Cohort Profile: Pregnancy And Childhood Epigenetics (PACE) Consortium.

Development Psychopathology in context: famil

Geographic distribution and the reproductive and demographic ecology of two congeneric seeder and resprouter tree species

The distribution limits of species are mainly related to climate but other environmental factors such as soil and fire may also play an important role in local population dynamics. Species that re-establish from seed after a severe disturbance (seeder species) should have different functional attributes from species that can survive a disturbance by vegetative regeneration (resprouters). The functional attributes will influence the establishment and survival of individuals and for trees, the stem size distributions provide a view of the history of the populations and may indicate the trajectories of the populations as they age. Two congeneric tree species – Allocasuarina fraseriana (a resprouter) and A. huegeliana (a seeder) are dominant to subdominant trees in forest and woodland vegetation of south western Australia and illustrate useful comparisons of functional attributes and population structures. Both species occupy fire prone vegetation, bear seeds in serotinous cones and are considered to regenerate new individuals after fire events. The seeder (Allocasuarina huegeliana) has smaller cones and seeds and more seeds cone-1 than the resprouter (A. fraseriana). The cones of the resprouter provide more protection against heat to the contained seeds than the seeder. It is generally considered that species in fire prone environments often rely on disturbance to provide suitable conditions for regeneration and recruitment between disturbances is poor. For a species killed by disturbance population structures years after the disturbance would be expected to be unimodal while a resprouter would have a multimodal structure, as adults would survive and remain in the population with the new recruits. Unexpectedly population structures for the two species we studied were very similar when compared at an overall landscape scale. We attribute this mainly to the ability of the species to recruit interfire. Best seedling recruitment does occur after fire, as this provides an environment with more nutrients and reduced competition for the seedlings. However interfire recruitment can be abundant in some habitats. The degree to which this occurs may vary in relation to co-occurring tree species and landscape position. In general, fuel reduction fires are being used to reduce the danger of high intensity fires as the climate becomes drier and hotter in parts of southern Australia and mild fires will influence recruitment of both species. Low intensity surface fires will remove interfire recruits of the seeder species, but may increase the density of small plants of the resprouter. Adults are unlikely to be damaged but size class structures will be different from those after stand replacing fires

Podocarpaceae in tropical forests: A synthesis

The Podocarpaceae comprises 18 genera and about 173 species of evergreen, coniferous trees and shrubs. It is the most successful gymnosperm family in angiosperm-dominated tropical forests (Brodribb, this volume). Podocarps are distributed mainly in the Southern Hemisphere, with populations also extending as far north as China and Japan and to Mexico and the Caribbean in the neotropics (Dalling et al., this volume; Enright and Jaffré, this volume; Adie and Lawes, this volume)

Microbial Populations and Enzyme Activities in Soils Fumigated with Methyl Bromide Alternatives

Methyl bromide (MeBr; CH3Br) use for soil fumigation will be banned in 2005 due to its ozone depleting properties. Potential alternative chemicals to replace MeBr include chloropicrin (CP; CCl3NO2), 1,3-dichloropropene (1,3-D; C3H4Cl2), iodomethane (IM; CH3I), and propargyl bromide (PrBr; C3H3Br). The goal of this research was to assess changes in soil fungal populations, microbial biomass C (MBc) and respiration, nitrification potential, and enzyme activities after fumigation with MeBr and alternative fumigants. Four formulations of alternative fumigants (CP, InLine [61% 1,3-D plus 33% CP], Midas [50% IM plus 50% CPJ, and PrBr) were applied at commercial rates through drip irrigation systems to two field plots located in main strawberry production areas in California, USA. Soil samples (0-15 cm) were taken at 1, 4, and 30 or 37 wk after fumigant application. Fumigation with MeBr plus CP and the alternative chemicals eliminated soil-borne fungal pathogens in soil and reduced culturable fungal populations up to 4 wk post fumigation. Soil microbial respiration decreased with fumigant application and was the least (>40% reduction relative to the control) in the PrBr treatment I wk after fumigation, while soil MBc was not affected by fumigation. The activities of acid phosphatase and arylsulfatase were generally lower in fumigated soils over the 30-or 37-wk study, and those of P-glucosidase and dehydrogenase were lower up to 4 wk past fumigation. Potential nitrification rates were substantially reduced (>55% reduction relative to the control) by the fumigants, but rates recovered toward the end of this study. Results of this study suggested that fungal populations and the activities of acid phosphatase and arylsulfatase were more sensitive to fumigation with the tested MeBr and the alternative fumigants than total microbial biomass, microbial respiration, nitrification, and the activities of dehydrogenases and P-glucosidase. Short-term impacts of MeBr and its alternative fumigants on microbial activities and enzymatic processes suggest that all the tested fumigants have the potential to alter important microbial and enzymatic functions such as nutrient cycling