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Photosynthetic Selection of Zea mays L. II. The Relationship Between CO₂ Exchange and Dry Matter Accumulation of Canopies of Two Hybrids¹

Carbon dioxide exchange rate (CER) responses to irradiance level and temperature, and dry matter accumulation of the above-ground portion of plants, were measured for field-grown multiplant canopies of the maize (Zea mays L.) hybrids NY821 L₁ x C153 L₁ and NY821 H₆ x C153 L₃. A semiclosed and an open arrangement of a field scale gasometric system were used to measure the CER's in daylight and in darkness respectively. The objective of the measurements as to relate canopy CO₂ exchange to dry matter accumulation rate of the above ground portion of the field grown canopies of each hybrid during grain filling.

Variation of solar irradiance at the top of the canopies and of plant age accounted for more than 90% of the variation of CERs measured in daylight. Variation of air temperature accounted for more than 77% of the variation of the CER's in darkness. The mean CERs in the dark changed less than 23 and 13% at 15 and 30 C, respectively, from the early dough to late dent stage. The CO₂ efflux in darkness was attributed largely to maintenance metabolism in vegetative tissues because the small changes or reductions of CERs in darkness were observed while mean cob and kernel dry weights increased 220% from early dough to late dent.

Cumulative CO₂ exchange from early dough to late dent was computed from regression models of the irradiance and temperature responses for each hybrid, and climatic data. The ratio of above-ground dry weight change to cumulative CO₂ exchange deviated from an expected value of 0.65 for both hybrids: they were 0.77 and 0.59 for L₁ x L₁ and H₆ x L₃, respectively.

A dry weight loss of from 11.7 to 16% from the vegetative tissues was larger than the substrate requirement for the estimated CO₂ efflux that was attributed to maintenance metabolism from early dough to late dent. Part of the weight loss could have resulted from remobilization of stored carbohydrates from the vegetative tissues to the cob and kernels.

Key Words: Respiration • CO₂ efflux • Temperature • Growth rate • Zea mayz L. • Maintenance • Corn

² Assistant professor, Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, Tex. and professor, Dep. of Agronomy, Cornell Univ., Ithaca, NY 14853.

Received for publication June 15, 1978.