Plant diversity effects on plant longevity and their relationships to population stability in experimental grasslands

Identifying to what degree inherent characteristics of plant species and their variation in response to their environment regulate the temporal stability of plant populations is important to understand patterns of species coexistence and the stability of ecosystems. Longevity is a key characteristic of plant life history and an important component of demographic storage, but age is usually unknown for herbaceous species. In a 12-year-old biodiversity experiment (Jena Experiment) comprising 80 grassland communities with six levels of plant species richness (1, 2, 4, 8, 16 and 60 species) and four levels of functional groups richness (1, 2, 3 and 4 functional groups), we studied populations of 38 dicotyledonous forb species (N = 1,683 plant individuals). The sampled individuals represented three plant functional groups (legumes, small herbs and tall herbs) and two different growth forms (species with long-lived primary roots and clonal species with rhizomes/stolons). We assessed the age of plant individuals by means of growth ring analysis and related the age of plant populations to their temporal stability in terms of peak biomass production. On average, plant species richness did not affect the mean age of the populations or the maximum age of individuals found in a population. Age of herbs with taproots increased and age of herbs with clonal growth decreased with increasing species richness, cancelling out each other when growth forms were analysed together. Mean population age was lowest for small herbs and highest for tall herbs, while legumes had an intermediate population age. Herbs with a taproot were on average older than herbs with a rhizome. Across all species-richness levels, populations with older individuals were more stable in terms of biomass production over time. Synthesis. Our study shows for the first time across multiple species that the longevity of forbs is affected by the diversity of the surrounding plant community, and that plant longevity as an important component of demographic storage increases the temporal stability of populations of grassland forb species

Entry of Plasma Sheet Particles into the Inner Magnetosphere Observed by POLAR/CAMMICE

Statistical results are presented from Polar/CAMMICE measurements of events during which the plasma sheet ions have penetrated deeply into the inner magnetosphere. Owing to their characteristic structure in energy-time spectrograms, these events are called intense nose events. Almost 400 observations of such structures were made during 1997. Intense nose events are shown to be more frequent in the dusk than in the dawn sector. They typically penetrate well inside L = 4, the deepest penetration having occurred around midnight and noon. The intense nose events are associated with magnetic (substorm) activity. However, even moderate activity (AE = 150-250 nT) resulted in formation of these structures. In a case study of November 3, 1997, three sequential inner magnetosphere crossings of the Polar and Interball Auroral spacecraft are shown, each of which exhibited signatures of intense nose-like structures. Using the innermost boundary determinations from these observations, it is demonstrated that a large-scale convective electric field alone cannot account for the inward motion of the structure. It is suggested that the intense nose structures are caused by short-lived intense electric fields (in excess of ∼1 mV/m) in the inner tail at L=4-5

Individual common variants exert weak effects on the risk for autism spectrum disorders.

While it is apparent that rare variation can play an important role in the genetic architecture of autism spectrum disorders (ASDs), the contribution of common variation to the risk of developing ASD is less clear. To produce a more comprehensive picture, we report Stage 2 of the Autism Genome Project genome-wide association study, adding 1301 ASD families and bringing the total to 2705 families analysed (Stages 1 and 2). In addition to evaluating the association of individual single nucleotide polymorphisms (SNPs), we also sought evidence that common variants, en masse, might affect the risk. Despite genotyping over a million SNPs covering the genome, no single SNP shows significant association with ASD or selected phenotypes at a genome-wide level. The SNP that achieves the smallest P-value from secondary analyses is rs1718101. It falls in CNTNAP2, a gene previously implicated in susceptibility for ASD. This SNP also shows modest association with age of word/phrase acquisition in ASD subjects, of interest because features of language development are also associated with other variation in CNTNAP2. In contrast, allele scores derived from the transmission of common alleles to Stage 1 cases significantly predict case status in the independent Stage 2 sample. Despite being significant, the variance explained by these allele scores was small (Vm< 1%). Based on results from individual SNPs and their en masse effect on risk, as inferred from the allele score results, it is reasonable to conclude that common variants affect the risk for ASD but their individual effects are modest

Old English macian, Its Origin and Dissemination

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66612/2/10.1177_007542428601900105.pd