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Month Aug. Sept. Day 26 28 2 4 9 11 16 18 23 Topic Introduction The ecosystem concept Climate/soils Soils II Ecosystem energy balance Water cycling Carbon GPP/NPP NEP C,M&M 1 2 3 4 4 5 6 6 Mg C ha-1 yr -1 Climate controls over NPP 25 20 l l l l l 15 10 5 0 0 2000 l 4000 6000 8000 Mean Annual Precipitation (mm) • At a global scale, NPP is strongly correlated with ppt and T • Water increases plant growth in drier ecosystems. Also increases decomposition and nutrient cycling. • In very wet ecosystems, ppt can limit NPP by decreasing light or nutrient availability Climate controls over NPP Mg C ha-1 yr -1 25 20 15 10 5 0 -15 -10 -5 l l l l 0 5 10 15 20 25 30 Mean Annual Temperature (ºC) • Temperature is related to growing season length • Temperature stimulates decomposition and nutrient cycling. 25 25 Mg C ha-1 yr -1 Mg C ha-1 yr -1 Climate controls over NPP 20 l l l l l 15 10 5 0 0 2000 l 4000 6000 20 15 10 5 8000 Mean Annual Precipitation (mm) 0 -15 -10 -5 l l l l 0 5 10 15 20 25 30 Mean Annual Temperature (ºC) In ecosystems where correlations suggest a strong climatic limitation of NPP, experiments and observations indicate that this is mediated primarily by climatic effects on belowground resources. Resource control • Proximate control over NPP is availability of resouces • Light, CO2, H2O, nutrients (N,P,K,Mg,Ca,…) • Many ecosystems increase NPP when N or P fertilizer is added. • Some ecosystems increase NPP when CO2 or H2O is added. • Where T has been manipulated, NPP doesn’t respond directly. Vitousek and Farrington 1997 Variation in NPP Global Potential Net Primary Productivity Mg C ha -1 yr-1 Biome Differences in NPP (Terrestrial) • Length of the growing season is the major factor that explains biome differences in NPP • Differences in leaf area account for most of the variation in biome NPP within a growing season • Leaf area, in turn, is determined by soil resources, climate, and time since disturbance • Disturbance substantially modifies the relationship between NPP and climate NEP is the balance between two large fluxes: GPP and ecosystem respiration Ecosystem Carbon Balance Net Ecosystem Production (NEP) = GPP - Recosys Recosys= Resp. of plants, animals, and soil microbes Net Ecosystem Exchange (NEE) is fairly similar, but… Remember to check the sign convention! Sensu Chapin et al. 2006 Flux to ecosystem Ecosystem accumulating C-sink Is + NEE accumulation of C in the ecosystem, or in the atmosphere? Ecosystem loosing C-source Flux to atmosphere Valentini et al. 1998 Ecosystem Carbon Balance Net Ecosystem Carbon Balance (NECB) = Net rate of C accumulation or loss dC/dt Sensu Chapin et al. 2006 Ecosystem Carbon Balance Net Ecosystem Carbon Balance (NECB) = GPP - Recosys other C transfers Recosys= Resp. of plants, animals, and soil microbes NECB = NPP Flateral -Rheterotrophic -Fdisturb -Fleach -Femiss Ecosystem Ecosystem Carbon Balance + NEP 0 - (a very long) time Atmosphere Steady state = NEP near zero Inputs = outputs Ecosystem Carbon Balance • Positive NECB; GPP > Recosys + other C losses; •ecosystem is removing C from the atmosphere = C sink • Negative NECB; GPP < Recosys + other C losses; •ecosystem is releasing C to the atmosphere = C source • Factors that affect GPP and C losses differentially will change NECB • Increased CO2 and N deposition have greater direct effect on GPP. Reduction in soil moisture in a wetland may have a greater effect on Rheterotroph and fire GPP is invariant across latitudes As a result, NEE decreases with latitude While Re decreases as latitude (T proxy) increases Valentini et al. 1998 Lecture ended here Eddy Covariance (NEE) Eddy Covariance Network Net Ecosystem Exchange Tower network observations show that most ecosystems that have been measured are net sinks for CO2 1. Ecosystems may be typically net sinks of C in between disturbance (no steady state) 2. Recent environmental changes such as increased atm. CO2 or N deposition may be stimulating GPP more than Recosystem 3. C loss through leaching and other transfers may be an important component of regional C balance 4. Mid-successional ecosystems with high NPP may be over represented in the network Ecosystem Ecosystem Carbon Balance + NEP 0 - time Atmosphere Net Biome Production (NBP) = NECB, integrated over large spatial scales to include removal of C by fire and harvest Sensu Schultze et al. 1997