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Leaf Gas Exchange in ‘Caucasian’ Bluestem in Relation to Light, Temperature, Humidity, and CO2 1
Author(s) -
Coyne Patrick I.,
Bradford James A.
Publication year - 1984
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1984.00021962007600010027x
Subject(s) - stomatal conductance , vapour pressure deficit , perennial plant , forage , relative humidity , humidity , zoology , water vapor , horticulture , chemistry , botany , analytical chemistry (journal) , photosynthesis , biology , transpiration , thermodynamics , physics , environmental chemistry , organic chemistry
Leaf gas exchange was measured in glasshouse‐grown Old World bluestem [ Bothriochloa caucasica (Trin.) C. E. Hubb cv. Caucasian] as a function of light, temperature, humidity, and CO 2 to provide a database for developing a model to aid in deriving specific genotypeenvironment combinations that result in optimum forage production. The CO 2 resistance pathway was partitioned into stomatal (r′ s and residual (r′ r ) components and a water‐use efficiency index (r′ s /r′ t where r′ 2 = r′ s +r′ t ) was calculated. Maximum CO 2 exchange rates (CER) were 40 µmol m− 2 s− 1 which are above the average of published rates of numerous C4 perennial grasses. Maximum r′ s /r′ t was about 70% of the theoretical potential and was markedly superior to comparable values from the literature. The r′ s /r′ t ratio declined rapidly as temperature was decreased or increased from the optimum for maximum CER (36 °C) due to the greater temperature sensitivity of r′ g compared to r′ s . The ratio of r′ s /r′ r was greater than unity for temperatures greater than 20 °C and photon flux densities greater than about 150 µmol m− 2 s− 1 and maximum r′ s r r at high light and T opt was about 2.5. Increasing the leaf‐air vapor pressure difference (VPD) resulted in linear reductions in CER and stomatal conductance (C a ). The decrease in CER per unit reduction in C a (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 CO 2 uptake as temperature was increased. Stomatal behavior may vary with growing conditions, but in this experiment, stomates did not operate to maintain internal CO 2 constant independent of ambient CO 2 and light. Caucasian bluestem's high CER and r′ s r t 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.