Regulation Mechanism Of Water Uptake By Maize Roots

Water uptake by roots plays an important role in the growth and development aswell as the yield of crops. In-depth understanding of the mechanism water uptake byroots and analysis the impact of different control measures on water uptake by rootare of scientific values and practical significance to water-saving, high-efficiency,high-yielding modern agriculture. To investigate the mechanism of water uptake bycrop roots, this research project chose maize as the plant material and employed acombination method of water culture experiment and pot experiment. The key cropindices, e.g., crop morphogenesis, physiological characteristics, water uptake abilityby roots, and water use efficiency were determined under different control measuresin terms of corn genotype (i.e., Hu4, Tian4, and478), water condition (i.e., wellwatered and water deficit conditions), and nitrogen (N) form of the fertilizer(nitrate-N and ammonium-N). The results should contribute to understanding of themechanism of efficient water use by crops. The main findings of this study were asfollows:(1) Water supply conditions substantially influenced the morphologicalcharacteristics of maize roots. There were significant variations among differentmaize genotypes. Hu4produced a larger root system than Tian4and478.Compared with well watered, water deficit increased the total root surface area andtotal root length while decreasing the root dry weight of different maize genotypes. Inaddition, water deficit significantly increased the length of primary and secondaryroots, the length and main root length of seminal roots, and the linear frequency andlength of first-order lateral roots. Under different water regimes, the root growth ofHu4was better than that of478and Tian4. As compared to478and Tian4, Hu4 had greater root dry weight, total root length, and total surface area. In particular, Hu4was characterized by large length of primary roots as well as large linear frequencyand length of first-order lateral roots, whereas the length of secondary roots showedno significant variations among different maize genotypes. Overall, the root growth ofHu4showed advantages in adapting to the water conditions.(2) Water supply conditions substantially influenced water uptake by maizeroots. There were significant variations among different maize genotypes atcellular, single root and whole root system levels, with the water uptake ability ofHu4was higher than that of Tian4and478. At cellular level, the turgor of corticalroot cells of the three maize genotypes decreased under water deficit, and the turgorranking was in the order Hu4> Tian4>478. But, the turgor of the three maizegenotypes was with no genotypic differences under the well watered condition. Aftertreated by HgCl2and2-mercaptoethanol under two water levels，cell hydraulicconductivity (Lpc) of the three maize genotypes were firstly decreased，then increased,and the final values were even lower than the original values. The results indicatedHgCl2inhibited the activity of aquaporins, and2-mercaptoethanol parted reversed theactivity of aquaporins. The Lpcof the three genotypes substantially decreased in thewater deficit treatment, and the Lpcranking was in the order Hu4> Tian4>478inthe two water treatments. At single root level, the hydrostatic hydraulic conductivity(Lpsr) of single roots varied among genotypes under the two water levels, with thehighest in Hu4and the lowest in478. Radial hydraulic conductivity (radial Lpsr) andaxial hydraulic conductance (Lax) of the three genotypes varied similarly as Lpsr, andwater stress decreased radial Lpsrand Lax. The osmotic Lpsrin the Hu4was thehighest (Hu4> Tian4>478) across the water conditions. The variations in hydraulicparameters were related to root anatomy. Radial Lpsrwas negatively correlated withthe ratio of cortex width to root diameter (R=–0.77, P <0.01), whereas Laxwaspositively correlated with the diameter of the central xylem vessel (R=0.75, P <0.01)and the cross-sectional area of xylem vessels (R=0.93, P <0.01). At whole rootsystem level, hydraulic conductivity (Lpwr) of the whole root system followed thesame trend under the two water conditions, with the highest values in the Hu4.Moreover, the Lpwrof each genotype substantially decreased under water deficit. (3) Soil moisture conditions and N forms significantly influenced the growthof the shoot and root system of maize. Compared with well watered condition,water deficit had an inhibitory effect on the growth of the shoot and root system ofmaize, which increased the root-to-shoot ratio and promoted the accumulation ofproducts of photosynthesis in the roots. Application of N fertilizer significantlyimproved plant growth in a dose-dependent manner. When applied at the same level,the mixture of nitrate-N and ammonium-N significantly increased plant biomass ofthe shoot and root system while significantly reducing the root-to-shoot ratio. Thus,this application of mixed N fertilizers was more conducive to plant growth, especiallythe root growth and development. Soil moisture conditions and N forms mainlythrough regulation of the net photosynthetic rate and the chlorophyll content of maizeleaves, further influencing the photosynthesis process and regulating growth of thecrop.(4) Soil moisture conditions and N forms significantly influenced thetranspiration and root water uptake capability of the above-ground part ofmaize, thereby regulating water balance in plant body. Under water deficit, thetranspiration and root water uptake capability of the above-ground part of maize weresignificantly lower than those under well watered condition. Under the same waterconditions, application of N fertilizers significantly improved transpiration rate of theabove-ground part and water uptake ability of maize roots, and the improvementeffect was stronger in higher-N treatments than in low-N treatments. Application ofnitrate-N mixed with ammonium-N was more effective than single use of the Nfertilizer in enhancing th e transpiration of the above-ground part of maize andimproving the water use efficiency of the biomass. On the other side, application ofnitrate-N alone enhanced the water uptake ability by roots at cellular and whole rootsystem levels, thus facilitating the plants to maintain good water conditions.