关键词: CO₂, 全球变化, 农作物生长, 产量, 水分, 氮, 碳固定, 开放系统

Abstract: Over the past decade, free-air CO₂ enrichment (FACE) experiments have been conducted on several agricultural crops:wheat(Triticum aestivum L.), perennial ryegrass (Lolium perenne), and rice(Oryza sativa L.) which are C₃ grasses; sorghum (Sorghum bicolor (L.) Möench), a C₄ grass; white clover (Trifolium repens), a C₃ legume; potato (Solanum tuberosum L.), a C₃ forb with tuber storage; and cotton (Gossypium hirsutum L.) and grape (Vitis vinifera L.) which are C₃ woody perennials. Using reports from these experiments, the relative responses of these crops was discussed with regard to photosynthesis, stomatal conductance, canopy temperature, water use, water potential, leaf area index, shoot and root biomass accumulation, agricultural yield, radiation use efficiency, specific leaf area, tissue nitrogen concentration, nitrogen yield, carbohydrate concentration, phenology, soil microbiology, soil respiration, trace gas emissions, and soil carbon sequestration.Generally, the magnitude of these responses varied with the functional type of plant and with the soil nitrogen and water status. As expected, the elevated CO₂ increased photosynthesis and biomass production and yield substantially in C₃ species, but little in C₄, and it decreased stomatal conductance and transpiration in both C₃ and C₄ species and greatly improved water-use efficiency in all the crops. Growth stimulations were as large or larger under water-stress compared to well-watered conditions. Growth stimulations of non-legumes were reduced at low soil nitro-gen, whereas elevated CO₂ strongly stimulated the growth of the clover legume both at ample and under low Nconditions. Roots were generally stimulated more than shoots. Woody perennials had larger growth responses to elevated CO₂, while at the same time, their reductions in stomatal conductance were smaller. Tissue nitrogen concentrations went down while carbohydrate and some other carbon-based compounds went up due to elevated CO₂, with leaves and foliage affected more than other organs. Phenology was accelerated slightly in most but not all species. Elevated CO₂ affected some soil microbes greatly but not others, yet overall activity appears to be stimulated. Detection of statistically significant changes in soil organic carbon in any one study was impossible, yet combining results from several sites and years, it appears that elevated CO₂ did increase sequestration of soil carbon.Whenever possible, comparisons were made between the FACEresults and those from prior chamber-based experiments reviewed in the literature. Over all the data and parameters considered in this review, there are only two parameters for which the FACE-and chamber-based data appear to be inconsistent. One is that elevated CO₂ from FACEappears to reduce stomatal conductance about one and a half times more than observed in prior chamber experiments. Similarly, elevated CO₂ appears to have stimulated root growth relatively more than shoot growth under FACEconditions compared to chamber conditions. Nevertheless, for the most part, the FACE-and chamber-based results have been consistent, which gives confidence that conclusions drawn from both types of data are accurate. However, the more realistic FACEenvironment and the larger plot size have enabled more extensive robust multidisciplinary data sets to be obtained under conditions representative of open fields in the future high-CO₂ world.