Effects of Temperature Variation at Different Times on Growth and Yield of Sugar Beet and Barley

Abstract

Sugar-beet and barley were grown in pots outdoors (environment N) and, for five successive 4-week periods starting at sowing, batches of plants were transferred to three growth rooms whose temperatures were either similar to the outdoor mean (environment ^M), or 3° C hotter (environment H) or 3° C colder (environment C). Some plants were harvested immediately after treatment; others were returned to environment N and harvested when mature. At the end of period 1, sugar-beet plants from environment M had more dry weight and leaf area than those outdoors. Immediately after spending later periods in environment M, plants had smaller leaves and similar dry weight to those continuously outdoors. These differences disappeared by maturity. Warmth in the growth rooms (i.e. the difference H—C) during periods 1, 2, and 3, while leaf area was increasing, increased the number and size of leaves and usually also dry weight; in later periods it had no effect. The effects induced during periods 2 and 3, but not period 1, persisted to maturity to give greater total and root dry weight and yield of sugar. The final effects on dry weight were much larger than those immediately after treatment, and were the result of differences in growth outdoors after treatment which depended on differences in leaf area; the efficiency of the leaves was not affected by previous treatment. Transferring barley to environment M from N had inconsistent immediate effects on leaf area and dry weight which disappeared by the final harvest. Transfer during periods 2 and 3, before the ears had started emerging, increased shoot number and delayed development. The proportion of the ears that ripened and the yield of grain were usually less for plants that had spent a period in environment M than for plants permanently outdoors, which also had some green ears. Warmth in the growth rooms during periods 1 and 2 increased dry weight and leaf area immediately, but had negligible effects at maturity because the increases in leaf area did not persist after ear emergence. Warmth later hastened death of leaves, decreased total dry weight immediately and also at maturity, but increased the proportion of ears that ripened and hence usually grain weight. Variation in leaf area duration after ear emergence (D), determined by effects on the time the ears emerged and the rate the leaves died, accounted for most of the variation in grain yield, but warmth after the ears emerged decreased grain yield less than proportionally to the decrease in D. Net assimilation rate (E) of sugar-beet was greater than of barley, and decreased less with age. E of both species was usually greater in environment M than outdoors in spite of less radiation. It was only slightly affected by temperature. Nitrogen and potassium uptake were increased by treatments that increased dry weight. The percentage contents suggest that extra uptake was a consequence and not a cause of the increase in dry weight.