Effects of Plant Substrate, Insecticide, and Blood Meal Status on the Efficacy of Barrier Treatments Against Aedes albopictus

The effects of 3 plant species (Cornus florida [dogwood], rhododendron X 'Chionoides' [rhododendron], and Ilex opaca [American holly]), 4 insecticide treatments (Demand® CS [lambda-cyhalothrin] at 6.25 ml[AI]/liter; Talstar® Professional [bifenthrin] at 7.81 ml[AI]/liter, and Suspend® Polyzone® [deltamethrin] at 11.72 ml[AI]/liter, and water), and 2 physiological states (blood-fed and unfed) were evaluated for knockdown (1 h) and mortality (24 h) against female Aedes albopictus over an 8-wk sampling period. Analyses determined that there was a significant interaction between the tested plant species and the insecticides evaluated. Significant differences were likewise observed between the insecticide treatments for unfed Ae. albopictus females, with Demand CS demonstrating the highest knockdown and mortality rates (from >90% to >10% at wk 8 and >95% to ∼50% at wk 8, respectively), followed by Talstar Professional (from >75% to <10% at wk 2 and >90% to <10% at wk 2, respectively) and Suspend Polyzone (from >20% to <10% at wk 8 and >25% to >50% at wk 8, respectively). All treatments were no longer significant for knockdown or mortality at the end of the 8-wk timeframe. Significant differences were also observed between insecticide treatments for blood-fed Ae. albopictus females; Demand CS showed high knockdown and mortality rates (from 100% to ∼50% at wk 8 and 100% to >60% at wk 8, respectively), Suspend Polyzone rates were similar to Demand CS (from >80% to ∼50% at wk 8 and ∼90% to >65% at wk 8, respectively), and both were followed by Talstar Professional (from 100% to <10% at wk 4 and 100% to <20% at wk 4, respectively). All tested pyrethroid sprays showed a significant increase in effectiveness against recently blood-fed Ae. albopictus females, as compared to the unfed females. These results suggest that Demand CS can be used as an effective barrier spray against Ae. albopictus adults due to the limited impact of target foliage, its long-term efficacy under environmental conditions, and its continued effectiveness regardless of the blood meal status of the target mosquito.

Can species distribution models and molecular tools help unravel disjunct distribution of Rhododendron arboreum?

The apparent absence of Himalayan low-elevation taxa in the central Indian region and resumption of their distribution in the high elevation of Western Ghats has puzzled biogeographers for several decades. Many theories have been proposed to explain this but attempts remain futile owing to insufficient empirical support. Here, we have employed a montane tree species, Rhododendron arboreum to investigate this pattern by integrating past ecological niche modelling with molecular signatures. Reconstruction of paleo-ecological niche from interglacial to Last Glacial Maxima (LGM) portrayed a gradual depletion of vegetation cover with extreme impoverishment in the Holocene. A similar pattern was also reflected from genetic signatures; population history revealed a very recent split between the Himalayas and Western Ghats in the late Quaternary. A few other tree species exhibiting the same disjunction demonstrated a similar modification of paleo-ecological niche from last interglacial. The study clearly indicated that the populations in the Western Ghats to be a relictual remnants of a once continuous distribution of R. arboreum.

Metabolite profiling of violet, white and pink flowers revealing flavonoids composition patterns in Rhododendron pulchrum Sweet

Flower color is the major characteristics and critical breeding program for most Rhododendron species. However, little is known about their coloration mechanism and color inheritance. In this study, petal pigment constituents of three Rhododendron pulchrum Sweet cultivars with different colors were clarified based on LCESI- MS/MS method. Using a broad-targeted metabolomic approach, a total of 149 flavonoids and their glycosylated or methylated derivatives were identified, including 18 anthocyanins (Pg, Cy, Dp, Pn, Pt, and Mv) and 32 flavonols (mainly kaempferol 3-O-glycosides and quercetin 3-O-glycosides). Moreover, anthocyanins were mainly represented by anthocyanidin-3-O-glycosides (glucoside, rutinoside, galactoside, and di-glycosides). Flavone and C-glycosylated flavone were major second metabolites responsible for the difference among three different R. pulchrum cultivars. The accumulation of total flavonoids displayed a clear phenotypic variation: cultivars 'zihe' and 'fenhe' were clustered together, while 'baihe' was clustered alone in the HCA analysis. The composition and content of anthocyanins were more complex in colored flowers ('zehe' and 'fenhe') than in white flower ('baihe'). This study further enhanced our understanding on the flavonoids profile of flower coloration and will provide biochemical basis for further genetic breeding in Rhododendron species.

Attracting Chrysopidae With Plant Volatiles for Lace Bug (Hemiptera: Tingidae) Control in Rhododendrons and Azaleas

The azalea lace bug (Stephanitis pyrioides Scott) (Hemiptera: Tingidae) is an invasive pest of rhododendrons and azaleas (Ericaceae: Rhododendron), which feeds on the underside of leaves causing chlorosis, reduced photosynthesis, and even plant death. While insecticides can control this pest, growers, landscape managers, and homeowners have requested softer alternatives. Augmentative release of predatory green lacewing Chrysoperla sp. (Neuroptera: Chrysopidae) eggs and larvae has reduced S. pyrioides, but large-scale implementation may not be practical nor cost-effective. Attracting naturally occurring Chrysopidae with plant volatiles may be an economical and convenient option. In this study, we tested whether volatile blends 1) attracted Chrysoperla sp., and 2) controlled S. pyrioides populations on Rhododendron spp. in farm or urban landscapes. Experimental plots contained different multicomponent lures placed aboveground next to infested plants. Adult Chrysoperla sp., other natural enemies, and S. pyrioides from egg to adult stages were monitored in both farm and urban landscapes for two summers. Overall, two out of three volatile blends consistently attracted Chrysoperla sp. to sticky traps near baited plants. Methyl salicylate + acetic acid + 2-phenylethanol (methyl salicylate blend) and acetophenone + acetic acid + 2-phenylethanol (acetophenone blend) captured more adult Chrysoperla sp. than control traps in farm landscapes. However, only the acetophenone blend was associated with a slight reduction of S. pyrioides. Additional research is needed to determine whether the phenology of the first generation of both species are synchronized for effective season biological control in the Pacific Northwest.

Soil nitrogen determines greenhouse gas emissions from northern peatlands under concurrent warming and vegetation shifting

Boreal peatlands store an enormous pool of soil carbon that is dependent upon - and vulnerable to changes in - climate, as well as plant community composition. However, how nutrient availability affects the effects of climate and vegetation change on ecosystem processes in these nutrient-poor ecosystems remains unclear. Here we show that although warming promoted higher CH4 emissions, the concurrent addition of N counteracted most (79%) of this effect. The regulation effects of the vegetation functional group, associated with the substrate quality, suggest that CH4 emissions from peatlands under future warming will be less than expected with predicted shrub expansion. In contrast, N2O flux will be enhanced under future warming with predicted shrub expansion. Our study suggests that changes in greenhouse gas emissions in response to future warming and shifts in plant community composition depend on N availability, which reveals the complex interactions that occur when N is not a limiting nutrient.

Microbial Decomposer Dynamics: Diversity and Functionality Investigated through a Transplantation Experiment in Boreal Forests

Litter decomposition is the main source of mineral nitrogen (N) in terrestrial ecosystem and a key step in carbon (C) cycle. Microbial community is the main decomposer, and its specialization on specific litter is considered at the basis of higher decomposition rate in its natural environment than in other forests. However, there are contrasting evidences on how the microbial community responds to a new litter input and if the mass loss is higher in natural environment. We selected leaf litter from three different plant species across three sites of different altitudinal ranges: oak (Quercus petraea (Matt.) Liebl., 530 m a.s.l), beech (Fagus sylvatica L., 1000 m a.s.l.), rhododendron (Rhododendron ferrugineum L., 1530 m a.s.l.). A complete transplantation experiment was set up within the native site and the other two altitudinal sites. Microbial community structure was analyzed via amplified ribosomal intergenic spacer analysis (ARISA) fingerprinting. Functionality was investigated by potential enzyme activities. Chemical composition of litter was recorded. Mass loss showed no faster decomposition rate on native site. Similarly, no influence of site was found on microbial structure, while there was a strong temporal variation. Potential enzymatic activities were not affected by the same temporal pattern with a general increase of activities during autumn. Our results suggested that no specialization in microbial community is present due to the lack of influence of the site in structure and in the mass loss dynamics. Finally, different temporal patterns in microbial community and potential enzymatic activities suggest the presence of functional redundancy within decomposers.

Clonal plasticity and diversity facilitates the adaptation of Rhododendron aureum Georgi to alpine environment

Four small oval populations and five large intensive populations of Rhododendron aureum growing at the alpine in Changbai Mountain (China) were studied in two types of habitat (in the tundra and in Betula ermanii forest). Identification and delimitation of genets were inferred from excavation in small populations and from amplified fragment length polymorphism (AFLP) markers by the standardized sampling design in large populations. Clonal architecture and clonal diversity were then estimated. For the four small populations, they were monoclonal, the spacer length (18.6 ± 5.6 in tundra, 29.7 ± 9.7 in Betula ermanii forest, P < 0.05) was shorter and branching intensity (136.7 ± 32.9 in tundra, 43.4 ± 12.3 in Betula ermanii forest, P < 0.05) was higher in the tundra than that in Betula ermanii forest. For the five large populations, they were composed of multiple genets with high level of clonal diversity (Simpson’s index D = 0.84, clonal richness R = 0.25, Fager's evenness E = 0.85); the spatial distribution of genets showed that the clonal growth strategy of R. aureum exhibits both guerilla and phalanx. Our results indicate that the clonal plasticity of R. aureum could enhance exploitation of resource heterogeneity and in turn greatly contribute to maintenance or improvement of fitness and the high clonal diversity of R. aureum increase the evolutionary rates to adapt the harsh alpine environment in Changbai Mountain.

Shrub growth and plant diversity along an elevation gradient: Evidence of indirect effects of climate on alpine ecosystems

Enhanced shrub growth and expansion are widespread responses to climate warming in many arctic and alpine ecosystems. Warmer temperatures and shrub expansion could cause major changes in plant community structure, affecting both species composition and diversity. To improve our understanding of the ongoing changes in plant communities in alpine tundra, we studied interrelations among climate, shrub growth, shrub cover and plant diversity, using an elevation gradient as a proxy for climate conditions. Specifically, we analyzed growth of bilberry (Vaccinium myrtillus L.) and its associated plant communities along an elevation gradient of ca. 600 vertical meters in the eastern European Alps. We assessed the ramet age, ring width and shoot length of V. myrtillus, and the shrub cover and plant diversity of the community. At higher elevation, ramets of V. myrtillus were younger, with shorter shoots and narrower growth rings. Shoot length was positively related to shrub cover, but shrub cover did not show a direct relationship with elevation. A greater shrub cover had a negative effect on species richness, also affecting species composition (beta-diversity), but these variables were not influenced by elevation. Our findings suggest that changes in plant diversity are driven directly by shrub cover and only indirectly by climate, here represented by changes in elevation.

Warm summers and moderate winter precipitation boost Rhododendron ferrugineum L. growth in the Taillefer massif (French Alps)

Rhododendron ferrugineum L. is a widespread dwarf shrub species growing in high-elevation, alpine environments of the Western European Alps. For this reason, analysis of its growth rings offers unique opportunities to push current dendrochronological networks into extreme environments and way beyond the treeline. Given that different species of the same genus have been successfully used in tree-ring investigations, notably in the Himalayas where Rhododendron spp. has proven to be a reliable climate proxy, this study aims at (i) evaluating the dendroclimatological potential of R. ferrugineum and at (ii) determining the major limiting climate factor driving its growth. To this end, 154 cross-sections from 36 R. ferrugineum individuals have been sampled above local treelines and at elevations from 1800 to 2100masl on northwest-facing slopes of the Taillefer massif (French Alps). We illustrate a 195-year-long standard chronology based on growth-ring records from 24 R. ferrugineum individuals, and document that the series is well-replicated for almost one century (1920-2015) with an Expressed Population Signal (EPS) >0.85. Analyses using partial and moving 3-months correlation functions further highlight that growth of R. ferrugineum is governed by temperatures during the growing season (May-July), with increasingly higher air temperatures favoring wider rings, a phenomenon which is well known from dwarf shrubs growing in circum-arctic tundra ecosystems. Similarly, the negative effect of January-February precipitation on radial growth of R. ferrugineum, already observed in the Alps on juniper shrubs, is interpreted as a result of shortened growing seasons following snowy winters. We conclude that the strong and unequivocal signals recorded in the fairly long R. ferrugineum chronologies can indeed be used for climate-growth studies as well as for the reconstruction of climatic fluctuations in Alpine regions beyond the upper limits of present-day forests.

Assessing atmospheric concentration of polychlorinated biphenyls by evergreen Rhododendron maximum next to a contaminated stream

Conifers are often used as an air passive sampler, but few studies have focused on the implication of broadleaf evergreens to monitor atmospheric semivolatile organic compounds such as polychlorinated biphenyls (PCBs). In the present study, the authors used Rhododendron maximum (rhododendron) growing next to a contaminated stream to assess atmospheric PCB concentrations. The present study area was located in a rural setting and approximately 2 km downstream of a former capacitor plant. Leaves from the same mature shrubs were collected in late fall 2010 and winter and spring 2011. Polychlorinated biphenyls were detected in the collected leaves, suggesting that rhododendron can be used as air passive samplers in rural areas where active sampling is impractical. Estimated ΣPCB (47 congeners) concentrations in the atmosphere decreased from fall 2010 to spring 2011 with concentration means at 3990 pg m(-3) , 2850 pg m(-3) , and 931 pg m(-3) in fall 2010, winter 2011, and spring 2011, respectively. These results indicate that the atmospheric concentrations at this location continue to be high despite termination of active discharge from the former industrial source. Leaves had a consistent pattern of high concentrations of tetra-CBs and penta-CBs similar to the congener distribution in polyethylene passive samplers deployed in the water column, suggesting that volatilized PCBs from the stream were the primary source of contaminants in rhododendron leaves. Environ Toxicol Chem 2016;35:2192-2198. © 2016 SETAC.

Above- and Belowground Biomass Allocation in Shrub Biomes across the Northeast Tibetan Plateau

Biomass partitioning has been explored across various biomes. However, the strategies of allocation in plants still remain contentious. This study investigated allocation patterns of above- and belowground biomass at the community level, using biomass survey from the Tibetan Plateau. We explored above- and belowground biomass by conducting three consecutive sampling campaigns across shrub biomes on the northeast Tibetan Plateau during 2011-2013. We then documented the above-ground biomass (AGB), below-ground biomass (BGB) and root: shoot ratio (R/S) and the relationships between R/S and environment factors using data from 201 plots surveyed from 67 sites. We further examined relationships between above-ground and below-ground biomass across various shrub types. Our results indicated that the median values of AGB, BGB, and R/S in Tibetan shrub were 1102.55, 874.91 g m-2, and 0.85, respectively. R/S showed significant trend with mean annual precipitation (MAP), while decreased with mean annual temperature (MAT). Reduced major axis analysis indicated that the slope of the log-log relationship between above- and belowground biomass revealed a significant difference from 1.0 over space, supporting the optimal hypothesis. Interestingly, the slopes of the allometric relationship between log AGB and log BGB differed significantly between alpine and desert shrub. Our findings supported the optimal theory of above- and belowground biomass partitioning in Tibetan shrub, while the isometric hypothesis for alpine shrub at the community level.

Factors Affecting Diet Variation in the Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Conservation Implications

The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) lives at one of the southernmost limits of the ptarmigan range. Their small population sizes and the impacts of global changes are limiting factors in the conservation of this threatened subspecies. An effective conservation policy requires precise basic knowledge of a species' food and habitat requirements, information that is practically non-existent for this Pyrenean population. Here, we describe the diet of a ptarmigan population in the Eastern Pyrenees, the environmental factors influencing its variability and the relationship between diet floristic composition and quality. Diet composition was determined by microhistological analysis of faeces and diet quality was estimated from free-urate faecal N content. Our results show that grouse diet is based mainly on arctic-alpine shrubs of the Ericaceae family, as well as dwarf willows (Salix spp.) and Dryas octopetala. The most frequently consumed plant species was Rhododendron ferrugineum, but its abundance in the diet was negatively related to the diet nitrogen content. Conversely, the abundance of Salix spp., grass leaves and arthropods increased the nitrogen content of the diet. Seasonality associated with snow-melting contributed the most to variability in the Pyrenean ptarmigan diet, differentiating winter from spring/summer diets. The latter was characterised by a high consumption of dwarf willows, flowers, arthropods and tender forb leaves. Geographic area and sex-age class influenced diet variability to a lesser extent. Current temperature increases in the Pyrenees due to global warming may reduce the persistence and surface area of snow-packs where preferred plants for rock ptarmigan usually grow, thus reducing food availability. The high consumption of Rh. ferrugineum characterised the diet of the Pyrenean population. Given the toxicity of this plant for most herbivores, its potential negative effect on Pyrenean ptarmigan populations should be evaluated.

Pollen development in Rhododendron in relation to winter dormancy and bloom time

Microsporogenesis and microgametogenesis of Rhododendron ledebourii (semi-deciduous), Rhododendron luteum (deciduous), and Rhododendron catawbiense (evergreen) were studied by light and electron microscopies in order to determine the stages of pollen development in relation to period of winter dormancy and bloom time throughout an annual growth cycle. Development of generative organs starts in June in R. ledebourii and in July in R. luteum and R. catawbiense and reaches completion about 11 months later. R. luteum and R. catawbiense microspores undergo meiosis at the end of the August and spend winter at the vacuolization stage. Mitosis with the formation of bicellular pollen grain occurs shortly before flowering at the beginning of June. R. ledebourii develops two types of flowers which differ in the timing of microgametogenesis. The first type is characterized by early microspore meiosis and mitosis leading to development of bicellular pollen grains by the end of August, and is prone to fall blooming during warm autumn temperatures. Microspores of the second flower type have a more prolonged vacuolization stage with mitosis and subsequent bicellular pollen grains occurring in November. By winter, flower buds in R. ledebourii are more advanced developmentally than in R. catawbiense and R. luteum, and bloom about 1 month earlier. The different strategies of pollen development identified both within and between these three Rhododendron species were recognized which are not associated with leaf drop during winter but appear to be related to the time of spring flowering and the frequency of autumn flowering.

EFFICACY OF FUNGICIDES AGAINST CALONECTRIA PAUCIRAMOSA IN POT AZALEA

Calonectria (formerly Cylindrocladium) infection of pot azalea (Rhododendron simsii Planch) is an important disease problem in which usually one or two of the four plants per pot show progressing leaf and especially stem lesions, leading to mortality of the respective plant and rendering the pot unmarketable. This may occur in a later stage of the growing season, leading to significant commercial losses. The main objective of this study was to test a range of fungicides for their efficacy against this pathogen. To test the fungicides, a bioassay was first developed in which mycelium and conidiospores of the pathogen were produced on Potato Dextrose Agar, blended in water, and dilutions of the resulting suspension inoculated at the base of 11-week-old cuttings three weeks after they had been trimmed. Disease progression was monitored up to 7 weeks post inoculation and a disease index on a scale of 0 to 3 was established. In the actual efficacy trial, the following fungicides (with corresponding active ingredient(s)) were tested as preventive treatments: Topsin M 70 WG (thiophanate-methyl), Sporgon (prochloraz), Signum (boscalid+pyraclostrobin), Switch (cyprodinyl+fludioxonil), Flint 50WG (trifloxystrobin), Ortiva Top (azoxystrobin+difenoconazole) and Fungaflor (imazalil). Disease expression started after about 2 weeks, increased approximately 1 index level, and leveled off 5 weeks after inoculation. The best control was observed with Sporgon, Ortiva Top and Signum. Switch produced intermediate effects and insufficient control was observed with Topsin, Flint and Fungaflor. These results explain why specific standard fungicide treatments, such as those with Topsin, fail to control the disease, while they can be effective against a different Calonectria species such as C. pseudonaviculata, the cause of boxwood blight.

Cold storage to overcome dormancy affects the carbon balance of azalea

Flower bud dormancy in azalea (Rhododendron simsii) is broken by artificial cold treatment and this will have its consequences on carbon reserves and photosynthesis. The effect of cold storage at 7 °C on carbohydrate and starch content in leaves and flower buds of an early ('Nordlicht') and semi-early ('M. Marie) flowering cultivar was quantified. Carbon loss due to respiration was lowest for 'M. Marie'. Photosynthetic measurements on 'Nordlicht' showed that photosynthesis 3 days after cold treatment (plants ready to flower) was improved compared to before cold treatment (plants with dormant flower buds).

[Distribution pattern of Rhododendron aganniphum var. schizopeplum population at the timberline of Sejila Mountains, Tibet of China]

Rhododendron aganniphum var. schizopeplum grows at the elevation of 4300-4500 m in Sejila Mountains, being a dominant species of shrub layer at the timberline of southeast Tibet. Based on the sampling plot investigation and basal diameter structure analysis, this paper studied the distribution pattern of R. aganniphum var. schizopeplum population at the timberline of Sejila Mountains. With the increase of altitude, the population density of R. aganniphum var. schizopeplum increased, but the population height decreased. At the same altitudes, the population density on the shady slope was larger than that on the sunny slope, while the basal diameter was smaller. On the two slope directions, the distribution of the basal diameter classes of the population appeared as "(see text for symbol)" shape, i. e., middle-aged individuals were more, while seedlings and saplings were relatively less. The intraspecific competition of R. aganniphum var. schizopeplum population was in the form of wave, being stronger on shady slope than on sunny slope, and existing self-thinning.

Promotion of flowering in azaleas by manipulating photoperiod and temperature induces epigenetic alterations during floral transition

The ability to control the timing of flowering is a key strategy for planning production in ornamental species such as the azalea; however, this requires a thorough understanding of floral induction pathways. DNA methylation is one of the main mechanisms involved in controlling the functional state of chromatin and gene expression in response to environmental and developmental signals. This work investigated the promotion of flowering in azaleas by the manipulation of environmental factors, using DNA methylation levels as a marker of floral bud development. The results showed that the change of long-day (LD) to short-day (SD) photoperiod is the primary factor responsible for floral induction in azaleas, whereas the existence of the previous cold period as well as the physiological memory are factors which improve floral production. Furthermore, for blooming to take place, 1300 units of growing degree days under an LD were necessary. The promotion of flowering in azaleas by alterations of photoperiod and temperature induced DNA methylation changes. The demethylation observed after the change from LD to SD is linked to a change in cell fate which is necessary for floral transition to take place and seems to be associated with the floral signal.

Effects of nutrient addition on leaf chemistry, morphology, and photosynthetic capacity of three bog shrubs

Plants in nutrient-poor environments typically have low foliar nitrogen (N) concentrations, long-lived tissues with leaf traits designed to use nutrients efficiently, and low rates of photosynthesis. We postulated that increasing N availability due to atmospheric deposition would increase photosynthetic capacity, foliar N, and specific leaf area (SLA) of bog shrubs. We measured photosynthesis, foliar chemistry and leaf morphology in three ericaceous shrubs (Vaccinium myrtilloides, Ledum groenlandicum and Chamaedaphne calyculata) in a long-term fertilization experiment at Mer Bleue bog, Ontario, Canada, with a background deposition of 0.8 g N m(-2) a(-1). While biomass and chlorophyll concentrations increased in the highest nutrient treatment for C. calyculata, we found no change in the rates of light-saturated photosynthesis (A(max)), carboxylation (V(cmax)), or SLA with nutrient (N with and without PK) addition, with the exception of a weak positive correlation between foliar N and A(max) for C. calyculata, and higher V(cmax) in L. groenlandicum with low nutrient addition. We found negative correlations between photosynthetic N use efficiency (PNUE) and foliar N, accompanied by a species-specific increase in one or more amino acids, which may be a sign of excess N availability and/or a mechanism to reduce ammonium (NH(4)) toxicity. We also observed a decrease in foliar soluble Ca and Mg concentrations, essential minerals for plant growth, but no change in polyamines, indicators of physiological stress under conditions of high N accumulation. These results suggest that plants adapted to low-nutrient environments do not shift their resource allocation to photosynthetic processes, even after reaching N sufficiency, but instead store the excess N in organic compounds for future use. In the long term, bog species may not be able to take advantage of elevated nutrients, resulting in them being replaced by species that are better adapted to a higher nutrient environment.

Epigenetic and physiological effects of gibberellin inhibitors and chemical pruners on the floral transition of azalea

The ability to control the timing of flowering is a key strategy in planning the production of ornamental species such as azaleas; however, it requires a thorough understanding of floral transition. DNA methylation is involved in controlling the functional state of chromatin and gene expression during floral induction pathways in response to environmental and developmental signals. Plant hormone signalling is also known to regulate suites of morphogenic processes in plants and its role in flowering-time control is starting to emerge as a key controlling step. This work investigates if the gibberellin (GA) inhibitors and chemical pinching applied in improvement of azalea flowering alter the dynamics of DNA methylation or the levels of polyamines (PAs), GAs and cytokinins (CKs) during floral transition, and whether these changes could be related to the effects observed on flowering ability. DNA methylation during floral transition and endogenous content of PAs, GAs and CKs were analysed after the application of GA synthesis inhibitors (daminozide, paclobutrazol and chlormequat chloride) and a chemical pruner (fatty acids). The application of GA biosynthesis inhibitors caused alterations in levels of PAs, GAs and CKs and in global DNA methylation levels during floral transition; also, these changes in plant growth regulators and DNA methylation were correlated with flower development. DNA methylation, PA, GA and CK levels can be used as predictive markers of plant floral capacity in azalea.

[Soil nitrogen mineralization and primary productivity in Rhododendron aureum community of snowpacks in alpine tundra of Changbai Mountain]

Based on continuous observation of soil temperature and in situ incubation, this paper studied the effects of snow packs on soil temperature, soil nitrogen (N) mineralization, and primary productivity of Rhododendron aureum community alpine tundra in Changbai Mountain. During the snow-covered period of non-growth season (from last October to early May), test soil had an increasing N content, and accumulated sufficient mineralized N for plant growth in the coming year. The soil under snow packs in snow-covered period had a mean temperature -3.0 degrees C, and its N mineralization was more vigorous, with available N increased by 3.88 g x m(-2); while the soil with no snowpack had a mean temperature -7.5 degrees C, and the available N only increased by 1.21 g x m(-2). During growth season (from mid May to late August), soil N content decreased. In autumn when plants stopped growing, soil available N content tended to increase. In winter, the soil temperature under snowpacks kept at around 0 degrees C or a little lower, which promoted soil N mineralization, while that with no snowpack was in a frozen status. The difference in soil N mineralization was the key factor resulting in the higher primary productivity of snowpack Rh. aureum community and the driving force for the spatial variation of vegetation.

Leaf life span optimizes annual biomass production rather than plant photosynthetic capacity in an evergreen shrub

*Owing to nitrogen (N) translocation towards new leaves, the shedding of old leaves can increase the whole-plant carbon gain. It occurs when their photosynthetic nitrogen use efficiency (PNUE) declines below a given threshold. *Here, we investigated variations in net photosynthetic capacity (A(max)), N resorption and PNUE in populations of Rhododendron ferrugineum presenting different mean leaf life spans (LLS). *Both populations had comparable annual leaf surface area production and A(max) across leaf-age cohorts. Branch photosynthetic capacity was up to 95% higher in the population with the longer LLS mainly because of the high contribution of old leaves to the total leaf area. Despite lower N concentrations, old leaves maintained relatively high A(max) and consequently PNUE that were higher than or similar to the values found in current-year leaves. *As the ratio of PNUE in old to PNUE in new leaves was always higher than the fraction of leaf N resorbed during leaf shedding, we concluded that leaf shedding did not improve plant photosynthetic capacity. We suggest that in R. ferrugineum, leaf shedding is mainly controlled by the leaf storage function and, therefore, that models aiming to explain LLS should not only consider the leaf carbon assimilation function, particularly in nutrient-poor habitats.

Epigenetic characterization of the vegetative and floral stages of azalea buds: dynamics of DNA methylation and histone H4 acetylation

Floral induction in plants is achieved through a complex genetic network and regulated by multiple environmental and endogenous cues. Epigenetic control is determinative in plants for coordinating the switch to flowering under favorable environmental conditions and achieving reproductive success. Global DNA methylation, whose increase is associated with heterochromatinization-cell differentiation, and histone H4 acetylation, which is linked to euchromatin, were analyzed in vegetative and floral buds of azalea in order to study the involvement of epigenetic mechanisms in the floral development of woody plants. The results showed an increase of DNA methylation in floral buds in contrast to the decrease observed for acetylated H4 (AcH4) levels. In addition, when the distributions of 5-mdC and AcH4 in vegetative and floral buds of azalea were analyzed by immunodetection, opposite patterns in their distribution were revealed and confirmed the existence of different cell types in the shoot apical meristem with varying degrees of differentiation.

Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau

BACKGROUND AND AIMS

Shrubs and dwarf shrubs are wider spread on the Tibetan Plateau than trees and hence offer a unique opportunity to expand the present dendrochronological network into extreme environments beyond the survival limit of trees. Alpine shrublands on the Tibetan Plateau are characterized by rhododendron species. The dendrochronological potential of one alpine rhododendron species and its growth response to the extreme environment on the south-east Tibetan Plateau were investigated.

METHODS

Twenty stem discs of the alpine snowy rhododendron (Rhododendron nivale) were collected close to the tongue of the Zuoqiupu Glacier in south-east Tibet, China. The skeleton plot technique was used for inter-comparison between samples to detect the growth pattern of each stem section. The ring-width chronology was developed by fitting a negative exponential function or a straight line of any slope. Bootstrapping correlations were calculated between the standard chronology and monthly climate data.

KEY RESULTS

The wood of snowy rhododendron is diffuse-porous with evenly distributed small-diameter vessels. It has well-defined growth rings. Most stem sections can be visually and statistically cross-dated. The resulting 75-year-long standard ring-width chronology is highly correlated with a timberline fir chronology about 200 km apart, providing a high degree of confidence in the cross-dating. The climate/growth association of alpine snowy rhododendron and of this timberline fir is similar, reflecting an impact of monthly mean minimum temperatures in November of the previous year and in July during the year of ring formation.

CONCLUSIONS

The alpine snowy rhododendron offers new research directions to investigate the environmental history of the Tibetan Plateau in those regions where up to now there was no chance of applying dendrochronology.

Endogenous sink-source interactions and soil nitrogen regulate leaf life-span in an evergreen shrub

How the balance between exogenous and endogenous nitrogen for shoot growth varies with soil nitrogen availability, and its consequences on leaf life-span, have rarely been studied within a single species in the field. In this study, we investigated two Rhododendron ferrugineum populations with contrasting leaf life-span. Soil nitrogen availability and nitrogen resorption of different leaf age classes were assessed, as were the interactions between plant compartments, using (15)N labelling and sink organ suppression. The population growing on poorer soil had a shorter leaf life-span (17.9 vs 21.5 months) and a higher net contribution of leaf reserves to shoot growth (32% vs 15%), achieved by faster nitrogen resorption and greater shedding of young nitrogen-rich leaves. For both populations, wood contributed to over 40% of shoot nitrogen demand. Both the negative relationship between current-year shoot mass and the percentage of 1-yr-old attached leaves and the delay of leaf shedding after bud removal suggest that shoot development has a strong effect on leaf life-span. Our results suggest that, contrary to the evolutionary response, plastic response to low soil nitrogen could reduce leaf life-span in evergreen plants. In addition, leaf life-span seems to be strongly influenced by the discrepancy between shoot nitrogen demand and soil nitrogen uptake rather than nitrogen demand alone.

NONADDITIVE EFFECTS OF LEAF LITTER SPECIES DIVERSITY ON BREAKDOWN DYNAMICS IN A DETRITUS-BASED STREAM

Since species loss is predicted to be nonrandom, it is important to understand the manner in which those species that we anticipate losing interact with other species to affect ecosystem function. We tested whether litter species diversity, measured as richness and composition, affects breakdown dynamics in a detritus-based stream. Using full-factorial analyses of single- and mixed-species leaf packs (15 possible combinations of four dominant litter species; red maple [Acer rubrum], tulip poplar [Liriodendron tulipifera], chestnut oak [Quercus prinus], and rhododendron [Rhododendron maximum]), we tested for single-species presence/absence (additive) or species interaction (nonadditive) effects on leaf pack breakdown rates, changes in litter chemistry, and microbial and macroinvertebrate biomass. Overall, we found significant nonadditive effects of litter species diversity on leaf pack breakdown rates, which were explained both by richness and composition. Leaf packs containing higher litter species richness had faster breakdown rates, and antagonistic effects of litter species composition were observed when any two or three of the four litter species were mixed. Less-consistent results were obtained with respect to changes in litter chemistry and microbial and macroinvertebrate biomass. Our results suggest that loss of litter species diversity will decrease species interactions involved in regulating ecosystem function. To that end, loss of species such as eastern hemlock (Tsuga canadensis) accompanied by predicted changes in riparian tree species composition in the southeastern United States could have nonadditive effects on litter breakdown at the landscape scale.

Effectiveness of management interventions to control invasion by Rhododendron ponticum

Rhododendron ponticum is an invasive species in many countries, including the United Kingdom, Ireland, Belgium, and France. It poses a serious threat to native flora and fauna, as it is capable of altering entire seminatural communities through its vigorous spread. Control is essential if the conservation value of some communities, such as oak woodland and lowland heath, are to be successfully maintained. Commonly used interventions are herbicide application, herbicide application postcut, and cutting (manual or mechanical) alone. Various techniques have been developed to apply these interventions, but often retreatment of the area is required, increasing the cost of control. Here, we evaluate the effectiveness of some commonly used interventions for R. ponticum control using a systematic review methodology. Eleven studies provided data for statistical analysis. Meta-analyses of captured data show that postcut application of the herbicide Glyphosate or applying the herbicides Metsulfuron-methyl or Imazapyr (no cut) can effectively reduce a R. ponticum stand. There is insufficient available experimental evidence for effectiveness of any other intervention. The systematic review process has demonstrated the lack of replicated studies with controls or long-term monitoring and increases the call for more rigorous monitoring of all conservation management interventions. The quality of experimental evidence of the effectiveness of some interventions contrasts with the acceptance of their use through dissemination of experience. The collection and objective review of experience will require active collaboration of organizations concerned with R. ponticum control.

[Drought resistibility of main tree species in water conservation forest of Qilian Moutains]

With P-V techniques, this paper determined and analyzed the water parameters of main tree species in the water conservation forest of Qilian Moutains. The results showed that the test water parameters varied with tree species, reflecting the complicacy of the drought-resistance mechanism of trees. Among 10 parameters, /phi pi100 - phi pi0/, RCV, ROWC0 epsilon(max) could reflect most information of drought resistibility. Based on their drought resistibility, the test tree species could be classified into 4 groups, i.e., high drought resistibility (Picea crassifolia and Rhododendron thymifolium ), sub-high drought resistibility (Sabina przeualwkii, Rhododendron anthopogonoides, Rhododendron capitaturn and Rhododendron przewalskii), low drought resistibility (Populus cathyana), and inferior drought resistibility (Poentilla fruticosa, Siraea salicifolia and Betula albosinensis). The relationships between predawn leaf water potential and soil water content could be well modeled by hyperbola function, power function or exponent function. Meanwhile, the test tree species could be also grouped as high potential delay dehydration species (Betula albosinensis and Rhododendron przeualskii), sub-high potential delay dehydration species (Picea crassifolia, Rhododendron thymifolium and Rhododendron capitatum), inferior potential tolerance species (Sabina przewalskii), and low potential tolerance species (Potentilla fruticosa, Spiraea salicifolia and Rhododendron anthopogonoides), based on their drought-resistance mechanism.

[Population structure and community characteristics of Pseudotaxus chienii in Fengyangshan National Natural Reserve]

Pseudotaxus chienii, an endemic plant in China, is one of the second grade state protection wild plants, and distributes in Fengyangshan Natural Reserve as one of its concentrative dwelling places. A survey in the region was carried out on 10 communities, which were dominated by P. chienii. The analysis on its size structure, spatial distribution pattern and community characteristics showed that the populations of P. chienii could grow in the communities dominated by Rhododendron simiarum, Fokienia hodginsii-R. simiarum, and evergreen broad-leaved forests. In R. simiarum communities, the size structure, survival curve, and overwhelming community distribution pattern of P. chienii showed a sustaining development, while in communities dominated by F. hodginsii-R. simiarum, though the size structure was declining, the survival curve was Deevy- III type. Plenty of plantlets were still existed, and the populations kept steady. Two types were considered to be the most suitable ones for P. chienii populations. The important value of P. chienii reached 5% - 10%. In evergreen broad-leaved forests, the populations of P. chienii showed to be a declining type, and the survival curve was Deevy- II type. The distribution pattern was random, indicating that P. chienii populations could not fit for survive in this kind of communities. Correlation analysis showed that P. chienii populations had a positive correlation with R. simiarum and F. hodginsii, but a negative correlation with Cyclobalanopsis stewardiana and Schima superba. P. chienii could associate to the habits with the community canopy density of about 0.6 - 0.8. From the results mentioned above, the populations of P. chienii could be able to sustain and develop, and the existing habitat in Fengyangshan should be protected effectively. The protection of P. chienii requires more basic work to establish efficient measures to protect its habitat.

[Vegetation biomass distribution characteristics of alpine tundra ecosystem in Changbai Mountains]

Climate change is one of the hotspots in global environment concerns, while alpine tundra ecosystem is most sensitive to global climate change. Because of the relatively small area of tundra, researches on alpine tundra ecosystem were much less. Based on the measurement of species biomass, dominant species organ biomass and vegetation biomass, this paper discussed the biomass spatial variation in alpine tundra ecosystem of Changbai Mountains. The results showed that among 43 species investigated, the first five species in biomass were Rhododendron chrysanthum (159.01 kg x hm(-2)), Vaccinium uliginosum var. alpinum (137.52 kg x hm(-2)), Vaccinium uliginosum (134.7 kg x hm(-2)), Dryas octopetala var. asiatica (131.5 kg x hm(-2)) and Salix rotundifolia (128.4 kg x hm(-2)), which were the dominant species in the alpine tundra ecosystem of Changbai Mountains. Along with increasing altitude, the ratio of below-/above-ground biomass and below-ground/total biomass gradually increased, while the vegetation biomass gradually decreased. The vegetation biomass showed a significant correlation with altitude in typical alpine tundra ecosystem of Changbai Mountains, and the average vegetation biomass was 2.21 t x hm(-2). Alpine tundra ecosystem is very important for microclimate regulation, soil improvement, water-holding, soil conservation, nutrient cycling, carbon fixation and oxygen production, and currently, it is the CO2 sink of Changbai Mountains.

Controlling Rhododendron ponticum in the British Isles: an economic analysis

What resources should be committed to the control of invasive species? This study is based on a survey of nature conservation and forestry authorities, wildlife trusts and private landowners which investigated the extent of the ecological and economic impacts of the invasive non-native plant Rhododendron ponticum in the British Isles. There are data on 52,000 ha of land affected by R. ponticum, more than 30,000 ha of it in nature reserves. For nearly all nature reserves, displacement of native species and habitat changes were both reported. In 2001, respondents controlled 1275 ha of R. ponticum at a cost of pound 670,924. To test the optimality of this, we apply a model of social expenditure. The external costs of R. ponticum control are estimated from the probability that it will spread to contiguous sites and the damage done on invaded sites. These are then used to calculate the socially optimal level of expenditure on R. ponticum control, and the funding gap it identified by comparing the result with current levels of expenditure. The results suggest that a socially optimal level of control effort requires a significant increase in social funding for R. ponticum control, although the size of the increase varies between landholders.

Frost resistance and ice nucleation in leaves of five woody timberline species measured in situ during shoot expansion

Frost resistance and ice nucleation temperatures of leaves, from bud swelling until after full expansion, were measured in situ for five major woody timberline species with recently developed field freezing equipment. Frost resistance determined in situ on leaves of attached twigs was significantly higher than values determined on detached leaves in laboratory tests (e.g., the temperature at which incipient frost damage was observed (LTi) was 1.2 degrees C higher for detached leaves than for attached leaves of Picea abies (L.) Karst.). Frost resistance of leaves of all species changed significantly during shoot expansion (e.g., changes of 7.2 and 11 degrees C for Rhododendron ferrugineum L. and Larix decidua Mill., respectively). Expanding leaves (between 0 and 60% of full expansion) were the most sensitive to frost, with LTi values ranging from -3.4 degrees C in R. ferrugineum to -6.3 degrees C in L. decidua. Among the studied species, P. abies and R. ferrugineum were the most frost sensitive throughout the shoot elongation period. In situ freezing patterns of leaves of attached twigs also differed from those of leaves of excised twigs. During leaf expansion, two distinct freezing exotherms were always registered in situ. The first freezing event (E1, high-temperature exotherm) was recorded at -1.5 +/- 0.2 degrees C and reflected extracellular ice formation. Exposure of leaves to temperatures at which E1 occurred was, in all cases, noninjurious. The low-temperature exotherm (E2) mostly coincided with frost damage, except for some stages of leaf expansion in R. ferrugineum and P. abies, indicating that in situ freezing exotherms were not accurate estimators of frost damage in these species.

Biological control of Phytophthora ramorumon rhododendron

Phytophthora ramorum was found in Poland in 2000 as the causal agent of rhododendron blight. Besides eradication of diseased plants and rhododendron growing around, chemical and biological control of the pathogen is necessary. In this study in vitro activity of grapefruit extract and chitosan in the inhibition of P. ramorum growth and sporulation and their efficacy in the control of leaf and stem rot development was evaluated. Amendment of V8 juice agar and soil leachate with grapefruit extract resulted in the inhibition of colony growth and sporulation of P. ramorum. Zoosporangia were more susceptible to the extract than pathogen hyphae and chlamydospores. Chitosan only slightly inhibited the colony growth and zoosporngia production. Spraying of rhododendron inoculated with P. ramorum with grapefruit extract at conc. 165 microg/cm3 inhibited 2-3 times the spread of necrosis on stems and leaves. Pre- and postinoculation spraying of rhododendrons with chitosan at conc. of 1000 microg/cm3 suppressed the disease spread about 40%.

Elevated Ultraviolet-B Radiation Induces Cross-protection to Cold in Leaves of Rhododendron Under Field Conditions¶

Previously, we have shown a cold-hardening response in Rhododendron 'English Roseum' exposed to elevated ultraviolet-B radiation (UV-B, 280-320 nm) under growth chamber conditions. We have conducted the present study under field conditions to provide for a higher ratio of photosynthetically active radiation to UV-B (PAR:UV-B) than is possible in the laboratory and to more accurately reflect natural conditions of solar irradiance. Leaf disks taken after 3 months from UV-B-exposed plants exhibited a greater tolerance to freezing temperatures than those from control plants that received no supplemental UV-B exposure during this time. Leaf disks taken from UV-B-irradiated plants survived temperatures below -8 degrees C, whereas control disks were killed at -6 degrees C. Cold hardiness did not significantly increase until September, when environmental cues such as decreasing day length and night temperatures also may have enhanced hardening. Our field findings confirm our previous laboratory study, demonstrating that elevated UV-B induces cross-protection to cold in Rhododendron leaf tissues.

Screening of remote Rhododendron species and hybrids for interspecific hybridization with R. simsii hybrids

To introduce yellow, blue or orange pigmentation in the Rhododendron subgenus Tsutsusi (including R. simsii hybrids) by classical breeding, intersubgeneric pollination experiments involving Hymenanthes, Pentanthera and Rhododendron (including Vireya) species and hybrids were started. Prefertilization research by pollen tube staining revealed a different behaviour between bilateral crosses. Ovule culture was applied as a means to save a substantially larger amount of hybrid embryos from abortion. Though flower/seed capsule abortion eliminated many crosses in an early developmental stage, ovules of many crosses could be initiated in vitro on various time intervals after pollination. Germination was achieved on basal Rhododendron medium + 50 mg/l GA3. Green seedlings were obtained after Tsutsusi x Hymenanthes, Hymenanthes x Tsutsusi, Tsutsusi x Rhododendron, Rhododendron x Tsutsusi and Vireya x Tsutsusi pollination. Many seedlings have little growth vigour and next to green seedlings albino seedlings occur frequently, depending on the pollination type. The first true leaves of many assumed hybrids obviously lack chlorophyll. The ploidy level of Vireya x Tsutsusi and Tsutsusi x Pentanthera seedlings is intermediate, which strongly suggests their hybrid origin. Molecular analysis through SSR confirmed the interspecific charachter of seedlings in half of the crosses tested.