Pocono mesic till barrens in retreat: topography,fire and forest contagion effects

The Pocono mesic till barrens (PMTB) are a unique assemblage of fire-maintained shrub communities that support numerous rare species. Historically these barrens covered a large area in the vicinity of Long Pond, Pennsylvania, USA. However, due largely to regional fire suppression instituted in the early 1960s, over 70% of the area covered by barrens succeeded to fire-intolerant forest that does not support the rare species. We investigated the influence of forest proximity on barrens succession across three geomorphic types during periods of high fire frequency and fire suppression, testing the hypothesis that forest processes such as seed rain, shading, and detrital enrichment of soils enhances barrens succession through a contagion effect. Evidence of a forest contagion effect should be shown by increased rates of barrens succession with increasing proximity to the nearest forest edge. In order to detect a forest contagion effect, barrens persistence and barrens succession were modeled in proximity zones of 0-50 m, 50-100 m, 100-200 m, and greater than 200 m from the nearest forest edge. We used existing GIS data layers for fire, geomorphology, and vegetation distribution in 1938, 1963, and 1992. The layers were modified and overlain using ArcView software to determine persistence and succession rates for each unique combination of layers in each proximity zone from 1938 to 1963 (pre-fire suppression) and 1963 to 1992 (post-fire suppression). ANCOVA results indicate that proximity to the nearest forest edge significantly affected barrens persistence rates in both time periods, but succession rates were significantly affected in 1938 to 1963 only. Twenty-eight percent of the 1938 barrens succeeded to forest by 1963; 56% of the 1963 barrens became forest by 1992. Results support previous findings that barrens persistence is enhanced by increased fire frequency, and that barrens persist longer where they overlie flat glacial till than on other geomorphology types.     

Penetration, Development and Emigration of Juveniles of the Nematode Meloidogyne arenaria in Myrobalan Plum (Prunus cerasifera) Clones Bearing the Ma Resistance Genes

Penetration, development and emigration of M. arenaria in the roots of three Myrobalan plum (Prunus cerasifera) clones genetically characterized for their resistance to root-knot nematodes (RKN) were studied during the 10 (penetration) and 15 (emigration) days following the date of inoculation (D) of 2500 juveniles (J2s) per plant into the soil. Miniaturized tests were conducted on the two resistant clones P.2175 (Ma1 gene) and P.1079 (Ma2 gene) and the susceptible clone P.2032 (recessive for both genes), obtained from micropropagated plantlets and grown in mini-containers under controlled conditions at 25°C in a growth chamber. For penetration and development studies, nematodes in the roots were recovered by the acid fuchsin-lactophenol staining technique. Equivalent numbers of J2s were recovered in all the clones at D+1 and D+2. Subsequently, the numbers increased rapidly in P.2032 and were significantly different from those in P.1079 and P.2175 that remained at a low level. No swollen larvae were observed in the resistant clones. In P.2032, the first swollen larvae were observed at D+4, the first females were observed at D+12, whereas the first females with attached egg sacs and the first new-generation J2s were obtained between D+21 and D+28. Our data suggest that the resistance phenomenon does not act on the very early nematode penetration but acts later by preventing feeding-site induction and development into the third-stage. For emigration studies, plants in which J2s had been allowed to penetrate for two days (from D to D+2) were washed free of soil, repotted and then, after various periods of growth, soil-free roots were placed under a mistifier to evaluate the numbers of emigrating individuals. Emigration of J2s from the roots occured mainly from D+2 to D+4 in all the genotypes and was very limited from D+4 to D+10. There was no significant differences in the number of emigrated juveniles between the resistant and susceptible clones, indicating that emigration cannot explain the difference in the numbers of nematodes recovered in the roots.     

Phosphorylation by p38 MAPK as an alternative pathway for GSK3beta inactivation

Glycogen synthase kinase 3beta (GSK3beta) is involved in metabolism, neurodegeneration, and cancer. Inhibition of GSK3beta activity is the primary mechanism that regulates this widely expressed active kinase. Although the protein kinase Akt inhibits GSK3beta by phosphorylation at the N terminus, preventing Akt-mediated phosphorylation does not affect the cell-survival pathway activated through the GSK3beta substrate beta-catenin. Here, we show that p38 mitogen-activated protein kinase (MAPK) also inactivates GSK3beta by direct phosphorylation at its C terminus, and this inactivation can lead to an accumulation of beta-catenin. p38 MAPK-mediated phosphorylation of GSK3beta occurs primarily in the brain and thymocytes. Activation of beta-catenin-mediated signaling through GSK3beta inhibition provides a potential mechanism for p38 MAPK-mediated survival in specific tissues.     

Effect of Foliar Application of Phosphorus on Winter Wheat Grain Yield,Phosphorus Uptake,and Use Efficiency

ABSTRACT

One would expect foliar applied phosphorus (P) to have higher use efficiencies than when applied to the soil, but limited information is available concerning this. Experiments were conducted in 2002, 2003, and 2004 to determine the effect of foliar applications of P on winter wheat grain yields, P uptake, and use efficiency. Twelve treatments containing varying foliar P rates (0, 1, 2, and 4 kg ha^{? 1} in 2002 and 2003 and additional 8, 12, 16, and 20 kg ha^{? 1} in 2004) with and without pre-plant rates of 30 kg ha^{? 1} were evaluated. Foliar applications of P at Feekes 7 generally increased grain yields and P uptake versus no foliar P. Use efficiency was higher when P was applied at Feekes 10.54. Results from this study suggested that low rates of foliar applied P might correct mid-season P deficiency in winter wheat, and that might result in higher P use efficiencies.     

Effects of a plant parasitic nematode (Heterodera trifolii) on clover roots and soil microbial communities

We studied the effects of the root endoparasitic nematode Heterodera trifolii on rhizodeposition and the root architecture of white clover (Trifolium repens). Rhizosphere solutions were collected from the root systems of plants growing with and without H. trifolii (200 juveniles per inoculated plant) in sand-based microlysimeters. The organic carbon (C) content of these solutions was analyzed, and they were applied to plant-free soils to investigate microbial responses. Although plant biomass was unaffected by nematodes, the architecture of the root systems was significantly altered, with a decrease in overall root length and an increase in the density of lateral branches from the primary root. The presence of nematodes reduced the concentration of organic compounds in the rhizosphere solutions but only on the final sampling date (75 days). Analysis of microbial signature phospholipid fatty acids revealed no change in the structure of the microbial communities in soils to which rhizosphere solutions were applied. However, these microorganisms did respond with changes in substrate utilization patterns (community-level physiological profiles). Microbes in soils that received rhizosphere solutions from the nematode-infected clover showed lower utilization of most substrates but higher utilization of oligosugars. These responses appear to be related to changes in roots and rhizodeposition associated with nematode infection of clover roots. The results of this study suggest that root herbivory can negatively impact carbon-limited soil microbial communities via changes in root architecture that moderate rhizodeposition.     

商陆(Phytolacca acinosa Roxb.)的锰耐性和超积累

超积累植物的确证对成功实施重金属污染环境植物修复是必不可少的。通过野外调查和营养液培养试验 ,研究超积累植物商陆 (PhytolaccaacinosaRoxb )的锰富集特性 ,结果表明 ,商陆对生长介质中的Mn具有很强的耐性和累积能力。商陆在锰含量高达 114× 10 3 mgkg-1的尾矿废弃地上依然生长良好 ,叶锰含量最高达 19 3× 10 3 mgkg-1。温室培养条件下 ,当生长介质中Mn浓度为 8 0 0 0mmolL-1时 ,虽然其生物量与对照相比有所降低 ,但植株仍能生长。随着生长介质中Mn浓度的升高 ,商陆叶和茎的Mn含量逐渐增加 ,生物富集系数则逐渐降低 ,但是地上部分锰积累量则先增加后减少。当Mn浓度为 5 0 0 0mmolL-1时 ,商陆地上部分锰积累量达到最大值 2 5 8 2mgplant-1;当Mn浓度为 12 0 0 0mmolL-1时 ,商陆仍能完成整个生命周期 ,叶锰含量达到最大值 36 4× 10 3 mgkg-1,生物富集系数为 5 5。不同锰供应水平下 ,商陆吸收的锰有87%～ 95 %被转移到地上部分。这进一步验证商陆的锰超积累特性 ,为利用超积累植物对大面积污染土壤实施植物修复提供了有力证据 ,对锰污染土壤和水体实施植物修复具有很大的应用前景     

Biofumigant Biomass,Nutrient Content,and Glucosinolate Response to Phosphorus

Information on biofumigant-green manure vegetative biomass, nutrient, and glucosinolate content sensitivity to phosphorus (P) is lacking for species used in potato and sugarbeet production. Therefore, available P effects on field-grown condiment yellow mustard (Sinapis alba, cv. IdaGold) and oilseed radish (Raphanus sativa, cv. Colonel) were evaluated (2001–03). Low soil P was generally more limiting to radish foliage P concentrations or uptake than to the mustard, suggesting inherent differences in their ability to access and accumulate P. While radish P and S concentrations increased with higher P, concentrations in mustard were either unaffected or reduced. Foliage P concentrations were more closely related to biomass of radish (r² = 0.46) than mustard (r² = 0.11). Mustard exceeded radish in biomass and S accumulation. Phosphorus effects on glucosinolates producing ionic or isothiocyanates were relatively insignificant. These biofumigants differ appreciably in their ability to access and accumulate P, but P effects on nutrient content or glucosinolates were minor.     

Nomenclature and genetic relationships of apples and pears from Terceira Island

Heritage apple (Malus domestica Borkh. hybrids) and pear (Pyrus communis L. hybrid) trees grow in villages throughout Terceira Island, Azores, Portugal. Some of these pears have different names but similar morphology. The objective of this study was to determine synonymy, homology, and phylogeny of apples and pears from Terceira and to examine potential relationships of the island pears with standard apples and pears of Portuguese or American descent. Nine apple microsatellite markers were used to determine genetic relationships. Distance- and parsimony-based cluster analysis grouped these genotypes into separate apple and pear clades. The Terceira apples were divided into two clades: the maçā and the reineta-reinette. Among the 17 heritage apple genotypes, seven unique accessions were identified and four groups of synonyms, or possibly clones, were detected including: ‘Reineta Agosto’ and ‘Reineta Verde’ from Altares; ‘Reineta Castanha’ and ‘Reineta Verde Miuda’; ‘Maçā Pêra,’ ‘Maçā Calhau’, ‘Pêro Branco’ from Salga and from Terra-Chā and ‘Maçā Marmelo’; and the five genotypes ‘Maçā Sao Joao’, ‘Malápio Rosa’, ‘Maçā Gaspar’, ‘Maçā Branca’ and ‘Maçā Pato’. In addition, two homonyms were detected. ‘Pêro Vermelho’ from Terra Chā was a separate genotype from a tree from Doze Ribeiras of the same name, but Pêro Branco from Terra Chā appears to be a clone that can be distinguished by an additional allele at CH1F07a from a tree with that name from Salga. One pair of apple clones, ‘Reineta Agosto’ and ‘Reineta Verde’ from Altares appear to be derived from an unreduced gamete of ‘Golden Delicious.’ Another apple genotype ‘Maçā Acida’ could be a sibling of the ‘Maçā Pêra’ clonal group. Other tested standard apples from the US genebank were unrelated to Terceira genotypes. Of the seven heritage pears, five unique genotypes and one pair of synonyms were detected. ‘Pêra Papo Pintassilgo’ from Raminho and ‘Pêra Vermelha’ from the nursery of Serviço de Desenvolvimento Agario da Terceira (SDAT) were synonyms. ‘Passans du Portugal’ was related to ‘Pêra Cabaca’ but other standard pears from the US genebank were unrelated to Terceira genotypes. Future studies will include additional apple and pear cultivars from other Islands of the Azores and continental Portugal, and wild Asian species to further explore genetic relationships.     

Regulation of blood glucose by hypothalamic pyruvate metabolism

The brain keenly depends on glucose for energy, and mammalians have redundant systems to control glucose production. An increase in circulating glucose inhibits glucose production in the liver, but this negative feedback is impaired in type 2 diabetes. Here we report that a primary increase in hypothalamic glucose levels lowers blood glucose through inhibition of glucose production in rats. The effect of glucose requires its conversion to lactate followed by stimulation of pyruvate metabolism, which leads to activation of adenosine triphosphate (ATP)-sensitive potassium channels. Thus, interventions designed to enhance the hypothalamic sensing of glucose may improve glucose homeostasis in diabetes.     

Whole farm implications on the application of variable rate technology to every cropped field

In the last 10 years precision agriculture has evolved and it is now possible to manage cropping inputs at the sub field scale. However, the expected return generated by these management practices varies with the amount and predictability of the spatial variation in crop yield across the field and may vary from field to field across the farm. We analysed the spatial variation of crop yield from 20 fields totalling 2832 ha from a 5200 ha farm in Western Australia at the field and the sub field scale to determine the economic value of introducing variable rate management (VRT) strategies to fields across the entire farm. In this case study, 6 out of 20 fields generated an additional economic payoff of AU$15/ha when managed with VRT over uniform management. Sensitivity analysis found that the starting levels of soil fertility were an important driver of the payoff for managing a field with VRT. If starting soil fertility was low and uniform across the field, then no fields generated an economic return of more than AU$7.00/ha when managed with VRT. Other factors, including commodity price, fertiliser price, amount of variation in crop yield within the field moderately increased the value of adopting VRT across fields within farm the value of VRT increased if fertiliser budgets were constrained, particularly if the yield distribution of the field was negatively skewed. While VRT does add value to many fields across the farm, the gains are small and the technology must be implemented cheaply for it to be viable.