Number Of Reproductive Structures Research Articles

Arbuscular mycorrhizal fungi provides enhanced development and reduced mite incidence in Phaseolus vulgaris L. by direct root colonization and via the common mycorrhizal network

Arbuscular mycorrhizal fungi (AMF) are important to agriculture due to positive effects on development and resistance to attack by herbivores in agricultural crops. AMF can affect a single plant by directly colonizing its roots and two or more plants through the common mycorrhizal network (CMN). This work aimed to analyze the influence of AMF on the development of Phaseolus vulgaris and on the incidence of the mite Tetranychus urticae in bean plants colonized directly by mycorrhizal propagules or linked by the CMN. The root systems of two plants were either separated by an impassable barrier so that one or both plants could be colonized by the mycorrhizal propagules without forming the RMC, or they were separated by a steel mesh that allowed the outer hyphae of the AMF on the roots of one of the plants to colonize the non-mycorrhizal roots of the other plant and form the RMC. The mite infestation occurred first on one plant and at the end of the experiment on all. Percentage of mycorrhizal colonization, dry mass of aerial part and roots, number of reproductive structures and mite incidence were analyzed. The colonization by the mycorrhizal propagules and the hyphae of the MRC positively influenced the vegetative and reproductive development of P. vulgaris and resulted in lower mite incidence on the leaflets of the plants. Therefore, direct colonization of P. vulgaris roots by AMFs and via CMR improves plant development and resistance of bean plants to T. urticae mite infestation.

Herbarium macroalgae specimens reveal a rapid reduction of thallus size and reproductive effort related with climate change

Understanding and forecasting the effects of climate changes on vulnerable species are leading concerns for ecologists and conservation biologists. Herbaria are invaluable for use in long-term data series, and one of the few available methods for quantifying biodiversity changes over large periods of time. Gelidium canariense is an endemic and habitat-forming macroalga of the Canary Islands that coexists with two other habitat-forming Gelidiales: G. arbuscula and Pterocladiella capillacea. This study assesses long-term changes in thallus size and reproductive effort of all specimens deposited in the Herbarium of Universidad de La Laguna of these three Gelidiales species. Also assessed were the effects of seawater temperature and increased incident light on net primary production (NPP), and the effects of extreme desiccation conditions on the relative water content and NPP of the three Gelidiales species. The length of the thallus of the endemic species G. canariense was halved during the past 40 years. The shortening of the thallus coincided with a significant decrease in the number of reproductive structures in both Gelidium species. These morphological changes coincide with a significant increase of the sea surface temperature, air temperature above sea surface and ultraviolet radiation in the studied area. The experiments have revealed the deleterious effects of extreme desiccation and extreme irradiance on all three species. Hence, these results suggest that air temperature and irradiance are related with these morphological changes over time in the habitat-forming Gelidium species and that are most likely compromising the survival of their populations which are already declining.

Floral traits and reproductive success variation among inflorescence orders in Eryngium maritimum.

Eryngium maritimum L. is considered a key species in dunes of the western Mediterranean. Although Northern European populations are endangered, the Mediterranean populations show a good conservation status, despite a lack of studies of the reproductive requirements and strategies of this species. This study aims to analyse the reproductive biology of a population of E. maritimum in the western Mediterranean (Balearic Islands, Spain), specifically focusing on differences in morphometric and reproductive traits among inflorescence orders. Capitulum size, number of flowers, fruit set and seed set were analysed to evaluate the morphological and reproductive differences among inflorescence orders. The association between subterranean development and investment in reproductive structures was also studied along the dune location. Breeding system was analysed, evaluating self-pollination capacity at capitulum level and the pollen/ovary ratio. Finally, floral visitors were assessed. Morphometric and reproductive traits showed a decline in size and production from early to subsequent inflorescence orders. A correlation between width of stem base (caudex) and number of reproductive structures was observed, whereas seashore distance did not affect the reproductive development. Flowering occurred during summer, from May until late July, while fructification took place from the middle of August until the last days of September. Pollinator exclusion treatments induced a fruit and seed set decline. Twenty-one species of floral visitor were found. First and second inflorescence orders contributed to the generation of seeds, displaying high fruit and seed production, while other inflorescence orders seemed to attract pollinators. Reproductive and non-reproductive development could depend on the capacity to reallocate resources from underground to aerial structures, which seemed to be superior in samples with highly developed caudices. In the studied population, inner areas closest to the seashore showed a delay in anthesis, which could be related to microclimate differences along the coast-to-inland gradient. Pollination is strongly entomophilous and showed low levels of self-compatibility at capitulum level. Considering these results, for habitat conservation the reported microclimate diversity should be taken into consideration, with a focus on conservation of the pollinator populations.

Population structure and phenology of Discocactus zehntneri Britton & Rose subsp. petr-halfarii (Zachar) M.R. Santos & M.C. Machado (Cactaceae), a critically endangered Brazilian cactus subspecies

Discocactus zehntneri Britton & Rose subsp. petr-halfarii (Zachar) M.R. Santos & M.C. Machado (Cactaceae) is a Critically Endangered Brazilian cactus subspecies. There is no information on its population structure and phenological pattern. Thus, this study characterises population structure and determines the phenological pattern and germinative behaviour of this subspecies. We marked all individuals in the population and measured their diameter to create four age categories: seedling, juvenile, stem >5cm diameter without cephalium and reproductive plant. To carry out phenological assessments, we selected fifty plants. We monitored the plants monthly for two years. For each plant, we observed the number of reproductive structures and correlated them with climatic data. We found 1975 individuals grouped in subpopulations that grow in areas ranging from 800 to 2000m2. Most individuals were seedlings and juveniles, and adult plants accounted for about 25% of the population. The flowering period started in November and extends to June, peaking in flower production between November and February, the months with higher rainfall and maximum temperatures. Fruiting was shorter, less intense and occurred between December and April. We observed only thirty-seven fruits in 163 flowers (22.7%) and recorded seed germination only in the presence of light (>90%). The results indicate that this cactus subspecies has a well-defined period of flowering and fruiting. Reproductive plants, fruits and seeds are few, which may affect the species maintenance in the environment.

Cranberry response to sulfentrazone rate, timing, and application volume

AbstractThe recent registration of sulfentrazone, a selective, soil-applied, PRE herbicide labeled for control of various weeds in cranberry, expanded the number of modes of action that could be used in the crop. A 2018 preliminary study in Massachusetts showed that high rates of sulfentrazone applied at the cabbage head stage reduced the number of flowering uprights (vertical stems) without impacting the final yield. To clarify the use patterns needed to promote crop safety when using sulfentrazone, six studies were conducted in New Jersey and Massachusetts in 2019 and 2020. Studies compared sulfentrazone applications made at two timings (spring dormant, SD; or cabbage head [CH] stage), two rates (280 and 420 g ai ha−1), and three application volumes simulating either chemigation (3,740 L ha−1) or boom application (190 L ha−1 alone or followed by 0.25 cm water wash-off). Boom application studies in New Jersey in 2018 and 2019 did not show significant long-lasting injury (necrosis or stunting). However, a comprehensive observation of cranberry uprights 8 wk after treatment showed a high rate of terminal bud necrosis, a reduction in the number of reproductive structures, and the development of axillary shoots associated with a high rate of sulfentrazone applied at CH. A mitigation study conducted in 2019 and 2020 confirmed the safety of chemigated sulfentrazone at the high rate with no yield reduction, regardless of crop stage at application. Washing off the herbicide from the cranberry canopy immediately after boom application did prevent the necrosis of terminal bud and the related development of nonproductive secondary shoots. Considering the results of this study, application of sulfentrazone over the top of cranberry vine before scales of the terminal bud start loosening would be prudent practice at this time.

Direct and indirect effects of climate change squeeze the local distribution of a habitat-forming seaweed

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 626:43-52 (2019) - DOI: https://doi.org/10.3354/meps13080 Direct and indirect effects of climate change squeeze the local distribution of a habitat-forming seaweed Gustavo M. Martins1,2,*, Christopher D. G. Harley3,4, João Faria1, Maria Vale1,5,6, Stephen J. Hawkins6,7, Ana I. Neto1, Francisco Arenas8 1cE3c-Centre for Ecology, Evolution and Environmental Changes/Azorean Biodiversity Group & University of the Azores, 9501-801 Ponta Delgada, Açores, Portugal 2AQUAZOR - Aquicultura e Biotecnologias Marinhas dos Açores, Rua da Pranchinha 92, 9500-331 Ponta Delgada, Açores, Portugal 3Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada 4Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada 5Regional Fund for Science and Technology (FRCT), 9500-336 Ponta Delgada, Açores, Portugal 6Ocean and Earth Science, National Oceanography Centre Southampton, Waterfront Campus, University of Southampton, European Way, Southampton SO14 3ZH, UK 7Marine Biological Association of UK, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK 8Group of Aquatic Ecology and Evolution, Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, 4450-208 Matosinhos, Portugal *Corresponding author: martinsgm@gmail.com ABSTRACT: Predictions concerning biological responses to climate change are based primarily on environmental tolerances of individual species. However, biological interactions and the way these may be altered by changes in climate can also be important drivers of ecological change. A combination of observational and experimental studies was conducted to test the factors controlling the vertical distribution of the canopy-forming alga Fucus guiryi, a cold-water seaweed and ecological engineer. We found that F. guiryi transplanted to areas just above its upper limit of distribution died rapidly, whereas survivorship was high in unmanipulated controls and individuals translocated to areas within the species’ vertical range. Towards the lower limit of its vertical range, unprotected F. guiryi were heavily grazed by a warm-water fish, Sarpa salpa, and percent cover, frond length, and number of reproductive structures were all reduced compared to experimentally protected individuals. Observations over a period of 2 yr suggest that grazing is stronger towards the lower limit of distribution, especially during the warmer seasons of the year. Commercial landing records indicate that the abundance of S. salpa was positively related to warmer sea surface temperatures. Our results highlight the interplay between abiotic and biotic factors in determining the vertical distribution of F. guiryi and suggest that predicted increases in temperature during this century may lead to local extinctions of this ecosystem engineer through the combination of increased physiological stress at its upper limit of distribution and grazing at its lower limit, which, together, act to squeeze its vertical distribution in the rocky intertidal. KEY WORDS: Biotic interactions · Distribution · Fucus guiryi · Physical stress · Rocky intertidal · Grazing Full text in pdf format Supplementary material PreviousNextCite this article as: Martins GM, Harley CDG, Faria J, Vale M, Hawkins SJ, Neto AI, Arenas F (2019) Direct and indirect effects of climate change squeeze the local distribution of a habitat-forming seaweed. Mar Ecol Prog Ser 626:43-52. https://doi.org/10.3354/meps13080 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 626. Online publication date: September 12, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Microhabitat characteristics and impacts of invasive species for the triple-ribbed milkvetch (Astragalus tricarinatus [Fabaceae]) in the San Bernardino Mountains, California.

Astragalus tricarinatus A.Gray is a federally-listed short lived perennial herb endemic to southern California. Its primary habitat is along the ecotone of the Mojave and Colorado Deserts in the San Bernardino and Little San Bernardino Mountains between 390 and 1525 m. Discovery of this species' upland habitat has prompted research into the ecology of populations across its range, as the life history and threats may be different from those of the previously-known wash populations. Our study sought to further document A. tricarinatus distribution and abundance within its range, as well as quantify impacts to its growth and reproductive efforts associated with co-occurring native and invasive plant species. We mapped all known localities in our study area on aerial imagery then used this to visually recognize its typical edaphic habitat and identify new potential sites. Where A. tricarinatus was found, we established plots in which plant size, the number of reproductive structures, and microhabitat characteristics were recorded. Two new occurrences (defined here as >1 km away from known localities) were recorded within its existing range as well as a previously undocumented locality between two known occurrences containing an estimated 2600 plants. Most plants were found on south and east aspects, and on slopes ranging from 30–45°. We found that increases in invasive cover correlated with a decrease in production of reproductive structures. As a federally-listed species occurring in steep, remote habitats with few threats, these findings suggesting an association between invasive species presence and reduced reproductive structures should be further investigated experimentally, as they affect population dynamics and conservation of this species.

Disease where you dine: plant species and floral traits associated with pathogen transmission in bumble bees

Hotspots of disease transmission can strongly influence pathogen spread. Bee pathogens may be transmitted via shared floral use, but the role of plant species and floral trait variation in shaping transmission dynamics is almost entirely unexplored. Given the importance of pathogens for the decline of several bee species, understanding whether and how plant species and floral traits affect transmission could give us important tools for predicting which plant species may be hotspots for disease spread. We assessed variation in transmission via susceptibility (probability of infection) and mean intensity (cell count of infected bees) of the trypanosomatid gut pathogen Crithidia bombi to uninfected Bombus impatiens workers foraging on 14 plant species, and assessed the role of floral traits, bee size and foraging behavior on transmission. We also conducted a manipulative experiment to determine how the number of open flowers affected transmission on three plant species, Penstemon digitalis, Monarda didyma, and Lythrum salicaria. Plant species differed fourfold in the overall mean abundance of Crithidia in foraging bumble bees (mean including infected and uninfected bees). Across plant species, bee susceptibility and mean intensity increased with the number of reproductive structures per inflorescence (buds, flowers and fruits); smaller bees and those that foraged longer were also more susceptible. Trait-based models were as good or better than species-based models at predicting susceptibility and mean intensity based on AIC values. Surprisingly, floral size and morphology did not significantly predict transmission across species. In the manipulative experiment, more open flowers increased mean pathogen abundance fourfold in Monarda, but had no effect in the other two plant species. Our results suggest that variation among plant species, through their influence on pathogen transmission, may shape bee disease dynamics. Given widespread investment in pollinator-friendly plantings to support pollinators, understanding how plant species affect disease transmission is important for recommending plant species that optimize pollinator health.

Plant reproduction is altered by simulated herbicide drift to constructed plant communities.

Herbicide drift may have unintended impacts on native vegetation, adversely affecting individual species and plant communities. To determine the potential ecological effects of herbicide drift, small plant community plots were constructed using 9 perennial species found in different Willamette Valley (OR, USA) grassland habitats. Studies were conducted at 2 Oregon State University (Corvallis, OR, USA) farms in 2 separate years, with single and combined treatments of 0.01 to 0.2× field application rates (f.a.r.) of 1119 g ha-1 for glyphosate (active ingredient [a.i.] of 830 g ha-1 acid glyphosate) and 560 g ha-1 a.i. for dicamba. Plant responses were percentage of cover, number of reproductive structures, mature and immature seed production, and vegetative biomass. Herbicide effects differed with species, year, and, to a lesser extent, farm. Generally, 0.1 to 0.2× f.a.r. of the herbicides were required to affect reproduction in Camassia leichtlinii, Elymus glaucus, Eriophyllum lanatum, Festuca idahoensis, Iris tenax, and Prunella vulgaris. Eriophyllum lanatum also had a significant increase in percentage of immature seed dry weight with 0.01× f.a.r. of dicamba or the combination of glyphosate plus dicamba. Other species showed similar trends, but fewer significant responses. These studies indicated potential effects of low levels of herbicides on reproduction of native plants, and demonstrated a protocol whereby species growing in a constructed plant community can be evaluated for ecological responses. Environ Toxicol Chem 2017;36:2799-2813. Published 2017 SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Effects of ocean acidification on population dynamics and community structure of crustose coralline algae.

Calcification and growth of crustose coralline algae (CCA) are affected by elevated seawater pCO2 and associated changes in carbonate chemistry. However, the effects of ocean acidification (OA) on population and community-level responses of CCA have barely been investigated. We explored changes in community structure and population dynamics (size structure and reproduction) of CCA in response to OA. Recruited from an experimental flow-through system, CCA settled onto the walls of plastic aquaria and developed under exposure to one of three pCO2 treatments (control [present day, 389±6 ppm CO2], medium [753±11 ppm], and high [1267±19 ppm]). Elevated pCO2 reduced total CCA abundance and affected community structure, in particular the density of the dominant species Pneophyllum sp. and Porolithon onkodes. Meanwhile, the relative abundance of P. onkodes declined from 24% under control CO2 to 8.3% in high CO2 (65% change), while the relative abundance of Pneophyllum sp. remained constant. Population size structure of P. onkodes differed significantly across treatments, with fewer larger individuals under high CO2. In contrast, the population size structure and number of reproductive structures (conceptacles) per crust of Pneophyllum sp. was similar across treatments. The difference in the magnitude of the response of species abundance and population size structure between species may have the potential to induce species composition changes in the future. These results demonstrate that the impacts of OA on key coral reef builders go beyond declines in calcification and growth, and suggest important changes to aspects of population dynamics and community ecology.

Grazing impact on desert plants and soil seed banks: Implications for seed-eating animals

We assess whether the knowledge of livestock diet helps to link grazing effects with changes in plant cover and soil seed bank size, aiming at inferring the consequences of grazing on seed-eating animals. Specifically, we test whether continuous and heavy grazing reduce the cover, number of reproductive structures and seed reserves of the same grass species whose seeds are selected and preferred by granivorous animals in the central Monte desert, Argentina. Grass cover and the number of grass spikes usually diminished under grazing conditions in the two localities studied (Telteca and Ñacuñán), and soil seed bank was consistently reduced in all three years evaluated owing to a decline of perennial grass and forb seeds. In particular, the abundance of those seeds selected and preferred by birds and ants (in all cases grass species) declined 70–92% in Ñacuñán, and 52–72% in Telteca. Reduction of perennial grass cover and spike number in grazed sites reinforced the causal link between livestock grazing and the decline of grass soil seed reserves throughout failed plant reproduction. Grass seed bank depletion suggests that grazing may trigger a “cascade” of mechanisms that affect the abundance and persistence of valuable fodder species as well as the availability of seed resources for granivorous animals.

Multiple-scale environmental modulation of lichen reproduction

It is necessary to understand how environmental changes affect plant fitness to predict survival of a species, but this knowledge is scarce for lichens and complicated by their formation of sexual and asexual reproductive structures. Are the presence and number of reproductive structures in Lobaria pulmonaria, a threatened lichen, dependent on thallus size, and is their formation sequential? Does any size-dependence and sequential formation vary along a climate gradient? Generalized linear mixed models were used to explore the effect of environmental predictors on the size and presence/abundance of each reproductive structure and to determine the probability of a given-sized thallus to develop any reproductive structure. The largest individuals are more likely to develop reproductive structures, and the lichen uses a mixed strategy of early asexual reproduction and late sexual. Macro and microclimatic variables also influenced reproductive capacity. Relationships among climate conditions and lichen size and reproductive capacity can compromise the future viability of the species in the most southern populations of Europe.

Parcelamento do fertilizante fosfatado no algodoeiro em sistema de cultivo irrigado e de sequeiro

Objetivou-se, com este trabalho, avaliar a aplicação parcelada de doses de fósforo na cultura do algodão nos sistemas de cultivo sob irrigação e de sequeiro, visando à maior eficiência da adubação fosfatada em comparação com a aplicação tradicional, apenas em semeadura. O experimento foi conduzido em Neossolo Quartzarênico, na região Norte de Minas Gerais. Adotou-se o delineamento blocos ao acaso, com três repetições. Os tratamentos consistiram das doses 50 e 120 kg ha-1 de P2O5 aplicadas parcelamente de quatro formas: PS, P1, P2 e P3 [100/0; 75/25; 50/50 e 25/75% da dose do fertilizante fosfatado aplicado, respectivamente, na semeadura e aos 35 dias após a emergência (DAE)], nos cultivos de sequeiro e irrigado. Dois tratamentos adicionais, sem P, nos cultivos sem e com irrigação, completaram os dezoito tratamentos estudados. O aumento das doses de P incrementou a massa da parte aérea seca e o número de estruturas reprodutivas aos 80 DAE, a eficiência relativa da adubação fosfatada e a produtividade de algodão em caroço. A resposta às doses de P ocorreu apenas sob irrigação. A aplicação parcelada do fertilizante fosfatado não aumentou a eficiência da adubação na cultura do algodão em Neossolo Quartzarênico.

Effects of wave exposure on population and reproductive phenology of an algal turf, Gelidium pusillum (Gelidales, Rhodophyta), Songkhla, Thailand

The effect of wave exposure on the population and reproductive phenology of the common red alga, Gelidium pusillum (Stackhouse) Le Jolis, was investigated between July 2003 and June 2004, at Suan Song Tha Le, Songkla Province, Thailand. Lengths of thalli, percentage cover, percentage of reproductive fronds and the number of reproductive structures were examined monthly in relation to different degrees of wave exposure (sheltered vs. exposed), temperature, rainfall, day length and tidal cycles. Frond length and percentage cover of G. pusillum were different among sites and seasons. Shorter fronds were found on the exposed shore which had a greater percentage cover. Fronds bleached and died off during the summer months (April and May), which resulted in shorter fronds and reduced percentage cover in June. The thalli reproduced throughout the year, with a predominance of tetrasporophytes. The highest percentage of tetrasporic fronds was 33% in February 2004 and 13% of cystocarpic fronds in April 2004, but male gametophytic fronds were never observed. Rainfall showed a strongly negative influence on reproduction since no reproductive fronds were observed during the rainy season ( R 2 = 0.49, P = 0.01). The dominance of G. pusillum at this study site and throughout elsewhere in turf habitats might be a function of persistent vegetative growth, densely clumped, and the ability to reproduce almost throughout the entire year.

Damage and shade enhance climbing and promote associational resistance in a climbing plant

1 Associational resistance occurs when one plant species gains protection from its consumers by association with a defended species. In semi-arid ecosystems of Chile, the perennial herb Convolvulus chilensis (Convolvulaceae) suffers heavy herbivory by small mammals when growing prostrate but plants seem to be protected when they are climbing onto cacti or thorny shrubs (nurse species). 2 Field observations suggest that damaged main stems have a greater number of small lateral stems, which greatly enhance climbing success. In this field study we addressed whether C. chilensis shows associational resistance by climbing onto nurse species, and evaluated whether damage and also shade (a cue for neighbour presence) elicit architectural responses that enhance climbing probability. 3 We documented associational resistance for C. chilensis: climbing individuals growing associated with cacti and thorny shrubs suffered less herbivory (percentage of damaged stems: 35 vs. 98) and had greater reproductive output (number of reproductive structures at the end of the season: 150 vs. 0) than prostrate individuals growing in isolation. Experimental clipping of the main stem caused plants to produce a greater number of lateral stems both in sun (70% increase) and in shade (66% increase) treatments. Moreover, stem damage caused a 50% increase in the number of stems actually climbing on a support, but only in shade. 4 Synthesis. We show for the first time that phenotypic responses to herbivory of the potentially protected species may enhance association with the defended nurse species, thereby promoting associational resistance. This finding adds a new perspective for mechanistic studies of positive interactions among plants, suggesting that behavioural responses of the protégée may mediate the magnitude of nurse effects.

Resistência a benzimidazóis por Guignardia citricarpa

O objetivo deste trabalho foi avaliar a resistência de Guignardia citricarpa aos fungicidas carbendazim e piraclostrobina, por meio de avaliação do crescimento em meio de cultura, decomposição de tecido foliar e produção de corpos de frutificação. Para isso, o fungo G. citricarpa foi isolado de lesões de frutos de laranja (Citrus sinensis), produzidos em área com intensa aplicação de fungicida. Os isolados obtidos foram avaliados quanto à sensibilidade aos fungicidas piraclostrobina e carbendazim, nas dosagens de 0,5, 1 e 2 µg mL-1 de i.a., para se verificar o efeito da pressão de seleção causada pelo uso destes compostos em áreas citrícolas. Embora tenha sido observada redução efetiva no número de estruturas reprodutivas e na decomposição de folhas e frutos infectados com G. citricarpa, após a aplicação dos fungicidas, 7,5% dos isolados avaliados sobre meio de cultura apresentaram resistência a esse fungicida, o que indica que pode ocorrer seleção de isolados resistentes no campo. Para a piraclostrobina não foi observada resistência, o que indica que pode ser um composto alternativo para ser utilizado de forma alternada com carbendazim, para diminuir as chances de ocorrência de resistência do patógeno.

Inbreeding depression and selfing rate of Ipomoea hederacea var. integriuscula (Convolvulaceae)

Inbreeding depression and selfing rate were investigated in the self-compatible vine Ipomoea hederacea to assess the variability of the breeding system. Inbreeding depression differed between populations and the magnitude varied at germination, growth (as measured by aboveground biomass), and reproductive potential. Plants from Macon County, Alabama, USA, had significant inbreeding depression (31%) at germination, but no significant inbreeding depression for aboveground biomass or number of reproductive structures (buds and flowers) at 45 d post germination in the greenhouse or in the field. Plants from Morgan County, Alabama, however, had significant inbreeding depression (>50%) for all three stages in the greenhouse. In allozyme comparisons, five of the 11 I. hederacea populations surveyed had high selfing rates (66.66-92.53%) and high levels of homozygosity (F(IS) = 0.500-0.861) in 2003, and three of four populations surveyed in 2004 had selfing rates that exceeded 50%. High selfing rates, high levels of homozygosity, and low levels of inbreeding depression suggest that inbreeding depression may not present a significant barrier to the transmission of selfing alleles in some populations of I. hederacea, but does not account for the maintenance of a mixed mating system in other populations.

The effect of wasps and ants on the reproductive success of the extrafloral nectaried plant Turnera ulmifolia (Turneraceae)

Summary 1. To assess the effectiveness of extrafloral nectaries (EFN) as a defensive mechanism of plants it is vital to use a multiple interactions approach and assess the contribution of all visiting species and their interactions. 2. The effect of EFN‐visiting ants (Camponotus planatus, C. abdominalis, Conomyrma sp., Crematogaster brevispinosa, Forelius sp., Pseudomyrmex sp.) and wasps (Polistes instabilis, Polybia occidentalis) on the reproductive success (estimated as the number of reproductive structures) of Turnera ulmifolia (Turneraceae) was experimentally evaluated. Herbivory effects were tested using Euptoieta hegesia larvae (caterpillars), which is the main herbivore of this plant. The study was done in a coastal sand dune scrub in Veracruz, México. 3. Wasps and ants were selectively excluded using a two‐factor design (Wasps, Ants) block design, both factors with two levels (absent, present). The response variables were an index of herbivory per branch and the number of buds, flowers, ripe and unripe fruit per plant, and the seed/fruit ratio per branch. 4. After a week of placing the larvae on experimental plants, they were significantly more frequent on plants where wasps and ants had been experimentally excluded. 5. Wasp presence was associated significantly with greater numbers of buds, flowers, ripe fruit and seeds. When acting separately, wasps and ants exerted a positive effect in decreasing herbivory levels and increasing the number of unripe fruit; when acting together, however, their effect was not additive. 6. This is the first demonstration of a positive effect on the plant by wasps associated with EFN. The ecological implication of this finding is that the function of EFN and the ultimate effects on a plant will probably depend on the array of organisms visiting its EFN.

Growth and climatic response of male and female trees of Austrocedrus chilensis, a dioecious conifer from the temperate forests of southern South America

In dioecious plants, males and females usually differ in the amount of resources devoted to reproduction. As a consequence of potential tradeoffs between reproductive and vegetative functions, sexes can exhibit distinctive growth patterns. We analyzed differences between male and female trees in average radial growth, interannual radial growth variation, and, through dendrochronological reconstruction, growth response to temperature and rainfall in 15 stands of the dioecious conifer Austrocedrus chilensis, occurring in Nahuel Huapi National Park, Argentina. Patterns of resource allocation in this species are typical of most dioecious plants in that females invest several times more carbon and nitrogen into reproduction than males. Consistent with theory, we found that in seven stands males grew faster than females. In three stands, however, females grew faster than males, whereas in the other five no significant differences between sexes were detected. In addition, within a stand one sex could grow faster than the other during some periods, while at other times the reverse was true. We found no evidence that females exhibited higher interannual growth variation than males. Growth responded positively to precipitation and negatively to temperature over the growing season. However, neither the direction nor the magnitude of the correlations between annual growth and seasonal climatic variables differed between males and females. Possible factors that could contribute to reducing the differences in the cost of reproduction between males and females in A. chilensis are i) the photosynthetic activity of developing female cones, ii) differences in carbon assimilation efficiency between sexes, and iii) a more strict regulation of the number of reproductive structures produced annually among the females. We hypothesize that the spatio-temporal mosaic in growth differences between sexes we report here might be attributed to chance colonization of disturbed sites by either fast- or slow-growing male and female genotypes rather than by stand characteristics. A general implication is that very little might be concluded about the consequences of the differential cost of reproduction between sexes in any dioecious species from studies focused on a single population or even a few populations.

Resposta de cultivares de algodão ao boro em solução nutritiva

Em lavouras de algodão (Gossypium hirsutum) que receberam calagem, é comum o aparecimento de deficiência de B. Há recomendações de adubação boratada, baseadas nas respostas da variedade IAC 20, que não é mais cultivada. O objetivo do trabalho foi avaliar a resposta dos cultivares CNPA-ITA 90 (Deltapine) e IAC 22 ao B, comparadas à IAC 20. Plantas de algodão foram cultivadas em solução nutritiva contendo 0, 7, 14, 21 e 28 mmol L-1 de B. As plantas do tratamento sem boro foram descartadas por não apresentarem crescimento suficiente para análise. Foi analisada a produção de matéria seca e absorção de B. As três variedades apresentaram resposta semelhante aos níveis de B da solução, tanto em termos de produção de matéria seca, como em número de estruturas reprodutivas e teor de B nos tecidos. O nível de 21 mmol L-1 de B foi suficiente para a máxima produtividade para as três variedades, correspondendo a teores foliares (3as e 4as folhas a partir do ápice, na época do florescimento) de 16 mg kg-1.