Dinitrogen fixation and infection of grass leaves byPseudomonas rubrisubalbicans andHerbaspirillum seropedicae

Bacteria causing mottled stripe disease in sugar cane, known asPseudomonas rubrisubalbicans, were shown to be able to fix molecular N₂ and to grow on it. The root associated diazotroph known asHerbaspirillum seropedicae, after artificial inoculation caused mottled stripe disease symptoms on sorghum and Napier grass but not on sugar cane. Both bacteria could be reisolated from leaves even 60 days after. Sugar cane leaves contained large numbers of these bacteria even in the uninoculated controls. Additional physiological characteristics of six strains ofP. rubrisubalbicans were compared with those of twoH. seropedicae strains and were shown to be very similar.     

The life cycle of Anguina agrostis: Development in host plant

Bird A.F. and Stynes B.A. 1981. The life cycle of Anguina agrostis: Development in the host plant. Internationaljournal for Parasitology11: 431–440. The growth and development of the infective second stage “dauer” larvae (DL₂) of Anguina agrostis into adults have been followed under field conditions in rye grass (Lolium rigidum). Three moults were observed to occur during the parasitic phase of development. From the third (second parasitic) moult onwards, there was much more variability in the size of the female nematodes than in the males and sexual dimorphism became very pronounced. The transition from the DL₂ to the second stage parasitic larva (PL₂) is marked by the disappearance of the numerous lipid storage granules which are characteristic of the DL₂, and the development in the PL₂ of an intestine which becomes more pronounced in each succeeding stage, particularly in the adult female. Anguina agrostis is unusual among parasitic nematodes in that the DL₂ has the thickest cuticle of all stages, including adults. The L₄ and adult males have thicker cuticles than the females at the same stages of development. Moulting appears to involve resorption of the innermost basal zone of the shed cuticle as well as morphological and chemical changes to the epicuticle.     

Turfgrass (Cynodon dactylon L.) sod production on sandy soils: II. Effects of irrigation and fertiliser regimes on N leaching

The effects of irrigation and fertiliser regimes on N leaching from the production of couch grass (Cynodon dactylon L.) sod, on a free-draining sandy soil, were evaluated in a 22-month field study. The experimental design used a randomised-block, split-plot design with three replicates. Main plots consisted of two irrigation treatments: 70 and 140% daily replacement of pan evaporation; four subplot fertiliser types (water-soluble (predominately NH₄NO₃), control-release, pelletised poultry manure and pelletised biosolids); and three N application rates (100, 200 and 300 kg N ha⁻¹ per crop). Nitrogen leaching was assessed by measuring the leachate volumes and concentrations of N species leached from soil lysimeters (250 mm in diameter by 950 mm in length) installed in 10 m² turfgrass plots. Nitrogen leaching ranged from 33 to 167 kg N ha⁻¹ over 22 months, depending upon the irrigation and fertiliser treatment. Irrigation treatment affected N leaching more than fertiliser treatment, and increasing the irrigation from 70 to 140% replacement of daily pan evaporation increased N leaching for all fertiliser types, and by up to four times. Forty six to 76% of losses occurred from the high irrigation treatments during the first 16 weeks after the turfgrass was planted as rhizomes. By contrast, N leaching did not appear to increase following harvest of sod. At the high irrigation treatment, N leaching was greater for the pelletised biosolids than the control-release; while at the low irrigation treatment, N leaching did not vary between fertiliser types. A significant proportion of the N leached was in the organic form. Therefore, we recommend total N and mineral N be measured when assessing N leaching from turfgrass. Nitrogen leaching from turfgrass production is low from all fertiliser types when the irrigation matches turfgrass water use and N is applied at a rate and frequency that approximates turfgrass requirements. Section Editor: P. J. Randall     

A proposed CO2-controlled mechanism of woody plant invasion in grasslands and savannas

We propose that elevated CO₂ may have a significant positive effect on woody plant success and thus favour tree invasion and thickening in grass‐dominated ecosystems. We note that savanna tree biomass is strongly constrained by disturbance, particularly fire, and that elevated CO₂ could act to reduce this constraint. Our argument combines knowledge of tree recovery from injury after grassland fires, with theory about carbon acquisition and carbohydrate storage patterns in C3 woody plants in response to elevated CO₂. We propose simply that elevated CO₂ will tend to favour regrowth of juvenile trees trapped (sometimes for decades) in the ‘topkill’ zone, thus allowing them to escape more readily from periodic fires as CO₂ continues to rise. Little empirical evidence exists to test this hypothesis, even though the process may have important implications for tree/grass codominated ecosystems currently in a dynamic equilibrium.     

Distribution,community characteristics and classification of Stipa tianschanica var. klemenzii steppe in China

Stipa tianschanica var. klemenzii steppe is the most typical formation of desert steppe in China. Based on the primary plots data obtained from fieldworks during the growing seasons from 2010 to 2016 as well as some earlier records, we studied the Stipa tianschanica var. klemenzii steppe across China systematically, including the eco-geographical distributions, community characteristics and classifications. The results showed that S. tianschanica var. klemenzii steppe distributed mainly on the Ulan Qab Plateau and western Xilin Gol Plateau. Due to the arid biotope of S. tianschanica var. klemenzii steppe, quantitative characteristics of the assemblage including height, coverage, biomass and species richness were normally lower than that of most Stipa formations in Eurasian steppe region. Moreover, 165 seed plants belonging to 85 genera and 29 families were recorded in the 80 study sites, in which rare species (occurrence frequency <20%) made up 87% of the total plants while common species and constant species could only be found occasionally. Species with the occurrence frequency exceeding 50% included S. tianschanica var. klemenzii, Convolvulus ammannii, Cleistogenes songorica, Allium tenuissimum. In addition, Hemicryptophyte and therophyte were the two dominant life forms, covering 55% and 20% of the species, respectively. As for the ecological type of water, typical xerophytes accounted for 47% of all species which is followed by super-xerophytes and meso-xerophytes. Middle Asian areal-type and east Palaeo-North areal-type were the two major floristic elements, containing 37% and 26% of the species, respectively. Based on the life forms and dominances of the species within the community, S. tianschanica var. klemenzii steppe in China could be classified into 6 association groups, 29 associations.     

Drought mildly reduces plant dominance in a temperate prairie ecosystem across years

1. Shifts in dominance and species reordering can occur in response to global change. However, it is not clear how altered precipitation and disturbance regimes interact to affect species composition and dominance.
2. We explored community‐level diversity and compositional similarity responses, both across and within years, to a manipulated precipitation gradient and annual clipping in a mixed‐grass prairie in Oklahoma, USA. We imposed seven precipitation treatments (five water exclusion levels [?20%, ?40%, ?60%, ?80%, and ?100%], water addition [+50%], and control [0% change in precipitation]) year‐round from 2016 to 2018 using fixed interception shelters. These treatments were crossed with annual clipping to mimic hay harvest.
3. We found that community‐level responses were influenced by precipitation across time. For instance, plant evenness was enhanced by extreme drought treatments, while plant richness was marginally promoted under increased precipitation.
4. Clipping promoted species gain resulting in greater richness within each experimental year. Across years, clipping effects further reduced the precipitation effects on community‐level responses (richness and evenness) at both extreme drought and added precipitation treatments.
5. Synthesis: Our results highlight the importance of studying interactive drivers of change both within versus across time. For instance, clipping attenuated community‐level responses to a gradient in precipitation, suggesting that management could buffer community‐level responses to drought. However, precipitation effects were mild and likely to accentuate over time to produce further community change.

     

FXR在胃粘膜肠化生及胃癌中的表达及其意义研究

目的:研究FXR在胃炎,胃粘膜肠化生及胃癌组织中的表达,分析其在胃癌发生中的意义。方法:采用免疫组化方法检测FXR在55例胃炎组织,61例胃黏膜肠化生组织及61例胃癌组织中的表达,利用统计学方法 SPSS17.0软件分析其在三种组织中的表达变化,结合文献回顾,分析FXR在胃癌发生中的意义。结果:FXR在胃黏膜肠化生中的表达明显高于胃炎组织(P0.05),而在胃癌组织中,FXR的表达显著低于胃粘膜肠化生组织(P0.05)。结论:FXR是一个潜在的胃癌发生生物标记物,其具体机制有待于进一步探索。