As above,not so below: Long-term dynamics of net primary production across a dryland transition zone

Drylands are key contributors to interannual variation in the terrestrial carbon sink, which has been attributed primarily to broad-scale climatic anomalies that disproportionately affect net primary production (NPP) in these ecosystems. Current knowledge around the patterns and controls of NPP is based largely on measurements of aboveground net primary production (ANPP), particularly in the context of altered precipitation regimes. Limited evidence suggests belowground net primary production (BNPP), a major input to the terrestrial carbon pool, may respond differently than ANPP to precipitation, as well as other drivers of environmental change, such as nitrogen deposition and fire. Yet long-term measurements of BNPP are rare, contributing to uncertainty in carbon cycle assessments. Here, we used 16 years of annual NPP measurements to investigate responses of ANPP and BNPP to several environmental change drivers across a grassland–shrubland transition zone in the northern Chihuahuan Desert. ANPP was positively correlated with annual precipitation across this landscape; however, this relationship was weaker within sites. BNPP, on the other hand, was weakly correlated with precipitation only in Chihuahuan Desert shrubland. Although NPP generally exhibited similar trends among sites, temporal correlations between ANPP and BNPP within sites were weak. We found chronic nitrogen enrichment stimulated ANPP, whereas a one-time prescribed burn reduced ANPP for nearly a decade. Surprisingly, BNPP was largely unaffected by these factors. Together, our results suggest that BNPP is driven by a different set of controls than ANPP. Furthermore, our findings imply belowground production cannot be inferred from aboveground measurements in dryland ecosystems. Improving understanding around the patterns and controls of dryland NPP at interannual to decadal scales is fundamentally important because of their measurable impact on the global carbon cycle. This study underscores the need for more long-term measurements of BNPP to improve assessments of the terrestrial carbon sink, particularly in the context of ongoing environmental change.     

Individual differences in sensitivity to bitter-tasting substances

Perception of several bitter-tasting compounds was tested in52 subjects. Stable individual differences in the perceivedintensity of the bitterness of suprathreshold concentrationsof quinine sulfate (QSO₄) and urea were found. Whereas 18 subjectsjudged selected concentrations of these compounds to be equallybitter, 17 found QSO₄ to be more bitter than urea, and 17 foundurea to be more bitter than QSO₄. These reliable individualdifferences were significantly related to threshold sensitivityto QSO₄; that is, individuals who perceived QSO₄ to be moreintense than urea at suprathreshold concentrations also hadlower QSO₄ thresholds than did those who perceived urea to bemore intense than QSO₄. There appeared to be no relationshipbetween the relative perceived intensities of these compoundsand rating of the bitterness of PROP (6-n-propylthiouracil).However, QSO₄-sensitive individuals tended to find the bitternessof suprathreshold caffeine and sucrose octaacetate to be greaterthan that of suprathreshold magnesium sulfate, whereas the reversewas true for urea-sensitive individuals. This pattern parallelsthe pattern of cross-adaptation among these compounds reportedby other investigators. These results are consistent with theexistence of multiple bitter transduction sequences and suggestthat individual differences in response to various bitter compoundsmay reflect differences in teh relative availability of specifictransduction sequences.     

Use of the polymerase chain reaction and 16S rRNA sequences for the rapid detection of Brochothrix spp. in foods

Oligonucleotide primers were designed against rRNA sequences to give a DNA-based PCR assay for the rapid identification/detection of Brochothrix spp. The PCR products could be confirmed by hybridization to an internal oligonucleotide probe. The method successfully and sensitively detected/identified these organisms in pure cultures but was of limited value as a detection method because the detection sensitivity, in relation to conventional plate counts, varied and the assay sensitivity was reduced in the presence of staphylococci. Furthermore, sensitivity was also lost when the assay was applied directly to meat samples. However, a separation step using a lectin (from Agaricus bisporus ) immobilized on magnetic beads prior to the PCR assay, allowed the direct detection of low numbers (> 10 cfu g^-1) of Brochothrix in meat samples within a working day.     

Experimental analysis of patch dynamics in tallgrass prairie plant communities

Abstract. Previous research has indicated that patch structure at small spatial scales (<100m²) in tallgrass prairies was defined by a diverse array of infrequent species because dominant species occurred in all samples at this scale. Also, patch structure was not significantly different from that derived from random species associations. Based on these results, we hypothesized that remo val of a dominant species would have no effect on patch structure in these prairies. We tested this hypothesis by removing a dominant grass, Schizachyrium scoparium (Poaceae), from half of each of four 10 m × 10 m study blocks, and comparing differences in patch structure between control and removal halves before and after removal. The minimum resolution in our study was 1 m². Patches of similar species composition were defined by cluster analysis of presence/absence data and cover data. Patch sizes ranged from 1 to 34 m². Following the removal of S. scoparium there was an overall increase in the number of species in the removal half of each block compared to pre-treatment levels. However, the number of patch types and number of spatially mapped groups, based on presence/absence or cover data, did not change between control and removal plots after the removal of S. scoparium. This supports the hypothesis that removal of a large, dominant species would have no effect on patch structure at this scale of resolution in these prairies. Thus, patch structure, as defined here, is an emergent property in these grasslands that is not predictable from changes in species composition. This property of stochastic patch structure results from interactions of processes operating at scales both larger and smaller than our scale of resolution. Stochastic models may provide a reasonable approach to modelling small-scale patch dynamics in tallgrass prairie communities.     

Murine FGF-4 gene expression is spatially restricted within embryonic skeletal muscle and other tissues

Fibroblast growth factors are believed to play many distinct roles in vertebrate development, owing to their ability to stimulate cell growth, prevent cell death, determine cell fate, and inhibit terminal differentiation in a variety of in vitro culture systems. We have used in situ hybridization to localize fibroblast growth factor-4 (FGF-4, also termed HST and K-FGF) gene expression in 7.5 to 16.5 day gestation mouse embryos. Seven discrete sites of gene expression were detected: (1) primitive streak (E7.5–8.5); (2) paraxial presomitic mesoderm in the trunk (E7.5–11.5); (3) primitive neuroectoderm (E8.0–8.5); (4) pharyngeal pouch endoderm (E8.5–9.5); (5) branchial arch ectoderm (E8.5–9.5); (6) limb apical ectoderm (E10.5–12.5), and (7) skeletal myoblast groups (E9.5–13.5). FGF-4 gene expression is spatially restricted within many of these sites. The profile of FGF-4 gene expression among skeletal muscle groups is overlapping, but distinct, from that of FGF-5, thereby revealing myoblast heterogeneity at the molecular level and suggesting distinct roles for multiple FGFs in muscle development.     

Strain distribution pattern in AXB and BXA recombinant inbred strains for loci on murine Chromosomes 10, 13, 17, and 18

Strain distribution patterns (SDPs) of selected loci previously mapped to murine Chromosomes (Chrs) 10, 13, 17, and 18 are reported for the AXB, BXA recombinant inbred (RI) strain set derived from the progenitor strains A/J (A) and C57BL/6J (B). The loci included the simple sequence length polymorphisms (D10Nds1, D10Mit2, D10Mit10, D10Mit14, D13Mit3, D13Nds1, D13Mit10, D13Mit13, D13Mit7, D13Mit11, D17Mit18, D17Mit10, D17Mit20, D17Mit3, D17Mit2, D18Mit17, D18Mit9, and D18Mit4), the restriction fragment length polymorphisms Pdea and Csfmr, and the biochemical marker AS-1. These loci were chosen because they map to genomic regions that had few or no genetic markers in the AXB, BXA RI set. Several of these loci also were typed in backcross progeny of matings of the (AXB)F₁ to strain A or B. The strain distribution patterns for chromosomes 10, 13, 17, and 18 are reported, and the gene order and map distances determined from the backcross data. The addition of these markers to the AXB, BXA RI strain set increases the genomic region over which linkage for new markers can be detected.     

Characterization of a proteinaceous antimicrobial produced by Lactobacillus helveticus CNRZ450

An antimicrobial substance which resembles a bacteriocin was identified in culture supernatant fluids of Lactobacillus helveticus strain CNRZ450. The bacteriocin was active against a narrow range of strains from closely rested species of homofermentative lactobacilli. Its mode of action appeared to be bacteriostatic. Partial purification of the bacteriocin suggested that it was a complex protein with a mol. wt of between 30 and 50 kDa, although there is some evidence that the polypeptide monomer has a mol. wt of around 17 kDa. There was no evidence indicating an extrachromosomal location for its genetic determinant. PCR generated an amplicon from total DNA from strain CNRZ450 using primers based on the helJ gene sequence. A fragment showing homology to this amplicon was located in an Eco RI digest of total DNA from strain CNRZ450. The pattern obtained was different from that obtained with the helveticin J producer strain NCFB481. It is possible, therefore, that the antimicrobial from strain CNRZ450 is related to helveticin J at the DNA sequence level although the physical properties of the two antimicrobials reveal several differences.