Spatial Pattern and Temporal Dynamics of Bryophyte Assemblages in Saline Grassland

Dynamics of bryophyte assemblages of saline grassland were studied in Hungary. A survey was carried out in two permanent plots by annual sampling of 0.25-m² quadrats over a 9-year period. The study investigated: i) the extent of spatial and temporal dependence of the assemblages and individual species; ii) the turnover of individual species and its relationship to life-strategy types and iii) the effect of annual weather conditions on species performance. One of the plots showed succession; the frequency of some perennial species increased, while that of some short-lived species decreased; this process was independent of local weather conditions. The other plot showed a non-directional fluctuation, which was partly related to precipitation in winter and early spring. The spatial and temporal dependence of this assemblage was low; many short-lived species had a high turnover in the studied community. In stable periods, neutral dynamic processes characterize the bryophyte assemblages of the studied saline grassland and the occurrences of species were more or less independent in space and time. Short-lived species showed high fluctuations and were probably influenced by weather conditions or other factors. However, the frequency of perennial species, which were influenced by local conditions, could directionally change displacing the short-lived ones during succession. The relationships between turnover and life-strategy types were weak, both the group of colonist and shuttle species were dynamically heterogeneous. Longer observations are needed for a clearer exploration of the relationships between vegetation changes and weather conditions.     

Altitudinal distribution patterns of bryophytes in the Canary Islands and vulnerability to climate change

We report the pattern of bryophyte distribution through the elevation gradient of three Canary Islands (Fuerteventura, Tenerife and Gomera) assessing their vulnerability risk to climate change. We considered a conservative scenario of upslope climatic shift of 200–400 m and a drop in the upper limit of the cloud belt from 1500 to 1000 m. Climate change vulnerability was analyzed from the overlap between the predicted shift in isotherms or cloud-belt edges and the current species range, following the Colwell and colleagues's model.Liverworts show narrower ranges and tend to live at lower elevations than mosses. Perennials and long-lived shuttle species establish in the upper localities. Many perennials and most of the long-lived shuttle species grow in cloud forests. Many annual shuttle species and colonists establish in the lowest localities. Colonists also occupy the harsh summit in the highest islands.In accordance with the Colwell model, most elements of this bryoflora appears vulnerable to rapid climatic change. Upland extinction and contraction challenges the bryoflora on the driest, lowest island Fuerteventura; range-shift gaps do this on the highest island Tenerife. Liverworts tend to be more vulnerable to range-shift gaps; mosses are more vulnerable to upland extinction. On the lowest island, perennials and long-lived shuttle species are more vulnerable to upland extinction; perennials are also vulnerable to range-shift gaps. Colonists are most vulnerable to upland contraction or extinction on the high islands Gomera and Tenerife. Annual shuttle species tend to be more vulnerable to lowland attrition on these high, most humid islands. Many elements of the bryoflora of the upper limit of the cloud forests appear to be vulnerable, while most of the flora of other cloud forest areas presumably will not be so affected, with the exception of the most restricted species.A simple model illustrates the feasibility of preliminary assessments of climate change on organisms which show a lack of published detailed information on their distribution and biology. This assessment gains by incorporating estimates of biological attributes.     

The interplay of pollination,costs of reproduction and plant size in maternal fertility limitation in perennial <Emphasis Type="Italic">Paeonia officinalis</Emphasis>

Although several factors can limit female fertility in perennial plants, rarely have they been jointly studied in a single species over several years. In this study we experimentally manipulate seed production and simultaneously analyse the potential contribution of pollen limitation, costs of reproduction and plant size to variation in seed output over a 3-year period in the perennial herb Paeonia officinalis, in southern France. Since this rare species is threatened by forest closure in many sites we also examine the causes of female fertility variation in relation to habitat closure (open habitat vs. woodland). P. officinalis has a partial self-incompatibility system and only very low ability for autonomous self pollination in the absence of pollinators. However, supplementary pollination of individual plants in three consecutive years did not significantly increase seed production above natural levels. Forest closure was associated with a decline in ovule and seed production, which again was not due to pollen limitation since supplementary pollination had no significant effect on seed set in the woodland habitat. Comparison of the maternal fertility of plants which were previously excluded from reproduction with those which were hand pollinated to maximise seed set in two previous years produced no evidence that seed production in year three is limited by costs associated with prior reproduction. Likewise, flowering probability was not related to prior seed production but was however positively related to plant size. The absence of any influence of pollen limitation or prior reproduction on seed production suggests that sub-maximal seed production in long-lived perennial herbs may be part of a size-dependent strategy that maximises life-time seed production and fitness without compromising survival.     

Colonization and early succession on anthropogenic soils

Abstract. This paper reports on vegetation development on permanent experimental plots during five years of succession. Nine (1 m²) plots were filled with three typical substrates from man-made habitats of urban and industrial areas in the region of Berlin. The three substrates (a commercial ‘topsoil’, a ruderal ‘landfill’ soil and a sandy soil), differ in organic matter and nutrient contents. Relevés of species composition and percent cover of each species present were made monthly during the growing season from the start of vegetation development. This paper describes the different successional pathways on topsoil and ruderal soil and the colonization process on sandy soil. On topsoil, ruderal annuals are dominant in the first year and are replaced by short-lived perennials from the second year. Those species were replaced by long-lived perennial herbs (Ballota nigra or Urtica dioica) from the third year of succession onwards. On the ruderal land-fill soil the early successional stages are less sharp and the perennial Solidago canadensis is able to dominate within one year after the succession was initiated. On sandy soil there is still an ongoing colonization process, where pioneer tree species like Betula pendula and Populus nigra play a main role. The importance of ‘initial floristic composition’, the role of substrate for community structure and the peculiarities of successional sequences on anthropogenic soils in the context of primary and secondary successions are discussed.     

Association between cacti and nurse perennials in a heterogeneous tropical dry forest in northwestern Mexico

Abstract. The Sierra de La Laguna, Baja California Sur harbors the only tropical dry forest of the Peninsula. An inventory of the perennial plants was carried out at the eastern part of this mountain range. Plant spatial distribution was analyzed considering the species composition and vertical stratification of plant clusters in a study plot of 2 500 m². A plant cluster was defined as a group of at least three individuals with a maximum distance between plants of 1 m. Soil physical-chemical characteristics and soil surface temperatures were compared between shade and sun conditions. The tropical dry forest of Baja California Sur presents a highly aggregated pattern of species distribution. Most of the perennial plants grow clumped, yet not all of the six cactus species recorded were significantly associated with them. Pattern analysis revealed that only Stenocereus thurberii and Ferocactus peninsulae were aggregated and associated to perennial plants. There is no replacement pattern between cacti and perennial plants. Nutrient content, including soil fertility, between shade and sun conditions does not seem to explain the patchy distribution of perennial plants, while the differences in solar radiation between these conditions appear to be restrictive and determinant of this spatial pattern of distribution.     

Flexible life history responses to flower and rosette bud removal in three perennial herbs

In a garden experiment we investigated the response to continuous removal of either flower buds or rosette buds in three perennial grassland species ( Hypochaeris radicata , Succisa pratensis and Centaurea jacea ), which differ in longevity and flowering type. We distinguished two possible responses: compensation for lost buds by making more buds of the same type, and switching towards development of other life history functions. Both responses were demonstrated in our experiment, but bud removal had significantly different effects in each of the three species. The degree of compensation and the expression of trade-offs between life history functions differed markedly between species and seem related to longevity and developmental constraints. With respect to switching, our results suggest costs of reproduction and a trade-off between life history functions, at least for Hypochaeris and Succisa . For these species weight of new rosettes increased when resource allocation to flowering was inhibited. In Hypochaeris, we see that both compensation for lost flower buds and switching from lost rosette buds increased production of flower buds, underscoring the pivotal role of sexual reproduction in this short-lived species. The most prominent response seen in Centaurea is compensation for lost rosette buds, indicating that this long-lived species with monocarpic rosettes relies on rosette formation. Although Succisa does respond to bud removal, time is an important constraint in this species with long-lived rosettes and preformed flowering stalks. Trade-offs in Succisa seem to operate at a larger time scale, requiring long-lasting experiments to reveal them. We conclude that the response of these species to inflicted damage is likely to be linked to their longevity and developmental constraints.     

Seedling emergence and survival in contrasting soil microsites in Patagonian Monte shrubland

Abstract. The potential of two perennial species (Larrea divaricata and Stipa tenuis) to colonize different soil microsites was analyzed in the Patagonian Monte shrubland. We hypothesize that the short-lived grass S. tenuis is more able to colonize the soil of microsites beneath vegetation patches where N-fertility is higher than those in bare soil, while the long-lived shrub L. divaricata colonizes different soil microsites irrespective of their N fertility. A greenhouse experiment was carried out to evaluate the emergence and survival of both species in different soil microsites at different water, inorganic N and seed densities. In all cases soil microsites were seed limited since the addition of viable seeds increased seedling emergence. Both species showed, however, different abilities to emerge and survive in different soil microsites. Microsites of bare soil were more favourable for seedling emergence and survival of L. divaricata than those beneath vegetation patches, independent of their water status. This ability of L. divaricata can not be explained on the basis of increased water or N availability, but probably because of lower salt content of bare soil. The addition of inorganic N reduced the survival of L. divaricata in both microsites but increased individual plant performance. The emergence and survival of S. tenuis was not different in both types of soil microsites but the addition of inorganic N increased seedling emergence and plant biomass. According to these results, emergence and plant performance of S. tenuis may be promoted during humid years by increased concentration of inorganic N. Since N mineralization occurs at a higher rate in soil microsites beneath vegetation patches than in those of bare soil, higher plant performance and probably establishment of S. tenuis is to be expected. These results are consistent with an existing conceptual model of plant dynamics under various grazing intensities in the Patagonian Monte shrubland based on previous field observations.     

Recolonization potential of bryophyte diaspore banks in harvested boreal mixed-wood forest

Bryophyte diaspore banks are a potential source of reproductive propagules that may be able to colonize newly available habitat after forest harvesting. However, their role and the factors influencing the successful establishment of species remain poorly understood. To investigate these aspects of diaspore banks, we obtained mineral soil samples from mixed and coniferous stands of boreal mixed-wood forest in northern Alberta, Canada, which had recently experienced a range of harvesting intensities. Samples were germinated in growth cabinets under two light regimes. The composition of germinated bryophyte species was compared among forest types, harvesting intensities, and light levels, and also related to edaphic conditions and geographic location of the sample site. Germinated species composition was not related to forest type or harvesting intensity, but was associated with measured edaphic variables and geographic space, indicating that similarity in species composition reflected similarity in edaphic conditions and spatial proximity. This was partly because of spatial dependence of edaphic variables. Light intensity had a significant influence on the development of species assemblages and individual species responses. Richness and cover of acrocarpous mosses (fugitive, colonist, and shuttle life-history strategies) were significantly reduced under low light conditions, but pleurocarpous mosses (perennial strategy) were not affected. Shannon diversity and the frequency of reproduction were significantly greater with high light. Pleurocarpous mosses that are characteristic of intact forests germinated frequently, suggesting that diaspore banks may influence their recovery after disturbance. Diaspore banks are a repository of species at sites affected by forest harvesting; however, diaspore germination and establishment will be constrained by the local environment, including edaphic conditions and light intensity.     

Relationship between photosynthetic rate,water use and leaf structure in desert annual and perennial forbs differing in their growth

Specific leaf area (SLA) is a key trait to screen plants for ecological performance and productivity; however, the relationship between SLA and photosynthesis is not always up-scalable to growth when comparing multiple species with different life cycles. We explored leaf anatomy in annual and perennial species of Physaria, and related it to photosynthesis and water loss. The annual Physaria gracilis had higher SLA, thinner leaves, and lower investment in protective tissues, than perennial P. mendocina. Physaria angustifolia (annual), and P. pinetorum (perennial) showed intermediate values. Both perennials had a thicker palisade and high photosynthesis, relative to annuals. The larger leaf veins of perennials should allow high water availability to the mesophyll. The thicker palisade should determine high resistance to water flow and help explain their high water-use efficiency. These leaf functions reflect the construction of long-lived leaves that efficiently use resources under environmental limitations of arid environments.

     

SEASONAL NUTRIENT DYNAMICS,NUTRIENT RESORPTION,AND MYCORRHIZAL INFECTION INTENSITY OF TWO PERENNIAL FOREST HERBS

Patterns of mycorrhizal infection, seasonal foliar nutrient concentrations, nutrient allocation to shoots and rhizomes, and nutrient resorption were measured in relation to soil nutrient availability in two species of perennial forest herbs, Geranium maculatum L. and Polygonatum pubescens Pursh., in four forest stands in southern and central Ohio. The percentage of plants with V-A mycorrhizae and the proportion of root length colonized by VAM structures increased with decreasing nutrient availability in both species. Foliar N and P concentrations in plants from lower fertility sites were as high, or higher, than those in plants from higher fertility sites; as a result, tissue nutrient enrichment ratios (foliar concentration/soil available concentration) increased with decreasing fertility. Proportional resorption of N and P generally decreased with decreasing nutrient availability, a pattern inconsistent with those exhibited by woody plants in these forest stands. We hypothesize that the inverse relationship between nutrient uptake efficiency (via mycorrhizae) and nutrient use efficiency (resorption) exhibited by these forest understory herbs, but not by trees or herbs from high-light environments, may be related to low-light limitation of energy reserves in the forest understory.     

Old-field successional dynamics on the Inland Pampa,Argentina

Abstract. The first 10 yr of old-field successional dynamics on the Argentine Inland Pampa were studied on a series of adjacent plots established consecutively between 1978 and 1989. We examined differences in species abundance patterns among plots in order to detect the spatial and temporal variability of succession. Perennial grasses steadily increased in cover and replaced the dominant annual species after 5 yr. Pioneer dicots persisted in older seral stages with 20 — 23 species/plot. Overall, exotic species (mostly the grasses Lolium multiflorum and Cynodon dactylon) contributed much to the plant cover in these communities. Native grasses comprised 45 % of total cover at years 7 — 10 of succession, but occurred with less than 7 species/plot. Substantial variation was found in the successional pathway, which reflected the particular sequence from annual forbs to short-lived and perennial grasses in the various plots. The course of succession was apparently influenced by a 2-yr period of unusually high rainfall. Deyeuxia viridiflavescens, a native perennial grass virtually absent before the wet period, spread over the study area and dominated seral communities for 3 yr, irrespective of plot age. Climatic conditions thus affected the successional turnover of life forms by increasing the rate of colonization by perennial grasses. We further point out the constraints imposed on secondary succession by the life histories of ‘available’ species.     

Competition and coexistence of rhizomatous perennial plants along a nutrient gradient

I studied competition and coexistence of three tall clonal perennial plant species, Calamagrostis epigejos (L.) Roth, Solidago canadensis L., and Tanacetum vulgare L. along a gradient of soil productivity over five years. A replacement series field experiment was conducted with high, moderate and low fertility levels in 1m×1m plots. There were significant effects of soil type on ramet density (P<0.001), mean height (P<0.01), and total biomass (P<0.01). Ramet density, mean height, and total biomass increased with increasing soil fertility. There were also significant effects of mixture on ramet density (P<0.01), but not on mean height and total biomass for all species. Significant neighbor effects on ramet density and total biomass (P<0.01) were found for Solidago, showing that it is important whether Tanacetum or Calamagrostis is its neighbor within mixtures. During the five years there was only one case of competitive exclusion: Calamagrostis excluded Solidago on the most fertile substrate in the fifth growing season. In most cases species coexisted over the five years. Each of the three species was able to dominate in at least one combination of substrate type and mixture. The experiment showed that asymmetric competition for light on substrates of high fertility, symmetric competition for nutrients on nutrient-poor soil and positive interactions especially on substrates of intermediate fertility played a role. A founder effect was evident in aggregated mixtures of Calamagrostis and Solidago on the nutrient-rich substrate. A conceptual model of the relative importance of root competition for soil nutrients, shoot competition for light, and positive interactions along the fertility gradient is presented. The model emphasizes that positive interactions play an important role over a broad range of the productivity scale with a peak at intermediate levels of fertility. On the substrate of high productivity shoot competition for light is more important than positive interactions and root competition for soil nutrients as well. The competitive superiority of Calamagrostis on the most productive substrate was evident only in the long run. Rare events like extreme summer drought or selective herbivore pressure caused a switch in dominance in mixtures with Solidago, respectively Tanacetum. The guerrilla growth strategy of Calamagrostis and interference competition through a dense cover of aboveground biomass and litter could further cause competitive exclusion.     

A set of polymorphic microsatellites for Vochysia ferruginea,a promising tree for land reclamation in the Neotropics

Vochysia ferruginea Mart. (Vochysiaceae) is a gap colonist of Neotropical forest. Because of its high tolerance of low‐nutrient acidic conditions and high aluminium and iron concentrations, and its high potential seed and pollen dispersal, it is a promising timber species for commercial development as reclaimed forest on degraded land. We present here primer sequences for 10 polymorphic simple sequence repeat (SSR) loci for use with V. ferruginea to assess fine scale genetic structure and gene flow dynamics.     

Effects of chronic herbivory and historic land use on population structure of a forest perennial,Trillium catesbaei

Question: How have long-term herbivory and past land use impacted the population structure of Trillium catesbaei, a long-lived rhizomatous herb? Location: Western Great Smoky Mountains National Park, Tennessee, USA. Methods: We examined T. catesbaei populations at three sites: (1) Cades Cove (CC), an area of intensive historic land use that has been maintained as open fields and woodlots with a history of chronic deer herbivory, (2) Whiteoak Sink (WOS), a reference area with similar land-use history, geology, and soils that has succeeded to closed-canopy forest with relatively low levels of deer herbivory, and (3) Leadbetter Ridge (LBR), an area of primary forest that has never received significant anthropogenic disturbance. Trillium catesbaei is the most common Trillium species at the three study sites, but smaller in stature, shorter lived, and more of a habitat generalist. Results: Chronic herbivory in CC has created a highly-truncated age structure with no plants older than 9 years, while plant ages at the other sites were more evenly distributed. Compared to WOS, plants in CC were younger at a given height and more likely to flower when younger. Across all life stages, populations at CC contained 68 × fewer plants than WOS. The age structures of WOS and LBR were similar. Compared to published age estimates for other Trillium species, our results suggest that T. catesbaei is relatively short lived within the genus. Conclusions: Chronic herbivory had pronounced effects on the population structure of a perennial herb. Other long-lived herbaceous species may exhibit similar truncated age structures and flowering by younger and smaller plants. Habitat generalist species within a genus, such as T. catesbaei, that are able to reproduce more quickly may persist longer under chronic herbivory. However, chronic herbivory has likely caused the loss of herbaceous species from CC and may eventually cause the local extirpation of T. catesbaei populations.     

A set of polymorphic microsatellites for Vochysia ferruginea,a promising tree for land reclamation in the Neotropics

Vochysia ferruginea Mart. (Vochysiaceae) is a gap colonist of Neotropical forest. As a result of its high tolerance of low‐nutrient acidic conditions and high aluminium and iron concentrations, and its high potential seed and pollen dispersal, it is a promising timber species for commercial development as regenerated or reclaimed forest on degraded land. We present here the primer sequences for 10 polymorphic simple sequence repeat loci for use with V. ferruginea to assess fine‐scale genetic structure and gene flow dynamics.     

Coordinated changes in photosynthesis,water relations and leaf nutritional traits of canopy trees along a precipitation gradient in lowland tropical forest

We investigated leaf physiological traits of dominant canopy trees in four lowland Panamanian forests with contrasting mean annual precipitation (1,800, 2,300, 3,100 and 3,500 mm). There was near complete turn-over of dominant canopy tree species among sites, resulting in greater dominance of evergreen species with long-lived leaves as precipitation increased. Mean structural and physiological traits changed along this gradient as predicted by cost–benefit theories of leaf life span. Nitrogen content per unit mass (N_mass) and light- and CO₂-saturated photosynthetic rates per unit mass (P_mass) of upper canopy leaves decreased with annual precipitation, and these changes were partially explained by increasing leaf thickness and decreasing specific leaf area (SLA). Comparison of 1,800 mm and 3,100 mm sites, where canopy access was available through the use of construction cranes, revealed an association among extended leaf longevity, greater structural defense, higher midday leaf water potential, and lower P_mass, N_mass, and SLA at wetter sites. Shorter leaf life spans and more enriched foliar ¹⁵N values in drier sites suggest greater resorption and re-metabolism of leaf N in drier forest. Greater dominance of short-lived leaves with relatively high P_mass in drier sites reflects a strategy to maximize photosynthesis when water is available and to minimize water loss and respiration costs during rainless periods. Overall, our study links coordinated change in leaf functional traits that affect productivity and nutrient cycling to seasonality in lowland tropical forests.     

Multigenerational inbreeding in <Emphasis Type="Italic">Succisa pratensis</Emphasis>: Effects on fitness components

We examined the effects of repeated inbreeding on fitness components of the long-lived perennial Succisa pratensis (Dipsacaceae). Plants from six populations differing in size were used to establish lines with expected inbreeding coefficients f of 0, 0.5 and 0.75. The effects of different inbreeding levels were measured for seed set, seed mass, percentage germination and seedling relative growth rate. Seed set decreased following one generation of inbreeding and seedling growth rate decreased after two generations of inbreeding. Our study indicated that the mutational load is difficult to purge and that continued inbreeding tends to affect important traits in S. pratensis. Although the partial dominance hypothesis for inbreeding depression seems to account for the results, the overdominance hypothesis cannot be ruled out completely. Overall, we conclude that the response of a long-lived plant, such as S. pratensis, to repeated inbreeding does not differ from that of other plant species with shorter life spans, surely because the mechanisms that account for inbreeding depression are universal for all plant species.     

Effects of woodlot isolation on the dispersion of plants with fleshy fruits

By relating species presence, number and density to the perimeter and isolation of small (0.1–2.75 ha) homogeneous woodlots (n = 43), indications were obtained that some fleshy-fruited species are negatively affected by woodlot isolation. The number of fruit-bearing herbaceous perennial species increased with woodlot area, probably because of the increasing heterogeneity of the herb layer. The density of individuals of the investigated species were negatively correlated to woodlot area. There were also some indications thatthe presence/absence of species was related to the length of the forest edge (e.g. Hederá helix). Because woodlot area and shape index were strongly correlated, the effects of increased forest area and forest edge were hard to separate. The probability of occurrence of Lonicera periclymenum and the density oí Ilex aquifolium decreased with an increasing degree of isolation of present forest islands. The chance of occurrence of L. periclymenum decreased also with the degree of isolation in the past, measured from topographical maps of about 60 yr ago. The total area of broad-leaved forest within a radius of 500 m, as well as the distance to the nearest connecting landscape element, seem to be good indicators of woodlot isolation.     

Correlated evolution of life history and host range in the nonphotosynthetic parasitic flowering plants Orobanche and Phelipanche (Orobanchaceae)

Most members of the nonphotosynthetic parasitic genera Orobanche and Phelipanche (Orobanchaceae) have narrow host ranges, and, as they grow on perennial hosts, are (at least potentially) perennial themselves. A few species, however, have wide host ranges and grow on annual hosts, and are thus (at least facultatively) annuals themselves. Among the latter are the weedy species, which include economically important pest taxa such as Orobanche crenata or Phelipanche aegyptiaca. Using a phylogenetically based maximum likelihood approach, which takes phylogenetic and branch length uncertainty into account, we can show that the life trait host range and life history evolve in a correlated fashion. This supports the hypothesis that parasite specialization is associated with predictable resources (i.e. long-lived hosts) and generalism with unpredictable ones (i.e. short-lived hosts), a pattern often found in animal parasites. The mechanisms and temporal sequence of the life trait changes and their interrelations remain speculative.     

Forest tree genomics: growing resources and applications

Over the past two decades, research in forest tree genomics has lagged behind that of model and agricultural systems. However, genomic research in forest trees is poised to enter into an important and productive phase owing to the advent of next-generation sequencing technologies, the enormous genetic diversity in forest trees and the need to mitigate the effects of climate change. Research on long-lived woody perennials is extending our molecular knowledge of complex life histories and adaptations to the environment - enriching a field that has traditionally drawn biological inference from a few short-lived herbaceous species.