 2x faster than global average (Chapin et al. 2005) ! ! • Multiple ecological consequences ! • Increased shrub cover and canopy height ! • Earlier snowmelt ! • Increased N+P availability !
Respiration in arctic plants ! • Few prior measurements (McNulty et al. 1988; Bliss and Dawson 1993; Atkin and Cummins 1994; Collier 1996; Collier and Cummins 1996; Arnone and Korner 1997; Shaver 1998; Muraoka et al. 2008) ! ! • Fewer comparing rates across environmental variation (Atkin and Cummins 1994; Shaver et al. 1998; Arnone and Korner 1997) ! ! • Ecosystem measurements do not capture foliar fluxes ! No existing quantification of foliar CO 2 release in the light. ! ! ! Only ecologically relevant measure in Arctic ecosystems ! ! ! ! Also environmentally sensitive !
Arctic carbon budget Controls on respiration ! under change ! A R" "" Environmental ! "" " """""""""Plant" """ Soil/!!! !!!!! !!!!!!!!!Heterotroph!! Biotic ! Cellular (Species/ processes ! phenology) !
Chapter 3 ! Foliar and cellular carbon cycling responses to a nitrogen and phosphorus gradient ! Mary A. Heskel, O. Roger Anderson, Owen K. Atkin, Matthew H. Turnbull, and Kevin L. Griffin* ! • Aboveground NPP controlled by N+P in tundra (Bret-Harte et al. 2004; Mack et al. 2004, Chapin et al. 1995) ! ! • Soil N+P limitation expected to relax with warming and shrub cover (Shaver and Chapin 1986; Hobbie et al. 2002; Weintraub & Schimel 2005; Nadelhoffer et al. 1991) ! ! • Few multi-level studies (Baddeley et al. 1994; Arens et al. 2008) ! ! • Physiological response is poorly characterized ! ! *Heskel et al. 2012 American Journal of Botany !
0 0 2 = 0.999 2 = 0.695 ! R ! R 2 = 0.674 2 = 0.104 40 40 " R " R % Inhibition 30 30 20 20 10 10 0 0 1 2 3 0 0.25 0.5 0.75 1 Leaf N concentration (%) Leaf P concentration (%) • Decoupled photosynthetic and respiratory responses ! less C gain under high N+P ! ! • Cross-taxa decrease of inhibition of R by light ! ! • Species specific organelle response !
Chapter 4 ! Differential physiological responses to environmental change promote woody shrub expansion ! Mary Heskel, Heather Greaves, Ari Kornfeld, Laura Gough, Owen K. Atkin, Matthew H. Turnbull, Gaius Shaver, and Kevin L. Griffin* ! Can foliar physiology explain woody shrub dominance under warming and fertilization? ! ! ! *Heskel et al. Ecology and Evolution, In press. !
300 A B 1 % Change in species cover 200 Relative species cover 0.75 100 0.5 0 0.25 -100 0 GH NP GHNP CT GH NP GHNP 8 8 b CT GH NP GHNP 6 Carbon gain efficency 6 a a a a a a a a 4 a 4 a a 2 2 0 0
Can foliar physiology explain woody shrub dominance under warming and fertilization? ! ! ! • Physiological advantage ! dominance of B. nana under long-term warming, but not under fertilization ! ! • Increased N+P availability may not translate into higher C assimilation per leaf ! – Morphological response ! resources allocated to growth (Bret-Harte et al. 2001, 2002) !
Chapter 5 ! Seasonality of foliar respiration: response to long-term warming and short-term temperature variability ! Mary A. Heskel, Owen K. Atkin, Matthew H. Turnbull, and Kevin L. Griffin* ! Respiration ! R light : R dark ! Leaf9out ! !!Mid9Season !!!!!!!!!!Senescence! GROWING!SEASION !! *Heskel et al. Functional Ecology, In review. !
Betula Eriophorum 15 15 A B 1 -1 ) -2 s ! Betula CT ! Betula WG 2 m 10 10 ! Eriophorum CT max ( µ mol CO " Eriophorum WG 0.8 5 5 A R light / R dark 0.6 0 0 0 0 C D 0.4 F E -1 ) 4 -2 s 6 2 m 0.2 3 light ( µ mol CO 4 2 0 R 2 1 160 170 180 190 200 210 Julian Day 0 0 160 170 180 190 200 210 160 170 180 190 200 Julian Day Julian Day • Stronger seasonal and thermal response in respiration than photosynthesis ! • Inhibition of R varies within growing season ! • No clear short-term thermal acclimation of R ! – High intra-seasonal temperature variability !
Chapter 6 ! Examining intra-canopy carbon cycling patterns in an Arctic shrub community ! Mary A. Heskel, Matthew H. Turnbull, and Kevin L. Griffin* ! • Shrub canopy height increase (Walker et al. 2006; Elmendorf et al. 2012) ! ! • Can influence climate (Loranty et al. 2012; Bonfils et al. 2012 ! ! • Increased complexity, and intra-canopy variation not yet addressed ! Myers-Smith et al. 2011 ! *Heskel et al. Physiologia Plantarum, In review. !
0 0 -2 ) 2 m Leaf Area Index (m 1 1 2 2 2010 • Significant leaf trait 2011 3 3 80 100 120 140 160 180 200 80 100 120 140 160 180 response… ! 2 g -1 ) 2 g -1 ) SLA (cm SLA (cm ! • No significant variation 0 0 in gas exchange ! -2 ) 2 m Leaf Area Index (m 1 1 2 2 2010 2011 3 3 1 1.5 2 2.5 3 1 1.5 2 2.5 3 -2 ) -2 ) N (g m N (g m No clear indication of canopy optimization !
Chapter 7 ! Bringing the Kok effect to light: ! Integrating daytime respiration and net ecosystem exchange ! Mary A. Heskel, Matthew H. Turnbull, and Kevin L. Griffin* ! Leaf ! ! ! ! ! ! ! ! Ecosystem ! R L! R D! • Details light inhibition of respiration at leaf level ! • Reviews incorporation in eddy co-variance studies; suggests potential 13 C/ 12 C ecosystem application ! *Heskel et al. Ecosphere, In review. !
Arctic carbon budget under change ! 10 Species / Community ! Mean R Light / R Dark = 0.62 ! 8 2 = 0.82 R - Shrubs may have 6 greater physiological Light R 4 adaptive ability ! 2 ! 0 Ecosystem ! 0 2 4 6 8 10 ! R Dark - Overestimate GPP ! • ~ 37% average inhibition ! - C cycle under change? ! • Decreases with energy demand ! • N, P, early season growth ! • Possible increase with warmth? !
Controls on respiration ! Thermal acclimation* ! ! N+P response* ! ! Duration effects ! Environmental ! Biotic ! Cellular (Species/ processes ! - Shrub > non- phenology) ! shrub species ! ! - Higher in early Organelle size + density ! season ! ! Energy demand for growth ! ! ! ! Light inhibition varies with energy demand ! !
Future applications of research ! Modeling Arctic C exchange ! Scaling up to Ecosystem ! • Landscape description ! • Stable isotope ratios of C ! • Shrub / non shrub cover ! ! • Ecosystem chamber CO 2 • Approximate N availability ! fluxes ! • LAI ! ! • Eddy covariance corrections ! • Ambient temperature/light ! ! ! Other ecological changes ! • Respiration* ! • Fire / Drought ! • Degree of inhibition ! ! • Temperature response ! • Latitudinal transects ! • Seasonal timing ! ! • Space for time ! thermokarsts ! *Stems, roots, and soil !
Acknowledgements ! ! Advisors: Kevin Griffin, Hilary Callahan ! Committee: Shahid Naeem, O. Roger Anderson, Matthew H. Turnbull ! ! Griffin Lab " Callahan Lab ! Owen K. Atkin (ANU) " Heather Greaves (Idaho) " Ari Kornfeld (Carnegie) E3B Department " Lourdes, Maria, Chiconia, Amy ! EDC at Toolik Field Station " Arctic LTER ! Gus Shaver & Ed Rastetter (MBL) !
• Quantification of ecologically relevant measures of foliar respiration ( R Light ) ! ! • Response of foliar C fluxes to warming- mediated environmental variation !
Shrub expansion feedback network ! Myers9Smith!et!al.!2011!
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