The fate of forests and the carbon they contain is critical to determining future climates. Trees are important carbon stores because of their size and longevity, but for these same reasons, they are difficult to study in manipulative experiments. Growth chambers introduce undesirable artifacts to the growth environment. Free-Air CO2 Enrichment (FACE) is representative of natural conditions, but expensive. Due to the tight coupling of CO2 with other limiting factors in photosynthesis (water, light, nutrients), environmental stressors must be studied in combination; however, FACE is so expensive that diverse study designs have not been possible. We developed a low-cost alternative for testing the effects of elevated CO2 on tree seedlings, to study their responses to future climates.
This summer, we will conduct a pilot study treating valley oak (Quercus lobata) seedlings with elevated (700ppm) CO2 levels. Plants will be grown in an outdoor plot in Davis, California, with screens around each sub-plot to aid in CO2 control. The plant microenvironment will be minimally affected due to turbulent mixing of air within the plot.
Over the course of 12 weeks, we will measure plant height, stomatal conductance, and chlorophyll fluorescence. Before and after the experimental period, we will measure light-response curves for a subsample of plants. After harvesting, we will measure biomass, root length, and stomatal density.
Results/Conclusions
In this pilot study, we will build CO2 enrichment apparatus for six plots, each containing 10 seedlings. There will be two replicate plots at each of three treatment levels: ambient CO2, elevated CO2, and negative control. CO2 will be continuously pumped into the elevated plots, with levels monitored by a LiCOR 840 and CR3000 datalogger. Preliminary testing of the CO2 control apparatus shows it is capable of maintaining a mean concentration of 707.5 ppm (sd = 54), with a minimum of 513 and a maximum of 1085 ppm. These numbers compare favorably to similar experiments in the literature (e.g. Leadley et al. 1997) and are significantly better than the control afforded by a conventional FACE design.
Our modular, highly portable design can be used to greatly expand the scope of FACE studies across different plant types and ecosystems. We plan to apply these methods in forest systems as diverse as Sierran mixed conifer and northeastern mixed hardwood forests. Our data will help us determine the best applications of our design, to advance understanding of plant physiological responses to climate change.