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Equations for the Rate of Dark Respiration of White Clover and Grain Sorghum, as Functions of Dry Weight, Photosynthetic Rate, and Temperature¹

Equations were designed to be used in computer models of photosynthesis and respiration in crops. They were developed from new experimental data on the rates CO₂ exchange of whole plants grown under constant conditions. The dark respiratory rate was separated into two components. The "maintenance" component was taken to be the efflux of CO₂ after more than 48 hours in the dark at constant temperature. This component was proportional to the dry weight of the plant (W), and was a strong function of temperature (T). The proportionality constant (c) was about twice as great for clover (Trifolium repens L.) as it was for sorghum (Sorghum bicolor L.), at the same temperature. The "growth" component was taken to be the difference between the "maintenance" component and the total efflux during a normal night period (N). This component was proportional to the total influx during the previous daytime period (D), and the proportionality constant (k) was independent of species and temperature. The values of c and k were in good agreement with values calculated by Penning de Vries, using the principles and equations of biochemistry.

The experimental data were best fitted by the following equations:

For clover at 30C: N = 0.14 D + 0.0143W

For sorghum at 30C: N = 0.14 D + 0.0054W

Temperature dependence of maintenance coefficient:

c_T = c₃₀ (0.044 + 0.0019 T + 0.0010 T²)

where N = night total of CO₂ evolved in g•12h^-l•plant^-1,

D = daytime total of CO₂ taken up in g•12h^-1•plant^-1,

W = CO₃ equivalent of dry weight in g•12h^-1•plant^-1,

T = temperature in °C.

Key Words: Computer models • Growth • Maintenance • CO₂ exchange

² Associate Professor, Department of Soil and Crop Sciences.

Received for publication January 14, 1974.

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