CARDINOT, G.

DIAS-FILHO, M.

MOUTINHO, P.

NEPSTAD, D. C.

RAY, D.

SOLORZANO, L.

TOHVER, I.

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Drought effects on net primary productivity and its allocation in an east-central Amazonforest: results from a throughfall exclusion experimentP MOUTINH01, NEPSTAD, D C1 2, M DIAS-FILH03, D RAv', L SOLORZAN02, GCARDINOT1, I TOHVER1•Institutional Affiliations:Instituto de Pesquisa Ambiental da Amazonia', Brasil,Woods Hole Research Center', USA,Embrapa Amazonia Oriental, Belém, Brasie.Large areas of Amazon forest are exposcd to severc drought stress, and may expericncegrcater drought stress in the future through the interacting effects of global warming,ENSO, and deforestation-inhibition ofrainfall. We established a partial throughfallexclusion experiment (one-hectare treatrnent and control plots) in east-central Amazonia(FLONA Tapajós) in 1998 to help provide a more integrated understanding of forestresponses to drought. During the first ycar ofthe cxpcrimcnt, partial (40%) throughfallcxclusion indueed a decline in both leaf photosynthetic eapaeity and diameter growth ofsmall trees. During the seeond year ofthroughfall exclusion, when deep soil depletionoeeurred, stem !f0wth of trees up to 50 em dbh was suppressed at the rate of 2 Mgbiomass ha' yr . It was only after excluding a total of 1600 mm ofthroughfall, duringthe seeond post-treatment.dry season, that pre-dawn leafwater potential declined,inhibiting leafproduetion and lowering LAI by 1.5 units. Henee, leaffall responded todrought only after 2 years oftreatment; the mortality ofunderstory trees «2 em dbh)increased three-fold after two years. ln sum, this Amazon forest effeetively avoideddrought-induced leaf shedding and mortality of adult trees during two years of partialthroughfall exclusion by tapping soil moisturc to 20 m depth. Carbon aeeumulation instcms-the aboveground C pool with the slowest tumover ratc-was the most sensitiveto drought.Address of eorresponding author (Moutinho):Instituto de Pesquisa Ambiental da Amazônia - IPAMSede BelémAv. Nazare 669, Centro.66035-170 Belém, PA, Brasilcmails:in.\ I:!\:yr. ~.~_;_"{'<:1~; i t,·I.~~!',1r;.ll!;Lbr~JT~_iY..~~.\\'JJ.1>- ,()r~:1~(lh)rZdl\(\O(f \.\ h r c. (l!.t;

Drought effects on net primary productivity and its allocation in an east-central Amazon forest: results from a throughfall exclusion experiment.

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