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Light – life energy source Light absorbed, reflected and transmitted Absorption spectrum of Chlorophyll a Absorption and action spectra (role of accessory pigments) Primary productivity Chlorophyll a Chlorophyll at the sea-surface in Eilat Sea-surface Chlorophyll (Observatory Pier, daily) 4.0 3.5 ugr Chl / L 3.0 2.5 2.0 1.5 1.0 0.5 0.0 1988 1989 1990 1991 1992 1993 1994 1995 Year 1996 1997 1998 1999 2000 2001 2002 Measuring primary productivity מדידת יצרנות ראשונית ונשימה ברמת החברה בבתי גידול מימיים בשיטת החמצן • • • • • • • • Photosynthesis: 6CO2 + 6H2O C6H12O6 + 6O2 Respiration: C6H12O6 + 6O2 6CO2 + 6H2O The goal: Determine the community's Gross Primary Productivity (GPP), the Net Primary Productivity (NPP), and Respiration (R), all in [mg-C m-3 of water]. Since we measure C production and respiration indirectly, by measuring changes in the concentration of dissolved oxygen, we need to convert masses of Oxygen to Carbon. Note that photosynthesis generates 6 moles of O2 (192 gr-Oxygen / L) for every 6 moles CO2 (72 gr-Carbon / L) that get fixed. Thus a conversion factor needs to be used: 72/192 = 0.375 Also, since the efficiency of the process is about 86% (some 14% of the oxygen produced is used for photosynthesis-related processed other than fixing carbon), an equivalent ("Quotient") of 1.16 is used for the Oxygen-Carbon conversion (1 / 1.16 = 0.86). The Respiration Quotient (RQ) is 1.0 (since the source is a complete "burning" of organic carbon) מדידת יצרנות ראשונית ונשימה ברמת החברה בבתי גידול המשך- מימיים בשיטת החמצן Thus – if after T hours of incubation we measured Oxygen changes (mg/L) and term these: Il and Fl - the initial and final concentrations in the light bottle Id and Fd- - the initial and final dark bottle The following equations should be used: Respiration rate (mg-C L-1 hr-1) = 0.375 * 1.0 * (Id – Fd) / T Gross Primary Production (GPP) = 0.375 * 0.86 * [(Id-Fd) – (Il-Fl)] / T Net Primary Production (NPP) = GPP - R PI - Curve