The role of catastrophic death of Calluna in heathland dynamics

In the Breckland heaths of East Anglia large patches of Calluna are often killed by adverse climatic conditions or insect attack. This paper studies one site, Cavenham Heath, where large areas of Calluna were killed between 1976–1979, and shows that older stands were most affected, and recovery was slowest compared to either younger stands, or stands with an uneven-aged structure. Moreover, where Calluna death was most severe, directional succession to birch woodland was accelerated. At this site, although Calluna regeneration has been previously assumed to be initiated by endogenous factors (i.e. by the life cycle of the Calluna), it is also clearly interrupted by exogenous factors. The implications of these results for heathland conservation are discussed, and it is suggested that intervention management by cutting and burning, to maintain large areas of Calluna in the building phase, may be the most appropriate long term strategy.This work was funded in part by the Nature Conservancy Council as part of its research programme into nature conservation. I thank Mr D. Malins and Mrs D. Reynolds for assistance in both the field and the laboratory, Ms S. Ide and Mr J. Pattin-gale for preparing the figures, and Professor C. H. Gimigham, Dr J. Miles and Dr I. C. Prentice for helpful comments on earlier drafts of this paper.     

Inferring temporal shifts in landuse intensity from functional response traits and functional diversity patterns: a study of Scotland's machair grassland

Plant functional response traits, which consistently respond to the environment, are useful for identifying drivers of vegetation change, particularly in response to disturbance gradients. Similarly, functional diversity indices have proven useful for investigating processes governing community assembly, particularly patterns of functional convergence/divergence. This study investigated the functional ecology of biodiverse, seminatural coastal grasslands (Scottish machair) at the national scale. We examined temporal shifts in functional response traits and functional diversity metrics using a series of null model, multivariate and regression analyses. The aim was to link temporal shifts in traits and diversity metrics to environmental variables in which to gauge the contribution of landuse change to plant functional composition and processes governing plant assembly. We observed significant shifts in the composition of 8 out of 12 functional response traits at the national scale, whereas at the regional scale all traits displayed at least one significant shift. Ordination of response traits found PC axis 1 (accounting for 39% of the variation) to be positively correlated to vegetation height and negatively correlated to specific leaf area, similar to that expected along a disturbance gradient. Significant changes in functional diversity indices were also observed at both national and regional scales, with varying convergence/divergence patterns observed across individual regions. We found functional richness (t = 4.87, p < 0.001) and divergence (t = 9.3, p < 0.001) to increase along PC axis 1, suggesting greater convergence and lower divergence along a disturbance gradient. This study demonstrates the potential for using functional diversity indices in combination with response traits as a sensitive method for detecting landuse change and its impacts on biodiversity. We conclude that landuse change, particularly management declines and intensification is a major driver governing change among the functional composition and functional diversity for machair grasslands, influencing convergence/divergence patterns, and subsequently community assembly processes.     

Growth of Rhodopseudomonas capsulata under anaerobic dark conditions with dimethyl sulfoxide

The photosynthetic bacterium, Rhodopseudomonas capsulata, could be cultured anaerobically in the absence of light on a synthetic medium with glucose as the carbon source only when dimethyl sulfoxide (DMSO) was added. The extent of growth was proportional to both DMSO and glucose concentrations. Optimal growth was achieved with 20 mm DMSO and 0.25% glucose. Under the best conditions, cells divided with a doubling time of 12 h. Pyruvate also supported the anaerobic dark growth of R. capsulata when DMSO was present. R. capsulata, R. sphaeroides, and R. palustris strains were all able to grow under anaerobic dark conditions with DMSO. Experiments using [¹⁴C]DMSO showed that more than 95% of the ¹⁴C was converted by cultures of R. capsulata to a volatile compound, identified as dimethyl sulfide (DMS) by gas chromatography, thus demonstrating that DMSO was being reduced to DMS during growth. These results indicate that R. capsulata requires a terminal electron acceptor for anaerobic dark growth and that DMSO can serve that function.     

Structural requirements for steroid inhibition of sheep lymphocyte mitogenesis in vitro

The inhibitory effects of different steroids and related compounds on sheep peripheral blood lymphocytes (PBL) during exposure to the mitogen, phytohemagglutinin (PHA), have been measured by the reduction of [3H]thymidine incorporation into DNA. Dose-response curves showed that a maximum (or near maximum effect) was achieved at a steroid concentration of 12.5 microM. At this dose 19 of 41 compounds significantly reduced thymidine incorporation by activated PBL (P less than 0.01 to P less than 0.001). The greatest reduction was observed with 17-hydroxyprogesterone (-59%, i.e. reduced by 59% compared with vehicle control, 100%) greater than androstenedione greater than epitestosterone greater than estradiol-3-methyl ether greater than 20 alpha-dihydroprogesterone greater than medroxyprogesterone acetate greater than 5 beta-pregnane-3,20-dione greater than 5 alpha-pregnane-3,20-dione (-24%). Among the steroids which showed the greatest inhibitory effect, 6 had a 4-en-3-one group in ring A, 4 had a saturated ring A (pregnane or androstane) and one had a 3-methyl ether group and a phenolic ring A. The wide range of structures represented by these inhibitory steroids suggests that inhibition of lymphocyte mitogenesis involves more than one mechanism.     

Protein kinases in protists

Summary The vast preponderance of our understanding of protein kinases comes from studies of mammalian or of other higher eukaryotic systems. A survey of the Wilson reference databank yielded 3,807 citations for protein kinases; only nine of these were reports of protein kinases in protists. It is apparent, nonetheless, that this understudied group offers unique opportunities for resolving the mechanisms by which protein kinases mediate a variety of cellular processes. Moreover, generalities about cofactor requirements (e.g., Ca²⁺ alone activates many protist protein kinases), substrate specificity, and the nature of the enzymes themselves (monomeric versus dimeric cyclic-nucleotide dependent protein kinases) will certainly need to be modified.     

Some factors affecting successional change on uranium mine wastes: Insights for ecological restoration

Question: Are growth form and dispersal-mode replacement during vegetation succession in semi-arid Mediterranean conditions affected by the starting quality of the substrate and by site aspect? Location: Central-western Spain. Methods: We monitored successions on three waste materials left after uranium mining: unbroken waste, broken waste and wastes amended with a sandy material (Arkoses); both north and south aspects were also studied on each substrate. Results: The substrate starting quality had the greatest influence on spontaneous succession, separating the poorer quality substrates (broken and unbroken wastes) from the better ones (Arkoses) and two reference communities (Topsoil and Dehesa). The importance of aspect was confirmed then within each substrate type. Most species with a short life span (mostly annuals and a few biennials), together with some woody species on Arkoses, showed no response to age (years following the deposition of new soil). Others short-lived species declined over time on the poorer wastes but not on the better Arkoses. There was a tendency for life form replacement (from thero-phytes to hemicryptophytes) during succession only on the poorer-quality substrates. No dispersal-mode replacement sequence was found. Conclusion: Improving the abiotic conditions of the substrate had a great effect on vegetation succession, but this effect was modified by aspect. Aspect took longer to induce differences in floristic composition on the poorer substrates, where succession was slower. Some trends in species responses to successional change were found by considering species traits, particularly life-form.