The Reciprocal Transfer of Radiocarbon between a Developing Tiller and its Parent Shoot in Vegetative Plants of Lolium multiflorum Lam.

The transfer of ¹⁴C-labelled assimilates between a tiller andits parent shoot was examined in young plants of Lolium multiflorumLam. Radiocarbon was exported freely from an expanded laminato sinks within the shoot axis from which it originated andto the root system. Lesser amounts of radiocarbon were exportedto the other shoot. It is suggested that the reciprocal exchangeof radiocarbon between tiller and main shoot occurred principallyvia a direct pathway through stem tissues rather than via apathway involving the roots.     

The Interdependence of Tillers in Lolium multiflorum Lam.--a Quantitative Assessment

Experiments were made to determine the extent of reciprocaltransfer of products (derived from the assimilation of ¹⁴CO₂)between various parts of the young vegetative grass plant (Loliummultiflorum Lam.). When individual laminae on different tillerswere supplied with ¹⁴CO₂, 47–64 per cent of the fixedcarbon was exported after 24 h. The principal sinks were theroot system and the shoot or tiller to which the fed leaf wasattached. Other tillers also received significant quantitiesof radiocarbon. When whole tillers were supplied with ¹⁴CO₂the percentage of fixed radiocarbon exported within 24 h rangedfrom 14–31 per cent. Of this, 50–74 per cent wasrecovered from the root system (except in the case of exportfrom the youngest tiller) but exchange of material between tillersalso occurred.A reciprocity diagram is presented and it is concludedthat despite the magnitude of the exchange no tiller showedan over-all net gain or loss. The main shoot and the tillersdiffered in the extent of their carbon exchange and in theirdegree of independence. The oldest daughter tiller of the mainshoot was the most independent and the main shoot most interdependent.     

Distribution of current photosynthate in two Guinea grass (Panicum maximum Jacq.) cultivars

In a glasshouse experiment, different tiller categories (main, young primary, and old primary) of two Guinea grass cultivars, Momba?a and Tanzania, were (14)C-labelled to investigate C translocation between tillers. In both cultivars, young primary tillers retained less radiocarbon (79%) than main (86%) and old primary (87%) labelled tillers, suggesting that the photosynthetic capacity of the young tillers exceeds their capacity either to store or use that photosynthate for growth and maintenance. In cv. Tanzania the old primary tillers translocated more photoassimilate to their daughter tillers and to the rest of the plant than cv. Momba?a, suggesting either higher vascular connectivity between tillers or stronger diurnal fluctuations in sink-source balance in Tanzania than Momba?a. For unlabelled tillers, specific activities were almost always higher in roots than in shoots, although total radiocarbon uptake by roots was reduced in younger tillers with low root mass. Where young primary tillers were labelled, the largest single repository of exported photoassimilate was the main tiller roots, indicating that daughter tillers may make an important contribution to the maintenance of older roots on mature tillers.     

An appraisal of ear, leaf and stem 14CO2 assimilation, 14C-assimilate distribution and growth in a reproductive seed crop of amenity Lolium perenne

In seed crops of Lolium perenne, yield may be reduced by competition for a limited assimilate supply from sinks other than the ear. This study was undertaken to evaluate the priorities for allocation of assimilate within the crop from all photosynthetic sites on the main reproductive tiller after anthesis. Ear, stem and leaves were fed with ¹⁴CO₂ on two occasions; the assimilatory efficiency of these sources and the magnitude and pattern of ¹⁴C-assimilate export from each was determined. The growth of each part of the main tiller and subtending tillers was also measured. Stem elongation apparently dominated the current assimilate resource and the ear did not become a net importer of assimilate until this process had ceased. Assimilate allocation to the tillers was high throughout. The nature of any competition between these sinks is discussed. When crop growth was contrasted with that in a previous year, environmental factors were implicated as determinants of priority for assimilate allocation to each sink. Sources of carbon for seed filling are also discussed as is the relevance of these findings to seed crop management.     

Frost damage and winter nitrogen uptake by the grass Poa pratensis L.: consequences for vegetative versus reproductive growth

Frost damage can decrease nitrogen uptake by grasses over winter, and it can also decrease biomass production over the following growing season. However, it is not clear to what extent reduced nitrogen uptake over winter decreases grass production, or whether is it merely a symptom of root damage. We examined the growth response of the grass Poa pratensis L. (Kentucky bluegrass) to variation in the timing of freezing and nitrogen availability over winter in London, Ontario, Canada. All tillers were transplanted into untreated soil in early spring, and at peak seed maturation, root, shoot, and reproductive biomass were measured. There was an interaction between freezing and increased winter nitrogen availability, whereby nitrogen addition increased tiller biomass under ambient temperatures, but decreased tiller biomass in combination with a late winter freeze. The nitrogen response of ambient temperature tillers occurred primarily via increased seed production, whereas for frozen tillers seed production was generally absent. Our results support the hypothesis that nitrogen uptake over winter can increase growing season productivity in P. pratensis, but also demonstrate that increased nitrogen availability increases tiller vulnerability to frost. These results have important implications for grass responses to the alteration of soil freezing dynamics with climate change.     

Effects of Ear Removal on Photosynthesis, Carbohydrate Accumulation and on the Distribution of Assimilated 14C in Wheat

Removal of an ear from a tiller of a wheat plant growing inthe field did not result in any marked change in the net photosyntheticrate of the subtending flag leaf, even during the period whenthe ear would normally have received large amounts of assimilatefrom the flag leaf. Following ear removal, there was an increasein the amount of ethanol-soluble and ethanol-insoluble carbohydratesin the remaining organs of the tiller. ¹⁴C labelling studiesshowed that a new pattern of translocation was established within2–3 days of ear removal, and the tiller exported assimilateto other tillers on the plant, and possibly to the roots.     

松嫩平原两个趋异类型羊草无性系种群特征的比较研究

松嫩平原上羊草(Leymus chinensis(Tzvel.)Tzvel.)有两个趋异类型:灰绿型和黄绿型。两个类型羊草的分蘖节一般均存活2～4年,最多可存活5年;根茎一般存活2～3年,最多可存活4年。两个类型无性系种群的分蘖株均为增长型的年龄结构类型。种群根茎的累积长度,灰绿型为18035cm/m~2,黄绿型为21218cm/m~2,其中,均以1、2龄占绝对比重。两个类型均以1龄分蘖株生产力最大,至3龄分蘖株明显减小;各龄根茎的生物量随着年龄的增加呈直线下降;1龄根茎的营养繁殖力甚强,至8月中旬所形成的芽数均已远远多于地上全部分蘖株数;2龄根茎尚存在较小的营养繁殖潜力,3、4龄根茎均已丧失了营养繁殖力。两个类型羊草无性系种群都是通过根茎芽补充更新。     

The patterns of growth, assimilation of 14CO2 and distribution of 14C-assimilate within vegetative plants of Loliumperenne at low and high density

The patterns of growth, assimilation of ¹⁴CO₂ and distribution of ¹⁴C-labelled assimilate were followed for 12 wk from sowing in individual plants of Lolium perenne grown in miniswards at either low (500 plants m^-2) or high (5000 plants m^-2) density. At the latter density, plants were characterised by a 50% reduction in RGR, by the production of fewer tillers, especially second- and third-order tillers, and by a reduction in mean tiller weight. All the green and senescing leaves of each tiller assimilated ¹⁴CO₂ and the overall assimilatory capacity of a tiller was directly related to its dry weight. At both densities the plant consisted of a main shoot and established tillers with comparable assimilatory activities and a range of developing tillers that assimilated relatively small amounts of ¹⁴CO₂. As each successive primary tiller developed it was supplied with assimilate from the main shoot and the degree of support was inversely proportional to the dry weight of the tiller. At both densities it was concluded that the first primary tiller could be regarded as an independent assimilatory unit when it reached a dry weight of about 25 mg even though some import of main shoot assimilate continued until the tiller was double this weight. The supply of assimilate to the root system was greatly reduced at both densities compared with previous observations on plants grown singly.     

Tiller demography in seashore populations of Agrostis stolonifera,Festuca rubra and Poa irrigata

Abstract. The dynamics of tillers in natural populations of three cohabiting perennial grass species, Agrostis stolonifera, Festuca rubra and Poa irrigata (= Poa pratensis ssp. irrigata) were studied for five years in a Baltic seashore meadow. The process of tiller population maintenance was very dynamic. Both birth and death rates of tillers were high, particularly in A stolonifera, and the turnover rate of the populations was high. Recruitment was mainly by vegetative tillers, produced continuously throughout the growing season. The proportion of flowering tillers was low, but varied between years. Considerable year-to-year variation was also found in birth and death rates. Despite this between-year variation and the differences found between species in flowering frequency, pattern of survivorship and tiller longevity, population sizes of the species remained relatively constant.     

GROWTH AND NUTRITION OF TIMOTHY (PHLEUM PRATENSE)

Individual tillers of timothy ( Phleum pratense ) growing from seed in pots were labelled and their life history studied over a period of two years.
The leaf axil position of the first-produced tiller depended on its time of origin. A minimum of five leaves on the parent axis was necessary before its appearance, and no tiller emerged from the axil of any of the three terminal leaves of a shoot.
Ear-bearing capacity was high in early-formed tillers, but decreased progressively with later dates of origin despite favourable day length; all tillers arising after the end of July failed to produce inflorescences. A greater proportion of tillers on the main stem formed ears than secondary tillers of the same age. Time of ear emergence varied only within a few days for all tillers arising before the end of April. The number of leaves formed up to ear emergence varied linearly with date of origin and tiller position, the lowest recorded number being six.
Dry weight and length of inflorescence as well as seed yield per tiller varied linearly with the date of origin of tillers. Primary tillers generally had longer and heavier inflorescences and produced more seed per stem than secondary tillers of the same age.
Tillers arising at all times were found to have a limited span of life, not normally exceeding just over a year. The mean age of ear-bearing tillers varied linearly with their date of origin. Death-rates of all tillers generally increased with their age. Relative death-rates of fertile and vegetative tillers rose rapidly in the autumn but decreased during winter and early spring. Vegetative tillers which elongated in the year of formation survived for a shorter time than equivalent tillers in which stem elongation was delayed until the following year.
The perennial habit of grasses is discussed in relation to tiller survival. Successive new formation and death of tillers keep the plant in a condition of continuous dynamic change.     

Tolerance and compensatory response of rice to sugarcane borer (Lepidoptera: Crambidae) injury

A 3-yr field experiment was conducted to evaluate the tolerance and compensatory response of rice (Oryza sativa L.) to injury caused by sugarcane borer, Diatraea saccharalis (F.), as affected by cultivar (Cocodrie, Francis, and Jefferson), stage of crop growth during which the injury occurred (third tiller stage, panicle differentiation stage, and heading stage), and sugarcane borer density. The proportion of rice tillers with sugarcane borer injury (leaf and leaf sheath injury and/or stem injury) was lower when injury occurred at the third tiller stage (0.05) than at panicle differentiation (0.19) and heading (0.18). When injury occurred at the two latter stages, both the proportion of tillers with injury and the proportion of tillers with stem injury were negatively correlated with rainfall. Rainfall resulted in dislodgement and mortality of sugarcane borer eggs and larvae before the larvae entered the stems. Rice plant density in this study (111.1 plants/m2) was higher than recorded for previous research on rice compensation using potted rice or conducted in low-density hill production systems (26.7-51.3 plants/m2). Two mechanisms of within-plant tolerance/compensation were observed. Stem injured plants produced approximately 0.69 more tillers than uninjured plants, whereas tillers with leaf and leaf sheath injury produced larger panicles, up to 39.5 and 21.0% heavier than uninjured tillers, when injury occurred at third tiller stage and at panicle differentiation, respectively. Rice yield was not reduced with up to 23% injured tiller and up to 10% injured stems at the third tiller stage, 42% injured tillers and 17% injured stems at panicle differentiation, and 28% injured tillers and 14% injured stems at heading. Significant between-plant compensation was not detected, suggesting competition between adjacent plants is not significantly reduced by injury. Our results suggest that rice can tolerate and/or compensate for a level of stem borer injury previously considered to be economically damaging.     

Cocksfoot (Dactylis glomerata) Grown for Production of Seed

In grasses grown for production of seed under field conditions,it has been found that only a small proportion of tillers produceinflorescences. For a period of 23 weeks from 4 February 1963a study was made of cocksfoot grown for production of seed inan attempt to discern whether the ability of tillers to becomereproductive was related to specific morphological features.Most tillers which initiated spikelets were rooted, and rootsquickly developed on unrooted tillers which had initiated spikelets.It appeared that larger tillers, judged on the basis of dry-weight,were more likely to become fertile than smaller tillers; importantfeatures of tiller size were the length of the stem and theweight of green leaf (lamina) borne by the tiller. The potentialnumber of inflorescences was reduced considerably by the death,in June, of tillers with completely differentiated apices.     

冬小麦拔节期不同茎蘖对低温胁迫的反应及抗冻性评价

以小麦济南17和山农8355为材料,在低温胁迫条件下,测定了不同茎蘖功能叶和叶鞘超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性及丙二醛(MDA)和可溶性蛋白含量,并利用主成分分析、聚类分析对其抗冻性进行综合评价.结果表明： 低温胁迫条件下,小麦拔节期不同茎蘖功能叶和叶鞘中SOD、POD和CAT活性均不同程度地上升,MDA和可溶性蛋白含量则不同程度地上升或下降.利用主成分分析和聚类分析,将济南17不同茎蘖分为3类：主茎和一级分蘖Ⅰ、Ⅱ属强抗冻蘖组,一级分蘖Ⅲ、Ⅳ和二级分蘖Ⅰp属中度抗冻蘖组,二级分蘖Ⅱp属弱抗冻蘖组;将山农8355不同茎蘖分为3类：主茎和一级分蘖Ⅰ、Ⅱ、Ⅲ属强抗冻蘖组,一级分蘖Ⅳ和二级分蘖Ⅰp属中度抗冻蘖组,二级分蘖Ⅱp属弱抗冻蘖组.表明冬小麦拔节期不同茎蘖存在抗冻性差异,且低位蘖较高位蘖抗冻.
     

Growth and carbon allocation of Agropyron desertorum following autumn defoliation

Summary Growth and carbon allocation of a cool season tussock grass, Agropyron desertorum, following defoliation of newly initiated tillers in the autumn of 1988 and 1989 were investigated. Tiller density and mortality, reproductive shoot density, root density, biomass, individual tiller weight, carbon allocation, and soil water depletion were used to evaluate the response of A. desertorum to autumn grazing. Tiller recruitment was lower in the autumn-defoliated treatment in both years compared with the control because of the cessation of tiller development following autumn defoliation. Autumn defoliation also significantly reduced the movement of ¹³C to the roots in 1988 but not in 1989. Soils were cooler and drier in 1989. Other plant growth measurements and soil water depletion rates were not different between treatments. Autumn defoliation in 1988 did not influence tiller recruitment in the following autumn. Two consecutive years of autumn defoliation did not affect tiller overwinter mortality or peak standing crop in 1990.     

Effects of resource availability on integration and clonal growth inMaianthemum bifolium

The aim of this study was to investigate whether resource availability affects the degree of physiological integration and the growth pattern of interconnected ramets in the clonal plantMaianthemum bifolium (L.)F.W. Schmidt (Liliaceae), a rhizomatous herb of European forests, by studying it at two contrasting South Swedish beech forest sites termed “poor” and “rich”. The degree of physiological integration was studied by tracing the pattern of¹⁴C translocation and in a cutting experiment involving rhizome severing and defoliation treatments. The size of the plants, growth of new rhizomes, branching frequency, distance between shoots and the internode length were compared. The plants were larger, rhizomes had greater specific mass (mg mm^?1), internodes were shorter and branching frequency higher at the rich site. The cutting treatments reduced the growth of new rhizomes at both sites, and new rhizome segments had lower specific mass in treated plants than in controls, showing the importance of physiological integration for new growth. Translocation of¹⁴C in May showed that the young rhizome tip was a strong sink for carbon. Basipetal translocation to older portions of the rhizome system was greater at the rich site than at the poor site. In September, four months after labelling, the rhizome tips were still strongly labelled with¹⁴C and basipetal translocation had increased at both sites. Plants at the rich site appeared to translocate larger amounts of¹⁴C basipetally than plants at the poor site. It is concluded thatM. bifolium shows a plastic response to resource availability by varying rhizome growth and branching frequency, but the degree of physiological integration is probably only indirectly affected through an increased number of sinks (new rhizome branches) along the ramet system at the rich site.     

Unique responses of respiration,growth, and non-structural carbohydrate storage in sink tissue of conifer seedlings to an elevation gradient at timberline

The role of carbon balance, and particularly carbon sinks, to forest boundaries and climate responses is a major question in forest ecophysiology. At timberline, low-temperature limitations on carbon-sink processes of stem and especially root tissue have been implicated in hypotheses of the upper range limits to tree distributions. Studies on carbon sinks in root and stem tissue of trees at timberline typically report variation in only one carbon sink, such as either growth, respiration, or non-structural carbohydrates (NSCs). However, these carbon sinks may differ in their response to elevation. We asked how three carbon-sink processes in root and stem tissue (i.e. all tissue below the crown of needles) change in conifer seedlings growing from the lower (2450 m) to the upper (3000 m) edges of the timberline ecotone throughout their first growth season. We repeatedly measured respiration (mg⁻¹ and individual⁻¹), growth (relative growth rates [RGR] and biomass), and NSCs in root and stem tissue of Abies lasiocarpa and Pseudotsuga menziesii.RGR of root and stem tissue were less at the upper compared to lower elevation, but only for the first few weeks of the growing season. Total biomass of root and stem tissue was generally less at the upper site, apparently due to low early season RGR, but ultimately did not significantly differ between sites by the end of the growing season. Unlike growth, respiration rates (mg⁻¹) did not differ between elevations during any period of the growing season. Nevertheless, total respiration of CO₂ from root and stem tissue (individual⁻¹) was 22% less at the upper site, which was attributable to less biomass. NSCs of root and stem tissue, specifically starch, were overall greater at the upper site, particularly for A. lasiocarpa at the end of the season, which did not parallel spatiotemporal trends in growth or respiration. The differences in seasonal trends and the effects of elevation on carbon sinks indicate a degree of independence or uncoupling of growth, respiration, and NSCs of root and stem tissue, which is not commonly appreciated in hypotheses about physiological limitations for trees at timberline.     

Rates of Leaf and Tiller Production in Young Spaced Perennial Ryegrass Plants in Relation to Soil Temperature and Solar Radiation

In an experiment designed to investigate the rate of leaf appearanceand tiller production in young spaced plants of three clonesof perennial ryegrass grown in the field, it was found thatthe rate of leaf appearance per tiller increased linearly withmean soil temperature up to approx. 14 °C. The rate of productionof tillers in relation to the rate of leaf appearance (sitefilling) appeared to be virtually independent of weather conditions.In plants which were adequately established, but still relativelysmall, site filling was equal to or exceeded the theoreticalsteady state; all the tiller buds which were being formed weredeveloping into visible tillers. Thus the relative rate of tillerproduction was controlled by the rate of leaf appearance. Inlarger plants site filling was less complete, and site redundancieswere probably caused by within-plant competition for light atthe tiller bases. Lolium perenne L., perennial ryegrass, tillering, leaf production, solar radiation, soil temperature     

Effect of decapitation on absorption,translocation, and phytotoxicity of imazamethabenz in wild oat (Avena fatua L.)

The release of apical dominance by the physical destruction in situ of the apical meristem and associated leaf primordia (decapitation) promoted the growth of tillers in non-herbicide-treated wild oat plants, as indicated by increased tiller lengths and fresh weights. At 96 h after [¹⁴C] herbicide treatment following decapitation, the absorption of [¹⁴C]imazamethabenz and total translocation of radioactivity were respectively increased by 28% and 49%. By 96 h after [¹⁴C]imazamethabenz application, the radioactivity detected in the roots of decapitated plants was 45% higher than that in the roots of nondecapitated plants while the radioactivity in tillers of decapitated plants was 2.6-fold that in tillers of intact plants. Decapitation together with foliar spraying of imazamethabenz at 200 g ha^–1 further reduced tiller fresh weight, greatly decreased the total tiller number, and thereafter significantly increased overall phytotoxicity by 32% as measured by total shoot fresh weight. The results of this study support the hypothesis that main shoot apical dominance limits translocation of applied imazamethabenz to lateral shoots, rendering tillers less susceptible to growth inhibition by the herbicide.     

毛苔草地下构件对不同水文情势和水文经历的生长响应

通过幼苗移植水位控制试验,研究了三江平原毛苔草地下构件生长对不同水文情势及水文经历的响应.结果表明：毛苔草地下构件生长对不同水文情势的响应具有显著差异;在毛苔草生长旺盛期,其根茎及不定根长度随淹水程度的增加而缩短,到生长末期,干旱处理下毛苔草根茎及不定根长度仍然最大,但在持续淹水处理下,毛苔草根茎及不定根长度由旺盛期到末期的增幅最大,说明生长季内稳定的低水分条件对毛苔草根茎及不定根的生长较为有利;在生长旺盛期和末期,干湿交替处理下毛苔草根茎、不定根及地下总生物量均最高;不同水文经历下,以前期干湿交替、后期干旱处理下毛苔草根茎的鲜、干质量最大,而生长季内始终经历干湿交替处理下毛苔草的不定根及地下总生物量最大.比较地下构件在生物量积累中所占的比重发现,各水文情势下,生长季末期毛苔草总生物量明显向根茎转移;整个生长季内,干旱处理下毛苔草根茎生物量的比重明显高于其他处理.在淹没水文情势下,毛苔草地下构件生长缓慢,但淹没抑制消除后,其生长过程可通过根茎萌发得以延续.     

半湿润地区氮磷钾配施对强筋小麦功能叶光合速率的影响

选用优质强筋小麦品种陕253为材料,研究了不同氮磷钾肥水平及组合对小麦生育后期主茎、主茎分蘖Ⅰ和主茎分蘖Ⅱ功能叶净光合速率的影响,结果表明:在不同的NPK肥配比处理中,功能叶净光合速率在蘖位、叶位间差异均极其显著,不同生育期间存在明显差异,具体表现为:孕穗期高于灌浆期,主茎>主茎分蘖Ⅰ>主茎分蘖Ⅱ,旗叶高于倒二叶.孕穗期以N225P120K120处理对茎蘖功能叶光合速率影响最为明显,分别比CK1和CK2增加20.41%和25.76%;灌浆期以N135P225K120处理对茎蘖旗叶净光合速率作用显著,分别比CK1和CK2增加43.48%和10.83%.研究发现,在一定磷钾肥基础上通过调节氮肥可以调节孕穗期茎蘖功能叶净叶光合速率,提高钾肥用量有利于提高灌浆期各茎蘖功能叶的净光合速率.