☆ 4.2 Article

Diurnal and Seasonal Patterns in Ecosystem CO2 Fluxes and Their Controls in a Temperate Grassland

RANGELAND ECOLOGY & MANAGEMENT (2010)

Journal

RANGELAND ECOLOGY & MANAGEMENT

Volume 63, Issue 1, Pages 62-71

Publisher

SOC RANGE MANAGEMENT

DOI: 10.2111/08-066.1

Keywords

closed-chamber technique; ecosystem respiration; net ecosystem exchange; plant assimilation; temporal scales

Funding

US National Science Foundation [DEB-0318716]
Swiss National Science Foundation [PBEZ-104320, PBEZA-104320]
Office of Agriculture, Bureau for Economic Growth, Agriculture and Trade, United States Agency for International Development [PCE-G-00-98-00036-00]

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Abstract

There is considerable interest in understanding processes of carbon dioxide (CO2) uptake and release in grasslands and the factors that control them. Many studies have investigated how CO2 fluxes vary over time (monthly, seasonally, annually). However, with the exception of net ecosystem CO2 exchange (NEE) and ecosystem respiration (R-eco), little information is available on diurnal flux patterns, despite their importance in determining total ecosystem CO2 gains and losses. To better understand these variations, we measured CO2 fluxes (NEE, R-eco, soil respiration [R-soil], canopy respiration [R-canopy], plant assimilation [assimilation]) with a climate-controlled closed-chamber system over 24 h once a month from May to September during the 2005 growing season in a mesic grassland in Yellowstone National Park. We also assessed how environmental factors (photosynthetic active radiation [PAR], air temperature, soil temperature, soil moisture) were associated with these diurnal and seasonal flux patterns to identify the main drivers of the fluctuations in CO2, Measurements were conducted simultaneously on two plots: one irrigated, the other unirrigated. Absolute values of all fluxes were greatest in midsummer (June-July), and lowest in spring and fall (May, September) at both plots. Variation in soil moisture as a result of irrigation did not lead to pronounced differences in seasonal CO2 fluxes and did not influence the diurnal patterns of CO2 uptake and release. Instead, the diurnal and seasonal variations of our ecosystem fluxes were related to PAR and temperature (air/soil) and soil moisture and temperature (air/soil), respectively, at both plots. Thus, continued anthropogenic increases in greenhouse gas emissions that are expected to change the intensity of radiation, temperature, and precipitation may strongly affect the diurnal and seasonal patterns in CO2 uptake and release. Such chamber-based information combined with the measurement of environmental variables could be important for modeling CO2 budgets when no continuous measurements are available or affordable.

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Eighteen years of upland grassland carbon flux data: reference datasets, processing, and gap-filling procedure

Bruna. R. R. Winck, Juliette M. G. Bloor, Katja Klumpp

Summary: Plant-atmosphere exchange fluxes of CO2 measured with the Eddy covariance method are important for assessing ecosystem carbon budgets. This study presents eddy flux measurements for a managed upland grassland in France over a 20-year period. Pre-processing and post-processing approaches were used to overcome data gaps in the long-term datasets. The resulting datasets can be used for studying the impact of climate change on grassland ecosystems and for model evaluation and validation in carbon-cycle research.

SCIENTIFIC DATA (2023)