Small amounts of ammonium (NH$ _4^+ $) can increase growth of maize (Zea mays)

Nitrate (NO$ _3^ - $ ) and ammonium (NH$ _4^+ $ ) are the predominant forms of nitrogen (N) available to plants in agricultural soils. Nitrate concentrations are generally ten times higher than those of NH$ _4^+ $ and this ratio is consistent across a wide range of soil types. The possible contribution of these small concentrations of NH$ _4^+ $ to the overall N budget of crop plants is often overlooked. In this study the importance of this for the growth and nitrogen budget of maize (Zea mays L.) was investigated, using agriculturally relevant concentrations of NH$ _4^+ $ . Maize inbred line B73 was grown hydroponically for 30 d at low (0.5 mM) and sufficient (2.5 mM) levels of NO$ _3^ - $ . Ammonium was added at 0.05 mM and 0.25 mM to both levels of NO$ _3^ - $ . At low NO$ _3^ - $ levels, addition of NH$ _4^+ $ was found to improve the growth of maize plants. This increased plant growth was accompanied by an increase in total N uptake, as well as total phosphorus, sulphur and other micronutrients in the shoot. Ammonium influx was higher than NO$ _3^ - $ influx for all the plants and decreased as the total N in the nutrient medium increased. This study shows that agriculturally relevant proportions of NH$ _4^+ $ supplied in addition to NO$ _3^ - $ can increase growth of maize.     

Natural abundance radiocarbon in soil microbial biomass: Results from a glacial foreland

We present a method for determining the natural abundance radiocarbon (¹⁴C) content of soil microbial biomass (SMB) based on existing fumigation-extraction procedures. We applied the technique to soils from the foreland of the Ödenwinkelkees glacier in the Austrian Alps, which has a well-characterised chronosequence of soils at different stages of development. Across the chronosequence, SMB contained post-bomb levels of ¹⁴C, suggesting it was substantially composed of carbon that had been fixed since the 1960s. Comparison of our results with previous findings from the same site showed that at most stages in the sequence the SMB had a similar ¹⁴C content to the bulk soil organic matter (SOM). However, soil respired CO₂ was ¹⁴C-depleted relative to SMB, indicating that at least a component of the microbial community was mineralising some older carbon. In the most recently exposed soils, SMB was ¹⁴C-enriched compared to both soil respiration and SOM, suggesting that a small component of the microbial biomass that utilises older carbon contributes disproportionately more to the CO₂ efflux. Although other interpretations are possible, this explanation is consistent with the notion that early on in the succession a large proportion of the microbial biomass is dormant.     

An assessment of the effect of Sitka Spruce (Picea sitchensis Bong. Carr) plantation forest cover on carbon turnover and storage in a peaty gley soil

We investigated carbon (C) incorporation and sources of C in the surface CO₂ flux at two sites in northern England on peaty (stagnohumic) gley soil, one afforested by Picea sitchensis, the other under continuous Molinia grassland cover. Radiocarbon (¹⁴C) derived from atmospheric nuclear weapons testing was used to trace the incorporation of C into the soil and sources of C in the soil CO₂ flux from the soil surface and deeper layers. Larger values of ¹⁴CO₂ in surface flux were found at the afforested site (109–110 per cent modern (pM) compared with 107–108 pM at the grassland site). Surface litter fractions (O_i horizon) from the afforested site showed larger ¹⁴C signatures than the equivalent fractions in the grassland (113–115 pM in the forest compared with 106–109 pM in the grassland). Fine root fractions (<2 mm, O_e horizon) had similar signatures at both sites (109 pM in the forest compared with 109–111 pM in the grassland). Humified fractions at 10‐cm depth (O_a horizon) showed smaller signatures (100–103 pM) in the forest than the equivalent fraction in the grassland soil (106–114 pM). According to a mixing model that takes into account pool size and ¹⁴C signature, the contributions to surface CO₂ fluxes from slow turnover fractions that had resided in the soil for more than one year were greater at the forested site than the grassland site, but contributions from fast‐turnover C fixed within the year prior to study showed the opposite trend. The results, taken together with previous work indicating that both site preparation and clear‐felling lead to a net loss of C, indicate that long‐term fixation in deep soil organic fractions is limited on this soil type under plantation forest over 40–50‐year commercial rotations.     

The Rhizofiltration of Sodium from Hydroponic Fluid using Scented Geraniums

The ability of two scented geraniums, Pelargonium sp. `Frensham' and Pelargonium sp. `Citrosa' to tolerate and accumulate salt was assessed in a hydroponic system under greenhouse conditions. Rooted cuttings were exposed to a range of salt concentrations (0 to 200 mM NaCl) over a two-week period. No visible signs of phytotoxicity were observed on scented geranium plants grown in solutions up to 100 mM sodium chloride. Tolerance to salt exposure was assessed with chlorophyll a fluorescence parameters. A significant decline in the efficiency of the photosystem (Fv/Fm) was observedin Frensham plants exposed to 200 mM NaCl for 14 days. The numberand size of active reaction centers (Fv/Fo) declined with increasing NaCl treatments in both species. Total chlorophyll content of both species decreased with increasing salt treatmentas a result of significant reductions in the chlorophyll acontent. At higher levels of sodium chloride treatment, salt extrusion was observed on the petioles and the leaf lamina. An accumulation in excess of 3.7 and 2.6% of the dry weight of Frensham plants as sodium was observed in shoots and roots, respectively. The effect of the accumulated sodium on the physiology of scented geraniums was assessed through biochemicalanalysis. The determination of amino nitrogen and stress-relatedmarkers revealed an initial increase in 4-aminobutyrate, proline,asparagine, glutamine, and alanine in the root tissues. Shoot analysis showed gradual increases in asparagine, aspartate, andalanine. These data provide the first evidence for the salt tolerating and accumulating potential of Pelargonium sp. and demonstrate the efficacy of this plant species for the remediation of salt contaminated hydroponic solutions.     

Prenatal and postnatal influences on growth and fat measurements in swine

Data from 153 foster groups, each consisting of a dam and a nurse, were analyzed separately for breed (Lacombe, Yorkshire) parity (first, second), and sex of piglet (boar, gilt) to estimate prenatal, postnatal and prenatal X postnatal influences on growth and fat measurements. Significant differences were not observed between breeds, parity and sex of piglets; the estimates were pooled over these traits. Prenatal effects were the major contributing factor in the determination of preweaning growth rate, weaning weight, postweaning average daily gain and allometric growth coefficient, rib and loin fat deposition coefficients. Postnatal influence was of minor importance and the prenatal X postnatal interaction was of negligible consequence. These observations indicated that crossfostering of piglets between parities and breeds without regard for the sex of the piglet would not seriously bias subsequent performance testing results. Heritability estimates for weaning weight, postweaning growth rate and backfat thickness differed from published values.     

Plant-Available Phosphorus after Application of Synthetic Chelating Agents

Fertilizer phosphorus (P) can become immobilized in acidic soils through bonds with iron (Fe) and aluminum (Al). Two chelating agents, ethylenediamine tetraacetic acid disodium salt (EDTA) and hydroxyethyl ethylenediamine triacetic acid (HEEDTA), were tested in a greenhouse study for efficiency at increasing plant-available P to corn (Zea mays L.). Fertilizer P was added with or without chelate to the center of pots, simulating a starter band of P. Without the presence of chelates, biomass above and below ground increased linearly as P fertilizer rates increased at 0, 9.6, 19.3, 28.9, and 38.5 kg P ha^?1. Applications of EDTA and HEEDTA did not significantly increase water-soluble P (WSP), Mehlich 1 P, and Mehlich 3 P compared to soils without chelates. Applications of EDTA increased P uptake in the belowground biomass. Despite previous research showing that chelates increased WSP in soils, a decrease in P sorption was not observed with the additions of chelating agents to soils.     

Changes in the conservation status of Australian birds resulting from differences in taxonomy, knowledge and the definitions of threat

When the conservation status of Australian bird taxa in 1992 was retrospectively reassessed in 2000, the status of nearly 70% had to be changed. About 20% of the differences could be attributed to changes in the predictions of extinction probability. Most differences arose from refinement of ICUN Red List Categories and Criteria. Research showed that some populations were more threatened than realised and a few changes resulted from taxonomic revision. Funds might have been distributed differently had the adjusted analysis been available in 1992. Nevertheless, comparisons between either the original or the revised 1992 list and the 2000 list demonstrate degeneration in overall status of threatened birds in Australia. It is concluded that trends in conservation status are a valid long-term measure of the risk of biodiversity loss. Stabilisation of IUCN Red List definitions should mean that an increasing proportion of the status flux should be attributable to real changes in extinction probability.