Neighbour influence on the tiller demography of two perennial pampa grasses

Abstract. The aim of this study was to evaluate the possibility to use neighbour species composition to explain demographic variations in seasonal tillers in perennial grasses. Two warm-season species of the Argentina flooded pampa, Paspalum dilatatum and Sporobolus indicus, were used as models. Tiller structure and dynamics of target plants and the identity of their nearest neighbours were analyzed within a natural grassland community for an entire annual growth cycle. Canonical Correlation Analysis of tillering behaviour of target plants and neighbour species composition showed significant relationships for summer neighbourhood data. Community components affecting tiller demography were identified, and their spatial variation was described as different gradients of neighbourhood composition (NCG). NCG varied between target species, determining different spatial variation in neighbouring canopy dynamics and tiller dynamics. The tiller structure and dynamics of P. dilatatum plants were significantly correlated with the seasonal pattern of their neighbouring canopy density (NCD). Plants placed on the NCD-fluctuating extremes along NCG showed an unstable modular structure and short-lived tillers, as compared to those placed in the centre of the gradient. Relative density of the neighbouring canopy showed little variation along the NCG of S. indicus plants, which presented a tiller structure more stable and uniform than P. dilatatum plants did. Identification of NCG may be a promising approach to understanding changes in tiller dynamics of target species in relation to spatial and temporal changes in community structure.     

Facilitative effect of Lotustenuis on Paspalumdilatatum in a lowland grassland of Argentina

We studied the responses in growth and N content of the perennial grass Paspalum dilatatum to the substitution of Lotus tenuis for a whole group of species, the dicotyledons of a natural grassland community, in the Salado lowland Pampas of Argentina. Two kinds of manipulations were performed in the field: removal of alien dicots with herbicide application, and introduction of L. tenuis, resulting in a combination of four treatments, arranged in a 2 × 2 factorial randomized block design. Leaf area per tiller of P. dilatatum was higher when it was growing near L. tenuis; this increase was the result of a greater leaf elongation rate and slower leaf senescence. In the vicinity of L. tenuis, P. dilatatum exhibited an increase in tiller production and a decrease in tiller death. More tillers were functional at the end of the growing season and their aboveground biomass was 5␣times higher than for plants growing in plots where the community dicots were removed. This increment was accompanied by a higher N content. Growth enhancement of P. dilatatum plants when L. tenuis was the␣immediate neighbour is interpreted as the result of facilitation mediated by higher N availability, and not as a consequence of a release from competition exerted by the community dicots. Competition and facilitation did not interact to produce an increase in the vegetative output of Paspalum dilatatum plants growing under these field conditions. It is on these grounds that Lotus tenuis might be considered as a keystone species in the managed grassland. Received: 5 July 1997 / Accepted: 12 December 1997     

Morphological Constraints of Shoot Demography of a Clonal Plant: Extra- and Intravaginal Tillers of Festuca rubra

Abstract Festuca rubra forms tillers in two different ways: extravaginally and intravaginally. Demography of these two tiller types was observed in seventeen selected tussocks of Festuca rubra s.s. over four growing seasons. Extravaginal tillers were bigger at birth and on the average produced twice as many daughter tillers per tiller. In general, the natality and mortality of extravaginal tillers were less regular than that of intravaginal tillers. Overall tillering rate per tiller was correlated with the density of the surrounding vegetation; mortality, natality and tiller life span were not. High density of the surrounding vegetation did not result in increased formation of extravaginal tillers. The proportion of the extravaginal tillers was not correlated with the density of the F. rubra tussocks. There is no evidence for foraging by extravaginal tillers, but they do act as founders of small clusters of tillers.     

Spatial arrangement of tiller replacement in Agropyron desertorum following grazing

Summary The spatial arrangement of tiller replacement was assessed on grazed and ungrazed tussocks of Agropyron desertorum (Fisch. ex Link) Schult. for three annual cycles. Frequency distributions of the number of replacement tillers per single progenitor were also determined. Tiller replacement was usually greater on the perimeter of tussocks than within the core, with or without grazing. Replacement was inversely related to grazing intensity, both on the perimeter and within the core of tussocks. Heights of replacement tillers on the perimeter or within the core seldom differed. Furthermore, grazing seldom affected the number of replacement tillers per progenitor. Greater tillering on the perimeter than within the core indicates that the tussocks were expanding. Apparently, grazing neither enhances tussock expansion and subsequent disintegration, nor does it necessarily lead to patches of tillers (multiple tillering per progenitor) within tussocks of A. desertorum.     

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.     

The Effect of Light Quality on Shoot Extension Growth in Three Species of Grasses

The effect of light quality on the extension growth of vegetativeshoots and on the final size of their leaves was investigatedin plants of Lolium multiflorum, Sporobolus indicus and Paspalumdilatatum. Three experimental approaches were used, (a) redor far-red end-of-day irradiations of sunlight-grown plants,(b) different red/far-red ratios of white light in a growthroom and (c) sunlight enrichment with radiation of differentred/far-red ratios or with different amounts of far-red lightduring the photoperiod. Plants treated with end-of-day far-redor low red/far-red ratios throughout the photoperiod developedlonger leaves and, as a result, longer shoots. This effect wasmore marked in leaf sheaths than in blades. Tiller extensionand leaf sheath length increased with the amount of far-redadded to sunlight in a simple hyperbolic relationship. Theseresults show that vegetative grass shoots respond to light qualityin a way similar to internodes of dicotyledonous plants. Lolium multiflorum Lam., Sporobolus indicus (L.), Paspalum dilatatum (Poir.), leaf growth, tiller growth, photomorphogenesis     

Hormonal regulation of tiller dynamics in differentially-tillering rice cultivars

Tiller number can contribute significantly to yield potential of rice, but little knowledge is available on hormonal regulation of tillering and tiller dynamics. In the present study, Indole-3-acetic acid (IAA), kinetin (6-furfuryl amino purine) and Gibberellic acid (GA₃) treatments have been applied at the early tillering stage to two rice cultivars that contrast for tiller number. The responses of the hormones were studied on growth, development, grain yield, senescence patterns, assimilate concentration of the panicle and ethylene production in different classes of tillers. The leaf area, panicle grain number, fertility percentage and grain yield of tillers were higher in the low-tillering cultivar than that of high-tillering cultivar; the treatment of kinetin was more effective in the latter than in the former. High ethylene production was responsible for reduction of growth duration and grain yield of the tillers. Kinetin application reduced ethylene production of the late-tillers significantly for the benefit of grain yield.     

Population differentiation in the tiller architecture of Microstegium vimineum (Poaceae) in relation to habitat

Grass tillers grow by addition of modular units known as phytomers. Differences in phytomer organ size produce subindividual variation with potential adaptive value. Here, patterns in organ mass along tillers in the invasive annual Microstegium vimineum are related to habitat and tiller architecture. In an earlier study, seed families were collected from two populations: one from a sunny, woodland edge and the other from a shady understory in New Jersey, USA. Plants from these seeds were grown in a greenhouse. Phytomers along primary tillers were divided into culms, leaves, and cleistogamous or chasmogamous spikelets and seeds, dried and weighed. These data were used to examine the quantitative genetics of subindividual variation among families and populations, and the relationship of tiller fitness (based on total seed mass) to the mean or subindividual variance of phytomer traits. Phytomer position along a tiller was the major determinant of organ mass. Leaf mass increased from basal to upper nodes; cleistogamous reproductive mass decreased from upper to lower nodes. Phytomer organs were heaviest in the population from the sunny habitat. Family explained < 18% of variation in organ mass. Tiller fitness was positively correlated with mean culm, and leaf mass, but negatively correlated with coefficients of variation. Field‐collected tillers showed evidence of selection for increased leaf mass. Subindividual variation in M. vimineum is mostly due to phytomer position along a tiller and the prevailing light environment. Differentiation between sunny and shady populations suggests selection favors heavier phytomer leaves and culms, especially in the shady understory where this species is most invasive.     

Subtle topographical differences along a floodplain promote different plant strategies among Paspalum dilatatum subspecies and populations

It was hypothesised that subtle topographical differences might cause the existence of ecotypes along a floodplain. The apomict grass Paspalum dilatatum subspecies dilatatum inhabits flood‐prone lowlands as well as nearby uplands in the floodplains of Argentina, while the sexual P. dilatatum subspecies flavescens almost exclusively inhabits the uplands. The aim of the present study was to identify the different traits that allow these P. dilatatum populations to inhabit different habitats. Plants of P. dilatatum were reciprocally transplanted between uplands and lowlands. Morphophysiological traits related to flooding tolerance were measured during a flood. Subspecies dilatatum from the uplands and subspecies flavescens showed a high physiological performance in the uplands but a considerable decrease in stomatal conductance, net photosynthesis rates and tiller number in the flooded lowlands. In contrast, the subspecies dilatatum from the lowlands showed relatively lower and stable stomatal conductance, photosynthesis rates and leaf water potential at both sites. Subspecies dilatatum from the lowlands outperformed upland populations at the lowland site with respect to tillering. Leaves of subspecies dilatatum from the lowlands that had grown at the lowland habitat had a lower blade/sheath proportion than leaves of plants transplanted to the uplands. This behavior did not occur in both upland populations. Results suggest that dilatatum Lowland plants have the typical strategy of stress‐tolerant genotypes and that the upland populations are adapted to habitats where competitive species are selected. In conclusion, habitats with subtle differences in topographic level can favour both ecotypic differentiations within an apomict subspecies but also the maintenance of morphophysiological similitudes between coexisting upland populations belonging to different subspecies.     

Morphological Analysis of Tillering in Agropyron spicatum and Agropyron desertorum

The caespitose grasses Agropyron spicatum and Agropyron desertorumexhibit a striking difference in tillering response followingexperimental clipping treatment, with plants of A. desertorumproducing up to 18 times more tillers. The two species are similarin many aspects of their phenology and physiology. Previousexamination of current photosynthate production and levels ofstored carbohydrates indicate only slight differences betweenthe species. The possible role of three anatomical/morphologicalconstraints in controlling tillering was examined. No evidencefor such constraints was found. A basal cluster of buds is presenton the parent tillers. The mean bud number per tiller was similarfor both species and the range (3–9) was identical. Nearlyall of the bud apical meristems appeared anatomically viablethroughout the growing season and vascular development occurredto within 250 to 490 µm of the various bud apices of bothspecies. Both normal fall tillers and summer tillers producedunder clipping treatment originated from the largest, most distalbuds of the basal cluster of buds. However, precocious, morphologicallydistinctive, second-order tillers occasionally grew out fromthe smaller, most basal buds of some elongating fall tillers. Agropyron spicatum, Agropyron desertorum, bluebunch wheatgrass, crested wheatgrass, bud, tiller, tillering ability, meristematic potential, vascular development, regrowth     

Tillering in grain sorghum over a wide range of population densities: identification of a common hierarchy for tiller emergence,leaf area development and fertility

Most studies of tiller development have not related the physiological and morphological features of each culm to its subsequent fertility. This introduces problems when trying to account for the effects of tillering on yield in crop models. The objective of this study was to detect the most likely early determinants of tiller fertility in sorghum by identifying hierarchies for emergence, fertility and grain number of tillers over a wide range of assimilate availabilities. Emergence, phenology, leaf area development and dry weight partitioning were quantified weekly for individual tillers and main culms of tillering and uniculm plants grown at one of four densities, from two to 16 plants m(-2). For a given plant in any given density, the same tiller hierarchy applied for emergence of tillers, fertility of the emerged tillers and their subsequent grain number. These results were observed over a range of tiller fertility rates (from 7 to 91%), fertile tiller number per plant at maturity (from 0.2 to 4.7), and tiller contribution to grain yield (from 5 to 78 %). Tiller emergence was most probably related to assimilate supply and light quality. Development, fertility and contribution to yield of a specific tiller were highly dependent on growing conditions at the time of tiller emergence, particularly via early leaf area development of the tiller, which affected its subsequent leaf area accumulation. Assimilate availability in the main culm at the time of tiller emergence was the most likely early determinant of subsequent tiller fertility in this study.     

Estimation of Potential Tiller Production and Site Usage During Tall Fescue Canopy Development

Tiller appearance in tall fescue (Festuca arundinacea Schreb.)occurs in an orderly, predictable manner with the potentialfor a high degree of synchronization among tillers on a givenplant. Estimates of potential cumulative tiller production (Tmax)are made for synchronous (Tmax_lx = 2^Lx+1 – 1, where Lxis the axil number of the youngest leaf on the main stem whichbears an emerged tiller) and non-synchronous (Tmax₁ = 2^L–NLAT–1,where L is the number of leaves on the main stem and NLAT thenumber of leaves above the youngest primary tiller at its appearance)conditions. A method for determining the degree of synchronizationand an equation for estimating site usage are also presented.Early in seedling development, site usage of a tall fescue populationwith high tillering capacity was near 90%, and tillering wasregulated largely by rate of tiller site formation. As the canopydeveloped the phyllochron (time between successive leaf appearances)and NLAT increased, slowing the rate of tiller production intemporal terms and in relation to leaf appearance, respectively.Beyond 45 d after planting, site usage decreased rapidly, furtherreducing tiller production. High tiller production appearedto be associated with synchronized tiller appearance, with alack of synchrony being associated with decreased site usage.Tillers formed in prophyll axils were less likely to be in synchronywith other tillers and frequently failed to appear. In contrastwith branching in dicotyledons, apical dominance appears toplay a minor role in regulating tillering in tall fescue Tillerproduction initially appears to proceed at near maximum ratesthen is down-regulated during later development by longer phyllochrons,slower rate of tiller elongation and reduced site usage. Festuca arundinaceaSchreb., tall fescue, tiller production, leaf appearance, site usage, leaf elongation rate, synchronization, phyllochron, canopy development     

Natural variation in Tiller Number 1 affects its interaction with TIF1 to regulate tillering in rice

Tiller number per plant—a cardinal component of ideal plant architecture—affects grain yield potential. Thus, alleles positively affecting tillering must be mined to promote genetic improvement. Here, we report a Tiller Number 1 (TN1) protein harbouring a bromo-adjacent homology domain and RNA recognition motifs, identified through genome-wide association study of tiller numbers. Natural variation in TN1 affects its interaction with TIF1 (TN1 interaction factor 1) to affect DWARF14 expression and negatively regulate tiller number in rice. Further analysis of variations in TN1 among indica genotypes according to geographical distribution revealed that low-tillering varieties with TN1-hap^L are concentrated in Southeast Asia and East Asia, whereas high-tillering varieties with TN1-hap^H are concentrated in South Asia. Taken together, these results indicate that TN1 is a tillering regulatory factor whose alleles present apparent preferential utilization across geographical regions. Our findings advance the molecular understanding of tiller development.     

Effects of bison grazing on Andropogon gerardii and Panicum virgatum in burned and unburned tallgrass paririe

Summary Responses to clipping and bison grazing in different environmental contexts were examined in two perennial grass species, Andropogon gerardii and Panicum virgatum, on the Konza Prairie in northeastern Kansas. Grazed tillers had lower relative growth rates (RGR) than clipped tillers following defoliation but this difference was transient and final biomass was not affected by mode of defoliation. Grazed tillers of both species had higher RGR throughout the season than ungrazed tillers, resulting in exact compensation for tissue lost to defoliation. However, A. gerardii tillers which had been grazed repeatedly the previous year (1988) had reduced relative growth rates, tiller biomass and tiller survival in 1989. This suggests that the short-term increase in aboveground relative growth rates after defoliation had a cost to future plant growth and tiller survival.In general, the two species had similar responses to defoliation but their responses were altered differentially by fire. The increase in RGR following defoliation of A. gerardii was relatively greater on unburned than burned prairie, and was influenced by topographic position. P. virgatum responses to defoliation were similar in burned and unburned prairie. Thus grazing, fire, and topographical position all interact to influence tiller growth dynamics and these two species respond differently to the fire and grazing interaction. In addition, fire may interact with grazing pattern to influence a plants' grazing history and thus its long-term performance.     

Leaf and Tiller Production of Prairie Grass (Bromus willdenowii Kunth) and Two Ryegrass (Lolium) Species

A detailed morphological study of three prairie grass cultivars(Bromus willdenowii Kunth) was conducted under ‘vegetative’and ‘reproductive’ growth conditions (short andlong photoperiods) and at different temperatures. Perennialryegrass (Lolium perenne L.) and Westerwolds ryegrass (Loliummuhiflorum Lam.) were compared during vegetative growth. Prairie grass had higher leaf appearance rates (leaves per tillerper day) and lower site filling (tillers per tiller per leafappearance interval) than the ryegrass species. Tillering rates(tillers per tiller per day) were also lower, except under vegetativeconditions at 4C. Low tiller number in prairie grass was notdue to lack of tiller sites but a result of poor filling ofthese sites. Lower site filling occurred because of increaseddelays in appearance of the youngest axillary tiller and lackof axillary tillers emerging from basal tiller buds. In prairiegrass, no tillers came from coleoptile buds while only occasionallydid prophyll buds develop tillers. Low tiller number in prairiegrass was compensated for by greater tiller weight. Prairiegrass had more live leaves per tiller, greater area per leafand a high leaf area per plant. Considerable variation between cultivars was found in prairiegrass. The cultivar ‘Bellegarde’ had high leaf appearance,large leaves and rapid reproductive development, but had lowlevels of site filling, tillering rate, final tiller numberand herbage quality during reproductive growth. ‘Primabel’tended to have the opposite levels for these parameters, while‘Grasslands Matua’ was intermediate and possiblyprovided the best balance of all plant parameters. prairie grass, Bromus willdenowii Kunth, perennial ryegrass, Lolium perenne L., Westerwolds ryegrass, Lolium multiflorum Lam., temperature, photoperiod, leaf appearance, leaf area, tillering, site filling, tillering sites, yield     

Demography of three dominant sedges under contrasting grazing regimes in the High Arctic

Abstract. Tiller demography of Carex aquatilis ssp. stans, Carex membranacea, and Eriophorum angustifolium ssp. triste was investigated in ungrazed and grazed high arctic vegetation on central Ellesmere Island, Canada. Tiller birth, growth, flowering and death were studied from excavated clonal fragments, and tiller density and biomass were studied from excavated turfs. Five life‐cycle stages were determined: dormant buds, juvenile, mature, flowering and dead tillers. A stage‐based transition matrix model was developed to estimate the long‐term dynamics of the sedge populations and to compare life‐history strategies between ungrazed and grazed populations. Short‐term and retrospective models, based on the growth during the sampling year and during the lifetime of the clonal fragments, respectively, were compared to see how well the short‐term model can describe demography of long‐lived plants. According to the short‐term model, tiller populations were decreasing (λ < 1 except for C. membranacea), whereas the retrospective model indicated that the tiller populations were increasing. Tiller population growth rates did not differ between ungrazed and grazed habitats. Nevertheless, the similar growth rates may be obtained by balanced differences in the vital rates between plants of the two habitats. The plants in the ungrazed habitat tended to remain in their current life‐cycle stage, whereas plants in the grazed habitat moved quickly to the next stage and died earlier. C. aquatilis ssp. stans appears to gain a competitive advantage over the other species under intensive grazing, as indicated by the higher tiller density and greater below‐ground biomass in grazed vegetation. The greater amount of below‐ground biomass apparently buffers C. aquatilis ssp. stans against grazing better than the other species.     

Response to Temperature in a Stand of Pearl Millet (Pennisetum typhoides S. & H.): V. DEVELOPMENT AND FATE OF TILLERS

The development of individual tillers in stands of pearl milletwas investigated in a suite of temperature-controlled glasshousesmaintained at mean air temperatures of 19, 22, 25, 28 and 31?C. The rate of leaf appearance of individual tillers was similarto that on the main culm but later tillers produced fewer leaves.Apical dissection revealed that 2–5 leaf primordia failedto emerge from some tillers and the cessation of developmentpreceded any external signs of premature senescence by 3–4weeks. The concept of thermal time is used to determine when leaf appearanceceased on individual tillers. Tiller development stopped synchronouslyat about 430 ?Cd in all treatments, indicating that it was relatedto a common physiological or environmental condition. This periodcorresponded to the start of stem elongation and closure ofcrop canopy but because temperature has a major influence onboth it was impossible to reach a firm conclusion about themechanisms responsible for the cessation of tiller development.The yield and fate of individual tillers are also presented. Key words: Tiller development, Millet, Temperature     

Axillary bud banks of two semiarid perennial grasses: occurrence, longevity, and contribution to population persistence

The occurrence, longevity, and contribution of axillary bud banks to population maintenance were investigated in a late-seral perennial grass, Bouteloua curtipendula, and a mid-seral perennial grass, Hilaria belangeri, in a semiarid oak-juniper savanna. Axillary buds of both species were evaluated over a 2-year period in communities with contrasting histories of grazing by domestic herbivores. A double staining procedure utilizing triphenyl tetrazolium chloride and Evan's blue indicated that both viable and dormant axillary buds remained attached to the base of reproductive parental tillers for 18–24 months which exceeded parental tiller longevity by approximately 12 months. Bud longevity of the late-seral species, B. curtipendula, exceeded bud longevity of the mid-seral species, H. belangeri, by approximately 6 months. Younger buds located on the distal portion of the tiller base were 3.2 and 1.4 times more likely to grow out than older proximal buds of B. curtipendula and H. belangeri, respectively. The percentage of older proximal buds, which included comparable portions of viable and dormant buds, that grew out to produce tillers following mortality of parental tillers was 6.0% for B. curtipendula and 8.4% for H. belangeri. In spite of the occurrence of relative large axillary bud banks for both species, the magnitude of proximal bud growth did not appear sufficient to maintain viable tiller populations. We found no evidence to support the hypothesis of compensatory bud growth on an individual tiller basis for either species. Grazing history of the communities from which the buds were collected did not substantially affect the number, status, longevity, or outgrowth of axillary buds on an individual tiller basis for either species. However, long-term grazing by domestic herbivores influenced axillary bud availability by modifying population structure of these two species. Bud number per square meter for B. curtipendula was 25% lower in the long-term grazed compared to the long-term ungrazed community based on a reduction in both tiller number per plant and plant number per square meter. In contrast, bud number per square meter for H. belangeri was 190% greater in the long-term grazed than in the long-term ungrazed community based on a large increase in plant density per square meter. Minimal contributions of axillary bud banks to annual maintenance of tiller populations in this mid- and late-seral species underscores the ecological importance of consistent tiller recruitment from recently developed axillary buds. Consistent tiller recruitment in grasslands and savannas characterized by intensive grazing and periodic drought implies that (1) bud differentiation and maturation must be remarkably tolerant of adverse environmental conditions and/or (2) tiller recruitment may resume from buds that mature following the cessation of severe drought and/or grazing, rather than from mature buds that survive these disturbances. These scenarios warrant additional research emphasis given the critical importance of this demographic process to tiller replacement in species populations and the maintenance of relative species abundance in grasslands and savannas. Received: 12 August 1996 / Accepted: 30 December 1996     

Spatial pattern and process at the plant neighbourhood scale: insights from communities dominated by the clonal grass Elymus repens (L.) Gould

Question: How do clonal traits of a locally dominant grass (Elymus repens (L.) Gould.) respond to soil heterogeneity and shape spatial patterns of its tillers? How do tiller spatial patterns constrain seedling recruitment within the community? Locations: Artificial banks of the River Rhône, France. Material and Methods: We examined 45 vegetation patches dominated by Elymus repens. During a first phase we tested relationships between soil variables and three clonal traits (spacer length, number of clumping tillers and branching rate), and between the same clonal traits and spatial patterns (i.e. density and degree of spatial aggregation) of tillers at a very fine scale. During a second phase, we performed a sowing experiment to investigate effects of density and spatial patterns of E. repens on recruitment of eight species selected from the regional species pool. Results: Clonal traits had clear effects – especially spacer length – on densification and aggregation of E. repens tillers and, at the same time, a clear response of these same clonal traits as soil granulometry changed. The density and degree of aggregation of E. repens tillers was positively correlated to total seedling cover and diversity at the finest spatial scales. Conclusions: Spatial patterning of a dominant perennial grass responds to soil heterogeneity through modifications of its clonal morphology as a trade‐off between phalanx and guerrilla forms. In turn, spatial patterns have strong effects on abundance and diversity of seedlings. Spatial patterns of tillers most probably led to formation of endogenous gaps in which the recruitment of new plant individuals was enhanced. Interestingly, we also observed more idiosyncratic effects of tiller spatial patterns on seedling cover and diversity when focusing on different growth forms of the sown species.     

The effect of tiller removal and tiller defoliation on competition between the main shoot and tillers of spring barley

In glasshouse and field experiments the source-sink relations of the main shoot of plants of spring barley were modified by tiller removal and tiller defoliation. Decreasing competition by tiller removal promoted the growth of the residual main shoot and its component parts, and the earlier tillers were removed the greater was the effect. Stem dry weight was increased four-fold in the glasshouse by early tiller removal and was doubled in the field experiment. The grain yield of the main shoot ear was increased by 26 – 30% by tiller removal compared with tillering control plants and this was due to larger grains in all spikelet positions. On the other hand increasing competition by regular tiller defoliation had relatively little effect on the growth and development of the main shoot in the glasshouse study, but in the field the main shoot grain yield was reduced by 10% compared with the control. The main effect of tiller defoliation was on the development of tillers. In the glasshouse tillers survived repeated defoliation, continued to be produced, and the majority produced grain but with fewer and smaller grains per ear than in control plants. Tiller growth was supported by the import of assimilate from the main shoot and this was accompanied by an increase in the photosynthetic rate of the main shoot leaves. In the field all defoliated tillers died within 4 wk. These responses are discussed in terms of the physiological interrelations between the main shoot and tillers.