Annals of Botany 77: 487-496, 1996
© 1996 Annals of Botany Company
Growth and Partitioning in Pascopyrum smithii (C3) and Bouteloua gracilis(C4) as Influenced by Carbon Dioxide and Temperature
USDA-ARS, Rangeland Resources Research Unit, Crops Research Laboratory, 1701 Center Ave., Fort Collins, CO 80526-2083, U.S.A.
August 2, 1995 ; November 24, 1995
This study investigated how CO2and temperature affect dry weight (d.wt) accumulation, total nonstructural carbohydrate (TNC) concentration, and partitioning of C and N among organs of two important grasses of the shortgrass steppe,Pascopyrum smithii Rydb. (C3) andBouteloua gracilis(H.B.K.) Lag. ex Steud. (C4). Treatment combinations comprised two temperatures (20 and 35°C) at two concentrations of CO2(380 and 750 µmol mol-1), and two additional temperatures of 25 and 30°C at 750 µmol mol-1CO2. Plants were maintained under favourable nutrient and soil moisture and harvested following 21, 35, and 49d of treatment. CO2-induced growth enhancements were greatest at temperatures considered favourable for growth of these grasses. Compared to growth at 380 µmol mol-1CO2, final d.wt of CO2-enrichedP. smithiiincreased 84% at 20°C, but only 4% at 35°C. Final d.wt ofB. graciliswas unaffected by CO2at 20°C, but was enhanced by 28% at 35°C. Root:shoot ratios remained relatively constant across CO2levels, but increased inP. smithiiwith reduction in temperature. These partitioning results were adequately explained by the theory of balanced root and shoot activity. Favourable growth temperatures led to CO2-induced accumulations of TNC in leaves of both species, and in stems ofP. smithii, which generally reflected responses of above-ground d.wt partitioning to CO2. However, CO2-induced decreases in plant tissue N concentrations were more evident forP. smithii. Roots of CO2-enrichedP. smithiihad greater total N content at 20°C, an allocation of N below-ground that may be an especially important adaptation for C3plants. Tissue N contents ofB. graciliswere unaffected by CO2. Results suggest CO2enrichment may lead to reduced N requirements for growth in C3plants and lower shoot N concentration, especially at favourable growth temperatures.
Acclimation to CO2; blue grama; Bouteloua gracilis ; carbohydrate; climate change; global change; grass; growth; growth temperature optima; nitrogen; N uptake; Pascopyrum smithii; western wheatgrass
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