The Change Of The Water Uptake By Root Of Maize Under Drought Stress And Re-Watering

Water deficit is the main factor to limit growth and development of crops in arid and semi-arid area. Drought can make crops have a series respond of Physiological ecology, Biochemical and Morphological response, on the effect of overground is mainly due to stomatal closure and lessen of carbon dioxide supply reduction while caused by reduction of photosynthesis, at the same time on the effect of roots is limiting the growth of root system, reducing root effective absorption area. So the maintain to water absorbing capacity of roots under variable water conditions has important sense for enhancing the growth and development for crop in semi-arid area and agricultural production.In this study, maize (Zea mays L.; cv:Hudan4) were grown in pots. This experiment was designed to measure the photosynthesis, morphological parameter, the variation of water uptake by roots and relationship between root hydraulic conductivity and the variation of physiological process of overground during drought and re-watering at elongation stage and booting stage. This is helpful to understand the mechanism of compensating benefits after re-watering and to increase the crop yield. The key results as following:1. At elongation stage and booting stage of maize, the leaf net photosynthetic rate (Pn), stomatal conductance (Gs) and the intercellular CO2concentration (Ci) of the moderate water stress and severe water stress were reduced; after re-watering, these parameters were gradually recover, after the fourth of re-watering, Pn, Gs and Ci were recover to the control level, which the leaf can recover rapidly after the termination of water stress. Under drought stress, maximal efficiency of PSII (Fv/Fm) is reducing, which cause the lessen of photochemical activity to PSII Response Center of leaf and the increase of excitation energy. At elongation stage, compared with CK, the stomatal limiting value (Ls) of severe stress increased6.85%, Fv/Fm dropped1.72%, at booting stage, Ls of severe stress increased9.52%, Fv/Fm dropped0.61%, which indicated that the reduction of Pn was mainly resulted from stomatal limitation in two periods. the actual photochemical efficiency (ΦPS II) and photochemical quenching coefficient (qP) of drought treatments was lower than control, which suggested that drought stress resulted in the opening degree of PSII Response Center lower, photosynthetic electronic transfer activity reduced, the efficiency of primary light energy conversion reduced, finally cause light energy excess; at the same time, the NPQ increasing, it consumed excessive light energy, alleviate the damage of photosynthetic institutions of water stress. After re-watering, stomatal limitation remove, and chlorophyll fluorescence parameters also recover to the control basically.2. The plant height, leaf area and dry matter accumulation of were all reduced by severe drought significantly but recovered partly or completely after re-watering at different periods. After5days of rehydration, root surface area and root length recovered and had no significant difference with CK, but biomass still significant lower than CK. Growth index displayed consistent at two periods after re-watering, the recovery of leaf photosynthetic capacity was primary cause to the recovery of morphological parameters.3. The water uptake of root of maize was restricted by severe water deficit. At different water conditions, the hydraulic conductivity(Lpr) of maize at elongation stage showing that: moderate water stress (MS)> control (CK)>sever water stress (SS); After re-watering, the Lpr of MS increased slowly, While SS treatment rised up rapidly; the Lpr of SS was significantly higher than MS and CK after the forth day of re-watering. The probably reason was that the leaf area of moderate water stress was smaller which reduced transpiration loss of water at a certain extent. The variation range of dry weight of root of SS was small after re-watering, But the Lpr increased quickly, it was probably because that most of root system was died under severe stress, but new roots increased by rehydration and this may stimulated some of the inactivated root, which increased the water absorption function of root.4. The Lpr of maize under water stress during booting stage shows that:CK> MS> SS. After re-watering, the Lpr of MS and SS all rose up, at the third day of re-watering, Lpr of SS was significant higher than MS and CK. From the growth variation of root, it could be seen that root length of moderate water stress was maximum, and surface area was larger which can contribute to expand the scope of water absorption, enhancing the moisture absorption ability of root system. The Lpr of severe water stress was maximum, according to the analysis, the lowest level of surface area of root of was detect at sever stress, root water circulation of per unit area was highest which can lead to the Lpr increased; the increasing of new root and activity of partial inactivation root were excited which can make up the reduction of Lpr was caused by water deficit. After rehydration during the two periods, the gas exchange, chlorophyll fluorescence parameters and leaf water potential which were driven by the recovery of root hydraulic conductivity recovered gradually, the result illustrated that the recovery of water transport capacity of root plays an important role on the variation of physiological process of aboveground part.