开放系统中农作物对空气CO_2浓度增加的响应

Responses of agricultural crops to free-air CO_2 enrichment.

FACE试验 (free airCO2 enrichment)开展的 10多年中 ,供试农作物主要有 :C3 禾本科作物小麦(TriticumaestivumL .)、多年生黑麦草 (Loliumperenne)和水稻 (OryzasativaL .) ,C4禾本科类高粱(Sorghumbicolor (L .)M ench) ,C3 豆科植物白三叶草 (Trifoliumrepens) ,C3 非禾本科块茎状作物马铃薯 (SolanumtuberosumL .) ,以及多年生C3 类木本作物棉花 (GossypiumhirsutumL .)和葡萄 (VitisviniferaL .) .本文系统整理和分析了以下各项参数的结果 :光合作用、气孔导度、冠层温度、水分利用、水势、叶面积指数、根茎生物量累积、作物产量、辐射利用率、比叶面积、N含量、N收益、碳水化合物含量、物候变化、土壤微生物、土壤呼吸、痕量气体交换以及土壤碳固定 .CO2 浓度升高对农作物的影响作用主要表现在以下方面 :(1)促进了植物光合作用、增加了其生物量累积 ;(2 )显著提高C3 作物产量 ,但对C4作物产量的影响很小 ;(3)降低了C3 和C4作物气孔导度 ,非常显著地提高了所有作物的水分利用率 ;(4)对植物生长的促进作用在水分不足与水分充足时二者相当或前者大于后者 ;(5 )对非豆科植物生长的促进作用要受到土壤低N水平限制 ,而对豆科植物则不受氮肥水平限制 ;(6 )对根系生长的促进作用要大于地上部分 ;(7)

Over the past decade, free-air CO 2 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 C 3 grasses; sorghum (Sorghum bicolor (L.) Mench), a C 4 grass; white clover (Trifolium repens), a C 3 legume; potato (Solanum tuberosum L.), a C 3 forb with tuber storage; and cotton (Gossypium hirsutum L.) and grape (Vitis vinifera L.) which are C 3 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 CO 2 increased photosynthesis and biomass production and yield substantially in C 3 species, but little in C 4, and it decreased stomatal conductance and transpiration in both C 3 and C 4 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 CO 2 strongly stimulated the growth of the clover legume both at ample and under low N conditions. Roots were generally stimulated more than shoots. Woody perennials had larger growth responses to elevated CO 2, 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 CO 2, with leaves and foliage affected more than other organs. Phenology was accelerated slightly in most but not all species. Elevated CO 2 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 CO 2 did increase sequestration of soil carbon.Whenever possible, comparisons were made between the FACE results 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 CO 2 from FACE appears to reduce stomatal conductance about one and a half times more than observed in prior chamber experiments. Similarly, elevated CO 2 appears to have stimulated root growth relatively more than shoot growth under FACE conditions 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 FACE environment 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-CO 2 world.