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Pollen Quantity (pollen + quantity)
Selected AbstractsReduced reproductive success and offspring survival in fragmented populations of the forest herb Phyteuma spicatumJOURNAL OF ECOLOGY, Issue 6 2005ANNETTE KOLB Summary 1Habitat fragmentation, which reduces the size and increases the isolation of populations, is a major threat to biodiversity. For Phyteuma spicatum, a self-incompatible, rare understorey herb in deciduous forests of north-western Germany, I tested the hypotheses that: (i) fitness (in terms of reproductive success) is reduced in small or isolated populations, (ii) reproduction in small populations is reduced by pollen limitation and (iii) genetic effects cause fitness reductions in small populations. 2I compared the reproductive success of plants of Phyteuma in 14 populations of different size and degree of isolation. Seed production was, as predicted, positively related to population size but was also influenced by plant size, although not by population isolation, density or habitat quality. 3I performed supplemental hand-pollinations in 10 of the 14 populations using pollen from the same population (test for pollen quantity) or from another large population (pollen quality). The proportional difference in seed production between hand-pollinated plants and open-pollinated controls increased with decreasing population size, indicating pollinator limitation of reproduction in small populations. There was no difference between the two hand-pollination treatments, suggesting that a sufficient number of cross-compatible mates was available even in the smallest populations. 4Progeny from the 14 populations were grown for 32 weeks in a common environment. There was no effect of population size on germination, but final seedling survival was positively related to population size, and this relationship was more pronounced in the glasshouse than under more favourable growing conditions in a common garden. Genetic effects may thus reduce fitness (here measured in terms of survival) in plants from small populations, making them more susceptible to environmental stress. 5The results suggest that both reproduction and offspring performance may be reduced in small populations even of long-lived species such as Phyteuma spicatum. Different processes, such as pollen limitation and genetic deterioration, may interact and affect local population dynamics and the persistence of species in fragmented landscapes. [source] Pollen source and resource limitation to fruit production in the rare species Eremosparton songoricum (Fabaceae)NORDIC JOURNAL OF BOTANY, Issue 4 2010Xiang Shi Eremosparton songoricum (Litv.) Vass. is a rare, central Asian desert species which shows lower fruit set and seed set (<16%) than most hermaphroditic species. We hypothesized that fruit production was limited by pollen and resources. To evaluate potential fruit abortion due to pollen limitation, supplemental hand-pollination was undertaken, the mating system was investigated and the foraging behavior of pollinators was recorded. To investigate possibile resource limitation, flowers and young pods were artificially removed and fertilization were manipulated. The results showed that under natural pollination, the number of pollen deposited on the stigma greatly exceed the number of ovules per ovary. Mating system experiments showed that the species is self-compatible, but depended on pollinators to set seeds. Supplemental outcross pollination increased fruit set significantly. The most frequent effective pollinator Megachile terminate Morawitz, was observed pollinating many flowers of the same individual plant (74.5±1.3%). These results suggested that fruit production is affected by insufficient outcross pollen rather than by pollen quantity. Removal of 2/3 of the flowers and young pods led to significantly higher fruit set, as did addition of fertilizers (N,P,K: 0.025,0.05,0.013,g, N,P,K: 0.05,0.1,0.025,g) showing that reducing resource acceptors and increasing inorganic resources both helps to improve fruit set. We therefore conclude that reproductive success of E. songoricum is limited by both outcross pollen and available nutrients. [source] Tolerance to apical and foliar damage: costs and mechanisms in Raphanus raphanistrumOIKOS, Issue 12 2007Elin Boalt To study mechanisms underlying plant tolerance to herbivore damage, we used apical and foliar damage as experimental treatments to study whether there are similar tolerance mechanisms to different types of damage. We also studied whether tolerance to different types of damage are associated, and whether there is a cost involved in plant tolerance to different types of herbivore damage. Our greenhouse experiment involved 480 plants from 30 full-sib families of an annual weed Raphanus raphanistrum, wild radish, which were subjected to control and two different simulated herbivore damage treatments, apex removal and foliar damage of 30% of leaf area. Apical damage significantly decreased seed production, whereas foliar damage had no effect. There was a significant genetic variation for tolerance to foliar, but not apical damage. No costs were observed in terms of negative correlation between tolerance to either damage type and fitness of undamaged plants. Tolerances to apical and foliar damage were not significantly correlated with each other. We observed a larger number of significant associations between tolerance and reproductive traits than between tolerance and vegetative traits. Plant height and leaf size of damaged plants interacted in their association to tolerance to foliar damage. Inflorescence number and pollen quantity per flower of damaged plants were positively associated with tolerance to apical damage. In late-flowering genotypes, petal size of undamaged plants and pollen quantity of damaged plants were positively associated with tolerance to foliar damage. In summary, traits involved in floral display and male fitness were associated with plant tolerance to herbivore damage. [source] Cone abortion in Pinus halepensis: the role of pollen quantity, tree size and cone locationOIKOS, Issue 1 2002Shirrinka Goubitz This study describes the seasonal patterns of seed and cone abortion in natural Pinus halepensis trees and assesses the effects of pollen quantity, tree size and cone location on seed and cone abortion. The cone-set ratio was similar to the expected value, based on literature on woody perennials. The seed-ovule ratio, however, was almost twice as high as its expected value. The investment in protective cone elements was high and did not vary with the seed-ovule ratio of a cone. Pollination factors influenced cone abortion, as indicated by the high abortion rate at the end of the pollination period. Furthermore, abortive cones had lower pollination rates and lower pollen loads than well developed cones. Effects of resource availability were assessed as effects of tree size and cone position on twigs. Small trees aborted more cones than big trees and cone abortion was higher in apical cones than in basal cones. Abortion in P. halepensis is selective, mediated by both pollen quantity and resource availability. The relative importance of pollen and resources is suggested to be flexible, probably varying between trees and years. The high seed-ovule ratio of P. halepensis is the result of high pollination rate and selective abortion. The selective abortion might be due to the high allocation to protective cone elements relative to the allocation to seeds. [source] | ||||||||||