Showing papers by "Paul Hadley published in 1996"

The duration and rate of grain growth, and harvest index, of wheat (Triticum aestivum L.) in response to temperature and CO2

Abstract: Winter wheat (Triticum aestivum L. cv. Hereward) was grown in the field inside polyethylene-covered tunnels at a range of temperatures at either 380 or 684 μmol mol -1 CO 2 . Serial harvests were taken from anthesis until harvest maturity. Grain yield was reduced by warmer temperatures, but increased by CO 2 enrichment at all temperatures. During grain-filling, individual grain dry weight was a linear function of time from anthesis until mass maturity (attainment of maximum grain dry weight) within each plot. The rate of progress to mass maturity (the reciprocal of time to mass maturity) was a positive linear function of mean temperature, but was not affected by CO 2 concentration. The rate of increase in grain dry weight per ear was 2.0 mg d -1 greater per 1 °C rise, and was 8.0 mg d -1 greater at 684 compared with 380 μmol mol -1 CO 2 at a given temperature. The rate of increase in harvest index was 1.0% d -1 in most plots at 380 μmol mol -1 CO 2 and in open field plots, compared with 1.18% d -1 in all plots at 684 μmol mol -1 CO 2 . Thus, the increased rate of grain growth observed at an elevated CO 2 concentration could be attributed partly to a change in the partitioning of assimilates to the grain. In contrast, the primary effect of warmer temperatures was to shorten the duration of grain-filling. The rate of grain growth at a given temperature and the rate of increase in harvest index were only independent of the number of grains per ear above a critical grain number of 23-24 grains per ear (∼20 000 grains m -2 ).

Growth and yield of winter wheat (Triticum aestivum) crops in response to CO2 and temperature.

Abstract: Crops of winter wheat (Triticum aestivum L. cv. Hereward) were grown within temperature gradient tunnels at a range of temperatures at either c. 350 or 700 μmol mol -1 CO 2 in 1991/92 and 1992/93 at Reading, UK. At terminal spikelet stage, leaf area was 45 % greater at elevated CO 2 in the first year due to more tillers, and was 30 % greater in the second year due to larger leaf areas on the primary tillers. At harvest maturity, total crop biomass was negatively related to mean seasonal temperature within each year and CO 2 treatment, due principally to shorter crop durations at the warmer temperatures. Biomass was 6-31% greater at elevated compared with normal CO 2 and was also affected by a positive interaction between temperature and CO 2 in the first year only. Seed yield per unit area was greater at cooler temperatures and at elevated CO 2 concentrations. A 7-44 % greater seed dry weight at elevated CO 2 in the first year was due to more ears per unit area and heavier grains. In the following year, mean seed dry weight was increased by > 72 % at elevated CO 2 , because grain numbers per ear did not decline with an increase in temperature at elevated CO 2 . Grain numbers were reduced by temperatures > 31°C immediately before anthesis at normal atmospheric CO 2 in 1992/93, and at both CO 2 concentrations in 1991/92. To quantify the impact of future climates of elevated CO 2 concentrations and warmer temperatures on wheat yields, consideration of both interactions between CO 2 and mean seasonal temperature, and possible effects of instantaneous temperatures on yield components at different CO 2 concentrations are required. Nevertheless, the results obtained suggest that the benefits to winter wheat grain yield from CO 2 doubling are offset by an increase in mean seasonal temperature of only 1.0 °C to 1.8 °C in the UK.

The effect of temperature and photoperiod on the rate of flower initiation and the onset of dormancy in the strawberry (Fragaria x ananassa Duch.)

Abstract: SummaryThe effects of temperature and photoperiod on flower and inflorescence initiation during the autumn were investigated in the strawberry cv. Elsanta. The variation in starch under these environmental conditions was also recorded, to test whether this might provide a useful indicator of the onset of imposed and/or true dormancy. Photoperiod had no effect on the rate of flower initiation or final flower number in the primary, secondary or tertiary inflorescences. Temperature had little effect on the final flower number in the primary inflorescence. However, the rate of flower initiation increased linearly with increasing temperature in the secondary (r2 = 0.98) and tertiary inflorescences (r2 = 0.97), to an optimum of 18.6°C in the secondary and 19.9°C in the tertiary inflorescence, and declined at temperatures above these. The quantity of starch in the roots increased during the autumn, and the rate of increase was negatively correlated with temperature. This indicates that root starch concentration ...

The effect of temperature and CO2 on seed quality development in wheat (Triticum aestivum L.)

Abstract: Winter wheat (Triticum aestivum L.) cv. Hereward was grown in the field in two double-walled polyethylene-covered tunnels within each of which a temperature gradient was superimposed on diurnal and seasonal fluctuations in temperature. The mean temperature between anthesis and harvest maturity varied from 14.3 to 18.4°C among plots within these tunnels. The CO 2 concentration was controlled at different values in each tunnel ; seasonal mean concentrations were 380 and 684 μmol CO 2 mol -1 air. Crops were also grown outside the tunnels at ambient temperatures and CO 2 . Samples of seeds were harvested sequentially from each plot between anthesis and harvest maturity. Seed germination and seed survival during subsequent air-dry storage were determined for each sample. The onset of both ability to germinate and desiccation tolerance (ability to germinate after rapid desiccation to 10-15% moisture content and subsequent rehydration) coincided in all environments. Full germination capacity (>97%, determined at 10°C) was reached 4-18 d before the end of the seed-filling phase (mass maturity) in most cases. There was little or no decline in germination capacity during subsequent seed development and maturation. Differences in seed quality were evident, however, throughout seed development and maturation when seed survival curves during subsequent storage were compared. Potential longevity in air-dry storage (assessed by the value K i of the seed viability equation) improved consistently both before and after mass maturity. There was a significant positive relation between the rate of increase in potential longevity (dK i /dt) and temperature (the minimum temperature for seed quality development was 4.8°C), but neither CO 2 concentration nor production within the polyethylene tunnels affected this relation.

Developmental and tillering responses of winter wheat (Triticum aestivum) crops to CO2 and temperature

Abstract: Winter wheat (Triticum aestivum L., cv. Hereward) was grown in the field within four double-walled polyethylene-covered tunnels along which near-linear temperature gradients were imposed at normal atmospheric or at an elevated CO 2 concentration (c. 700 μmol mol -1 CO 2 ) in 1991/92 and in a further experiment in 1992/93. Development was more rapid the warmer the temperature. In 1991/92 an increase in mean seasonal temperature of 3.5 °C reduced the duration from sowing to harvest maturity (the stage when grain moisture content reduced naturally to 15-18 %) by c. 38 days, and reduced the duration from the double ridge stage to harvest maturity by c. 34 days. A similar difference resulted from only 1.6 °C warming in 1992/93. Although the range of mean seasonal temperatures differed between years, the relation between temperature and rate of development from sowing to harvest maturity was common to both years (base temperature, -0.8 °C; thermal time 2410 °C d). Carbon dioxide concentration had no effect on this relation or on that between temperature and the rate of development from sowing to the double ridge stage and from the double ridge stage to harvest maturity. Carbon dioxide enrichment increased tillering substantially in 1991/92; there were 200 more shoots m -2 at terminal spikelet formation in crops grown at elevated compared to normal CO 2 (additional shoots were principally coleoptile tillers and those developing after tiller 2) and this difference was reduced to 100 shoots m -2 approaching harvest maturity (additional shoots remaining were those developing after tiller 2). In contrast, no effect of CO 2 enrichment on tillering was detected at any stage of development in 1992/93. The number of tillers per plant at terminal spikelet formation was a linear function of main stem dry weight at this developmental stage; this relationship was not affected by year or CO 2 . As CO 2 enrichment increased main stem dry weight in the first year only, when main stem dry weights at normal CO 2 were only one half of those values determined in the following year, it is concluded that any benefit of increase in CO 2 concentration to tillering in winter wheat may be greatest in those crop production environments where main stem dry weights at terminal spikelet are least and vice versa.