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United States Department of Agriculture

Agricultural Research Service

Research Project: MANAGING FORAGE AND GRAZING LANDS FOR MULTIPLE ECOSYSTEM SERVICES

Location: Pasture Systems & Watershed Management Research

Title: Relationship between annual canopy photosynthesis and ecosystem respiration in humid-temperate pastures

Author
item Skinner, Robert

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 28, 2012
Publication Date: October 22, 2012
Citation: Skinner, R.H. 2012. Relationship between annual canopy photosynthesis and ecosystem respiration in humid-temperate pastures[abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. Paper No. 81-15.

Interpretive Summary: An intrepretive summary is not required.

Technical Abstract: Increasing nitrogen fertilization of a mature cool-season pasture increased annual photosynthetic C uptake (GPP) and forage yield but also increased ecosystem respiration (Re), such that net ecosystem exchange (NEE) and soil C sequestration were not affected by the increased fertility. A nine-year study monitoring carbon dioxide flux at two pasture sites examined in detail the relationship between photosynthesis and respiration under a range of environmental conditions. As expected, forage yield was highly correlated with GPP (P = 0.0006). However, yield was also positively correlated with Re ((P = 0.0004). No significant relationship existed between GPP or Re and NEE. Regressing Re against GPP yielded an equation with y-intercept near zero and slope of -0.96 (r**2 = 0.87, P is less than 0.0001) (according to meteorological sign convention, GPP is negative and Re is positive). In all cases, only a single equation was necessary to describe both pastures. Although the results suggest that GPP should exceed Re as productivity increased, the difference was so small that NEE would only be a slight sink of about -80 g CO2 m**-2 yr**-1 for the most productive year of the study.

Last Modified: 10/1/2014
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