Ecosystem : Theories, methods, lenses

Dr. Whendee Silver Ecology and Pop Quiz What is ? Ecosystem Ecology: the study of , the abiotic environment, and their interactions in a defined area where the connections within the area are stronger than the connections across boundaries What is biogeochemistry? Biogeochemistry: the study of the biological, chemical, physical, and geological processes and reactions that govern the environment Where does the in come from? Where does the energy in ecosystems come from? What are the essential macronutrients for most ? What are the essential macronutrients for most life?

Nitrogen (N), (P), (Ca), (Mg), (K), and (S) Can you name the big three greenhouse gases? Can you name the big three greenhouse gases?

Carbon dioxide (CO2), (N2O), and (CH4) Can you give their 100 year global warming potentials? Can you name the big three greenhouse gases?

Carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) Can you give their 100 year global warming potentials?

1, 298, 34 Ecosystem: Definitions and Terminology 420 Atmospheric CO2 concentrations are increasing

400

380

360

340 Carbon dioxide (ppm)

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300

1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Data: Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/) and Dr. Ralph Keeling, Scripts Institution of

Accelerated Growth in Eastern

McMahon et al PNAS 2010 Thesis statement: Atmospheric carbon dioxide concentrations, through its role in , is the dominant controller of ecosystem carbon storage.

Question: What is the ecosystem response to elevated carbon dioxide?

Hypothesis: Carbon dioxide is a key for growth, thus increased concentrations will stimulate plant growth, and greater plant growth will lead to greater overall carbon storage in the ecosystem. Net carbon balance of an ecosystem (net ecosystem production = NEP)

NEP = GPP - Rauto - Rhetero

Where: GPP is gross photosynthesis Rauto is plant respiration Rhetero is the respiration of How do you measure NEP? Eddy co-variance techniques measure CO2 in and CO2 out

• Good for net carbon balance • Not good for discerning mechanisms • Couple with round based measurements and models Free Air CO2 Enrichment (FACE) Other experimental approaches CO2 Exposure Methods: Pros and Cons Pots Seedlings or saplings, not representative of mature trees become root-bound No ecosystem interactions or Chambers and monoliths Artificial light, humidity and levels in the chambers No ecosystem processes Limited to one or a few low stature plants Free-Air Carbon Exposure Studies (FACE) conditions Plants compete for light, and soil

Expensive, much CO2 is advected away. Control at set point varies by +/- 10 to 20% Expensive to replicate Sampling effects Elevated CO2 Studies Plant growth (NPP) can be enhanced per unit of area after canopy closure in some , but not in others Aboveground plant growth (NPP) can be enhanced in some tree species, but not in others

) 12000

1 -

4 y 4 10000

2 -

8000

6000 Ambient Elevated 4000

2000

Aboveground NPP (g m AbovegroundNPP 0 Alnus Betula Fagus

Hoosbeek et al. 2011