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135 records · Page 8Linked to original sources
USGS2004

Chromosome numbers and karyotype evolution in holoparasitic Orobanche (Orobanchaceae) and related genera

Chromosome numbers and karyotypes of species of Orobanche , Cistanche , and Diphelypaea (Orobanchaceae) were investigated, and 108 chromosome counts of 53 taxa, 19 counted for the first time, are presented with a thorough compilation of previously published data. Additionally, karyotypes of representatives of these genera, including Orobanche sects. Orobanche and Trionychon , are reported. Cistanche ( x = 20) has large meta- to submetacentric chromosomes, while those of Diphelypaea ( x = 19) are medium-sized submeta- to acrocentrics. Within three analyzed sections of Orobanche , sects. Myzorrhiza ( x = 24) and Trionychon ( x = 12) possess medium-sized submeta- to acrocentrics, while sect. Orobanche ( x = 19) has small, mostly meta- to submetacentric, chromosomes. Polyploidy is unevenly distributed in Orobanche and restricted to a few lineages, e.g., O . sect. Myzorrhiza or Orobanche gracilis and its relatives (sect. Orobanche ). The distribution of basic chromosome numbers supports the groups found by molecular phylogenetic analyses: Cistanche has x = 20, the Orobanche -group ( Orobanche sect. Orobanche , Diphelypaea ) has x = 19, and the Phelipanche -group ( Orobanche sects. Gymnocaulis , Myzorrhiza , Trionychon ) has x = 12, 24. A model of chromosome number evolution in Orobanche and related genera is presented: from two ancestral base numbers, x h = 5 and x h = 6, independent polyploidizations led to x = 20 ( Cistanche ) and (after dysploidization) x = 19 ( Orobanche -group) and to x = 12 and x = 24 ( Phelipanche -group), respectively.

American Journal of Botany↗
USGS2005

Timing of seed dispersal generates a bimodal seed bank depth distribution

The density of soil seed banks is normally highest at the soil surface and declines monotonically with depth. Sometimes, for a variety of reasons, peak density occurs below the surface but, except in severely disturbed soils, it is generally true that deeper seeds are older. In seasonally dry habitats that develop deep soil cracks during the dry season, it is possible that some seeds fall down cracks and rapidly become deeply buried. We investigated this possibility for three dominant clonal perennials ( Scirpus maritimus , S. litoralis , and Juncus subulatus ) in the Doñana salt marsh, a nontidal marsh with a Mediterranean climate located in southwest Spain. Two species, which shed most of their seed during the dry season and have seeds with low buoyancy, had bimodal viable seed depth distributions, with peak densities at the surface and at 16–20 cm. A third species, which shed most seeds after soil cracks had closed and had seeds with high buoyancy, had viable seeds only in surface soil. Bimodal seed bank depth distributions may be relatively common in seasonally dry habitats with fine-textured soils, but their ecological significance has not been investigated.

American Journal of Botany↗
USGS2005

Seed storage conditions change the germination pattern of clonal growth plants in Mediterranean salt marshes

The effect of salinity level and extended exposure to different salinity and flooding conditions on germination patterns of three salt‐marsh clonal growth plants ( Juncus subulatus , Scirpus litoralis , and S. maritimus ) was studied. Seed exposure to extended flooding and saline conditions significantly affected the outcome of the germination process in a different, though predictable, way for each species, after favorable conditions for germination were restored. Tolerance of the germination process was related to the average salinity level measured during the growth/germination season at sites where established individuals of each species dominated the species cover. No relationship was found between salinity tolerance of the germination process and seed response to extended exposure to flooding and salinity conditions. The salinity response was significantly related to the conditions prevailing in the habitats of the respective species during the unfavorable (nongrowth/nongermination) season. Our results indicate that changes in salinity and hydrology while seeds are dormant affect the outcome of the seed‐bank response, even when conditions at germination are identical. Because these environmental‐history‐dependent responses differentially affect seed germination, seedling density, and probably sexual recruitment in the studied and related species, these influences should be considered for wetland restoration and management.

Doñana National Park↗
USGS2006

Salt tolerance and osmotic adjustment of Spartina alterniflora (Poaceae) and the invasive M haplotype of Phragmites australis (Poaceae) along a salinity gradient

An invasive variety of Phragmites australis (Poaceae, common reed), the M haplotype, has been implicated in the spread of this species into North American salt marshes that are normally dominated by the salt marsh grass Spartina alterniflora (Poaceae, smooth cordgrass). In some European marshes, on the other hand, Spartina spp. derived from S. alterniflora have spread into brackish P. australis marshes. In both cases, the non-native grass is thought to degrade the habitat value of the marsh for wildlife, and it is important to understand the physiological processes that lead to these species replacements. We compared the growth, salt tolerance, and osmotic adjustment of M haplotype P. australis and S. alterniflora along a salinity gradient in greenhouse experiments. Spartina alterniflora produced new biomass up to 0.6 M NaCl, whereas P. australis did not grow well above 0.2 M NaCl. The greater salt tolerance of S. alterniflora compared with P. australis was due to its ability to use Na + for osmotic adjustment in the shoots. On the other hand, at low salinities P. australis produced more shoots per gram of rhizome tissue than did S. alterniflora . This study illustrates how ecophysiological differences can shift the competitive advantage from one species to another along a stress gradient. Phragmites australis is spreading into North American coastal marshes that are experiencing reduced salinities, while Spartina spp. are spreading into northern European brackish marshes that are experiencing increased salinities as land use patterns change on the two continents.

American Journal of Botany↗
USGS2007

Genotype, soil type, and locale effects on reciprocal transplant vigor, endophyte growth, and microbial functional diversity of a narrow sagebrush hybrid zone in Salt Creek Canyon, Utah

When addressing the nature of ecological adaptation and environmental factors limiting population ranges and contributing to speciation, it is important to consider not only the plant's genotype and its response to the environment, but also any close interactions that it has with other organisms, specifically, symbiotic microorganisms. To investigate this, soils and seedlings were reciprocally transplanted into common gardens of the big sagebrush hybrid zone in Salt Creek Canyon, Utah, to determine location and edaphic effects on the fitness of parental and hybrid plants. Endophytic symbionts and functional microbial diversity of indigenous and transplanted soils and sagebrush plants were also examined. Strong selection occurred against the parental genotypes in the middle hybrid zone garden in middle hybrid zone soil; F1 hybrids had the highest fitness under these conditions. Neither of the parental genotypes had superior fitness in their indigenous soils and habitats; rather F1 hybrids with the nonindigenous maternal parent were superiorly fit. Significant garden-by-soil type interactions indicate adaptation of both plant and soil microorganisms to their indigenous soils and habitats, most notably in the middle hybrid zone garden in middle hybrid zone soil. Contrasting performances of F1 hybrids suggest asymmetrical gene flow with mountain, rather than basin, big sagebrush acting as the maternal parent. We showed that the microbial community impacted the performance of parental and hybrid plants in different soils, likely limiting the ranges of the different genotypes.

Utah↗
USGS2002

The flora of Oktibbeha County, Mississippi

We surveyed the flora of Oktibbeha County, Mississippi, U.S.A., from February 1994 to 1996. Occupying 118 square kilometers in east-central Mississippi, Oktibbeha County lies among 3 physiographic regions that include, from west to east, Interior Flatwoods, Pontotoc Ridge, and Black Prairie. Accordingly, the county harbors a diverse flora. Based on field work, as well as an extensive review of published literature and herbarium records at IBE and MISSA, we recorded a total of 1,148 taxa (1,125 species, 7 hybrids, 16 infraspecific taxa) belonging to 514 genera in 160 families, over 85% of all taxa documented were native. Compared to 3 other counties in east-central Mississippi, Oktibbeha County has the second largest recorded flora. The number of state-listed (endangered, threatened, or of special concern) taxa (67) documented in this survey far exceeds that reported from any other county in the region. Three introduced species, Ilex cornuta Lindl. & Paxton, Mahonia bealei (Fortune) Carrie??re, and Nandina domestica Thunb., are reported in a naturalized state for the first time from Mississippi. We also describe 16 different plant communities belonging to 5 broad habitat categories: bottomland forests, upland forests and prairies, aquatic habitats, seepage areas, and human-influenced habitats. A detailed description of the vegetation associated with each of these communities is provided.

SIDA, Contributions to Botany↗