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- Averill, Colin, et al.
(author)
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Microbial-mediated redistribution of ecosystem nitrogen cycling can delay progressive nitrogen limitation
- 2015
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In: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 126:1-2, s. 11-23
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Journal article (peer-reviewed)abstract
- Soil nitrogen (N) availability constrains future predictions of ecosystem primary productivity and carbon storage. The progressive N limitation (PNL) hypothesis predicts that forest net primary productivity (NPP) will decline with age, and that the response of NPP to elevated CO2 will attenuate through time due to negative feedbacks of NPP on the soil N cycle. A central assumption of the PNL hypothesis is that, without changes in exogenous exchange of N in an ecosystem, increases in plant N uptake require increased soil N cycling rates. However, at ecosystem scale, microbial N uptake exceeds plant uptake. Hence, a change in the partitioning of N between plants and soil microorganisms may represent an alternative mechanism to sustain plant N uptake in the face of PNL. To estimate N partitioning of total N cycling between plants and microbes, we measured and modeled growth and N uptake of trees, bacteria, saprotrophic fungi, and ectomycorrhizal fungi across a forest succession and N limitation gradient. The combined plant and ectomycorrhizal N uptake increased from early to late succession, and nearly matched saprotrophic N uptake in late successional sites, while total N cycling remained stable or even declined. Changes in microbial community structure can thus mediate a redistribution of ecosystem nitrogen cycling, allowing an increase in plant N uptake without concomitant increases in soil N cycling. We further suggest that microbe-mediated changes in N partitioning can delay PNL and may thereby act as a mechanism to extend the duration of the land carbon sink in response to rising atmospheric CO2.
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| 2. |
- Benomar, Anass, et al.
(author)
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Nonaneurysmal perimesencephalic subarachnoid hemorrhage on noncontrast head CT: An accuracy, inter-rater, and intra-rater reliability study
- 2024
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In: Journal of neuroradiology. - : MASSON EDITEUR. - 0150-9861 .- 1773-0406. ; 51:4
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Journal article (peer-reviewed)abstract
- Background and purpose: To evaluate the reliability and accuracy of nonaneurysmal perimesencephalic subarachnoid hemorrhage (NAPSAH) on Noncontrast Head CT (NCCT) between numerous raters. Materials and methods: 45 NCCT of adult patients with SAH who also had a catheter angiography (CA) were independently evaluated by 48 diverse raters; 45 raters performed a second assessment one month later. For each case, raters were asked: 1) whether they judged the bleeding pattern to be perimesencephalic; 2) whether there was blood anterior to brainstem; 3) complete filling of the anterior interhemispheric fissure (AIF); 4) extension to the lateral part of the sylvian fissure (LSF); 5) frank intraventricular hemorrhage; 6) whether in the hypothetical presence of a negative CT angiogram they would still recommend CA. An automatic NAPSAH diagnosis was also generated by combining responses to questions 2 -5. Reliability was estimated using Gwet 's AC1 ( K G ), and the relationship between the NCCT diagnosis of NAPSAH and the recommendation to perform CA using Cramer 's V test. Multi -rater accuracy of NCCT in predicting negative CA was explored. Results: Inter -rater reliability for the presence of NAPSAH was moderate ( K G = 0.58; 95%CI: 0.47, 0.69), but improved to substantial when automatically generated ( K G = 0.70; 95%CI: 0.59, 0.81). The most reliable criteria were the absence of AIF filling ( K G = 0.79) and extension to LSF ( K G = 0.79). Mean intra-rater reliability was substantial ( K G = 0.65). NAPSAH weakly correlated with CA decision ( V = 0.50). Mean sensitivity and specificity were 58% (95%CI: 44%, 71%) and 83 % (95%CI: 72 %, 94%), respectively. Conclusion: NAPSAH remains a diagnosis of exclusion. The NCCT diagnosis was moderately reliable and its impact on clinical decisions modest. (c) 2024 The Authors. Published by Elsevier Masson SAS. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
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