Qingzhen Jiang ¹, Susan Durham ², David Hole ¹ and Dominique Roche ¹

1 Department of plants, soils and biometeorology, Utah State University, Logan, 84322

2 Ecology Center, Utah State University, Logan UT 84322

Abstract The effects of awn removal on ear gas exchanges were studied on four barley genotypes (Morex, Harrington, TR306 and Steptoe). From ear emergence to grain maturity, plants were grown at two water level conditions (60% and 90% of soil water holding capacity) in growth chamber. Gas exchange measurements of ears were started at 10 days after anthesis. A Before-After Control-Impact Paired (BACIP) experimental design was used to assess the contribution of awns. Here ‘Impact' was awn removal on half the ears selected in similar stage after two successive days of measurements (‘Before' period). Measurements were further conducted on the following two successive days on both intact and deawned ears (‘After' period). CO₂ response curves were also made on four intact ears (‘before') and two intact and two deawned ears (‘after') the impact at each water level and for each genotype. Results showed that the applied moderate water stress did not affect gas exchange of bracts and awns of the barley ear. Net photosynthetic rates and transpiration rates decreased significantly upon awn removal but dark respiration rates were not affected. Awn removal affected transpiration rate more than photosynthetic rate which indicated a higher water use efficiency of awn. Compensation points for CO₂ of deawned ears were much larger than intact ears. Systematic measurement of dark respiration on ears measured for net photosynthetic rates clearly indicated that ear gross photosynthesis was largely underestimated while awn contribution was overestimated. Awn removal did not affect the number of fertile kernels, thousand-kernel weight and carbon isotope discrimination of grain. No differences were found between the four barley lines.