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 מימיים בשיטת החמצן - המשך Thus – if after T hours of incubation we measured Oxygen changes (mg/L) and term these: I l and F l - the initial and final concentrations in the light bottle I d and F d- - 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
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