膜下滴灌棉花采用“三水灌溉”法确保高产稳产

根据棉花各生长阶段水分供应充足与否对生长中心影响十分明显的特点,可将"干播湿出"膜下滴灌棉田灌水的主导作用划分为3个功能,即"长根水(苗蕾期)、健根水(始花期)和养根水(产量贡献水,花铃期)"。在苗期与蕾期,棉花的生长中心为根系,此期的水分供应充足与否直接影响到棉花群体的根系质量。因此,该阶段水分作用主要贡献于根系生长,可称之为"长根水";始花前后水分供应的主要作用在于解除由于自出苗以来土壤水分持续下降对棉花生长造成的水分胁迫,促进高产棉田应有的棉花根型结构与质量及地上部分应有营养体的建成,此期的水分供应称之为"健根水";自盛花以后到吐絮期,棉花生长重心为棉铃形成与产量密切相关的群体生殖生长,此期的水分供应目标在于保持根系较好的活力,为地上部分提供足够的水分与养分,故称之为"养根水"。在灌溉量的确定上,"长根水"即播后即灌的出苗水(450~600 m^3/hm^2)和"健根水"即始花前后棉花生长发育期的第1次灌溉(500~700 m^3/hm^2),以不造成深层渗漏为原则使根层(0~100 cm)尽可能多地持有水分。自生长阶段的第2次灌溉起即进入"养根水"管理阶段,应采取"轻勤浅"(灌水量300~400 m^3/hm^2,灌溉周期7~8 d,湿润锋深度60 cm左右)的灌溉方法 ,每次灌溉前的滴灌带下方0~60 cm土壤含水量约75%的田间持水量,使膜下滴灌棉花的产量潜力得到最大可能的挖掘。在棉花3个明显不同的生长发育阶段,水分对棉花生长发育的生理生态意义不相同,在水分管理上应有明显的区别性。

Effects of Nitrate on the Growth of Lateral Root and Nitrogen Absorption in Rice

Lateral root is primary organ for plant to explore and utilize soil nutrient efficiently. The development of lateral roots (LR) is controlled by both genetic factors and nutrient status in environment. To investigate the effects of nitrate (NO3-) on rice lateral root growth and nitrogen (N) uptake efficiency under upland condition, three treatments, including root-split culture and whole plant culture in N sufficient and deficient conditions, were used in a vermiculite culture experiment. Root-split treatment showed that the growth of lateral roots was stimulated by localized nitrate supply. However, in whole plant culture, elongation of lateral roots was induced by NO3- deficiency. The effects of NO3- on rice lateral root growth were genotype-dependent. Similar N concentration, soluble sugar concentration and N content in shoot were observed in both root-split treatment and whole plant culture under NO3- sufficient condition, suggesting that the nitrogen requirement for rice normal growth could be satisfied with only half of roots supplied with NO3-. In the root-split treatment, N uptake was positively correlated with the average of lateral root length (ALRL) in NO3--supplied side, suggesting that the ALRL is important for rice root N uptake in the environment where the nitrogen nutrient is limiting factor. No significant correlation was observed between N uptake and ALRL in whole plant culture under N sufficient condition, which implies that the length of lateral roots may not be the main factor to determine tire rice root N uptake in nutrient-rich zone. Morphological and metabolic evidence in this study provided some prospects for genetic improvement of root system characters to improve the efficiency of nutrient absorption in rice.

Effects of Different Kinds of Exogenous Auxin on the Growth of Rice Roots under Cadmium Stress

[Objective] The aim was to study the effect of different kinds of exogenous auxin on the growth of rice roots under cadmium stress.[Method] Oryza sativa L.cv Zhonghua No.11 was used as experimental materials to detect the effect of different kinds of exogenous auxin on the growth of rice roots.[Result] The results showed that 0.1 mmol/L Cd treatment could not only increase primary,adventitious and lateral root length but also lateral root number,whereas the shoot growth was inhibited.When supplemented with different concentrations of NAA,IAA,IBA and 2,4-D,the growth of root system varied and similar change trend had been found.At the auxin concentration of 10^-9-10^-7 mol/L in particular 10^-8 mol/L,all four kinds of auxin promoted the elongation growth of primary and adventitious roots,but inhibition was observed when auxin was higher than 10^-7 mol/L.The decreased shoot growth caused by Cd could not be counteracted by supplementing with the four kinds of auxin.However,at the auxin concentration of 10^-9-10^-8 mol/L,NAA could improve rice growth under Cd stress condition.The formation and development of lateral roots on primary and adventitious roots was not only similar but also different after applying the same concentration of four auxins.[Conclusion] The addition of suitable amount of auxin under cadmium stress （such as 10^-9-10^-8 mol/L of NAA and so on） could ease the damage of cadmium on plants to a certain extent.

Influence of CO_2 Doubling on Water Transport Process at Root/Soil Interface of Pinus sylvestris var. sylvestriformis Seedlings

Water transport at the root/soil interface of 1 year old Pinus sylvestris Linn. var. sylvestriformis (Takenouchi) Cheng et C. D. Chu seedlings under CO 2 doubling was studied by measuring soil electric conductance to survey soil water profiles and comparing it with root distribution surveyed by soil coring and root harvesting in Changbai Mountain in 1999. The results were: (1) The profiles of soil water content were adjusted by root activity. The water content of the soil layer with abundant roots was higher. (2) When CO 2 concentration was doubled, water transport was more active at the root/soil interface and the roots were distributed into deeper layer. It was shown in this work that the method of measuring electric conductance is an inexpensive, non_destructive and relatively sensitive way for underground water transport process.

Effects of Superoxide Radical on Root System Growth and Auxin Distribution in Rice

[Objective] This study aimed to investigate the effect of superoxide radical on root system growth and auxin distribution in rice （Oryza sativa L. cv Zhonghua No.11）. [Method] With rice Zhonghua No.ll as the experimental material, the effects of DDC （SOD inhibitor） and Tiron （superoxide radical scavenger） on the root system growth, superoxide radical generation and root system auxin distribution in rice were analyzed. [Result] The growth and elongation of primary and adventitious roots were significantly promoted by DDC, while Tiron significantly inhibited the growth and elongation of shoots, primary roots and their lateral roots, and also suppressed the formation and growth of the adventitious roots as well as the elongation of their lateral roots. The superoxide radical was increased with the induction of DDC, while Tiron decreased the accumulation of superoxide radical. Increased accumulation of auxin in the vascular bundle and behind the elongation zone was observed in DDC- treated roots, while the treatment with Tiron resulted in a decrease of auxin in the same position. [Conclusion] This study indicated that the regulation of rice root sys- tem growth by superoxide radical was closely related with the accumulation and distribution of auxin.

Effect of Polar Auxin Transport on Rice Root Development

Polar auxin transport (PAT) is critical in plant growth and development, especially polar differentiation and pattern formation. Lots of studies have been performed in dicots while relative less in monocots. Using two kinds of PAT inhibitors, 2, 3, 5-triiodobenzoic acid (TIBA) and 9-hydroxyfluorene-9-carboxylic acid (HFCA), it was shown that PAT is important for rice (Oryza sativa L. cv. Zhonghua 11) root development, including elongation of the primary roots, initiation and elongation of lateral roots, and formation of adventitious roots. Inhibition of PAT resulted in the shortened primary roots, less and shortened lateral and adventitious roots. Exogenously supplemented NAA can partially rescue the formation of adventitious roots but not lateral roots, while low concentration of NAA (0.1 mumol/L) could not rescue either of them, suggesting the possible different mechanisms of lateral and adventitious root initiations. Treatment of 30 mumol/L TIBA did not completely inhibit the initiation of lateral roots, and survival capacities of which were demonstrated through cross section experiments revealing the presence of primordial of lateral roots at different stages. Further studies through localized application of PAT inhibitors indicated that auxin flow, transported from coleoptiles to the base, is not only responsible for the auxin contents in stem nodes but also critical for initiation and elongation of adventitious roots.

Water status of bare-root seedlings of Chinese fir and Masson pine

Water relation parameters of bare-root seedlings of Chinese fir (Cunninghamia lanceolata Hook.) and Masson pine (Pinus massoniana Lamb.) were measured and changes of root growth potential as well as field survival rate of both species were studied after the bare-root seedlings were exposed in a sunny field condition. The results showed that Masson pine had a lower osmotic potential (-2.07Mpa) at turgor loss point and at full turgor (-1.29Mpa), compared with Chinese fir (-1.80Mpa and -1.08Mpa respectively). The parameter Vp/V0 (63.27%) of Masson pine was higher than that of Chinese fir (58.03%). This means that Masson pine has a stronger ability to tolerate desiccation, compared to Chinese fir according to analysis of above water relation parameters. Root growth potential and field survival rate decreased with prolonging duration of exposure. The field survival rate of both species was reduced to less than 40% after the seedling being exposed only two hours. Water poten-tials of 1.60 Mpa and -1.70 Mpa were suggested to be critical values for Chinese fir and Masson pine respectively in successful reforestation.

Stomatal Conductance, Growth and Yield of Pelargonium sidoides DC. in Response to Watering Frequency and Terminal Water Stress

Water is an important factor affecting growth, yield and distribution of different species. Plant response to water deficit can be in the form of physiological disorders, such as reduction in transpiration or assimilating partitioning to root growth. Sustainable use of water has become a priority in agriculture and thus innovative irrigation management practices are critical. The study aimed at investigating how watering frequency and terminal water stress influence growth of Pelargonium sidoides, an important medicinal plant in Southern Africa. The trial was a randomized complete block design with three replicates, and treatment factors were watering frequency （everyday, twice and once a week） and terminal water stress （no watering four weeks before harvesting, no watering two weeks before harvesting and no terminal stress）. There was an interacting effect of watering frequency and terminal water stress on biomass and fresh root yield. More frequent watering resulted in significantly higher biomass and fresh root yield, compared to other treatments. Watering everyday with terminal or no terminal water stress resulted in higher fresh root yield, compared to other watering treatments with terminal water stress. Plant height and leaf area were significantly affected by watering frequency and terminal water stress, respectively. A significant drop in stomatal conductance of plants watered everyday was observed 240 d after treatment implementation, such that there was no significant difference across all the three watering frequency treatments. In conclusion, farmers can save on irrigation costs by reducing watering frequency, as there was no significant difference on dry root yield.

Allelopathic Potential of Some Crop Residues on the Germination and Growth of Soybean （Glycine max L,） Merrill

Allelopathic potentials of aqueous water extracts from residues of sorghum stem, maize inflorescence and rice husks on the germination of soybeans （Glycine max. L.） were investigated. The result showed that the extracts brought about a considerable inhibition in the germination of soybean seeds, reductions in the radicle and plumule lengths of soybean seedlings. Whereas, the extracts of maize inflorescence and rice husk had more inhibitory effects on the growth of soybean radicle, all the three extracts demonstrated pronounced inhibitory effects on the growth of the plumule. The retardation of soybean germination, radicle and plumule growths were concentration dependents as the degree of retardations increases with increase in the concentration of the extracts. Statistical analysis （ANOVA, P = 0.05） revealed that there were no significant differences in the germination, radicle and plumule growths at 24 and 48 h experimental time when compared to the control. However, statistical differences abound in the growth parameters at 72 and 144 h experimental time.

MODELING AND ANALYSIS OF SALT TRANSPORT IN THE SINGLE CYLINDRICAL ROOT WITH FINITE LENGTH

A mathematical model for salt transport by a cylindrical root in an infinite extent of soil is derived and solved analytically by asymptotic matching of the inner and outer solutions. By asymptotic analysis it is shown that the salt solution uptake by a single cylindrical root in the absence of competition does not influence the overall salt concentration in the soil even when the soil moisture concentration is less than full saturation.