Rice plants (Oryza sativa L., cv. IR30) were grown in paddy culture in outdoor, naturally sunlit, controlled-environment, plant growth chambers at Gainesville, Florida, USA, in 1987. The rice plants were exposed throughout the season to subambient (160 and 250), ambient (330) or superambient (500, 660, 900 mu-mol CO2/mol air) CO2 concentrations. Total shoot biomass, root biomass, tillering, and final grain yield increased with increasing CO2 concentration, the greatest increase occurring between the 160 and 500 mu-mol CO2/mol air treatments. Early in the growing season, root:shoot biomass ratio increased with increasing CO2 concentration; although the ratio decreased during the growing season, net assimilation rate increased with increasing CO2 concentration and decreased during the growing season. Differences in biomass and lamina area among CO2 treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences in final grain yield among CO2 treatments. Doubling the CO2 concentration from 330 to 660 mu-mol CO2/mol air resulted in a 32% increase in grain yield. These results suggest that important changes in the growth and yield of rice may be expected in the future as the CO2 concentration of the earth's atmosphere continues to rise.
The study was carried out in northern Kenya in 1984-87. Forestomach volumes and digesta retention times were measured using Cr-EDTA or Co-EDTA as fluid markers and Ce-labelled particles or Cr-mordanted particles as particulate phase markers. Mean retention times of fluid and of particles were longer in the dry season than in the green season in all four animal species. The increase of particle mean retention time, as a percentage of the values in the green season, was highest in sheep (46%), followed by cattle (27%), goats (22%) and camels (18%). Forestomach volumes were also greater in the dry than in the green season; the increase was again highest in sheep (55%), followed by cattle (31%), goats (29%) and camels (28%). Outflow rates of fluid from the forestomach and the selectivity factor, by which small particles were retained longer in the forestomach than fluid, did not differ significantly between the seasons. It is suggested that the increase of forestomach volumes is an effective adaptation to dry-season pasture conditions. It enables the animals to retain feed particles longer in the forestomach and so improve fibre digestion when feed quality is low. Cattle and sheep, which depend on a poor quality diet, improve fibre digestion in this way in the dry season more effectively than camels and goats. Camels and goats, on the other hand, were able to select a diet of such quality, even in the dry season, that their need to augment fibre digestion was reduced.
The relationships between the amounts of nitrogen fertilizer applied and taken up by sugarbeet crops and the concentrations of sugar and alpha-amino-N in the storage root were examined using data obtained from fertilizer-response trials on different soils in the UK and Belgium between 1974 and 1985. On unmanured mineral soils, crop uptakes of N without fertilizer ranged from 65 to 190 kg/ha and increased linearly with the amount of fertilizer N applied. On organic soils or mineral soils that had received large applications of organic manure, crop uptakes of N were very large (295-383 kg/ha) and were not increased by applications of fertilizer N. The amino-N contents of harvested beet increased with crop N uptake. The distributions of crop N to the storage root and of storage-root N to amino-N differed, especially in manured, diseased and drought-affected crops. Greater proportions of crop N were present in the storage roots of manured crops than in conventionally fertilized crops, and more of the storage-root N was present as amino-N in crops affected by virus yellows or drought than in healthy, unstressed crops. The fresh weight concentrations of sugar in the storage root also differed between sites and years but were not consistently reduced by applications of fertilizer N at individual sites. However, when compared across sites, concentrations were negatively correlated with crop N uptakes and the amounts of N in storage roots. This was because particular crops grown on mineral soils with large applications of manure or on organic soils had large N uptakes and exceptionally low concentrations of sugar. The physiological implications of these relationships between N uptake and amino-N and sugar accumulation are discussed.