Experimental warming advances phenology of groundlayer plants at the boreal-temperate forest ecotone.

PREMISE OF THE STUDY: Changes to plant phenology have been linked to warmer temperatures caused by climate change. Despite the importance of the groundlayer to community and forest dynamics, few warming experiments have focused on herbaceous plant and shrub phenology. METHODS: Using a field study in Minnesota, United States, we investigated phenological responses of 16 species to warming over five growing seasons (2009-2013) at two sites, under two canopy covers, and in three levels of simultaneous above- and belowground warming: ambient temperature, ambient +1.7°C and ambient +3.4°C. We tested whether warming led to earlier phenology throughout the growing season and whether responses varied among species and years and depended on canopy cover. KEY RESULTS: Warming extended the growing season between 11-30 days, primarily through earlier leaf unfolding. Leaf senescence was delayed for about half of the species. Warming advanced flowering across species, especially those flowering in August, with modest impacts on fruit maturation for two species. Importantly, warming caused more than half of the species to either converge or diverge phenologically in relation to each other, suggesting that future warmed climate conditions will alter phenological relationships of the groundlayer. Warm springs elicited a stronger advance of leaf unfolding compared to cool spring years. Several species advanced leaf unfolding (in response to warming) more in the closed canopy compared to the open. CONCLUSIONS: Climate warming will extend the growing season of groundlayer species in the boreal-temperate forest ecotone and alter the synchrony of their phenology.

Model parameterization to simulate and compare the PAR absorption potential of two competing plant species.

Mountain pastures dominated by the pasture grass Setaria sphacelata in the Andes of southern Ecuador are heavily infested by southern bracken (Pteridium arachnoideum), a major problem for pasture management. Field observations suggest that bracken might outcompete the grass due to its competitive strength with regard to the absorption of photosynthetically active radiation (PAR). To understand the PAR absorption potential of both species, the aims of the current paper are to (1) parameterize a radiation scheme of a two-big-leaf model by deriving structural (LAI, leaf angle parameter) and optical (leaf albedo, transmittance) plant traits for average individuals from field surveys, (2) to initialize the properly parameterized radiation scheme with realistic global irradiation conditions of the Rio San Francisco Valley in the Andes of southern Ecuador, and (3) to compare the PAR absorption capabilities of both species under typical local weather conditions. Field data show that bracken reveals a slightly higher average leaf area index (LAI) and more horizontally oriented leaves in comparison to Setaria. Spectrometer measurements reveal that bracken and Setaria are characterized by a similar average leaf absorptance. Simulations with the average diurnal course of incoming solar radiation (1998-2005) and the mean leaf-sun geometry reveal that PAR absorption is fairly equal for both species. However, the comparison of typical clear and overcast days show that two parameters, (1) the relation of incoming diffuse and direct irradiance, and (2) the leaf-sun geometry play a major role for PAR absorption in the two-big-leaf approach: Under cloudy sky conditions (mainly diffuse irradiance), PAR absorption is slightly higher for Setaria while under clear sky conditions (mainly direct irradiance), the average bracken individual is characterized by a higher PAR absorption potential. (approximately 74 MJ m(-2) year(-1)). The latter situation which occurs if the maximum daily irradiance exceeds 615 W m(-2) is mainly due to the nearly orthogonal incidence of the direct solar beam onto the horizontally oriented frond area which implies a high amount of direct PAR absorption during the noon maximum of direct irradiance. Such situations of solar irradiance favoring a higher PAR absorptance of bracken occur in approximately 36% of the observation period (1998-2005). By considering the annual course of PAR irradiance in the San Francisco Valley, the clear advantage of bracken on clear days (36% of all days) is completely compensated by the slight but more frequent advantage of Setaria under overcast conditions (64% of all days). This means that neither bracken nor Setaria show a distinct advantage in PAR absorption capability under the current climatic conditions of the study area.

Ptaquiloside and Pterosin B Levels in Mature Green Fronds and Sprouts of Pteridium arachnoideum.

Pteridium arachnoideum, a fern of the Pteridium aquilinum species complex found in South America, is responsible for several different syndromes of poisoning. Cases of bovine enzootic hematuria and upper alimentary squamous cell carcinoma are both frequent occurrences in Brazil, whereas only bovine enzootic hematuria is noted with any frequency around the world. The reason for the high frequency of upper alimentary squamous cell carcinoma in Brazil is not currently known. One possible explanation may be the higher levels of ptaquiloside and pterosin B in Brazilian Pteridium than those present in the plant in other countries. However, these levels have not yet been determined in P. arachnoideum. Thus, the present study aimed to measure and compare ptaquiloside and pterosin B levels in mature green fronds and sprouts of P. arachnoideum collected from different locations in Brazil. Samples of P. arachnoideum were collected from the states of Minas Gerais and Rio Grande do Sul. A total of 28 mature leaf samples and 23 sprout samples were used. The mean concentrations of ptaquiloside and pterosin B present in the mature green fronds of P. arachnoideum ranged from 2.49 to 2.75 mg/g and 0.68 to 0.88 mg/g, respectively; in P. arachnoideum sprouts, mean concentrations of ptaquiloside and pterosin B ranged from 12.47 to 18.81 mg/g, and 4.03 to 10.42 mg/g for ptaquiloside and pterosin B, respectively. Thus, ptaquiloside and pterosin B levels in P. arachnoideum samples collected in Brazil were higher in sprouts than in mature green fronds, as observed in other countries. However, there was no variation in ptaquiloside levels among plants collected from different cities in Brazil. The high frequency of upper alimentary squamous cell carcinoma in Brazilian cattle may not be attributed to greater levels of ptaquiloside and pterosin B in P. arachnoideum than in other Pteridium species in other countries.

Control of Pteridium aquilinum: meta-analysis of a multi-site study in the UK.

BACKGROUND AND AIMS: A great deal of money is spent controlling invasive weeds as part of international and national policies. It is essential that the funded treatments work across the region in which the policies operate. We argue that experiments across multiple sites are required to validate these programs as results from single sites may be misleading. Here, the control of Pteridium aquilinum (bracken) is used as a test example to address the following four questions. (1) Does the effectiveness of P. aquilinum-control treatments vary across sites? (2) Is the best treatment identified in previous research (cutting twice per year) consistent at all sites, and if not why not? (3) Is treatment performance related to P. aquilinum rhizome mass, litter cover or litter depth at the various sites? (4) Does successful P. aquilinum control influence species richness? METHODS: Pteridium aquilinum-control treatments were monitored for 10 years using six replicated experiments and analysed using meta-analysis. Meta-regressions were used to explore heterogeneity between sites. KEY RESULTS: The effectiveness of treatments varied between sites depending on the measure used to assess P. aquilinum performance. In general, cutting twice per year was the most successful treatment but on some sites other, less expensive treatments were as good. The effectiveness of treatments at different sites was not related to rhizome mass, but the effectiveness of most applied treatments were inversely related to post-control litter. Effective treatment was also associated with high species richness. CONCLUSIONS: It is concluded that successful development of national weed control programs requires multi-site experimental approaches. Here, meta-analyses demonstrate that variation in effectiveness between sites could be explained in part by pre-specified variables. Reliance on data from a single site for policy formulation is therefore clearly dangerous.

Who will win where and why? An ecophysiological dissection of the competition between a tropical pasture grass and the invasive weed Bracken over an elevation range of 1000 m in the tropical Andes.

In tropical agriculture, the vigorously growing Bracken fern causes severe problems by invading pastures and out-competing the common pasture grasses. Due to infestation by that weed, pastures are abandoned after a few years, and as a fatal consequence, the biodiversity-rich tropical forest is progressively cleared for new grazing areas. Here we present a broad physiological comparison of the two plant species that are the main competitors on the pastures in the tropical Ecuadorian Andes, the planted forage grass Setaria sphacelata and the weed Bracken (Pteridium arachnoideum). With increasing elevation, the competitive power of Bracken increases as shown by satellite data of the study region. Using data obtained from field measurements, the annual biomass production of both plant species, as a measure of their competitive strength, was modeled over an elevational gradient from 1800 to 2800 m. The model shows that with increasing elevation, biomass production of the two species shifts in favor of Bracken which, above 1800 m, is capable of outgrowing the grass. In greenhouse experiments, the effects on plant growth of the presumed key variables of the elevational gradient, temperature and UV radiation, were separately analyzed. Low temperature, as well as UV irradiation, inhibited carbon uptake of the C4-grass more than that of the C3-plant Bracken. The less temperature-sensitive photosynthesis of Bracken and its effective protection from UV radiation contribute to the success of the weed on the highland pastures. In field samples of Bracken but not of Setaria, the content of flavonoids as UV-scavengers increased with the elevation. Combining modeling with measurements in greenhouse and field allowed to explain the invasive growth of a common weed in upland pastures. The performance of Setaria decreases with elevation due to suboptimal photosynthesis at lower temperatures and the inability to adapt its cellular UV screen.

Microbial degradation and impact of Bracken toxin ptaquiloside on microbial communities in soil.

The carcinogenic and toxic ptaquiloside (PTA) is a major secondary metabolite in Bracken fern (Pteridium aquilinum (L.) Kuhn) and was hypothesized to influence microbial communities in soil below Bracken stands. Soil and Bracken tissue were sampled at field sites in Denmark (DK) and New Zealand (NZ). PTA contents of 2.1 +/- 0.5 mg g(-1) and 37.0 +/- 8.7 mg g(-1) tissue were measured in Bracken fronds from DK and NZ, respectively. In the two soils the PTA levels were similar (0-5 microg g(-1) soil); a decrease with depth could be discerned in the deeper B and C horizons of the DK soil (weak acid sandy Spodosol), but not in the NZ soil (weak acid loamy Entisol). In the DK soil PTA turnover was predominantly due to microbial degradation (biodegradation); chemical hydrolysis was occurring mainly in the uppermost A horizon where pH was very low (3.4). Microbial activity (basal respiration) and growth ([3H]leucine incorporation assay) increased after PTA exposure, indicating that the Bracken toxin served as a C substrate for the organotrophic microorganisms. On the other hand, there was no apparent impact of PTA on community size as measured by substrate-induced respiration or composition as indicated by community-level physiological profiles. Our results demonstrate that PTA stimulates microbial activity and that microorganisms play a predominant role for rapid PTA degradation in Bracken-impacted soils.

UV-B effect on constituents of Azolla caroliniana.

Changes in growth and ultrastructure of Azolla caroliniana in response to elevated UV-B radiation were investigated. Exposure of plants to UV-B radiation for 1, 8, 16, 24 and 48 h exhibited a significant decrease in biomass and relative growth rate. This decrease resulted in an increase in doubling time over the control. Also, Chl a and b contents were significantly decreased especially after 16 h. The reduction was accompanied by a decrease in 5-aminolaevulinic acid content (precursor of chlorophyll). On the other hand, contents of carotenoid and UV-absorbing phenolic compounds (flavonoids and anthocyanins) were increased.

Productivity in a dominant herbaceous species is largely unrelated to soil macronutrient stocks.

To predict ecosystem responses to anthropogenic change it is important to understand how and where plant productivity is limited by macronutrient availability. Nitrogen (N) is required in large quantities for plant growth, and is readily lost through leaching or gas fluxes, but reactive nitrogen can be obtained through dinitrogen fixation, and phosphorus (P) is often considered a more fundamental long-term constraint to growth and carbon sequestration in terrestrial ecosystems. Phosphorus limitation may be becoming more prevalent due to widespread pollution by atmospheric N. Assessments of the effects of macronutrient availability on productivity in natural ecosystems are however scarce. We measured standing biomass of bracken Pteridium aquilinum as a proxy for productivity across sites with similar climate but varied geology. Total above-ground biomass varied from 404 to 1947gm-2, yet despite 12-fold to 281-fold variation in soil macronutrient stocks these were remarkably poor at explaining variation in productivity. Soil total nitrogen, organic phosphorus, calcium, magnesium and zinc had no relationship with productivity, whether expressed as concentrations, stocks or element/C ratios, and nor did foliar N/P. Soil potassium (K) and molybdenum stocks both showed weak relationships with productivity. The stock of K in bracken biomass was considerably greater as a proportion of soil stock than for other nutrient elements, suggesting that this nutrient element can be important in determining productivity. Moisture availability, as indicated by environmental trait scores for plant species present, explained considerably more of the variation in productivity than did K stock, with less production in wetter sites. Soil N/C ratio and organic P stock were relatively unimportant in determining productivity across these bracken sites. It is possible that more-direct measures of N and P availability would explain variation in productivity, but the study shows the importance of considering other essential elements and other environmental factors when predicting productivity.

Studies on phytoremediation of copper using Pteridium aquilinum (bracken fern) in the presence of biostimulants and bioassay using Clarias gariepinus juveniles.

A study was carried out to evaluate the uptake of copper from water containing 10 mg/L copper by Pteridium aquilinum (bracken fern) and Clarias gariepinus in the presence of five plant growth stimulants: Nitrogen: phosphorus: potassium (15-15-15: an inorganic fertilizer), pig, cattle, poultry, and a mixture of pig/cattle manures. A plant growth stimulant differentiated each treatment. A 96-hour bioassay using C. gariepinus was carried out at the end of the experiment to test the efficacy of the clean up by P. aquilinum. The control experiment contained no copper or plant growth stimulant. Fish survival, uptake of copper by P. aquilinum, C. gariepinus, concentration of copper in water, hematology and histopathology of the fish were assessed. Higher concentrations of copper were reported in P. aquilinum than in water or C. gariepinus. Low fish mortality was reported with the highest being 20% in the cattle manure-containing treatment.

Observations of the spore, gametophyte and young sporophyte of Pteridium caudatum (L.) Maxon using scanning electron microscopy.

This paper describes the development of the sexual phase of the invasive fern, Pteridium caudatum, from spore germination to young sporophyte formation. Spores samples for gametophyte cultures were taken from various sporophytes and then sown on mineral agar with Thompson's media. Gametophytes were maintained under fluorescent light on a 12h light, 12h dark cycle at 24-25°C. Developmental phases were fixed in FAA-sucrose solution and processed for observation with the scanning electron microscope. Spores are trilete and germination takes place on the second day after sowing; germination is of the Vittaria-type. Adiantum-type prothallial development was observed. The differentiation of a two-dimensional thallus begins 5 days after germination maturation of adult gametophytes occurs about 30 days after sowing. Adult gametophytes are heart-shaped, bisexual and glabrous. Antheridia are formed by three cells: basal, annular and opercular cell with a pore. Archegonia have a neck of 4-cells. The young sporophyte becomes visible within 8 weeks after spores are sown. The taxonomic significance of the gametophyte morphology is discussed.

[Effects of bio-mulching on rhizosphere soil microbial population, enzyme activity and tree growth in poplar plantation].

Coriaria nepalensis, Pteridium aquilinum var. latiuscukum, Imperata cylindrical var. major, and Quercus fabric were used as mulching materials to study their effects on the rhizosphere soil microbial population and enzyme activity and the tree growth in poplar plantation. The results showed that after mulching with test materials, the populations of both bacteria and fungi in rhizosphere soil were more than those of the control. Of the mulching materials, I. cylindrical and Q. fabric had the best effect, with the numbers of bacteria and fungi being 23.56 and 1.43 times higher than the control, respectively. The bacterial and fungal populations in rhizosphere soil increased with increasing mulching amount. When the mulching amount was 7.5 kg m(-2), the numbers of bacteria and fungi in rhizosphere soil were 0.5 and 5.14 times higher than the control, respectively. Under bio-mulching, the bacterial and fungal populations in rhizosphere soil had a similar annual variation trend, which was accorded with the annual fluctuation of soil temperature and got to the maximum in July and the minimum in December. The urease and phosphatase activities in rhizosphere soil also increased with increasing mulching amount. As for the effects of different mulching materials on the enzyme activities, they were in the order of C. nepalensis > P. aquilinum > I. cylindrical > Q. fabric. The annual variation of urease and phosphatase activities in rhizosphere soil was similar to that of bacterial and fungal populations, being the highest in July and the lowest in December. Bio-mulching promoted the tree height, DBH, and biomass of poplar trees significantly.

Competing conservation goals, biodiversity or ecosystem services: element losses and species recruitment in a managed moorland-bracken model system.

Conservation management in Europe is often geared towards restoring semi-natural ecosystems, where the objective is to reverse succession and re-establish early-successional communities, to comply with national and international conservation targets. At the same time, it is increasingly recognised that ecosystems provide services that contribute to other, possibly conflicting policy requirements. Few attempts have been made to define these conflicts. Here, we assess some potential conflicts using a Calluna vulgaris-dominated moorland invaded by bracken (Pteridium aquilinum) as a model system, where the current policy is to reverse this process and restore moorland. We examined impacts of bracken control treatments on services (stocks and losses of C and mineral nutrients), litter turnover and biodiversity within a designed experiment over 7 years. Bracken litter was >2000 g m(-2) in untreated plots, and treatments reduced this quantity, and its element content, to varying degrees. Cutting twice per year was the most successful treatment in reducing bracken litter and its element content, increasing litter turnover, and increasing both mass and diversity of non-bracken vegetation. Diversity was greatest where bracken litter had been reduced, but species composition was also influenced by light sheep grazing. There was a significant loss of some chemical elements from bracken that could not be accounted for in other pools, and hence potentially lost from the system. In absolute terms large amounts of C and N were lost, but when expressed as a percentage of the total amount in the system, Mg was potentially more important with losses of almost a third of the Mg in the surface soil-vegetation system. There is, therefore, a potential dilemma between controlling a mid-successional invasive species for conservation policy objectives, especially when that species has evolved to sequester nutrients, and the negative effect of increasing environmental costs in terms of carbon accounting required, the potential input of nutrients to aquatic systems, and long-term nutrient loss. There is, therefore, a need to balance conservation goals against potential damage to biogeochemical structure and function.

The effectiveness of asulam for bracken (Pteridium aquilinum) control in the United Kingdom: a meta-analysis.

Bracken (Pteridium aquilinum) is a major problem for livestock-based extensive agriculture, conservation, recreation, and game management globally. It is an invasive species often achieving dominance to the detriment of other species. Control is essential to maintain plant communities such as grassland and lowland heath or if extensive grazing by domestic stock, particularly sheep, is to be viable on upland margins. Bracken is managed primarily by herbicide application or cutting but other techniques including rolling, burning, and grazing are also utilized. Here we evaluate the evidence regarding the effectiveness of asulam for the control of bracken. Thirteen studies provided data for meta-analyses which demonstrate that application of the herbicide asulam reduces bracken abundance. Subgroup analyses indicate that the number of treatments had an important impact, with multiple follow-up treatments more effective than one or two treatments. Management practices should reflect the requirement for repeated follow-up. There is insufficient available experimental evidence for quantitative analysis of the effectiveness of other management interventions, although this results from lack of reporting in papers where cutting and comparisons of cutting and asulam application are concerned. Systematic searching and meta-analytical synthesis have effectively demonstrated the limits of current knowledge, based on recorded empirical evidence, and increasing the call for more rigorous monitoring of bracken control techniques. Lack of experimental evidence on the effectiveness of management such as rolling or grazing with hardy cattle breeds contrasts with the widespread acceptance of their use through dissemination of experience.

The structure and development of haustorial placentas in leptosporangiate ferns provide a clear-cut distinction between euphyllophytes and lycophytes.

This light and electron microscope study revealed that leptosporangiate ferns have highly distinctive gametophyte-sporophyte junctions characterized by sporophytic haustoria, the absence of intraplacental spaces and degenerating cells, and the early appearance of wall ingrowths in both generations. Other notable cytological features are highly pleomorphic plastids and mitochondrial aggregates in the gametophytic placental cells. Close similarities with the gametophyte-sporophyte junctions in Tmesipteris and major differences from those of homosporous lycophytes are in line with the placement of psilophytes and ferns in the same clade and distance both from lycophytes. A smooth interface between the two generations in Azolla suggests a clear-cut discontinuity between homosporous and heterosporous ferns, although this is the only heterosporous fern investigated to date. Similarities between the gametophyte-sporophyte junctions of leptosporangiate ferns and hornworts, when balanced against differences between them, are considered more likely the result of parallel evolution rather than homology.

Exposure to Asulox inhibits the growth of mosses.

Asulox is a herbicide used to control bracken. Its effects on mosses were investigated to ascertain whether exposure proved as detrimental as found in parallel studies on pteridophytes. Mature gametophytes of 18 mosses were exposed to a range of concentrations of Asulox under standard conditions and the effects on growth monitored. Plants were cut to a standard length, exposed to Asulox solution for 24 h, grown for 3 weeks and total elongation (main stem and branches) measured. EC50 values were calculated and species ranked according to sensitivity. The effects of exposure on total elongation were compared with those on main stem elongation alone. Under the conditions tested, the total elongation of all species was inhibited after exposure to Asulox. The amount of elongation observed after exposure was different for different species and inhibition of elongation occurred at different exposure concentrations. A single regression equation was not adequate to describe the dose response curves of all species tested. An ability to produce secondary branches may confer increased tolerance to Asulox exposure. It is concluded that mosses suffer detrimental effects after exposure to Asulox at concentrations similar to those that affect fern gametophytes such as bracken.