In China, wheat is next to rice the second most important food crop. It is mainly planted in semi-arid and semi-humid areas, and drought is its greatest stress. Drought stress can cause a series of physiological, biochemical, and morphological responses in crops, which has been extensively studied. However, questions remain regarding effects of stress relief on subsequent crop growth, and whether the adverse effects of the stress on the crops can be eliminated. The Triticum aestivum (AABBDD) is a polyploidy of different sources; it has three groups of chromosomes, A, B and D. It was obtained by hybridizing Triticum dicoccum (AABB) with Aegilops tauschii (DD). This experiment therefore is designed to study changes of photosynthesis and WUE of wheat of different ploidy under changing water environment, thus providing a theoretical basis for studies on water-saving, drought-resistance and seed-breeding physiology of the wheat.
In this research, net photosynthetic rates of wheat of different ploidy all decreased in the course of the drought. That of the A. tauschii began to drop obviously when the FRWC (field relative water content, FRWC= field water content / field water capacity×100%) was 44.1% and to 73.1% of that of the CK; That of the T. dicoccum began to drop obviously when the FRWC was 25.8% and to 83.3% of that of the CK, and that of the T. aestivum cv. yumai49 began to drop obviously when the FRWC was 23.6% and to 65.6% of that of the CK. After rewatering, photosynthetic rates of the experimental groups all recovered, albeit to different degrees for wheat of different ploidy. Two hours after rewatering, net photosynthetic rate of A. tauschii rebounded to 77.5% of that of the CK; net photosynthetic rate of T. dicoccum climbed to 753% of that of the CK, while net photosynthetic rate of yumai49 shot to 102.4% of that of the CK, indicating a strong post-drought ultra-compensation effect.
In this experiment, leaf transpiration rate of T. dicoccum decreased more rapidly than net photosynthetic rate of this variety. On the third day of the experiment, when FRWC was 47.6%, net photosynthetic rate was 99.7% of that of the CK, while transpiration rate had dropped to 90.3% of that of the CK. This is an important drought-adapting mechanism. But transpiration of A. tauschii did not show a similar adaptation. WUE ranking at leaf level was T. dicoccum＞yumai49＞A. tauschii while water was normally supplied; WUE of T. dicoccum and yumai49 was respectively 14.7% and 5.1% higher than that of the CK when the drought-rewatering treatment was applied. However, WUE of A. tauschii did not rise. At present, only primary researches have been conducted regarding photosynthetic physioecological responses of wheat of different ploidy to drought and rewatering treatments. The biochemical basis of these responses remains to be discovered by further studies.