Aphid genotypes vary in their response to the presence of fungal endosymbionts in host plants

Genetic variation for fitness‐relevant traits may be maintained in natural populations by fitness differences that depend on environmental conditions. For herbivores, plant quality and variation in chemical plant defences can maintain genetic variation in performance. Apart from plant secondary compounds, symbiosis between plants and endosymbiotic fungi (endophytes) can produce herbivore‐toxic compounds. We show that there is significant variation among aphid genotypes in response to endophytes by comparing life‐history traits of 37 clones of the bird cherry‐oat aphid Rhopalosiphum padi feeding on endophyte‐free and endophyte‐infected tall fescue Lolium arundinaceum. Clonal variation for life‐history traits was large, and most clones performed better on endophyte‐free plants. However, the clones differed in the relative performance across the two environments, resulting in significant genotype × environment interactions for all reproductive traits. These findings suggest that natural variation in prevalence of endophyte infection can contribute to the maintenance of genetic diversity in aphid populations.     

Influence of soil and microclimate on species composition and grass encroachment in heath succession

Aims and Methods Mostly due to land use changes, European heathlands have become increasingly rare. In addition, the increasing amount of atmospheric nitrogen deposition has resulted in an encroachment of grasses and a loss in species diversity. Despite many investigations, information about the precise environmental parameters that determine the development and maintenance of heathland vegetation is still insufficient. In order to determine the environmental factors that control heath succession and grass encroachment, and to develop appropriate management schemes, we studied the influence of several soil and microclimate parameters on species composition and vegetation characteristics in five successional stages in a coastal heathland on the island of Hiddensee, north-east Germany, where the encroachment of Carex arenaria has become a major problem.Important findings We recorded the highest plant species richness in grey dune and birch forest plots, while the encroachment of C. arenaria let to a significant decline in plant species richness. The most important environmental factors influencing species richness and distribution of single species were microclimate, soil moisture, soil pH and the C/N ratio. While many studies reported the importance of differences in nutrient availability, we found no significant correlations between soil nutrient availability and vegetation pattern. Environmental conditions in dense C. arenaria stands, especially soil properties (e.g. soil pH), showed great differences in comparison to the other successional stages. However, no correlations between the encroachment of C. arenaria and single environmental factors were found. Our results show that not only soil nutrients are important abiotic factors in heaths but that also microclimate and soil moisture play an important role and that many factors are involved in heath succession and in the promotion of grass encroachment. Management plans for the conservation and restoration of heathlands should therefore focus on the specific site conditions and should take several abiotic and biotic factors into account.     

A polymorphism in XKR4 is significantly associated with serum prolactin concentrations in beef cows grazing tall fescue

Fescue toxicosis is a common syndrome of poor growth and reproductive performance of beef cattle grazing endophyte‐infected tall fescue infected with Lolium arundinaceum Schreb. Together with decreased feed intake, decreased growth rates and tissue necrosis due to vasoconstriction, depressed circulating serum prolactin concentrations are typically observed in cattle afflicted with fescue toxicosis. Polymorphisms within the XK, Kell blood group complex subunit‐related family, member 4 (XKR4) gene located on BTA14 have been previously reported to be associated with rump fat thickness, residual feed intake, average daily feed intake and average daily gain in cattle. Associations also have been reported between XKR4 genotype and effectiveness of the dopamine antagonist iloperidone as a treatment of schizophrenia in humans. Domperidone, a related dopamine antagonist, mediates effects of fescue toxicosis on livestock, including restoring depressed concentrations of prolactin. A mixed‐breed population of 592 beef cattle grazing endophyte‐infected tall fescue was used to examine the association between XKR4 genotype and circulating prolactin concentrations. The SNP rs42646708 was significantly (P = 0.0002) associated with serum prolactin concentrations and explained 2.45% of the phenotypic variation. Effect of genotype at the SNP was tested across five breeds, with significant associations within both Angus (P = 0.0275) and Simmental (P = 0.0224) breeds. These results suggest XKR4 may play a role in mediating the negative effects of fescue toxicosis, and polymorphisms within this gene may be useful markers for selection for genetic resistance to the debilitating effects of endophyte‐infected tall fescue.     

Agro-ecology of onion couch (Arrhenathemm elatius var. bulbosum).

The agro-ecology of onion couch (Arrhenatherum elatius var. bulbosum), a well known weed of arable land is studied. Contribution of seeds from onion couch and a more widespread variety of Arrhenatherum elatius: tall oat-grass, towards future ingress of onion couch in arable fields has indicated that the tall oat-grass variety is not a potential weed of arable land. It appears that vegetative propagules rather than the seeds are the effective means of propagation of the onion couch variety in arable fields. An experiment performed to test any modifying effect of the soil texture indicated that onion couch is restricted to loamy soils and there is a complete absence from heavy clays and sandy soils. This could be due to the moist and protective micro-environment provided by the texture of the soils to partially buried vegetative propagules of onion couch, which are susceptible to drought.     

Dynamics of nitrogen remobilization in defoliated Phleum pratense and Festuca pratensis under short and long photoperiods

The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy (Phleum pratense L. cv. Bodin) and meadow fescue (Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 mM NH₄NO₃ and pre-treated by extending the 11 h photosynthetically significant light period either by 1 h (short-day or SD plants) or 7 h (long-day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, ¹⁵N-labelled NH₄⁺ or NH₄⁺+ NO₃^? was supplied over a 20-day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO₃^? reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO₃^? uptake restarting 1 or 2 days earlier than NH₄⁺ uptake, even when NH₄⁺ was the only form of N supply. LD timothy plants supplied solely with NH₄⁺ were slowest to resume uptake of mineral N. Supplying NO₃^? in addition to NH₄⁺ after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short-term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink-driven rates of N remobilization and their interactions with mineral N uptake following defoliation.     

Use of two grasses for the phytoremediation of aqueous solutions polluted with terbuthylazine

The capacity of two grasses, tall fescue (Festuca arundinacea) and orchardgrass (Dactylis glomerata), to remove terbuthylazine (TBA) from polluted solutions has been assessed in hydroponic cultures. Different TBA concentrations (0.06, 0.31, 0.62, and 1.24 mg/L) were chosen to test the capacity of the two grasses to resist the chemical. Aerial biomass, effective concentrations (to cause reductions of 10, 50, and 90% of plant aerial biomass) and chlorophylls contents of orchardgrass were found to be more affected. Tall fescue was found to be more capable of removing the TBA from the growth media. Furthermore, enzymes involved both in the herbicide detoxification and in the response to herbicide-induced oxidative stress were investigated. Glutathione S-transferase (GST, EC. 2.5.1.18) and ascorbate peroxidase (APX, EC. 1.11.1.11) of tall fescue were found to be unaffected by the chemical. GST and APX levels of orchardgrass were decreased by the treatment. These negative modulations exerted by the TBA on the enzyme of orchardgrass explained its lower capacity to cope with the negative effects of the TBA.     

草坪草-高羊茅遗传育种研究进展

随着我国草坪业的快速发展 ,草坪草遗传育种工作越来越受到人们的关注。简要介绍了高羊茅的育种历史和现状 ,并对高羊茅植株再生体系的建立及遗传转化方面的研究进展进行了综述。此外 ,还提出了我国高羊茅育种的几点建议。     

Relative impacts of disturbance and temperature: persistent changes in microenvironment and vegetation in retrogressive thaw slumps

In the Low Arctic, a warming climate is increasing rates of permafrost degradation and altering vegetation. Disturbance associated with warming permafrost can change microclimate and expose areas of ion-rich mineral substrate for colonization by plants. Consequently, the response of vegetation to warming air temperatures may differ significantly from disturbed to undisturbed tundra. Across a latitudinal air temperature gradient, we tested the hypothesis that the microenvironment in thaw slumps would be warmer and more nutrient rich than undisturbed tundra, resulting in altered plant community composition and increased green alder ( Alnus viridis subsp. fruticosa ) growth and reproduction. Our results show increased nutrient availability, soil pH, snow pack, ground temperatures, and active layer thickness in disturbed terrain and suggest that these variables are important drivers of plant community structure. We also found increased productivity, catkin production, and seed viability of green alder at disturbed sites. Altered community composition and enhancement of alder growth and reproduction show that disturbances exert a strong influence on deciduous shrubs that make slumps potential seed sources for undisturbed tundra. Overall, these results indicate that accelerated disturbance regimes have the potential to magnify the effects of warming temperature on vegetation. Consequently, understanding the relative effects of temperature and disturbance on Arctic plant communities is critical to predicting feedbacks between northern ecosystems and global climate change.     

Prescribed Fire and Herbicide Effects on Soil Processes During Barrens Restoration

Prescribed fire has become a common tool of natural area managers for removal of non‐indigenous invasive species and maintenance of barrens plant communities. Certain non‐native species, such as tall fescue (Festuca arundinacea), tolerate fire and may require additional removal treatments. We studied changes in soil N and C dynamics after prescribed fire and herbicide application in remnant barrens in west central Kentucky. The effects of a single spring burn post‐emergence herbicide, combined fire and herbicide treatments, and an unburned no‐herbicide control were compared on five replicate blocks. In fire‐plus‐herbicide plots, fescue averaged 8% at the end of the growing season compared with 46% fescue cover in control plots. The extent of bare soil increased from near 0 in control to 11% in burned plots and 25% in fire‐plus‐herbicide plots. Over the course of the growing season, fire had little effect on soil N pools or processes. Fire caused a decline in soil CO₂ flux in parallel to decreased soil moisture. When applied alone, herbicide increased plant‐available soil N slightly but had no effect on soil respiration, moisture, or temperature. Fire‐plus‐herbicide significantly increased plant‐available soil N and net N transformation rates; soil respiration declined by 33%. Removal of non‐native plants modified the chemical, physical, and biological soil conditions that control availability of plant nutrients and influence plant species performance and community composition.     

Drought survival in Dactylis glomerata and Festuca arundinacea under similar rooting conditions in tubes

Drought survival in perennial forage plants involves different adaptative responses such as delay of dehydration through water uptake, limitation of water loss and tolerance of tissues to dessication. To compare the importance of these responses in contrasting cultivars of forage grasses at the whole plant level, we carried out two experiments under glasshouse conditions. Plants of cocksfoot (Dactylis glomerata L.) cultivars, cvs. Currie, Medly (both of Mediterranean origin) and Lutetia (of continental origin), and of tall fescue (Festuca arundinacea L.) cv. Centurion (Mediterranean) were grown in 60 cm-deep cylinders to eliminate the effect of differences of root depth on water availability whilst allowing severe drought to be imposed at a realistic rate. In both experiments, the cvs. were ranked similarly for plant survival, with high mortality for Centurion, low for the Mediterranean cocksfoots Currie and Medly, and intermediate for Lutetia. These differences could not be ascribed to water use during most of the drought period since water uptake and decrease in leaf extension were not significantly different between species and cultivars. However, resistant cvs. of cocksfoot were able to extract water for a longer period and at a lower soil water potential (s) than other cvs. The critical s at plant death was –3.8 and –3.6 MPa for Medly and Currie and –3.0-,–2.6 MPa for Lutetia and Centurion. Moreover, at a low soil water reserve (15–2%), membrane stability and water content were maintained for longer in enclosed immature leaf bases of cocksfoots cultivars, whereas the fescue Centurion exhibited accelerated lamina senescence and steady increase of membrane damage in surviving tissues. Therefore, it is proposed that the drought resistance of tall fescue in the field can mainly be ascribed to its ability to develop a deep root system. In cocksfoot, dehydration tolerance in surviving tissues and the ability of roots to extract water at low soil water potentials may, in addition to root depth, contribute significantly to plant survival under severe drought.