Extracellular enzyme activity in the mycorrhizospheres of a boreal fire chronosequence

Saprotrophic microbes are typically credited with producing extracellular enzymes that recycle organic matter, though roots and mycorrhizal fungi also can contribute and may compete with the saprotrophs. We examined extracellular enzyme activity associated with the mycorrhizospheres of arbuscular mycorrhizal, ectomycorrhizal, dual-colonized (arbuscular and ectomycorrhizal), and ericoid mycorrhizal plants in a fire chronosequence in Alaska. Bulk soil and soil from beneath host plants were gathered in July 2004 and assayed for five enzymes that target organic C, P, and N substrates. Compared to bulk soil, activities of the C-targeting enzymes β-1,4-glucosidase and peroxidase were lower in arbuscular mycorrhizospheres and ericoid mycorrhizospheres, respectively. Moreover, extracellular enzyme activity varied among mycorrhizosphere types. Specifically, N-targeting leucine aminopeptidase was highest in arbuscular mycorrhizospheres, followed by ericoid and ectomycorrhizal/dual-colonized mycorrhizospheres; β-1,4-glucosidase had the reverse pattern. In addition, enzymatic stoichiometry suggested that extracellular enzyme producers invested more in C-acquisition than in N-acquisition in recent fire scars compared to mature forests. These data extend previous findings that roots and mycorrhizal fungi compete with saprotrophs by showing that the strength of this effect varies by mycorrhizal host. As a result the community composition of mycorrhizal host plants might mediate enzymatic activity in boreal soils.     

The effect of dicyandiamide on pasture nitrate concentration,yield and N offtake under high N loading in winter and spring

High nitrate () concentrations in pastures and forages represent a health risk to grazing livestock. A field trial was conducted on the Lincoln University Dairy Farm, New Zealand, to investigate the effects of applying the nitrification inhibitor dicyandiamide (DCD) on soil extractable N and pasture concentrations in winter and spring. Treatments were control (T1), urea (T2), urea + DCD (T3), May urine + DCD (T4), August urine + DCD (T5), May urine (T6) and August urine (T7). Urine treatments were applied to the ryegrass‐white clover pasture in either May or August. The DCD treatments were applied at 10 kg DCD ha^?1 in May and August and urea at 25 kg N ha^?1 at selected intervals. Soil samples (0‐ to 75‐ and 75‐ to 150‐mm horizons) were taken regularly to monitor soil and ammonium () levels. Six pasture harvests were conducted from August 2007 to March 2008 and samples analysed for ‐N concentrations and total N content. Application of DCD significantly (P < 0·001) increased total dry‐matter (DM) production by 39 and 42% for the autumn and spring urine treatments, respectively, compared to the urine‐alone treatments. In addition, the application of DCD also significantly (P < 0·001) increased DM yield by 12% on the urea‐only treatment. DCD significantly (P < 0·001) reduced pasture concentrations in both autumn‐ and spring‐applied urine treatments where DCD was applied. This was directly linked to reductions in soil , and increases in soil , from DCD application. The preferential uptake by pasture for ‐N over ‐N may also have been a contributing factor. DCD application can therefore substantially reduce pasture ‐N concentrations to safe levels under high N‐loading (urine patch) conditions.     

Evaluation of Pseudopteroxazole and Pseudopterosin Derivatives against Mycobacterium tuberculosis and Other Pathogens

Pseudopterosins and pseudopteroxazole are intriguing marine natural products that possess notable antimicrobial activity with a commensurate lack of cytotoxicity. New semi-synthetic pseudopteroxazoles, pseudopteroquinoxalines and pseudopterosin congeners along with simple synthetic mimics of the terpene skeleton were synthesized. In order to build structure-activity relationships, a set of 29 new and previously reported compounds was assessed for in vitro antimicrobial and cytotoxic activities. A number of congeners exhibited antimicrobial activity against a range of Gram-positive bacteria including Mycobacterium tuberculosis H₃₇Rv, with four displaying notable antitubercular activity against both replicating and non-replicating persistent forms of M. tuberculosis. One new semi-synthetic compound, 21-((1H-imidazol-5-yl)methyl)-pseudopteroxazole (7a), was more potent than the natural products pseudopterosin and pseudopteroxazole and exhibited equipotent activity against both replicating and non-replicating persistent forms of M. tuberculosis with a near absence of in vitro cytotoxicity. Pseudopteroxazole also exhibited activity against strains of M. tuberculosis H₃₇Rv resistant to six clinically used antibiotics.     

Trends and management implications of human‐influenced life‐history changes in marine ectotherms

Evidence is accumulating that many marine ectotherms are undergoing rapid changes in their life‐history characteristics. These changes have been variously attributed to fisheries‐induced evolution, inhibited adult growth rate due to oxygen limitation at higher temperatures, and plastic responses to density dependence or changes in ocean productivity. Here, we review the diverse underlying mechanisms by which plastic and evolutionary responses to climate change and fisheries are likely to produce similar life‐history trends in harvested marine ectotherms, leading to faster life‐histories with earlier maturation and smaller adult size‐at‐age. While mechanistically understanding these growth and maturation changes may be difficult, it is becoming clear that changing life‐histories will lead to modified population dynamics, productivity and natural mortality of the affected species. We discuss how the observed and expected life‐history changes could affect the assumptions and uncertainty within single and multispecies models currently used in marine ecosystem management, highlighting that models which allow for dynamic life‐history traits often report significantly different estimates of stock biomass. Given that both climate‐ and harvest‐induced life‐history changes are likely to intensify and possibly amplify each other, there is an urgent need to adequately assess the implications of faster life‐histories for marine ecosystem management. This is especially true for data‐poor stocks, where growth and maturation are not regularly assessed. Targeted monitoring can be used to inform responsive management, but for improved sustainability outcomes, a precautionary approach to management that is robust to life‐history trends is advised.     

Growth and gut morphology of diploid and triploid juvenile Atlantic cod (Gadus morhua)

The objective of this paper was to compare the growth and gut morphology of juvenile diploid and triploid Atlantic cod (Gadus morhua) reared under similar conditions. Individually tagged 36‐week‐old diploid (mean weight 49.3 ± 13.8 g) and triploid (mean weight 43.6 ± 11.2) juvenile cod were measured at intervals during a 29‐week growth trial. Data for weight, length, condition factor (K), hepato‐somatic index (HSI), gonado‐somatic index (GSI), Relative Gut Length (RGL) and pyloric caeca number were collected and results were analysed in relation to ploidy status, gender and family contribution. At the end of the experiment, only one family (M2xF3) had many representatives with a relatively even distribution of sexes and ploidies. Diploid females were significantly heavier and had higher K than triploid females in the M2xF3 family (body weight 371.2 ± 120.2 vs. 298.4 ± 100.7 g; K 1.1 ± 0.1 vs. 0.93 ± 0.1), but no differences were found between diploid and triploid males. In the other families (pooled data), no differences in body weight were found between the ploidy groups. In general, triploids had a shorter intestine (RGL) and fewer pyloric caeca than their diploid siblings regardless of gender suggesting possible impairments in nutrient utilization and growth.     

Management strategy evaluation: best practices

Management strategy evaluation (MSE) involves using simulation to compare the relative effectiveness for achieving management objectives of different combinations of data collection schemes, methods of analysis and subsequent processes leading to management actions. MSE can be used to identify a ‘best’ management strategy among a set of candidate strategies, or to determine how well an existing strategy performs. The ability of MSE to facilitate fisheries management achieving its aims depends on how well uncertainty is represented, and how effectively the results of simulations are summarized and presented to the decision‐makers. Key challenges for effective use of MSE therefore include characterizing objectives and uncertainty, assigning plausibility ranks to the trials considered, and working with decision‐makers to interpret and implement the results of the MSE. This paper explores how MSEs are conducted and characterizes current ‘best practice’ guidelines, while also indicating whether and how these best practices were applied to two case‐studies: the Bering–Chukchi–Beaufort Seas bowhead whales (Balaena mysticetus; Balaenidae) and the northern subpopulation of Pacific sardine (Sardinops sagax caerulea; Clupeidae).     

Liming an acid soil treated with diverse silicon sources: Effects on silicon uptake by sugarcane (Saccharum spp. hybrids)

Highly weathered soils are typically acid, with low plant-available silicon (Si), and may also be high in soluble aluminum (Al). We tested whether pre-liming an acid soil prior to silicate fertilizer application improved Si uptake by sugarcane (Saccharum spp. hybrids), feasibly through elimination of reactive Al. Three trials with potted sugarcane were grown in an acid soil. Treatments included 11 different Si sources and 1- or 3-month pre-liming periods. Soil and plant tissue Si content and yield were determined. Pre-liming for a 1- or 3-month period did not increase plant Si uptake and reduced available soil Si throughout. Alkaline Si sources produced significantly more plant-available Si and greater plant uptake than non-alkaline sources. Silicon and lime treatments did not significantly increase yield. We conclude that pre-liming an acid soil before Si application is unlikely to significantly improve Si uptake by sugarcane.     

Combining isotopic signatures of n(Sr)/n(Sr) and light stable elements (C,N, O,S) with multi-elemental profiling for the authentication of provenance of European cereal samples

The aim of this work (from the FP6 project TRACE) was to develop methods based on the use of geochemical markers for the authentication of the geographical origin of cereal samples in Europe (cf. EC regulations 2081/92 and 1898/06). For the first time, the potential usefulness of combining n(⁸⁷Sr)/n(⁸⁶Sr) and δ¹³C, δ¹⁵N, δ¹⁸O and δ³⁴S isotopic signatures, alone or with key element concentrations ([Na], [K], [Ca], [Cu] and [Rb], progressively identified out of 31 sets of results), was investigated through multiple step multivariate statistics for more than 500 cereal samples collected over 2 years from 17 sampling sites across Europe representing an extensive range of geographical and environmental characteristics.