金沙江干旱河谷退化草地群落对氮磷施肥的反应

在云南省境内的金沙江干旱河谷区, 选择退化严重的草地群落研究氮磷施肥对群落动态的影响。经过一个生长季的施肥处理, 结果表明, 除大量施磷肥处理(20 g·a^-1·m^-2)时, 可能因施磷过多群落生物量和密度没有出现增加外。其余的施氮和施磷处理均导致群落地上生物量和密度增加, 而且施氮处理引起群落地上生物量和密度增加的程度都高于施磷处理。说明在干旱河谷退化严重的草地生态系统, 氮是限制系统恢复的主要因素。施肥后禾本科草本植物密度大量增加, 而乔灌木密度增加不明显, 群落在短期内变成以禾本科草本植物为主的状态。施氮和施磷没有引起群落种数量和植物多样性指数的明显变化。试验结束时土壤的铵态氮、硝态氮和有效磷浓度没因施肥而增加, 但施肥处理的植物体氮和磷浓度增加。     

Molecular characterization of avian-like H1N1 swine influenza a viruses isolated in Eastern China, 2011

Currently, three predominant subtypes of influenza virus are prevalent in pig populations worldwide: H1N1, H3N2, and H1N2. European avian-like H1N1 viruses, which were initially detected in European pig populations in 1979, have been circulating in pigs in eastern China since 2007. In this study, six influenza A viruses were isolated from 60 swine lung samples collected from January to April 2011 in eastern China. Based on whole genome sequencing, molecular characteristics of two isolates were determined. Phylogenetic analysis showed the eight genes of the two isolates were closely related to those of the avian-like H1N1 viruses circulating in pig populations, especially similar to those found in China. Four potential glycosylation sites were observed at positions 13, 26, 198, 277 in the HA1 proteins of the two isolates. Due to the presence of a stop codon at codon 12, the isolates contained truncated PB1-F2 proteins. In this study, the isolates contained 591Q, 627E and 701N in the polymerase subunit PB2, which had been shown to be determinants of virulence and host adaptation. The isolates also had a D rather than E at position 92 of the NS1, a marker of mammalian adaptation. Both isolates contained the GPKV motif at the PDZ ligand domain of the 3′ end of the NS1, a characteristic marker of the European avian-like swine viruses since about 1999, which is distinct from those of avian, human and classical swine viruses. The M2 proteins of the isolates have the mutation (S31N), a characteristic marker of the European avian-like swine viruses since about 1987, which may confer resistance to amantadine and rimantadine antivirals. Our findings further emphasize the importance of surveillance on the genetic diversity of influenza A viruses in pigs, and raise more concerns about the occurrence of cross-species transmission events.     

Reactivity of [PdCl(μ-med)]2 with monodentate or bidentate ligands. Structure of the dinuclear complexes [Pd(μ-med)(PPh3)]2(BF4)2 and [Pd(μ-med)(bpy)]2(BF4)2. [Hmed=N-(2-mercaptoethyl)-3,5-dimethylpyrazole]

Treatment of the ligand N-(2-mercaptoethyl)-3,5-dimethylpyrazole with [Pd(CH₃COO)₂]₃ and reaction of [PdCl(μ-med)]₂ with pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ produced the following complexes: [Pd(CH₃COO)(μ-med)]₂, [Pd(μ-med)(py)]₂(BF₄)₂ and [Pd(μ-med)(PPh₃)]₂(BF₄)₂. Similar reactions carried out with 2,2^′-bipyridine (bpy) or 1,3-bis(diphenylphosphino)propane (dppp) produced [Pd(μ-med)(bpy)]_x(BF₄)_x (x=1 or 2) and [Pd(μ-med)(dppp)]_x(BF₄)_x (x=1 or 2). Treatment of [Pd(μ-med)(bpy)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced [Pd₃Cl₂(μ-med)₂(bpy)₂](BF₄)₂. Treatment of [Pd(μ-med)(dppp)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced a mixture of [Pd(μ-Cl)(dppp)]₂(BF₄)₂ and [Pd(μ-med)₂(dppp)]²⁺. X-ray crystal structures of [Pd(μ-med)(PPh₃)]₂(BF₄)₂ · 2CH₃CN and [Pd(μ-med)(bpy)]₂(BF₄)₂ · 0.5CH₃OH are presented.     

Elevated CO2 and plant nitrogen-use: is reduced tissue nitrogen concentration size-dependent?

Plants often respond to elevated atmospheric CO₂ levels with reduced tissue nitrogen concentrations relative to ambient CO₂-grown plants when comparisons are made at a common time. Another common response to enriched CO₂ atmospheres is an acceleration in plant growth rates. Because plant nitrogen concentrations are often highest in seedlings and subsequently decrease during growth, comparisons between ambient and elevated CO₂-grown plants made at a common time may not demonstrate CO₂-induced reductions in plant nitrogen concentration per se. Rather, this comparison may be highlighting differences in nitrogen concentration between bigger, more developed plants and smaller, less developed plants. In this study, we directly examined whether elevated CO₂ environments reduce plant nitrogen concentrations independent of changes in plant growth rates. We grew two annual plant species. Abutilon theophrasti (C₃ photosynthetic pathway) and Amaranthus retroflexus (C₄ photosynthetic pathway), from seed in glass-sided growth chambers with atmospheric CO₂ levels of 350 mol·mol^–1 or 700 mol·mol^–1 and with high or low fertilizer applications. Individual plants were harvested every 2 days starting 3 days after germination to determine plant biomass and nitrogen concentration. We found: 1. High CO₂-grown plants had reduced nitrogen concentrations and increased biomass relative to ambient CO₂-grown plants when compared at a common time; 2. Tissue nitrogen concentrations did not vary as a function of CO₂ level when plants were compared at a common size; and 3. The rate of biomass accumulation per rate of increase in plant nitrogen was unaffected by CO₂ availability, but was altered by nutrient availability. These results indicate that a CO₂-induced reduction in plant nitrogen concentration may not be due to physiological changes in plant nitrogen use efficiency, but is probably a size-dependent phenomenon resulting from accelerated plant growth.     

δ13C and δ15N changes after dietary shift in veliger larvae of the slipper limpet Crepidula fornicata: an experimental evidence

δ¹³C and δ¹⁵N measurements are still poorly conducted in benthic invertebrate larvae. To assess the δ¹³C and δ¹⁵N changes occurring after a dietary shift, experiments were conducted on veliger larvae of Crepidula fornicata fed with two cultured microalgae (Isochrysis galbana and Pavlova lutheri) of known isotopic composition, ¹³C-enriched and ¹⁵N-depleted compared to the initial values of the larvae. Rapid changes in larval δ¹³C and δ¹⁵N were observed after the dietary shift, with an increase in δ¹³C and a decrease in δ¹⁵N. After 19 days of feeding, isotopic equilibrium was still not reached, a period which is close to the duration of the pelagic life of the larvae. This implies that the isotopic composition measured in field-collected larvae might only partly reflect actual larval feeding but also the parental isotopic signature, especially during the early developmental stages. Isotopic measurements in marine invertebrate larvae should thus be interpreted cautiously. In planktonic food web investigations, the study of field-collected larvae of different size/developmental stage may reduce potential misinterpretations.     

The role of below-ground competition during early stages of secondary succession: the case of 3-year-old Scots pine (Pinus sylvestris L.) seedlings in an abandoned grassland

In abandoned or extensively managed grasslands, the mechanisms involved in pioneer tree species success are not fully explained. Resource competition among plants and microclimate modifications have been emphasised as possible mechanisms to explain variation of survivorship and growth. In this study, we evaluated a number of mechanisms that may lead to successful survival and growth of seedlings of a pioneer tree species (Pinus sylvestris) in a grass-dominated grassland. Three-year-old Scots pines were planted in an extensively managed grassland of the French Massif Central and for 2 years were either maintained in bare soil or subjected to aerial and below-ground interactions induced by grass vegetation. Soil temperatures were slightly higher in bare soil than under the grass vegetation, but not to an extent explaining pine growth differences. The tall grass canopy reduced light transmission by 77% at ground level and by 20% in the upper part of Scots pine seedlings. Grass vegetation presence also significantly decreased soil volumetric water content (Hv) and soil nitrate in spring and in summer. In these conditions, the average tree height was reduced by 5% compared to trees grown in bare soil, and plant biomass was reduced by 85%. Scots pine intrinsic water-use efficiency (A/g), measured by leaf gas-exchange, increased when Hv decreased owing to a rapid decline of stomatal conductance (g). This result was also confirmed by δ ¹³C analyses of needles. A summer ¹⁵N labelling of seedlings and grass vegetation confirmed the higher NO₃ capture capacity of grass vegetation in comparison with Scots pine seedlings. Our results provide evidence that the seedlings' success was linked to tolerance of below-ground resource depletion (particularly water) induced by grass vegetation based on morphological and physiological plasticity as well as to resource conservation.     

The glutamine commute: take the N line and transfer to the A

The transfer of glutamine between cells contributes to signaling as well as to metabolism. The recent identification and characterization of the system N and A family of transporters has begun to suggest mechanisms for the directional transfer of glutamine, and should provide ways to test its physiological significance in diverse processes from nitrogen to neurotransmitter release.     

Une nouvelle espèce de Podocnemis (Pleurodira, Podocnemididae) provenant du Néogène de la formation Solimões, Acre, Brésil

A Neogene turtle from Brasil is described. It represents the first find of a new species close to the extant Podocnemis sextuberculata. Both species constitute a new clade in the genus. The synapomorphies they share and the differences between them are given. P. negrii nov. sp. is the second fossil species of the genus, after P. bassleri from the Neogene of Peru, which constitutes another clade with the extant P. expansa. The relationships between these two clades and the other species of the genus are not determinate.