Stomatal control of gas exchange in barley awns

Abstract

SUMMARY The gas exchange of barley ears and awns was measured in the field using a gas analysis system and a diffusion porometer. Awn stomatal resistance decreased with increasing irradiance but to a smaller extent than leaf stomatal resistance. Measurements on ears immediately before and after successively removing awns showed that awn transpiration and photosynthesis were proportional to awn area and that awns accounted for 73% of transpiration by the ear. Although the maximum rates of photosynthesis of which awns were capable declined with age, awns accounted for 80–115% of the net CO2 uptake of complete ears because the ears‐less‐awns could respire more CO2 than they absorbed. Ear photosynthesis accounted for 52% of the weekly increment in ear dry weight after ear emergence, but 5 weeks later photosynthesis by the ear balanced respiration. Overall photosynthesis by the ear accounted for 35 % of its final weight. Differences in the light response curves of leaves and ears can be fully accounted for by the different relationships between stomatal resistance and irradiance of the two organs.

Diurnal courses and factorial dependencies of leaf conductance and transpiration of differently potassium fertilized and watered field grown barley plants

“…He calculated the abaxial surface of the hypostomatous awns of one ear to be 42 cm 2. Taking this value as representative, maximal awn transpiration determined by Biscoe et al (1973) would amount to 2.8 mg U 2 0 cm 2 h-l, which is of similar magnitude as our measurements. Awn stomata respond to solar radiation (Biscoe et al, 1973) and are probably affected also by other micrometeorological factors and by the ear water status, as can be deduced from the diurnal courses depicted in Figure 7.…”

“…Taking this value as representative, maximal awn transpiration determined by Biscoe et al (1973) would amount to 2.8 mg U 2 0 cm 2 h-l, which is of similar magnitude as our measurements. Awn stomata respond to solar radiation (Biscoe et al, 1973) and are probably affected also by other micrometeorological factors and by the ear water status, as can be deduced from the diurnal courses depicted in Figure 7. Patterns of increase and decrease of awn resistances to water vapour transfer were similar to those of the flag leaves and did not simply passively follow the evaporative demands.…”

“…Buttrose and May, 1959;Thorne, 1965). Biscoe et al (1973) determined by means of gas exchange measurements and diffusion porometry stomatal resistances of barley awns to be in the range 3 to 6 s cm-x which resulted in maximal transpiration rates of about 160 mg H 2 0 ear -1 h -1. 73% of the total transpiration of ears originated from the awns, the rest from the lemmas.…”

Use of the root contact concept, an empirical leaf conductance model and pressure-volume curves in simulating crop water relations

“…However, using the projected area underestimates CAI especially of awns. Biscoe et al (1973) found that 73% of ear transpiration may originate from awns and that transpiration was proportional to awn area as calculated from single awn area. They also found a low g value of awns as compared to flag leaves.…”

Awn contribution to gas exchanges of barley ears

“…In barley, ear carbon exchange, transpiration, and respiration rates peak near anthesis, begin to decline 9 to 12 d after anthesis (DDA), and cease about 30 DDA (Kjack and Witters 1974). Estimates of the contribution made by ear photosynthesis to final grain mass of barley vary from as little as 13 % (Biscoe et al 1973) to as much as 70 % (Thorne 1963). Thus, ear metabolism makes a critical contribution to world food production of C 3 cereals and should not be ignored.…”