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Increased N (increased + n)
Selected AbstractsIncreased N affects P uptake of eight grassland species: the role of root surface phosphatase activityOIKOS, Issue 10 2010Yuki Fujita Increased N deposition may change species composition in grassland communities by shifting them to P limitation. Interspecific differences in P uptake traits might be a crucial yet poorly understood factor in determining the N effects. To test the effects of increased N supply (relative to P), we conducted two greenhouse fertilization experiments with eight species from two functional groups (grasses, herbs), including those common in P and N limited grasslands. We investigated plant growth and P uptake from two P sources, orthophosphate and not-readily available P (bound-P), under different N supply levels. Furthermore, to test if the N effects on P uptake was due to N availability alone or altered N:P ratio, we examined several uptake traits (root-surface phosphatase activity, specific root length (SRL), root mass ratio (RMR)) under varying N:P supply ratios. Only a few species (M. caerulea, A. capillaris, S. pratensis) could take up a similar amount of P from bound-P to that from orthophosphate. These species had neither higher SRL, RMR, phosphatase activity per unit root (Paseroot), nor higher total phosphatase activity (Pasetot: Paseroot times root mass), but higher relative phosphatase activity (Paserel: Pasetot divided by biomass) than other species. The species common from P-limited grasslands had high Paserel. P uptake from bound-P was positively correlated with Pasetot for grasses. High N supply stimulated phosphatase activity but decreased RMR and SRL, resulting in no increase in P uptake from bound-P. Paseroot was influenced by N:P supply ratio, rather than by only N or P level, whereas SRL and RMR was not dominantly influenced by N:P ratio. We conclude that increased N stimulates phosphatase activity via N:P stoichiometry effects, which potentially increases plant P uptake in a species-specific way. N deposition, therefore, may alter plant community structure not only by enhancing productivity, but also by favouring species with traits that enable them to persist better under P limited conditions. [source] Contrasted effects of increased N and CO2 supply on two keystone species in peatland restoration and implications for global changeJOURNAL OF ECOLOGY, Issue 3 2002Edward A. D. Mitchell Summary 1,Significant areas of temperate bogs have been damaged by peat harvesting but may regenerate. These secondary mires, if well managed, may act as strong C sinks, regulate hydrology and buffer regional climate. 2,The potential effects of bog regeneration will, however, depend on the successful establishment of the principal peat formers ,Sphagnum mosses. The influence of hydrology and microclimate on Sphagnum re-growth is well studied but effects of elevated CO2 and N deposition are not known. 3,We carried out two in-situ experiments in a cutover bog during three growing seasons in which we raised either CO2 (to 560 p.p.m.) or N (by adding NH4NO3, 3 g m,2 year,1). The two treatments had contrasting effects on competition between the initial coloniser Polytrichum strictum (favoured by high N) and the later coloniser Sphagnum fallax (favoured by high CO2). 4,Such changes may have important consequences for bog regeneration and hence for carbon sequestration in cutover bogs, with potential feedback on regional hydrological and climatic processes. [source] Allometric analysis reveals relatively little variation in nitrogen versus biomass accrual in four plant species exposed to varying light, nutrients, water and CO2PLANT CELL & ENVIRONMENT, Issue 10 2007CARL J. BERNACCHI ABSTRACT Nitrogen concentrations in plant tissues can vary as a function of resource availability. Altered rates of plant growth and development under varying resource availabilities were examined to determine their effects on changes in whole-plant N use efficiency (NUE). Three species of old-field annuals were grown at broadly varying light, nutrient and water levels, and four species at varying atmospheric concentrations of CO2. Study results show highly variable N accrual rates when expressed as a function of plant age or size, but similar patterns of whole-plant N versus non-N biomass accrual over a wide range of environmental conditions. However, severely light-limited plants showed increased N versus biomass accrual for two of three species, and severely nutrient-limited plants had decreased N versus biomass accrual for all species. Whole-plant N accrual versus age and N versus biomass accrual increased under saturating water for two of three species. A marginally significant, modest decrease in N versus biomass accrual was found at high CO2 levels for two of four species. Physiological adjustments in NUE, expressed as N versus biomass accrual, were limited to environments with severely limited or overabundant resources. [source] Cerebrospinal fluid of brain trauma patients inhibits in vitro neuronal network function via NMDA receptors,ANNALS OF NEUROLOGY, Issue 4 2009Frauke Otto MD Neurological diseases frequently induce pathological changes of cerebrospinal fluid (CSF) that might secondarily influence brain activity, as the CSF,brain barrier is partially permeable. However, functional effects of CSF on neuronal network activity have not been specified to date. Here, we report that CSF specimens from patients with reduced Glasgow Coma Scale values caused by severe traumatic brain injury suppress synchronous activity of in vitro-generated neuronal networks in comparison with controls. We present evidence that underlying mechanisms include increased N -methyl- D- aspartate receptor activity mediated by a CSF fraction containing elevated amino acid concentrations. These proof-of-principle data suggest that determining effects of CSF specimens on neuronal network activity might be of diagnostic value. Ann Neurol 2009;66:546,555 [source] | ||||||||||