Search

Premise of research. Seed ontogeny between fertilization and seed maturity is a neglected life history stage in demographic studies, yet this period may have profound consequences for seed set and seedling vigor. For plant species with multiovulate linear fruits, it is possible to record the relative position of each ovule, thereby allowing investigators to assess whether ovule development occurs at random or whether it exhibits unique discernible patterns within fruits. We studied effects of ovule position on patterns of ovule development, seed mass, and seedling size within linear pods of Cercis canadensis. Methodology. Fruits were collected from multiple trees at each of three sites in southeastern Michigan. Intraovary ovule position and developmental fate (i.e., undeveloped ovule, aborted ovule, insect-damaged seed, and mature seed) and seed mass were determined. Seedling performance from three seed size classes was also monitored. Seedling traits included days to emergence, height, leaf area, and seedling biomass. Pivotal results. Three-fourths or more of all ovules within fruits across the populations reached seed maturity. Patterns of seed maturation and abortion were nonrandom and significantly depended on populations, individuals, and ovule positions within fruits. Probability of seed maturation within individual fruits was lowest at the basal end and highest at either the center or the distal end, suggesting the existence of a fertilization gradient. Conversely, frequencies of undeveloped ovules and aborted seeds were highest at the bases of fruits. Insect-damaged seeds accounted for 1%–3% of all ovules and occurred randomly. Seeds located in basal sections of fruits were also smaller than seeds located in central and distal sections. Seed mass was positively correlated with all measures of seedling performance. Conclusions. Patterns of ovule development and seed maturation were determined to be nonrandom within fruits of C. canadensis. Ovule position influences abortion and maturation of seeds, seed mass, and early seedling vigor and has the potential to affect overall plant fitness. [ABSTRACT FROM AUTHOR]

Premise: In many flowering plants, flowers contain more ovules than fruits have seeds. What determines which ovules become seeds? When photosynthates are limited, as may happen when plants lose leaf area to herbivory, fewer fertilized ovules become seeds. Methods: Greenhouse‐grown ramets of distinct individuals of a perennial herbaceous legume were manually defoliated to various levels determined in the field, then self‐ or cross‐pollinated. For each seed produced, we recorded its position in the fruit and its mass. From a subset of seeds from different treatments and positions in the fruits, we grew seedlings and measured their dry mass. Results: Ovules were aborted more frequently in fruits from flowers that were self‐pollinated and from those on plants with higher levels of defoliation. Ovules in the basal portion of the fruits were more likely to be aborted than those at the stigmatic end; this pattern was most pronounced for fruits after self‐pollination with high levels of defoliation. Total number of seeds produced and seed mass per pod were greatest in cross‐pollinated fruits after no or low levels of defoliation. Mean individual seed mass was greater for fruits with fewer seeds, indicating a trade‐off between seed number and seed mass. Seedling dry mass (a measure of vigor) was greatest for seeds in the middle positions of fruit produced by cross‐pollination after severe herbivory; no positional differences were seen for seeds from self‐pollinated fruits. Conclusions: Observed locations of seed abortion may have been selected not only by defoliation, but in part by propensity for dispersal, while positional differences in seedling vigor may be related to seed size and differential maternal allocation based on pollination treatment and leaf area lost. [ABSTRACT FROM AUTHOR]

Seed predators sometimes inflict non‐lethal seed damage. We asked whether seed size modulates the location of insect seed damage and examined whether location‐specific damage on the embryo influences early plant development (embryo survival, germination, seedling emergence and performance). We used intact and weevil‐infested seeds of a prevalent California oak tree Quercus agrifolia as study model. We conducted observational and manipulative studies (simulate partial embryo damage). Seed size significantly affected the location of insect damage within the seed and, in turn, the probability of embryo damage, with larger seeds showing lower probability of embryo damage. The location of the larva exit hole was strongly associated with the probability of embryo damage, with 0.9 probability when the exit hole is located <5 mm from the embryo. Partial damage on the embryo was found in ca 11% of the infested seeds (n = 250). Among them, 63% showed damage only on the inner part (plumule) of the embryo. Damage on the plumule (the rudimentary shoot) was more lethal than damage on the radicle, particularly at the emergence phase, when success rate of plumule‐damaged seeds decreased by half as compared to that of radicle‐damaged seeds. Plumule‐damaged seeds also emerged much later and performed more poorly than radicle‐damaged seeds. Furthermore, seedlings that emerged from plumule‐damaged seeds showed poorer physiological parameters (lower chlorophyll and nitrogen content) than those emerged from radicle‐damaged seeds. Overall, intact seeds performed better than both types of damaged seeds. We highlight that seed size and its associated differential location of seed damage determines the occurrence of embryo damage and the region affected within the embryo (e.g. plumule versus radicle) which, in turn, affects important components of plant fitness. Different selective pressures affecting mostly the plumule (insects) versus the radicle (embryo‐clipping rodents) may contribute to elucidate the co‐evolutionary dynamics of seeds and their predators. [ABSTRACT FROM AUTHOR]

[Display omitted] Plant recruitment is limited by seed predation. However, seeds that are only partially consumed can still contribute to regeneration provided the embryo remains viable. Seed size and shape are important traits that influence the relative location of the embryo, as well as its survival and further development. Yet, it is unclear whether the interaction of seed size and shape affects seed tolerance to partial damage and initial seedling performance. We evaluated the effects of simulated partial damage in three different acorn shapes (flattened, triangular and typical) on early seedling establishment in the threatened Quercus insignis , the largest-seeded oak species worldwide. We also distinguished between lateral acorn damage (pericarp damage only) and cotyledon damage (1/3 of the reserves), using acorn size as a covariate. For this, we recorded the germination, emergence and performance (total height, basal diameter, specific leaf area, total leaf area, above and belowground dry biomass) of each seedling after 110 days of growth. Seed shape influenced the rate and percentage of acorn germination, seedling emergence and performance. Typical-shaped acorns germinated at higher rates and produced more seedlings with higher performance. Simulated damage increased the rate and percentages of germination and emergence, but did not affect performance (except for specific leaf area). Seed size favored performance but not germination or emergence, and no significant interaction was found between acorn shape and seed size with respect to germination, emergence or performance, depending on each damage treatment. Our results suggest that acorn size allows tolerance to partial seed predation, since low to moderate acorn damage (<1/3 of cotyledon lost) had no negative effect on germination or emergence. Larger seed size could therefore not only support seedling performance, but also help to meet the nutritional requirements of small and mid-size predators without risking the integrity or development of the embryo. Acorn shape should therefore be considered in basic and applied oak ecology since seed morphology seems to influence not only germination and emergence, but also seedling performance. These results may have important eco-evolutionary implications in the context of seed-predator interactions, since certain shapes tolerate damage better than others and may thus benefit from the selection pressures exerted by seed foragers, both predators and dispersers. In addition to acorn size, managers should consider acorn shape and its relationship to early seedling establishment, as well as the potential for using partially damaged acorns in oak forest restoration projects. [ABSTRACT FROM AUTHOR]

Intraspecific variation in seed size may result from life-history constraints or environmental conditions experienced. This variation in seed size is likely to affect the early stage of invasion as seed size may contribute to the success or failure of population establishment. However, only a few studies have examined seed size variability and its causes and consequences for invaders so far. Using the invasive herb Lupinus polyphyllus, we estimated seed mass variation within and among 39 populations from two different geographic regions in a part of the invaded range. We empirically and experimentally evaluated the effect of seed number and environmental conditions (e.g. geographic region, habitat type, intraspecific competition) on seed mass, emergence and seedling performance. Seed mass varied threefold, being largest among individual plants within populations and smallest among populations. Variation in seed mass was neither related to seed number nor the environmental conditions examined, but led to differences in offspring performance, with emergence and seedling size increasing with seed mass. Larger L. polyphyllus seeds were better establishers than smaller seeds regardless of environmental conditions, indicating that the success of L. polyphyllus invasions is likely to depend positively on seed mass. Our results suggest that some plant species such as the invasive L. polyphyllus may not show an adaptive response in seed mass to resources or environmental conditions, which may partly explain their ability to colonise a range of different habitats. [ABSTRACT FROM AUTHOR]

Summary • Senna obtusifolia (sicklepod) is a troublesome weed in many agronomic cropping systems in the southeastern USA with varying fertility regimes. This series of experiments was initiated to determine the impact of nutrient availability on reproductive output and maternal effects. • Experiments were conducted with plants growing in soil in growth chambers for 120 d. Offspring growth was evaluated in hydroponics. • Plants grown under higher nutrient conditions had greater reproductive biomass, number of seeds and total seed biomass. Individual seed mass distributions were slightly affected, with negative skewness decreased at higher nutrition. Seed germination rates were influenced primarily by seed size, as small seeds germinated faster than large seeds. The nitrogen content of seeds increased with increasing seed size and was higher in the high nutrition treatment. Seedlings arising from maternal plants grown under high nutrition grew more rapidly than did seedlings arising from maternal plants grown in a low nutrient regime. • The results suggest that S. obtusifolia reproduction and offspring competitiveness can be strongly influenced by the fertilization regimes used in different agronomic crops and rotations. [ABSTRACT FROM AUTHOR]