Physiological regulation of high transpiration efficiency in winter wheat under drought conditions

Pot experiments were conducted to study the variation and physiological regulation of transpiration efficiency (TE) of four winter wheat (Triticum aestivum L.) varieties that are widely grown in different ecological regions in North China. Plants were grown under two soil moisture regimes, normal and drought stress. The results showed that under drought stress condition, both TE at plant level and TE at leaf level (TEl) increased significantly. The transpiration rate (Tr) was reduced more strongly than leaf net CO2 assimilation rate (Pn). The decline of Tr was mainly affected by stomatal conductance and the decline of Pn was affected by non-stomatal factors, which was confirmed by the decline in net photosynthetic oxygen evolution rate. The leaf soluble sugar content and proline content were significantly increased under drought stress. The stomatal density was increased and the stomatal length was reduced. These results led us to make the following conclusions: (1) Under drought stress, the increase in TEl appears to be regulated in two ways: via the stomata by regulating Tr, and independent of the stomata through regulation of Pn; regulation via the stomata was more sensitive; (2) Osmotic adjustment was closely correlated to the non-stoma-tal regulation, and stomatal aperture was closely correlated to the stomatal way.