Integrated system for photosynthesis and greenhouse gas flux measurements

点击翻译按钮获取中文摘要

Non-CO2 greenhouse gases contribute ~30% to net climate forcing that drives climate change: nitrous oxide (N2O) and methane (CH4) are of particular importance, with terrestrial ecosystems acting as both important sinks and sources for these gases. Non-CO2 greenhouse gases have recently been emphasized from a policy perspective, as emissions are unintentional and often represent economic losses, but there are important science gaps needed to inform policy and management practices. Until recently it was assumed that soils were the primary sites of exchange of N2O and CH4; however, recent studies have discovered that substantial exchange of these gases that occurs through plants, in particular trees. A better understanding of these fluxes is needed to develop management practices that reduce sources and enhance sinks of non-CO2 greenhouse gases. Photosynthetic gas-exchange is the main physiological process by which plants exchange gases with the atmosphere - including CO2 and water vapor as well as trace gases dissolved in the xylem stream; however, there have been few measurements that link CO2 flux with the flux of other greenhouse gases. Our research group has recently documented substantial uptake of CH4 by tree foliage in managed forests in Ontario but understanding the mechanisms (e.g., is CH4 oxidation due to methanotrophic bacteria within tree leaves?) and controls (e.g., how does this vary with changes in light and temperature?) for these processes requires a gas-exchange system that integrates photosynthesis measurements with trace gas fluxes. In addition to CH4 flux, N2O flux mediated by plants is likely to be important in managed systems with high N inputs, such as urban forests and green roofs. Recent innovations in spectroscopic gas analysis allow for rapid and accurate measurements of both N2O and CH4 concentrations. We request funds for a one-of-a-kind system that integrates photosynthetic measurements with a rapid N2O and existing field-portable CH4 analyzer, allowing for studies of fluxes of all three greenhouse gases (N2O, CH4 and CO2) by leaves, stems, and other plant organs, as well as measurements of soil and whole-system fluxes. The measurements allowed by this system will permit a better understanding of mechanisms involved in greenhouse gas exchange in managed ecosystems and will facilitate development of management approaches with the ultimate goal of enhancing climate mitigation by managed forests and urban living infrastructure.