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Summary • The dynamics of silica deposition and Si aggregates formation in inner tangential walls of root endodermal cells, which occurs as an additional stage of endodermal development in sorghum (Sorghum bicolor), were studied. • An environmental scanning electron microscope (ESEM) and X-ray microanalyzer (EDAX) were used to study sorghum roots grown hydroponically with Si (+ Si medium) and without Si (– Si medium). • Silica aggregates were absent in roots of plants cultivated in – Si medium. However, their additional formation on fully mature and thickened endodermal cell walls took place when plants grown in – Si medium were transferred to + Si medium. The beginning of Si aggregates formation was observed and Si deposition detected 2 h after transfer to + Si medium. • By dipping the apical root half in + Si medium, the silica aggregates were formed in the endodermis at the basal part of the root. This supports the hypothesis of outward Si transport from the xylem to the endodermis rather than radial inward Si movement and its deposition at the point of the apoplastic barrier represented by the endodermis.

Confidor, an imidacloprid insecticide, was used in two applications at four rates (47.6, 71.4, 95.2, and 119 g a.i./ha) for indirectly controlling Tomato yellow leaf curl virus (TYLCV) in field plantings of tomato. This spray regimen was compared with standard applications of cypermethrins at 10- to 15-day intervals throughout the growing season. In three field trials, a combination of integrated pest management (IPM) practices and two applications of Confidor at the two highest rates immediately after planting and 6 weeks later, protected tomato plants against the disease until 12 weeks after sowing. All rates of Confidor reduced disease incidence compared with standard chemical control applied in an integrated strategy, and quantitative efficacy increased with increase of insecticide rate. In the three seasons, the mean incidence of TYLCV 12 weeks after sowing was 42.7% in plots not adopting IPM compared with 15.7% in those that did. Disease incidence was reduced by Confidor treatments to 2.2 to 17%. Confidor-treated plots consistently had higher yields than control plots, and the yields decreased with the decrease in the rate of Confidor application. Confidor offers several advantages over standard applications of cypermethrins to control TYLCV. When applied immediately after planting, its long-lasting systemic activity protected the crop against the disease during early stages of growth. In addition, it reduced the number of sprays and increased tomato yield.

The distribution of plant species and relationships between species and soil factors in the east central part of Gurbantunggut Desert was studied to provide more insight into the flora and determine differences in vegetation across various parts of the desert. Two-way Cluster Analysis showed that the vegetation in the area could be divided into three groups, the first group was dominated by the shrub species, Ephedra przewalskii and the grass species, Carex physodes mainly in areas of flat grounds and gentle slopes; the second group was dominated by C. physodes, Artemisia songorica and A. xerophytica mainly on the slope of sand dunes and the third group was dominated by the shrub species, Haloxylon persicum mainly on the top of sand dunes. There was no difference in plant density between Groups 1 and 2 but there was a significant decrease in Group 3. Soil water under vegetation Group 3 was much lower than that in the other two groups at all soil depths. The EC, organic matter, total P and soluble Na, Ca and Mg varied very similarly with soil water. Canonical correspondence analysis (CCA) satisfactorily assessed the species-soil relations in the area. The distribution of plant species was strongly correlated with the soil factors of water content, organic matter, EC and nutrients. The variations in species occurrence explained by the three CCA axes were about 70%, indicating that some explanatory site variables may exist outside our studied parameters. Soil texture is suggested to be included in future studies to improve the explanation of CCA.

Our objectives were to determine the influence of salinity on root cell wall composition in soya beans and the possible mechanism of salt tolerance. Two soya bean cultivars, Touzan 69 (salt sensitive) and Dare (salt tolerant), were selected as experimental material for comparison. Root growth was clearly inhibited by salinity in both cultivars, but Touzan 69 showed more severe reductions in root length than Dare. In the 0–5 mm root segment (from root tip), the total cell wall sugar content of Touzan 69 decreased considerably due to salinity as were the pectin, hemicellulose and cellulose fractions. In Dare, NaCl treatments only caused a slight decrease in the pectin fraction and no marked change in hemicellulose and cellulose fractions. Without salt treatment, the pectin fraction accounted for about 40 % and cellulose for 30 % of cell wall composition in the 0–5 mm root segment; in the 5–10 segment (from root tip), pectin and cellulose accounted for 27 % and 45 % in Touzan 69, and 34 % and 38 % in Dare. The percentage of pectin decreased and that of cellulose increased in the 5–10 mm root segment compared with the 0–5 mm segment. This indicates that pectin largely regulates cell growth, as the 0–5 mm region is considered the elongation zone of soya bean roots. Salt treatment decreased the percentage of pectin, but increased that of cellulose across root zones of the two cultivars, suggesting that salt presence may increase cell wall rigidity, and thus, inhibits root growth. Dare was able to maintain its main root cell wall substances, an apparent advantage for root cell growth that may overall improve its salt tolerance. Also, the less reduction in cell wall uronic acid was of some benefit in the positive regulation of root cell growth in Dare. The changes in cell wall composition, especially the pectin content had a close relation with the regulation of root growth. The difference in salt tolerance between the two tested cultivars can partly be explained on the basis of these changes in response to salinity. Sugar compounds in each cell wall constituent and their functions in ion transport as well as the relationship between root cell wall and soya bean salt tolerance need to be further investigated.

The biosynthetic relationship between acutumine 1 and dechloroacutumine 2 was studied using (13)C-labeled tyrosine and (3)H-labeled 2 as tracers. (13)C-NMR spectra of (13)C-labeled 1 and 2 showed that the alkaloids, each composed of two molecules of tyrosine, are derived from the same biosynthetic pathway. Feeding Menispermum dauricum (Menispermaceae) roots, cultured in a chloride-enriched medium, with (3)H-labeled 2 demonstrated that 1 is the only alkaloid metabolite of 2. Conversion (5%) of the exogenously applied 2, taken up by the roots, into 1 showed that 2 is the precursor of 1. Incomplete conversion of 2 into 1 suggests accumulation of the exogenously applied 2 in cell organelles and/or compartmentation of the enzymes involved in the biosynthesis of 1.

Seeds of Panicum miliaceum, P. sumatrense, Setaria glauca and S. italica were raised in polyvinylchloride (PVC) tubes filled with sandy soil in a greenhouse to determine the effect of preand post-heading water deficit on growth and grain yield. Water stress treatment was initiated 25 days after sowing. The grain yield of S. italica and S. glauca decreased 80 and 70%, respectively, under water stress; and that of P. miliaceum and P. sumatrense decreased 36 and 20%, respectively. The reductions were ascribed to smaller number of grains per panicle, smaller number of panicles and lighter total dry weight. The grain yield decreased when water stress was imposed before heading in S. italica and S. glauca ,but both before and after heading in P. miliaceum and P. sumatrense. Mild water stress decreased the leaf water potential of all millets. Osmotic adjustment of the leaf could not explain the interspecific difference in drought tolerance. Water stress increased the root growth of S. italica ,S. glauca and P. sumatrense at deeper soil layers at heading. At harvest, it also increased root growth at deeper soil layers in S.italica and S. glauca. There was a significant correlation between grain yield and root dry weight among the millets except S. italica. The drought tolerant millet showed greater drought tolerance to water deficit not only at the vegetative stages but also at the reproductive stages than two susceptible millets.

To analyze how silicon (Si) fertilizer improves plant growth under water stress, we investigated the growth and root responses of sorghum seedlings to Si application. Seedlings were grown hydroponically at two Si levels (0 and 1.78 mM) and under two water stress conditions simulated with polyethylene glycol. The reduction in dry weight due to stress was alleviated by Si application, accompanied by an increase in root water uptake. Silicon application decreased the osmotic potential of the roots without affecting their water content, showing that osmotic adjustment occurred to increase water uptake. An assessment of root solutes suggested that soluble sugar and amino acids (alanine and glutamic acid) were osmolytes responsible for this adjustment. Root anatomical traits related to water transport were not affected by the Si application. These results improved our understanding of the physiological mechanisms that underlie the Si-induced increases in sorghum growth and water uptake under water stress.

Sorghum [Sorghum bicolor (L.) Moench] was grown hydroponically with or without 50 ppm silicon (Si), and exposed to water stress from 10 days after sowing (DAS). At 15 and 23 DAS, we measured dry weight and diurnal variations in photosynthetic rate (P N), stomatal conductance (g s), transpiration rate (T), leaf water potential (ψ L), and water uptake rate (23 DAS only). The reduction in dry weight at 23 DAS caused by water stress was ameliorated by silicon. Under water stress, silicon-treated seedlings showed higher g s, P N, and T than untreated ones. ψ L remained almost constant within treatments throughout the daytime. Water uptake rate was reduced by water stress, but the reduction was ameliorated by silicon. We conclude that silicon enhanced water uptake and g s, improving water supply to the leaves. These effects of silicon occurred soon after exposure to water stress.

To clarify whether silicon application could improve root growth of rye (Secale cereale L.) under drought, a pot experiment was conducted under two soil water regimes (soil water contents were kept at 0.015–0.030 or above 0.050 g g−1 for dry and well-watered conditions, respectively). Silicon increased dry weight of rye but did not affect shoot/root ratio under the well-watered condition, while it lowered the ratio under the dry condition. Water use and leaf water potential were increased by silicon under the well-watered condition, although photosynthetic rate, stomatal conductance and water use efficiency were not affected. Under the dry condition, silicon-supplied ryes showed higher photosynthetic rate, stomatal conductance, water use and leaf water potential than silicon-deficient ones. These results suggested that silicon increased dry matter production of ryes under drought, enabling them to allocate more assimilates to root. This resulted in lowering of the shoot/root ratio and better adap...

The effects of defoliation on soybean [Glycine max (L.) Merr.] growth and yield have been well studied, but relatively little is known about its nitrogen (N) accumulation after defoliation. An experiment was conducted to examine soybean recovery and N accumulation following defoliation. The indeterminate cultivar (‘Tousan 69’) was planted in a greenhouse, and two defoliation treatments (no defoliation and 67% defoliation) were imposed at the R2 stage when plants had at least one flower in the two uppermost nodes. At 0, 15, 30 and 45 days after defoliation (DAD), plants were destructively sampled to measure dry mass production, nitrogen accumulation and nitrogen fixation. Seed yield and N concentration also were measured at maturity. Neither the seed yield nor its N concentration was affected by defoliation. Although defoliation temporarily reduced soybean dry weight and N accumulation during 15 DAD, defoliated plants completely recovered their dry weight and N accumulation 30 DAD. There was littl...

Severe soil erosion and its attendant negative impact on the ecosystem and rural livelihoods constitute the most critical ecological and social issue on the Loess Plateau in China. Environmental education is one of the most important measures for soil and water conservation. Recently, significant progress has been made in the social, basic and scientific aspects of environmental education in China. However, the authors' observations show that farmers and herdsmen on the Loess Plateau have little access to environmental education, and especially to appropriate learning materials on soil and water conservation. It is therefore recommended that (a) funding for education on soil and water conservation should be increased, (b) an association of farmers or herdsmen should be established to focus on soil and water conservation, (c) locally appropriate learning materials should be developed, and (d) education on soil and water conservation should be integrated with poverty reduction programmes.

Effects of silicon (Si) application on photosynthesis of solution-cultured cucumber seedlings were investigated under osmotic stress and unstressed conditions. In unstressed conditions, silicon application had no effect on growth and photosynthetic parameters. The responses of the photosynthetic parameters to abruptly imposed osmotic stress did not differ between silicon treatments. After 1 week exposure to osmotic stress, growth reduction was observed, but it was less severe in seedlings grown with silicon than in those without silicon. Although there were no differences between silicon treatments in stomatal conductance, transpiration rate, cuticular transpiration, or xylem sap exudation rate under osmotic stress, leaf intercellular carbon dioxide (CO2) concentration was significantly lower and photosynthetic rate tended to be higher in seedlings supplied with silicon. These results suggested that the silicon-induced alleviation of growth reduction under osmotic stress in cucumber was due to am...

Field water stress is a common problem in crop production, especially in arid and semi-arid zones and it is widely hypothesized that silicon (Si) could reduce water stress in plants. We set up a greenhouse study to evaluate some silicon sources—potassium silicate (K2SiO3), calcium silicate (CaSiO3) and silica gel for growth and nutrient uptake by four grass species under adequate and deficit irrigation. The four species studied were Rhodes grass (Chloris gayana), Timothy grass (Phleum pratense), Sudan grass (Sorghum sudanense) and Tall fescue (Festuca arundinacea). For all species, the biomass yield response to applied silicon under deficit irrigation was significantly better than under adequate irrigation. The yield response of Rhodes grass across silicon sources was 205% under deficit irrigation compared with only 59% under adequate irrigation; for Sudan grass it was 49% compared with 26% and for Timothy, it was 48% compared with a mere 1%. The higher responses under deficit irrigation suggest ...

The objective was to study soil water conservation and physiological growth of wheat (Triticum aestivum L.) using composted cattle manure applied either as mulch or incorporated with soil at 20 Mg ha -1 . Haruhikari, a relatively drought-sensitive and Hongmangmai, a relatively drought-tolerant wheat, were the cultivars studied under both adequate and deficit irrigation. Fourteen weeks after sowing (WAS), the number of tillers and leaves was significantly reduced by 19 % and 30 % respectively under deficit irrigation and Hongmangmai produced slightly (10 %) more tillers than Haruhikari. Unlike mulching, the incorporation of manure had favourable effects on plants in terms of shoot dry mass (SDM) by 36 % and number of tillers and leaves by 40 %. Haruhikari produced substantially (29 %) greater root mass under adequate irrigation but Hongmangmai produced slightly (2.7 %) more roots and responded much better to manure use whether under adequate or deficit irrigation. As a result, Hongmangmai suffered less severe reductions in tillers and biomass under water stress. In comparison, the mulched manure treatment saved 15 % and 64 % respectively more water than the control and the treatment incorporating manure, but this advantage in water-saving did not translate to superior plant growth. Leaf water potential (ψ 1 ) under adequate irrigation significantly exceeded that under deficit irrigation by 27 % and the ψ l of Haruhikari exceeded that of Hongmangmai by 15 %. However, Hongmangmai may be considered more tolerant of dehydration since it maintained much higher net photosynthetic rates (P N ) even with a lower leaf water potential. The reduction in the P N and intracellular carbon dioxide concentration (C i ) of the cultivars under deficit irrigation was on account of decreasing stomatal conductance (g s ) and transpiration rate but on average, the g s of Hongmangmai significantly exceeded that of Haruhikari by as much as 0.53 under adequate irrigation and 0.22 under deficit irrigation. In conclusion, we suggest that the drought tolerance of Hongmangmai was related to its superior root growth and greater ability than Haruhikari, to efficiently utilize incorporated manure for growth under water stress.

Effects of silicon application on stomatal conductance in sorghum were investigated. Sorghum seedlings were grown in culture solution containing 0 or 1.67 mM silicon. On ninth day after giving silicon treatment, when there were no differences in shoot and root growth between the silicon-supplied and silicon-deficient treatments, seedlings were exposed to gradually increasing light intensity, combination of sudden increase and decrease in light intensity, and water stress induced by mixing sorbitol with the culture solution. There was increased stomatal conductance with increasing light intensity and no significant difference was observed between the two silicon treatments. Under water stress, the stomatal conductance of silicon-supplied seedlings was higher than that of silicon-deficient seedlings. The higher stomatal conductance in silicon-supplied seedlings under water stress was attributed to increased leaf water potential due to silicon-induced enhancement of hydraulic conductance. The results indicated that silicon application could affect stomatal conductance in sorghum seedlings through the modification of plant water relations.

Three diploid (Triticum boeoticum, AA; Aegilops speltoides, BB and Ae. tauschii, DD), two tetraploid (T. dicoccoides, AABB and T. dicoccon, AABB) and one hexaploid (T. vulgare, AABBDD) varieties of wheat, which are very important in the evolution of wheat were chosen in this study. A pot experiment was carried out on the wheat under different water and nutrient conditions (i) to understand the differences in biomass, yield, water use efficiency (WUE), and nutrient (N, P and K) use efficiency (uptake and utilization efficiency) among ploidies in the evolution of wheat; (ii) to clarify the effect of water and nutrient conditions on water and nutrient use efficiency; and (iii) to assess the relationship of water and nutrient use efficiency in the evolution of wheat. Our results showed that from diploid to tetraploid then to hexaploid during the evolution of wheat, both root biomass and above-ground biomass increased initially and then decreased. Water consumption for transpiration decreased remarkably, correlating with the decline of the growth period, while grain yield, harvest index, WUE, N, P and K uptake efficiency, and N, P and K utilization efficiency increased significantly. Grain yield, harvest index and WUE decreased in the same order: T. vulgare > T. dicoccon > T. dicoccoides > Ae. tauschii > Ae. speltoides > T. boeoticum. Water stress significantly decreased root biomass, above-ground biomass, yield, and water consumption for transpiration by 47-52%, but remarkably increased WUE. Increasing the nutrient supply increased wheat above-ground biomass, grain yield, harvest index, water consumption for transpiration and WUE under different water levels, but reduced root biomass under drought conditions. Generally, water stress and low nutrient supply resulted in the lower nutrient uptake efficiency of wheat. However, water and nutrient application had no significant effects on nutrient utilization efficiency, suggesting that wheat nutrient utilization efficiency is mainly controlled by genotypes. Compared to the other two diploid wheats, Ae. squarrosa(DD) had significant higher WUE and nutrient utilization efficiency, indicating that the D genome may carry genes controlling high efficient utilization of water and nutrient. Significant relationships were found between WUE and N, P and K utilization efficiency.

Ascorbate (AsA) is a major antioxidant and free-radical scavenger in plants. Monodehydroascorbate reductase (MDAR; EC 1.6.5.4) is crucial for AsA regeneration and essential for maintaining a reduced pool of AsA. To examine whether an overexpressed level of MDAR could minimize the deleterious effects of environmental stresses, we developed transgenic tobacco plants overexpressing Arabidopsis thaliana MDAR gene (AtMDAR1) in the cytosol. Incorporation of the transgene in the genome of tobacco plants was confirmed by PCR and Southern-blot analysis and its expression was confirmed by Northern- and Western-blot analyses. These transgenic plants exhibited up to 2.1-fold higher MDAR activity and 2.2-fold higher level of reduced AsA compared to non-transformed control plants. The transgenic plants showed enhanced stress tolerance in term of significantly higher net photosynthesis rates under ozone, salt and polyethylene glycol (PEG) stresses and greater PSII effective quantum yield under ozone and salt stresses. Furthermore, these transgenic plants exhibited significantly lower hydrogen peroxide level when tested under salt stress. These results demonstrate that an overexpressed level of MDAR properly confers enhanced tolerance against ozone, salt and PEG stress.

We have previously reported the ability of porous glass material (PGM) to adsorb phosphate and that calcium contributed to this process. In the present investigation, the possible use of PGM to improve water quality (wastewater in particular) and the subsequent use of phosphate-adsorbed PGM as fertilizer were examined. We confirmed the phyto-availability of phosphate adsorbed onto PGM using tomato cultivation and an assay of truog-phosphate levels. Adsorption and release of phosphate in PGM was controlled by particle size. The findings suggest the possibility of using PGM of different particle sizes for efficient phosphate recycling in soil-water/plant systems.

An experiment was conducted to determine if salinity stress alters the response and tolerance of soybean to defoliation. Four soybean [Glycine max(L.) Merr.] cultivars (‘Tachiutaka,’ ‘Tousan 69,’ ‘Dare’ and ‘Enrei’) in a growth chamber were exposed to two salinity treatments (0 and 40 mM NaCl) and two defoliation treatments (with and without defoliation). The interactive effects of salinity stress and defoliation on growth rate, leaf expansion, photosynthetic gas exchange, and sodium (Na+) accumulation were determined. The decrease in growth rate resulting from defoliation was more pronounced in plants grown under salinity stress than in those grown without the stress. Without salinity stress, defoliated plants of all four cultivars had leaf-expansion similar rates to those of the undefoliated ones, but the photosynthetic rates of their remaining leaves were higher than those of undefoliated plants. However, with salinity stress, defoliated ‘Tachiutaka’ and ‘Tousa 69’ had lower leaf expansion and...

The spatial distribution of lateral roots in the soil is an important factor influencing water and nutrient absorption. However, lateral root development has rarely been studied in detail, especially concerning morphological variations, mainly because such examinations are both time-consuming and laborious. We measured the number and length of all first-order lateral roots on the seminal roots of maize (Zea mays L.) and wheat (Triticum aestivum L.) to investigate variations in linear frequency and length. This was conducted with reference to species, root types, and positions on their parental roots. Although the linear frequency of first-order lateral roots varied along the root axis in maize, the variation was not as great as in wheat. Variations were found in the length of lateral roots among plant species, root types, and positions on their parental root axes. Such variations in the length of lateral roots along the root axes were caused by differences in the elongation period of lateral roots rather than those in the elongation rate. Additionally, we examined the effects of soil drying on lateral root development. As a response to soil drying, the length of lateral roots varied depending on the period they were placed under the stressed condition. Moderate soil drying could also accelerate the elongation of some lateral roots. Variations in the length of first-order lateral roots and their responses to soil drying could help distribute their tips thoroughly throughout the soil. This might be adaptive for water absorption for root system development when resources are limited.

Ascorbate (vitamin C) is a potent antioxidant protecting plants against oxidative damage imposed by environmental stresses such as ozone and drought. Dehydroascorbate reductase (DHAR; EC 1.8.5.1) is one of the two important enzymes functioning in the regeneration of ascorbate (AsA). To examine the protective role of DHAR against oxidative stress, we developed transgenic tobacco plants overexpressing cytosolic DHAR gene from Arabidopsis thaliana. Incorporation of the transgene in the genome of tobacco plants was confirmed by polymerase chain reaction and Southern blot analysis, and its expression was confirmed by Northern and Western blot analyses. These transgenic plants exhibited 2.3–3.1 folds higher DHAR activity and 1.9–2.1 folds higher level of reduced AsA compared with non-transformed control plants. The transgenic plants showed maintained redox status of AsA and exhibited an enhanced tolerance to ozone, drought, salt, and polyethylene glycol stresses in terms of higher net photosynthesis. In this study, we report for the first time that the elevation of AsA level by targeting DHAR overexpression in cytosol properly provides a significantly enhanced oxidative stress tolerance imposed by drought and salt.

The effects of five rates [0 (control), 1, 2, 4 and 6 Mg ha−1] of calcium silicate on the growth and water consumption by rhodes grass (Chloris gayana Kunth) and sudan grass (Sorghum sudanense Piper) under wet and dry soil water regimes (60 g and 30 g H2O kg−1 soil respectively) were evaluated in a pot experiment. The effect of the application of silicate on plant biomass was similar to that of the control. However, the shoot and root dry mass varied significantly (P

Conserving irrigation water resources is a most important measure for sustainable wheat production in the North China Plain. In the present study, the effect of phosphorus (P) application for saving irrigation water was evaluated. The application of fertilizer P increased nitrogen and phosphorus uptake, shoot biomass, head number, seed number and, consequently, grain yield, and increased soil water use and seasonal evapo-transpiration. The lower the volume of irrigation water applied, the more obvious were these effects. When winter wheat was basally fertilized with 88.5 kg P2O5/ha and irrigated with 90 mm at the jointing stage, the highest fertilizer P use efficiency, apparent P recovery and net profit (due to irrigation and/or fertilizer P) were obtained. The results suggested that fertilizer P should be used for saving irrigation water resources in the North China Plain.

Accurate estimation of microbial adenosine 5′-triphosphate (ATP) is a pre-requisite to quantify the impact of varying environments on microbial activity of soil. We investigated the effectiveness of a high efficiency soil ATP determination method (PA) [Webster, J.J., Hampton, G.J., Leach, F.R., 1984. ATP in soil: a new extractant and extraction procedure. Soil Biology & Biochemistry 4, 335–342] in 10 Ontario (Canada) soils collected along a 100 m transect and spanning a textural class gradient ranging from a sandy loam to clay loam with increasing organic matter. Modifications of the method involved using an extract of autoclaved soil to make the standard curve, as it was found that the light emitted by ATP luciferin–luciferase bioluminescence reaction in the pure extractant was different from that in the extracts. Replacing Tricine with Tris buffer in the assay significantly improved the light emission. On an average, the internal standard calibration method (ISM) measured a smaller amount of extracted ATP (1199 ng ATP g−1 soil) and a lower recovery of ATP spike (82.4±7.2%) than did the standard curve method (SCM) (1246 ng ATP g−1 soil and 91.2±4.5%, respectively) (P

In the North China Plain (NCP), more than 70% of irrigation water resources are used for winter wheat (Triticum aestivum L.). A crucial target of groundwater conservation and sustainable crop production is to develop water-saving agriculture, particularly for winter wheat. The purpose of this study was to optimize irrigation scheduling for high wheat yield and water use efficiency (WUE). Field experiments were conducted for three growing seasons at the Wuqiao Experiment Station of China Agriculture University. Eleven, four and six irrigation treatments, consisting of frequency of irrigation (zero to four times) and timing (at raising, jointing, booting, flowering and milking stage), were employed for 1994/95, 1995/96 and 1996/97 seasons, respectively. Available water content (AWC), rain events, soil water use (SWU), evapotranspiration (ET) and grain yield were recorded, and water use efficiency (WUE) and irrigation water use efficiency (IWUE) were calculated. The results showed that after a 75-mm pre-sowing irrigation, soil water content and AWC in the root zone of a 2-m soil profile during sowing were 31.1% (or 90.7% of field capacity) and 16.1%, respectively. Rainfall events were variable and showed a limited impact on AWC. The AWC decreased significantly with the growth of wheat. At the jointing stage no water deficits occurred for all treatments, at the flowering stage water deficits were found only in the rain-fed treatment, and at harvest all treatments had moderate to severe soil water deficits. The SWU in the 2-m soil profile was negatively related to the irrigation water volume, i.e. applying 75 mm irrigation reduced SWU by 28.2 mm. Regression analyses showed that relationships between ET and grain yield or WUE could be described by quadratic functions. Grain yield and WUE reached their maximum values of 7423 kg/ha and 1.645 kg/m3 at the ET rate of 509 and 382 mm, respectively. IWUE was negatively correlated with irrigated water volume. From the above results, three irrigation schedules: (1) pre-sowing irrigation only, (2) pre-sowing irrigation + irrigation at jointing or booting stage, and (3) pre-sowing irrigation + irrigations at jointing and flowering stages were identified and recommended for practical winter wheat production in the NCP.

The analytical results of 53 manure samples determined by wet digestion and dry ashing procedures were compared in order to evaluate their relative suitability for recovering different nutrient elements in manure and manure compost. Wet digestion recovered greater amounts of phosphorus (P), potassium (K), calcium (Ca), manganese (Mn), and zinc (Zn) in more samples than dry ashing. Nutrient contents in the samples were highly variable, with coefficients of variation (CV) ranging from 38% for magnesium (Mg) to 161% for copper (Cu) analyzed by the wet digestion procedure, and from 47% to 138% for Mg and Cu analyzed by the dry ashing procedure. The mean values of P, K, Ca, Mn, and Zn averaged for the 53 samples were significantly higher using wet digestion than dry ashing procedure, but both procedures recovered comparable amounts of iorn (Fe), Mg, and Cu. Correlations analysis between both procedures for each element showed reasonable to fair agreements for Ca (R 2 = 0.93), K (R 2 = 0.93), P (R 2 = 0.90), Mg...

The effects of silicon application on the drought tolerance of sorghum (Sorghum bicolor (L.) Moench) were investigated for two cultivars differing in drought susceptibility. Silicon application ameliorated the decrease in dry weight under drought stress conditions, but had no effect on dry matter production under wet conditions. Under dry conditions, silicon-applied sorghum had a lower shoot to root (S/R) ratio, indicating the facilitation of root growth and the maintenance of the photosynthetic rate and stomatal conductance at a higher level compared with plants grown without silicon application. The diurnal determination of the transpiration rate indicated that the silicon-applied sorghum could extract a larger amount of water from drier soil and maintain a higher stomatal conductance. Very similar effects of silicon application were observed for both cultivars regardless of their drought susceptibility. These results suggest that silicon application may be useful to improve the drought tolerance of sorghum via the enhancement of water uptake ability.

An environmentally controlled experiment was conducted in growth chambers to investigate the interactive effects of salinity and air humidity on two cultivars of tomato (Lycopersicon esculentum Mill.), Daniela (relatively salt tolerant) and Naomi (relatively salt sensitive). One month after germination, the plants were exposed for 15 days to factorial combinations of two salinity levels, 0 (control) and 80 mM sodium chloride (NaCl), and two relative humidity (RH) levels, 30% and 70%. The NaCl treatment decreased the growth of cv. Naomi by 34% and 21% at 30% and 70% RH, respectively, while there was no decrease in the growth of cv. Daniela at 30% RH and only a slight decrease at 70% RH. Under NaCl treatment, cv Daniela had significantly lower Na+ concentrations in leaves and stems and a higher root-to-shoot ratio than cv. Naomi at both relative humidities. Salt tolerance of cv. Daniela may be related to its high root-to-shoot ratio and its ability to exclude Na+ from the shoot. NaCl-treated plants...

Common buckwheat (Fagopyrum esculentum Moench cv. Tsushima) and Tartary buckwheat (F. tataricum (L.) Gaertn. cv. Pontivy) were grown in a nutrient solution with or without added NaCl to investigate interspecific differences in their responses to salinity, based on their dry-matter production. The mechanism of salt tolerance was also studied. Addition of 100 mM NaCl to the culture solution (salt treatment) lowered the plant growth rate to 48% and 16% of the control in Tsushima and Pontivy, respectively, and decreased the net assimilation rate and mean leaf area of Pontivy more severely than in Tsushima. The salt treatment decreased the leaf growth rate and leaf area per leaf to 30% and 72% of the control, respectively, in Tsushima, and to 12% and 52%, respectively, in Pontivy. It decreased the photosynthetic rate to 67% and 35% of the control, and stomatal conductance to 25% and 15% of the control in Tsushima and Pontivy, respectively. It also decreased the transpiration rate to 41% and 30% of the control in Tsushima and Pontivy, respectively, and increased the wateruse efficiency 1.6 times in Tsushima, but did not influence the wateruse efficiency in Pontivy. In the saline solution, the accumulation of Na + in leaves and stem was greater in Pontivy than in Tsushima, but that in the roots, was greater in Tsushima than in Pontivy. In both species, Na + accumulated rapidly in the leaves after removal of the roots in the saline solution. We conclude that the difference in salt tolerance between common and Tartary buckwheat may result from the difference in accumulation of Na + in leaves and absorption of Na + bv the roots.

Common buckwheat (Fagopyrum esculentum Moench cv. Shinano No.1) and Tartary buckwheat (F. tataricum (L.) Gaertn. cv. Nepal) were grown in pots to examine their responses to soil flooding. Flooding treatment was carried out during the early growth stage by completely submerging the pots in a nutrient solution from 12 to 36 days after sowing. The plant growth rate, relative growth rate and mean leaf area under the flooding treatment were reduced to 72, 90 and 83% of the control, respectively, in Shinano No.1, and to 29, 71 and 45% of the control, respectively, in Nepal. The excess moisture stress had no effect on the net assimilation rate (NAR) in Shinano No.1, but lowered the NAR to 68% of that in the control in Nepal. Excess moisture stress decreased the total leaf area to 76 and 34% of the control in Shinano No.1 and Nepal, respectively. Leaf growth rate, number of leaves and leaf area per leaf, which influenced the total leaf area, were reduced by the excess soil moisture. The relative water content of leaves was unchanged in Shinano No.1, but was decreased in Nepal. Reduction in bleeding from the cut end of stem due to flooding was greater in Nepal than in Shinano No.1. Excess moisture stress reduced the K+ concentration of the stem and increased the Na+ concentration of leaves, stem and roots more strongly in Nepal than in Shinano No.1. Development of adventitious roots in the surface layer of the nutrient solution was better in Shinano No.1 than in Nepal. In conclusion, Shinano No.1 (common buckwheat) had a stronger tolerance to excess soil moisture than Nepal (Tartary buckwheat). In Shinano No. 1, leaf growth and photosynthetic rate were not markedly affected and the capacity of absorbing water and nutrients was retained by developing adventitious roots in the solution above the surface of the soil keeping proper physiological activity under excess moisture conditions.

ケイ酸には作物の各種ストレス耐性を高める効果があることが知られているが, 耐乾性に及ぼす影響については研究の遅れが指摘されている. これは, 既往の報告では, 蒸散に関わる形質に限定してケイ酸の効果が論じられてきたためである. 最近, 水吸収や水輸送に関する研究が行われはじめ, ケイ酸がそれらの性質にも関与していること, および, ケイ酸施用が植物種によって異なる影響を及ぼすことが示唆された. 一方, 組織や細胞レベルでの乾燥耐性にもケイ酸の関与が示唆されている. 本稿では最近の報告を中心にケイ酸と作物の耐乾性との関わりを整理し, 耐乾性を高めるためのケイ酸利用の可能性について検討した.

The greatest fear of global climate change is drought. World-wide, 61% of countries receive rainfall of less than 500 mm annually; domestication of wheat first occurred in such a semiarid region of southwestern Asia, and it seems that wheat foods originally came from dryland gardens. Wheat plants respond to drought through morphological, physiological and metabolic modifications in all plant parts. At the cellular level, plant responses to water deficit may result from cell damage, whereas other responses may correspond to adaptive processes. Although a large number of drought-induced genes have been identified in a wide range of wheat varieties, a molecular basis for wheat plant tolerance to water stress remains far from being completely understood. The rapid translocation of abscissic acid (ABA) in shoots via xylem flux, and the increase of ABA concentration in wheat plant parts correlate with the major physiological changes that occur during plant response to drought. It is widely accepted that ABA mediates general adaptive responses to drought. For a relatively determinate target stress environment, and with stable genotype × environment interaction, the probability for achieving progress is high. This approach will be possible only after we learn more about the physiology and genetics of wheat plant responses to water stress and their interactions. The difficulties encountered by molecular biologists in attempting to improve crop drought tolerance are due to our ignorance in agronomy and crop physiology and not to lack of knowledge or technical expertise in molecular biology. Copyright © 2005 Society of Chemical Industry

The difference in rooting pattern between two grain sorghum cultivars differing in drought tolerance was investigated under drought stress. The cultivars, Gadambalia (drought-tolerant) and Tabat (drought-susceptible), were grown in bottomless wooden or acrylic root boxes to examine root parameters. Gadambalia consistently exhibited higher dry matter production and leaf water potential than Tabat under drought stress in both root boxes. In the experiment with wooden root boxes, under a drought condition, Gadambalia extracted more water from deep soil layers (1.1-1.5 m), which was estimated from the reduction in soil water content, than Tabat. This was because Gadambalia had a significantly higher root length density in these soil layers. The high root length density was due to enhanced lateral root development in Gadambalia. In the other experiment with acrylic root boxes, though total root length in the upper soil layer (0-0.5 m) was declined by limited irrigation in both cultivars, the reduction in Gadambalia was moderate compared with that in Tabat owing to the maintenance of fine root growth. Unlike Tabat, Gadambalia had an ability to produce the nodal roots from higher internodes even under drought, which resulted in the high nodal root length of Gadambalia. The growth angle of nodal roots was significantly correlated with root diameter, and the nodal roots from the higher internodes had large diameters and penetrated into the soil more vertically. These results indicate that the responses of roots (i.e. branching and/or growth of lateral root, and nodal root emergence from higher internodes) to soil dryness could be associated with the drought tolerance of Gadambalia.

We investigated net photosynthetic rate (PN) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The PNof ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (gs) was similar for the two cultivars, but intercellular CO2concentration (Ci) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (ψ1) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ψ1between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained PNof flag leaf during grain filling under drought stress. The higher PNof ear in Hongmangmai under drought could also be related to its drought resistance.

We investigated the relative importance of pre-anthesis assimilates stored in plant parts, mainly in the stem, and post-anthesis photosynthesis to drought resistance in wheat (Triticum aestivum L.) cultivars Hongwangmai (drought resistant) and Haruhikari (drought sensitive) subjected to two soil moisture regimes: irrigated and non-irrigated. In the irrigated treatment, soil moisture was maintained near field capacity throughout the growing season, while in the non-irrigated treatment water was withheld from 81 d after sowing until maturity. Drought stress reduced grain yield of Hongwangmai and Haruhikari by 41 and 60 %, respectively. Remobilization of pre-anthesis assimilates to the grain (remobilization) was reduced by drought in Hongwangmai but increased in Haruhikari. The contribution of pre-anthesis assimilates to the grain decreased under non-irrigated treatment in Hongwangmai. However, under water stress, Hongwangmai maintained a higher net photosynthetic rate in the flag leaf than Haruhikari. These results indicated that maintenance of post-anthesis photosynthetic rate was related to drought resistance in Hongwangmai rather than to remobilization under drought stress.

ひげ根型根系の形態を規定している重要な要因の一つは, 個々の節根の伸長方向である. 節根は傾斜重力屈性を示し, 様々な方向に伸長しているが, その伸長方向を決定する様相やメカニズムについては必ずしも明らかでない. そこで, 本研究では, トウモロコシとソルガムを圃場で栽培し, 節根の出現直後における伸長方向の決定過程を詳細に観察するとともに, 重力感受部位と考えられる根冠の形態との関係を検討した. すなわち, 異なる生育段階に, 根端まで採取できた節根の出現部位 (トウモロコシは第4～9節, ソルガムは第7～10節) を同定し, 伸長角度を記録するとともに, 根長, 根端の直径および根冠の長さと幅を測定した. トウモロコシおよびソルガムのいずれの場合も, 節根は茎から出現した直後, 伸長に伴って下向きに屈曲したが, その様相は節位によって異なった. また, 節根の伸長に伴って根端直径や根冠の幅は減少していたが, 根冠の長さは逆に増加している場合があった. すなわち, 根の伸長に伴って根端の直径に対して根冠が相対的に大型化するとともに, 伸長角度が大きくなっていた. そこで, 根冠の長さ/根端直径比と伸長角度との関係をみると, 有意な正の相関関係が認められた. このように, 節根の下方向への屈曲と根冠の相対的な大型化とが時間的に対応していたことから, 根の伸長方向の変化を重力感受の観点から説明できる可能性が示唆された.

Soil samples were collected from a field with a long-term (10 yr) oily wastewater application history, containing 70 mg g–1 of oil and grease and an accumulation of heavy metals, and also from a short-term (1 yr) wastewater application involving different rates of waste, tillage, and nitrogen (N) fertilization. Prior to ATP extraction, the soils were incubated at 22 °C and a water potential of –60 kPa for 21 d and 2 d for the long- and short-term trials, respectively. The light emitted from the bioluminescence reaction was partly quenched in the extract of steam-sterilized long-term waste-treated soil, and curvilinearly responded to the addition of ATP at concentrations higher than 4 ng ATP per assay in contrast to the linear response from the pure extractant and the extract of control soil. Calibration curves developed from the extracts of steam-sterilized soils were used for calculating ATP in that given soil. ATP determined in the long-term treated soil was as high as 3201 ng (g soil)–1. Still, residual oil to ATP concentration ratio was about an order of magnitude higher in the long- than in the short-term waste-treated soil, reflecting the accumulation of recalcitrant material. In the short-term treated soils, ATP ranged from 355 to 760 ng (g soil)–1 and responded to the rate of waste application, tillage, and fertilization. The use of ATP measurement has potential for assessing land management effects and developing tillage and fertilization recommendations for enhanced biodegradation of the oil waste. Kann ATP in Boden mit industriellen Olruckstanden bestimmt werden? Bodenproben wurden von zwei Feldern (1: 10-jahrige Abwasserverrieselung, Akkumulation von 70 mg g–1 olhaltigen Ruckstanden und Schwermetallen, 2: 1-jahrige Abwasserverrieselung in Verbindung mit verschiedenen Raten von Abfall, Bodenbearbeitung und Stickstoffdungung) entnommen. Vor der ATP-Extraktion wurde der Boden bei 22 °C und einem Matrixpotenzial von –60 kPa fur 21 bzw. 2 Tage inkubiert. Das Licht aus der Biolumineszenzreaktion wurde im Extrakt der autoklavierten, langjahrig mit Abwasser behandelten Bodenproben teilweise gedampft, und reagierte exponentiell auf die Zufuhrung von > 4 ng ATP pro Ansatz. Im Gegensatz dazu zeigten reines Extraktionsmittel und Extrakt aus dem Kontrollboden eine lineare Reaktion. Die Kalibrierkurven aus den Messwerten der Extrakte der autoklavierten Boden wurden fur die Berechnung der ATP-Konzentration im gegebenen Boden genutzt. In dem langjahrig behandelten Boden wurden hohe ATP-Werte von 3201 ng g–1 bestimmt. Die Verhaltnisse von Restol zu ATP waren im langjahrig behandelten Boden um eine Grosenordnung hoher als im kurzzeitig behandelten Boden, was eine Akkumulation abbauresistenten Materials widerspiegelt. In den kurzzeitig behandelten Boden variierte der ATP-Gehalt im Bereich von 355 bis 760 ng g–1 und reagierte somit auf die Abwasserverrieselung, die Bodenbearbeitung und die Dungung. Somit konnen ATP-Messungen die Ableitung von Bodenbearbeitungs- und Dungungsempfehlungen fur eine erhohte Biodegradation olhaltiger Abfalle unterstutzen.

To obtain a greater yield per unit rainfall is one of the most important challenges in dryland wheat production. Highly efficient use of limited water may be one means of achieving this goal. This paper reviewed wheat physiological adaptation and benefits associated with water deficit and variable conditions. In addition, it reveals the compensatory effect of limited irrigation and fertilizer supplement on wheat water-use efficiency (WUE) and highlights the breeding of new varieties for high WUE that could improve wheat productivity under water-limited environments in the semiarid area. Considerable potential for further improvement in wheat productivity in semiarid area seems to depend on effective conservation of moisture and efficient use of this limited water. Different crops, soil and water management strategies should be adjusted according to the conditions that prevail in the various semiarid areas. By combining soil and water conservation approaches with regulating the cropping system by ...

A field study was conducted to evaluate the drought tolerance of three sorghum [Sorghum bicolor (L.) Moench] cultivars, Gadambalia, Arous elRimal and Tabat, and quantify the physiological bases for differences in their drought tolerance. Water stress reduced shoot dry mass of Gadambalia, Arous elRimal and Tabat by 43, 46 and 58 %, respectively. The respective reduction in leaf area of the three cultivars was 28, 54 and 63 %. The reduction in net photosynthetic rate, stomatal conductance and transpiration rate due to water stress was lowest in Gadambalia and highest in Tabat. The leaf water potentials and relative water contents of Gadambalia under wet and dry treatments were similar, while those of Tabat were significantly reduced by water stress. The lowest and highest liquid water flow conductance was displayed by Tabat and Gadambalia, respectively. Drought tolerance in Gadambalia is associated with its smaller leaf area, higher liquid water flow conductance, and ability to maintain high leaf water potential, relative water content, stomatal conductance, transpiration rate and photosynthetic rate under drought stress.

Ethylene involvement in germination of Striga hermonthica (Del.) Benth., an important root parasitic weed on poaceous crops, was investigated at the physiological and molecular levels. Seeds, conditioned at 30°C for 14 days, were treated with ethylene, ethephon or 1-aminocyclopropane-1-carboxylic acid (ACC). Ethylene consistently induced low germination. Ethephon and ACC effectively stimulated germination at concentrations of 0.01 and 1 mM, respectively. In contrast to ethylene, both ethephon and ACC acted in a concentration-dependent manner. Germination induced by the synthetic strigolactone GR24 was inhibited by aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene. ACC reversed the inhibition caused by AVG. When seeds were treated with GR24 in sealed vials, ethylene concentration in headspace gas increased prior to the onset of germination. Total RNA extracted from germinating seeds 12 h after GR24 treatment was used for PCR-based amplification of cDNA fragments encoding the ACC synthase- and oxidase-active site domains. Two distinct cDNA fragments encoding ACC synthase (SHACS1 and SHACS2) and one encoding ACC oxidase (SHACO1) were cloned and sequenced. Southern analysis suggested that each of the cloned genes was present as a single copy in the genome of S. hermonthica. Northern analyses showed that SHACSI exhibited a temporal change in expression peaking at 10 h after GR24 treatment, which coincided with a steady increase in ethylene concentration. SHACS2 was expressed at a low level with a similar trend. SHACO1 exhibited a temporal change in expression peaking at 15 days during conditioning, when seed response to GR24 was maximal. In summary, expression of ACC synthase and ACC oxidase genes was found to be responsive to a germination stimulant and to conditioning, respectively. The implications of these findings with respect to germination of S. hermonthica under field conditions are discussed.