Seasonal dynamics of soil, litter, and ecosystem respiratory carbon dioxide fluxes as indicated by stable isotope analyses Jean Ometto, Luiz Martinelli, F Yoko Ishida & Edmar Mazzi Cena – University of São Paulo, Brasil Jim Ehleringer, Tomas Domingues Univeristy of Utah, USA H Jackson Silva, Sebastião Lopes UFPA – Santarém, Brasil Joe Berry Carnegie Institution, USA

(Ometto et al, submitted)

Focus of heat in 1998 in the BR Amazon source: IBAMA-PROARCO

cici caca

Measurements δ 13 C and δ 18 O of CO 2 – Keeling plots –Ecosystem –Soil – surface / profile –Decaying wood; leaves –Troposphere –River DIC δ 18 O –leaf water, –soil/stem water, –water vapor δ 13 C and δ 15 N –Leaves – spp (legumes / non-legumes) –Wood / bark –Litter –SOM

Leaves sampling for δ 13 C CHO

Air Sampling δ 13 C CO 2

Results Carbon isotopic variation within the canopy Seasonal isotopic variation of fixed organic carbon Isotopic variation on the ecosystem respired 13 CO 2 associated to logging activities Isotopic variation of soil respired CO 2 – Importance of the litter for the 13 C signal

c i /c a = C = m c i /c a = C = m c i /c a = C = m c i /c a = C = m

= δ 13 CO 2 canopy – δ 13 C leaf Flona - Santarém

Results Carbon isotopic variation within the canopy Seasonal isotopic variation of fixed organic carbon Isotopic variation on the ecosystem respired 13 CO 2 associated to logging activities Isotopic variation of soil respired CO 2 – Importance of the litter for the 13 C signal

Seca Floresta Control Plot Dry Plot Wet season Dry seasonWet seasonDry season

Seasonal variation of the upper canopy leaves d13C at k83 logged forest

Results Carbon isotopic variation within the canopy Seasonal isotopic variation of fixed organic carbon Isotopic variation on the ecosystem respired 13 CO 2 associated to logging activities Isotopic variation of soil respired CO 2 – Importance of the litter for the 13 C signal

Liana cutting Logging

Liana cutting Logging

(1)Before logging the two years were generally similar. (2)From Sept to April the logged forest lost about 2 TC more than during the previous year, presumably because of decomposition of slash and reduced leaf area (3)After May the years were similar, presumably because fast growing plants are now filling the gaps. LoggingWet season begins Years converge Before logging after logging M.Goulden, S.Miller δ 13 C R-CO 2

Cumulative NEE BLUE: PRE-LOGGING GREEN: POST-LOGGING 2000/ / δ 13 C R-CO 2

1- The heavier signal prior to the logging Can be related to a practice that consist on cutting lianas 6 to 8 months before the logging starts. Lianas are important on the system water cycle Lianas are isotopically heavy and the slash decomposing could contribute to a heavier respired CO 2. What the isotopes are showing us:

2 - Strong heavy signal in the dry season after logging The daily cycles of Net Ecosystem Exchange (NEE) during the 2001 dry season after the harvest showed less afternoon uptake and less nighttime efflux (respiration) than during the 2000 pre- harvest dry season. The reduction is of order 15%, consistent with the fraction of gaps left by the logging Heavy 13 C signal Reducing in photosynthetic rates – lower ci/ca Strong increment of slash to the system – decomposition

13 C of the respired CO2 and the ci:ca ratio of the upper canopy trees

Isotopic composition of the respired CO2 and the ci:ca ratio calculated from the 13 C of the organic matter on the top of the canopy

Results Carbon isotopic variation within the canopy Seasonal isotopic variation of fixed organic carbon Isotopic variation on the ecosystem respired 13 CO 2 associated to logging activities Isotopic variation of soil respired CO 2 – Importance of the litter for the 13 C signal

C of the respired CO 2 – keeling plot intercept

13 C Litter fall isotopic composition variation at km 67 in 2003

13 C

Final remarks Different compartments of the ecosystem present consistent isotopic data allowing predictions with certain degree of confidence; The isotopic signature of the ecosystem respired CO 2 reflects the seasonality of the precipitation and is consistent with the ci/ca ratio calculated from the d13C of the upper canopy leaves; The litter fall reflects mainly the isotopic signature of the upper third canopy leaves and therefore a seasonality associated to ppt; As widely known litter is an important component for soil CO2 efflux and the isotopic difference to the bulk soil respiration allow us to partitioning the importance of each of this compartments;