1. Moisture availability constrains soil trace gas fluxes in an eastern Amazonian regrowth forest Moisture availability constrains soil trace gas fluxes in an eastern Amazonian regrowth forest Steel Vasconcelos, Daniel Zarin, Eric Davidson, Francoise Ishida, Elisana Santos, Maristela Araújo, Débora Aragão, Lívia Rangel-Vasconcelos, Francisco Oliveira, William McDowell, Claudio Carvalho University of Florida Woods Hole Research Center Instituto de Pesquisa Ambiental da Amaznia Instituto de Pesquisa Ambiental da Amazônia Universidade Federal Rural da Amaznia Universidade Federal Rural da Amazônia University of New Hampshire Embrapa Amaznia Oriental Embrapa Amazônia Oriental

2. CO 2, N 2 O, and CH 4 greenhouse gases CO 2, N 2 O, and CH 4 greenhouse gases NO precursor of O 3 NO precursor of O 3 Gas production and consumption strongly linked to the availability of soil moisture Gas production and consumption strongly linked to the availability of soil moisture Limited understanding of the mechanisms that control variation in soil trace gas emissions Limited understanding of the mechanisms that control variation in soil trace gas emissions Rainfall, litterfall, and decomposition confounding factors in observational studies Rainfall, litterfall, and decomposition confounding factors in observational studies Very few manipulative studies in tropical forests Very few manipulative studies in tropical forests Introduction

3. Quantify the impacts of soil moisture availability on trace gas fluxes in a regrowth forest stand in eastern Brazilian Amazonia Quantify the impacts of soil moisture availability on trace gas fluxes in a regrowth forest stand in eastern Brazilian Amazonia Objective

4. Pará State, Brazil Pará State, Brazil Regrowth forest (13 years old in 2000) Regrowth forest (13 years old in 2000) Rainfall = 2540 mm Rainfall = 2540 mm T air = 24 – 27 o C T air = 24 – 27 o C Oxisol Oxisol Study area

5. Treatments = control, irrigation, and litter removal Treatments = control, irrigation, and litter removal Replicates = 4 Replicates = 4 Plot size = 20 m x 20 m Plot size = 20 m x 20 m Experiment layout

6. Treatment Dry-season irrigation (5 mm d -1 )

7. CO 2 NO, N 2 O, CH 4 TechniqueIRGAChemiluminescence Gas chromatography Collars per plot 32 Frequencybi-weeklybi-monthly Measurement dates 6018 Trace gas measurements

8. Statistical analysis Repeated measure analysis: treatment, date, and treatment x date effects Repeated measure analysis: treatment, date, and treatment x date effects Contrast analysis: season (wet vs. dry) and treatment within season effects Contrast analysis: season (wet vs. dry) and treatment within season effects

9. Irrigation increases soil water availability

10. Irrigation increases soil respiration CO 2 efflux during the dry season CO 2 efflux during the dry season Irrigation maintained wet season R soil levels Irrigation maintained wet season R soil levels Soil CO 2 pulse events Soil CO 2 pulse events

11. Irrigation does not affect NO efflux

12. Irrigation increases N 2 O efflux Wet season efflux > dry season efflux Wet season efflux > dry season efflux Irrigation > control Irrigation > control

13. Irrigation increases CH 4 efflux Wet season efflux > dry season efflux Wet season efflux > dry season efflux Irrigation efflux > control efflux Irrigation efflux > control efflux

14. Moisture availability constrains CO 2, N 2 O, and CH 4 emissions during the dry season Moisture availability constrains CO 2, N 2 O, and CH 4 emissions during the dry season The substantial impacts of soil moisture on soil CO 2 efflux may have important implications for soil respiration modelling approaches The substantial impacts of soil moisture on soil CO 2 efflux may have important implications for soil respiration modelling approaches Conclusion

15. Next step: examining mechanisms Treatments: control (C) root exclusion (NR) litter removal (NL) litter removal + root exclusion (NLNR) Root respiration = C – NR Microbial respiration litter = C – NL Microbial respiration soil = C – NLNR Trenching experiment

16. Osório Oliveira, Glebson Souza, Evandro Silva (MANFLORA field assistants) Osório Oliveira, Glebson Souza, Evandro Silva (MANFLORA field assistants) Raimundo da Silva (Estação Experimental de Castanhal – UFRA) Raimundo da Silva (Estação Experimental de Castanhal – UFRA) The Andrew W. Mellon Foundation and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil for the grants Acknowledgements