Density- and growth stage-dependent responses to defoliation in two rhizomatous grasses

Summary Responses to defoliation were studied in two tallgrass prairie perennials (Andropogon gerardii and Panicum virgatum) established from seed at three densities. P. virgatum was also grown from transplanted rhizomes of established clones. Plants of both species displayed a continuum of responses to defoliation, from large reductions in biomass, tillering and seed production to significant increases in one or more performance measures. In crowded populations, defoliation shifted plants into subordinate positions within the competitive hierarchy. Plants competing intraspecifically and those that were initially small suffered more from defoliation than either plants grown at low density or those that were larger than their neighbors. At the highest plant density, the effects of defoliation or initial plant size were overshadowed by the effects of crowding. When defoliated and grown at similar densities, P. virgatum and A. gerardii grown from seed showed large reductions in biomass, seed production, and new rhizome production, but established P. virgatum ramets grown from rhizomes showed increases in these performance measures. Thus, herbivory may be particularly detrimental to P. virgatum during juvenile stages before perennating organs have developed. Overcompensation of P. virgatum clones in response to defoliation only occurred if all ramets within the clone were defoliated. In clones containing both defoliated and undamaged ramets, there were no differences in their performance, suggesting that genets are capable of integrating the effects of differential defoliation among shoots. Defoliated P. virgatum clones allocated a smaller fraction of their total biomass to new rhizomes, indicating that the short-term regrowth response following defoliation may incur a longer-term cost associated with gradual reduction in biomass of the perennating organs and reduced genet success.     

Allocation strategies and seed traits are hardly affected by nitrogen supply in 18 species differing in successional status

Species performance depends on ecological strategies, revealed by suites of traits, conferring different relative ecological advantages in different environments. Although current knowledge on plant strategies along successional gradients is derived from studies conducted in situ, actually quantifying these strategies requires disentangling the effects of environmental factors from intrinsic differences between species.Here we tested whether allocation strategies and seed traits differ among successional stages and nitrogen levels. To this aim, we assessed biomass and nitrogen allocations and seed traits variations for 18 species, differing in life history and belonging to three stages of a Mediterranean old-field succession. These species were grown as monocultures in an experimental garden under limiting and non-limiting nitrogen supply.Early successional species allocated allometrically more nitrogen and proportionally more biomass to reproduction, and set more seeds than later successional species. Seed mass increased with successional status and was negatively related to seed number. Early successional species thus produced more but less-provisioned seeds, suggesting better colonization abilities. These patterns were not the sole consequence of the replacement of annuals by perennials along the successional gradient, since comparable trends were also observed within each life history. Allocation patterns were generally not altered by nitrogen supply and the higher nitrogen content in vegetative organs of plants grown under high nitrogen supply was not retranslocated from leaves to seeds during seed development.We therefore conclude that differences in plant ecological strategies in species characteristics from contrasting successional stages appear to be intrinsic properties of the studied species, and independent from environmental conditions.     

A Comparison of Aluminum Resistance among Polygonum Species Originating on Strongly Acidic and Neutral Soils

Two kinds of Polygonum species (Polygonum aviculare L. and Polygonum lapathifolium L.) grown in tea garden soils at pH around 3.5 and one Polygonum bungeanum Turcz grown in neutral soils were collected to investigate the mechanisms involved in their high Al resistance. Hydroponic experiments showed that the root elongation was only inhibited by 15% in P. aviculare and 35% in P. lapathifolium after exposure to 50 μM Al for 24 h. Their Al resistance was respectively higher than and similar to that in an Al resistant buckwheat (Fagopyrum esculentum Moench) cultivar. In contrast, P. bungeanum was much more Al sensitive since the root elongation was inhibited by 80% under the same condition. The difference in Al resistance among Polygonum species was confirmed in a 10-d intermittent Al treatment experiment, the root biomass of the first two species were unaltered and decreased by 50% in the latter species. However, high Al accumulation was not found in the leaves, indicating these species were not Al accumulators. Oxalate efflux was detected in root exudates of both Al resistant species, efflux initiated within 30 min treatment of 50 μM Al. No organic acid anions were detected in the root exudates of the Al sensitive species. The anion channel inhibitor phenylglyoxal (PG) inhibited the oxalate efflux greatly. Inhibition of root elongation was greater in the presence of PG, confirming that oxalate efflux was associated with the Al resistance. However, since the efflux rate was much lower than their related species buckwheat, other mechanisms must be involved in Al resistance and these need to be studied further.     

中国蓼属植物二新种

报道了中国蓼属两新种。蜀蓼（Polygonum shuense）与大理蓼（P.subscapsum）相似,但基生叶的基部渐狭,沿叶柄下延,边缘具圆齿,花白色,花柱3,离生,瘦果长卵形,无光泽可以区别。察隅蓼（P.chayuum）产西藏,这个新种的茎不分枝,自基部至中部无叶,仅有托叶鞘,叶着生于茎的上部,这些特征奇特,明显不同于其它种类。     

Dynamic phenotypic plasticity for root growth in Polygonum: a comparative study

Species differences in patterns of phenotypic plasticity may be an important aspect of adaptive diversity. Plasticity for functionally important root traits was studied in inbred field lineages of Polygonum persicaria and P. cespitosum (Polygonaceae). Replicate seedlings were grown in plexiglass rhizotrons under a range of constant and temporally variable moisture treatments. Plasticity was determined for final whole-plant biomass, root biomass allocation, and absolute and proportional root length. The dynamic aspect of root plasticity was examined by digitizing weekly tracings of the proportional deployment of each plant's root system to different vertical soil layers. Plants of both species expressed significant functionally adaptive phenotypic plasticity in the relative allocation, length, and vertical deployment of root systems in response to contrasting moisture conditions. Plasticity patterns in these closely related species were in general qualitatively similar, but for most traits differed in the magnitude and/or the timing of the plastic response. Dynamic changes in root deployment were more marked as well as faster in P. persicaria. Species differences in patterns of individual plasticity were generally consistent with the broader ecological distribution of P. persicaria in diverse as well as temporally variable moisture habitats.     

Stem Elongation Response to Neighbour Shade in Sprawling and Upright Polygonum Species

Shading by neighbouring plants, which reduces energy for photosynthesisand lowers the ratio of red:far red light, can trigger a stemelongation or ‘overtopping’ response in herbaceousplants. We compared the stem elongation response of two Polygonumspecies in a greenhouse experiment. P. sagittatum, a sprawling,vine-like annual, and P. hydropiperoides, an upright perennial,were grown from seeds at three levels of neighbour shade producedby crowding a cohort of real neighbour plants or adult-sizedfake neighbour plants that provided shade and reduced the red:far-redratio. We hypothesized that the annual would show a more pronouncedelongation response to developing or adult neighbour shade becausevine-like plants are less mechanically constrained to remainupright and self-supporting. Internodes on stems of bothP. sagittatumand P. hydropiperoides increased in length as the amount ofshading by real or fake neighbours increased. P. sagittatumclimbed on adjacent plants, and had longer stems with more nodesthan those of P. hydropiperoides. Although both P. sagittatumand P. hydropiperoides tended to elongate with crowding, thegreater elongation response to both real and fake neighboursshown by the sprawling annual reflects its ability to extendupward into a canopy beyond self-supporting height. Self-supportingP. hydropiperoides can extend upward with, or overtop, cohortneighbours, but might less readily elongate into an extant canopy.In dense stands, P. sagittatum can become structurally dependenton close P. hydropiperoides neighbours. Our results suggestthat the elongation response of P. sagittatum to neighbourscan contribute to structural dependence and could facilitatecoexistence of these species.Copyright 2000 Annals of BotanyCompany Neighbour effects, light variation, red:far-red, plant growth strategy, Polygonum sagittatum, Polygonum hydropiperoides, smartweeds     

Populational dynamics of three annual species of alpine plants in the Rocky Mountains

Summary Survivorship, fecundity, and seed bank size were measured over two years in alpine populations of the annuals, Koenigia islandica, Polygonum confertiflorum, and P. douglasii. The major loss of individuals from all populations occurred between seed dispersal and germination. Survival of vegetative plants to maturity was high in all species, usually above 80%, and the average number of seeds produced per plant was less than 10 in all species in both years. Seed banks existed for all three species but were small since more than 80% of the viable seeds in the soil germinated in the spring. Both survival and fecundity were negatively correlated with density in P. confertiflorum. These patterns of population dynamics are similar to those found in many annuals of temperate environments.     

Ultrasculpture of achene surface in Polygonum section Polygonum (Polygonaceae) in Russia

Based on SEM examination of 47 specimens and 33 species from Russia and Europe, this is a survey of achene surface ultrasculpture in 6 subsections of annual species of Polygonum. Early and late achenes detected in most species possess sound distinctions in achene shape, size, color and exocarp structure. Late achenes with early and fast seed germination preserve exocarp structure typical for premature achenes of both types: thin colorless walls and vast cavities, thin cuticle and insignificant wax deposits. Early achenes destined for long-term preservation in soil are thickwalled and covered with thick and smooth cuticles and wax layers. The structure of achene surfaces changes substantially during maturing, especially in early achenes: coarse or foveo-rugulate background becomes minutely rough, foveosmooth or minutely reticulate. Verrucae are not obligatory ornaments. Depending on their location and arrangement of exocarp cells the surface is evenly verrucate (subsect. Paatula Tzvel.), linear-verrucate (subsect. Salsuginea Tzvel.) or striate-verrucate (subsect. Humifusa Tzvel., most species in subsect. Polygonum ). Smooth and glossy achenes are more common in permanently wet environments (subsect. Maritima Tzvel., Arenaria Tzvel., P. arenastrum and P. calcatum from subsect. Polygonum ). In places with fluctuating availability of water the achenes have heavier sculpturing and thicker cutin and wax coverings. A broad range of surface sculptures in some species and their similarity across taxonomically distant taxa decrease the value of the characters for taxa identification.     

Effects of microsite conditions on seedling establishment on the foreland of Coleman Glacier,Washington

Abstract. Questions: How do physical microsite conditions of microsites affect germination and seedling survival in different successional stages? Do different species germinate in similar microsites in a given successional stage? Location: Coleman Glacier foreland, Mount Baker, Washington State, USA. Methods: Two methods were used to characterize safe sites. 1. Grids of 300 10 cm × 10 cm plots were located in four different age classes on the foreland. 2.105 pairs of plots, with and without seedlings of Abies amabilis, were located in each age class. For each plot we identified all seedlings and all individuals < 1 m tall. Microsite characteristics such as topography and presence of rocks or woody debris were noted for each plot. Microsite characteristics were compared between plots with and without each species. In addition we examined the effect of distance from seed sources on the presence of Alnus viridis seeds and seedlings in a newly disturbed area. Results: In early successional sites, seedlings of several species were positively associated with depressions and presence of rocks, and negatively associated with ridges. Patterns were generally consistent among species. In later succession, seedlings were not significantly associated with any microsite characteristics. For Alnus viridis, seed density decreased with distance from seed sources but seedling density did not. Conclusions: Because of harsh conditions in early succession, physical microsites are important, and most species have similar microsite requirements. In later succession, physical microsites characteristics are not as important and are more variable. Microsites appear to be more important than seed rain in controlling the distribution of Alnus viridis in early succession.     

Effects of arbuscular mycorrhizal fungi and soil developmental stages on herbaceous plants growing in the early stage of primary succession on Mount Fuji

A pot culture experiment was conducted to examine the effects of arbuscular mycorrhizal (AM) fungi and soil developmental stages on the growth and nutrient absorption of pioneer plants growing in the early stage of primary succession on Mt. Fuji. Four herbaceous plants, Polygonum cuspidatum (Polygonaceae), Miscanthus oligostachyus (Gramineae), Aster ageratoides var. ovatus (Compositae), and Hedysarum vicioides (Leguminosae), were grown from seed in soils collected from two different successional stages, bare ground and an herbaceous plant community. Spores of indigenous AM fungi collected from the herbaceous plant community were used as inoculum. The initial colonizer P. cuspidatum showed very low levels of AM colonization (<0.4%), whereas the average AM colonization levels of M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides were within the range of 13–49%. AM fungi had positive effects on the growth and N acquisition of the leguminous species (H. vicioides) irrespective of soil developmental stages. In contrast, AM colonization did not increase the plant dry weight and N content of the non-leguminous species (P. cuspidatum, M. oligostachyus, and A. ageratoides var. ovatus) in both soil developmental stages. A positive effect of AM colonization on P content was observed in M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides only in soil collected from the herbaceous plant community. P. cuspidatum showed no or a negative response to AM colonization in all cases. These results suggest that the effect of AM fungi on plant growth depends more on the plant species than soil developmental stages in the early stage of primary succession in this volcanic area.     

Phenotypic Plasticity in the Annual Weed Polygonum aviculare

Reaction norms of fourteen life history and morphological traits were investigated in four tetra- and two hexaploid genotypes of the annual weed species complex, Polygonum aviculare. The plants were cultivated in six treatments consisting of factorial combinations of three pot sizes and two fertility levels. All characters, except life span, were plastic but the relative importance of genotype (G), treatment (T) and interaction (G × T) to total variance was strongly trait-specific. Consistent genetic differentiation, not correlated with ploidy level, was found in metamer size and life history: genotypes originating from trampled sites had smaller metamers and shorter shoots while those originating from sites with a short growing season, due to weeding activities, had a shorter life span, an earlier flowering date and a higher biomass allocation to reproduction compared to genotypes from less disturbed sites. Significant variation was found in reaction norms for all characters, including a lower amount of plasticity in metamer size in genotypes with numerous metamers and a lower amount of plasticity in total weight in shortlived genotypes. This suggested that variation in phenotypic plasticity reflected developmental constraints imposed by contrasting life span and metamer size in different genotypes. There was no evidence for niche differentiation along the soil resource gradient, suggesting that the species is comprised of “general purpose” genotypes with respect to soil fertility. It is concluded that the Polygonum aviculare complex has evolved a “dual” adaptive strategy i.e. a combination of genetic polymorphism and high phenotypic plasticity.     

PERSISTENCE OF AMBROSIA TRIFIDA POPULATIONS IN OLD FIELDS AND RESPONSES TO SUCCESSIONAL CHANGES

A population of Ambrosia trifida L. (Asteraceae) in an annually ploughed field and an adjacent 15-year old population in an old field were compared to determine how plant responses, genotypic composition, and genetic variability change in populations over successional time. The two populations were originally part of a large contiguous population in an annually ploughed field. When individuals from the two populations were grown from seed in a common garden, they showed several significant differences in characteristics indicating different genotypic compositions in the two populations. Individuals from the old field population showed earlier emergence, lower leaf mortality, and greater numbers of leaves, biomass, seed production, and reproductive allocation relative to plants from the annually ploughed field. When sown in the field in a reciprocal transplant experiment, individuals from the two populations also differed in patterns of emergence, survivorship, yield, and fecundity. When grown together in a pairwise competition experiment, individuals from the old field population showed competitive superiority with respect to growth and seed production. This genetic differentiation between populations of different successional ages may be explained by natural selection imposed by the changing environment over successional time. However, the history and characteristics of these populations are such that founder effects may also be important in explaining the differences between them. A comparison of levels of variability in 14 different characters of individuals of the two populations showed no evidence that genetic variability in A. trifida populations declined over successional time.     

三江平原恢复湿地土壤种子库特征及其与植被的关系

通过幼苗萌发法和样方调查相结合的方法对三江平原不同演替恢复阶段的种子库特征及其与植被的关系进行了研究。将开垦湿地、不同演替恢复阶段湿地以及天然湿地不同土壤层次(0-5、5-10 cm和根茎)的种子库在两种水分条件下(湿润、淹水10 cm)进行萌发处理。结果表明: 随着演替恢复阶段的进行, 种子库的结构和规模逐渐扩大, 地表群落表现出由旱生物种占优势的群落逐渐演变成以小叶章(Calamagrostis angustifolia)占优势的湿生群落的演替趋势。恢复7年湿地、恢复14年湿地、天然湿地土壤种子库萌发物种数分别为24种、29种、39种, 植被物种数为21种、25种、14种。湿地类型、水分条件和土壤层次均显著影响种子库萌发的物种数及幼苗数(p < 0.01)。种子库具有明显的分层现象, 天然湿地0-5 cm土层种子库种子萌发密度是5-10 cm土层的4倍左右, 而恢复湿地仅1.3倍左右, 且土层间萌发物种相似性系数较低。湿润条件下的萌发物种数显著高于淹水条件, 且两种水分条件下萌发物种的生活型不同。由于恢复时间较短, 不同演替恢复阶段的种子库与植被相似性维持在30%以下。湿地中根茎分蘖出大量的湿地物种, 对于小叶章等优势物种的繁殖具有重要作用。研究表明, 在开垦湿地退耕后的次生演替阶段, 种子库能够保持大量的湿地物种, 通过对湿地种子库与植被的关系研究, 能够为三江平原湿地群落演替与湿地恢复提供策略指导。     

Seed-bank and dynamics of a Polygonum hydropiper L. community along the Po river (Central-West Italy)

ABSTRACT

The seed-bank and the dynamics of a Polygonum hydropiper L. community were investigated. The study area is located along the Po river in the Central-West Po plane (Northern Italy), in Piedmont, near Alessandria. The seed-bank in the soil was investigated by means of a simplified procedure of seasonal sampling and germination tests while the dynamics of the Polygonum community was investigated within a permanent square. Results indicate that: i) The Polygonum hydropiper community has strong growth potential because it has a source of biodiversity in its reservoir of germinable seeds of different species. River overflows act both as disturbance and as vectors for propagules, selecting the species that can grow and develop within the vegetation, and the species that will be left as seeds in the soil; ii) species diversity and dominance vary with vegetation stage (seed bank, pioneer stages and mature stages); iii) two types of seed-bank were present in the soil we analysed: a transient one and a persistent one.     

The effects of seed weight on growth and competitive ability of Rumex acetosella from two successional old-fields

Summary The effects of seed size on growth, biomass allocation and competitive ability of Rumex acetosella plants grown either individually or in competition were studied in two populations (6 months and 15 years old respectively) sampled from a postcultivation successional gradient. For plants grown individually there were highly significant effects of seed weight on growth after 43 days, with a higher relative growth rate (RGR) observed for plants raised from heavier seeds. However at the end of the experiment, seedlings developed from lighter seeds had a RGR 2 times greater than those from heavier seeds. Final biomass of the two types was not significantly different after 73 days of growth. When plants were grown individually, there were only slight differences between populations, but when grown in monocultures of 4 plants per pot, plants from the old population had higher root and leaf biomass per pot whereas those from the young population had a higher reproductive effort per pot. This suggests that a trade-off between allocation to sexual and vegetative reproduction occurs over successional time. In mixtures of light and heavy seeds, plants from light seeds were shorter, had fewer leaves and lower biomass than plants from heavy seeds, which were also taller and produced more dry matter than plants grown from heavy seeds in monoculture. The significant effects of seed weight and population on biomass parameters persisted unit the end of the experiment. Seedlings from heavy seeds were strong competitors: those from the young population grew better in the presence of neighbors than in monoculture and those from the late successional population suppressed the more the growth of their partners. Seedlings from light seeds were subordinate competitors. These results suggest that seedlings from seeds of different sizes benefit from contrasting ecological conditions and that selection acts on reproductive output along successional gradients.     

Seed Size,Seed Germination,and Seedling Survival of Brazilian Tropical Tree Species Differing in Successional Status1

Seed germination and seedling establishment patterns have been used to classify species as shade tolerant or intolerant. The main objective of this research was to investigate, under controlled conditions, seed germination of species from different successional positions as well as to follow seed germination and seedling survival under natural shade in the field. The species studied were Solarium granuloso‐leprosum, Trema micrantha, Cecropia pachystachya, Croton piptocalyx, Bauhinia forficata subsp. pruinosa. Senna macranthera, Schizolobium parahyba, Piptadenia gonoacantha, Chorisia speciosa, Pseudobombax grandiflorum, Ficus guaranitica, Esenbeckia leiocarpa, Pachystroma longifolium, Myroxylon peruiferum, and Hymenaea courbaril. Field trials were carried out at Santa Genebra Municipal Reserve, Campinas, SP, Brazil, at the forest edge and in the understory. No significant correlations were detected between successional status and seed size or seed water content. Light‐regulated germination was present only in small‐seeded species. In field experiments, most species, including the light‐sensitive ones, were able to germinate under the canopy, where a low red/far‐red ratio predominates. Most species, mainly those of early‐ and intermediate successional positions, presented low seedling survival rates under shade. Myroxylon peruiferum was the most shade tolerant species, while 5. granuloso‐leprosum, C. speciosa, P. gonoacantha, F. guaranitica, T. micrantha, and 5. parahyba were the most shade intolerant. These latter species showed little or no survival under the shade conditions.     

Development of polymorphic microsatellite markers in a perennial herbaceous plant,Polygonum cuspidatum (Polygonaceae)

Six single‐locus, polymorphic microsatellite markers in a perennial herbaceous plant, Polygonum cuspidatum, were developed. Tests to amplify these six loci in another Polygonum species failed, suggesting that the six markers are specific to P. cuspidatum.     

CHROMOSOMAL ANALYSES AND THE ORIGIN OF ALLOPOLYPLOID POLYPODIUM VIRGINIANUM (POLYPODIACEAE)

Polypodium virginianum L. has been treated as a morphologically and chromosomally variable species. Recently, however, two species have been named from within the P. virginianum complex. Chromosome counts reported here confirmed that these segregate species, P. appalachianum Haufler and Windham and P. sibiricum Siplivinskij, are diploids with n = 37. It was further hypothesized that hybridization between these diploids initiated the allotetraploid P. virginianum. Naturally occurring, sterile triploid plants obtained from habitats in which the putative allotetraploid was sympatric with its presumed diploid progenitors have been verified isozymically as backcross hybrids. Meiotic chromosomal behavior showed that the triploids contained univalents and bivalents in nearly equal numbers, confirming that tetraploid P. virginianum contained one genome from each diploid. Observation of three to six trivalents in triploid preparations suggested that the diploids are still closely related genetically. This hypothesis was supported by isozymic studies which found a genetic identity of 0.610 between P. appalachianum and P. sibiricum, a value much higher than the average identity for congeneric fern species studied to date (0.33) and higher than any other species pair in the P. vulgare L. complex (average I = 0.307). These chromosomal and isozymic data help to resolve a biosystematic riddle that has interested pteridologists for over 40 years.     

<Emphasis Type="Italic">Polygonum viviparum</Emphasis> mycobionts on an alpine primary successional glacier forefront

Polygonum viviparum is one of the first ectomycorrhizal (EM) plant species colonising primary successional sites at the Rotmoos glacier forefront (Tyrolean Alps, Austria). On a site with soil development of about 150 years (2,400 m above sea level), mycobionts of P. viviparum were identified by morphotyping and fungal ribosomal deoxyribonucleic acid internal transcribed spacer sequencing. For studying seasonal dynamics and spatial heterogeneity, ectomycorrhizae were sampled on five plots during all seasons. P. viviparum root tips were always EM. In total, 18 mycobiont taxa of the following genera were identified: Cenococcum (1), Cortinarius (2), Helvella (1), Inocybe (3), Russula (1), Sebacina (2), Thelephora (2) and Tomentella (6). All were non-specific EM partners of EM plants. As early as 2 weeks after spring snow melt, EM were well developed, vital and showed high mycobiont diversity. The relative abundance of senescent root tips was lowest in spring and increased throughout the year, with a maximum in winter (frozen soil). Thus, mycobiont growth and physiological activity obviously start when soil is still under snow cover: We speculate that water availability is one important initiation factor for mycorrhizal development under snow cover, when temperatures still range around the freezing point. Irrespectively of the season, most abundant mycobionts at this primary successional site belonged to the genera Tomentella, Sebacina and Cenococcum, also in frozen soil. Spatial heterogeneity was high when considering species composition and diversity indices. Overall mycobionts species richness was restricted at this site, probably because of the limited availability of fungal partners. We regard the presence/absence of fungal partner and limiting abiotic impacts of the environment as key factors for the symbiotic status of P. viviparum. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.