The effects of earthworm functional group diversity on earthworm community structure

A comprehensive understanding of how species/functional group interactions determine population dynamics, community composition and their effect on ecosystem functioning is necessary if we are to understand the consequences of species loss. This paper presents data from a mesocosm experiment, based on the simplex design, to examine the effect of interactions between earthworm functional groups, food supply and initial overall biomass on community structure. All communities containing anecic species moved towards domination by anecics. The survival of anecics remained constant irrespective of initial conditions, with no effect of initial community structure, food supply or initial biomass. The proportional biomass of epigeics increased when they were placed in communities dominated by anecics. Initial overall biomass had a significant effect on the survival of endogeics, with increased survival at low biomass. Juvenile production was significantly increased in communities that contained a higher initial abundance of epigeics. The anecics had significantly increased production of juveniles at lower levels of initial biomass. Overall, earthworm functional group diversity had an idiosyncratic effect on earthworm assemblage structure but the presence of synergistic interactions suggests that the persistence and optimal contribution of the earthworm assemblage to ecosystem service is dependent on the presence of a number of functional groups.     

Assessing the usefulness of B‐mode and colour Doppler sonography,and measurements of circulating progesterone concentrations for determining ovarian responses in superovulated ewes

The main goal of this study was to assess the usefulness of two imaging modalities, namely the B‐mode and colour Doppler sonography, and serum progesterone (P₄) concentrations for determining the ovarian response in superovulated ewes. Twenty‐four sexually mature Santa Inês ewes underwent the superovulatory treatment consisting of eight injections of porcine FSH (total dose of 200 or 133 or 100 mg; n  =  8 ewes/total dose) given at 12‐hr intervals and initiated 48 hr before CIDR ^® (Pfizer Inc., Auckland, New Zealand) removal. Six days after natural mating, the ovaries of all donor ewes were visualized and examined with transrectal ultrasonography and then with videolaparoscopy to identify and enumerate corpora lutea (CL ) and luteinized unovulated follicles (LUF s). Jugular blood samples were collected just prior to ovarian examinations. The total number of CL (r  =  .78 and 0.83, p  <  .0001) and LUF s (r  =  .74 and 0.90, p  <  .0001) enumerated using the B‐mode and colour Doppler ultrasonographic technique, respectively, were correlated with that ascertained by videolaparoscopy. Circulating concentrations of P₄ were related directly to the number of healthy CL (r  =  .73, p  =  .0002) and inversely to the number of prematurely regressing CL (r  = ?.46, p  =  .03), but the accuracy of predicting the number of short‐lived CL with serum P₄ concentrations was very poor. The present results indicate that ultrasonographic imaging and serum P₄ measurements on the day of embryo recovery are useful indicators of total/normal CL numbers and both ultrasonographic techniques can be used to quantify LUF s in superovulated ewes.     

Habitat selective factors influencing the structural composition and functional capacity of microbial communities in agricultural soils

Key physicochemical factors associated with microbial community composition and functions in Australian agricultural soils were identified. Soils from seven field sites, with varying long-term agricultural management regimes, were characterised physicochemically, on the basis of their bacterial and fungal community structures (using PCR-DGGE), and by assessing potential catabolic functions (MicroResp?). Soil type, rather than agricultural management practice, was the key determinant of microbial community structure and catabolic function (P<0.05). Following multivariate analysis, soil pH was identified as the key habitat-selective physicochemical soil property associated with variation in biological diversity and profiles of organic substrate utilisation. In particular, the capacity of soils to catabolise different C-substrates was closely correlated (ρ=0.604, P=0.001) to pH. With decreasing pH, the catabolism of common low molecular weight organic compounds (especially cysteine and aspartic acid) declined, however catabolism of two others (lysine and arginine) increased. Shifts in the capacity of soil microbiota to cycle common organic compounds have implications for overall geochemical cycling of C and N in acidifying soils. The genetic structure of the bacterial communities in soil strongly correlated with pH (ρ=0.722; P=0.001) and that of soil fungi with pH and % sand (ρ=0.323; P=0.006). Catabolic function was more closely associated with the structure of the bacterial than fungal communities. This work has shown that soil pH is a primary driver of microbial diversity and function in soil. Agricultural management practices thereby act to selectively shift populations and functions against this background.