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Carbon-nitrogen cycle interactions, ozone stress, and N emissions speciation Peter Thornton, J.-F. Lamarque, M. Vertenstein, N. Rosenbloom External N Cycling Internal N Cycling Deposition/ Fixation Retranslocation Nitrification/ Denitrification Fire Losses Plant Uptake Litterfall Leaching Immobilization Atmospheric CO2 Atmospheric N species Legend Vegetation Biomass C flux N flux Temp sensitivity Soil Organic Matter Coupled Carbon-Nitrogen dynamics • Strong feedback between decomposition and plant growth: soil mineral N is the primary source of N for plant growth. • Can result in a shift from C source to C sink under warming. P.E. Thornton, NCAR Land biosphere sensitivity to increasing atmospheric CO2 (L) CLM-C CLM-CN (CO2,Nfix,dep) CLM-CN (CO2,Nfix) CLM-CN (CO2) C4MIP models C4MIP mean Results from offline CLM-CN, driven with CAM climate, in carbon-only (CLM-C) and carbon-nitrogen (CLM-CN) mode, from present to 2100. Using SRES A2 scenario assumed CO2 concentrations. Land biosphere sensitivity to increasing atmospheric CO2 (L) CLM-CN (CO2,Nfix,dep) CLM-CN (CO2,Nfix) CLM-CN (CO2) Evidence that increasing Nlimitation under rising CO2 has an important effect on the transient behavior of L, and that consideration of anthropogenic N deposition reverses this trend by around 2060. Cumulative land carbon uptake and net ecosystem exchange, 1850-2100 Total C uptake (PgC) Mean NEE (PgC/y) Expt 1850-2000 2000-2100 1980-2000 2080-2100 N dep 16 50 -0.24 -0.73 CO2 fert 61 220 -0.98 -2.56 CO2+Ndep 79 301 -1.31 -4.13 223 843 -3.80 -10.75 CLM-C 5 0 4 -5 3 -10 CLM-C CLM-CN 2 -15 1 -20 0 -25 Tair Prcp Coupling C-N cycles buffers the interannual variability of NEE due to variation in temperature and precipitation (global means, control simulations). NEE sensitivity to Prcp (PgC / mm d -1) NEE sensitivity to Tair (PgC / K) NEE sensitivity to Tair and Prcp (interannual variability) Potential for complex climate feedbacks depending on the spatial patterns of changing temperature and precipitation. NPP variability dominates the Tair and Prcp response in most locations, but HR dominates that Prcp response in cold climates, due to feedback between snowpack, soil warming, and enhanced HR. NEE sensitivity to Tair and Prcp: effects of rising CO2 and anthropogenic N deposition 60 % change from control 40 20 0 -20 CLM-C: +CO2 CLM-CN: +CO2 CLM-CN: +CO2 +Nmin -40 Tair Prcp Carbon-only model has increased sensitivity to Tair and Prcp under rising CO2. CLM-CN has decreased sensitivity to both Tair and Prcp, due to increasing N-limitation. Summary of plant response to ozone stress H 2O O3 ? leaf cuticle S S Problems: Plant responses: • Wound/defense response (VOCs) • Reduced mesophyll conductance • Reduced chloroplast function • Reduced stomatal conductance ? CO2 Chloroplast • Species-specific responses • Species mixes and competition important • Few observations on native species • Strong interaction with water stress response Speciation of land N emissions Nitrification vs. denitrification depends on aerobic state of soil, probably at the microscopic scale. Sophisticated models already exist, and it should be possible to adapt them for use in CLM-CN. Agricultural emissions could be tied to new efforts with crop modeling.