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This article in AJ

  1. Vol. 76 No. 1, p. 107-113
    Received: Mar 9, 1983

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Leaf Gas Exchange in ‘Caucasian’ Bluestem in Relation to Light, Temperature, Humidity, and CO21

  1. Patrick I. Coyne and
  2. James A. Bradford2



Leaf gas exchange was measured in glasshouse-grown Old World bluestem [Bothriochh caucasica (Trin.) C. E. Hubb CY. Caucasianj as a function of light, temperature, humidity, and C02 to provide a database for developing a model to aid in deriving specific genotypeenvironment combinations that result in optimum forage production. The C02 resistance pathway was partitioned into stomatal (rs and residual (rr) components and a water-use efficiency index (rs/rt where r2 = rs+rt) was calculated. Maximum C02 exchange rates (CER) were 40 µmol m−2s−1 which are above the average of published rates of numerous C4 perennial grasses. Maximum rs/rt was about 70% of the theoretical potential and was markedly superior to comparable values from the literature. The rs/rt ratio declined rapidly as temperature was decreased or increased from the optimum for maximum CER (36 °C) due to the greater temperature sensitivity of rg compared to rs. The ratio of rs/rr was greater than unity for temperatures greater than 20 °C and photon flux densities greater than about 150 µmol m−2s−1 and maximum rsrr at high light and Top was about 2.5. Increasing the leaf-air vapor pressure difference (VPD) resulted in linear reductions in CER and stomatal conductance (Ca). The decrease in CER per unit reduction in Ca (ratio of regression slopes) resulting from the imposition of atmospheric water stress increased from 2.3 at 15 °C to 4.2 at 35 °C showing increased stomatal control of C02 uptake as temperature was increased. Stomatal behavior may vary with growing conditions, but in this experiment, stomates did not operate to maintain internal C02 constant independent of ambient C02 and light. Caucasian bluestem's high CER and rsrt are consistent with its demonstrated forage production potential. Together, these attributes suggest a promising role for the Old World bluestems (Bothriochlocr spp.) on marginal cropland sites in the Southern Plains to complement and supplement native range.

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