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CROP PHYSIOLOGY & METABOLISM

Gas Exchange and Water Relations in Diploid and Tetraploid Russian Wildrye

USDA-ARS, Northern Great Plains Research Laboratory, P.O. Box 459, Mandan, ND 58554

Corresponding author (franka{at}mandan.ars.usda.gov)

Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] is a drought tolerant, cool-season forage grass used in seeded pastures in the Northern Great Plains where water often limits production. Seedling vigor is generally poor in diploid cultivars, but tetraploid germplasm has improved seedling vigor. Objectives of this study were to determine the relationships between water-use efficiency (WUE), carbon isotope discrimination (CID), and gas exchange rates for a diploid cultivar (Vinall) and a tetraploid entry over 3 yr, two water treatments (50 and 150% of mean monthly precipitation), and two fertilizer rates (10 and 134 kg N ha^-1) in a rain shelter. The tetraploid entry exhibited higher carbon exchange rate (CER), stomatal conductance (gs), and transpiration (T) than the diploid entry at the 50% but not the 150% water treatment. Leaf water potentials (LWP) were 0.6 and 0.3 MPa less negative for the tetraploid entry than diploid entry at the 50 and 150% water treatment, respectively. Values of CER averaged 12.4 and 14.2 µmol m^-2 s^-1, T averaged 5.2 and 6.0 mmol m^-2 s^-1, and gs averaged 0.21 and 0.28 mol m^-2 s^-1 for the diploid and tetraploid entry, respectively. The diploid entry had a significantly greater CID, averaging 20.37 compared with 19.65 for the tetraploid entry and CID was negatively associated with WUE. The more favorable plant water relations, gas exchange, and dry matter production under limited soil water suggests tetraploid populations of Russian wildrye should be emphasized in future breeding and management programs.

Abbreviations: CER, carbon exchange rate • Ci/Ca, atmospheric carbon dioxide concentration/leaf intercellular carbon dioxide concentration • CID, carbon isotope discrimination • GDD, growing degree-days • gs, stomatal conductance • LWP, leaf water potential • T, transpiration • WUE, water-use efficiency

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