GROWTH AND NUTRITION OF TIMOTHY (PHLEUM PRATENSE L.)

During the first year of growth of timothy, variations in nitrogen supply affected the number of tillers and leaves, leaf area and dry weight, but had little influence on relative growth and net assimilation rates, except at very low levels of nitrogen. Differentiation and ear emergence occurred slightly earlier at high nitrogen and ear length was increased; there was also an increase in the proportion of fertile tillers among the total number produced after the first few weeks of tillering. The effect of nitrogen supply on the number, dry weight and ear length of early primary tillers was small but became larger in later tillers. Irrespective of the level of nitrogen supply, tillers had particularly high net assimilation rates during the first few weeks following their appearance.     

GROWTH AND NUTRITION OF TIMOTHY (PHLEUM PRATENSE)

All tillers of timothy ( Phleum pratense ) growing in sand culture were labelled at weekly intervals. At each of eighteen dates between June and December a sample of plants was harvested, and dry weight and leaf area were determined for each group of tillers.
Tiller production was continuous throughout the experiment. Only those tillers which appeared before the end of July were able to form inflorescences, but among them the proportion of tillers with ears decreased with increasing lateness of origin.
Dry weight per plant increased rapidly for the first 14 weeks, and then did not change significantly until the end of the experiment. The flowering tillers lost dry weight after seed maturation; vegetative tillers, although smaller in size, continued to increase in number and weight. Dry weight per inflorescences was greatest in the main stem and decreased in subsequent tillers.
Leaf area per plant rose to a maximum soon after ear emergence and then declined, largely because the loss in leaf surface sustained by the flowering tillers was not offset by a corresponding increase in the vegetative tillers. Leaf area ratio decreased at first rapidly but later more gradually, while net assimilation rate was relatively high until maximum leaf area was almost attained, but then fell continuously to negligible values by October. Relative growth rate decreased throughout the experiment.
Initially the growth of the plant was largely determined by the flowering tillers in which, in close resemblance to the cereal plant, leaf area ratio and relative growth rate declined continuously. Tillers which did not flower were successively smaller in size and, because of their later origin, were exposed to less favourable environmental conditions by the time they had increased sufficiently in number to affect the growth of the plant.     

EFFECT OF THE PARENTAL NUTRIENT REGIME ON GROWTH OF THE PROGENY IN ABUTILON THEOPHRASTI (MALVACEAE)

Two genets of Abutilon theophrasti were clonally replicated and grown to maturity in a glasshouse at two levels of nutrient supply. The seeds produced were weighed and the resulting seedlings exposed to two nutrient levels during development. The progeny plants were harvested on three occasions, and leaf areas and dry weights of the different plant parts were determined. At the early stages of growth an increase in the maternal nutrient supply significantly increased seedling height, cotyledon area, and leaf areas, and seed weight had a significant effect on several traits. The maternal nutrient addition had no significant effect at a later stage of growth (35 d after sowing), but at 56 d after sowing it did affect offspring leaf areas and dry weights. Significant interaction terms indicate that the response to parental nutrient addition may depend both on genotype and on the nutrient status of the progeny. Different plant characters are differentially sensitive to maternal conditions and these may be expressed at different stages of development.     

EFFECTS OF SINGLE AND MULTIPLE EXPOSURES OF FERULIC ACID ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF PHASEOLUS VULGARIS BBL-290

Phaseolus vulgaris BBL-290 plants were grown in growth chambers in the Southeastern Plant Environment Laboratory and exposed to either single (at seedling, flower, or podfill) or multiple (biweekly or weekly) treatments of ferulic acid (FA). In the first experiment, plants were harvested one week after FA treatment (0, 1.0, 2.0 mM) and at final harvest (56 days old). FA delayed leaf expansion during the seedling and flowering stages. The total plant leaf area and the plant dry weight of plants treated with 1.0 and 2.0 mM FA as seedlings were reduced one week after treatment by 38–48%. The total plant leaf area and the plant dry weight of plants treated at flowering with 2.0 mM FA were reduced by 25% one week after treatment. Treatment with 2.0 mM FA at podfill caused the senescence and abscission of older leaves and reduced total plant leaf area, plant dry weight and mean pod dry weight by 54, 40, and 48%, respectively, one week after treatment. The plants treated at the seedling and flowering stages recovered by final harvest. In a subsequent experiment, FA (0, 0.50, 1.0, 1.5 mM) reduced total plant leaf area at the seedling and flowering stages but not at podfill. The youngest expanding leaves were most sensitive to FA at flowering. The leaf area of these leaves was reduced by 35 and 25%, one and two weeks after treatment, respectively. Their absolute growth rates were reduced from 31 to 56% one week after treatment at flowering. Their relative growth rates were reduced by 50% one week after treatment. Growth rates then recovered within two weeks after treatment. In the final experiment, biweekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area but did not affect any other growth parameters. Weekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area up to 34%, absolute growth rate up to 58%, leaf number up to 31% and pod number up to 58%. As the frequency of exposure to FA increased, the concentration necessary to affect bean plant growth and development decreased.     

EFFECTS OF RELATIVE HUMIDITY AND TYPE OF CONTAINER ON THE GROWTH OF F1 HYBRID ANNUALS IN CONTROLLED ENVIRONMENTS

The effects of three levels of relative humidity (40%, 65%, and 90%) and two types of containers (clay and plastic) on the seedling growth of three F₁ hybrid annuals were determined after 14 days of controlled-environment treatment. Forty percent relative humidity was severely limiting to the seedling growth of ‘Blue Blazer’ ageratum (Ageratum houstonianum Mill.), ‘Pink Cascade’ petunia (Petunia hybrida Vilm.), and ‘Double Eagle’ marigold (Tagetes erecta L.). Raising the relative humidity to 65% resulted in striking increases in fresh weight, dry weight, and leaf area, especially when clay containers were used. Height of the main shoot was increased significantly at 65% relative humidity but node number was influenced only slightly. Increasing the relative humidity further to 90% had no significant effect on fresh weight, dry weight, or percent dry weight for any of the three species, in either container. Leaf area was increased significantly at 90% only in ageratum seedlings grown in clay pots. Each species responded differently to the type of container used. The fresh weight and dry weight of petunia seedlings were significantly greater in plastic pots at every level of humidity while those of marigold seedlings were unaffected by the type of container used. Ageratum seedlings, on the other hand, had significantly greater fresh weights and dry weights in clay pots only at 90% relative humidity.     

Dry matter production and partitioning in potato plants subjected to combined deficiencies of nitrogen, phosphorus and potassium

Three experiments examined effects on growth, dry matter partitioning and nutrient uptake in potato plants grown in large pots under different combinations of adequate and deficient levels of nitrogen, phosphorus and potassium. N supply affected the growth of all leaves, with low N reducing both the size of individual leaves and the extent of branch growth. P and K availability affected the growth of later formed leaves and only when both were deficient was branch growth substantially reduced. At later stages of growth, total green leaf area was significantly reduced by deficiency of each of the nutrients. Partitioning of dry matter to tubers was markedly reduced by K deficiency and increased in one experiment by P deficiency. When both P and K were deficient, partitioning approximated that under non‐limiting conditions. Leaf weight ratio (LWR) was higher under K deficiency, but not when P was also deficient, and was consistently higher when the ratio of K : P in dry matter was less than approximately five. In these experiments, LWR was not consistently related to shoot N% and N supply had relatively little effect on partitioning. There were large treatment effects on tuber dry matter percentage, characterised by significant interactions especially between N and K. Deficiency of one nutrient increased the concentration of others but uptake was highly regulated as crop content of all three nutrients was reduced when the supply of any one was deficient. The results show that the response of potatoes to single deficiencies may be influenced greatly by the levels of other nutrients.     

EFFECTS OF DAY AND NIGHT TEMPERATURE AND TYPE OF CONTAINER ON THE GROWTH OF F1 HYBRID ANNUALS IN CONTROLLED ENVIRONMENTS

The effects of three day/night temperatures (18/12 C, 24/18 C, and 30/24 C), and two types of containers (clay and plastic) on the seedling growth of three F₁ hybrid annuals were determined after 14 days of controlled-environment treatment. A day/night temperature of 18/12 C was severely limiting to the early seedling growth of ‘Blue Blazer’ ageratum (Ageratum houstonianum Mill.), ‘Pink Cascade’ petunia (Petunia hybrida Vilm.), and ‘Double Eagle’ marigold (Tagetes erecta L.). Raising the day/night temperature to 24/18 C resulted in striking increases in growth in both clay and plastic pots. Fresh and dry weights of tops for all three species were increased four- to fivefold, and leaf areas of ageratum and petunia were increased more than fivefold irrespective of container. Height and node number were also increased significantly but to a much lesser degree. A day/night temperature of 30/24 C appeared to be optimum for early seedling growth of F₁ hybrid annuals the optimum being based on dry matter accumulation, stem elongation, node development, and leaf area production. Growth of lateral shoots was greatly stimulated at 30/24 C, especially in marigold. There were no appreciable differences in fresh or dry weight of tops or in leaf area between plants in clay and plastic containers at any of the three day/night temperatures.     

Developmental Physiology of Sugar Beet: I. THE INFLUENCE OF LIGHT AND TEMPERATURE ON GROWTH

Sugar beet plants were grown for 12 weeks from emergence ingrowth rooms at temperatures of 10, 17, 24 and 31 °C and20, 50, 80, and 110 cal visible radiation cm^-2d^-1, and the changeswith time in their dry weight, leaf area, leaf numbers, andstorage root sugar determined. The first stage of growth wasdominated by the development of the shoot, but the storage rootgradually assumed increasing importance and eventually grewat a faster rate and to a greater weight than the shoot. Therelative growth rate and final yield of dry matter of the shootwere greatest at 24 °C and of the root between 17 and 24°C. The relative rate of expansion and the final area ofthe leaf surface were also greatest at 24 °C, whilst therates of production and of unfolding of leaves were greatestat about 17 °C. All these attributes were increased withincreased radiation. Net assimilation rate increased almostproportionately with radiation and was not significantly affectedby temperature.The relationships of total leaf area with plantdry weight, root dry weight with shoot dry weight, and totalleaf number with plant dry weight were scarcely affected bychanges in radiation, but were much influenced by temperature.Plants of the same dry weight generally had bigger roots andsmaller areas of leaf surface as temperatures departed from24 °C and had most leaves at 17 °C. Sugar concentrationsin the storage root were greatest at 17 °C, but the totalamount of sugar was about the same at 17 and 24 °C. Theconcentration of sugar in the storage root depended on rootsize.Thus, temperature affected both the rate and pattern ofdevelopment, and radiation affected the rate but not the patternof development.     

PHOSPHORUS AND THE GROWTH OF JUVENILE MACROCYSTIS PYRIFERA (PHAEOPHYTA) SPOROPHYTES1

The effect of phosphate (P_i) supply on growth rate and tissue phosphorus content of juvenile Macrocystis pyrifera (L.) C. Ag. sporophytes was examined. Sporophytes were batch cultured in aquaria with flowing recirculated seawater enriched by 30 μM nitrate. Each aquarium was supplemented with a different seawater P_i concentration, 0, 0.3, 1, 2, 3, and 6 μM. Sporophyte mean specific growth rates declined with time in all cultures presumably due to the normal developmental decrease in the proportion of meristematic tissue of each plant. Growth rate declines were more pronounced in cultures that were nutrient limited. Sporophyte growth was P-limited after two-week exposure to P_i less than 1 μM, corresponding to a tissue P concentration of less than 0.20% dry weight. Plants cultured at 6 μM P_i contained tissue P levels of 0.53% dry weight after three weeks. Luxury consumption and storage of P occurred.     

Growth and carbon economy of a fast-growing and a slow-growing grass species as dependent on nitrate supply

In previous experiments systematic differences have been found in the morphology, carbon economy and chemical composition of seedlings of inherently fast- and slow-growing plant species, grown at a non-limiting nutrient supply. In the present experiment it was investigated whether these differences persist when plants are grown at suboptimal nutrient supply rates. To this end, plants of the inherently fast-growing Holcus lanatus L. and the inherently slow-growing Deschampsia flexuosa (L.) Trin. were grown in sand at two levels of nitrate supply. Growth, photosynthesis, respiration and carbon and nitrogen content were studied over a period of 4 to 7 weeks. At low N-supply, the potentially fast-growing species still grew faster than the potentially slow-growing one. Similarly, differences in leaf area ratio (leaf area:total dry weight), specific leaf area (leaf area:leaf dry weight) and leaf weight ratio (leaf dry weight:total dry weight), as observed at high N-supply persisted at low N-availability. The only growth parameter for which a substantial Species × N-supply interaction was found was the net assimilation rate (increase in dry weight per unit leaf area and time). Rates of photosynthesis, shoot respiration and root respiration, expressed per unit leaf, shoot and root weight, respectively, were lower for the plants at low N-availability and higher for the fast-growing species. Species-specific variation in the daily carbon budget was mainly due to variation in carbon fixation. Lower values at low N were largely determined by both a lower C-gain of the leaves and a higher proportion of the daily gain spent in root respiration. Interspecific variation in C-content and dry weight:fresh weight ratio were similar at low and high N-supply. Total plant organic N decreased with decreasing N-supply, without differences between species. It is concluded that most of the parameters related to growth, C-economy and chemical composition differ between species and/or are affected by N-supply, but that differences between the two species at high N-availability persist at low N-supply.     

岩棉育苗对番茄幼苗生长发育的影响

采用岩棉和营养土方作育苗基质,观测了基质对番茄幼苗各时期生长的影响。其试验结果是：以岩棉作基质培育功苗能增加番茄幼苗全株的干重,其中幼苗根系的干重增加较为显著。在播种２４ｄ内,岩棉育苗的幼苗高度、茎干重、叶面积和干重的增长略低于营养土方育苗,２４ｄ以后,岩棉育苗则增长迅速,说明岩棉育苗具有增加幼苗干物质累积、培育壮苗的特点,证实岩棉是一种良好的育苗基质。     

THE EFFECT OF GIBBERELLIC ACID ON LEAF AREA AND DRY-MATTER PRODUCTION IN MAJESTIC POTATO

When gibberellic acid (50 p.p.m. in aqueous solution) was sprayed twice or six times at weekly intervals on potato plants (var. Majestic) with a low or high nitrogen supply it did not affect rate of leaf production on the main axis, but caused earlier senescence of leaves, especially with the more frequent spraying, and inhibited leaf production and growth on laterals of the high-nitrogen plants at nodes 10 and 11 but not at other nodes. This central region of the stem appears to have a low growth potential, probably because it lies midway between two zones of active growth, viz. the basal branches and the younger leaves on the main stem. Competition between these is increased by gibberellic acid. Gibberellic acid increased leaf area even when lack of nitrogen was restricting growth but this did not produce extra dry matter. Tuber weight was increased more in high-nitrogen plants by two sprayings than by six sprayings. The net assimilation rate of low-nitrogen plants was halved by spraying but was not changed in high-nitrogen plants where the value was similar to that of low-nitrogen control plants. The high-nitrogen plants had absorbed nearly all the available nitrogen between the second and third harvests, but plants treated with gibberellic acid, nevertheless, had more total dry weight and tuber dry weight than the controls. The nitrogen content of the leaves expressed on an area basis was lower in sprayed plants and, with continued spraying, fell at the third harvest to equal that of low-nitrogen plants. Evidently, the effect of gibberellic acid depended on the interaction between the rate of application and the nitrogen supply, but further work is necessary to define the conditions that give the maximal effect on dry-matter production.     

THE EFFECT OF GROWTH IRRADIANCE ON THE COUPLING OF CARBON AND NITROGEN METABOLISM IN CHAETOMORPHA LINUM (CHLOROPHYTA)

The influence of growth irradiance on the non-steady-state relationship between photosynthesis and tissue carbon (C) and nitrogen (N) pools in Chaetomorpha linum (Muller) Kutzing in response to abrupt changes in external nitrogen (N) availability was determined in laboratory experiments. For a given thallus N content, algae acclimated to low irradiance consistently had a higher rate of light-saturated photosynthesis (P_max normalized to dry weight) than algae acclimated to saturating irradiance; for both treatments, P_max was correlated to thallus N. Both P_max and the photosynthetic efficiency (α_dw) were correlated in C. linum grown at either saturating or limiting irradiance over the range of experimental conditions, indicating that variations in electron transport were coupled to variations in C-fixation capacity despite the large range of tissue N content from 1.1% to 4.8%. Optimizing both α and P_max and thereby acclimating to an intermediate light level may be a general characteristic of thin-structured opportunistic algae that confers a competitive advantage in estuarine environments in which both light and nutrient conditions are highly variable. Nitrogen-saturated algae had the same photosynthesis–irradiance relationship regardless of light level. When deprived of an external N supply, photosynthetic rates did not change in C. linum acclimated to low irradiance despite a two-fold decrease in tissue N content, suggesting that the active pools of chlorophyll and Rubisco remained constant. Both α and P_max decreased immediately and continuously in algae acclimated to high irradiance on removal of the N supply even though tissue N content was relatively high during most of the N-starvation period, indicating a diversion of energy and reductant away from C fixation to support high growth rates. Carbon and nitrogen assimilation were equally balanced in algae in both light treatments throughout the N-saturation and -depletion phases, except when protein synthesis was limited by the depletion of internal N reserves in severely N-starved high-light algae and excess C accumulated as starch stores. This suggests that the ability for short-term adjustment of internal allocation to acquire N andC in almost constant proportions may be especially beneficial to macroalgae living in environments characterized by high variability in light levels and nutrient supply.     

Responses of wetland graminoids to the relative supply of nitrogen and phosphorus

The biomass production of wetland vegetation can be limited by nitrogen or phosphorus. Some species are most abundant in N-limited vegetation, and others in P-limited vegetation, possibly because growth-related traits of these species respond differently to N versus P supply. Two growth experiments were carried out to examine how various morphological and physiological traits respond to the relative supply of N and P, and whether species from sites with contrasting nutrient availability respond differently. In experiment 1, four Carex species were grown in nutrient solutions at five N:P supply ratios (1.7, 5, 15, 45, 135) combined with two levels of supply (geometric means of N and P supply). In experiment 2, two Carex and two grass species were grown in sand at the same .ve N:P supply ratios combined with three levels of supply and two light intensities (45% or 5% daylight). After 12-13 weeks of growth, plant biomass, allocation, leaf area, tissue nutrient concentrations and rates and nutrient uptake depended signi.cantly on the N:P supply ratio, but the type and strength of the responses differed among these traits. The P concentration and the N:P ratio of shoots and roots as well as the rates of N and P uptake were mainly determined by the N:P supply ratio; they showed little or no dependence on the supply level and relatively small interspeci.c variation. By contrast, the N concentration, root mass ratio, leaf dry matter content and speci.c leaf area were only weakly related to the N:P supply ratio; they mainly depended on plant species and light, and partly on overall nutrient supply. Plant biomass was determined by all factors together. Within a level of light and nutrient supply, biomass was generally maximal (i.e. co-limited by N and P) at a N:P supply ratio of 15 or 45. All species responded in a similar way to the N:P supply ratio. In particular, the grass species Phalaris arundinacea and Molinia caerulea showed no differences in response that could clearly explain why P. arundinacea tends to invade P-rich (N-limited) sites, and M. caerulea P-limited sites. This may be due to the short duration of the experiments, which investigated growth and nutrient acquisition but not nutrient con­servation.     

Effect of Nutrition on the Short-term Response of Molinia caerulea to Defoliation

Overwintering, rooted basal internodes of Molinia caerulea (L.)Moench were taken from the field and subjected to four nutritiontreatments [an adequate (high) and suboptimal (low) level ofnitrogen (N) x an adequate (high) and suboptimal (low) levelof phosphorus (P)] and three degrees of defoliation (12 treatmentsin total). Growth parameters were studied using both non-destructivemeasurements and destructive harvesting. High N supply and highP supply increased both the number of tillers and mass of eachtiller. Interactions between the effects of N and P did occurfor several growth variables; in general this was due to anabsence of a response to P supply at low N. Defoliation reducedthe dry weight of basal internodes and roots produced and temporarilyreduced leaf dry weight per tiller. There were no effects ofdefoliation on tillering. Interactions of defoliation with bothN supply and P supply were observed. Leaf extension rate wasincreased by defoliation at low, but not high N, and the adverseeffects of defoliation on root dry weight and root/shoot (R/S)ratios were proportionally greater at low N. The results arediscussed in relation to other investigations which have reportedcontrasting aspects of Molinia growth in response to both nutrientsand defoliation. Molinia caerulea, purple moor grass, nitrogen, phosphorus, defoliation     

INTERACTIVE EFFECTS OF GIBBERELLIC ACID AND SALINITY ON THE GROWTH OF BEANS

Nieman , R. H., and Leon Bernstein . (U. S. Salinity Laboratory, Riverside, Calif.) Interactive effects of gibberellic acid and salinity on the growth of beans. Amer. Jour. Bot. 46(9): 667–670. 1959.—Dwarf red kidney bean plants, grown from the primary leaf stage to maturity on a graded salt series (0, 1.5, 3.0 and 4.5 atm. O.P. NaCl added to a base nutrient solution), showed a progressive and highly significant growth depression with increasing concentration of NaCl. At low levels of salinity (0 and 1.5 atm. O.P.), gibberellic acid applied as a spray to primary leaves, in concentrations of 10 and 100 p.p.m. in distilled water, increased the stem length, fresh and dry wt. of both the top and the root, the yield of green beans, area per leaf, and the total leaf area per plant. At high levels of salinity (3.0 and 4.5 atm. O.P.) growth was so severely suppressed that the expression of all gibberellin effects, except the increase in stem length, was essentially prevented. Gibberellin was, therefore, ineffective in overcoming the salt-induced suppression of growth. An increased rate of water use per unit leaf area was quite consistently observed with the gibberellin-treated plants. This may be simply the result of the increased exposure to light and to air movement of leaves on an elongated stem.     

EFFECTS OF SULFUR DIOXIDE AND OZONE ON GROWTH OF HYBRID POPLAR LEAVES

Hybrid poplar plants were exposed to 0.5 ppm SO₂, 0.25 ppm O₃ or 0.5 ppm SO₂ + 0.25 ppm O₃, 12 hr/day for 24 days to ascertain their effects on leaf growth and abscission. The data revealed that both O₃ alone and O₃ + SO₂ promoted leaf abscission, while SO₂ alone had no effect. Leaf area and dry weight were reduced while leaf abscission was stimulated by ozone fumigation. The interaction found between SO₂ and O₃, with all the parameters measured, was an antagonistic relationship in which SO₂ reduced the toxic effect of ozone. The data analyzed, in relation to leaf position, demonstrated that ozone did not affect development of the six youngest rapidly growing leaves. However, ozone significantly reduced both leaf area and leaf weight, at later stages of development.     

Effects of temperature on the development and growth of winter wheat roots

Wheat plants were grown in columns of soil until early stem elongation at a wide range of constant root temperatures. Two light environments were imposed and three levels of nitrogen fertilizer added at sowing. Shoot and root development and growth were measured by destructive sampling to investigate the combined effects of temperature and changing nutrient and assimilate supply. Both mainstem leaf and root axis production were linearly related to thermal time above a base temperature of 0°C. Low irradiance affected the appearance of mainstem tillers and associated nodal root axes. Nitrogen had little effect on shoot or root development but increased shoot area between 6 and 8 mainstem leaves. Higher temperatures and supplementary light resulted in larger root systems when compared at equivalent times after sowing. Total root length and root dry weight increased exponentially with thermal time, based on the mean of 4 cm soil and 2 cm air temperatures, but no single relation existed for all temperature and light treatments. Total plant dry matter, root length and root dry weight increased linearly with accumulated, intercepted, photosynthetically active radiation. Root growth responded less than the shoot to supplementary light. Increasing temperature reduced the proportion of root weight to total plant weight.     

Tillers Do Not Influence Phytotoxicity of Imazamethabenz in Wild Oat (Avena fatua)

The response of wild oat to imazamethabenz varies with the growth stage, but the role of tillers in this regard is unclear. Removal of tillers at the three-leaf stage before spraying with imazamethabenz did not significantly affect the total shoot fresh weight measured 3 weeks later. The leaf area and dry weight of intact plants at the three-leaf stage were 17–21% greater than for plants with coleoptilar and first leaf main shoot tillers (T0 and T1) removed. The greater leaf area may have increased herbicide interception per plant. Similar fresh weight reductions in main shoot, total tillers, and total shoots were found whether imazamethabenz was applied to the plant at the two-leaf without tillers or the three-leaf with two tillers stage. Imazamethabenz applied only to the main shoot reduced total shoot dry weight more than an equivalent amount of imazamethabenz applied only to tiller T1 or applied over the whole shoot. Imazamethabenz had the least inhibitory effect on whole plant growth when applied only to T1. When ¹⁴C-herbicide was applied to the first main shoot leaf of plants at the three-leaf stage with two tillers, the ¹⁴C translocated 38% to roots, 33% to the main shoot, and nearly 30% to all tillers. When ¹⁴C-herbicide was applied to the first leaf of T1 then the ¹⁴C translocated 50% to T1, 25% to the main shoot, 20% to roots, and 5% to all other tillers. The translocation pattern and fresh weight values suggested that the presence of early tillers during herbicide application neither increased nor decreased imazamethabenz efficacy in wild oat. Received June 4, 1997; accepted June 5, 1997     

水分胁迫下盆栽冬小麦根系生长与苗系生长及某些生理特性的关系

水分胁迫下,盆栽冬小麦根干重和根长密度呈直线正相关。鉴于根长密度反映了土壤中根系最活跃的部分［５］,是研究植物根系吸收水分和养分的最优参数之一［６］,本文用之研究了它与地上部生物量、净同化速率、叶水势和叶片相对含水量、气孔阻力和蒸腾速率的关系。结果表明,根长密度与净同化速率和地上部干重呈直线负相关,与叶水势和叶片相对含水量呈直线正相关;与气孔阻力呈直线负相关,与蒸腾速率呈直线正相关。为实验室进行冬小麦生长控制与生理特性控制提供了一定的基础。