Consequences of the Elimination of Old Leaves upon Spring Phenological Events and the New Leaves Nutrient Concentration in a Wintergreen Woody Species in the Southern Hemisphere

Previous studies analyzed the importance of old leaves conservancy for wintergreen species plant growth only after early spring old leaves elimination. However, carbon and nutrient resources for growth could have already been translocated from old leaves to shoots during autumn. In this work, the effect of old leaves absence on the leaf mass per area (LMA, g m⁻²) and nutrient concentration of new spring leaves, shoot growth, and flowering was studied in Aristotelia chilensis, an Andean Patagonic woody wintergreen species of Argentina. Plants were studied after autumn defoliation (AD) or late winter defoliation (WD) and results were compared to those of undamaged control plants (CO). The new leaves LMA and mineral nutrient (N, P, K, and Mg) concentration values did not decrease in AD or WD compared to CO plants. Conversely, CO plants showed higher flowering intensity and shoot lengthening compared to AD or WD plants. There were not remarkable differences regarding the defoliation time, though non-flowering shoots grew in a lesser degree than the flowering shoots in WD plants. It was concluded that A. chilensis old leaves cohort is an important source to shoot growth and flowering but their absence does not affect the new leaves structure or nutritional status from early spring in either AD or in WD plants. New leaves formation probably is guaranteed by resources (carbon and nutrients) previously stored in stems or even in the buds containing the preformed leaves since March, by the end of summer. Provided the availability of complete resources for the new leaf flush independently of the old leaves A. chilensis would restore the carbon balance as soon as possible to resume the growth of heterotrophic tissues at normal rates. Endogenous response to counterbalance the old leaves absence on non-flowering shoots was more effective when there was greater lag time between defoliation and shoot growth resume. Flowering and non-flowering shoots compete for the available resources when A. chilensis have not yet expanded leaves and shoots supporting reproductive structures were stronger sinks compared to non-flowering shoots in WD plants.     

Importance of the gradient in photosynthetically active radiation in a vegetation stand for leaf nitrogen allocation in two monocotyledons

Carex acutiformis and Brachypodium pinnatum were grown with a uniform distribution of photosynthetic photon flux density (PFD) with height, and in a vertical PFD gradient similar to the PFD gradient in a leaf canopy. Distribution of organic leaf N and light-saturated rates of photosynthesis were determined. These parameters were also determined on plants growing in a natural vegetation stand. The effect of a PFD gradient was compared with the effect of a leaf canopy. In Brachypodium, plants growing in a vegetation stand had increasing leaf N with plant height. However, distribution of leaf N was not influenced by the PFD gradient treatment. The gradient of leaf N in plants growing in a leaf canopy was not due to differences within the long, mostly erect, leaves but to differences between leaves. In Carex, however, the PFD gradient caused a clear increase of leaf N with height in individual leaves and thus also in plants. The leaf N gradient was similar to that of plants growing in a leaf canopy. Leaf N distribution was not affected by nutrient availability in Carex. In most cases, photosynthesis was positively related to leaf N. Hence, lightsaturated rates of photosynthesis increased towards the top of the plants growing in leaf canopies in both species and, in Carex, also in the PFD gradient, thus contributing to increased N use efficiency for photosynthesis of the whole plant. It is concluded that in Carex the PFD gradient is the main environmental signal for leaf N allocation in response to shading in a leaf canopy, but one or more other signals must be involved in Brachypodium.     

Population dynamics ofHeloniopsis orientalis C. Tanaka (Liliaceae) in natural forests — Annual life cycle

Annual changes in the leaves and reproductive organs ofHeloniopsis orientalis C. Tanaka (Liliaceae), a perennial evergreen herb, were studied from 1991 to 1997 in two areas of South Korea, Namhansanseong and Maranggol. The period for active growth in the leaves was from mid-March to early June. Average leaf angle was 70° in early June, decreasing to 50° in late October. From December until June of each following year, leaf angle was maintained a 0° to horizontal. The specific leaf area (SLA) value was 185 cm².g^-1 early in the growing season, increasing to 332 cm²g^-1 in early June. By the end of October, SLA had decreased to 159 cm²g^-1, after which it increased again from March to June. Because the SLA curve had two peaks, it was inferred thatH. orientalis possesses two means for survival: 1) an anti-freezing mechanism by which its leaves thicken during the winter, and 2) a reallocation of energy from old leaves to new leaves or to reproductive organs.H. orientalis flowered in a semi-enclosed state in late March. Blooming out of the bract, the front of the flower faced the ground. Growth of the peduncle ended in early June, at which point it was 60 cm long. At that time, the fruit was oriented so that the seeds were dispersed upward. Therefore one can see thatH. orientalis has two physiological features that enhance long-distance seed dispersal — a rather long peduncle relative to overall plant size and an upward seed-dispersal mechanism. In the Namhansanseong area, energy from the roots and old leaves was translocated to new leaves early in the growing season (from late March to early May). However, after mid-May, energy was re-translocated from new leaves to the roots. Moreover, the leaves on flowering plants grew more slowly than on non-flowering plants because energy was translocation to the reproductive organs. Therefore, new leaf growth depended on energy stores of the roots and the biomass of old leaves early in the growing season.     

Nest-site selection by the harvest mouse<Emphasis Type="Italic">Micromys minutus</Emphasis> in seasonally changing environments

We studied nest-site selection of harvest miceMicromys minutus (Pallas, 1771) for clarifying plant community characters suitable for nesting. We surveyed newly constructed nests in a marsh population and various plant characters likely to affect nest-site selection throughout the breeding season. The harvest mouce used common reedMiscanthus sacchariflorus and Japanese pampas grassMiscanthus sinensis more frequently than expected by the propotions of their areas occupied in summer, but shifted toCarex confertiflora after October. Although reed grassPhragmites communis was dominant in the marsh, mice did not choose this species. The 2 grass species selected in summer had a larger number of leaves per unit area, and the most selected species had a higher stem density. Both of these plant traits indicate a richness of nesting materials. The rapid increase in selection forCarex from autumn to winter was likely due to its leaf freshness and/or flexibility, as leaves ofCarex maintained a high level of chlorophyll content until winter. The harvest mouse appeared to flexibly change its selection for nesting plants in response to seasonal environmental changes. We also discuss the implications of our findings in terms of harvest mouse habitat conservation.     

Variation in evergreen and deciduous species leaf phenology in Assam, India

In the present study phenological activities such as leaf and shoot growth, leaf pool size and leaf fall were observed for 3 years (March 2007–March 2010) in 19 tree species (13 evergreen and 6 deciduous species) in a wet tropical forest in Assam, India. The study area receives total annual average rainfall of 2,318 mm of which most rain fall (>70 %) occurs during June–September. Both the plant groups varied significantly on most of the shoot and leaf phenology parameters. In general, growth in deciduous species initiated before the evergreen species and showed a rapid shoot growth, leaf recruitment and leaf expansion compared to evergreen species. Leaf recruitment period was significantly different between evergreen (4.2 months) and deciduous species (6.8 months). Shoot elongation rate was also significantly different for evergreen and deciduous species (0.09 vs. 0.14 cm day^?1 shoot^?1). Leaf number per shoot was greater for deciduous species than for evergreen species (34 vs. 16 leaves). The average leaf life span of evergreen species (328 ± 32 days) was significantly greater than that of deciduous species (205 ± 16 days). The leaf fall in deciduous species was concentrated during the winter season (Nov–Feb), whereas evergreens retained their leaves until the next growing season. Although the climate of the study area supports evergreen forests, the strategies of the deciduous species such as faster leaf recruitment rate, longer leaf recruitment time, faster shoot elongation rate during favorable growing season and short leaf life span perhaps allows them to coexist with evergreen species that have the liberty to photosynthesize round the year. Variations in phenological strategies perhaps help to reduce the competition among evergreen and deciduous species for resources in these forests and enable the coexistence of both the groups.     

Ecological characteristics of aSuaeda japonica population and the effects of early-season air temperatures on population formation

A natural, tidal-flat population ofSuaeda japonica was studied to determine how air temperatures early in the growing season affected population formation. Changes in germination rates, density, standing crop (amount of biomass aboveground), and plant heights and weights were monitored from February 1999 to September 2000. Seed germination occurred between mid-February and early May in 1999, and from mid-February to mid-April in 2000. The daily mean air temperature fluctuated below and over 0°C through the end of March in 1999 and until mid-March in 2000. Seedling losses due to freezing were greater in 1999 than in 2000. Densities in 1999 and 2000 were 790 and 2201 plants/m² in the early growing season, and 578 and 803 plants/m² later on, respectively. Therefore, the density and mortality ofS. japonica was higher in 2000 than in 1999. Values of correlation were low between density and standing crop, but diverse between density and height. The variation in standing crops was remarkable but that of height was small among sites. Frequencies of size classes, based on height, followed normal distribution curves over time, but those based on weight were very great in the lower classes over the entire growing season.     

In vitro flowering of indica rice (Oryza sativa L. spp. indica)

Nodal explants of rice cultivar Pathumthani 1 (PT1; short-day photoperiod insensitive) were collected, surface-disinfected, and cultured on modified MS medium under in vitro conditions for 90 d. A total of 60% nodal explants generated flowering plantlets (with one inflorescence per cluster). The net photosynthetic rate was greater, and soluble sugars (including glucose, fructose, and sucrose) accumulated to higher levels in the leaves of flowering as compared to non-flowering plants. In contrast, chlorophyll a, chlorophyll b, total chlorophyll, and total carotenoid content were enriched to a greater degree in the leaves of non-flowering as compared to flowering plants. Also, growth performance parameters, including plant height, number of leaves per plant, leaf area, fresh weight, and dry weight of plantlets derived from seedlings were superior to those of plantlets derived from nodal explants. In addition, the protocol proved to successfully induce flowering in KDML 105, a short-day photoperiod-sensitive rice cultivar.     

Leaf phenology, seasonal changes in leaf quality and herbivory pattern of Sanguisorba tenuifolia at different altitudes

Leaf demography, seasonal changes in leaf quality and leaf-beetle herbivory of a herbaceous perennial plant, Sanguisorba tenuifolia, were compared between low- and high-elevation sites. Leaf nitrogen concentration was higher and leaf mass per area (LMA) was lower at the higher site than at the lower one. At the lower site, with a long growth period, plants produced many leaf cohorts and leaves emerged throughout the growing season. At the higher site, with a short growth period, however, leaf emergence was concentrated early in the growing season. The improvement of leaf quality and acceleration of leaf emergence at higher altitude are seen as adaptations to a short growing season. Results of a feeding trial suggested that leaf quality for the leaf-beetle Galerucella grisescens was higher at the higher site, but plants at the higher site showed less damage. Oviposition of G. grisescens was seasonal and unimodal at both altitudes, but the period of oviposition was shorter and its density lower at the higher site. The low temperature and short growth period at the higher site appear to reduce the activity of the leaf-beetles, resulting in a decrease in damage by herbivory, despite better leaf quality. Received: 11 December 1997 / Accepted: 24 July 1998     

Effects of post-chilling temperature on growth and variegation in Solomon's Seal

Effects of temperature were studied on the current and following season's growth of shoots from chilled rhizomes of Variegated Solomon's Seal. The rate of progress to completed elongation of the aerial shoot in chilled plants increased linearly with increasing temperature up to 28°C (24 h mean). A post‐chilling thermal time of 658 ± 47°Cd (> ‐1.3°C) was required for aerial shoots to become fully extended. Temperatures of 28°C and 33°C accelerated aerial shoot senescence and decreased rhizome and root dry weights, as compared with 18°C and 23°C treatments. Leaf number and variegation were not affected by temperature treatments during current growth season and all plants produced 12–13 leaves with between 7% and 9% leaf area variegated. Leaf variegation, however, was significantly increased in plants that had been grown after chilling at 28°C during the preceding growing season. Proteins of approximately 26, 32 and 62 kDa were present in the green parts of leaves but not in the white parts.     

Interspecific and intraspecific differences in shoot and leaf lifespan of four Carex species which differ in maximum dry matter production

The effect of N supply on shoot and leaf lifespan was investigated in established stands of four herbaceous Carex species which differed in maximum dry matter production. These species were, in rank order of increasing maximum dry matter production (per unit ground area): Carex diandraC. rostrata. The observed patterns of shoot and leaf turnover were compared with data on leaf characteristics and nitrogen use efficiency indices of these species. There was no consistent difference in shoot production (number of shoots produced per unit ground area) between species with low production and those with high production: Carex diandra (low production) and C. lasiocarpa (high production) had high shoot production, while shoot production in c. rostrata (low production) and C. acutiformis (high production) was much lower. The rank order of the mean lifespan of shoots was: C. diandra. Thus, the lifespan of shoots increased with increasing maximum dry matter production of these Carex species. In all species, increased N supply led to a significant reduction in shoot lifespan. The reduction of shoot lifespans in response to enhanced N supply will result in increased nutrient turnover rates in these species. There was no consistent difference in the number of leaves produced per shoot between low-production and high-production species. C. diandra and C. lasiocarpa had relatively low leaf production, while C. rostrata and C. acutiformis had relatively high leaf production per shoot. Thus, this pattern is opposite to the pattern in shoot production. The rank order of the mean lifespan of leaves was: C. diandra. This implies that the high-production species had longer mean leaf lifespans than the low-production species. Mean leaf lifespan was not significantly affected by enhanced N supply, except in C. diandra, where leaf lifespan decreased in response to enhanced N supply. Shoot lifespans did not show any significant relation with the specific leaf area (SLA, leaf area per unit leaf mass) or the leaf area ratio (LAR, leaf area per unit plant mass) of the species under study. There was, however, a negative relation (r ²=0.71) with the nitrogen concentration in the leaves. Shoot lifespans were positively related (r ²=0.79) with whole-plant nitrogen use efficiency (NUE, dry matter production per unit N-loss) and with the mean residence time of nitrogen (MRT, the average time-span during which a unit of nitrogen is present in the plant) (r ²=0.78), but not with the nitrogen productivity (A, annual dry matter production per unit N in the plant). Leaf lifespan was positively related with the mean residence time of nitrogen in the plants (r ²–0.70). For all the other parameters, there were no significant relations with leaf lifespan. From these results we conclude that: (1) at the stand level, shoot and leaf lifespans are positively related with maximum dry matter production; and (2) shoot and leaf lifespan are important determinants of whole-plant nitrogen economy.     

Leaf development of the ostrich fern Matteuccia struthiopteris (L.) Todaro

The timing of emergence of the three different leaf types of Matteuccia struthiopteris is described from plants sampled over the course of a growing season. Vegetative leaves were first to appear, followed five weeks later by sporophylls and cataphylls. Leaf number and type, and total leaf dry weight per plant were assessed in weekly transects. Vegetative fronds contributed the most to total leaf dry weight, which increased during the first four weeks, and then remained constant for the remainder of the season. Cataphylls, although numerous by the end of the season, contributed little weight. Sporophylls occurred on the widest plants with the most vegetative leaves and greatest leaf weight, whereas cataphylls occurred on most plants except the smallest. Experimentally defoliated plants were re-examined in late summer. Following initial harvest, plants often produced a second smaller set of leaves. These were restricted to vegetative leaves and cataphylls. Ability to reissue leaves, especially vegetative fronds, declined very quickly after the first few weeks in the growing season. Defoliated plants draw on the extensive reservoir of developing leaves which are found on the rhizome, thus possibly diminishing the ability of the plant to withstand regular harvesting of the young fronds for food. Individual leaves were tagged and measured over the growing season. Non-linear regression curves fitted to the growth data for the three types of leaves indicate that growth was described best by a monomolecular growth curve for the vegetative and fertile fronds. Cataphyllar growth could be described equally well by either a monomolecular or a logistic function.     

Matter-economical roles of the evergreen foliage ofAucuba japonica,an understory shrub in the warm-temperate region of Japan

Leaf demography and productivity ofAucuba japonica, an understory shrub in the warm-temperate region, were examined and dry matter economy was analyzed to evaluate the roles of the evergreen foliage. Turnover of leaves occurred during a short period in spring. The mean leaf life span was about 2.6 years. Annual NAR (net assimilation rate) of each sample shoot was calculated from the biomass and the total dead mass estimated from scars of leaves and floral parts. The average NAR was 1.34±0.22 g·g⁻¹·yr⁻¹. The ratio of dry matter produced by leaves during their whole life span to the initial investment was 3.45±0.37. The annual NAR calculated for individual plants was negatively related to the life span of their leaves. The seasonal change in SLW (specific leaf weight) showed that the reserve material in leaves was accumulated from autumn to early spring and was consumed for the growth of new organs in the following season. The dry matter withdrawn in spring from the overwintering foliage amounted to 40% of dry mass of the new organs developed.     

Relationships Between Nitrogen and Water Concentration in Shoot Tissue ofMolinia caeruleaDuring Shoot Development

Plants ofMolinia caeruleawere supplied with either a low (0.2mol m^-3) or high (10 mol m^-3) supply of nitrogen over two growingseasons. A total of 14 destructive plant harvests were made:when plants were in an over-wintering state prior to the secondseason; immediately following bud burst; and on 12 further occasionsthroughout the second season. The relationships between shootnitrogen concentration on a dry mass basis, shoot water contentand plant developmental stage were investigated. Shoot nitrogenconcentration on a dry mass basis fell as the growing seasonprogressed. In contrast, the concentration of nitrogen in tissuewater after bud burst showed only a slight reduction. The concentrationof nitrogen both on a dry mass basis and in tissue water wasgreater for plants receiving the higher supply of nitrogen.Shoot water content was highest immediately following bud burstthen declined as the season progressed, with plants receivingthe low nitrogen supply having slightly greater shoot watercontents. It was concluded that the decline in shoot nitrogenconcentration ofM. caeruleaon a dry mass basis as the mass increasedwas mainly explained by changes in shoot water content. Theobserved increase in the rate of decline of both shoot nitrogenconcentration and water content with increased shoot mass coincidedwith the cessation of leaf tissue production and was thereforedue to a switch from the production of leaves to other tissues.Copyright1999 Annals of Botany Company Molinia caerulea(L.), purple moor grass, nitrogen, water content, shoot development.     

Leaf isotopic (δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N) and nitrogen contents of<Emphasis Type="Italic"> Carex</Emphasis> plants along the Eurasian Coastal Arctic: results from the Northeast Passage expedition

We conducted surrogate in-situ physiological performance measures (¹³C and ¹⁵N) of Carex plants from 15 Eurasian Coastal Arctic sites. Leaf carbon isotope discrimination (LCID) of Carex plants exhibited significant differences between sites (populations). Additionally, LCID was inversely correlated with mean annual temperature and stomatal density, and to a lesser extent, with the depth of thaw. Leaf ¹⁵N values of Carex plants exhibited significant differences between sites without differences among ramet age classes, and the leaf ¹⁵N values were inversely correlated with mean annual precipitation. These ranges of Carex leaf gas exchange and mineral nutrition across the Eurasian Arctic may contribute to Carexs dominance in coastal tundra systems. Also, the inverse correlation between LCID, precipitation, and temperature indicates that, as precipitation increases and temperatures continue to warm in Eurasia, leaf gas exchange may actually be lower in the future, leading to reductions in shoot growth and lower above-ground biomass production.     

Fungal entomopathogens as endophytes: can they promote plant growth?

Two experimental replicates were conducted to test whether strains of Beauveria brongniartii (BIPESCO2 and 2843) and Metarhizium brunneum (BIPESCO5) can endophytically colonise Vicia faba plants and improve their growth by comparing them with an endophytic strain of B. bassiana (NATURALIS^®). The plants were inoculated through foliar spray and the effect of inoculation on plant height, leaf pair number, fresh root and shoot weights was measured at 7 and 14 days post inoculation (dpi). Endophytic colonisation of different plant parts with the tested fungal strains were confirmed 7 and 14?dpi through re-isolation of inoculated fungi onto selective media and subsequent Simple Sequence Repeat (SSR) marker-based genetic identification. All tested strains were able to endophytically colonise leaves, stems, and even roots of inoculated plants 7 and 14?dpi, but per cent colonisation varied significantly among strains and plant parts within each sampling date. Foliar inoculation of plants with the tested strains increased plant height, leaf pair number, fresh shoot and root weights; however the increase was not always consistent across sampling dates in both experimental replicates. This study provides the first evidence for the endophytic colonisation of plants with two strains of B. brongniartii, an important biocontrol agent of Melolontha melolontha and other scarab beetles in several European countries, and thus extends previous reports on the ability of entomopathogenic fungi to act as endophytes. It also presents possible explanations for the lack of consistency in the plant growth promotion obtained by the foliar inoculation of entomopathogenic fungi.     

Microbial populations,fungal species diversity and plant pathogen levels in field plots of potato plants expressing theBacillus thuringiensis var.tenebrionis endotoxin

The environmental release of genetically engineered (transgenic) plants may be accompanied by ecological effects including changes in the plant-associated microflora. A field release of transgnic potato plants that produce the insecticidal endotoxin ofBacillus thuringiensis var.tenebrionis (Btt) was monitored for changes in total bacterial and fungal populations, fungal species diversity and abundance, and plant pathogen levels. The microflora on three phenological stages of leaves (green, yellow and brown) were compared over the growing season (sample days 0, 21, 42, 63 and 98) for transgenic potato plants, commercial Russet Burbank potato plants treated with systemic insecticide (Di-Syston) and commercial Russet Burbank potato plants treated with microbialBtt (M-Trak). In addition, plant and soil assays were performed to assess disease incidence ofFusarium spp.,Pythium spp.,Verticillium dahliae, potato leaf roll virus (PLRV) and potato virus Y (PVY). Few significant differences in phylloplane microflora among the plant types were observed and none of the differences were persisent. Total bacterial populations on brown leaves on sample day 21 and on green leaves on sample day 42 were significantly higher on the transgenic potato plants. Total fungal populations on gree leaves on sample day 63 were significantly different among the three plant types; lowest levels were on the commerical potato plants treated with systemic insecticide and highest levels were on the commercial potato plants treated with microbialBtt. Differences in fungal species assemblages and diversity were correlated with sampling dates, but relatively consistent among treatments.Alternaria alternata, a common saprophyte on leaves and in soil and leaf litter, was the most commonly isolated fungus species for all the plant treatments. Rhizosphere populations of the soilborne pathogensPythium spp.,Fusarium spp. andV. dahliae did not differ between the transgenic potato plants and the commercial potato plants treated with systemic insecticide. The incidence of tuber infection at the end of the growing season by the plant pathogenV. dahliae was highest for the transgenic potato plants but this difference was related to longer viability of the transgenic potato plants. This difference in longevity between the transgenic potato plants and the commercial + systemic insecticide potato plants also made comparison of the incidence of PVY and PLRV problematic. Our results indicate that under field conditions the microflora of transgenicBtt-producing potato plants differed minimally from that of chemically and microbially treated commerical potato plants.     

Sowing and transplantation of Adonis ramosa (Ranunculaceae) for the establishment of a new population in a seminatural broad-leaved deciduous forest floor

Adonis ramosa (Ranunculaceae) is a plant whose risk of extinction is increasing in Japan. In this study, we show that there is a significant possibility of establishing an A. ramosa population by sowing seeds or transplanting plants in a seminatural broad-leaved deciduous forest floor. Immediately after seed collection in early June, seeds were sown either in pots that were watered periodically or in a deciduous forest floor where the soil surface was prepared. In the following spring, 30–40% of the seeds germinated. Of the one-year-old plants buried at a depth of 2 cm and two-year-old plants buried at a depth of 2 or 8 cm in the fall, 96% sprouted leaves in the following spring. However, 79% of the one-year-old plants buried at a depth of 8 cm sprouted leaves. In spring, the number of leaves, the widths of individual plants, and the heights of the two-year-old plants were greater than those of the one-year-old plants. The dry weights of one- and two-year-old plants in fall after one spring growing season increased by 1.6–2.3 times and by 2.3–5.1 times, respectively, compared to the dry weight at the time of transplanting. Also, the dry weights of the plants transplanted at a depth of 8 cm were higher than those of plants transplanted at a depth of 2 cm for both one- and two-year-old plants. The results suggest that the growth conditions at a depth of 8 cm are more favorable than those at a depth of 2 cm.     

Seasonal growth and biomass ofTrapa japonica Flerov in Ojaga-Ike Pond,Chiba, Japan

In order to determine the seasonal growth and biomass ofTrapa japonica Flerov, field observations were carried out at Ojaga-ike Pond, Chiba, Japan, during 1979 and 1980. In spring, the plant showed exponential growth (c. 0.080 g g⁻¹ day⁻¹) and shoot elongation was as rapid as 10 cm day⁻¹. The plant attained its maximum biomass (380.5±35.1 g m⁻²) in late August, and about 50% of this was concentrated in the topmost 30-cm stratum (645.7±33.1 g m⁻³); maximum total stem length exceeded 6m. The plant produced large (500–800 mg per fruit), but small numbers of nut-like fruit (maximum, 5 fruits per rosette). Defoliation occurred almost linearly with time at a rate of 30.6 leaves m⁻² day⁻¹; annual net leaf production was estimated to be about twice as large as the seasonal maximum leaf biomass. While the number of leaves per rosette showed moderate seasonal change, rosette density, rosette area and leaf dry weight changed considerably during the year. From the negative log-log correlation between mean total leaf dry weight per rosette and rosette density, density-dependent rosette growth was assumed. The cause of the wide spread of this species in aquatic habitats is briefly discussed in terms of its seed size and morphology.     

Leaf position,light levels,and nitrogen allocation in five species of rain forest pioneer trees

We used path analysis to ask whether leaf position or leaf light level was a better predictor of within-plant variation in leaf nitrogen concentration in five species of rain forest pioneer trees (Cecropia obtusifolia, Ficus insipida, Heliocarpus appendiculatus, Piper auritum, and Urera caracasana) from the Los Tuxtlas Biological Station, Veracruz, Mexico. Three hundred seventy-five leaves on 28 plants of the five species were analyzed for leaf nitrogen concentration, leaf mass per area, and leaf light interception at different positions (= nodes) along a shoot. Mean values of leaf nitrogen concentration ranged from 0.697 to 0.993 g/m² in the five species, and varied by as much as 2.24 g/m² among leaves on individual plants. Leaf position on the shoot explained significantly more of the within-plant variation in leaf nitrogen concentration than did leaf light level in four of the five species: Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum (branch leaves only), and Urera caracasana. However, individual species differed considerably in the patterns of nitrogen allocation and leaf mass per area among leaves on a shoot. These results suggest that leaf nitrogen deployment in these plants is, in part, developmentally constrained and related to the predictability of canopy light distribution associated with plant growth form.     

Life history and population dynamics of the Japanese Yam,Dioscorea japonica Thunb.

The adaptive significance of the emergence mode ofDioscorea japonica was studied with respect to initial plant size (seed, bulbil and tuber) and light intensity, using mathematical simulation based on Yokoi's (1976) model. Under 1.5% full sunlight conditions, plants emerging with only one leaf did not develop a shoot system throughout the growing period (Hori and Oshima, 1986). Simulation indicated that, for this species of plant under poor productive conditions, the optimal time for switch-over from the vegetative to reproductive growth phase to maximize the tuber weight at the end of the growing period, occurred immediately following the start of autotrophic growth. By means of shoot growth patterns, small and large size plants acquired the ability of shade tolerance and shade avoidance, respectively. Further, the life history ofD. japonica could be expressed as a flow chart based on plant size and light intensity data.