3 research outputs found
Inter-and intraspecific variation in fern mating systems after long-distance colonization: the importance of selfing
<p>Abstract</p> <p>Background</p> <p>Previous studies on the reproductive biology of ferns showed that mating strategies vary among species, and that polyploid species often show higher capacity for self-fertilization than diploid species. However, the amount of intraspecific variation in mating strategy and selfing capacity has only been assessed for a few species. Yet, such variation may have important consequences during colonization, as the establishment of any selfing genotypes may be favoured after long-distance dispersal (an idea known as Baker's law).</p> <p>Results</p> <p>We examined intra-and interspecific variation in potential for self-fertilization among four rare fern species, of which two were diploids and two were tetraploids: <it>Asplenium scolopendrium </it>(2n), <it>Asplenium trichomanes </it>subsp. <it>quadrivalens </it>(4n), <it>Polystichum setiferum </it>(2n) and <it>Polystichum aculeatum </it>(4n). Sporophyte production was tested at different levels of inbreeding, by culturing gametophytes in isolation, as well as in paired cultures with a genetically different gametophyte. We tested gametophytes derived from various genetically different sporophytes from populations in a recently planted forest colonized through long-distance dispersal (Kuinderbos, the Netherlands), as well as from older, less disjunct populations.</p> <p>Sporophyte production in isolation was high for Kuinderbos genotypes of all four species. Selfing capacity did not differ significantly between diploids and polyploids, nor between species in general. Rather selfing capacity differed between genotypes within species. Intraspecific variation in mating system was found in all four species. In two species one genotype from the Kuinderbos showed enhanced sporophyte production in paired cultures. For the other species, including a renowned out crosser, selfing capacity was consistently high.</p> <p>Conclusions</p> <p>Our results for four different species suggest that intraspecific variation in mating system may be common, at least among temperate calcicole ferns, and that genotypes with high selfing capacity may be present among polyploid as well as diploid ferns. The surprisingly high selfing capacity of all genotypes obtained from the Kuinderbos populations might be due to the isolated position of these populations. These populations may have established through single-spore colonization, which is only possible for genotypes capable of self-fertilization. Our results therewith support the idea that selection for selfing genotypes may occur during long-distance colonization, even in normally outcrossing, diploid ferns.</p
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Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands.
Grasslands are subject to considerable alteration due to human activities globally, including widespread changes in populations and composition of large mammalian herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and these changes likely interact with increases in soil nutrient availability. Given the scale of grassland soil fluxes, such changes can have striking consequences for atmospheric C concentrations and the climate. Here, we use the Nutrient Network experiment to examine the responses of soil C and N pools to mammalian herbivore exclusion across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized with NPK + micronutrients). We show that the impact of herbivore exclusion on soil C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are smaller upon herbivore exclusion. The highest mean soil C and N pools were found in grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion was contingent on temperature - herbivores likely cause losses of C and N in colder sites and increases in warmer sites. Additionally, grasslands that contain mammalian herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the importance of conserving mammalian herbivore populations in grasslands worldwide. We need to incorporate local-scale herbivory, and its interaction with nutrient enrichment and climate, within global-scale models to better predict land-atmosphere interactions under future climate change