The effects on yield of controlled water stress applied at various stages of development were studied on two varieties of soybean (Glycine max (L.) Merr.), ‘Ransom’ and ‘Bragg.’ The plants were grown in a controlled environment chamber at 28/17 C with a 9‐hour photoperiod at 450 hlx and an interrupted dark period. Interruption of the dark period was suspended for 7 days to induce flowering. Groups of plants were subjected to water stress during flower induction, flowering, pod formation, and pod filling. Leaf water potential during stress fell as low as —23 bars, but after rewatering the potential of plants in all treatments returned approximately to normal. Plants stressed during flower induction and flowering produced fewer flowers, pods, and seeds than controls because of a shortened flowering period and abortion of some flowers. Stress during early pod formation caused greatest reduction in number of pods and seeds at harvest. However, yield as measured by weight of seeds was reduced most by stress during early formation and pod filling. Water stress at no stage of growth materially affected the oil or protein content of the seeds.

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Growth and yield responses of a semi‐dwarf spring wheat (Triticum aestivum L.; cv. GWO 1809) to two CO2 concentrations and two water stress regimes were studied in controlled environment chambers of the Duke Univ. Phytotron. Groups of plants in low (350 ppm), or high (1,000 ppm) CO2 environments were subjected to water stress By withholding irrigation starting at the 10th day after the beginning of anthesis. A second drying cycle beginning 5 days after termination of the first cycle was also given to some of the plants. Water potential of the flag leaves of the main stem of the plants in each CO2 environment reached a minimum of −13 bars at the end of the first drying cycle and −17 bars at the end of the second cycle.Under well‐watered conditions high CO2 enhanced the rate of tiller production by 43% and significantly increased grain yield, total dry matter, and number and size of the grains.As water stress developed, the osmotic potentials of the high CO2. plants decreased at a faster rate and resulted in maintenance of higher turgor pressures at the end of each stress cycle compared to the low CO2 plants. Osmotic potentials of the leaves of both high and low 2 plants decreased faster in the second drying cycle than in the first.Significantly fewer and smaller grains were produced on the plants grown under water stress in both CO2 concentrations compared to unstressed plants. In general, high CO2 plants under water stress conditions had a grain yield and total dry matter production equal to the unstressed, low CO2 plants. Thus, CO2 enrichment increased the yield potential of the water limited wheat plants due probably to osmotic adjustment by an increased concentration of solutes in their leaves.

1. Environmental change has the potential to influence trophic interactions by altering the defensive phenotype of prey. 2. Here, we examine the effects of a pervasive environmental change driver, elevated atmospheric concentrations of CO 2 (eCO 2), on toxin sequestration and flight morphology of a specialist herbivore. 3. We fed monarch butterfly larvae, Danaus plexippus, foliage from four milkweed, Asclepias, species of varying chemical defence profiles grown under either ambient or eCO 2. We also infected a subset of these herbivores with a protozoan parasite, Ophryocystis elektroscirrha, to understand how infection and environmental change combine to alter herbivore defences. We measured changes in phytochemistry induced by eCO 2 and assessed cardenolide, toxic steroid, sequestration and wing morphology of butterflies. 4. Monarchs compensated for lower plant cardenolide concentrations under eCO 2 by increasing cardenolide sequestration rate, maintaining similar cardenolide composition and concentrations in their wings under both CO 2 treatments. We suggest that these increases in sequestration rate are a by-product of compensatory feeding aimed at maintaining a nutritional target in response to declining dietary quality under eCO 2. 5. Monarch wings were more suitable for sustained flight (more elongated) when reared on plants grown under eCO 2 or when reared on Asclepias syriaca or Asclepias incarnata rather than on Asclepias curassavica or Asclepias speciosa. Parasite infection engendered wings less suitable for sustained flight (wings became rounder) on three of four milkweed species. Wing loading (associated with powered flight) was higher on A. syriaca than on other milkweeds, whereas wing density was lower on A. curassavica. Monarchs that fed on high cardenolide milkweed developed rounder, thinner wings, which are less efficient at gliding flight. 6. Ingesting foliage from milkweed high in cardenolides may provide protection from enemies through sequestration yet come at a cost to monarchs manifested as lower quality flight phenotypes: rounder, thinner wings with lower wing loading values.

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