Ecological differentiation ofEuphorbia lasiocaula andE. sinanensis (Euphorbiaceae) I plant height,phenology and allocation to stems and leaves

Resource allocation and the seasonal change of stem length inEuphorbia lasiocaula Boiss. andE. sinanensis (Hurusawa) T. Kurosawa et H. Ohashi were examined in 10 populations on hills in Miyagi Prefecture, northern Japan. Differences were found in the diameter of stem, stem/leaf ratio of dry weight, vegetative dry weight/leaf area, and the beginning, end and duration of stem growth.Euphorbia lasiocaula has a thicker stem, a larger stem/ leaf ratio, a larger vegetative dry weight/leaf area, a later beginning and end of stem growth and a longer period of stem growth thanE. sinanensis. These differences support the relationships among plant height, resource allocation and phenology predicted by the mathematical models of Givnish (1982) and Sakai (1991, 1994). The tall and thick stems ofE. lasiocaula are considered to be favorable for capturing sunlight in grassy places, causing it to allocate much of its resources to the stems. On the other hand,E. sinanensis is considered to be adapted to deciduous forest floors or forest margins because it completes growing before it is shaded by canopy trees or by tall herbs, which is enabled by the larger allocation of resources to the leaves.     

羊草克隆种群的螺旋扩张规律

羊草是欧亚大陆草原东部区域的一个优势物种。其优势地位的取得是羊草种群年复一年不断克隆复制过程中进行螺旋扩张的结果,其中,每一个螺旋圆环代表一个生长季,进而每个生长季可再分为不同的种群成长阶段,执行不同的生存发展策略:5月下旬—7月下旬为成熟扩张期,羊草的成熟母株通过水平伸长根茎执行扩张策略;7月下旬—10月下旬为幼苗占领期,通过地下芽输出为地上子株执行占领策略;10月下旬—来年3月下旬为羊草的休眠期;3月下旬—4月下旬为它的生长准备期;4月下旬—5月下旬为生长巩固期,子株发育为成熟的母株,完成了领地的彻底控制,执行的是巩固策略。羊草的游击型分株和密集型分株源自于共同的母株,二者位置相互分开,不但可以避免内部竞争,而且通过根茎之间的连接进行资源共享,从而在对外竞争中始终处于优势地位,这是羊草的克隆区隔避险策略;羊草种群通过产生遗传异质性的种子来避免因外界环境条件巨变所造成的整体灭绝,执行的是一种有性繁殖避险策略。羊草在既定策略基础上也表现出明显的二八规律,即通过80%比例的密集型分株进行旧领地的巩固,以20%比例的游击型分株进行新领地的扩张。总之,羊草通过扩张,占领,巩固,再扩张,再占领,再巩固,这样的年复一年的螺旋扩张,成为了当地的优势物种。其研究结果能为提高羊草生产力和种子产量及恢复受损草原生态系统提供十分重要的科学支持。     

Effects of lead contamination on the clonal propagative ability of Phragmites australis (common reed) grown in wet and dry environments

Clonal propagation is important for the survival and maintenance of the common reed Phragmites australis. Pot culture experiments were conducted to investigate the effects of lead (Pb) concentration (0, 500, 1500, 3000, 4500 mg·kg^?1) and water stress on the clonal reproductive ability of this species. The Pb concentration found in plant organs, in decreasing order, was roots >shoots >rhizomes. There was a negative relationship between the growth of clonal propagative modules (excluding axillary shoot buds) and Pb concentrations, which caused a decrease in biomass, rhizome growth and number of axillary and apical rhizome buds. Daughter axillary shoots exhibited a tolerance strategy, with no significant change in their number; the axillary and apical rhizome buds, daughter apical rhizome shoots and rhizomes exhibited compensatory growth during the late stage of Pb (excluding 4500 mg·kg^?1) treatment in a wet environment. Pb applications above 500 mg·kg^?1 reduced these parameters significantly in the drought treatment, except for the number of axillary shoot buds, which did not change. Our results indicate that clonal propagative resistance to Pb contamination can occur via tolerance strategies, compensatory growth and a Pb allocation strategy, enabling these reeds to maintain population stability in wet environments. However, clonal modular growth and reproductive ability were inhibited significantly by the interaction between drought and Pb, which would cause a decline in P. australis populations in a dry environment. Lead concentrations of 4500 and 500 mg·kg^?1 in soils might meet or exceed the Pb tolerance threshold of clonally propagated reeds in wet and dry environments, respectively.     

Root biomass,root distribution and the fine-root growth dynamics of Quercus coccifera L. in the garrigue of southern France

Quercus coccifera L., the characteristic scrub oak of the garrigue, covers more than 100,000 ha in southern France alone. Precipitation in this area averages 900 mm/year and summer rains are not rare. A total belowground biomass of 7.2 kg/m², including rhizomes and lignotubers, was harvested. Roots were concentrated in the uppermost 50 cm of the soil. It was hypothesized that low winter temperatures inhibit active fine-root growth. This hypothesis was tested by means of fine-root extractions of soil samples from 0–50 cm depth from November 1987 to June 1988. Although the fine-root analysis could not be extended into late summer and fall, the data supported the hypothesis. Ratios of live/dead fine roots reached their minimum at 0.2–0.3 from December to April. They increased to 1.0–1.2 during late spring and early summer. Initiation of fine-root growth in early April was synchronous with bud break. Starch contents of roots, rhizomes, and lignotubers fluctuated from 4.3% in January to 8.3% in April. The starch stored in belowground organs of Q. coccifera in a closed canopy stand amounted to about 500 g/m² in April. This amount declined to 400 g with bud burst and fine-root growth initiation.     

Nitrogen translocation via rhizome systems in monoclonal stands ofReynoutria japonica in an oligotrophic desert on Mt Fuji: Field experiments

Mechanisms which enableReynoutria japonica, a dominant pioneer herb, to be successful in maintaining large stands in an oligotrophic volcanic desert on Mt Fuji were investigated with special reference to its nitrogen acquisition.Reynoutria japonica forms circular stands, each of which comprises only one genet. As a stand develops outwards, the number of aerial shoots per unit area decreases in the center. Shoots grow vigorously in the peripheral area where the available nitrogen from soil and precipitation (about 2.4 g m⁻² year⁻²) was much less than total nitrogen in the shoots (6.1–9.1 g m⁻²). Leaf nitrogen content per unit mass was also greater in the leaves of the peripheral shoots. When rhizomes extending radially from the center to the periphery were severed, the dry mass of shoots in the periphery diminished by 75% on a ground area basis. In the periphery, leaf nitrogen content also reduced significantly and no flowers were produced. When fertilizer was applied to the peripheral shoots with severed rhizomes, neither growth, survival nor flower production of the shoots was significantly smaller than the control levels. In these shoots, it is also found that the nitrogen content in the youngest leaves decreased for about 1 month and then increased to above that in the control leaves. These results suggest that (i) nitrogen accumulated in the central part is translocated to peripheral shoots via rhizomes, and that long-distance translocation enables the stands to develop outwards, and (ii) aerial shoots in the periphery utilize the nitrogen translocated by rhizomes in the beginning of the growth season, whereas once the shoots have established, they begin to take up nitrogen with their own roots. Since the peripheral shoots are in sunnier environments than the shoots inside the stand, the acropetal nitrogen translocation via rhizomes will raise the production efficiency of a whole stand.     

Growth forms of Leymus chinesis (Poaceae) at the different developmental stages of the natural population

The manner in which the density of Leymus chinensis increases from a single plant to a dominant population can be understood by tracing the development of a population from early to late stages. Parent shoot density, above‐ground dry weight, spike density, heading rate and spike dry weight, density of spreading shoots (buds/daughter shoots in apical/axillary rhizomes) and clumping shoots (buds/daughter shoots in axillary parent shoots), and young rhizome length and weight were investigated in the same quadrats for a low density/early stage (LE) population and a high density/late stage (HL) population. Clonal growth (buds/daughter shoots formation) and sexual reproduction (spikes formation) increased while rhizome storage (young rhizome weight) decreased during the transition from LE to HL. In a LE population an outward occupation strategy was employed, with a high proportion of spreading shoots. As the population density gradually increased until HL, an inward consolidation strategy increasing shoot amount in previously occupied areas, was adopted. This was characterized by a high proportion of clumping shoots. Interestingly, the trade‐off between spreading and clumping shoots can be adjusted by the duration of young rhizome elongation during a growth season. In other words, compared with a HL population, a LE population shortened the duration of young rhizome elongation during the growth season, which resulted in more time for the production of axillary spreading shoots along the rhizomes, and high amounts and proportions of total spreading shoots. The special growth patterns, that is, trade‐offs among growth forms, allow L. chinensis to establish dominant populations throughout the eastern Eurasian Steppe.     

Population dynamics,productivity and biomass allocation ofZizania latifolia in an aquatic-terrestrial ecotone

The population and production ecology of aZizania latifolia stand at a sheltered shore of the Hitachi-Tone River were investigated. Shoot emergence was observed twice a year; the fist was a synchronized shoot emergence in April and the second was from August to October. Aboveground biomass was mostly occupied by leaves and peaked at 1500 g dry weight m⁻² in August. The belowground biomass also reached its peak, 750 g dry weight m⁻², in August. The secondary shoots were small in spite of their high density. Leaves were produced continuously throughout the season. The leaf life span was as short as 55.6 days for cohorts that emerged from May through to September. Total annual net production ofZ. latifolia could be more than 3400 g dry weight m⁻². Shoot clusters of several centimeters were observed in April. The following self-thinning caused a regular distribution of the remaining shoots in August. Most shoots produced in August to October were found near a shoot persisting since April. They showed more concentrated distribution than shoots in April. A large biomass allocation to leaves and the ability to produce many clump shoots during the late growing period may facilitate dominance ofZ. latifolia in relatively sheltered sites.     

Fine-scale dynamics of rhizomes in a grassland community

Spatial dynamics in grassland communities are constrained by the belowground spatial distribution of roots and rhizomes. Their dynamics are difficult to measure as underground data collection tends to be destructive and cannot be repeated at the same plot over time. We investigated rhizome dynamics indirectly by examining rhizome spatial structure on long‐term grassland study plots where aboveground shoot counts have been recorded using a fine‐scale grid over nine years. Number of rhizome apical ends, basal ends and total rhizome length of both live and dead rhizomes were obtained from the data by scanning rhizomes and processing them by GIS vectorization. These rhizome variables were correlated with the above‐ground shoot counts in grid cells over varying temporal lags. There was a general decrease in the intensity of correlation between live rhizomes and shoot counts with increasing time lags. Correlation of dead rhizomes increased with increasing time lag, reaching a maximum after several years, and then declined. Species differed strongly in the change of rhizome‐shoot counts correlation over varying time lags. These differences were used to infer rhizome growth dynamics, namely rhizome growth rate and lifespan, and rhizome mean decomposition time. The species involved differed in all these traits. Mean rhizome growth rate ranged from 0.2 (Polygonum bistorta) to 3.3 cm ur^?1 (Deschampsia flexuosa); mean rhizome lifespan ranged from 5 yr (Anthoxanthum alpinum) to over 8 yr (Nardus stricta) and mean decomposition time from one growing season (Anthoxanthum) to 7 yr (Polygonum). Presence of dead rhizomes below living rhizomes or aboveground shoots was taken as an indication of fine‐scale replacements between species. These were highly non‐random, with some species pairs replacing significantly more frequently. These differences in rhizome growth parameters underlie different strategies of horizontal growth and dieback between species. These can serve as one of the mechanisms of species replacements and contribute to the fine‐scale coexistence of species.     

Age-specific seasonal storage dynamics of<Emphasis Type="Italic">Phragmites australis</Emphasis> rhizomes: a preliminary study

Age-specific seasonal rhizome storage dynamics of a wetland stand of Phragmites australis (Cav.) Trin. ex Steud. in Japan, were investigated from April to October 2000. For each sampling date, above- and below-ground biomass and age-specific rhizome bulk density, ?_rhiz were measured. Seven rhizome age classes were recognized, from <1 year to six years old, based on their position within the branching hierarchy as main criteria and rhizome color, condition of nodal sheaths and condition of the shoots attached to vertical rhizomes as secondary criteria. P. australis stand was moderately productive, having a net aerial and below-ground production of 1980 and 1240 g m^?2, respectively, and a maximum mean shoot height of 2.33 ± 0.12 m. In spring, shoot growth started at the expense of rhizome reserves, decreasing the rhizome biomass as well as ?_rhiz. Both parameters reached the seasonal minimum in May followed by a subsequent increase, indicating a translocation of reserves to rhizomes from shoots after they become self supporting. For each sampling date, ?_rhiz increased with rhizome age. Given that the quantity of reserves remobilized by the rhizomes for spring shoot growth, as assessed by the drop in bulk density from April to May, were positively correlated (r = 0.97, P < 0.05) with rhizome age, it is proposed that for spring shoot formation older rhizomes remobilize stored reserves more actively than younger ones. Given that the accumulation of rhizome reserves (rise in bulk density) from May to August, May to September or May to November was negatively correlated (r = 0.97, 0.92 and 0.87, respectively, P < 0.05) with rhizome age, it seemed possible that younger rhizomes were ‘recharged’ at a higher rate than older ones. These resource allocation mechanisms pertaining seasonal rhizome storage dynamics are of paramount importance in formulating management and conservation strategies of wetlands and aquatic habitats. Our results indicate that a harvest of above-ground biomass from May to June would be more effective in reducing the growth than a harvest in July to August or later, when rhizome reserves have already been replenished. However, the latter may remove a larger shoot bound nutrient stock, still preserving a healthy stand for the subsequent years.     

Leaf endophyte Neotyphodium coenophialum modifies mineral uptake in tall fescue

Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon and Hanlin, a fungal endophyte found primarily in shoots of tall fescue (Festuca arundinacea Shreb.), can modify rhizosphere activity in response to phosphorus (P) deficiency. In a controlled environment experiment, two cloned tall fescue genotypes (DN2 and DN4) free (E-) and infected (E+) with their naturally occurring endophyte strains were grown in nutrient solutions at low P (3.1 ppm) or high P (31 ppm) concentrations for 21 d. Endophyte infection increased root dry matter (DM) of DN4 by 21% but did not affect root DM of DN2. Under P deficiency, shoot and total DM were not affected by endophyte but relative growth rate was greater in E+ than E- plants. In high P nutrient solution, E+ plants produced 13% less (DN2) or 29% more (DN4) shoot DM than E- plants. Endophyte affected mineral concentrations in roots more than in shoots. Regardless of P concentration in nutrient solution, E+ DN2 accumulated more P, Ca, Zn and Cu but less K in roots than E- plants. When grown in high P nutrient solution, concentrations of Fe and B in roots of E+ DN2 plants were reduced compared with those of E- plants. Concentrations of P, Ca and Cu in roots of DN4 were less, but K was greater in E+ than E- plants. In shoots, E+ DN2 had greater concentrations of Fe and Cu than E- DN2, regardless of P concentration in nutrient solution. Genotype DN4 responded to endophyte infection by reducing B concentration in shoots. Nutrient uptake rates were affected by endophyte infection in plants grown in low P nutrient solution. A greater uptake rate of most nutrients and their transport to shoots was observed in DN2, but responses of DN4 were not consistent. Results suggest that endophyte may elicit different modes of tall fescue adaptation to P deficiency. This revised version was published online in June 2006 with corrections to the Cover Date.     

CHANGES IN STARCH DISTRIBUTION IN THE OVERWINTERING ORGANS OF TYPHA LATIFOLIA (TYPHACEAE)

Histochemical determinations for storage of carbohydrates in rhizomes, roots, and young shoots of Typha latifolia L. (Typhaceae) were conducted during the overwintering period from November to April. Early winter analysis showed that rhizomes and roots contained large amounts of starch (45.03% and 22.80% dry weight, respectively). The major storage tissue was parenchyma of the rhizome central core. From winter into spring a gradual decrease in storage starch in the rhizome and root occurred concurrently with starch accumulation near zones of rapid development in young shoots (buds), but the rhizome retained much starch (27.40% dry weight) into the start of its 2nd yr.     

Effect of nitrogen addition and drought on above-ground biomass of expanding tall grasses <Emphasis Type="Italic">Calamagrostis epigejos</Emphasis> and <Emphasis Type="Italic">Arrhenatherum elatius</Emphasis>

Tall expansive grasses act as serious weeds since they spread intensively and are a important threat to biodiversity of various plant communities. A field experiment was set up based on three sets of paired plots, where Calamagrostis epigejos and Arrhenatherum elatius dominated and a mixture of both these tall grasses occurred. Parallel plots were treated by additional amounts of nitrogen (50 kg N ha⁻¹) for six years (2002–2007). Above-ground biomass was harvested in both wet (2004) and dry (2007) years, separated in individual fractions, and weighed to determine the above-ground biomass. We wanted to know if a higher nitrogen availability in dry year can support above-ground growth of expansive tall grasses C. epigejos and A. elatius and what their competitive ability of these tall grasses in mixture is in dry conditions. Drought resulted in a decrease in above-ground biomass production of studied tall expansive grasses, and, in a relative increase in mortality of A. elatius shoots in comparison with C. epigejos. Drought can substantially reduce the effect of applied nitrogen on above-ground growth of expansive tall grasses. However, A. elatius appears to be producing more above-ground biomass after application of N even in relatively dry conditions.     

Cultivation of Miscanthus under West European conditions: Seasonal changes in dry matter production,nutrient uptake and remobilization

There is increasing interest in cultivation of Miscanthus as a source of renewable energy in Europe, but there is little information on its nutrient requirements. Our aim was to determine the nutrient requirement of an established Miscanthus crop through a detailed study of nutrient uptake and nutrient remobilization between plant parts during growth and senescence. Therefore dry matter of rhizomes and shoots as well as N, P, K and Mg concentration under three N fertilizer rates (0, 90, and 180 kg N ha-1) were measured in field trials in 1992/93 and at one rate of 100 kg N h-1 in 1994/95.Maximum aboveground biomass in an established Miscanthus crop ranged between 25-30 t dry matter ha-1 in the September of both trial years. Due to senescence and leaf fall there was a 30% loss in dry matter between September and harvest in March. N fertilization had no effect on crop yield at harvest. Concentrations of N, P, K and Mg in shoots were at a maximum at the beginning of the growing period in May and decreased thereafter while concentrations in rhizomes stayed fairly constant throughout the year and were not affected by N fertilization.Nutrient mobilization from rhizomes to shoots - defined as the maximum change in nutrient content in rhizomes from the beginning of the growth period measured in 1992/93 was 55 kg N ha-1, 8 kg P ha-1, 39 kg K ha-1 and 11 kg Mg ha-1. This is equivalent to 21 N, 36 P, 14 K and 27 Mg of the maximum nutrient content of the shoots. Nutrient remobilization from shoots to rhizomes defined as the increase in nutrient content of rhizomes between September and March measured in 1994/95 was 101 kg N ha-1, 9 kg P ha-1, 81 kg K ha-1 and 8 kg Mg ha-1 equivalent to 46 N, 50 P, 30 K and 27 Mg of nutrient content of shoots in September. Results showed that nutrient remobilization within the plant needs to be considered when calculating nutrient balances and fertilizer recommendations.     

δ13C analysis of phloem sap carbon: novel means of evaluating seasonal water stress and interpreting carbon isotope signatures of foliage and trunk wood of Eucalyptus globulus

A recently described phloem-bleeding technique was used to study seasonal changes in δ¹³C, sugar levels and the amino acid:sugar balance of phloem translocate of 2- to 3-year old trees of Eucalyptus globulus at a rain-fed site (Eulup) and a waste-effluent-irrigated site (Albany) in south-west Australia. δ¹³C of phloem sap from the Eulup site fluctuated widely between winter (−27.6‰) and peak summer stress (−20.2‰), compared with a much smaller range of −28.4 to −26.3 at Albany. Seasonal changes in sugar concentrations in sap fluctuated closely with those of phloem δ¹³C, with highest concentrations and least negative δ¹³C values at times of greatest soil water deficit. Molar ratios of amino acids to sugars in phloem sap were similar between plantations in winter through to early summer. They then remained high at the nitrogen-rich effluent-treated site, but fell dramatically once soils dried out at Eulup. Mature leaf dry matter sampled at peak yearly stress (early autumn) showed more negative δ¹³C values than concurrently harvested phloem sap or recently initiated shoot apex dry matter, presumably because the sampled foliage had laid down its structural carbon earlier under relatively unstressed winter/spring conditions. Differences between Albany and Eulup were much greater for δ¹³C of phloem and new apical dry matter than for dry matter of mature foliage. Comparisons of δ¹³C signatures of phloem sap carbon with those of dry matter of nascent xylem tissues showed seasonal fluctuations in δ¹³C of phloem translocate which were mirrored a month or so later by those for xylem carbon. δ¹³C analyses of trunk growth rings from Eulup and Albany showed well-defined seasonal oscillations over the first 2 or 3 years of growth until irrigation commenced at Albany. Fluctuations in δ¹³C at the latter site then became noticeably less pronounced than at Eulup. Future use of phloem sap δ¹³C and solute analyses for studying seasonal water and nutrient status of E. globulus is discussed. Received: 9 April 1998 / Accepted: 20 August 1998     

扎龙湿地芦苇种群不同龄级根茎构件的季节动态

克隆植物根茎具有营养繁殖和扩展种群的功能,也是芽和分株生理整合的通道。根茎构件具有出生、死亡及年龄等种群统计特征,不同龄级根茎的季节动态可以反映根茎的存活和衰老过程。采用单位土体挖掘取样,对扎龙湿地4个生境芦苇种群根茎构件进行野外调查,比较不同龄级根茎长度、生物量和干物质贮量的季节动态。结果表明:7—10月份,1a根茎长度、生物量和干物质贮量均呈指数函数增加,在生长季中后期有一个持续时间较长的生长和物质积累时期。6—10月份,2a、3a根茎长度呈线性函数增加,4—6a根茎长度呈线性函数减少;2—4a根茎生物量和2—5a根茎干物质贮量呈二次函数先减少后增加,5a、6a根茎生物量和6a根茎干物质贮量呈幂函数减少。整个生长期内,根茎长度和根茎生物量均以3a最大,根茎长度以最高的6a最小,根茎生物量以最低的1a最小;根茎干物质储量以5a最大,以最低的1a最小。4个生境芦苇种群根茎长度、生物量和干物质贮量在龄级间的差异及差异序位稳定,在新根茎的产生、老根茎的存活以及根茎寿命与养分消耗和储藏上均具有稳定的生物学特性,不同龄级根茎在种群中的地位和作用以及对种群的贡献不同。     

扎龙湿地不同生境芦苇种群根茎数量特征及动态

采用单位土体取样,计测长度和生物量的调查与统计方法,对扎龙湿地保护区4个生境芦苇种群根茎数量特征进行比较分析。结果表明,芦苇5月10日左右返青后进入营养生长期,根茎长度6—8月份缓慢增加,8—10月份显著增加,后期是前期的3.5—10.3倍,生长季中后期是种群新根茎补充和生长的主要时期,不仅实现了种群空间扩展,并为营养繁殖储备更多繁殖芽;根茎生物量和干物质贮量6—8月份逐渐减少,8—10月份又逐渐增加,均以生长季末期的10月份最大,并均显著地(P0.05)高于其他月份,种群根茎养分的消耗主要供给根茎芽的萌发和幼株生长,根茎养分的储藏又为翌年种群的更新及扩展提供物质保障,种群对地下根茎存在明显的养分"超补偿性"贮藏现象。种群根茎长度和生物量均以湿生生境最大,依次为旱生生境、水生生境,盐碱生境最小,根茎干物质贮量以旱生生境最大,依次为湿生生境、水生生境,盐碱生境最小。种群根茎长度与返青后实际生长时间之间均较好地符合直线函数关系,种群根茎生物量和干物质贮量与生长时间之间较好地符合二次曲线函数关系,R2在0.804—0.997之间,拟合方程均达到了显著或极显著(P0.01)水平。4个生境芦苇种群在根茎长度、生物量、干物质贮量等数量特征均表现出由遗传因素控制的比较稳定的季节动态规律,在生境间的差异及其差异序位又均基本稳定,均表现出明显的土壤因子环境效应,其中土壤含水量、有机质、速效氮为正向驱动,p H、速效磷为负向驱动,土壤含水量、p H对根茎数量特征的驱动作用更突出。     

Flower removal increases rhizome mass in natural populations of Alstroemeria aurea (Alstroemeriaceae)

Plant architecture and phenotypic plasticity under natural conditions remain little known for many rhizomatous species. This study evaluates, in situ, the plastic responses of Alstroemeria aurea plants from three Patagonian populations to flower or flowering-shoot removal. The size and architecture of treated and untreated plants were assessed. Nutrient contents (N, P and K) were evaluated for rhizomes and roots developed in two successive years. Those plants that were deprived of their inflorescences developed, on average, a heavier rhizome than both control plants and plants from which flowering shoots had been removed. Neither of the two treatments applied altered the number of metamers or the branching pattern of the rhizomes. The contents of N, P and K were higher in rhizomes than in roots. In summer, nutrients were more concentrated in inflorescences and the new rhizome segment than in the rhizome segment developed in the previous year. The idea that fruiting failure in A. aurea promotes resource re-assignment from aerial shoots to rhizomes without altering the architecture of plants is supported. The development of the underground portion of aerial shoots in late summer-autumn allows A. aurea plants to take full advantage of short growth periods, but would impose a limit to plasticity.     

THE DISTRIBUTION AND ACCUMULATION OF SELENIUM IN ROOTS AND SHOOTS OF PLANTS NATURALLY GROWN IN THE SOILS OF KEBAN’S PB-ZN-F MINING AREA,TURKEY

The objective of this study is to determine the distribution factors and enrichment coefficients between soil and plant parts by studying the accumulation and distribution of selenium (Se) in the roots and shoots of different plants. The plants (9 samples of Euphorbia macroclada, 5 samples of Verbascum cheiranthifolium, 8 samples of Astragalus gummifer) and their associated soil samples were collected from the Keban mining area. The roots and the shoots of these plants, together with the associated soils, were analyzed by ICP-MS. The mean Se value of the contaminated surface soils was found to be two to five times higher than those of previously studied uncontaminated surface soils. Se concentrations of the plant parts were lower than those in their associated alkaline soils, where the plants were grown, except for in the shoots of A. gummifer. Mean Se concentrations in the roots of E. macroclada, V. cheiranthifolium, and A. gummifer were 0.82, 0.22, and 0.47 mg kg^?1 on a dry weight basis, respectively, while Se concentrations were 0.29, 0.26, and 2.66 mg kg^?1 in the shoots on a dry weight basis, respectively. The enrichment coefficients and the distribution factors of those plants were lower than 1, except for the distribution factors of V. cheiranthifolium and A. gummifer plants. Thus, it appeared that the shoots of these plants could make them efficient bioaccumulator plants for Se because of high distribution factors and enrichment coefficients. Due to such factors, they can also be used to clean or rehabilitate soils and areas contaminated with Se.     

Influence of shade timing on an Equisetum arvense L. population

Equisetum arvense L. is a perennial pteridophyte that grows in open sites. In Tokyo, the plant has photosynthetic shoots from late March to November. However, in some populations, these shoots are lost before summer because of shading by taller plants. To investigate the contribution of shoots that remain on the plant for a certain duration, in terms of the maintenance of the E.arvense population, tubers were cultivated under different light conditions and the dry weight of growth, photosynthetic rates and respiration rates were measured. Individual growth was simulated on the basis of matter production and its partitioning. Biomass at the start of the next growing season (the initial size) was seriously decreased by shading before July. However, shading after July had little effect on the initial size of the next season plants. Thus, E.arvense can maintain its population if its shoots are retained until summer.     

Seasonal patterns of partitioning and remobilization of 14C in the invasive rhizomatous perennial Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decraene)

Resource partitioning between shoot growth, storage and reproduction is poorly understood in many clonal plant species. This study documents seasonal patterns of growth, ¹⁴C-labelled photoassimilate distribution and remobilization in the invasive rhizomatous species Fallopia japonica (Japanese knotweed). Biomass accumulation above- and below-ground in F. japonica was rapid. By September, rhizome biomass had increased 18-fold from the initial harvest in May (representing 48% of total plant biomass) and this was maintained over winter. Patterns of ¹⁴C allocation from F. japonica shoots labelled at different times of year show that as the season progressed, the rhizomes became an increasingly important sink for current assimilate (the percentage of ¹⁴C recovered from rhizomes was 35% in August and 67% in September) and the corresponding retention of assimilate by established shoots declined. The percentage of ¹⁴C exported to roots was greatest in August. Relatively little photoassimilate was exported to other shoots on the plant, or to flowers. Recycling of photoassimilate was fairly tight in this species and ¹⁴C fixed by shoots in early May 1999 or September 1999 was remobilized to the rhizome prior to shoot senescence and death. Some of this ¹⁴C was then remobilized to new shoots early the following spring. These characteristics may contribute to the success of F. japonica in colonizing a variety of contrasting habitats, often with serious management implications.