A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

AbstractChris DoughtyUC IrvineLBA-ecology group CD-04Conference registration # - CDOU-0502Email – Chris__doughty@hotmail.comAddress – Projeto LBA Componente- ecologiaRua 24 de Outubro, 3707 – MapiriSantarem – Para – BrasilCep. 68.040-010Title - An investigation of the post-noontime decline in photosynthesis in tropical forestsUsing the eddy covariance technique over a tropical rainforest in Santarem, Brazil, acontinuous decline in photosynthesis in the afternoon has been noted even after lightdifferences have been eliminated. This study attempts to understand what causes thispost-noontime decline in photosynthesis. Although there are many possibilities, thisstudy focuses on the decline either being caused by water stress of the tree or an internalcircadian rhythm. Using the platform tower at site 83 in the Tapajos national forest,leaves of several tree species were continually lit with 1000 micromoles of light and keptat constant temperature and humidity levels for a period of 24 hours as photosynthesismeasurements were taken every 20 minutes using a Licor 6400. In addition, waterpotential measurements using a pressure chamber were taken every 2 hours. These twomeasurements will determine if photosynthesis changes over the course of a day despiteconstant conditions and also how water potential changes over the course of a day. Ifunder constant conditions photosynthesis is lowest at night when water potential is alsolikely to be lowest then this indicates the decline may be due to a circadian rhythm. Ifhowever, photosynthesis is highest at night, this indicates that the decline is likely due towater stress in the tree.