Heterogeneity of genetic parameters for calving difficulty in Holstein heifers in Ireland

Calving difficulty is a trait that greatly affects animal welfare, herd profitability, and the amount of labor required by cattle farmers. It is influenced by direct and maternal genetic components. Selection and breeding strategies can optimize the accuracy of genetic evaluations and correctly emphasize calving difficulty in multiple-trait indices provided there are accurate estimates of genetic parameters. In Ireland, large differences exist in the age at which heifers first give birth to calves. The objective of this study was to estimate genetic parameters for calving difficulty in first-parity Holsteins and to determine whether these differed with age of the heifer at calving. Transformed calving difficulty records for 18,798 Holstein heifers, which calved between January 2002 and May 2006, were analyzed using univariate, multitrait, and random regression linear sire-maternal grandsire models. The model that 1) fitted a second-order random regression of dam age at first parity for the direct component, 2) treated the maternal component as a single trait regardless of dam age, and 3) fitted a single residual variance component was optimal. Heritabilities for direct (0.13) and maternal (0.04) calving difficulty were significantly different from zero. These 2 components were moderately negatively correlated (¿0.47). Estimates of direct genetic variance and heritability were heterogeneous along the dam age trajectory, decreasing initially with dam age before subsequently increasing. Heritability estimates ranged between 0.11 and 0.37 and were higher for records with younger and older dams at parturition. Genetic correlations between the direct components of calving difficulty decreased from unity to 0.5 with increasing distance between dam ages at parturition. The results of this study indicated that heterogeneity of direct genetic variance existed for calving difficulty, depending on dam age at first parturition

Exploring interactions of plant microbiomes

A plethora of microbial cells is present in every gram of soil, and microbes are found extensively in plant and animal tissues. The mechanisms governed by microorganisms in the regulation of physiological processes of their hosts have been extensively studied in the light of recent findings on microbiomes. In plants, the components of these microbiomes may form distinct communities, such as those inhabiting the plant rhizosphere, the endosphere and the phyllosphere. In each of these niches, the "microbial tissue" is established by, and responds to, specific selective pressures. Although there is no clear picture of the overall role of the plant microbiome, there is substantial evidence that these communities are involved in disease control, enhance nutrient acquisition, and affect stress tolerance. In this review, we first summarize features of microbial communities that compose the plant microbiome and further present a series of studies describing the underpinning factors that shape the phylogenetic and functional plant-associated communities. We advocate the idea that understanding the mechanisms by which plants select and interact with their microbiomes may have a direct effect on plant development and health, and further lead to the establishment of novel microbiome-driven strategies, that can cope with the development of a more sustainable agriculture

Effect of population density of Pseudomonas fluorescens on production of 2,4-diacetylphloroglucinol in the rhizosphere of wheat

The role of antibiotics in biological control of soilborne pathogens, and more generally in microbial antagonism in natural disease-suppressive soils, often has been questioned because of the indirect nature of the supporting evidence. In this study, a protocol for high pressure liquid chromatography/mass spectrometry is described that allowed specific identification and quantitation of the antibiotic 2,4-diacetylphloroglucinol (Phl) produced by naturally occurring fluorescent Pseudomonas spp. on roots of wheat grown in a soil suppressive to take-all of wheat. These results provide, for the first time, biochemical support for the conclusion of previous work that Phl-producing fluorescent Pseudomonas spp. are key components of the natural biological control that operates in take-all-suppressive soils in Washington State. This study also demonstrates that the total amount of Phl produced on roots of wheat by P. fluorescens strain Q2-87, at densities ranging from approximately 105 to 107 CFU/g of root, is proportional to its rhizosphere population density and that Phl production per population unit is a constant (0.62 ng/105 CFU). Thus, Phl production in the rhizosphere of wheat is strongly related to the ability of the introduced strain to colonize the roots

Aridland constructed treatment wetlands I: Macrophyte productivity, community composition, and nitrogen uptake

Urbanized areas increasingly rely on constructed treatment wetlands (CTW) for cost effective and environmentally-based wastewater treatment. Constructed treatment wetlands are particularly attractive treatment options in arid urban environments where water reuse is important for dealing with scarce water resources. Emergent macrophytes play an important role in nutrient removal, particularly nitrogen (N) removal, in CTW. However, the role of plant community composition in nutrient removal is less clear. Numerous studies have shown that macrophyte species differentially affect N uptake processes (e.g., direct plant uptake, coupled nitrification–denitrification, soil accretion). However, many of these studies have been based on small-scale experiments and have been carried out in mesic environments, which means that their findings are difficult to extrapolate to aridland CTW systems. Our study sought to examine the relationships among emergent macrophyte productivity, plant community composition, and N uptake [by both the plants and the entire ecosystem] at a 42 ha CTW in arid Phoenix, Arizona, USA. We quantified above- and belowground biomass bimonthly and foliar N content annually for four species groups (Typha latifolia + Typha domingensis, Schoenoplectus californicus + Schoenoplectus tabernaemontani, Schoenoplectus acutus, and Schoenoplectus americanus) from July 2011 to September 2013. We quantified dissolved inorganic N fluxes into and out of the system and compared plant N removal to total system fluxes. Additionally, we estimated monotypic N content for each to compare the system’s current community composition and plant N removal to hypothetical scenarios in which the system was dominated by only one species. Peak aboveground biomass ranged from 1586 ± 179 (SE) to 2666 ± 164 (SE) gdw m−2 of which Typha spp. accounted for an increasing portion (>66%). We observed widespread ‘thatching’ – the toppling of large stands of macrophytes – that was likely related to a decline in peak biomass from July 2011 to July 2012. The foliar N content was similar among the species groups and N content for all species combined, at peak biomass, was 31 ± 8 N g m−2. This measured foliar N content was higher than our estimates of the foliar N content in hypothetical monotypic stands, suggesting that the system’s actual community composition performed better, in terms of direct plant N uptake, than if the system had been planted with only one species group. Overall, direct plant N uptake accounted for 7% of inorganic N inputs and 19% of whole-system inorganic N removal. Our findings suggest that managers and designers should consider diverse plant communities rather than monotypic stands when designing, constructing, and managing CWT wetland systems. Future research is needed to elucidate those management strategies that might best promote or preserve diverse plant communities in these systems in a cost effective manner

Aridland constructed treatment wetlands II: Plant mediation of surface hydrology enhances nitrogen removal

Constructed treatment wetlands have been well established as effective and sustainable solutions to the problem of urban water treatment and reuse. However, treatment wetlands located in aridland cities may behave differently relative to their more mesic and humid counterparts, and this could potentially impact their ability to deliver the ecosystem services that are expected of them. Specifically, in hot, dry climates large water losses via evaporation and plant transpiration may comprise a major component of whole-system water budgets. Our primary goal was to develop a rigorous and informed model of how well these “working wetlands” function in hot, arid climates by developing and comparing robust water and nutrient budgets, as our process-based understanding of how mesic constructed wetlands function may not be readily transferred to arid climates where constructed wetlands are becoming increasingly widespread. At the Tres Rios constructed treatment wetland in Phoenix AZ USA, we quantified water losses via plant transpiration and open water evaporation as well as inorganic N loads into and from the whole wetland system and into the vegetated marsh. We found that water losses due to transpiration and evaporation were remarkably high when compared to most mesic constructed wetlands. Total water losses via evaporation and transpiration peaked at 300,000 m3 mo−1 (714 L H2O m−2 mo−1) in the hot, dry summer months and averaged more than 70% of the whole-system water losses over a 27 month time period. At the same time, the vegetated marsh removed nearly all of the inorganic N that was supplied to it. Large transpirative water losses moved large volumes of replacement water into the marsh via a “biological tide” that provided more opportunities for vegetation and soil microbes to process N and other target solutes. This enhanced the N treatment efficacy of the Tres Rios constructed treatment wetland relative to humid, mesic systems. To our knowledge, this is the first time that biotically-mediated surface hydrology has been demonstrated in any wetland