This Major Research Instrumentation award funds the acquisition and development of a next-generation system for measuring plant and ecosystem gas-exchange. The new instrument builds on the Carnegie Institution's work in an area that continues to provide fundamental insights for plant physiology and biochemistry, plant evolution, plant ecology, ecosystem ecology, and global biogeochemistry. The new system will incorporate recent technology developments, including cavity ring-down spectroscopy (CRDS, for NH3 and stable isotopes) and dual quantum cascade lasers (for COS) into a single system that can measure all NH3, COS, CO2, H2O with high speed and accuracy, at the very low concentrations typical of ambient conditions, at the plant and ecosystem scale. The next-generation gas exchange system will enhance research and teaching infrastructure for a range of users, including faculty and post-docs at three of the Carnegie Institution's departments (Global Ecology, Plant Biology, Geophysical Laboratory), graduate and undergraduate students from regional universities and collaborators from around the world. Results from the studies conducted with the new system will be broadly disseminated through abstracts and peer reviewed publications, as well as by active participation at professional meetings.
Earth’s biosphere is dependent on metabolic energy from photosynthesis. Furthermore, the carbon cycle, hydrologic cycle and physical climate system are strongly coupled with the photosynthetic activities of plants. However, we don’t have very good tools to study this key process over the range of scales significant for understanding the biosphere. The upgrade in instrumentation provided by this MRI grant has enabled several creative new approaches to this problem. Studies of c3/c4 evolution - PhD student Jennifer Johnson completed a study for her thesis on plants of the genus Flavaria some of which have photosynthetic properties intermediate between the C3 and C4 pathways and others which have normally functioning C3 and C4 pathways. Dr. Johnson’s work came up with new metrics to analyze the performance of these intermediate species and a new hypothesis for how the C4 pathway could have evolved in this genus. Her work was honored as the best student presentation at the ESA meeting in 2014. This work is relevant to plant breeding and genetic engineering of agricultural crops. For example the Gates Foundation is now investing large sums into a project to introduce c4-photosynthesis into rice. It is estimated that this could nearly double the productivity of rice if it were successful. Knowledge of the steps that evolution took in making this transition can provide invaluable guidnce. Studies of stomatal development and function. Stomata control water loss by leaves and their functional properties are key in linking the hydrologic cycle to photosynthesis. PhD student Graham Dow conducted research using genetic and physiological tools to clarify the roles of developmental mechanisms that control the size and density of stomata on the epidermis, the physiology of the guard cell and the development of mesophyll tissue in determining the functional properties of the leaf system. This work is a major breakthrough in understanding the basis for the elegant control properties. Graham used quantitative measurements to show that the anatomical dimensions and density of stomata laid down during leaf development are at least as important as the physiological mechanisms that cause the pores to open and close in response to signals like the concentration of CO2. Studies of forest response to drought. Recent severe droughts in the Western US have been associated with heavy damage to forests of the region. The aspen trees of the Rocky Mountains have been particularly hard hit with large areas of this iconic forest being killed. While it is not clear that this event is specifically caused by climate change, it is exactly the type of response that is expected from climate models forced with greenhouse gases. However, models do not now have the capacity to simulate these impacts of climate change. Dr. Bill Anderegg, a recent PhD. from our group has examined the physiological and hydrological mechanisms that result in tree death, and has developed a model that accurately simulates the boundary between effected and unaffected stands as monitored by remote sensing and based on a modeled re-construction of the 2002 drought. These studies have used gas exchange and stable isotope measurements conducted with equipment provided by the MRI. Measurement of Photosynthesis at large geographic scales. One of the weakest links in our understanding of photosynthesis in the Earth System is the inability to measure this process at scales larger than a typical agricultural field. At these larger scales, the CO2 concentration in the atmosphere responds to the combined influence of photosynthesis and respiration. Often these nearly cancel, hence there is no good way to check on models of either of these processes. Berry and co-workers have conducted studies with another trace gas, carbonyl sulfide (OCS) which can serve as a proxy for photosynthesis. It is taken up in parallel with CO2, but there is no analog to respiration in terrestrial ecosystems. Therefore, OCS has the potential for integrating photosynthesis over large spatial scales. The challenge is that the abundance of OCS is only on millionth that of CO2. Special instrumentation purchased with this grant has enabled us to demonstrate the ability to measure OCS flux by eddy covariance. This work has led to newly funded studies that will apply this methodology to studies of photosynthesis of the Amazon basin. Measurement of photosynthesis from space. Recent advances in spectroscopy have made it possible to separate photons emitted by plants as chlorophyll fluorescence from the more abundant flux of reflected sunlight. The fraction of photons re-emitted as fluorescence is very dynamic and is under metabolic control. Therefore, it can be regarded as a product of photosynthesis. This measurement from space opens up the possibility for direct sensing of a physiological process from space. Spectrometers purchased with this grant are being used to conduct ground-based measurements need to establish the theoretical framework required to interpret these new measurements from space.
