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1.
Horsenettle ( Solanum carolinense L.) is a weed species that can spread via the root system and root fragments. This study investigated the developmental pattern of the subterranean system of horsenettle in an experimental plot containing plastic plates that limited the radial growth of the individual plants in each section of the plot. The vertical architecture of the root system in the 10 month old and 16 month old plants was elucidated by excavating the plants from the experimental plot. The root system consisted of a reiterative arrangement of branching root units, which grew horizontally and then bent vertically. The relationship between the morphology of the branching roots and the vegetative reproduction in a 17 month old plant was investigated. Different sections of the rooting system had different functions: the bending part forms new shoots; the horizontal part extends into the surrounding area; and the vertical part is used for storage. Consequently, the subterranean system of horsenettle develops through a reiterative arrangement of the branching root unit, which has functionally differentiated parts.  相似文献   

2.
The sites of uptake of chlorsulfuron in maize (Zea mays L.) were investigated at three different growth stages. Exposure of seedling roots, or shoots separately, to herbicide-treated sand over 4 days resulted in inhibition of both roots and shoots. Exposure of seedling roots to chlorsulfuron-treated soil over 21 days severely inhibited both roots and foliage, while separate shoot exposure also reduced both foliage and root growth. After plant emergence, exposure of the crown root node, growing point and lower stem to treated soil reduced foliage and root growth, but exposure of the shoot above the growing point caused only slight inhibition of foliage and had no effect on roots. The herbicide safener 1,8-naphthalic anhydride (NA) applied as a dust (10 g kg?1 seed weight), or as a 50 mg 1?1 suspension in water to maize seeds, reduced the root inhibition by chlorsulfuron in 4-day-old seedlings. NA completely prevented both foliage and root injury when chlorsulfuron was placed in soil in the shoot zone before emergence, or in the shoot zone below the soil surface after plant emergence. NA slightly decreased injury to foliage, but not to roots when chlorsulfuron was placed in soil in the root zone before emergence. NA seed treatment protected both roots and foliage against injury from foliarly applied chlorsulfuron. Plants were also protected when a suspension of NA in water was sprayed on the foliage seven days before chlorsulfuron. When a mixture of NA and chlorsulfuron was applied to foliage, root injury was reduced more than foliage injury.  相似文献   

3.
Perennial weeds are often controlled by mechanical means, which aim at stimulating axillary and adventitious buds to sprout. This happens when the apical dominance of the main shoot is removed by defoliation or when the underground system is fragmented. By repeating the measures, the result is a depletion of storage compounds, which weakens the plants and reduces their capacity to grow and reproduce. However, timing is critical. Earlier research has indicated that emergence from fragments of Sonchus arvensis cease during a period in autumn, while the seasonal pattern of sprouting in Cirsium arvense appears to be inconsistent. We studied the emergence pattern of defoliated plants with undisturbed root systems, from late summer to early spring. Potted plants grown outdoors were exhumed at regular intervals, put under forcing conditions for 4 weeks, after which shoots above and below soil level were counted and weighed together with the remaining root systems. In both species, the number and weight of emerged shoots decreased during a period in the autumn. In C. arvense, underground shoots were constantly produced during the same period, while fewer underground shoots were present in S. arvensis. For the latter species, apical dominance does not fully explain the effect; thus, endodormancy might be involved. Root weight increased until withering and did not explain the lack of emergence. Our results suggest an impaired sprouting capacity of undisturbed root systems of C. arvense and S. arvensis during September–October, which has implications for the timing and method of control of these species.  相似文献   

4.
以夏玉米(zea may L. cv.)为试验材料,采用防雨棚下桶栽土培方法,进行调亏灌溉(Regulated deficit irrigation,RDI)对根、冠生长的影响研究,旨在寻求适宜的水分调亏阶段和调节亏水度,为建立节水高产、优质高效作物RDI模式提供技术参数。试验采用二因素随机区组设计,设置4个水分调亏阶段:三叶～拔节(Ⅰ),拔节～抽穗(Ⅱ),抽穗～灌浆(Ⅲ),灌浆～成熟(Ⅳ);每个调亏阶段设置3个水分调亏度:轻度调亏(L)、中度调亏(M)和重度调亏(S),土壤相对含水率分别为60%～65%FC(Field capacity)、50%～55%FC和40%～45%FC;设全生育期保持适宜土壤水分(75%～80%FC)作为对照(CK)。分别在水分调亏期间和复水后测定各处理根系参数和地上干物质质量。结果表明,玉米生长中、后期水分调亏具有促进根系发育和减缓根系衰亡的"双重效应",反映出玉米根系在生育后期比生育前期对水分适应能力强的特性。玉米根冠比(R/S)受水分影响最大的阶段是三叶-拔节期,受水分影响最小的阶段是灌浆期;拔节-抽穗期水分调亏期间能显著增大R/S,复水后分配到冠层与根系的物质比较平衡,维持较为适宜的R/S,表明此阶段为通过RDI调控玉米R/S的适宜阶段。玉米三叶-拔节期水分调亏改善了穗部性状,表明在作物营养生长阶段的适度水分调亏有利于作物生殖生长。RDI可以有效调控根/冠生长关系,提高经济产量。  相似文献   

5.
Following seed treatment of wheat (Triticum aestivum L.) with 14C-labelled triticonazole at a dose of 1·8 g kg-1 seed, the uptake of radioactivity by shoots and roots was investigated from the two- to three-leaf stage up to the beginning of the booting phase, 80 days after sowing. Triticonazole equivalents taken up by wheat plants reached 5·7% and 14·6% of the applied dose in the shoots and the roots, respectively. Between the two- to three-leaf stage and the beginning of the booting phase, the concentration of triticonazole equivalents in the shoots decreased from 2·5 to 0·15 μg g-1 fresh weight. This was attributed to uptake of triticonazole by roots not keeping pace with shoot growth and increased retention in the roots of triticonazole taken up. The main factor limiting the uptake of triticonazole by the roots may be the rapid growth of the uptake-active apical root parts out of the dressing zone which had formed in the soil. Distribution of triticonazole equivalents taken up by the main shoot showed a decreasing concentration gradient from the oldest to the youngest leaf. An increase in the seed treatment dose was investigated as a way to increase the concentration of triticonazole in the shoots, but its influence remained limited. © 1998 SCI  相似文献   

6.
Summary. Studies were conducted to determine the effects of herbicide placement at different zones of maize (Zea mays L.) and pea (Pisum sativwm L.) shoots below the soil surface after emergence. Soil was removed from around the shoots and replaced with herbicide-treated soil. A wax barrier ensured separate exposure of the zones to treated soil. EPTC, chlorpropham, propham and sulfallate did not affect pea shoot growth, but in maize the shoot zone adjacent to the crown root node was extremely sensitive. Treatment in this area markedly reduced growth and severely inhibited the crown roots. The difference in susceptibility between these species may he due to the location of the growing point relative to the treated soil. Shoots of maize and pea were sensitive to diuron. In maize the shoot adjacent to the crown root node and the tissue of the first internode were the most susceptible. In pea the- uppermost shoot (beneath the soil surface) was the most sensitive. Trifluralin did not affect growth of maize and pea when placed in the shoot zone after emergence, although the crown roots of maize were severely inhibited. Naptalam, dalapon and 2,4-D did not affect growth of maize under similar conditions, and of these only 2,4-D reduced growth of pea. Zone d'abiorption des tiges pour les herbicides appliqués sur h sol  相似文献   

7.
Water extracts obtained from the roots, shoots, and fruits of mature wild onion ( Asphodelus tenuifolius ) plants and soil taken from an A. tenuifolius field were used to determine their allelopathic effects on the germination and seedling growth of chickpea ( Cicer arietinum ) in the laboratory. The roots, shoots, and fruits of A. tenuifolius were soaked individually in water in a ratio of 1:20 (w/v) for 24 h to prepare the extracts. Distilled water was used as the control. The germinated seeds were taken out from the Petri dishes and counted every day for 12 days. The seeds of chickpea were also sown in sand and in each of the controlled, normal soil and the soil taken from the A. tenuifolius -infested field in Petri dishes to record the length and weight of the roots and shoots 18 days after sowing. The mean germination time reached the maximum amount for the stem and fruit extracts. The fruit extract caused the most reduction in the germination index and the germination percentage of chickpea. The different wild onion organ extracts significantly reduced the root and shoot length and biomass of the chickpea seedlings compared with the distilled water. The fruit extract of wild onion proved to be the most detrimental to the root length, shoot length, and dry weight of the chickpea seedlings. The soil beneath the A. tenuifolius plants significantly reduced the emergence, root length, shoot length, shoot dry weight, and seedling dry weight but increased the root dry weight of the chickpea seedlings. It is suggested that A. tenuifolius releases phytotoxic compound(s).  相似文献   

8.
Glyphosate ? ? Mention of irademark or proprietary product does not constitute a gtiarantee or warranty oC the product by the U.S. Department of Agriculture and does nut imply its approval to the exclusion of other products thai may also be suitable.
was sprayed at 0009–1·12 kg a.i. ha?1 on the foliage of large potted glasshouse-grown Canada thistle [Cirsium arvense (L.) Scop.], which had extensive, well-developed roots. Increasing the glyphosate rate progressively reduced the total number of visible adventitious root buds plus emerged secondary shoots per plant proportionately more than root biomass, 10 days after treatment. Cortical tissue of thickened propagative roots became soft, water-soaked, darkened, and some regions decomposed, exposing strands of vascular tissue. Lateral roots completely decomposed. When thickened roots were segmented to stimulate secondary shoot emergence from root buds 10 days after foliar treatment, Fewer secondary shoots emerged than expected from the number of visible adventitious root buds present on both control and herbicide-treated plants. Increasing the rate of glyphosate also reduced the regrowth potential of root buds proportionately more than root biomass. Regrowth potential was measured as the number of emerged secondary shoots 35 days after segmenting unearthed roots from plants that had been sprayed 10 days earlier. When foliar-applied at 0·28 kg ha?1, glyphosate decreased the regrowth potential of root buds to zero in 2 and 3 days, as measured by secondary shoot dry weight and number, respectively, even though root fresh weight was unchanged 3 days after foliar treatment. These dose-response and time-course experiments demonstrate that glyphosate did not reduce root biomass as much as it decreased root bud numbers and secondary shoot regrowth potential from root buds.  相似文献   

9.
This laboratory reported that isopropyl-3-chlorocarbanilate-phenyl-U-14C (chlorpropham-phenyl-14C) was absorbed, translocated, and metabolized by soybean plants. Both polar metabolites and insoluble residues were found in roots, whereas only polar metabolites were found in shoot tissues. In both roots and shoots the polar metabolites were shown to be the O-glucoside of isopropyl-2-hydroxy-5-chlorocarbanilate (2-hydroxy-chlorpropham). In shoot tissue there were other polar metabolites that were not identified. The experiments with soybeans have been repeated, but with new isolation and purification procedures. The plants were root treated with both chlorpropham-phenyl-14C and isopropyl-3-chlorocarbanilate-2-isopropyl-14C. The roots and shoots were extracted and separated into the polar, nonpolar, and insoluble metabolic components, using the Bligh-Dyer extraction method. The polar metabolites were separated by gel permeation chromatography. Further purification was accomplished on Amberlite XAD-2. The polar metabolites from the shoot and root tissues were hydrolyzed either by β-glucosidase or hesperidinase. The enzyme liberated aglycones were derivatized and separated by gas-liquid chromatography, and the components were characterized by mass spectrometry or NMR. The results of this study showed that the polar metabolites of soybean shoots were 2-hydroxy-chlorpropham and isopropyl-4-hydroxy-3-chlorocarbanilate (4-hydroxy-chlorpropham). These two hydroxy-chlorpropham metabolites were found in soybean shoots at a ratio of approximately 1:1. The only aglycone found in root tissue was 2-hydroxy-chlorpropham. Using the new procedures, no evidence was obtained for the presence of the unidentified polar metabolites that were previously observed in shoot tissues.  相似文献   

10.
When Achillea millefolium L. (yarrow) seedlings were grown in the field in association with a pea (Pisum sativum L.) crop vegetative growth of yarrow was significantly reduced by 6 weeks after emergence. Flowering was totally suppressed while the pure stand of yarrow developed flower clusters at 13 weeks after seedling emergence. Rhizome development occurred at 8 weeks after seedling emergence in the pure stand, but not until 15 weeks when grown with pea. The early suppression of seedling yarrow in a glasshouse experiment was associated with root interference, although by 5 weeks shoot interference by pea plants was important in reducing yarrow growth. The greatest suppression of yarrow occurred when both roots and shoots of the two species were allowed to interfere. Yarrow had low aggressivity against pea when grown in various combinations in a replacement series experiment in the glasshouse.  相似文献   

11.
A. WALKER 《Weed Research》1973,13(4):407-415
Summary. Turnip, lettuce and ryegrass seedlings showed toxicity symptoms following shoot exposure to atrazine, linuron and aziprotryne at soil concentrations less than would be obtained from normal field applications. Responses following shoot exposure to simazine and lenacil were much less. Root exposure to all five herbicides caused seedling death at concentrations lower than those required for 'shoot-zone' toxicity. Pronamide and chlorpropham were tested against ryegrass only and at the concentrations examined were toxic only when localized in the shoot zone. Root exposure suppressed root growth, but the shoots were able to grow normally if the soil was kept sufficiently moist. Shoots contained more 14C-atrazine at emergence after shoot exposure compared with root exposure, but there was little subsequent uptake from the shoot zone. There was extensive uptake from the root zone after emergence. In the shoot-zone treatments, concentrations in the plant were high at emergence but were rapidly diluted by plant growth, whereas with root exposure, they increased throughout the experiments. The possible significance of these results to herbicide bebaviour under field conditions is discussed.
La distribution verticale des herbicides dans le sol et leur disponibilité pour les plantes: absorption comparée par la partie aèrienne et par les radnes  相似文献   

12.
The effect of localized placement of trifluralin on uptake patterns of soil-applied 45Ca in vetch (Vicia sativa L.), pea (Pisum sativum L.) and soybean (Glycine max) and 32P in vetch and pea was investigated in two soil zones in the roots and in the shoot zone before and after plant emergence. When trifluralin was in the upper root zone severe inhibition of lateral roots occurred as well as a marked decrease in uptake of 45Ca and 32P from this zone. Root growth in the lower zone was unaffected, but uptake of 45Ca and 32P was slightly reduced. Compensatory adventitious root growth as well as a marked increase in uptake of 45Ca and 32P occurred in the shoot zone. Neither root growth nor uptake of 45Ca or 32P in the upper root zone were affected by the presence of trifluralin in the lower root region. When trifluralin was placed in the shoot zone after plant emergence, adven-titious roots on the shoots were inhibited and uptake of 45Ca and 32P was reduced.  相似文献   

13.
以郑单958和鲁单981为研究对象,进行水培分根试验,在正常供水和水分胁迫条件下,分别以均匀低浓度硝酸盐处理主根和种子根(LPR-LSR)、局部高浓度硝酸盐处理主根（HPR-LSR）和局部高浓度硝酸盐处理种子根（LPR-HSR）,测定分析根系形态、生物量以及氮含量。结果表明：与氮低效鲁单981相比,氮高效郑单958具有较高的主根根长、根表面积、根系生物量、地上部生物量和氮累积量。水分胁迫条件下,郑单958和鲁单981的主根的根长、根表面积、根体积、地上部生物量和氮累积量总体上均低于正常水分条件。玉米主根和种子根对局部高浓度硝酸盐的反应存在差异。与均匀低浓度硝酸盐处理相比,局部高浓度硝酸盐处理促进正常水分条件下主根和种子根根系的生长,尤其是根长和根系表面积;在正常水分条件下,主根根长和根系表面积增加幅度范围为6.8%~27.3%和1.9%~21.9%,除HPR-LSR处理条件下的郑单958外,种子根根长和根系表面积增加幅度范围为30.4%~92.7%和10.5%~135.1%;在水分胁迫条件下,主根根长和表面积增加幅度范围为24.6%~152.9%和62.1%~229.9%,然而种子根根长降低了10.0%~29.9%,表明水分胁迫会影响种子根对高浓度硝酸盐的响应。除水分胁迫条件下LPR-HSR处理外,局部高浓度处理可同时增加两侧根系的生物量和氮累积量。无论是正常供水还是水分胁迫,与LPR-LSR处理相比,局部高浓度硝酸盐供应均能够增加地上部生物量以及氮累积量,在LPR-HSR处理条件下,增加幅度范围分别在35.0% ~107.9%和162.9%~291.1%,在HPR-LSR处理条件下分别为56.7%~109.4%和204.1%~377.0%,HPR-LSR处理条件下增加幅度较大,表明在氮素非均匀分布环境中,当主根处于高浓度硝酸盐区域时将会更显著促进生物量的增加和氮累积。  相似文献   

14.
Imazapyr absorption, translocation, root release and metabolism were examined in leafy spurge (Euphorbia esula L.). Leafy spurge plants were propagated from root cuttings and [14C]imazapyr was applied to growth-chambergrown plants in a water + 28% urea ammonium nitrate + nonionic surfactant solution (98.75 + 1 + 0.25 by volume). Plants were harvested two and eight days after herbicide treatment (DAT) and divided into: treated leaf, stem and leaves above treated leaf, stem and leaves below the treated leaf, crown, root, dormant and elongated adventitious shoot buds. Imazapyr absorption increased from 62.5% 2 DAT to 80.0% 8 DAT. Herbicide translocation out of the treated leaf and accumulation in roots and adventitious shoot buds was apparent 2 DAT. By the end of the eight-day translocation period only 14% of applied 14C remained in the treated leaf, while 17% had translocated into the root system. Elongated and dormant adventitious shoot buds accumulated 3.2- and 1.8-fold more 14C, respectively, 8 DAT than did root tissue based on Bq g?1 dry weight. Root release of 14C was evident 2 DAT, and by 8 DAT 19.4% of the 14C reaching the root system was released into the rooting medium. There was no metabolism of imazapyr in crown, root or adventitious shoot buds 2 DAT; however, imazapyr metabolism was evident in the treated leaf 2 and 8 DAT. Imazapyr phytotoxicity to leafy spurge appears to result from high imazapyr absorption, translocation to underground meristematic areas (roots and adventitious shoot buds), and a slow rate of metabolism.  相似文献   

15.
Summary. We conducted studies to determine the effects on corn (Zea mays L, var. Indiana 654) and pea (Pisum sativum L. var. Alaska) of localizing various herbicides in the soil, using a double plastic pot technique which ensured separate exposure of the root and shoot zones of the plants to treated soil. Effects on corn and pea were similar in relation to site of uptake. 2,4-D-amine, naptalam, simazine, diuron and dalapon-sodium entered primarily through the roots. Some shoot entry and also severe inhibition of roots occurred in soil treated with 2,4-D and naptalam; these were noticed only to a slight extent with the other three herbicides. EPTC, chlorpropham and trifluraiin were most effective when applied to the shoot zone. Little effect on foliage growth was evident when the root zone alone was treated. However, roots in treated soil were severely inhibited by these three herbicides. Dinoseb displayed a contact type of action, injuring both shoots and roots. Treatment of both zones had an additive effect. Entry of chlorthal-methyl which was tested on a susceptible species, sorghum (Sorghum vulgare Pers.) was mainly through the shoot, with only a slight effect on top growth when roots alone were treated. Roots in treated soil were slightly inhibited. Localisation de l'absorption des herbicides appliqués sur le sol  相似文献   

16.
Gibson  Foin  & Hill 《Weed Research》1999,39(3):181-190
The relationship between root and shoot growth were determined for water-seeded rice and Echinochloa phyllopogon in greenhouse experiments. When grown in monoculture at four nitrogen rates (0, 60, 120, 180 kg N ha−1), root dry weight was highly correlated with canopy structure for both species. Echinochloa phyllopogon showed a significantly stronger response to the nitrogen rate than rice. When rice and E. phyllopogon were grown in competition, with roots either separated or allowed to mingle, root competition contributed more than shoot competition to reductions in the growth of the target species. The results suggest that root competition may be the primary mechanism determining competitive outcomes between water-seeded rice and E. phyllopogon . The importance of root competition and the relationship between root and shoot growth demonstrated in this study suggest that researchers should not rely solely on correlations between shoot traits and competitive ability as evidence that competition is primarily for light. Our results also suggest the importance of considering the whole plant when assessing rice cultivars for competitive ability.  相似文献   

17.
The effect of injury on disease incidence, incubation period and lesion development rate on caraway roots by Mycocentrospora acerina was studied in three laboratory experiments. After inoculation with M. acerina, disease incidence of injured roots was significantly (P< 0.001) higher than of non-injured roots. The incubation period of M. acerina was significantly (P < 0.001) shorter on injured roots than on non-injured roots. The incubation period shortened with increasing root injury level. Younger injured roots tended to be more resistant to M. acerina infection than older injured roots, expressed by longer incubation periods. The lesion development rate was, on average, higher on heavily injured roots than on non- or slightly injured roots. The lesion development rate remained fairly constant after the first emergence of the symptoms on the caraway root, until the whole root was colonized. Caraway roots carefully dug up in autumn frequently showed injuries enabling M. acerina to penetrate the roots. However, the correlation between root injury and root rot after cold storage was weak. Injury of roots had a stimulating effect on infection and development of M. acerina, but roots without wounds could be infected too. Some relevant field observations are discussed.  相似文献   

18.
根系分区灌水对苹果水分状况及生长的影响   总被引：5，自引：0，他引：5  
以2年生分根盆栽皇家嘎拉(RoyalGala)苹果为试材,通过全部根系、3/4、2/4、1/4根系体积灌水、全部根系不灌水5种处理研究了根系分区灌水对苹果叶水势、气孔阻力以及枝叶生长变化的影响。结果表明,3/4、2/4、1/4根系体积灌水在植株叶水势变化不明显时气孔阻力增大,新梢和叶片生长同时受到抑制,并且根系干旱的体积愈大,抑制作用愈强。  相似文献   

19.
A series of pot experiments were undertaken to assess the selectivity of the pre-emergence herbicide 4-(2, 6-dichlorobenzyloxymethyl)-4-ethyl-2, 2, -dimethyl-1, 3-dioxolan (WL 29,226) against a number of annual weeds in wheat. When applied at dose rates of 0.5–2 kg/ha it gave good control of a number of annual monocotyledonous weeds, including Alopecurus myosuroides (blackgrass), without any adverse effects on the crop. WL 29,226 is relatively immobile in soil, remaining at the soil surface and thus favouring uptake via the emerging shoot. Since WL 29,226 is transported predominantly via the xylem, to reach its site of action in the regions of cell division, and hence to be effective, the compound has to penetrate the shoot either at or below the stem apex. The roots are inhibited only when these come into direct contact with the compound. Selectivity of the herbicide is dependent upon the relative anatomical positions of the stem apices of the weeds and the crop with respect to the soil surface. Mesocotyl elongation in many of the weed species was such that the meristematic tissue was raised to the soil surface and into contact with the compound during the emergence of the shoot. In contrast, the stem apex of wheat remained some distance below the soil surface until considerably later, by which time the leaf sheaths offered protection to the meristematic tissue from direct contact with the herbicide. Selectivity is further enhanced in the field as a result of both the depth of planting for wheat and the tendency of many annual weed species to germinate more readily when near the soil surface. Tolerance of the wheat is lost where it germinates in direct contact with the herbicide, due to the lack of any biochemical selectivity. Under field conditions WL 29,226 gives good control of many dicotyledonous species. In pot experiments, however, these exhibit some tolerance to the compound. Radio-tracer studies indicate that the tolerance shown by the shoots of these plants is due to limited transport of the herbicide from the shoot to its site of action at the apex. This suggests that control of broad-leaved weeds occurs predominantly through an inhibition of root growth. However, in species such as sugar-beet, soyabean and cotton a rapid rate of root elongation confers increased tolerance to the compound. Availability of WL 29,226 for uptake by young seedlings is favoured by soil moisture. Low temperatures further improve performance by reducing the rate of shoot emergence and hence prolonging contact with the compound at the most sensitive stage of growth. After emergence uptake of the compound via the shoot becomes a less efficient mode of entry.  相似文献   

20.
The undisturbed growth and regenerative capacity of the root system of Cirsium arvense (L.) Scop, were studied in one glasshouse and one field experiment. In the glasshouse experiment, two lengths of root fragment from the same clone, previously grown at two nitrogen levels, were planted in boxes. Plants that developed from these fragments were inspected on eight occasions to assess their undisturbed development and growth, above and below ground, and their regenerative capacity after disturbance by burial at different points of development. The initial nitrogen content of the roots had no effect on growth measurements, but longer root fragments produced greater masses of primary shoots, new roots and shoots from the new roots than did shorter ones. After disturbance at early stages (4-7 leaves with a minimum length of 5 cm), plants originating from shorter root fragments did not regrow at all. Plants originating from longer root fragments exhibited a minimum regenerative capacity when disturbed at the eight-leaf stage. In the field experiment, root fragments of length 12 cm. from the same clone, were planted in October 1991 at 5 cm or 20 cm depth. Plants that developed from these fragments were studied on 12 occasions, from April to July 1992. Plants emerging from a depth of 20 cm reached a point of positive net assimilation 28 days (380 day degrees) later than those developing from a depth of 5 em. The plants exhibited a minimum regenerative capacity when their primary shoots had. on average. 10 (plants from 5-cm root fragments) or seven (plants from 20-cm root fragments) expanded leaves.  相似文献   

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