1. Michela Figueira Lab. Ecologia Isotópica – CENA/USP CD-02 / ND-02 Yoko Ishida, Eric Davidson, Luiz A. Martinelli, Gabriela Nardoto, Jean P. Ometto, Ima Vieira, C. Carvalho, A. Almeida, K. Pantoja Evidence of increasing leakiness of the nitrogen cycle along a secondary forest chronosequence in Eastern Amazonia Foto: B. Kruijt

2. Investigating the N cycle in Secondary Forests… OVERVIEW: → Increase in Amazon deforestation → Abandonment of areas → Increase in areas of secondary forests Secondary forests: Reservoir of genetic diversity of forests species; regulators of hydrologic function of the landscape; ecological corridors Nitrogen: Cycling influenced by biotic interactions ; limiting nutrient for primary production How do nitrogen cycling processes change during Amazonia’s secondary succession?

3. Objective: To investigate the nitrogen dynamics in a primary forest and along a chronosequence of secondary forests in Eastern Amazon What we did ? Determination of  15 N, C and N concentrations in soil and vegetation Measurements of N 2 O and NO emissions from soil

4. NH 4 + NO 3 - N2N2 OM Mineralization nitrification N 2 O + N 2 + NO denitrification Biological fixation NH 3 volatilization 0‰ 15 to 35‰ 0 to 33‰ 29‰ -2 to +2‰ Isotopic Fractionation in the Nitrogen Cycle Source: Högberg, 1997

5. 1. Secondary forests in earlier stages: CLOSED N CYCLE ↓ gaseous losses, ↓ fractionation, ↓ foliar  15 N 2. As the secondary forest ages : LESS CLOSED N CYCLE ↑ gaseous losses, ↑ fractionation, ↑ foliar  15 N Hypothesis

6. SECONDARY FOREST Gaseous N losses (NO + N 2 O) 15 N 14 N 15 N 14 N 15 N PRIMARY FOREST Closed N cycle less 15 N fractionation Leaching 14 N 15 N 14 N 15 N 14 N Gaseous N losses (NO + N 2 O) Open N cycle 15 N-enrichment 15 N

7. Fonte: INPE PRODES Digital, 2004. Deforestation 2002/2003 Deforestation until 2002 Study sites

8. Secondary forests in São Francisco do Pará – State of Pará, Brazil General aspects: Predominant vegetation: secondary forest Mean annual precipitation: 2500 – 3000 mm, with a distinct dry season from June to November. Average air temperature: 26 0 C Land-use change : shifting cultivation (slash and burn agriculture): Fonte: Vieira et al., 2003

9. W. Schroeder

10. Secondary forests areas previously used by shifting cultivation (slash and burn agriculture): Young secondary forests: 6 years Intermediate secondary forests : 20 years Advanced secondary forests : 40 years Primary forest Field sampling

11. Leaf Sampling Leaves: ~ 30 trees per site Chemical analyses : determination of total N and C by elemental analyzer Nitrogen isotope ratios (δ 15 N) – isotopic ratio mass spectrometer

12. Trace gases measurements Y. Ishida

13. Results

14. Physical-chemical characterization of the superficial soils (0-10cm deep) from the studied sites

15. Nutritional composition of leaves

16. Nitrogen trace gas emissions from soils

17. Variation in the foliar  15 N

18. Efficiency of nutrient use a la Vitousek high efficiency low efficiency Dry mass : N ratio of litterfall

19. Gas flux (kg N.ha -1.yr -1 )  15 N ( o / oo ) N-litterfall (kg N.ha -1.yr -1 ) young intermediate advanced Primary forest As the secondary forest ages … rates of litterfall - N increase rates of N gas losses increase the ecosystem become enriched in 15 N Young secondary forests… low rates of litterfall-N low emissions of N gases little enrichment of foliar 15 N

20. Conclusion Nitrogen cycle is more closed during the first stages of secondary succession and becomes more open as the secondary forest ages

21. Muito obrigada!