Woody invasion of grasslands: evidence that CO2 enrichment indirectly promotes establishment of Prosopis glandulosa

Grasslands worldwide have been invaded by woody species during the last200 years. Atmospheric CO₂ enrichment may indirectly havefacilitatedinvasion by reducing soil water depletion by grasses. We used a two-stepcorrelative approach to test this hypothesis with the invasive and native shrubhoney mesquite (Prosopis glandulosa Torr. var.glandulosa). 1) Water content to 0.15 m depthwas measured in grassland exposed to a CO₂ gradient from 200 to 550mol/mol to evaluate the prediction that CO₂enrichment lessens soil water depletion by grasses. 2) Soil water content andemergence and survival of mesquite seedlings were measured in adjacentgrasslandplots from which grass roots were excluded to 0.15 m depth toreduce water depletion or that were irrigated to increase soil water levels.With these measurements, we tested the hypothesis that mesquite establishmentislimited by water.Excluding grass roots doubled emergence of mesquite and almost tripledthe fraction of emergent seedlings that survived for 12 weeks following thefirst of two plantings. Seedlings were taller, heavier, and had greater leafarea when grown without grass roots. Root exclusion did not measurably affectsoil water during the 3-week period of seedling emergence, but soilwatercontent over the 12 weeks that seedling survival was studied was higher inplotsfrom which grass roots were excluded and following an April than May planting.Survivorship of mesquite seedlings correlated positively with soil watercontent. Percentage survival of seedlings increased from 1.5% to15% and 28% at the soil water content measured in grasslandexposed to CO₂ concentrations of 270 (preindustrial), 360 (current),and 550 mol/mol (future), respectively. We infer thatrecent and projected increases in atmospheric CO₂ concentration maybe large enough to increase establishment of invading mesquite seedlings ingrasslands that are severely water-limited.     

Carotenemia in mentally retarded children I. Incidence and etiology

The incidence and etiology of carotenemia in mentally retarded children were examined. Fasting serum carotenoid and vitamin A levels were measured in 77 profoundly mentally retarded children aged 3 to 19 years who were receiving a standard diet containing 2000 IU of carotene (expressed in terms of vitamin A activity) and supplemented by 2000 IU of vitamin A daily. Seventeen of the 77 patients had serum carotenoid levels of more than 300 μg./ml. The particulate size of food had a significant inverse relationship to serum carotenoid levels and was an important factor in determining carotenemia. The serum vitamin A level was also higher in children on homogenized diet than in those on pureed feeds, while the lowest level was noted among patients on a chopped diet. Besides particulate size of food, other factors may also be operative in determining carotenemia.     

Dispersed activity during passive movement in the globus pallidus of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated primate

Parkinson's disease is a neurodegenerative disorder manifesting in debilitating motor symptoms. This disorder is characterized by abnormal activity throughout the cortico-basal ganglia loop at both the single neuron and network levels. Previous neurophysiological studies have suggested that the encoding of movement in the parkinsonian state involves correlated activity and synchronized firing patterns. In this study, we used multi-electrode recordings to directly explore the activity of neurons from the globus pallidus of parkinsonian primates during passive limb movements and to determine the extent to which they interact and synchronize. The vast majority (80/103) of the recorded pallidal neurons responded to periodic flexion-extension movements of the elbow. The response pattern was sinusoidal-like and the timing of the peak response of the neurons was uniformly distributed around the movement cycle. The interaction between the neuronal activities was analyzed for 123 simultaneously recorded pairs of neurons. Movement-based signal correlation values were diverse and their mean was not significantly different from zero, demonstrating that the neurons were not activated synchronously in response to movement. Additionally, the difference in the peak responses phase of pairs of neurons was uniformly distributed, showing their independent firing relative to the movement cycle. Our results indicate that despite the widely distributed activity in the globus pallidus of the parkinsonian primate, movement encoding is dispersed and independent rather than correlated and synchronized, thus contradicting current views that posit synchronous activation during Parkinson's disease.     

Referate

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Zur ökologie der wichtigsten in Deutschland an getreide schädlichen pentatomiden II

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