1. CH10: Insights from Experimentation

2. FIGURE 10.1 Photomicrograph of a stomata on the underside of a leaf.
Source: Dan Hungerford.

3. FIGURE 10.2 Plankton response to ocean acidification.
Planktonic algae have calcium carbonate skeletons (coccoliths) that are affected by the pH of seawater. In the upper panels (a-c) are plankton grown in seawater with a pH similar to current. The lower panels represent deformities of coccoliths in plankton grown in seawater with an acidity similar to that expected when atmospheric CO2 has doubled. Source: Riebesell et al. (2000). Reproduced with permission from Nature.

4. FIGURE 10.3 Laboratory and greenhouse experiments.
Diffusers and enclosures may be used to maintain constant elevated CO2 levels, whereas greenhouses or other warming devices may be used to manipulate temperature. Source: Courtesy of Scottish Crop Research Institute.

5. FIGURE 10.4 Decline in single-plant studies, increase in whole-vegetation experiments.
The blue bars indicate total number of publications from 1987 to The green bars indicate the change in percentage publication between the first half of the time period (1987–1991; top bar) and the second half of the time period (1992–1996; bottom bar). Source: Korner (2000). Reproduced with permission from the Ecological Society of America.

6. FIGURE 10.5 Increase in biomass for various categories of species (herbaceous and woody C3 plants, C4 species, and CAM species).
Graphs show an increase in biomass enhancement ratio, a measure of increase in biomass. Box plots such as these indicate the 5th (bottom horizontal line), 25th (bottom line of box), 50th (midline of box), 75th (top line of box), and 95th (upper horizontal line) percentiles of the distribution. Source: Poorter and Navas (2003).

7. FIGURE 10.6 Acclimation to elevated CO2 over time.
Trees grown under elevated CO2 show a strong response initially, but the response declines strongly with time. Source: Idso (1999).

8. FIGURE 10.7 Biomass enhancement for seven tropical plant species grown in isolation and in a mixed community.
The CO2 enhancement observed in the isolated trial is not evident in the mixed community. Source: Poorter and Navas (2003).

9. FIGURE 10.8 Effects of experimental conditions on increase in biomass under enhanced CO2.
(a) Biomass enhancement ratio of plants grown in isolation versus plants grown in monoculture (r = −0.25, n = 27, p > 0.2). (b) Isolated plants versus plants grown in a mixed culture (r = 0.04, n = 33, p > 0.8). (c) Plants grown in monoculture versus plants grown in a mixture of species (r = 0.58, n = 50, p < 0.001). Dotted line 5 1:1. Source: Poorter and Navas (2003).

10. FIGURE 10.9
Active (a) and passive (b) warming experiments. The active warming devices include the use of infrared warming lamps. Passive warming depends on blocking of air circulation or intensification of sunlight to create warmth. Passive warming devices are often simply circles or boxes of glass or clear plastic, which act much like miniature greenhouses but allow multispecies interactions and have minimal impact on received precipitation. Source: (a) Courtesy of Charles Musil. (b) From the National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara.

11. FIGURE 10.10 Transplantation and open-top chamber experiments.
Transplantation preserves plant–plant interactions and soil properties (a). It is usually implemented with the movement of plants embedded in whole soil. Open-top chambers (b) preserve plant and soil relationships over a limited area. Source: Finnish Forest Research Institute.

12. FIGURE 10.11 Free air CO2 enrichment (FACE) experiments.
FACE experiments use massive diffusers to elevate CO2 concentrations over a large area (a). Diffusers are often arrayed around a central measurement tower. Effects on grassland (b), forest (c), other vegetation types and crops have been measured with FACE experiments. Source: (a) Courtesy of Jeffrey S. Pippen. (b) Courtesy of Professor Josef Nösberger, Swiss Face Experiment (ETH Zurich). (c) From Brookhaven National Laboratory.

13. FIGURE 10.12 Response to warming.
The effects of warming on (a) soil moisture, (b) soil respiration, (c) N mineralization, and (d) plant productivity are shown for multiple studies from throughout the world. Measured mean effects at each study site are indicated by open circles; bars indicate 95% confidence intervals. The vertical line indicates no effect. Source: Rustad (2001).

14. FIGURE 10.13 Acclimation in experimental and natural settings.
Single-plant experiments seldom span time frames long enough to detect acclimation. Whole-ground experiments, usually conducted over longer time frames, clearly show the effect of acclimation. Source: Idso (1999).

15. FIGURE 10.14 Slumping arctic soils lead to changed vegetation composition.
Source: Kokelj et al. (2009).

16. Relevance of Living Plants to Atmospheric CO2 Concentrations.
The influence of the biosphere on the composition of the atmosphere, carbon cycles, and climate varies across timescales. On timescales of decades, human pollution and forest destruction may cause major increases in atmospheric CO2 that will not be removed by the oceans and other natural sinks for hundreds of thousands of years. On scales of thousands to millions of years, the ocean will absorb and buffer short-term changes in CO2. On long timescales of tens of millions of years, photosynthesis generated the oxygen content of the atmosphere. Source: Korner (2000). Reproduced with permission from the Ecological Society of America.