Heinjo J. During

Exploitation of environmental heterogeneity by spatial division of labour in a clonal plant.

1. The economic principle of spatial division of labour comprises two basic features, specialization in the performance of specific tasks and close co-operation by potentially independent, spatially separated subunits of a higher-level organizational system. Space-economic theory predicts large benefits from such a spatial division of labour if essential resources are heterogeneously distributed and if high-availability zones for these resources do not spatially coincide. In this paper, evidence is provided that a spatial division of labour may also occur in clonal plants growing in spatially heterogeneous environments. 2. Clonal fragments of the stoloniferous herb Trifolium repens L., consisting of two interconnected groups of ramets, were exposed to contrasting levels of light and water supply. Ramet groups specialized morphologically in the uptake of the locally most abundant resource and they exchanged both water and assimilates. This division of labour significantly increased the performance of the entire plant in terms of fitness-related traits such as biomass and atonal offspring production. 3. It is concluded that spatial division of labour may contribute to the apparent success of clonal plant species in many natural habitats by enabling them to efficiently exploit environmental patchiness. The implications of these results for the understanding of foraging strategies of clonal plants and the general notion of habitat heterogeneity in plant ecology are discussed.

High benefits of clonal integration in two stoloniferous species, in response to heterogeneous light environments

1 In natural habitats, essential resources for plant growth are heterogeneously distributed in space, resulting in environmental patchiness with favourable and less favourable microhabitats. Clonal plants may benefit from their ability to share resources between connected ramets experiencing contrasting levels of resource supply. This hypothesis was tested with clones of Potentilla reptans and P. anserina, consisting of a mother rosette and a number of daughters on an attached stolon, grown under homogeneously high and low light conditions, as well as in spatially heterogeneous light environments in which either mother or daughters were shaded. Biomass data were used to carry out an analysis of the costs and benefits of clonal integration. 2 Both species showed high benefits of integration. In P. reptans, connections to unshaded clone-parts enhanced biomass production of the shaded part. In contrast to the prediction that clonal integration would result in costs to unshaded clone-parts connected to shaded parts, unshaded ramets of both species developed higher instead of lower dry weights when connected to a shaded part. Thus, unshaded ramets actually benefitted from integration. 3 It is hypothesized that these unexpected benefits of integration were due to mutual support of connected clone-parts growing in shaded and unshaded patches. The high evaporative demands of the unshaded clone-parts probably resulted in water being translocated from shaded to unshaded ramets while, at the same time, carbohydrates were translocated from unshaded to shaded ramets. 4 We discuss implications of this suggested bidirectional transport of two different resources for the ecological significance of physiological integration in clonal plants and for the notion of habitat heterogeneity.

Effects of bryophytes on seedling emergence and establishment of short-lived forbs in chalk grassland

(1) Spatial and temporal variation in bryophyte cover and its effect on differentiation of the regeneration niche in a Dutch chalk grassland was investigated. (2) Seedling emergence was negatively correlated with bryophyte cover in Carlina vulgaris, Euphrasia officinalis and to a lesser extent in Linum catharticum; no significant correlation could be found for Gentianella germanica or Scabiosa columbaria. (3) Seedling mortality was lower with high bryophyte cover in Carlina vulgaris and Linum cartharticum. (4) Removal of bryophytes in the previous autumn increased emergence and survival in Linum catharticum, but had no effect on the other species. (5) Radiant flux and red/far-red quotient were shown to be reduced below a bryophyte cover.

Diversity models applied to a chalk grassland

In a permanent plot experiment started in 1971, the effects of several management regimes on diversity of a Dutch chalk grassland have been investigated and the results have been compared to existing models predicting general trends in diversity. Treatments included grazing, mowing, and leaving untouched; in the mown plots, the effects of fertilizing and sod cutting were also studied. Grazing resulted in the highest diversity, leaving untouched in the lowest (ca. 42 and 15 spp. per m2, respectively). Within the mown plots, fertilizing decreased diversity. The effects of sod cutting disappeared after some years. The results conform best with the response surface model of Huston (1979) relating diversity to frequency of population reduction and rate of competitive displacement, but a slight modification of the shape of the surface is suggested.

ON PLASTIC AND NON-PLASTIC VARIATION IN CLONAL PLANT MORPHOLOGY AND ITS ECOLOGICAL SIGNIFICANCE

Morphological plasticity in clonal plants has received wide attention because localized plastic changes in spacer length, branching intensity and branching angle may enable clonal plants to place ramets selectively in the more favourable microhabitats within a heterogeneous environment. These responses have been interpreted in terms of foraging behaviour.Studies of morphological plasticity in clonal plants are usually carried out with one or two genotypes of a species, or with material of unknown genetic origin. Based on the concept of phenotypic plasticity, it is argued that such studies do not reveal whether plasticity in a population can be modified by natural selection. In addition, responses are often evaluated at two environmental conditions only, which may underestimate plasticity. Hence, our information on the ecological and evolutionary significance of morphological plasticity in clonal plants is still very incomplete.Two examples are given to show that stolon internode and rhizome lengths may vary considerably within an individual plant. Only a minor part of this variation may be plastic, i.e. the variation is hardly changed by the environmental conditions to which the plants are subjected. Hence, non-plastic variation in clonal morphology may exceed the degree of morphological plasticity. The non-plastic variation seems to originate from species-specific patterns of stolon and rhizome development.Marked non-plastic variation may obscure the effects of morphological plasticity on the placement pattern of ramets in the field, suggesting that plasticity in clonal morphology may not be very effective in terms of foraging for favourable patches. Possible reasons for the low levels of plasticity of clonal spacers are discussed.

Detect thy neighbor: Identity recognition at the root level in plants

Some plant species increase root allocation at the expense of reproduction in the presence of non-self and non-kin neighbors, indicating the capacity of neighbor-identity recognition at the root level. Yet in spite of the potential consequences of root identity recognition for the relationship between plant interactions and community structure and functioning, this phenomenon still remains poorly understood. We first critically assess the evidence for the existence of self/non-self and kin recognition at the root level in plants. While root identity recognition most likely exists to some degree, there remain valid points of criticism regarding experiments that have documented this, particularly concerning the effects of pot volume in self/non-self recognition experiments and the roles of size inequality and asymmetric competition in kin recognition studies. Subsequently we review and propose some plausible physiological mechanisms that may underlie these responses. Finally we briefly discuss the relation between under- and aboveground interactions and the potential consequences of root identity recognition for agriculture, and conclude with raising several questions for future studies.

Light partitioning among species and species replacement in early successional grasslands.

Abstract We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above-ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan. Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above-ground architecture of these two species. In all stands light capture of plants increased with their above-ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better-lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands ‘later successional’ species had higher light harvesting efficiencies for the same plant height than ‘early successional’ species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves. This shows how plant stature, plasticity in above-ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series. Nomenclature: Makino (1962); Ohwi (1965). Abbreviations: LAI = Leaf area index; LAR = Leaf Area Ratio; LMR = Leaf Mass Ratio; PPFD = Photosynthetically active photon flux density; SLA = Specific Leaf Area.

The reproductive biology of Polytrichum formosum : clonal structure and paternity revealed by microsatellites

Using highly polymorphic microsatellite markers, we assessed clonal structure and paternity in a population of the bryophyte species Polytrichum formosum. Identical multilocus genotypes of individual shoots were almost never observed in spatially separated cushions, but were found to be highly clustered within moss cushions. Therefore, asexual reproduction through dispersal of gametophyte fragments is not very important in P. formosum. However, asexual reproduction on a very localized scale through vegetative growth of genets (branching of gametophytes via clonal growth of rhizomes) is very extensive. The patchy spatial distribution of genets and the absence of intermingling among genets suggest that this species follows a ‘phalanx’ clonal growth strategy. Vegetative proliferation of genets will increase their size, and, consequently, will have considerable fitness consequences for individuals in terms of increased genet longevity and reproductive output. Although paternity analysis of sporophytes confirmed male genet size, i.e. gamete production, to be an important determinant of male reproductive fitness, it also showed that the spatial distance to female genets is the predominant factor that governs male reproductive success. Moreover, we showed that male gamete dispersal distances in P. formosum are much further than generally assumed, and are in the order of metres rather than centimetres. Combining the findings, we conclude that the high genotypic diversity observed for this facultatively clonal species is most likely explained by a preponderance of sexual reproduction over clonal reproduction.

SPATIOTEMPORAL DYNAMICS IN MOUNTAIN GRASSLANDS: SPECIES AUTOCORRELATIONS IN SPACE AND TIME

Permanent plots with a fine scale recording system were used to trace the spatiotemporal process within two mountain grasslands in the Krkonoše Mts., Czech Republic. The analysis used autocorrelation over increasing lags in space and/or time. MoransI was used to measure the autocorrelation. There was a lot of variation between species both in spatial and temporal correlograms. The spatiotemporal pattern of species correlated well with the growth form of the species and the degree of its clonality. Clonally-growing species tended to have high clumping at distances of a few cells, whereas rosette species often did not show any clumping. The type of clonal growth (compact vs. long spacers) is well corrlated, with the temporal correlogram (species mobility). There is a relation between low mobility and high clumping at low distances. Attempts to explain the mechanisms of species coexistence in these grasslands should take into account the particular structure of the fine-scale dynamics of these communities of predominantly clonal plants. *** DIRECT SUPPORT *** A02DO006 00007

Use of rbcL and trnL-F as a Two-Locus DNA Barcode for Identification of NW-European Ferns: An Ecological Perspective

Although consensus has now been reached on a general two-locus DNA barcode for land plants, the selected combination of markers (rbcL + matK) is not applicable for ferns at the moment. Yet especially for ferns, DNA barcoding is potentially of great value since fern gametophytes—while playing an essential role in fern colonization and reproduction—generally lack the morphological complexity for morphology-based identification and have therefore been underappreciated in ecological studies. We evaluated the potential of a combination of rbcL with a noncoding plastid marker, trnL-F, to obtain DNA-identifications for fern species. A regional approach was adopted, by creating a reference database of trusted rbcL and trnL-F sequences for the wild-occurring homosporous ferns of NW-Europe. A combination of parsimony analyses and distance-based analyses was performed to evaluate the discriminatory power of the two-region barcode. DNA was successfully extracted from 86 tiny fern gametophytes and was used as a test case for the performance of DNA-based identification. Primer universality proved high for both markers. Based on the combined rbcL + trnL-F dataset, all genera as well as all species with non-equal chloroplast genomes formed their own well supported monophyletic clade, indicating a high discriminatory power. Interspecific distances were larger than intraspecific distances for all tested taxa. Identification tests on gametophytes showed a comparable result. All test samples could be identified to genus level, species identification was well possible unless they belonged to a pair of Dryopteris species with completely identical chloroplast genomes. Our results suggest a high potential of the combined use of rbcL and trnL-F as a two-locus cpDNA barcode for identification of fern species. A regional approach may be preferred for ecological tests. We here offer such a ready-to-use barcoding approach for ferns, which opens the way for answering a whole range of questions previously unaddressed in fern gametophyte ecology.