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A growing body of evidence shows that aboveground and belowground communities and processes are intrinsically linked, and that feedbacks between these subsystems have important implications for community structure and ecosystem functioning. Almost all studies on this topic have been carried out from an empirical perspective and in specific ecological settings or contexts. Belowground interactions operate at different spatial and temporal scales. Due to the relatively low mobility and high survival of organisms in the soil, plants have longer lasting legacy effects belowground than aboveground. Our current challenge is to understand how aboveground–belowground biotic interactions operate across spatial and temporal scales, and how they depend on, as well as influence, the abiotic environment. Because empirical capacities are too limited to explore all possible combinations of interactions and environmental settings, we explore where and how they can be supported by theoretical approaches to develop testable predictions and to generalise empirical results. We review four key areas where a combined aboveground–belowground approach offers perspectives for enhancing ecological understanding, namely succession, agro-ecosystems, biological invasions and global change impacts on ecosystems. In plant succession, differences in scales between aboveground and belowground biota, as well as between species interactions and ecosystem processes, have important implications for the rate and direction of community change. Aboveground as well as belowground interactions either enhance or reduce rates of plant species replacement. Moreover, the outcomes of the interactions depend on abiotic conditions and plant life history characteristics, which may vary with successional position. We exemplify where translation of the current conceptual succession models into more predictive models can help targeting empirical studies and generalising their results. Then, we discuss how understanding succession may help to enhance managing arable crops, grasslands and invasive plants, as well as provide insights into the effects of global change on community re-organisation and ecosystem processes.

A new precision half-life measurement of 29P was conducted using the TwinSol β-counting station at the University of Notre Dame Nuclear Science Laboratory. The resulting value of t1/2new=4.1055(44)s is the most precise 29P half-life measurement to date. Utilizing this measurement and reevaluating the world data leads to a new world average of t1/2world=4.1031(58)s, which improves the Birge ratio from 3.11 to 1.45 and is 2.3 times more precise than the previous world value. The new Cabibbo-Kobayashi-Maskawa matrix element Vud for 29P shifts closer into agreement with the superallowed pure Fermi value. The uncertainty in the mixed transition value of Vud, however, is still dominated by the Fermi to Gamow-Teller mixing ratio ρ. Using the new world half-life and assuming the validity of the standard model, a new predicted value for ρ and its associated correlation parameters have been evaluated in order to guide future determination of ρ. [ABSTRACT FROM AUTHOR]

We report a new precision half-life measurement of 20F, performed using the β-counting station of the University of Notre Dame's Nuclear Science Laboratory. The measured half-life of 11.0160(41)stat(155)sys s resulting from this work will help resolve the longstanding discrepancy between two earlier sets of high-precision half-life measurements. [ABSTRACT FROM AUTHOR]

Background: The precise determination of the Ft value in T=1/2 mixed mirror decays is an important avenue for testing the standard model of the electroweak interaction through the determination of Vud in nuclear β decays. 11C is an interesting case, as its low mass and small QEC value make it particularly sensitive to violations of the conserved vector current hypothesis. The present dominant source of uncertainty in the 11CFt value is the half-life. Purpose: A high-precision measurement of the 11C half-life was performed, and a new world average half-life was calculated. Method: 11C was created by transfer reactions and separated using the TwinSol facility at the Nuclear Science Laboratory at the University of Notre Dame. It was then implanted into a tantalum foil, and β counting was used to determine the half-life. Results: The new half-life, t1/2=1220.27(26) s, is consistent with the previous values but significantly more precise. A new world average was calculated, tworld1/2=1220.41(32) s, and a new estimate for the Gamow-Teller to Fermi mixing ratio ρ is presented along with standard model correlation parameters. Conclusions: The new 11C world average half-life allows the calculation of a Ftmirror value that is now the most precise value for all superallowed mixed mirror transitions. This gives a strong impetus for an experimental determination of ρ, to allow for the determination of Vud from this decay. [ABSTRACT FROM AUTHOR]

A new precision half-life measurement of 25Al was conducted using the TwinSol β-counting station at the University of Notre Dame. The new measured value of t1/2new=7.1657(24) s is in good agreement with the most recent measurement, while being 3 times more precise. Using these new measurements, an evaluation of the 25Al half-life has been performed, leading to an average half-life of t1/2world=7.1665(26) s, which is 5 times more precise than it's predecessor and has a more satisfactory Birge ratio of 1.1. To aid in future measurements of correlation parameters, a new Fermi to Gamow-Teller mixing ratio ρ and correlation parameters for this mixed transition have been calculated assuming the standard model validity using the new world half-life. [ABSTRACT FROM AUTHOR]

Generally, effects of herbivory on plant fitness have been measured in terms of female reproductive success (seed production). However, male plant fitness, defined as the number of seeds sired by pollen, contributes half of the genes to the next generation and is therefore crucial to the evolution of natural plant populations. This is the first study to examine effects of insect herbivory on both male and female plant reproductive success. Through controlled field and greenhouse experiments and genetic paternity analysis, we found that foliar damage by insects caused a range of responses by plants. In one environment, damaged plants had greater success as male parents than undamaged plants. Neither effects on pollen competitive ability nor pollinator visitation patterns could explain the greater siring success of these damaged plants. Success of damaged plants as male parents appeared to be due primarily to changes in allocation to flowers versus seeds after damage. Damaged plants produced more flowers early in the season, but not more seeds, than undamaged plants. Based on total seed production, male fitness measures from the first third of the season, and flower production, we estimated that damaged and undamaged plants had equal total reproductive success at the end of the season in this environment. In a second, richer environment, damaged and undamaged plants had equal male and female plant fitness, and no traits differed significantly between the treatments. Equal total reproductive success may not be ecologically or evolutionarily equivalent if it is achieved differentially through male versus female fitness. Genes from damaged plants dispersed through pollen may escape attack from herbivores, if such attack is correlated spatially from year to year.

Hybrid zones often are intermediate in their habitat, and have individuals that are intermediate genetically to those of either parental species. Recently, a number of studies has addressed the distribution of herbivores and parasites in hybrid zones of their hosts. Mechanisms that underlie these distributions include behavioral, environmental and genotypic differences between hybrids and their parental species., (Copyright © 1994. Published by Elsevier Ltd.)

The diversity of indirect interactions that can occur within communities is large. Recent research on indirect interactions is scattered in the literature under numerous labels. The definition of indirect effects is an important aspect of their study, and clarifies some of the subtle differences among indirect effects found in natural communities. Choosing which species to study, how to manipulate species and for what duration, which attributes to measure and, finally, which analytical techniques to use are all problems facing the community ecologist. Ultimately, we are striving for the best means of determining the relative importance of direct and indirect effects in structuring communities., (Copyright © 1991. Published by Elsevier Ltd.)