Seed rain of fleshy and dry propagules in different habitats in the temperate rainforests of Chiloé Island,Chile

In temperate rainforests on Chiloé Island in southern Chile (42°S), most canopy trees bear fleshy, avian‐dispersed propagules, whereas emergent tree species have dry, wind‐borne propagules. In the present study, the following hypothesis was tested: regardless of species, fleshy propagules are deposited in greater numbers in canopy gaps and in forest margins and hence have a more heterogeneous seed shadow than wind‐dispersed propagules. To test this hypothesis, the seed rains of these two types of propagules were compared in the following forest habitats: (i) tree‐fall gaps (edges and centre); (ii) forest margins with adjacent pastures; and (iii) under closed canopy (forest interior). Seed collectors (30‐cm diameter) were placed in two (15 and 100 ha) remnant forest patches (n = 60–100 seed collectors per patch) distributed in the four habitats. Seeds were retrieved monthly from each collector during two reproductive seasons (1996, 1997). In both years, the seed rain was numerically dominated by two species with dry propagules (Laureliopsis philippiana and Nothofagus nitida) and three species with fleshy fruits (Drimys winteri, Amomyrtus luma, and Amomyrtus meli). The seed shadows of the two species with dry, wind‐dispersed seeds differed markedly. Seeds of L. philippiana were deposited predominantly in canopy openings, whereas N. nitida seeds fell almost entirely in the forest interior. The fleshy‐fruited species, Drimys and Amomyrtus spp., had similar seed deposition patterns in the various habitats studied, but the between‐year differences in seed rain were greater in Drimys winteri than in Amomyrtus spp. Although no more than 10% of fleshy‐fruited propagules reached the margins of the patch, approximately 7% of these were carried there by birds. Every year, canopy gaps (pooling data from edges and centres) concentrated approximately 60% of the total seed rain of both propagule types in both forest patches. Forest margins received less than 20% of the total seed rain, which was largely dominated by fleshy‐fruited species. Seed shadows were a species‐specific attribute rather than a trait associated with propagule type and dispersal mode.     

Community structure and demography of small-mammal populations in insular montane forests in southern India

bstract Small mammals were studied in insular montane forest patches in the Upper Nilgiris in southern India from February 1994 to September 1996. Nine patches were selected at two sites, one with a single large 600-ha patch, the other with several small patches ranging in size from 0.2 to 60 ha. The population characteristics and community structure of small mammals were studied in relation to patch size and habitat structure within the patches. The two most abundant species were Rattus rattus (2–36 individuals/ha) and Suncus montanus (0–11 individuals/ha), while the abundance of seven other species recorded were very low. The population characteristics of R. rattus examined were density, biomass, proportions of juveniles, sub-adults and adults, mean weight of all animals, mean weight of adults, sex ratio and persistence. The proportion of adults, sub-adults, mean weight of animals, and mean weight of adult males were correlated with patch size. Persistence of sub-adult females in the large patch was especially high. The density and biomass of other small-mammal species were also studied. Two indices of diversity, species richness and proportion of R.␣rattus were compared as measures of community structure. Seven habitat characteristics were measured; of these, canopy cover, canopy height and tree density were correlated with the size of the patch. Density and biomass of species other than R. rattus and proportion of R. rattus were correlated with canopy height. Density and biomass of species other than R. rattus were highest in smaller patches. While the population characteristics of R. rattus may be affected by patch size, the density of rare species may be influenced by factors related to lower canopy height. Migration between patches may be an important factor in maintaining populations in these patches. Received: 5 January 1998 / Accepted: 23 March 1998     

Arbuscular mycorrhizal propagules in soils from a tropical forest and an abandoned cornfield in Quintana Roo, Mexico: visual comparison of most-probable-number estimates

The present study was aimed at comparing the number of arbuscular mycorrhizal fungi (AMF) propagules found in soil from a mature tropical forest and that found in an abandoned cornfield in Noh-Bec Quintana Roo, Mexico, during three seasons. Agricultural practices can dramatically reduce the availability and viability of AMF propagules, and in this way delay the regeneration of tropical forests in abandoned agricultural areas. In addition, rainfall seasonality, which characterizes deciduous tropical forests, may strongly influence AMF propagules density. To compare AMF propagule numbers between sites and seasons (summer rainy, winter rainy and dry season), a “most probable number” (MPN) bioassay was conducted under greenhouse conditions employing Sorgum vulgare L. as host plant. Results showed an average value of 3.5 ± 0.41 propagules in 50 ml of soil for the mature forest while the abandoned cornfield had 15.4 ± 5.03 propagules in 50 ml of soil. Likelihood analysis showed no statistical differences in MPN of propagules between seasons within each site, or between sites, except for the summer rainy season for which soil from the abandoned cornfield had eight times as many propagules compared to soil from the mature forest site for this season. Propagules of arbuscular mycorrhizal fungi remained viable throughout the sampling seasons at both sites. Abandoned areas resulting from traditional slash and burn agriculture practices involving maize did not show a lower number of AMF propagules, which should allow the establishment of mycotrophic plants thus maintaining the AMF inoculum potential in these soils.     

Effects of resource availability and propagule supply on native species recruitment in sagebrush ecosystems invaded by Bromus tectorum

Resource availability and propagule supply are major factors influencing establishment and persistence of both native and invasive species. Increased soil nitrogen (N) availability and high propagule inputs contribute to the ability of annual invasive grasses to dominate disturbed ecosystems. Nitrogen reduction through carbon (C) additions can potentially immobilize soil N and reduce the competitiveness of annual invasive grasses. Native perennial species are more tolerant of resource limiting conditions and may benefit if N reduction decreases the competitive advantage of annual invaders and if sufficient propagules are available for their establishment. Bromus tectorum, an exotic annual grass in the sagebrush steppe of western North America, is rapidly displacing native plant species and causing widespread changes in ecosystem processes. We tested whether nitrogen reduction would negatively affect B. tectorum while creating an opportunity for establishment of native perennial species. A C source, sucrose, was added to the soil, and then plots were seeded with different densities of both B. tectorum (0, 150, 300, 600, and 1,200 viable seeds m⁻²) and native species (0, 150, 300, and 600 viable seeds m⁻²). Adding sucrose had short-term (1 year) negative effects on available nitrogen and B. tectorum density, biomass and seed numbers, but did not increase establishment of native species. Increasing propagule availability increased both B. tectorum and native species establishment. Effects of B. tectorum on native species were density dependent and native establishment increased as B. tectorum propagule availability decreased. Survival of native seedlings was low indicating that recruitment is governed by the seedling stage.     

Effects of Caragana microphylla patch and its canopy size on “islands of fertility” in a Mongolian grassland ecosystem

In arid and semiarid regions, variations in “islands of fertility” accompanied by discontinuous vegetation is frequently observed. However, the effects of vegetation patches on soil, including the influence of canopy size, are not fully understood, particularly under conditions of severe grazing. We examined the effects of patches of mound-forming shrub, Caragana microphylla, and the plant’s canopy size on these islands of fertility in a heavily grazed Mongolian grassland. In 11 patches with various canopy sizes (32.5–180 cm in diameter), we compared the chemical properties of soils among three microsites: Mound, Below, and Around, which were inside, below, and outside of C. microphylla mounds, respectively. Total carbon (C) and most essential elements for the plants were more concentrated in Mound, but total nitrogen (N) and nonlimiting elements, such as exchangeable sodium (Na), did not significantly differ among microsites. Larger canopies more strongly affected the enrichment of total C and most essential elements, including total N, in Mound. These results suggest that C. microphylla patches substantially enrich total C and most essential elements and that the extent of enrichment was intensified with canopy size. However, under severe grazing, total N may be relatively more affected by the redistribution of resources through grazing, particularly when the canopy size is small.     

Low plant density enhances gene dispersal in the Amazonian understory herb Heliconia acuminata

In theory, conservation genetics predicts that forest fragmentation will reduce gene dispersal, but in practice, genetic and ecological processes are also dependent on other population characteristics. We used Bayesian genetic analyses to characterize parentage and propagule dispersal in Heliconia acuminata L. C. Richard (Heliconiaceae), a common Amazonian understory plant that is pollinated and dispersed by birds. We studied these processes in two continuous forest sites and three 1‐ha fragments in Brazil's Biological Dynamics of Forest Fragments Project. These sites showed variation in the density of H. acuminata. Ten microsatellite markers were used to genotype flowering adults and seedling recruits and to quantify realized pollen and seed dispersal distances, immigration of propagules from outside populations, and reproductive dominance among parents. We tested whether gene dispersal is more dependent on fragmentation or density of reproductive plants. Low plant densities were associated with elevated immigration rates and greater propagule dispersal distances. Reproductive dominance among inside‐plot parents was higher for low‐density than for high‐density populations. Elevated local flower and fruit availability is probably leading to spatially more proximal bird foraging and propagule dispersal in areas with high density of reproductive plants. Nevertheless, genetic diversity, inbreeding coefficients and fine‐scale spatial genetic structure were similar across populations, despite differences in gene dispersal. This result may indicate that the opposing processes of longer dispersal events in low‐density populations vs. higher diversity of contributing parents in high‐density populations balance the resulting genetic outcomes and prevent genetic erosion in small populations and fragments.     

Frankia and Alnus rubra Canopy Roots: An Assessment of Genetic Diversity, Propagule Availability, and Effects on Soil Nitrogen

The ecological importance of microbial symbioses in terrestrial soils is widely recognized, but their role in soils that accumulate in forest canopies is almost entirely unknown. To address this gap, this study investigated the Frankia–Alnus rubra symbiosis in canopy and forest floor roots at Olympic National Park, WA, USA. Sixteen mature A. rubra trees were surveyed and Frankia genetic diversity in canopy and forest floor nodules was assessed with sequence-based nifH analyses. A seedling bioassay experiment was conducted to determine Frankia propagule availability in canopy and forest floor soils. Total soil nitrogen from both environments was also quantified. Nodules were present in the canopies of nine of the 16 trees sampled. Across the study area, Frankia canopy and forest floor assemblages were similar, with both habitats containing the same two genotypes. The composition of forest floor and canopy genotypes on the same tree was not always identical, however, suggesting that dispersal was not a strictly local phenomenon. Frankia seedling colonization was similar in canopy soils regardless of the presence of nodules as well as in forest floor soils, indicating that dispersal was not likely to be a major limiting factor. The total soil nitrogen of canopy soils was higher than that of forest floor soils, but the presence of Frankia nodules in canopy soils did not significantly alter soil nitrogen levels. Overall, this study indicates that the Frankia–A. rubra symbiosis is similar in canopy and forest floor environments. Because canopy roots are exposed to different environmental conditions within very small spatial areas and because those areas can be easily manipulated (e.g., fertilizer or watering treatments), they present microbial ecologists with a unique arena to examine root–microbe interactions.     

Colonization of subtidal macroalgae in a fucalean-dominated algal assemblage,southwestern Australia

The influence of fucalean canopy species and dominant understory macroalgae on algal colonization was investigated to evaluate whether layering contributes to patterns in algal diversity. Patterns in recruitment were compared among total-clearing, understory-removal, canopy-removal, and undisturbed plots (plot area = 0.25 m²), using a randomized block design in depths <10 m and 10–20 m at Woody Island, Western Australia. To evaluate if propagules were available in the water column above the canopy layer, settlement plates (plate area = 0.04 m²) were deployed in depths <10 m, 10–20 m, and >20 m. A total of 198 macroalgal species was recorded. Biomass of the understory species Osmundaria prolifera Lamouroux and Botryocladia sonderi Silva was similar between canopy-removal and undisturbed plots. Diversity of macroalgae was similar in the presence and absence of a canopy layer. Taxa found in the canopy showed different patterns in recruitment. Cystoseiraceae recruited predominantly in total-clearings in both depth strata. Sargassaceae recruited most abundantly in depths <10 m. Density of canopy taxa on settlement plates was similar with depth (20–30 juveniles per plate), and juveniles were mainly Cystoseiraceae. In contrast to kelp beds or forests, patterns in algal colonization appeared to be maintained by environmental factors or processes other than the direct effects of layering in the subtidal fucoid-dominated assemblages at Woody Island. Handling editor: K. Martens     

Rapid detection of arbuscular mycorrhizae in roots and soil of an intensively managed turfgrass system by PCR amplification of small subunit rDNA

 Arbuscular mycorrhizal fungi (AMF) were detected in uninoculated soil and roots of turfgrass (Agrostis palustris) by direct extraction and PCR amplification of the small subunit rRNA gene. Sequence analysis of the cloned PCR product confirmed the identity of the amplified DNA as an AMF sequence having 95% identity to Glomus intraradices. The sensitivity of the method was gauged by comparison with the most probable number analysis of infective propagules in an intensively managed turfgrass system having 56 propagules per 100 g soil. In contrast to the heavily managed system, infective propagule numbers were high in systems under moderate and limited management. The method described may be useful for rapid investigations of genetic diversity and community structure of AMF. Accepted: 8 January 1999     

Field evidence of dispersal of branchiopods, ostracods and bryozoans by teal (Anas?crecca) in the Camargue (southern France)

Invertebrate propagules may survive internal and external transports by waterbirds, thus facilitating their dispersal between aquatic habitats. However, field data on such transport remain limited, especially for exozoochory. We quantified and compared the rates of internal and external invertebrate transports simultaneously in a wintering population of teal (Anas crecca) in the Camargue (southern France). We inspected lower gut (rectum) contents of birds that had been shot (N = 366) and washed birds that had been live-trapped (N = 68) during the winters 2006–2007 and 2007–2008. At least one propagule was recorded in 2.5% and 10.3% of internal and external samples, respectively. Cladoceran, ostracod, plumatellid bryozoan and anostracan propagules were all recorded in both internal and external samples. Hatching confirmed their viability, except for anostracan eggs. At least three cladoceran species and two ostracod species were recorded, none of which had previously been shown to be dispersed by birds. Amongst external samples, we recorded a significant seasonal trend in 1 year with most propagules recorded before December, keeping with a seasonal decline in the availability of propagules on the water surface. This study provides evidence that teal may be important vectors of invertebrate dispersal both within the Camargue and along migratory flyways.     

Plant recolonization of reclamation areas from patches of salvaged forest floor material

Question

Understorey development is a great challenge in the restoration of many forest sites, particularly when sources of vegetation propagules are scarce. Can placement of propagule‐rich soil patches within reclaimed landscapes otherwise covered with propagule‐poor material promote the dispersal of vegetation from the patches into the surrounding areas?

Location

Large reclamation site in the Canadian (Alberta) boreal forest.

Method

Patches of propagule‐rich forest floor material were placed within a matrix of propagule‐poor peat material. Vegetation assessments (cover estimates, seed rain) were done surrounding these patches in the third and fourth growing seasons.

Results

There was significant egress of species from the patches into the peat after four growing seasons, and overall species associated with the patches had higher cover in the peat than species that were associated with the peat itself. While wind‐dispersed herbaceous species from the patches were found at the leading edge of the egressing community, most species used vegetative propagation, resulting in short egress distances. Several patch‐associated species were found in seed rain collected on the peat areas but were not observed in this material, suggesting seedbed limitations.

Conclusion

Despite the relatively short distance of egress, this experiment suggests that placement of propagule‐rich soil material within reclaimed landscapes will promote egress into adjacent propagule‐poor soil material.     

Propagule pressure governs establishment of an invasive herb

The success of plant invasions may be limited by the availability of propagules and/or of suitable microsites, with microsite availability being affected by, for example, disturbance and interspecific competition. A mechanistic understanding of the contributions of propagule pressure and microsite limitation to plant invasions is therefore required to minimise future invasions. Here, we investigated the relative roles of propagule pressure, the availability of microsites, and their interaction on the establishment of an invasive herb, Lupinus polyphyllus, in two geographic regions representing different climate and growth conditions in Finland (a more productive southern region and a harsher central region). We carried out a field experiment in 14 L. polyphyllus populations, in which we manipulated both propagule pressure and disturbance. In a complementary greenhouse experiment, we manipulated propagule pressure and interspecific competition. Seedling establishment of L. polyphyllus was higher in the more productive southern region than in the harsher central region. The number of L. polyphyllus seedlings increased with increasing propagule pressure regardless of disturbance or interspecific competition. However, the number of L. polyphyllus seedlings per sown seed (relative establishment) tended to decrease with increasing propagule pressure, indicating that the positive effect of propagule pressure on early invasion is partially counteracted by density-dependent mortality at high seed densities. Our results highlight the dominant role of propagule pressure over disturbance and interspecific competition in the establishment of L. polyphyllus, suggesting that the early stage of invasion is limited by the availability of propagules rather than the availability of suitable microsites.     

IMMUNOLOCALIZATION OF CENTRIN DURING FERTILIZATION AND THE FIRST CELL CYCLE IN FUCUS DISTICHUS AND PELVETIA COMPRESSA (FUCALES,PHAEOPHYCEAE)1

Antibodies that recognize the centrosome-associated protein centrin were used to characterize centrosomal origin and positioning during fertilization and the first cell cycle in Fucus distichus subsp. evanescens (C. Agardh) Powell and Pelvetia compressa (J. Agardh) De Toni. Centrin was identified in sperm, eggs, and zygotes on protein blots, indicating the protein is present in both gametes. Using immunofluorescence microscopy, centrin was found in discrete foci in sperm. In contrast, eggs lack centrosomes and centrin was not detectable by immunofluorescence, indicating that centrin was probably dispersed in the cytoplasm. Two foci of centrin were present on the nuclear envelope of zygotes, but microtubules remained dispersed over the zygotic nucleus. Centrin foci separated over the nuclear envelope as the first cell cycle progressed. Microtubules became concentrated at the centrin foci to form centrosomes that gave rise to the spindle poles at mitosis.     

Habitat use,feeding and territorial behavior of a Brazilian endemic damselfish <Emphasis Type="Italic">Stegastes rocasensis</Emphasis> (Actinopterygii: Pomacentridae)

This paper presents the results of the first field study of the Brazilian endemic damselfish Stegastes rocasensis. Underwater data were collected at the Fernando de Noronha Archipelago (NE Brazil), where four sites were visually assayed for local territorial and feeding behaviors, as well as habitat use. S. rocasensis preferentially fed on turf and macroalgae, and during the afternoon period. Its territory size ranged from 0.26 to 13.86 m² (1.61 ± 0.23 m²). Our findings suggest that adults preferably inhabit shallow, turf-rich areas, while sub-adults and juveniles occupy deeper areas with higher percent cover of invertebrates and hard corals, respectively. With regards to agonistic behaviors, pursuit of intruders was the most frequent reaction recorded (p < 0.001); the highest level of aggression was elicited by territorial herbivores (p < 0.001). Nevertheless, analysis of attacks elicited by different fish species within S. rocasensis’ territory showed that more attacks were launched on conspecifics than on other fish species.     

Human hydrographical changes interact with propagule predation behaviour in Sri Lankan mangrove forests

For mangroves with almost no tidal influence and a subsequent mosaic vegetation structure we describe the relation between propagule predators and both vegetation structure and environmental factors on a vegetation assemblage or ‘forest patch’ level. We then report the interaction between natural propagule predation and human influence. In different forest patches dominated by Avicennia officinalis, Excoecaria agallocha, Lumnitzera racemosa, Rhizophora apiculata or R. mucronata or in open or mixed areas identified from aerial photographs, the predation on propagules of A. officinalis, B. gymnorrhiza, R. apiculata and R. mucronata was monitored in a total of 24 experimental plots (3 per forest patch). Relationships to environmental factors (topography, water level, rainfall and season) on the level of predation were investigated. The highest predation intensity by crabs was on A. officinalis propagules, and in E. agallocha forest patches. Predation by crabs, snails, insects and mammals was observed, and the significant differences in predation intensity across species and across forest patches were explained directly by propagule predator identity and abundance, and by the interaction between rainfall, water level and microtopography. We illustrated how hydrography changes alter the behaviour of propagule predators and play a role in the shaping of vegetation structure by reconstructing the lagoon water level of a site over a period of 50 years based on rainfall data. This time frame covered both a condition without and with human impacts, and past and present propagule predation settings were confronted with the simulated hydrology. The importance of spatial and temporal microhabitat variations in opening multiple successional pathways in vegetation dynamics is illustrated, and is highly relevant for ecosystems with unpredictable or short-lived (< 20 years) patchy vegetation structures and microhabitats.     

Does Prunus serotina act as an aggressive invader in areas with a low propagule pressure?

Since most studies on Prunus serotina in Western Europe focused on heavily invaded areas, we wondered whether P. serotina also acts as an aggressive invader in areas with a low propagule pressure. Based on long-term data for the Liedekerke forest reserve, we found that connectivity to seed sources and light availability were the major drivers of P. serotina presence: long-distance dispersal events and ‘windows of opportunity’ seem to direct P. serotina colonization. In the studied forest, P. serotina could not be considered an aggressive invader since its spread slowed down rather quickly and did not hamper the establishment of native tree species. Furthermore, understory P. serotina showed low growth and seed production, while the high Rubus cover hampered germination and establishment. Nonetheless, calamities opening up the canopy layer in the few areas with high P. serotina sapling density might alter the course of the invasion process.     

Effect of liquid culture media on morphology,growth, propagule production,and pathogenic activity of the Hyphomycete,Metarhizium flavoviride

Two isolates of Metarhizium spp. were studied for propagule production, because of their pathogenic activity towards locusts and grasshoppers (Mf189 = M. flavoviride (or M. anisopliae var. acridum) strain IMI 330189, and Mf324 = M. flavoviride strain ARSEF324). Both isolates were grown in seven different liquid media, which have been developed for mass production of various Hyphomycetes, considered as candidates for microbial control of noxious insects. Shake-flask experiments were carried out at 28 °C in the dark. Production was quantified for 72 h and the effects of the tested media were evaluated on propagule concentration, morphology and pathogenicity. Based on preliminary experiments, all tested media were supplemented with 0.4% Tween 80 to avoid the formation of pellets and to produce unicellular propagules. Submerged propagule yields were higher withMf189 than with Mf324 in all seven media. While high concentrations of propagules (1.4 to 2.4 × 10⁸ propagules ml^-1 for MF189 and1.4 to 8.3 × 10⁷ propagules ml^-1 for Mf324) were produced in four media (Adamek, Catroux, Jackson, and Jenkins–Prior media), production of propagules was lower in the three other media (Goral, Kondryatiev, and Paris media). Both isolates produced oblong blastospore-like propagules, except in Kondryatiev medium in which they provided ovoid propagules. In this case, Mf189 submerged propagules looked like aerial conidia, but scanning observations did not demonstrate a typical conidiogenesis via phialides. In Kondryatiev medium, Mf324 submerged propagules were significantly smaller than aerial conidia. Infection potential of submerged propagules was assayed on Schistocerca gregaria. Second-instar larvae fed for 48 h on fresh wheat previously contaminated by a spraying suspension of each inoculum titrated at 10⁷ propagules ml^-1. All seven media produced submerged propagules that were highly infectious for S. gregaria larvae. Shake flask culture assays permitted us to select three low-costmedia, Adamek, Jenkins–Prior, and Catroux for improving scale-up of liquid fermentation focused on mass-production of Metarhizium propagules for mycoinsecticides devoted to locust control. This revised version was published online in June 2006 with corrections to the Cover Date.     

Location and interseasonal variation in flowering, propagule setting and propagule size in mangroves species of the family Rhizophoraceae

Three species of mangroves, Rhizophora stylosa, Rhizophora mangle (synonym R. samoensis) and Bruguiera gymnorhiza in the family Rhizophoraceae were studied to understand the flowering pattern, propagule development and the propagule size at maturity prior to dispersal from the mother plant. The study was conducted in the Wet and the Dry zones over two seasons in Viti Levu, the Main Island of Fiji. The flower number, number of propagules and propagule size at maturity were significantly different among three species and within species in the Dry and the Wet zones. Only 1–2% of total flowers in each species became mature propagules. This percentage was significantly lower in the Dry zone for all three species. Rhizophora stylosa produced the biggest size of propagules followed by Rhizophora mangle and Bruguiera gymnorhiza. Relatively longer and heavier propagules were recorded in the Wet zone and shorter and lighter in the Dry zone. Inter-seasonal differences were not significant for these characters. This could be mainly due to almost similar amount of rainfall, relative humidity and temperature regimes over two seasons within each zone.     

The influence of light on the growth of watercress (<Emphasis Type="Italic">Nasturtium officinale</Emphasis> R. Br.)

In stream ecosystems, the growth of aquatic primary producers is affected by spatial and temporal variations in the riparian canopy, which can influence the availability of light resources. Aquatic plants can acclimate to low light environments by employing a suite of morphological or physiological mechanisms to increase light capture or photosynthetic efficiency. Some species may also use alternate types of propagules to colonize environments with heterogeneous light environments. In a greenhouse experiment we examined the morphological and physiological response of watercress (Nasturtium officinale R. Br.) to a gradient of increasing light levels, which ranged from 7% ambient light to full sunlight. We also determined if watercress seedlings and vegetative fragments differed in their growth response to increasing light levels. Total biomass and root biomass of seedlings and vegetative fragments decreased with decreasing light levels. The difference in plant biomass across treatments was due to morphological changes in total canopy area and leaf area, both of which increased with decreasing light levels. Seedlings and vegetative fragments did not differ in their response to light availability, but vegetative fragments had higher final biomass as a result of higher initial biomass. Physiological acclimation to low light levels appears to be of secondary importance for watercress as the concentrations of total chlorophyll, chlorophyll a, chlorophyll b, and chlorophyll a:b did not differ among light levels or between seedlings and vegetative fragments. Seedlings and vegetative fragments grown under high light levels had a greater percentage of carbon and a lower percentage of nitrogen than plants grown under low light conditions. The results of this study indicate that watercress displays considerable morphological plasticity and acclimates to low light conditions primarily by increasing leaf area and canopy surface area. There is no evidence that the type of watercress propagule (seedling vs. vegetative fragment) imparts any growth advantage in low light environments and watercress grown from either type of propagule showed no differences in their morphological or physiological responses to varying light regimes. Handling editor: S. M. Thomaz     

Trade-off relationships between some reproductive characteristics in plants with special reference to life history stragegy

Several reproductive triats in plants were studied in more than 200 populations of 61 wild species from diverse ecological conditions. As a result, it was found that there occur three distinct types of plants in the energy allocation patterns to reproductive structures (RA) and the propagule output per plant (P_N), i.e. (1) the number of propagules per plant increases in response to the increase in RA (Type I), (2) the number of propagules decreases in response to the increase in RA (Type II), and (3) the RA remains constant despite the great differences in the propagule number per plant. A conspicuous trade-off relationship was also discovered to occur between the RA to a single propagule (R_A) and the propagule output per plant (P_N), such that log R_A=logC−blot P_N, or R_A=C/P_N ^b =CP_N ^−b , where C is a constant. The three different ranges ofb-values were recognized, i.e.b<1.0,b>1.0, andb=1.0, which correspond to Type I, Type II, and Type III, respectively. Related problems to the concept ofr- andK-strategy are also discussed.