CO₂‐Enrichment Effects on Soybean Physiology. II. Effects of Stage‐Specific CO₂ Exposure¹

Abstract

Soybeans [ Glycine max (L.) Merr ‘Wye’] were exposed to CO 2 ‐enriched atmospheres during specific stages of development Carbon dioxide enrichment from early pod development until plant maturity and from emergence to maturity increased seed yield 27 and 36%, respectively, compared with plants exposed to the normal atmospheric level of CO 2 . Plants receiving supplemental CO 2 from either emergence to anthesis or from anthesis through early pod development did not exhibit an increase in grain yield. During each period of exposure, CO 2 ‐enriched plants had higher rates of photosynthesis and accumulated significantly more starch, sucrose, and glucose in the leaves compared with nonenriched controls. After exposure to CO 2 was terminated, rates of photosynthesis declined to control values and the accumulated leaf carbohydrates were rapidly depleted. Accumulation and subsequent utilization of stored photosynthate did not appear to influence seed yield except when these stored reserves were available at the onset of the grain‐filling period. Seed yield increases attributable to CO 2 enrichment were the result of more pods per plant rather than increases in seed size. From the analysis of photosynthetic data and the trends in carbon accumulation and utilization, it appears that soybeans could support a higher degree of reproductive growth.