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Effect of Water Conductivity Characteristic of Sorghum under Drought Stress and Re-Watering

Posted by Fillingim
TAGS: SorghumSweet_sorghumWater_stress
RewateringHydraulic_conductivity
Water deficit is an main limiting factor for crops growth and development in arid and semi-arid areas, it can severely affect a series of physiological processes of plant. At present, more researches were focused on the changes of physiological and morphological indexes of sorghum and sweet sorghum under adversity situations, While the relations of root water conductivity, photosynthesis and growth were little under drought stress and re-watering. In this study, a sorghum(Sorghumbicolor Moench,jinza4) and sweet sorghum(Sorghumbicolor yajin13) variety was selected as the experimental materials, and potted experiment was designed to study and analyse the changes of the leaf gas exchange parametes, hydraulic conductivity of root and morphological indexes of growth, and analyse the relations between these parameters. The key results as following:With the drying of soil, the leaf net photosynthetic rate (Pn) and stomatal conductance(Gs) of sorghum was reduced. After the forth day of re-watering, these parameters were gradually recovered to control level. Under moderate drought condition, the intercellular CO2 concentration(Ci) was the lowest, the stomatal limiting value (Ls) was the highest, which indicated that the reduction of Pn was mainly resulted from stomatal limitation; while for severe water stress, the Ci was the highest, while the Ls was the lowest and the Gs was minimum, which suggested that the decrease of Pn was mainly attributed to the decline of diachyma cells photosynthetic activity, namely, the non-stomatal limitation; After re-watering, Ls was reduced and Ci was increased. Visible, the decline of sorghum photosynthetic capacity has a variational process of from stomatal limitation to the non-stomatal limitation with the drying of soil. Under moderate water stress, after the first day of re-watering, Ls sharply declined, Ci rapidly increased; As for severe water stress, it was happened the second day. After re-watering, Ls was declined and Ci was increased. At the same time, with the drying of soil, maximal efficiency of PSⅡ(Fv/Fm) of sorghum was gradually reducede, which indicated that water stress enhanced the photoinhibition and reduced the efficiency of primary light energy conversion of PSⅡ, After the forth day of re-watering, it gradually recovered to control level. The actual photochemical efficiency (ΦPSⅡ) and photochemical quenching coefficient(qP)was lower than control in the process of drought stress, After the second day of re-watering, these parameters were increased, which displayed that a certain hysteresis effect after re-watering.The non-photochemical quenching (NPQ) of sorghum was highest under SS treament, MS take the second place and the CK was lowest, which suggestted that a part light energy absorbed by PSⅡwas dissipated and can protected the photosynthetic tissue, alleviate the influence of water stress on the sorghum.The water treaments significantly effect the water absorbing of root, The hydraulic conductivity(Lpr) of sorghum under different water conditions was that moderate drought treament>control treament> severe water treament; After re-watering, The Lpr of MS was slowly increased, While SS rapidly rised, after the forth day of re-watering, Lpr of SS was significant higher than MS, and even exceeded CK. Further analysises found that the root length increaed under MS, it was beneficial of water absorption and transportation. At the same time, The surface area of leaf was smaller than CK which can reduce the loss of water; After re-watering, The changes of root parameters were little under SS, While the Lpr rapidly increased, the main reason was probably that re-watering can increase the recovery capacity of root activity.Under different water conditions, The changes of leaf gas exchange parametes of sweet sorghum were that Pn of sweet sorghum leaf under SS condition was the highest, After the forth day of re-watering, There was no difference between three treaments. Under water stress, The performance of Gs was that SS>CK>MS; The Ci was that CK was significantly higher than MS and SS treaments; The Ls of MS and SS treaments was significantly higher than CK treament. After the third day of re-watering, The Gs、Ci and Ls maintain stability and there was no difference between three treamnents. The Ci and Gs of MS treament was reduced and the Ls was increased; After re-watering, Gs and、Ci was gardually rised, Ls was reduced, Pn recovered to control level, Showing that the reduction of Pn was mainly resulted from stomatal limitation. The Ls and Gs of CK treament was low, While the Ci was the highest, Which suggested that the decreased of Pn was mainly attributed to the reduced of diachyma cells photosynthetical ability, the utilization of CO2 was low. Under SS treament, the Ls was highes and Ci was lowest,maybe related to the low Pn; After re-watering, the Ls and Gs reduced, Ci was increased which was the same as conrtrol. With the drying of soil, Fv/Fm of sweet sorghum leaf was gradually reduced; After the forth day of re-watering,there was no difference between three treaments.ΦPSⅡof SS treament was extremely higher than CK and MS treament; and descend after re-watering. TheΦPSⅡof MS treament was reduced;and begin to increase after re-watering. The changes of qP was the same asΦPSⅡ. The changes of fluorescence parameters were in line with photosynthetic parameters , which will explain the photosynthesis changes of sweet sorghum in fluorescence level.The performance of Lpr of sweet sorghum under different water conditions was that SS>CK>MS; after re-watering, the Lpr of SS treament was no difference with CK treament. The Lpr of MS treament was lowest. Further studies founding that the root surface area under MS treament was big, the water flow was reduced under unit time, unit pressure gradient and unit surface area of root.
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