Spatial variability in leaf N: detecting the elevated CO2 response in a  Eucalyptus woodland ecosystem in the      Cumberl...
Forest canopies are tall and variable
Leaf N is a key ecosystem variable                                         Eucalyptus                                     ...
Leaf N in plant canopies is relatively stable & can be remotely sensed                New Hampshire, USA                  ...
There is evidence that much of local-scale  canopy variation in leaf N concentration is tree-                       based ...
Study tract of native Cumberland Plain woodland               located in W. Sydney
Increasing global CO2 concentration                    400                                Direct measureAir [CO2] (ppm-v) ...
EucFACE  involves circularplots for free-air CO2     enrichment Plots are 25m diameter   and release CO2 in a  computer-co...
EucFACEA study of elevated CO2 effects on a mature grassy woodland                         ecosystem                   Fre...
Stepped increase in [CO2] in EucFACE                             540                                                      ...
Stepped increase in [CO2] in EucFACE                          125Daytime treatment [CO2] in ppm above ambient             ...
Simple hypotheses for elevated CO2 effects            on plant processesDo the effects we know at the small scalepropagate...
Leaf net photosynthesis (Anet) and leaf chemistryis safely measured at ~20m height in the canopy
Canopy access to top ofmature E. tereticornis at     22m height
Pretreatment leaf %N among 66 mature Eucalyptus  trees (6 month old leaves sampled in autumn)             Grand mean 1.73 ...
Power curves - likelihood we don’t detect a      CO2 effect on leaf N that is real                                        ...
How much sampling is needed to detect an                               CO2 effect on leaf N?                              ...
How much sampling? Power curves                              Effect size = 0.05            Effect size = 0.10        Effec...
Power - likelihood we don’t detect a CO2          effect on leaf N that is real                                           ...
Pretreatment leaf net photosynthetic capacity at390 ppm CO2 among 18 mature Eucalyptus trees (6      month old leaves samp...
Power - likelihood we don’t detect a  CO2 effect on photosynthesis that exists                                            ...
Conclusions – can we detect effects of    elevated CO2 at +150ppm on plants? This study evaluated variability in leaf N a...
Conclusions – continued We can statistically detect a CO2 effect decreasing  leaf N concentration by 15% with 3 rings and...
AcknowledgementsSee: www.uws.edu.au/hie/eucfaceEucFACE is an initiative supported by:              Commonwealth through DI...
How much did ↑CO2 drive increased          photosynthesis in the canopy?K. Crous, T. Gimeno data                          ...
What does is a free-air experiment?         FACE = free-air CO2 enrichment         [CO2] is computer-controlled         wi...
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David Ellsworth_Spatial variability in leaf N and detecting elevated carbon dioxide response in a Eucalyptus woodland ecosystem in the Cumberland Plain ('EucFACE')

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  • TERN 4th annual meeting, 18-20 Feb. 2013. Canberra, Australia.
  • Forest canopies are variable, tall and hard to sample
  • Power is the probability that the test will reject the null hypothesis when the null hypothesis is false.
  • Power is the probability that the test will reject the null hypothesis when the null hypothesis is false.
  • Power is the probability that the test will reject the null hypothesis when the null hypothesis is false.
  • Power is the probability that the test will reject the null hypothesis when the null hypothesis is false.
  • We would be trying to resolve about a 30% increase in Anet at 540ppm for three of these rings – that’s about a rate of 21 umol m-2 s-1
  • Power is the probability that the test will reject the null hypothesis when the null hypothesis is false. From Primer, it is when there are systematic differences between CO2 treatments but we fail to reject the null and conclude incorrectly that there is only random variation among experimental units.Used to compute minimum sample size required to be reasonably likely to detect an effect of a given size
  • Power is the probability that the test will reject the null hypothesis when the null hypothesis is false. Experiment won’t allow us to find ‘false positives’.
  • Power is the probability that the test will reject the null hypothesis when the null hypothesis is false. Experiment won’t allow us to find ‘false positives’.
  • David Ellsworth_Spatial variability in leaf N and detecting elevated carbon dioxide response in a Eucalyptus woodland ecosystem in the Cumberland Plain ('EucFACE')

    1. 1. Spatial variability in leaf N: detecting the elevated CO2 response in a Eucalyptus woodland ecosystem in the Cumberland Plain (‘EucFACE’) or: How much sampling may be needed?D. Ellsworth1, K. Crous1, B. Moore1, T. Gimeno1, J. Powell1, P. Reich1,2 David Ellsworth Hawkesbury Institute for the Environment University of Western Sydney, NSW AUSTRALIA D.Ellsworth@uws.edu.au
    2. 2. Forest canopies are tall and variable
    3. 3. Leaf N is a key ecosystem variable Eucalyptus ConfersNet photosynthesis greenness (nmol g s ) -2 -1 20 via N- 10 containing chlorophyll 0 10 20 30 40 -1 Leaf Narea (mg g ) N relates to leaf photosynthetic protein content N reflects nutritional content C/N ratio affects biogeochemical for herbivore feeding cycling
    4. 4. Leaf N in plant canopies is relatively stable & can be remotely sensed New Hampshire, USA Smith et al. (2002) Ecol. Applic. 12: 1286
    5. 5. There is evidence that much of local-scale canopy variation in leaf N concentration is tree- based E. microcorys: region,What kind of sampling is site and tree variance in Nneeded to resolve a plot-plot difference within anative Eucalypt woodlandfor leaf N and Anet?If we conduct anecosystem manipulation,are we able to detect theoutcome? Moore et al. (2004) Ecol. Monogr. 74: 553
    6. 6. Study tract of native Cumberland Plain woodland located in W. Sydney
    7. 7. Increasing global CO2 concentration 400 Direct measureAir [CO2] (ppm-v) 360 Icecore air The atmospheric gas CO2 is increasing in 320 the atmosphere Year 2010 in spite of 389 ppm 280 39% above pre-industrial international 1850 1900 1950 2000 agreements to control YEAR CO2 emissions Rate of increase [CO2] at 520 to 555 1970 – 1979: 1.3 ppm y-1 ppm is expected by 1980 – 1989: 1.6 ppm y1 2050 1990 – 1999: 1.5 ppm y-1 2000 - 2009: 1.9 ppm y-1 Data Source: P. Tans & T. Conway, NOAA/ESRL http://www.esrl.noaa.gov/gmd/ccgg/iadv
    8. 8. EucFACE involves circularplots for free-air CO2 enrichment Plots are 25m diameter and release CO2 in a computer-controlled fashion. There are 6 plots, 3 ambient and 3 ambient +150ppm CO2
    9. 9. EucFACEA study of elevated CO2 effects on a mature grassy woodland ecosystem Free-Air CO2 Enrichment Computer-controlled emission of CO2 from vent pipes CO2 Wind Calm CO2 Valve emitting CO2 Valves must be modulated rapidly: Valve closed < 10 sec response EucFACE controls plot [CO2] at 540 ppm after 6-month ramp-up period
    10. 10. Stepped increase in [CO2] in EucFACE 540 +150ppm +120ppm Treatment [CO2] +90ppm +60ppm +30ppm Step 2 Jan.Current [CO2] 390 level A/S S/O O/N N/D D/J J/F Years … Timeframe (months)
    11. 11. Stepped increase in [CO2] in EucFACE 125Daytime treatment [CO2] in ppm above ambient 100 540 75 50 Timeframe (months) 25 Month
    12. 12. Simple hypotheses for elevated CO2 effects on plant processesDo the effects we know at the small scalepropagate to affect ecosystem processes for a mature forest?
    13. 13. Leaf net photosynthesis (Anet) and leaf chemistryis safely measured at ~20m height in the canopy
    14. 14. Canopy access to top ofmature E. tereticornis at 22m height
    15. 15. Pretreatment leaf %N among 66 mature Eucalyptus trees (6 month old leaves sampled in autumn) Grand mean 1.73 ± 0.06% 1.69% 1.69% 1.76% 1.81% 1.77% 1.64%
    16. 16. Power curves - likelihood we don’t detect a CO2 effect on leaf N that is real Effect size = 0.15High probability of rejectingthe null and finding atreatment difference when Power (1-β) for leaf %Nthere actually is a differenceLow probability of rejectingthe null when it is actuallyfalse # trees sampled per plot
    17. 17. How much sampling is needed to detect an CO2 effect on leaf N? Effect size = 0.05 Effect size = 0.10 Effect size = 0.20Power (1-β) for leaf %N 2 4 6 8 10 2 4 6 8 10 2 4 6 8 10 # trees sampled per plot
    18. 18. How much sampling? Power curves Effect size = 0.05 Effect size = 0.10 Effect size = 0.20Power (1-β) for leaf %N 2 4 6 8 10 2 4 6 8 10 2 4 6 8 10 # trees sampled per plot
    19. 19. Power - likelihood we don’t detect a CO2 effect on leaf N that is real Effect size = 0.15High probability of rejectingthe null and finding atreatment difference whenthere actually is a difference Power (1-β) for leaf %NWith 2 leaves per tree, the possible minimum sample size to be reasonably likelyto detect a -15% effect on leaf N may be about 3 trees per plotLow probability of rejectingthe null when it is actuallyfalse # trees sampled per plot
    20. 20. Pretreatment leaf net photosynthetic capacity at390 ppm CO2 among 18 mature Eucalyptus trees (6 month old leaves sampled in autumn) Grand mean Anet = 16.4 ± 0.7 mmol CO2 m-2 s-1 or 72 nmol CO2 g-1 d.w. s-1 16.8 17.9 18.1 17.0 14.9 13.7
    21. 21. Power - likelihood we don’t detect a CO2 effect on photosynthesis that exists Effect size = 0.2 High probability of rejecting the null and finding a treatment difference when there actually is a difference Power (1-β) for AnetWith 2 leaves per tree, the possible minimum sample size to be reasonably likelyto detect a 20% effect on net photosynthesis may be about 3 trees per ring Low probability of rejecting the null when it is actually false # trees sampled per ring
    22. 22. Conclusions – can we detect effects of elevated CO2 at +150ppm on plants? This study evaluated variability in leaf N and Anet before the CO2 treatment in FACE started. The largest source of variability in N is tree-tree, not plot-plot. The experiment is robust enough that we can find a statistical difference when it really exists, with our minimal replication.
    23. 23. Conclusions – continued We can statistically detect a CO2 effect decreasing leaf N concentration by 15% with 3 rings and adequate tree subsamples, but not less. We can detect a 20% increase in Anet with eCO2 with our replication. FACE has now (2 wks ago) reached full treatment for [CO2].
    24. 24. AcknowledgementsSee: www.uws.edu.au/hie/eucfaceEucFACE is an initiative supported by: Commonwealth through DIISRT and the Australian Research Council
    25. 25. How much did ↑CO2 drive increased photosynthesis in the canopy?K. Crous, T. Gimeno data Ambient Elevated +37% 25 Pretreatmt 25 +17% 25 Net photosynthesis 20 20 20 (mol m s ) -2 -1 15 15 15 10 10 10 5 5 5 0 0 0 May 2012 Oct 2012 Feb 2013 est. (+15% in CO2) (+39% in CO2) Data from ‘old’ leaves at the canopy top of 18 Eucalyptus trees across the 6 plots. The expected enhancement is estimated from short-term [CO2] increases at leaf-level and this is an upper bound to what is possible.
    26. 26. What does is a free-air experiment? FACE = free-air CO2 enrichment [CO2] is computer-controlled within a large volume

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