ANATOMICAL AND PHYSIOLOGICAL ACCLIMATION OF FATSIA JAPONICA LEAVES TO IRRADIANCE

Anatomical and physiological leaf characteristics and biomass production of Fatsia japonica plants were studied. Plants were grown in a growth chamber at 300 μmol m^-2 s^-1 (high light) and 50 μmol m^-2 s^-1 (low light) photosynthetic photon flux density. Plants grown under high light showed a net maximum photosynthetic rate 44% higher than plants grown under low light; the light compensation point and the light saturation point were also higher in high-light plants. Photosynthetic oxygen evolution in isolated chloroplasts was about 40% higher in high-light plants. However, chlorophyll content on a dry weight basis, on a leaf area basis, and per chloroplast was greater in plants grown under low light. Leaf thickness in high-light plants was 13% higher than in low-light plants. The number of chloroplasts was 30% higher in high-light leaves, while chloroplast size was only slightly higher. Chloroplast ultrastructure was also affected by light. Leaf dry weight, leaf area, and biomass production per plant were drastically reduced under low light. Thus, F. japonica is a plant that is able to acclimate to different photosynthetic photon flux density by altering its anatomical and physiological characteristics. However, low-light acclimation of this plant has a considerable limiting effect on biomass production.     

Effects of competition,herbivory and substrate disturbance on growth and size structure in pin cherry (Prunus pensylvanica L.) seedlings

We examined separate and interactive effects of intraspecific competition, vertebrate browsing and substrate disturbance on the growth and size structure of pin cherry (Prunus pensylvanica L.) in the first two seasons of growth after clearcutting, in a hardwoods forest in New Hampshire, United States. Over the 15-month study period, 97.5% of 1801 individuals survived, and mean plant height increased from 4-fold at high density to 5-fold at low density. Relative height growth was significantly lower at higher plant densities in two of the three growth periods examined. Vertebrate browsers (moose and deer) significantly preferred taller plants. Browsed plants had higher relative height growth following browsing than unbrowsed plants (compensatory growth) at low and intermediate densities. The degree of compensation declined with density and compensation was not significant at the highest density level. At low and intermediate densities, plants browsed early in life regained height dominance through compensatory growth; they failed to regain dominance at high density. Because compensatory growth tended to offset the effects of size-selective browsing, there was no difference in the degree of size inequality between browsed and unbrowsed plots. However, size inequality increased with plant density. Substrate disturbance caused by logging had no significant effects on either relative height growth or size inequality. The slope of the relationship between relative height growth and initial height increased significantly with density and time, and was higher in unbrowsed than in browsed plots, suggesting that competition among plants was size-asymmetric. Despite the preference of browsers for large plants, there was a clear net growth advantage for plants of large initial size, when the effects of competition, browsing and compensatory growth were combined. The interactive effects of density and browsing demonstrate the importance of a multifactorial approach to the analysis of individual plant performance and population structure.     

张掖湿地芨芨草叶大小和叶脉密度的权衡关系

叶大小-叶脉密度的权衡关系是植物叶经济谱理论的基础, 对理解资源竞争条件下植物叶片的物理构建与生理代谢的关系具有重要的意义。该文采用标准化主轴估计(standardized major axis estimation, SMA)的方法, 按芨芨草(Achnatherum splendens)株丛密度设置I (>12丛·m^-2)、II (8-12丛·m^-2)、III (4-8丛·m^-2)和IV (<4丛·m^-2) 4个密度梯度, 以叶面积和叶干质量分别表示叶大小, 对张掖洪泛平原湿地不同密度条件下芨芨草种群的叶大小和叶脉密度的关系进行研究。结果表明: 随着芨芨草株丛密度的降低, 湿地群落的土壤含水量逐渐减小、土壤电导率逐渐增加, 芨芨草的净光合速率(P_n)、蒸腾速率(T_r)和分枝数呈先增大后减小的趋势, 叶面积、叶干质量、比叶面积和株高呈逐渐减小趋势、光合有效辐射(PAR)和叶脉密度呈逐渐增加趋势; 芨芨草叶大小和叶脉密度在高密度(I)和低密度(IV)样地均呈极显著负相关关系(p < 0.01), 中密度(II、III)样地二者呈显著负相关关系(p < 0.05); 叶大小和叶脉密度回归方程的SMA斜率在不同密度样地均显著小于-1 (p < 0.05), 即芨芨草叶大小和叶脉密度呈“此消彼长”的权衡关系。在高密度湿地群落芨芨草倾向于大叶片低叶脉密度的叶片构建模式, 在低密度湿地群落选择小叶片高叶脉密度的异速生长模式, 体现了密度制约下湿地植物的生物量分配格局和资源利用对策。     

Above-ground competition does not alter biomass allocated to roots in Abutilon theophrasti

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root:shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.     

Consumer–plant interaction strength: importance of body size,density and metabolic biomass

Explaining variability in the strength and sign of trophic interactions between primary consumers and plants is a long‐standing research challenge. Consumer density and body size vary widely in space and time and are predicted to have interactive effects on consumer–plant interactions. In a southern US salt marsh, we used replicate field enclosures to orthogonally manipulate the body size (mass) and density of a dominant consumer (a snail). We investigated impacts (leaf damage and biomass) on monocultures of cordgrass, the foundation species, over three months. Increasing consumer density and body size increased leaf damage additively and, as predicted, multiplicatively reduced plant biomass. Notably, size and density determined the sign of consumer impact on plants: low to medium densities of small consumers enhanced, while high densities of large consumers strongly suppressed, plant biomass. Finally, total consumer metabolic biomass (mass^0.75) within an enclosure parsimoniously explained plant biomass response, supporting theoretical predictions and suggesting that multiplicative effects of density and body size resulted from their effects on total metabolic biomass. The consequences of changes in consumer density and body size resulting from anthropogenic perturbations may therefore be predicted based on metabolic biomass. Synthesis Consumer size, density and biomass can all strongly affect consumer–plant interactions. Though density and body size have been extensively studied as drivers of variation in interaction strength, the role of biomass as the ultimate driver has been less appreciated. We manipulated body size and density of a single consumer species and, based on metabolic theory, integrated these into a single variable: total metabolic biomass. Our results suggest that changes in interaction strength attributed to size or density may in fact be due to changes in metabolic biomass. This metric could thus serve as a useful tool in further understanding species interactions.     

Trade-off between leaf size and vein density of Achnatherum splendens in Zhangye wetland

Aims Trade-offs between leaf size and vein density are the basis of the theory of leaf economics spectrum, and are to understand the relationship between the physical build and physiological metabolism of plant leaves under different degrees of competition for resources. Our objective was to study the changes in the relationship between leaf size and vein density (leaf dry biomass and leaf area) in Achnatherum splendens populations with four plant bundle densities located in the flood plain wetland of Zhangye. Methods The study site was located at floodplain wetlands of Zhangye, Gansu Province, China. Survey and sampling were carried out in the communities that A. splendens dominated. According to the plant bundle density, the A. splendens communities were divided into four density gradients with “bundle” for the sampling units, high density (I, > 12 bundle·m^-2), medium density (II, 8-12 bundle·m^-2), medium density (III, 4-8 bundle·m^-2) and Low density (IV, <4 bundle·m^-2). According to the density of each combination, we chose seven (5 m × 5 m) A. splendens samples, resulting in a total of 28 samples (4 × 7). The soil physical and chemical properties of four density gradients were investigated and six samples of A. splendens were used to measure the leaf area, leaf dry biomass and vein density in laboratory, and biomass of different organs was measured after being dried at 85 °C in an oven. 28 plots were categorized into three groups: high, medium and low density, and the standardized major axis (SMA) estimation method was used to examine the allometric relationships between leaf area, leaf dry biomass and vein density. Important findings The results showed that with the population density changed from high, medium, to low, the soil moisture decreased, and soil electric conductivityincreased. The leaf area, leaf biomass and height of A. splendens decreased, and the vein density, specific leaf area and photosynthetically active radiation (PAR) increased gradually. In addition, leaf net photosynthetic rate (P_n), transpiration rate (T_r) and twig number firstly increased then decreased. There was a highly significantly negative correlation (p < 0.01) between the leaf size and vein density on the high- and low-level densities (I, IV), whereas less significant (p < 0.05) on the level of medium density (II, III). The SMA slope of regression equation in the scaling relationships between leaf size and vein density was significantly smaller than -1 (p < 0.05).     

EFFECT OF DENSITY ON SECONDARY SEX CHARACTERISTICS AND SEX RATIO IN SILENE ALBA (CARYOPHYLLACEAE)

A field survey of plant and flower sex ratio and secondary sex characteristics was made in Silene alba. Female-biased plant sex ratios were found, as seems typical for the species. Sex ratio distribution correlated with a gradient of soil moisture (with the more moist area having a more female-biased ratio) and with changes in the density of Silene (intermediate and higher density areas having greater female bias). The floral sex ratio was significantly female-biased only at the site that was most female-biased in terms of plant sex ratio. Otherwise the population of flowers was significantly male-biased. Male and female plants harvested from the field differed in secondary sexual characteristics. Males had more flowers and invested proportionately more biomass in leaf, but less in root, stem and reproductive tissue than did females. Although both males and females were larger in terms of total dry weight at the moist site, males produced more flowers at the driest (high density) site. Here the female bias in plant sex ratio was intermediate, but the floral sex ratio was significantly male-biased. A glasshouse experiment was performed in which plants were grown at four densities. Density significantly influenced plant survivorship and the probability of flowering, and increased female bias in the pots, but it did not affect patterns of biomass allocation in flowering plants. Patterns of male and female biomass allocation did not differ in the experiment, except in terms of reproductive allocation (greater in females) and allocation to leaf, greater in males, but only at the lowest density. This work urges caution in interpreting differences between males and females in the field as secondary sex characteristics, since we find such properties to be overlapping under experimental conditions. It supports the idea that males and females of a species may sustain different reproductive output under differing conditions.     

Relatives growing together: pair density and kinship

Kin selection is often used to explain the evolution altruism towards relatives through favouring the evolution of kin recognition. However, it remains unclear whether kin recognition is affected by plant pair density and different degrees of relatedness. A two-factor experimental design of kinship (three kinship degrees including siblings, closely related strangers and distantly related strangers) and pair density (including relative small, medium and large pair densities) was conducted in this study. Plant competitive traits including rosette size, specific leaf area (SLA), stem elongation, root and leaf allocation, seed biomass and vegetative biomass were measured to reflect interactions among plants living with different relatives of Arabidopsis thaliana accessions [Columbia (Col-0), Landsberg erecta (Ler) and Wassileskijia (Ws)] in three different pair densities. The SLA only showed kinship effect, and siblings showed higher SLA than non-siblings in each pair density. The plant total biomass was only affected by pair density, which increased with decreases of pair density. The rosette size, stem elongation, root allocation and leaf allocation showed interactive effects of kinship and pair density. In the large pair density, the rosette size of siblings was lower than distantly related strangers, compared to closely related strangers; the stem elongation and root allocation were lower, while the seed biomass of siblings was higher than the closely or distantly related strangers. In the medium pair density, plants living with siblings or with closely related neighbours showed higher root allocation than with distantly related neighbours. In the small pair density, the plant rosette acted similarly to of which in the large pair density, and siblings showed higher root allocation than the two strangers. The other traits in each pair density showed no significant differences among kinship treatments. A relatively large pair density achieves kin recognition by deducing root competition ability and mutual shading, with increased efficient light capture and fitness. Similar such root and efficient light capture strategies were selected in medium pair density. Except the efficient light capture strategies, small pair density also displays allocation trade-offs between roots (decreased) and leaves (increased) for siblings. Moreover, kin responses on those attributes are also adjusted by kinship degree. Thus, kinships and pair density are important variables to mediate kin interactions.     

Limited effects of soil nutrient heterogeneity on populations of Abutilon theophrasti (Malvaceae)

An experiment was conducted to determine if spatial nutrient heterogeneity affects mean plant size or size hierarchies in experimental populations of the weedy annual Abutilon theophrasti Medic. (Malvaceae). Heterogeneity was imposed by alternating 8 × 8 × 10 cm blocks of low and high nutrient soil in a checkerboard design, while a homogeneous soil treatment consisted of a spatially uniform mixture of the two soil types (mixed soil). Populations were planted at three densities. The effect of soil type on the growth of individuals was determined through a bioassay experiment using potted plants. The high nutrient, low nutrient, and mixed soil differed in their ability to support plant growth as indicated by differences in growth rates and final aboveground biomass. Concentrations of N, K, P, and Mg, measured at the end of the growing season in the experimental plots, also differed among all three soil types. Nevertheless, nutrient heterogeneity had little effect at the population level. Mean maximum leaf width measured at midseason was greater for populations on heterogeneous soil, but soil treatment did not affect midseason measurements of plant height, total number of leaves per plant, or canopy width. Population density affected all these parameters except plant height. When aboveground biomass was harvested at the end of the growing season, soil treatment was found to have no main effect on mean plant biomass, total population biomass, the coefficient of variation in plant biomass, or the combined biomass of the five largest plants in the population, but mean plant biomass was greater for populations on heterogeneous soils at the intermediate planting density. Mean plant biomass, total population biomass, and the coefficient of variation in plant biomass all varied with planting density. Mortality was low overall but significantly higher on homogeneous soil across all three densities. Soil heterogeneity had its strongest effect on individuals. In heterogeneous treatments plant size depended on the location of the plant stem with respect to high and low nutrient patches. Thus, soil nutrient heterogeneity influenced whether particular individuals were destined to be dominant or subordinate within the population but had little effect on overall population structure.     

Density-dependent responses of Picea purpurea seedlings for plant growth and resource allocation under elevated temperature

This study was conducted to determine whether plants in the presence or absence of competition differ in their responses to warming, and whether density modifies the effect of warming. Picea purourea seedlings were grown under ambient and warming (ambient +2.2 °C) conditions in climate control chambers with two different planting densities. After 4 years, seedlings were harvested and measured for height, stem diameter, leaf area, structural biomass, carbon, nitrogen, chlorophyll and carbohydrate levels of needles, branches, stem and roots. At low density, warming increased height, stem diameter, total leaf area biomass production and carbohydrate concentration per seedling, while it decreased C/N ratio for all plant parts, but did not affect chlorophyll content. By contrast, at high density, although warming increased biomass and total leaf area, it did not affect plant height and stem diameter. At the same time, it had different effects on chlorophyll content, C/N ratio and carbohydrate levels among plant parts. On the other hand, high density limited plant growth and altered resource allocation pattern. Our study demonstrates that planting densities decreased the temperature-induced growth enhancement of P. purpurea seedlings and the effects of warming on resource allocation not only showed density-dependence, but also vary with tissue age classes and root diameter; the responses of plants to elevated temperature, acquired from plants growing as individuals, may not be applicable to plants grown under intraspecific competition as typically found in the field.     

Effects of shading and plant density on leaf growth of Viciafaba

Faba beans (Viciafaba cv. Maris Bead) were grown in the field at densities of 20 and 60 plants m^-2 and under zero, 34 and 56% reduction in incoming solar radiation. Measurements of the area of individual leaves were made every two days. Rates of leaf appearance and the duration of expansion of a leaf were virtually unaffected by the experimental treatments. Leaves required approximately 200 ^oC days (above 1 ^oC) from appearance to full expansion. Shading consistently increased specific leaf area but decreased leaf weight only at the greater shading level. At low density leaves were largest under 34% shade and smallest under 56% shade, but at high density there were no significant differences in leaf size.     

Net assimilation rate and shoot area development in birch (Betula pendula Roth.) at different steady-state values of nutrition and photon flux density

Summary Small birch plants (Betula pendula Roth.) were grown in a climate chamber at different, exponentially increasing rates of nitrogen supply and at different photon flux densities. This resulted in treatments with relative growth rate equal to the relative rate of increase in nitrogen supply and with different equilibrium values of plant nitrogen concentration. Nitrogen productivity (rate of dry matter increase per plant nitrogen) was largely independent of nitrogen supply and was greater at higher photon flux density. Leaf weight ratio, average specific leaf area (and thus leaf area ratio) were all greater at better nitrogen supply and at lower values of photon flux density. The dependencies were such that the ratio of total projected leaf area to plant nitrogen at a given photon flux density was similar at all rates of nitrogen supply. The ratio was greater at lower values of photon flux density. At a given value of photon flux density, net assimilation rate and net photosynthetic rate per shoot area (measured at the growth climate) were only slightly greater at better rates of nitrogen supply. Values were greater at higher photon flux densities. Acclimation of the total leaf area to plant nitrogen ratio and of net assimilation rate was such that nitrogen productivity was largely saturated with respect to photon flux density at values greater than 230 mol m^-2 s^-1. At higher photon flux densities, any potential gain in nitrogen productivity associated with higher net assimilation rates was apparently offset by lower ratios of total leaf area to plant nitrogen.     

Size-dependent variation of gender in high density stands of the monoecious annual,Ambrosia artemisiifolia (Asteraceae)

Summary We examined the relationship between size variability and the distribution of functional gender in stands of the monoecious, wind-pollinated annual Ambrosia artemisiifolia. Populations of 60 individuals were grown in the greenhouse at a density of 372 m^–2 and at two nutrient levels. Among the surviving plants, after self-thinning, variability in above-ground biomass and gender was higher in the high nutrient treatment. Among individuals there was a significant positive correlation between maleness and both height and biomass. Fecundity was also positively correlated with both measures of size. Based on the pattern of distribution of male and female flowers within the plant, it appears that the increase in maleness in larger plants is due to increased branching and axis elongation. These results demonstrate that competitive interactions, which lead to increased variability in biomass and fecundity, can also generate variability in gender within populations.     

The influence of plant density on the responses of Sinapis alba to CO2 and windspeed

Plants in nature live in populations of variable density, a characteristic which may influence individual plant responses to the environment. We investigated how the responses of Sinapis alba plants to different wind speeds and CO₂ concentrations could be modified by plant density. In our wind-density experiment the expectation that mechanical and physiological effects of wind will be ameliorated by growing in high density, as a result of positive plant interactions, was realised. Although individual plants were smaller at higher densities, the effect of increasing windspeed was much less than at lower plant densities. A similar reduced sensitivity of individual plant growth under high densities was also observed under CO₂ enrichment. When measured as a population or stand response, there was no effect of density on the CO₂ responses, with all stands showing very similar increases in total biomass with CO₂ enrichment. In the wind speed experiment, total biomass per stand increased significantly with density, although there was no effect of density on the wind speed response. Specific leaf area decreased with increasing wind speed and this response was significantly affected by the density at which the plants grew.     

Effects of Density and Extinction Coefficient on Size Variability in Plant Populations

The effects of density and extinction coefficient on size variability,as measured by the coefficient of variation of plant weightin even-aged monocultures, were investigated theoretically usinga diffusion model of growth and size distribution and a canopyphotosynthesis model over the range of densities at which self-thinning(size-dependent mortality) does not occur. Size inequality (thecoefficient of variation of plant weight) increases with increasingdensity or leaf area index at each growth stage. Plants witherect leaves are prone to lower size inequality than plantswith horizontal leaves. These results agree well with existingobservations on even-aged plant monocultures and suggest thatcompetition between plants is mainly one-sided (competitionfor light). One sided competition affects size variability througha G(t, x) function (mean growth of plants of size x at timet per unit time). Two-sided competition (including competitionfor nutrients) affects size variability through a D(t, x) function(variance of growth of plants of size x at time t per unit time).In this case, size inequality decreases with increasing density.The importance of studying size variability is emphasized. Helianthus annus L., size variability, size inequality, coefficient of variation, competition, density effect, extinction coefficient, diffusion model, canopy photosynthesis model     

Response of cowpea to variations in planting density and nutrient level

A greenhouse study was carried out using cowpea (Vigna unguiculata (L.) Walp.) grown in Perlite^® and inoculated with Nitragin^® to investigate the concentration of plant nutrients and planting density required for optimum biomass production. Five concentrations (full, 0.5, 0.2, 0.1 and 0.05 strength) of Bisseling's nutrient solution and five planting densities (one to five plants per pot) were tested in a factorial randomized Graeco-Latin square design. Growth was determined as fresh and dry weights of leaves, stems, petioles, roots, flowers and pods, and whole plant.Optimum biomass production was found at 0.5 strength nutrient solution and a density of one plant per pot. Plants were more sensitive to higher planting density than to alterations of nutrient level. Over a twenty-fold range of nutrient supply, whole plant biomass yield varied at most by 44%, whereas increasing planting density from one to five plants per pot decreased biomass production by as much as 77%. There is a decrease in the shoot/root ratio as nutrient level decreases. The data suggests a potential for higher seed production at the higher densities and lowest nutrient levels, but this data was inconclusive.     

EFFECTS OF SALINITY,NITROGEN, AND POPULATION DENSITY ON THE SURVIVAL,GROWTH, AND REPRODUCTION OF ATRIPLEX TRIANGULARIS (CHENOPODIACEAE)

Populations of Atriplex triangularis were grown under laboratory conditions in a growth chamber and manipulated in an inland Ohio saline pond in order to examine the relative effects of salinity, nitrogen fertilization, and population density on growth, reproduction, and survival. For laboratory plants, nitrogen fertilization was the most important variable, with biomass and reproductive effort being greatest at the high nitrogen level. As salinity increased, biomass decreased only in plants not limited by nitrogen. Increasing density caused biomass per plant to decrease at both high and low nitrogen levels. For field plants, density was the most important variable, with biomass per plant and survival both decreasing as density increased. As density increased, size inequality among individuals increased but biomass per unit area and individual reproductive effort remained relatively constant. Nitrogen fertilization slightly enhanced survival, but did not affect biomass. It is suggested that density-dependent processes may be significant even in relatively harsh physical environments.     

Testing of Corner’s rules across woody plants in Tiantong region,Zhejiang Province: effects of individual density

Aims Corner’s rules reflect the architectural strategies of plants with respect to deployment of twig size and leaf size, as well as of the number of twigs and leaves. The objective of this study was to examine how Corner’s rules would vary among plants with different individual densities.
Methods The study site is located in the Tiantong National Forest Park (29.87° N, 121.65° E), Zhejiang Province. We measured twig cross-sectional area (twig size), total leaf area (leaf size per twig), and the number of twigs at a given twig size (branching intensity) in woody plants across 25 plots differing in stem density to examine the effects of individual competition on Corner’s rules. The standardized major axis (SMA) analysis was conducted to determine the quantitative relationships of twig size with leaf size and branching intensity.
Important findings Significant, positive allometric relationships between cross-sectional area and total leaf area were found in individual plants across all communities. There was no significant difference among communities of different density intervals in the slope of the linear regression between cross-sectional area and total leaf area of individual plants, and the common slope of the regressions was significantly greater than 1 (p < 0.001). The intercept was significantly greater for plants in communities with higher density than in those with lower density (p < 0.001), indicating that plants in a high density community support greater total leaf area than in a low density community for a given twig size. In contrast, a significant, negative allometric scaling relationship was found between branching intensity and cross-sectional area in individual plants across different communities. Also, nosignificant difference was found among plants in communities of different density intervals in the slope of the regression between branching intensity and cross-sectional area, and the common slope of the regressions was significantly less than –1 (p < 0.001). The intercept for the regression relationship between twig area and branching intensity was the same among plants in communities of different density intervals (p > 0.05), suggesting that plants in a high density community do not deploy more twigs per twig size than in a low density community. In summary, this study demonstrated that plants responded to changes in individual density by maintaining an invariant regression slope for the twig size-leaf size relationship and the twig size-branching intensity relationship, and that the Corner’s rules were not affected by individual density of the communities in the Tiantong region. However, changes in the intercept of the regression between twig size and leaf size indicate that deployment strategies between twig and leaf sizes could be adjusted with increasing individual plant competition, thus structuring species coexistence through niche differentiation.     

The effects of density and spatial distribution on selection for emergence time in Prunella vulgaris (Lamiaceae)

We investigated the effects of both overall density and variation in local density on the relationship between emergence time and final biomass in Prunella vulgaris. The relationship between emergence time and final biomass was used to quantify the pattern of selection on emergence time. Seeds were planted in flats in three different spatial distributions (hexagonal, random, high variance) at each of three overall densities (308, 769, and 3,077 seeds/m²). Individual seedlings were marked upon emergence, and their final biomass was determined after 90 days of growth. With increasing overall density, mean plant biomass decreased, but the coefficient of variation in biomass and the magnitude of directional selection for early emergence increased. Increasing variation in the spatial distribution of the plants had no effect on mean plant biomass but did significantly increase the coefficient of variation in biomass at both low and medium densities. Both the magnitude of directional selection and the curvature in the relationship between emergence time and final biomass tended to increase with increased variation in the spatial distribution. Our results suggest that both overall plant density and the spatial distribution of individuals can affect the pattern of selection on plant traits.     

The effects of density on size-dependent gender plasticity in the monoecious species Sagittaria potamogetifolia (Alismataceae)

Aim

To test the fitness-gain curve model proposes that cosexual plants adjust their sex ratios and resource allocation depending on their size. In this study, the monoecious species Sagittaria potamogetifolia was used as a model to determine the effects of plant size and density on gender modification and reproductive allocation.