Non-random leaf orientation in Lactuca serriola L.

Abstract Leaf shapes and leaf orientation of Lactuca serriola serriola and serriola integrifolia were studied. Leaf shapes in L. serriola serriola differed greatly from those of L.serriola integrifolia, but leaf surface areas were similar. In exposed habitats, leaf orientation of cauline leaves of both forms was non-random, with leaves almost vertical and tending to orient with their lamina normal to the east and west. In the shade, cauline leaves oriented randomly. An experiment demonstrated that the orientation of leaves did not change significantly once they were fully expanded. The leaf orientation in L. serriola affected the diurnal distribution of solar irradiance intercepted by a leaf. Peak solar radiation fluxes are incident on the rosette leaves at midday, but on the cauline leaves the peak solar radiation flux occurs early in the morning and again late in the afternoon. The significance of this unusual leaf orientation is discussed in relation to water loss and carbon gain.     

Size-dependent reproduction in Australian alpine Ranunculus

Abstract The effect of plant size on reproduction in four species of alpine Ranunculus (R. muelleri, R. dissectifolius, R. graniticola and R. niphophilus) was investigated in two sites over two seasons in the field on a total of 190 plants. The effects of plant size (number of leaves) and number of flowers on the number of anthers, ovules and seed per flower and per plant were determined. There was a positive relationship between several measures of reproduction and plant size in all four species, indicating that reproduction is size-dependent. All the results indicate that the main factor controlling the amount of seed produced by alpine Ranunculus is the size of the plant. Specifically, bigger plants produced more seed by producing more flowers, not by producing more ovules per flower, or higher seed set per flower. Correspondingly, bigger plants produced more anthers by producing more flowers, rather than by producing flowers with more anthers. The total number of seeds produced by a plant was directly proportional to plant size in the four species. Therefore, reproductive effort should not vary with plant size in the four species.     

Effects of below- and above-ground herbivores on plant growth,flower visitation and seed set

Separate and combined effects of root and leaf herbivores on plant growth, flower visitation and seed set were tested in a factorial experiment using potted mustard, Sinapis arvensis, at an old fallow field. A 50% leaf removal by cabbageworms (Pieris rapae) when the seedlings had their first four leaves reduced plant height and shoot mass, and delayed the onset of flowering. Root herbivory by two wireworms (Agriotes sp.) over the whole experiment changed flower visitation; the number of flower visitors per plant was higher in plants with root herbivores than in plants without root herbivores. Combined leaf and root herbivory affected flowering period, number of fruits per plant and number of seeds per fruit. Plants attacked by leaf and root herbivores had a shorter flowering period and produced fewer fruits per plant than plants with root herbivores only. Although the experimental plants faced major herbivore-induced growth changes, plant reproduction (seed set and weight per plant) was similar in all treatments, documenting their ability to effectively compensate for leaf and root herbivory.     

Factors affecting fruit and seed production of Paeonia ostii “Feng Dan”, an economically important oil tree

Many factors may affect reproduction of animal-pollinated species. In this study, the effects of pollen limitation, attractive traits (flower number, plant height and flower width) and flowering phenological traits (flowering onset, duration and synchrony) on female reproduction, as well as the patterns of variation in fruit and seed production within plants, were investigated in Paeonia ostii “Feng Dan” over two flowering seasons (2018 and 2019). Fruit set was very high (90%), and pollen supplementation did not increase fruit and seed production in either year, indicating no pollen limitation. Fruit set, ovule number per fruit and mean individual seed weight per fruit were not affected by any of the six attractive and phenological traits in either year, whereas seed number per fruit was related to the three attractive traits in one or both years. Seed number per plant was positively affected by the three attractive traits and best explained by flower number in both years, but the effect of each of the three phenological traits on seed number per plant differed between years. Within plants, the fruit set, ovule number, seed set and seed number per fruit declined from early- to late-opening flowers, presumably because of resource preemption, but the mean individual seed weight did not vary across the flowering sequence. Our study shows that attractive traits of Paeonia ostii “Feng Dan” are more important than flowering phenological traits in the prediction of total seed production per plant.     

COMPONENTS OF SEED AND POLLEN YIELD OF LOBELIA CARDINALIS: VARIATION AND CORRELATIONS

Plants from three Lobelia cardinalis populations were grown under common garden conditions to assess intra- and interplant variation in seed and pollen production. Seed number per flower and mean seed weight varied systematically with floral position on the inflorescence (lowest values were from terminal flowers) but pollen grain number per flower did not vary systematically with floral position. Most of the remaining variance in seed and pollen grain number per flower and mean seed weight was distributed among plants; clones produced very similar amounts of pollen and seed. Seed yield was positively correlated with seed production per flower and with total flower production, but not with mean seed weight; pollen yield was also positively correlated with pollen grain production per flower and total flower production. Seed and pollen yield were simple linear functions of plant size but only pollen yield was a simple linear function of flower production; seed yield was a quadratic function in which the second order term was negative. This quadratic relationship resulted from a negative correlation between seed number per flower and total flower production. This correlation, in addition to the wide variation among plants in pollen number per flower, accounts for the weak correlation of seed and pollen yield. I conclude from these data that it is unlikely that plants in natural L. cardinalis populations transmit genes to the population's seed crop equally through pollen and ovules—emphasizing the importance of measuring both male and female components of reproductive success.     

Effects of above- and belowground herbivory on growth,pollination, and reproduction in cucumber

Plants experience unique challenges due to simultaneous life in two spheres, above- and belowground. Interactions with other organisms on one side of the soil surface may have impacts that extend across this boundary. Although our understanding of plant–herbivore interactions is derived largely from studies of leaf herbivory, belowground root herbivores may affect plant fitness directly or by altering interactions with other organisms, such as pollinators. In this study, we investigated the effects of leaf herbivory, root herbivory, and pollination on plant growth, subsequent leaf herbivory, flower production, pollinator attraction, and reproduction in cucumber (Cucumis sativus). We manipulated leaf and root herbivory with striped cucumber beetle (Acalymma vittatum) adults and larvae, respectively, and manipulated pollination with supplemental pollen. Both enhanced leaf and root herbivory reduced plant growth, and leaf herbivory reduced subsequent leaf damage. Plants with enhanced root herbivory produced 35% fewer female flowers, while leaf herbivory had no effect on flower production. While leaf herbivory reduced the time that honey bees spent probing flowers by 29%, probing times on root-damaged plants were over twice as long as those on control plants. Root herbivory increased pollen limitation for seed production in spite of increased honey bee preference for plants with root damage. Leaf damage and hand-pollination treatments had no effect on fruit production, but plants with enhanced root damage produced 38% fewer fruits that were 25% lighter than those on control plants. Despite the positive effect of belowground damage on honey bee visitation, root herbivory had a stronger negative effect on plant reproduction than leaf herbivory. These results demonstrate that the often-overlooked effects of belowground herbivores may have profound effects on plant performance.     

Variation and response to experimental warming in a New Zealand cushion plant species

Cold adapted plants, such as cushion plants, may be particularly sensitive to climate warming because of their compact growth form and high branch density. In the oceanic southern hemisphere, cushion communities tend to have large range distributions at low latitudes (sea level to low alpine), thus providing an opportunity to test the effects of temperature on plant morphology and reproduction across gradients. Using Donatia novae‐zelandiae as a model species, we compared the leaf morphology, reproduction and responses to warming. Two low‐alpine sites (Maungatua (880 m a.s.l.), Blue Mountains (1000 m a.s.l.)) and two sea‐level sites (Waituna 1 (0 m a.s.l.), Waituna 2 (0 m a.s.l.)) in South Island, New Zealand were used. Donatia novae‐zelandiae cushions differed significantly between the high‐elevation and sea‐level sites both morphologically and in terms of reproduction. High‐elevation cushions produced more flowers (threefold more flowers per plant) and seeds (sevenfold more seeds per capsule) than at sea level, but leaves were larger at sea level (in length and specific leaf area). The cushions were also twice as compact at the high‐elevation sites. After two growing seasons of artificial warming, seed production (35%), leaf length (7%) and width (13%), and specific leaf area (63%) significantly decreased in D. novae‐zelandiae plants; flower production was not significantly affected. Cushion plant morphology and reproduction were significantly affected by environmental drivers at their establishment sites, but all populations responded negatively to artificial warming of 1–3°C. Many cushion plants are considered keystone species because of their propensity to facilitate the growth and establishment of other plant species, the inferred negative effects of global warming on cushion plant species may have a cascading effect on other alpine plant groups.     

华北驼绒藜自然种群结实的花粉和资源限制

运用人工授粉、补充无机营养、去叶处理以及疏花处理研究了华北驼绒藜自然种群花粉和资源有效性对结实的影响,并进一步探讨了该植物的选择性败育现象和繁殖对策。结果表明:花粉来源而不是花粉数量对华北驼绒藜结实存在显著影响;同枝授粉结籽率和结实率均低于自然授粉,异株授粉则显著高于同枝授粉和自然授粉;异株授粉种子千粒重显著高于自然授粉和同株异枝授粉,极显著高于同枝授粉。华北驼绒藜结实存在资源限制,补充施肥提高了单枝开花数和结籽率。随摘除叶片数量的增加,结籽率明显降低,摘除叶片处理与对照之间均形成显著差异,摘除1/2叶、3/4叶以及去全叶处理使种子千粒重显著低于对照。人工疏花实验表明华北驼绒藜存在选择性败育现象。华北驼绒藜可根据花粉和资源的可利用性来调整性分配、授粉方式和结实以获得最大适合度,具有复杂的繁殖对策,表现出较好的环境适应性。     

Shoot and root physiological responses to localized zones of soil moisture in cultivated and wild lettuce (Lactuca spp.)

Cultivated crisphead lettuce (Lactuca sativa L.) has a shallower root system than its wild relative, Lactuca serriola L. The effects of localized soil water, at depth, on plant water relations, gas exchange and root distribution were examined in the two species using soil columns with the soil hydraulic-ally separated into two layers, at (0–20 cm and 20–81) cm, but permitting root growth between the layers. Three treatments were imposed on 7-week-old plants, and maintained for 4 weeks: (i) watering, both layers to field capacity; (ii) drying the upper layer while watering the lower layer to field capacity, and (iii) drying both layers. Drying only 0–20 cm of soil had no effect on leaf water status, net photosynthesis, stomatal conductance or biomass production in L. serriola compared to a well-watered control, but caused a short-term reduction (10 d) in leaf water status and photosynthesis in L. sativa that reduced final shoot production. The different responses may be explained by differences in root distribution. Just before the treatments commenced, L. serriola had 50% of total root length at 20–80 cm compared to 35% in L. sativa. Allocation of total biomass to roots in L. serriola was approximately double that in L. sativa. The wild species could provide germplasm for cultivated lettuces to extract more soil water from depth, which may improve irrigation efficiency.     

Field water relations of a compass plant, Lactuca serriola L.

Abstract Field water relations of Lactuca serriola serriola and L. serriola integrifolia were examined. Leaf conductance to water vapour was high early in the morning and declined rapidly during the midday hours. Leaf water potentials decreased to their minima early in the morning and remained low all day. Afternoon recovery of leaf conductance occurred occasionally. Leaf conductance was shown to have a linear response to vapour concentration difference. No differences were seen between L. serriola serriola and L. serriola integrifolia. The pattern of diurnal gas-exchange activity appeared to be complemented by the pattern of intercepted solar irradiance which results from the compass plant leaf orientation observed in L. serriola.     

Vegetative growth inRumex acetosella (Polygonaceae) originating from different geographic regions

Vegetative growth patterns ofRumex acetosella L. were investigated both in experimental conditions and in the field. Plants originating from geographically and ecologically contrasting areas expressed significant differentiation in height, weight, and leaf production, even at early stages. The plants belonging to subsp.angiocarpus grew thaller than other plants. The differences among populations grown in a uniform environment provide evidence for genetic differentiation in morphology. Plants in natural populations were considerably lighter than experimental plants, which intensively produced a large number of rosette leaves. These differences can be attributed to substantial phenotypic plasticity. When the correlation structure among the growth traits was analyzed, seed weight and early plant size appeared to influence future plant size.     

Consequences of a mixed reproductive system in the hog peanut,Amphicarpaea bracteata, (Fabaceae)

Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.     

Patterns of growth,reproduction, defense,and herbivory in the dioecious shrub Baccharis halimifolia (Compositae)

Summary Patterns of growth, reproduction, defense (leaf resin) and herbivory were compared between the sexes of the dioecious shrub Baccharis halimifolia (Compositae). Male plants possessed longer shoots and more tender leaves, grew faster, and flowered and senesced earlier than female plants. Levels of leaf nitrogen, water content, and acetone-soluble resin (shown to deter feeding by polyphagous insect herbivores) did not differ between male and female plants. When offered a choice between leaves from male and female plants, adults of two leaf beetles (Chrysomelidae), the monophagous Trirhabda bacharidis and the polyphagous Paria thoracica, both preferred to feed on male leaves. Similarly, the daily fecundity of older females of T. bacharidis was higher when they were fed leaves from male compared to female plants. However, adult survivorship and total fecundity of T. baccharidis did not differ between male and female leaf treatments. We attribute the feeding preference for and slight increase in fecundity on male plants to the tenderness of male leaves. Larvae of the fly Tephritis subpura (Tephritidae) fed exclusively in the sterile receptacle of male flower heads (85% infested), but the phenology was such that pollen production was not adversely affected. Larvae of two other flies Dasineura sp. and Contarinia sp. (Cecidomyiidae) occupied >95% of only female flower heads where they fed among and on the developing seeds. We conclude that foliage-feeding herbivores are unlikely candidates to explain the female-biased sex ratio (59% female) of B. halimifolia plants in the field, and that their preference for male plants is a result of plant characteristics (e.g. rapid growth) that have been selected by some other factor. However, our data on selective floral herbivory in B. halimifolia are in accord with the argument that dioecy reduces the inadvertent loss of flower parts of one sex when herbivores feed on flower parts of the opposite sex.     

Shading by invasive shrub reduces seed production and pollinator services in a native herb

Plant invasions disrupt native plant reproduction directly via competition for light and other resources and indirectly via competition for pollination. Furthermore, shading by an invasive plant may reduce pollinator visitation and therefore reproduction in native plants. Our study quantifies and identifies mechanisms of these direct and indirect effects of an invasive shrub on pollination and reproductive success of a native herb. We measured pollinator visitation rate, pollen deposition, and female reproductive success in potted arrays of native Geranium maculatum in deciduous forest plots invaded by the non-native shrub Lonicera maackii and in two removal treatments: removal of aboveground L. maackii biomass and removal of flowers. We compared fruit and seed production between open-pollinated and pollen-supplemented plants to test for pollen and light limitation of reproduction. Plots with L. maackii had significantly lower light, pollinator visitation rate, and conspecific pollen deposition to G. maculatum than biomass removal plots. Lonicera maackii flower removal did not increase pollinator visitation or pollen deposition compared to unmanipulated invaded plots, refuting the hypothesis of competition for pollinators. Thus, pollinator-mediated impacts of invasive plants are not limited to periods of co-flowering or pollinator sharing between potential competitors. Geranium maculatum plants produced significantly fewer seeds in plots containing L. maackii than in plant removal plots. Seed set was similar between pollen-supplemented and open-pollinated plants, but pollen-supplemented plants exhibited higher seed set in plant removal plots compared to invaded plots. Therefore, we conclude that the mechanism of impact of L. maackii on G. maculatum reproduction was increased understory shade.     

Urea as a promotive coupler of plant-herbivore interactions

Summary Growth responses of Kyllinga nervosa Steud., a sedge from the Serengeti short-grass plains, were examined in a factorial experiment which included clipped and unclipped plants, and nitrogen supplied as either urea or ammonium nitrate. Results were expressed in relation to three transfer processes: flow to grazers, flow to producers and flow to reproduction. Clipping increased biomass and nitrogen flow to grazers by significantly increasing nitrogen uptake, aboveground nitrogen flow, and the weights of and proportional allocation to green leaf production. This was at the expense of flow to vegetative and sexual reproduction, since the weights and proportional investments in roots, crowns and reproductive structures were reduced. Urea nutrition increased flow to grazers and plant reproduction through increases in green leaf weight, flower weight, allocation to green leaves, flowers and stems, and aboveground: belowground biomass ratios. Stimulation of aboveground productivity by urea was a consequence of increased tillering rates.Interactive responses of clipping and nitrogen source regulated plant growth, thus controlling flow to each transfer process. Combined effects of clipping and urea resulted in compensatory production of both green leaves and flowers, and maximized biomass and nitrogen flow to grazers. Both urea and clipping tightened herbivore-producer recycling by significantly reducing litter nitrogen and carbon masses. In contrast, when plants were unclipped and grown on NH₄NO₃, biomass allocation and weights of roots and crowns were increased at the expense of aboveground tissues, thus increasing flow to primary producers. Plant growth responses to experimental treatment combinations simulating nutritional status of grazed and ungrazed field plants indicate that urea represents a potential importance beyond it nitrogen contribution by introducing a positive feedback to herbivores.     

PATHOGEN IMPACT ON SEXUAL VS. ASEXUAL REPRODUCTIVE SUCCESS IN ARISAEMA TRIPHYLLUM

Populations of Arisaema triphyllum commonly harbor a systemic fungal pathogen, Uromyces ari-triphylli, which reduces leaf area and leaf longevity. Infected plants produced 42% fewer asexual progeny (cormlets). Furthermore, all asexual progeny from infected parents were themselves infected with Uromyces. Mean seed production of infected plants was only 21% of that among healthy plants. A hand pollination experiment demonstrated that 1) infected male plants can produce viable pollen, 2) the low seed production of naturally pollinated infected females was not due to inadequate pollination, and 3) seed production among healthy female plants was strongly pollinator limited. Seeds from infected and healthy parents had similar viability, and all seeds germinating from both types of parents were uninfected. The contrast in disease transmission to sexual vs. asexual progeny suggests that pathogen attack may be one selective factor favoring sexual reproduction in A. triphyllum populations.     

Quantitative trait loci associated with seed and seedling traits in Lactuca

Seed and seedling traits related to germination and stand establishment are important in the production of cultivated lettuce (Lactuca sativa L.). Six seed and seedling traits segregating in a L. sativa cv. Salinas x L. serriola recombinant inbred line population consisting of 103 F8 families revealed a total of 17 significant quantitative trait loci (QTL) resulting from three seed production environments. Significant QTL were identified for germination in darkness, germination at 25 and 35°C, median maximum temperature of germination, hypocotyl length at 72 h post-imbibition, and plant (seedling) quality. Some QTL for germination and early seedling growth characteristics were co-located, suggestive of pleiotropic loci regulating these traits. A single QTL (Htg6.1) described 25 and 23% of the total phenotypic variation for high temperature germination in California- and Netherlands-grown populations, respectively, and was significant between 33 and 37°C. Additionally, Htg6.1 showed significant epistatic interactions with other Htg QTL and a consistent effect across all the three seed production environments. L. serriola alleles increased germination at these QTL. The estimate of narrow-sense heritability (h²) of Htg6.1 was 0.84, indicating potential for L. serriola as a source of germination thermotolerance for lettuce introgression programs.     

Floral herbivory at different stages of flower development changes reproduction in <Emphasis Type="Italic">Iris gracilipes</Emphasis> (Iridaceae)

Floral herbivores and pollinators are major determinants of plant reproduction. Because interaction of floral herbivores and pollinators occurs when herbivores attack the flowers in the bud and flower stages and because the compensatory ability of plants is known to differ according to the timing of herbivory, the effects of herbivory may differ according to its timing. In this study, we investigated the effects of floral herbivory at different stages on fruit production and seed/ovule ratio at two sites of large populations of the perennial herb, Iris gracilipes for 2 years. Herbivory at the bud and fruit stages both tended to have negative effects on fruit production, but the former caused more severe damage. On the other hand, herbivory at the flower stage tended not to have negative effects on fruit production because the degree of flower loss was smaller in the flower stage. Although herbivory decreased fruit production, flowers did not compensate for the damage by increasing the seed/ovule ratio because reproduction of I. gracilipes was limited by pollen availability rather than resources. These results indicate that floral herbivory at different stages has different effects on plant reproduction.     

Occurrence of Bremia lactucae in Natural Populations of Lactuca serriola

In the period 1996–2001 the natural occurrence of Bremia lactucae (lettuce downy mildew) on Asteraceae plants was studied in the Czech Republic. Lactuca serriola (prickly lettuce) is the most common naturally growing host species of B. lactucae. Infection of plants was recorded during the whole vegetation season with the first occurrence in April and last in November. Bremia lactucae was found on host plants in all developmental stages. High percentages of naturally infected populations of L. serriola were recorded. Host plants exhibited broad variation in phenotypic expression of disease symptoms and degree of infection, however, the intensity of infection was rather low in the majority of populations. Geographic distribution of B. lactucae was studied in the two main parts of Czech Republic, central and southern Moravia, and eastern, northern and central Bohemia. Bremia lactucae was recorded in all these areas. Nevertheless, in the warmest parts of the Czech Republic (southern Moravia) only sporadic occurrence of the pathogen was recorded. Bremia lactucae infection on L. serriola and disease severity was judged also in relation to the type of habitat, and the size and density of host plant populations. However, no substantial differences among various habitats were found; only host plants growing in urban areas were frequently free of infection and the degree of infection was very low. Nevertheless, these plants were commonly infected with powdery mildew (Golovinomyces cichoracearum), which is most aggressive pathogen of this type of habitat.     

The effect of early blight disease caused by Alternaria solani on shoot growth of young tomato plants

The effect of increasing spore concentration of Alternaria solani (Early blight disease) on the shoot growth of young tomato plants was analysed. Changes in growth were related to the severity of infection which increased with increasing inoculum. Leaf production was not affected but dry weights and especially leaf expansion were decreased. The effective leaf areas of the five inoculated leaves (L1-L5 numbered from the plant base) were drastically decreased by expanding necrotic lesions and, to a lesser extent, by premature leaf fall. Healthy leaves expanding soon after inoculation (L6, L7) were markedly affected by the disease on the lower leaves and had decreased specific leaf areas (ratio of leaf area to leaf dry weight) but later formed (from L8) leaves were less affected and had greater specific leaf areas than equivalent leaves on uninoculated plants.