Morgan J A, LeCain D R, Read J J, Hunt H W, Knight W G
USDA/ARS Rangeland Resources Research Unit, Crops Research Lab., 1701 Centre Ave., Ft. Collins, CO 80526, USA Fax: +970-482-2909; e-mail:
U.S. Salinity Lab, 450 W. Big Springs Rd., Riverside, CA 92507, USA, , , , , , US.
Oecologia. 1998 May;114(4):483-493. doi: 10.1007/s004420050472.
The eastern Colorado shortgrass steppe is dominated by the C grass, Bouteloua gracilis, but contains a mixture of C grasses as well, including Pascopyrum smithii. Although the ecology of this region has been extensively studied, there is little information on how increasing atmospheric CO will affect it. This growth chamber study investigated gas exchange, water relations, growth, and biomass and carbohydrate partitioning in B. gracilis and P. smithii grown under present ambient and elevated CO concentrations of 350 μl land 700 μl l, respectively, and two deficit irrigation regimes. The experiment was conducted in soil-packed columns planted to either species over a 2-month period under summer-like conditions and with no fertilizer additions. Our objective was to better understand how these species and the functional groups they represent will respond in future CO-enriched environments. Leaf CO assimilation (A ), transpiration use efficiency (TUE, or A /transpiration), plant growth, and whole-plant water use efficiency (WUE, or plant biomass production/water evapotranspired) of both species were greater at elevated CO, although responses were more pronounced for P. smithii. Elevated CO enhanced photosynthesis, TUE, and growth in both species through higher soil water content (SWC) and leaf water potentials (Ψ) and stimulation of photosynthesis. Consumptive water use was greater and TUE less for P. smithii than B. gracilis during early growth when soil water was more available. Declining SWC with time was associated with a steadily increased sequestering of total non-structural carbohydrates (TNCs), storage carbohydrates (primarily fructans for P. smithii) and biomass in belowground organs of P. smithii, but not B. gracilis. The root:shoot ratio of P. smithii also increased at elevated CO, while the root:shoot ratio of B. gracilis was unresponsive to CO. These partitioning responses may be the consequence of different ontogenetic strategies of a cool-season and warm-season grass entering a warm, dry summer period; the cool-season P. smithii responds by sequestering TNCs belowground in preparation for summer dormancy, while resource partitioning of the warm-season B. gracilis remains unaltered. One consequence of greater partitioning of resources into P. smithii belowground organs in the present study was maintenance of higher Ψ and A rates. This, along with differences in photosynthetic pathway, may have accounted for the greater responsiveness of P. smithii to CO enrichment compared to B. gracilis.
科罗拉多东部的矮草草原以C4草细茎针茅为主，但也包含多种C4草，包括史密斯披碱草。尽管该地区的生态已得到广泛研究，但关于大气CO2浓度增加将如何影响它的信息却很少。这项生长室研究调查了在当前环境CO2浓度（350μl/L）和升高的CO2浓度（700μl/L）以及两种亏缺灌溉制度下生长的细茎针茅和史密斯披碱草的气体交换、水分关系、生长、生物量及碳水化合物分配情况。实验在装满土壤的柱体中进行，在类似夏季的条件下，种植这两个物种中的任意一种，为期2个月，且不添加肥料。我们的目标是更好地了解这些物种及其所代表的功能组在未来CO2浓度升高的环境中将如何响应。在CO2浓度升高时，两个物种的叶片CO2同化率（A）、蒸腾利用效率（TUE，即A/蒸腾作用）、植物生长和整株植物水分利用效率（WUE，即植物生物量生产/蒸散的水分）均有所提高，不过史密斯披碱草的响应更为明显。CO2浓度升高通过提高土壤含水量（SWC）和叶片水势（Ψ）以及刺激光合作用，增强了两个物种的光合作用、TUE和生长。在早期生长阶段，当土壤水分更充足时，史密斯披碱草的耗水量比细茎针茅大，而TUE比细茎针茅小。随着时间的推移，SWC下降与史密斯披碱草地下器官中总非结构性碳水化合物（TNCs）、储存碳水化合物（史密斯披碱草主要为果聚糖）和生物量的固存稳步增加相关，但细茎针茅则不然。在CO2浓度升高时，史密斯披碱草的根冠比也增加，而细茎针茅的根冠比对CO2不响应。这些分配响应可能是冷季草和暖季草进入温暖干燥的夏季时不同个体发育策略的结果；冷季的史密斯披碱草通过在地下固存TNCs来响应，为夏季休眠做准备，而暖季的细茎针茅的资源分配则保持不变。在本研究中，更多资源分配到史密斯披碱草地下器官的一个结果是维持了较高的Ψ和A速率。这一点，连同光合途径的差异，可能解释了史密斯披碱草比细茎针茅对CO2富集的响应更大的原因。
