Tiller Age Research Articles

Effects of Stepwise Raising of the Water Level on Tiller Growth in Rice Plants (Oryza sativa L.).

The effects of stepwise raising of the water level on tiller growth in rice plants were examined. When the plant age in leaf number of the main stem was 7.5, the plants were submerged to a level of the 7th leaf collar. Thereafter, as the plant's age advanced, the water level was raised to the level of the uppermost leaf collar. The length or the second tiller(T2), T3, T4, T7 in a deepwater plot was higher than in the control plot from the 6th or 18th day after the start of deepwater treatment. The response of tiller length to the treatment was similar to the main stem. Changes in age counted by the leaf numbers of T2, T3, T4 were simllar to the main stem, but the changes of T7 were not. The differences in relative tiller age between tillers(T2, T3, T4) and the main stem in the deepwater plot were smaller than in the control plot. The younger the tiller age at the start of treatment, the larger the difference in relative tiller age between the deepwater plot and the control plot. The starts of panicle differentiation in primary tillers were delayed by the treatment. In the treated plants, the starts in the primary tillers were more delayed than in the main stem. Therefore the effects of the deepwater treatment on tiller growth varied with the tiller growing stage at the beginning of treatment.

Tillering, Internode Development, and Dry Matter Partitioning in Creeping Bentgrass

High tiller density and stolon development are critical to wear tolerance and persistence of creeping bentgrass (Agrostis palustris Huds. synonym A. stolonifera L.). A better understanding of creeping bentgrass growth and development would be helpful in screening germplasm for improved turf characteristics. The objectives of this study were to determine tiller appearance and main stem elongation and development, and to determine above ground dry matter partitioning, in high and low tillering populations of creeping bentgrass grown under low light (150 μmol m−2 s−1). Individual, pregerminated seeds of cv. Emerald and germplasm UM67‐10 were transplanted into 10‐cm pots containing an 80:20 (v/v) sand:peat media. Two growth cabinet experiments were conducted under 16‐ and 8‐h photoperiod and 20/15°C day/night temperatures. Phenological development was monitored through 35 d after transplanting (DAT). Dry weight per tiller was correlated to tiller age for main stem and primary tillers (r = 0.98 and r = 0.99) and secondary tillers (r = 0.93 and r = 0.99) for UM67‐10 and Emerald, respectively, at 35 DAT. Dry weight per tiller was related to tiller elongation. Population differences for dry weight accumulationper day were significant (P = 0.05) for lower order tillers. The germplasm UM67‐10 initiated tillering earlier and main stem elongation later than Emerald. Tillers per plant were correlated to tiller appearance date. Elongating tiller weight within populations was related to main stem elongation date and its final length. Late season planting, when daylight is decreasing, will result in a bentgrass stand with fewer tillers per plant and with little elongated stem growth. Screening germplasm for tiller production in a growth cabinet may facilitate identifying grasses with high tiller density and improved wear tolerance.

Does selective defoliation mediate competitive interactions in a semiarid savanna? A demographic evaluation

Abstract. Three patterns of target‐neighbor plant defoliation were imposed on a late‐seral, perennial, C4‐grass, Bouteloua curtipendula, in three long‐term grazing regimes to determine the influence of selective defoliation on competitive interactions and species replacement in a semiarid savanna on the Edwards Plateau, Texas, USA. Short‐term (3‐yr) target plant defoliation did not significantly affect either tiller or plant responses in any of the three grazing regimes. Neighbor plant defoliation, either alone or in combination with target plants, produced a significant defoliation interaction with time for tiller number and basal area per plant, but not for tiller recruitment or mortality. The minimal effect of selective defoliation on the intensity of competitive interactions in this semiarid community indicates that selective grazing has a less definitive role in mediating herbivore‐induced species replacement than it does in mesic grasslands and savannas. This interpretation is discussed within the context of long‐term (45‐yr) change in herbaceous vegetation associated with grazing in this community.Cumulative tiller recruitment in the intensively grazed regime was only 44% of that in the ungrazed regime because of greater plant mortality and fewer surviving plants that recruited tillers. Target plant mortality (50%) only occurred in the intensively grazed regime and the proportion of target plants that initiated tillers decreased by 70, 48 and 32% in the ungrazed, moderately and intensively grazed regimes, respectively, during the final two years of the investigation. The decrease in cumulative tiller recruitment in all grazing regimes was probably mediated by a drought‐induced increase in median tiller age the second year of the study. However, tiller per tiller recruitment rate among plants that recruited at least one tiller remained relatively constant among grazing regimes and years. Intensive, long‐term grazing has modified the population structure of this late‐seral perennial grass to the extent that population responses to both herbivory and periodic drought have been altered in comparison with those of ungrazed and moderately grazed populations. Ecological consequences of a herbivore‐induced transition in population structure may be to minimize the effect of selective herbivory on competitive interactions and to function as an avoidance mechanism to reduce the probability of localized population extinction in response to intensive long‐term herbivory.

Demographic variability in tiller populations of two perennial pampa grasses

Abstract. The general objectives of this study were: (1) to investigate the importance of internal influences in regulating the tiller dynamics in natural populations of the warm‐season perennial grasses Paspalum dilatatum and Sporobolus indicus, coexisting in Argentine flooded pampa, in as much as they act independently of the underlying external environment, and (2) to evaluate the extent to which interactions between internal and external factors affect the variation in tiller dynamics within such populations. Within‐population variation in seasonal development of plants and tillers with different neighbour composition was studied for an annual growth cycle. Tiller survival and tillering were significantly influenced by tiller size. Tiller age influenced tiller fate, as suggested by the additive effects of age and size of tillers. These relationships varied with season and with species. Size and age of tillers showed additive effects with their neighbouring species on the tiller fate of P. dilatatum, but the effects of age and size of S. indicus changed according their neighbourhood. Tiller survival of S. indicus during the early growth season was more size‐dependent when the cold‐season species Poa lanigera, was the principal neighbour. Flowering and tillering probabilities were positively related through their common positive responses to tiller size. Tiller survival and recruitment between different seasons were strongly related. Independently of neighbour composition, tiller survival was generally inversely related to tiller recruitment in previous seasons. Therefore, significant density‐dependent mortality of tillers was found for both species during the early summer when tiller density was expressed by basal area units.

Plant Demographic Responses to Environmental Variation: Distinguishing between Effects on Age Structure and Effects on Age-Specific Vital Rates

1 The vital rates (e.g. fecundity, growth or mortality) of a plant population can each be expressed as the scalar product of the vectors nt, representing the age structure, and mt, representing the age-specific values of the vital rate. We hypothesize that environmental change can affect a vital rate of a plant population through one of two mechanisms: by changing the population age structure (hypothesis 1), or by altering the age-dependent vital rates (hypothesis 2). 2 We determined which of these hypotheses best explained the effects of different grazing treatments, applied in a field experiment, on the population tiller production of two pasture grasses, Agrostis stolonifera and Lolium perenne. 3 Monthly censuses of mean per capita tiller production were carried out for two years and grazing effects were detected in a number of censuses. 4 Tiller production by individual tillers was age-dependent and increased linearly with tiller age. 5 Grazing treatments significantly changed both the age structures (n,) of the tiller populations in most censuses and the regression of tiller production on age (m,) in a number of censuses. 6 Treatment effects on population tiller production predicted according to hypothesis 1 were calculated using measured values for n, specific to each grazing treatment and the mean values for m, over all treatments. Conversely, effects predicted according to hypothesis 2 were calculated using mean values for n, and values for m, specific to each grazing treatment. 7 The grazing effects on tiller production predicted by hypothesis 2 fitted the field data significantly for both species in all grazing treatments whereas hypothesis 1 never gave a significant fit. Therefore, grazing effects on population tiller production arose solely through changes in the age-specific values for tillering and never through effects on the population age structures. 8 We discuss the reasons for these results and consider the mechanisms of the responses to grazing. We also assess the use of these hypotheses in determining the ecological processes governing plant demographic change.

Effect of management factors on tiller dynamics in tall fescue: Tiller mortality

Abstract The effect of plant density (row spacing / seeding rate), cultivar choice, nitrogen (N) fertilization and close‐down date on tiller mortality in a dual purpose (forage and seed) tall fescue (Festuca arundinacea Schreb.) sward was examined over a two‐year period. Cajun had a consistently lower (P<0.01) tiller mortality than Roa in both seasons. An increase in row spacing or a decrease in seeding rate reduced (P<0.01) tiller mortality. Tiller mortality increased with increased levels of N‐fertilization. A relation between tiller age (time of origin) and mortality was identified. The youngest or least developed tillers were found to be less tolerant of stressful conditions than the older or better developed tillers. Tiller mortality was also shown to increase dramatically in spring, irrespective of the type of management applied.

Physiological integration among tillers of Holcus lanatus: age‐dependence and responses to clipping and competition

summaryThe ecological consequences of physiological integration among tillers were examined in a glasshouse experiment on the clonal grass Holcus lanatus L. We measured the effects of severing the internode connection between a tiller and its parent on the growth and survival of this marked tiller. The effects of three factors on the response to Severing were determined using this procedure: competition with the parent plant, by comparing tillers repotted in isolation with tillers remaining in the neighborhood of the parent; dipping treatment, comprising no clipping, clipping only the marked tiller and its daughter tillers or clipping the whole parent plant, including the marked tiller; and the change in the response with tiller age at severing, using four tiller ages (1, 2, 4 and 8 wk). These age, clipping and severing treatments wt‐re applied factorially.After 8 wk of growth the responses to severing of the marked tillers, were dependent on the age and clipping treatments. Severing always decreased survival and growth (tiller production, biomass and tiller extension) of the youngest tillers (ages 1 and 2wk), indicating that they were dependent on the parent to support their early growth. Age 4 tillers were able to support their own growth and grew hest in isolation; but when grown in the parent's neighbourhood competition with the parent reduced growth, although parental support ameliorated these effects. Some of the oldest tillers (age 8 wk) showed decreased growth when unsevered. This indicated an outflow of resources to the parent and suggested that integration allowed the control and coordination of tiller growth.The pattern of the severing effects was similar in all clipping treatments, varying only in degree. There was little evidence of increased support for clipped tillers or for a change in the pattern of integration when the whole plant was clipped, except that age 8 tillers showed a continued benefit of the connection, in contrast to the positive effect of severing in the other two clipping treatments. The extension rate of the marked tiller showed complex responses to clipping and severing treatments, including effects of integration on regrowth after clipping. This experiment has shown that the growth of tillers in H. lanatus is highly integrated but that this integration is extremely plastic in response to tiller age and, to a lesser extent, clipping treatment.

Effects of Kinetin on the Development of Tillers in Rice Plants.

水稲の分げつの発育に及ぼすサイトカイニンの影響を知るため, 水稲を水耕栽培し, 光強度, 窒素濃度などが異なる条件下でカイネチンを水耕液に加えて根から吸収させ, 植物体の生長, 分げつの出現率, 葉齢, 長さなどに対する影響を観察した. また, 異なる要素根からカイネチンを吸収させた時の影響の差異について観察した. 草丈, 苗齢, 葉長などは光強度, 窒素濃度, 吸収要素根を問わずカイネチンによって抑制され, 根数, 根長も少数の例外を除き抑制された. 分げつに対する影響は光条件によって大きく異なり, 自然光下ではカイネチンが分げつ数の増加を抑制し, 分げつの葉齢や長さに対しても一部の例外を除き抑制の傾向を示したが, 遮光下では分げつ数の増加を促進し, また分げつの葉齢や長さにも顕著な促進を示した. 遮光下で出現率が小さかった第2節, 第3節分げつは, カイネチン処理時既に発育を停止していたとみられるが, このような分げつ芽に対しカイネチンが発育を促進して出現率を高めた. 異なる要素根からカイネチンを吸収させても各節分げつに対する影響にはほとんど差異がなかった.

Character Expression of the Semidwarfing Gene sd-1 in Rice (Oryza sativa L.). II. Appearance and development of tillers.

イネ多収品種の育成に大きく貢献してきた半矮性遺伝子sd-1の形質発現について, 日本型長稈品種農林29号, これにsd-1を導入した準同質遺伝子系統SC-TN 1およびsd-1の供与親であるインド型品種台中在来1号を用いて, 分げつの出現率および出現後の発育を比較した. 総葉数では, 3品種間に差がほとんどなかった. 分げつ出現率においては, 上位節の1次分げつおよび2次分げつで多窒素, 少窒素両条件に共通して, 台中在来1号が日本型2品種より大きかった. 日本型2品種間では, 少窒素下での上位節1次分げつ, 少窒素, 多窒素両条件を通じて2次分げつでSC-TN 1が農林29号より大きかった. このことから, 半矮性遺伝子sd-1は発育しにくい分げつの出現率を高める効果をもつと考えられた. 1次分げつの葉齢が1に達する時期の主茎葉齢は, 半矮性2品種が農林29号より若く, 台中在来1号はSC-TN 1より若い傾向がみられ, 少窒素条件下ならびに上位節分げつで特にその傾向が強かった, 出現後の葉齢増加速度は上位節の分げつにおいてSC-TN 1が農林29号よりも大きい傾向がみられたが, 品種間差異は明らかでなかった. 半矮性品種は母茎に対する相対葉齢が大きいことが認められた. このことは, 分げつの葉齢が1に達する時期の早いことによると考えられた.

Tillering behavior in oryza sativa L. VII. Relation between tiller age and panicle formation in the individual tillers.

水稲の主茎と各分げつについて, 葉齢と幼穂発育過程との関係を調べた。水稲品種ササニシキを2期に分けて播種し (I, II区), 1ポット (1/5000 a) 当り3個体で育て供試した。個体内全茎の齢を同一視点から解析するために, 齢のスケールとして, 止葉抽出完了時を起点としてさかのぼって数えた葉齢 (補葉齢: cA) を用いた。また幼穂発育ステージ (PS) は, 止葉原基分化期から穎花原基分化後期までを12段階に分級する方式を用いた。主茎および分げつ位ごとの平均値でみると, PSとcAとは直線的な関係にあった。この関係は個々の茎においても認められた。また, 個体内でのPSとcAとの変動は, 幼穂分化開始から日数がたつほど大きくなった。PS 3以上の茎について, PS (y軸) とcA (x軸) との関係式を求めると, y=15.95-3.74xとなった。形態上幼穂分化開始と判断できるPS 3 (苞原基増加期) となる時の補葉齢を, この式から求めるとcA 3.5であった。また, 個々の茎の観察から, PS 2 (第1苞原基分化期) からPS 3に移行するのはcA 3.6からcA 3.3までであることが明かとなった。すなわち, 15枚の葉を持つ主茎から, 4または5枚の葉を持つ分げつまでを対象にしても, 幼穂分化開始 (PS 3) の時期は止葉から数えて4枚目の葉がほぼ半分ほど抽出した頃であった。また, 主茎に着目して, 幼穂発育ステージを推量できる外見上の齢として, 葉齢指数と補葉齢との関係を考察した。

Tillering behavior in Oryza sativa L. I. Growth correlation between the main stem and tillers.

水稲の孤立個体における主茎と分げつとの生長の相互関係を葉齢に着目して調べた. 個体の齢を表す「葉齢」を分げつの齢を表すのにも用い, 各分げつの葉位を, 主茎の同伸葉の葉位で表したものを各分げつの相対葉位と規定し, さらに, 相対葉位で表した各分げつの葉齢を相対葉齢と規定した. これにより, 主茎と各分げつ間の生長の比較が可能となった. また, 同伸分げつを位置づける相対分げつ位(RTP)を規定し, これにより相対葉位を算出した. ポットに1個体植えした水稲品種ササニシキ, トヨニシキ, アキヒカリに肥料を充分に与え, 湛水状態で育て, すべての葉に印をつけて観察した. 初期に出現した分げつには, 主茎同様に出葉転換期が認められ, 生理的な変化が個体全体でほぼ同時期に起きたことが示唆された. 栄養生長期後半の観察では, 同一日には分げつ次位が高いほど, 相対葉位の高い葉が出現し, それに伴いRTPの高い嬢分げつが出現した. 各分げつの相対葉齢から主茎の葉齢を差し引いた差を相対葉齢差(D)と規定すると, Dは生長とともに直線的に増加し, 播種後94日目, 止葉の抽出直前に最大となった. また, Dは分げつ次位が高いほど大きく, 各時期におけるDは, ほぼ分げつ次位に比例して増大した. Dの値の大きさには, 品種間で差が認められた.

Tillering behavior in Oryza sativa L. II. The tillering pattern as affected by the balance in the growth rate between the main stem and tillers.

Tillering behavior of rice plants (1 plant/pot) of three cultivars was investigated. In a rice plant, there are differences (D) in growth speed between the main stem and each tiller. In the previous paper, we prescribed a relative tiller age (RA) to the individual tillers, and compared the ages of every tiller with each other. In this paper, we investigated the relationship between D and the increasing pattern of tiller number. If there is no D, we can make a curve called a synchronous growth curve indicating the increasing pattern of tiller number when leaves of each tiller and leaves of the main stem expanded synchronously (synchronous growth). Using three cultivars, we analyzed the pattern of synchronous growth curves and discussed the differences in the tiller behavior among the cultivars. We simulated the synchronous growth curve when every tiller appears in a rice plant. Assuming the value of D, we also simulated the growth curve when every tiller appears. Compared the curve with the synchronous growth curve, we discussed the relationship between D and the increasing pattern of ti1ler number.

The effect of tiller length and age on herbage quality of hybrid Pennisetum canopies.

Whole plants were sampled every 10 or 11 days from field-grown P. americanum X P. purpureum canopies which were cut at intervals of 3 or 6 weeks. Tillers of varying lengths were analysed for in vitro dry matter digestibility (IVDMD). During the growing period, average whole tiller digestibility decreased, as did differences between tillers of different lengths. In 42-day-old herbage, no difference in IVDMD was found between 10 and 70 cm tillers. The decline in digestibility with time was attributed to (1) the appearance of tall tillers and (2) the detrimental effects of low light intensities on tillers growing deep in the canopy. Results suggested that it is doubtful whether tiller length or other morphological or physiological traits can be used to predict herbage digestibility, and that in breeding for better digestibility selection for stem digestibility per se should be more promising than selection for reduced stem growth. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Tiller appearance and death ofLolium perennein mixed swards grazed by dairy cattle at two stocking rates

Abstract Ryegrass tiller appearance, death, and density were examined in perennial ryegrass — white clover pastures stocked with 2.77 (LSR) or 4.28 (HSR) dairy cows per hectare. Rates of tiller appearance and death were highest between November and January and were low and variable between February and October. Tillering in autumn was low and similar to that in winter (27.8 and 27.7 tillers/m2 per day, respectively). The rate of tiller death (but not appearance) was influenced by stocking rate, and was greater (P<0.01) in LSR than HSR swards during spring (29.5 and 21.2 tillers/m2 per day, respectively) and summer (61.3 and 39.9 tillers/m2 per day, respectively). Higher tiller death rates in LSR swards resulted in lower (P<0.05) tiller density during summer and autumn and reduced heterogeneity of tiller age population. Herbage mass in autumn was composed of more (P<0.05) new tillers in LSR than HSR swards (61.1 and 46.4%, respectively). Herbage mass in winter and spring consisted of a variety of tiller ag...

The influence of tiller age and time of year on the growth ofThemeda tri andraandSporobolus fimbriatusin semi‐arid grassveld

Abstract Sequential growth measurements were made on successive populations of Themeda triandra and Sporobolus fimbriatus tillers initiated at different times of the year. The independent influences of tiller age and time of year on tiller growth were isolated by deriving growth indices for tillers of the same age at different times of the year and for tillers of all ages at each time of the year respectively. Isolating the effect of plant age on growth showed that T. triandra is most productive under a regime of long periods of undisturbed growth, while S. fimbriatus is better suited to frequent interruptions in growth. Isolating the effect of time of year shows that both species are particularly sensitive to perturbations in spring. However, the photosynthetic efficiency of T. triandra is strongly influenced by time of year while S. fimbriatus seems to be a more opportunistic assimilator of sunlight.

Tillering in ‘Grasslands Nui’ perennial ryegrass swards 2. Seasonal pattern of tillering and age of flowering tillers with two mowing frequencies

Abstract Tiller density, tiller appearance rate (TAR), tiller death rate (TDR), tiller survival, and age of reproductive tillers were measured for 2 years in well fertilised, irrigated swards of ‘Grasslands Nui’ perennial ryegrass (Lotium perenne L.) mown either frequently (F) or infrequently (I). Seasonal changes in tiller density, TAR, and TDR were similar in F and I, with patterns being similar in timing in both years. TAR was greatest in the regrowth immediately after defoliation of the main group of reproductive tiller apices. TAR was approximately 60% of this peak value during summer, declined during autumn, then increased in winter. TDR was greatest during summer and lowest during winter. Tiller density declined during reproductive growth, increased rapidly after interruption of reproductive growth, declined during late summer and autumn, then increased again during winter. Tiller density was greater in F and I, the difference being caused by more rapid tillering in F. Survival of tillers was little affected by mowing treatment, and the half-life of tagged tillers was 36 -143 days. Only a small proportion of tillers became reproductive. In the first year, after autumn establishment of the sward, reproductive tillers were formed during winter. In the second year, tillers formed before winter provided the majority of flowering tillers. Secondary reproductive tillers elongated after the main group of reproductive tillers were decapitated, and these later developing tillers included tillers that appeared in winter and spring.

Tillering in ‘Grasslands Nui’ perennial ryegrass swards 1. Effect of cutting treatments on tiller appearance and longevity, relationship between tiller age and weight, and herbage production

Abstract An irrigated ‘Grasslands Nui’ perennial ryegrass (Lolium perenne L.) sward was mown during reproductive growth and subsequent vegetative summer growth using 6 cutting treatments. The treatments included combinations of stages of interruption of reproductive development and regrowth intervals. Tagged ryegrass tillers were used to measure tillering, tiller longevity, and tiller weight at different ages. Periods of rapid tillering in spring before culm elongation started, and after interruption of reproductive growth were observed. Interruption of reproductive development at inflorescence emergence increased tillering in the second period compared with other treatments. Later interruption of reproductive development reduced the number of pre-flowering tillers surviving into summer. Longevity of tillers tagged at the start of the experiment was greatest with early interruption of reproductive growth followed by infrequent cutting. Youngest tillers were smallest, and new tillers took 60–100 days after...

Plant Colonization of Actively Sorted Stone Stripes in the Subantarctic

Three grasses (Phleum alpinum L., Deschampsia antarctica Desv., Festuca contracta T. Kirk) and one perennial herb (Acaena tenera Alboff) are the earliest important colonizers of small-scale sorted stone stripes in fellfield areas on South Georgia. Survival potential differs considerably between the grass species and appears to be related to both tiller and root morphology. The principal species, Phleum alpinum, produces stable islands later colonized by other species. Its growth form and life cycle appear to be especially well adapted to this habitat. The rate of downslope movement of plants on a given slope appears to be directly related to size. The age of individual Phleum plants was assessed using morphological features and a relationship derived between age and number of tillers. A model is proposed describing the development of Phleum in fellfield areas, and its relationship to stabilization of the soil.

Role of Panicle Exsertion in Water Stress Induced Sterility1

Although the sensitivity of crop species to water stress during reproductive growth stages is well documented, the causes of sterility are not understood. The role of decreased panicle exsertion as a causal factor of spikelet sterility in water stressed rice (Oryza sativa L.) was investigated. Rice cultivar IR36 was grown on a deep silty loam soil under full sprinkler irrigation for 77 days. A line source sprinkler system was then utilized during panicle exsertion and flowering to impose six continuously decreasing irrigation treatments. After the 15‐day treatment period, full sprinkler irrigation was resumed until maturity. Soil moisture extraction and plant water potential were monitored as soil and plant water stress progressed. Panicle exsertion rate was measured on tagged panicles which were later used to assess percent final panicle exsertion and percent sterility. The six irrigation treatments varied in grain yield from 5.0 t ha−1 to about 1 t ha−1 with corresponding increases in spikelet sterility of 16.6 and 74.2%. Panicle exsertion rate decreased linearly with decreasing mean daily leaf water potential. The degree of final panicle exsertion from the flagleaf sheath and percent spikelet sterility both decreased linearly with panicle exsertion rate. All spikelets left unexserted from the flagleaf sheath were sterile. Panicle exsertion rate was slightly confounded by tiller age in that late tillers in the well irrigated treatment had a slower exsertion rate and higher percent sterility than earlier tillers. The early tillers which exserted at rates of 4.5 to 5.5 cm day−1 under well watered conditions decreased to about 3.0 cm day−1 in the stressed plot and accounted for 25 to 30% spikelet sterility in the severely stressed treatment.

Life Histories of Tillers of Eriophorum Vaginatum in Relation to Tundra Disturbance

SUMMARY (1) Life-tables were constructed for vegetative tillers of Eriophorum vaginatum from undisturbed and disturbed tussock tundra in Alaska. Life-tables were also constructed for tillers from tundra that had been fertilized with N, P and K. The life-tables were used to estimate population parameters and to construct constant coefficient matrix models of tiller demography. (2) Tiller survival was lower in disturbed than it was in undisturbed tundra, and daughter tillers were produced sooner. Addition of nutrients (as fertilizer) produced no change in tiller survival and in the age distribution of daughter tiller production in the first year following fertilization. The shapes of the survival curves were intermediate between Deevey Type I and Deevey Type II curves. (3) The generation time for tillers in undisturbed tundra was 5.3 years-about twice as long as in disturbed tundra-while the annual rate of increase of tillers did not differ greatly. Fertilization produced large increases in the annual rate of increase, but the generation time was shortened only slightly. (4) Reproductive values, defined as the expected number of daughter tillers from tillers of a given age relative to the expected number from a tiller aged 0, fell into one of three patterns: (i), decline from maximum value at age 0; (ii), increase from age 0 followed by a monotonic decline; (iii), increase from age 0 followed by a gradual, irregular decline and a plateau in the older age classes. The peak in reproductive value for patterns (ii) and (iii) occurred 2-4 years after the onset of tillering at age 1 or 2 years; this result was attributed to increases in age-specific tillering rate with tiller age. (5) Sensitivity analysis of the matrix models revealed that sensitivity of the annual rate of increase to changes in tillering rate and survival declines with age. The annual rate of increase was equally sensitive to changes in tillering rate and survival from age 0 to age 3. In the older age classes the annual rate of increase was more sensitive to changes in tillering rate than to changes in survival.