Cuscuta campestris (field dodder).

The parasitic weed C. campestris is native to North America but has been introduced around the world and become a weed in many countries. It is by far the most important of the dodders, perhaps because of its wide host range. This ensures that there is a wide range of crop seeds that may be contaminated, and in which it may be introduced to new areas over both short and long distances. Once introduced it is almost certain that there will be suitable host plants on which it can thrive and be damaging, whether they are crops or wild species. Vegetative spread can be very rapid - up to 5 m in 2 months. It also has a wide tolerance of climatic conditions from warm temperate to sub-tropical and tropical.

Armillaria root rot fungi host single-stranded RNA viruses

Species of Armillaria are distributed globally and include some of the most important pathogens of forest and ornamental trees. Some of them form large long-living clones that are considered as one of the largest organisms on earth and are capable of long-range spore-mediated transfer as well as vegetative spread by drought-resistant hyphal cords called rhizomorphs. However, the virus community infecting these species has remained unknown. In this study we used dsRNA screening and high-throughput sequencing to search for possible virus infections in a collection of Armillaria isolates representing three different species: Armillaria mellea from South Africa, A. borealis from Finland and Russia (Siberia) and A. cepistipes from Finland. Our analysis revealed the presence of both negative-sense RNA viruses and positive-sense RNA viruses, while no dsRNA viruses were detected. The viruses included putative new members of virus families Mymonaviridae, Botourmiaviridae and Virgaviridae and members of a recently discovered virus group tentatively named “ambiviruses” with ambisense bicistronic genomic organization. We demonstrated that Armillaria isolates can be cured of viruses by thermal treatment, which enables the examination of virus effects on host growth and phenotype using isogenic virus-infected and virus-free strains.

Plant Community Establishment in a Coastal Marsh Restored Using Sediment Additions

A goal of wetland restoration is the establishment of resilient plant communities that persist under a variety of environmental conditions. We investigated the role of intraspecific and interspecific variation on plant community establishment in a brackish marsh that had been restored by sediment addition. Plant growth, sediment accretion, and surface elevation change in planted, not-planted, and nearby reference sites (treatments) were compared. Four perennial macrophytes were planted: Bolboschoenus robustus, Distichlis spicata, Phragmites australis, and Schoenoplectus californicus. There was 100% survival of the planted species, and all exhibited rapid vegetative spread. Intraspecific variation in stem height and cover was identified, and interspecific comparisons also indicated differences in species cover. Treatment comparisons revealed that final total cover at not-planted sites was equivalent to that at reference sites, and was highest at planted sites where P. australis became dominant. Species richness was initially highest at the reference sites, but final richness was equivalent among treatments. Soil surface elevation was greater at planted compared to not-planted and reference sites. Because of the rapid cover and increased surface elevation generated by planted species, the resiliency of restored coastal marshes may be enhanced by plantings in areas where natural colonization is slow and subsidence is high.

Bitter Panicgrass, Bitter Panicum, Panicum amarum

Bitter panicgrass is important in dune stabilization and building and often grows intermixed with sea oats onforedunes. It is also found spread throughout back dunes, interdunal swales, and coastal grasslands. This plantoccurs throughout coastal Florida, except for the Big Bend coast, west to New Mexico, and along coastal northeast states to Massachusetts. A significant proportion of bitter panicgrass reproduction is by vegetative spread; its seeds are often sterile.https://edis.ifas.ufl.edu/sg178 This publication is derived from information in SGEB-75/SG156, Dune Restoration and Enhancement for the Florida Panhandle, by Debbie Miller, Mack Thetford, Christina Verlinde, Gabriel Campbell, and Ashlynn Smith. https://edis.ifas.ufl.edu/sg156.

Genetic diversity within a population of Microlaena stipoides, as revealed by AFLP markers

Microlaena stipoides (Labill.) R.Br. (microlaena), a C3 perennial grass, is common within grazed native pastures in the high-rainfall zone (>550 mm average annual rainfall) of south-eastern Australia. It has the ability to spread via seed production or vegetatively, using both rhizomes and stolons. This experiment aimed to determine how variable a microlaena population was within a single area, with the aim of determining whether microlaena relied on seed or vegetative spread to sustain populations. Leaf samples of microlaena were collected from 85 locations, sampling two transects, within a pasture at Chiltern, in north-eastern Victoria (36°12ʹS, 146°35ʹE). The genetic diversity among samples was analysed using amplified fragment length polymorphism (AFLP) markers. We obtained 1612 fragments, using 10 primers combinations. Polymorphism for the markers ranged from 47% to 65%. These results indicated that the populations of microlaena that exist within the pasture at Chiltern are likely to have undergone some degree of outcrossing (Fst = 0.0219). It is likely that recruitment is occurring from sexual reproduction as well as via clonal spread within the microlaena population examined. This ability to use vegetative spread as well as both sexual and asexual reproduction may make populations of microlaena more resilient in the longer term.

Impact of weather on dynamics of plant functional groups in an abandoned limestone grassland

We examined to what extend the rate and direction of changes in unmanaged grassland depend on fluctuations in climatic conditions. Vegetation data from permanent plots in a semi-natural grassland in southern Poland collected over 12 years were used. Relations between weather variables, time, and the cover of 41 more frequent species and 14 plant functional groups were analysed. The greatest effect on the dynamics of species and functional groups had precipitation in spring and/or early summer, particularly in the current year. The majority of plant groups were significantly affected also by the temperature in spring and early summer in one of the three previous years. During 12 years, the cover of annuals and biennials, short plants, and plants with small leaves decreased, while the cover of taller plants, plants with larger leaves, and with vegetative spread increased. The analyses suggest that these successional changes were not directly associated with climatic conditions but were affected by them indirectly through interspecific competition. The fluctuations in climatic conditions, chiefly precipitation, had a significant effect on both the composition and the rate of changes in abandoned grassland. The increase in the cover of tall perennial species with broad leaves hindered succession towards woodland despite of the presence of woods in the closed vicinity. It can be expected that during drier periods colonisation of grassland by later successional species could be easier.

Regeneration of Nardus stricta subalpine grasslands in the Giant Mountains (Krkonoše)

The origin of <em>Nardus stricta</em> dominated subalpine grassland (Nardo-Caricion rigidae alliance) is a frequently discussed topic in the Giant Mountains (Karkonosze in the Czech Republic). Many researchers considered them, as secondary stands arisen after Pinus mugo removal and by consequent oligotrophization of original plant communities, caused by long-term rough grazing and hay making activities without manuring. On the contrary, they are recognized as natural due to inability of generative reproduction of <em>N. stricta</em> and the very slow vegetative spread there. The aim of this study was to find proofs for generative reproduction of mat grass in subalpine conditions of the Giant Mountains. We identified a <em>Pinus mugo</em> nursery with arable land abandoned in 1956 and compared its vegetation with that of the surrounding area. Dense and homogenous sward dominated by <em>N. stricta</em> developed during the succession on the old arable land for 48 years, and it is an indisputable proof of generative reproduction of <em>N. stricta</em> there. Synthesizing historical facts on human activities in the past and the results of our contemporary vegetation analysis, we conclude that the Nardo-Caricion rigidae grassland was capable to spread relatively quickly, when agricultural activities above the upper timber line were introduced.

Changes in plant species composition in abandoned and restored limestone grassiands - the effects of tree and shrub cutting

Abandoned semi-natural limestone grasslands are often overgrown by shrubs and trees. Little is know if and to what extant xerothermic limestone grasslands can be restored by tree cutting. This was tested in a 12-year experiment after the clearing of a 35-year-old secondary pine wood developed on unmanaged grassland in the close proximity of not overgrown old grassland. After 12 years, there were no significant differences in the number of field layer species on the plots in the old and restored grasslands. But over this period the number of meadow species increased in all sites, while the number of xerothermic calcareous species increased significantly only in the old grassland plots. The developing shrub layer negatively influenced the number of nitrophilous and ruderal species in grasslands restored in the former close and open woods, and the number of all species, including the number of non-tufted perennials and perennials with vegetative spread, in the former open wood. The number of meadow species increased in years with higher precipitation in late spring and early summer. The obtained results suggest that in overgrowing grasslands shrubs and trees should be cut every few years, before their covers increase to about 30%. However, this treatment alone will not stop the changes to communities with dominance of tall and vegetatively spreading grasses and forbs. Cutting trees and shrubs in sites where most grassland species have already vanished, without additional managements supporting their dispersal, seedling recruitment and development, is not sufficient to restore limestone grasslands rich in xerothermic species.

“Recalcitrant understory layers” revisited: arrested succession and the long life-spans of clonal mid-successional species

In their recent review of arrested succession, Royo and Carson ( A.A. Royo and W.P. Carson. 2006. Can. J. For. Res. 36: 1345–1362 ) demonstrate that “recalcitrant understory layers” are widespread and pervasive modifiers of ecosystems and disruptors of forest regeneration. They rightly point out that many plant species associated with arrested succession are characterized by rapid vegetative spread. Extending their review, we point out that most of such species are clonal or thicket-forming and suggest that an additional reason why these plants so effectively suppress succession for extended periods is their long life-spans.