Summary 0 A dwarf shrub heath in subarctic Sweden was subjected to factorial manipulation of air temperature\ water and nutrient supply for 4 years[ The responses of the vegetation to the perturbations were then assessed by point intercept "quadrat# analy! sis followed by determination of above!ground biomass[ 1 Nineteen vascular and 12 non!vascular species "or species groups# were recorded and the most dramatic response was that of the grass Calama`rostis lapponica to nutrient addition\ with abundance being stimulated by a factor of more than 07 compared with plots not subjected to nutrient addition[ Calama`rostis lapponica did not show any signi_cant responses to temperature or water alone but there was a synergistic interaction between all three variables[ 2 The abundance of the dominant dwarf shrubs "Empetrum hermaphroditum\ Vac! cinium vitis!idaea\ V[ myrtillus and V[ uli`inosum# was una}ected by the perturbations but elevated temperature stimulated the biomass of V[ uli`inosum by 014) and total shrub biomass by 05)[ The low ratio of current year|s growth to standing biomass may have concealed other responses of the dwarf shrub group to the perturbations[ 3 The response of the non!vascular~ora to the perturbations was either neutral or negative\ with lichens showing the most dramatic responses[ Lichen biomass on temperature! and nutrient!amended plots was 45) and 07)\ respectively\ of that on unperturbed plots[ Nutrients also exerted a negative e}ect on the biomass of bryophy! tes\ and the combined biomass of lichens and bryophytes on nutrient!treated plots was almost a third of that on plots which did not receive additional nutrients[ 4 Total above!ground biomass was not a}ected by the perturbations but the total number of interceptions determined by point quadrat analysis was greater on the elevated temperature and nutrient!treated plots[ Point quadrat analysis also revealed an accumulation of litter and standing dead material in response to the nutrient and temperature perturbations\ both singly and in combination\ suggesting a faster turnover of plant material[ 5 Both temperature and nutrients increased canopy height and also interacted syn! ergistically such that together they resulted in a mean canopy height of 03[8 cm compared with 7[9 cm in plots subjected to neither perturbation[ 6 Nutrient addition lowered species richness by 06[6)\ mainly through its impact on the mosses and lichens[ 7 In general\ nutrient addition elicited the greatest response\ followed by temperature\ with water exerting little measurable in~uence[ There were a number of important interactions that were often synergistic\ and some involved water[ 8 Species| responses were highly individualistic and changes in the community were mediated through the response of a small number of key species already present in the community\ with no invasion of new species[ In the short term at least\~oristic diversity may decline as understorey species become less abundant and immigration by new species is inhibited by the dominance of clonal a...

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SliMMARYTotal moss cover and the gro-\\th responses of the t-wo dominant bryophytes vi-ithin a sub-arctic heath ecosystem, Polytrichum commune Hedw. and Hylocomium splendens (Hedw.) Br. Eur., were investigated in response to simulated environmental change. Temperature, water supply and nutrients (NPK fertilizer) were increased in a factorial field study in Swedish Lapland, After 3 yr of treatment, total moss cover on fertilized plots was found to be less than 50 ",, of that on unfertilized plots, H. splendens made a smaller contribution to total cover, and also had fewer shoots on the fertilizer treated plots. The relative contribution of P. commune to the bryophyte community was greater on the fertilized plots, although total shoot numbers of P. commune were not greater. There was. however, a larger number of dead shoots of P. commune on the fertilized plots. Total moss cover, relative contribution to moss cover by P. commune and H. splendens, and the numbers of shoots of these two species, were unresponsive to both the temperature and water treatments. The growth of the current year's segment of H. splendens w-as retarded hy both the fertilizer and temperature treatments. Furthermore, the dry weight of the physiologically acti\-e shoot was found to be significantly altered by all three treatments. The current year's growth of P. commune showed increases in d, wt and morphological parameters in response to the fertilizer treatment. There were also interactive effects of both the fertilizer and temperature treatments with the water treatment on the current year's stem length increment.

BackgroundMicrosatellites are widely used for many genetic studies. In contrast to single nucleotide polymorphism (SNP) and genotyping-by-sequencing methods, they are readily typed in samples of low DNA quality/concentration (e.g. museum/non-invasive samples), and enable the quick, cheap identification of species, hybrids, clones and ploidy. Microsatellites also have the highest cross-species utility of all types of markers used for genotyping, but, despite this, when isolated from a single species, only a relatively small proportion will be of utility. Marker development of any type requires skill and time. The availability of sufficient “off-the-shelf” markers that are suitable for genotyping a wide range of species would not only save resources but also uniquely enable new comparisons of diversity among taxa at the same set of loci. No other marker types are capable of enabling this. We therefore developed a set of avian microsatellite markers with enhanced cross-species utility.ResultsWe selected highly-conserved sequences with a high number of repeat units in both of two genetically distant species. Twenty-four primer sets were designed from homologous sequences that possessed at least eight repeat units in both the zebra finch (Taeniopygia guttata) and chicken (Gallus gallus). Each primer sequence was a complete match to zebra finch and, after accounting for degenerate bases, at least 86% similar to chicken. We assessed primer-set utility by genotyping individuals belonging to eight passerine and four non-passerine species. The majority of the new Conserved Avian Microsatellite (CAM) markers amplified in all 12 species tested (on average, 94% in passerines and 95% in non-passerines). This new marker set is of especially high utility in passerines, with a mean 68% of loci polymorphic per species, compared with 42% in non-passerine species.ConclusionsWhen combined with previously described conserved loci, this new set of conserved markers will not only reduce the necessity and expense of microsatellite isolation for a wide range of genetic studies, including avian parentage and population analyses, but will also now enable comparisons of genetic diversity among different species (and populations) at the same set of loci, with no or reduced bias. Finally, the approach used here can be applied to other taxa in which appropriate genome sequences are available.

Summary1 Arti®cial environmental gradients were established in a series of pot experiments to investigate the eect of salinity, sediment type and waterlogging on the growth, and interactions between Spartina anglica and Puccinellia maritima. In each experiment, one environmental variable was manipulated and plants grown in pairwise combinations to examine the eect of the environmental factor on the intensity of intra-and interspeci®c interactions, quanti®ed using the Relative Neighbour Eect (RNE) index. 2 Puccinellia was found to exert an asymmetric, one-way competitive dominance above ground over Spartina in experiments where gradients of sediment type and waterlogging were established. The intensity of the competition was highest in conditions with the least abiotic stress and lower or non-existent where stress was increased. 3 The intensity of the above-ground competition was greatest in loam and least in sand sediments. Reduction in competitive intensity in sand was accompanied by an increase in below-ground Spartina biomass and it is suggested that the production of rhizomes is a potential mechanism by which this species can expand vegetatively into areas without competition. 4 Interspeci®c competition on Spartina from Puccinellia also varied in intensity in the waterlogging experiment, being more intense in non-immersed treatments, where abiotic stress was reduced. 5 The competitive dominance of Puccinellia and the competition avoidance mechanism shown by Spartina in these experiments help to explain the successional interactions between the species along environmental gradients in natural salt marsh communities.

Soil holds 75% of the total organic carbon (TOC) stock in terrestrial ecosystems. This comprises ecosystem-derived organic carbon (OC) and black carbon (BC), a recalcitrant product of the incomplete combustion of fossil fuels and biomass. Urban topsoils are often enriched in BC from historical emissions of soot and have high TOC concentrations, but the contribution of BC to TOC throughout the urban soil profile, at a regional scale is unknown. We sampled 55 urban soil profiles across the North East of England, a region with a history of coal burning and heavy industry. Through combined elemental and thermogravimetic analyses, we found very large total soil OC stocks (31-65 kg m(-2) to 1 m), exceeding typical values reported for UK woodland soils. BC contributed 28-39% of the TOC stocks, up to 23 kg C m(-2) to 1 m, and was affected by soil texture. The proportional contribution of the BC-rich fraction to TOC increased with soil depth, and was enriched in topsoil under trees when compared to grassland. Our findings establish the importance of urban ecosystems in storing large amounts of OC in soils and that these soils also capture a large proportion of BC particulates emitted within urban areas.

Urban trees sequester carbon into biomass and provide many ecosystem service benefits aboveground leading to worldwide tree planting schemes. Since soils hold ∼75% of ecosystem organic carbon, understanding the effect of urban trees on soil organic carbon (SOC) and soil properties that underpin belowground ecosystem services is vital. We use an observational study to investigate effects of three important tree genera and mixed-species woodlands on soil properties (to 1 m depth) compared to adjacent urban grasslands. Aboveground biomass and belowground ecosystem service provision by urban trees are found not to be directly coupled. Indeed, SOC enhancement relative to urban grasslands is genus-specific being highest under Fraxinus excelsior and Acer spp., but similar to grasslands under Quercus robur and mixed woodland. Tree cover type does not influence soil bulk density or C∶N ratio, properties which indicate the ability of soils to provide regulating ecosystem services such as nutrient cycling and flood mitigation. The trends observed in this study suggest that genus selection is important to maximise long-term SOC storage under urban trees, but emerging threats from genus-specific pathogens must also be considered.