Hydraulic Architecture Traits In Maize And Sorghum Of Differing Drought Resistance

In this paper, the stem and leaf hydraulic architectures and the coordination between leafwater transport capacity and photosynthesis during gradually soil drying-down were studiedin two maize (Zea mays L.) cultivars (Shandan21, Zhengdan958) and two sorghum(Sorghum bicolor L.)(Jinzhong405, Jinza12) cultivars of differing drought resistance byfield plot and pot experiments. The main purpose was to demonstrate hydraulic mechanismsrelated with drought resistance, thus provide certain theoretical basis for improving droughtresistance of crops by transgenic breeding. The major results were as follows:(1) Water transport capacity and the vulnerability to embolism were compared in maizeand sorghum of differing drought resistance. There was no significant differences in stemhydraulic efficiency between two maize cultivars, but drought-resistant ‘Zhengdan958’ hadlower leaf hydraulic efficiency than drought-sensitive ‘Shandan21’. The stem and leaf ofdrought-resistant ‘Zhengdan958’ had greater resistance to cavitation than drought-sensitive‘Shandan21’. The drought-resistant ‘Jinza12’ sorghum had lower stem hydraulic efficiencythan drought-sensitive ‘Jinzhong405’, but the ‘Jinza12’ had higher leaf hydraulic efficiencythan ‘Jinzhong405’. The stem and leaf of ‘Jinza12’ had greater resistance to cavitation than‘Jinzhong405’. There was no significant differences in stem hydraulic efficiency betweenmaize and sorghum, two sorghum cultivars had lower leaf hydraulic efficiency than twomaize varities, sorghum had weaker resistance to cavitation than maize in stem, but higherresistance to cavitation than maize in leaf. The results showed that the relationship betweenhydraulic efficiency and drought resistance was diverse in different maize and sorghumcultivars, while the resistance to cavitation of stem and leaf was closely related with droughtresistance in two maize or two sorghum cultivars, however the relationship was true only forleaf-level resistance to cavitation across different crops.(2) Stem anatomy showed that there was no significant differences in vessel diameterand vascular bundles per stem area in stem between two maize cultivars as well as twosorghum cultivars. The vessel diameter in stem of maize was bigger than sorghum, butvascular bundles per stem area in stem of maize was fewer than sorghum. For the leaf anatomical structure, vessel diameter in large vascular bundles in maize ‘Shandan21’ wasbigger and vascular bundle number was more than ‘Zhengdan958’, vessel diameter in largevascular bundles and vascular bundle number in sorghum ‘jinza12’ was bigger than‘Jinzhong405’. The vessel diameter in large vascular bundles and vascular bundle number inmaize was bigger than sorghum.(3) The hydraulic safety and stomatal characteristics in maize and sorghum indicated thatthere was little difference of leaf water potential at stomata closure for the two maize cultivars,while leaf water potential at stomata closure of drought-resistant sorghum ‘Jinza12’ waslower than that of sorghum ‘Jinzhong405’. Leaf water potential at stomata in maize washigher than sorghum. There was no difference in the water safety margin between the twomaize and the two sorghum cultivars, while the water hydraulic margin in maize wasnarrower than sorghum, which indicated that sorghum had higher water safety margin.(4) Water transport capacity was closely related with photosynthesis during water stressprocess. The drought-resistant ‘Zhengdan958’ maize had greater photosynthesis than‘Shandan21’, the drought-resistant ‘Jinza12’ sorghum had greater photosynthesis than‘Jinzhong405’, drought-resistant sorghum had higher photosynthesis than maize during waterstress process. Fluorescence parameters also proved this point. The net photosynthetic ratedropped before the declining of water transport capacity in maize, it was contrary to sorghum.Sorghum maintained certain photosynthesis at low water potential compared with maize.