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SUMM.'^RVFoliar uptake and release of inorganic nitrogen compounds were studied by immersing current-year shoots of Scots pine {Pinus syhestris L.) and Norway spruce [Picea ahies (L.) Karst] in either NH^"-or NOg'-rain solutions at different N concentrations. The effects of N form, N concentration and tree species on ion influx and efflux were investigated.Spruce shoots absorbed NH^"^ from the external solution. Uptake apparently occurred by diffusion rather than by H"' or base cation exchange as commonly accepted, and increased iinearly with NH^"^ concentration in the external solution. In contrast, pine shoots released NH^* to the external solution. The different reactions of spruce and pine may refiect species differences in physical and chemical properties or differences in tissue N concentration. If the latter is the case, a tree's N status may determine whether the canopy acts as a source or sink for NH,', influencing deposition rates to the needle surface. The results show that where NHj* concentration on the needle surface exceeds 4 mg t"', foliar uptake may make a significant contribution to N status. In the absence of N'H^^-base cation exchange, atmospheric inputs of NH^"^ to the canopy appear unlikely to be directly responsible for the nutrient deficiencies typical of Dutch forest decline.Neither spruce or pine shoots were able to utilize NO^" in the external solution and generally released NO3". Adverse effects resulting from foliar accumulation of wet-deposited NO3" appear unlikely. However, higher NO3" concentrations and longer residence times than simulated in this experiment may result in foliar uptake of NOj" in the field.

Evidence before this study: Acute appendicitis is the most common general surgical emergency in children. Its diagnosis remains challenging and children presenting with acute right iliac fossa (RIF) pain may be admitted for clinical observation or undergo normal appendicectomy (removal of a histologically normal appendix). A search for external validation studies of risk prediction models for acute appendicitis in children was performed on MEDLINE and Web of Science on 12 January 2017 using the search terms ["appendicitis" OR "appendectomy" OR "appendicectomy"] AND ["score" OR "model" OR "nomogram" OR "scoring"]. Studies validating prediction models aimed at differentiating acute appendicitis from all other causes of RIF pain were included. No date restrictions were applied. Validation studies were most commonly performed for the Alvarado, Appendicitis Inflammatory Response Score (AIRS), and Paediatric Appendicitis Score (PAS) models. Most validation studies were based on retrospective, single centre, or small cohorts, and findings regarding model performance were inconsistent. There was no high quality evidence to guide selection of the optimum model and threshold cutoff for identification of low-risk children in the UK and Ireland. Added value of this study: Most children admitted to hospital with RIF pain do not undergo surgery. When children do undergo appendicectomy, removal of a normal appendix (normal appendicectomy) is common, occurring in around 1 in 6 children. The Shera score is able to identify a large low-risk group of children who present with acute RIF pain but do not have acute appendicitis (specificity 44%). This low-risk group has an overall 1 in 30 risk of acute appendicitis and a 1 in 270 risk of perforated appendicitis. The Shera score is unable to achieve a sufficiently high positive predictive value to select a high-risk group who should proceed directly to surgery. Current diagnostic performance of ultrasound is also too poor to select children for surgery. Implications of all the available evidence: Routine pre-operative risk scoring could inform shared decision making by doctors, children, and parents by supporting safe selection of lowrisk patients for ambulatory management, reducing unnecessary admissions and normal appendicectomy. Hospitals should ensure seven-day-a-week availability of ultrasound for medium and high-risk patients. Ultrasound should be performed by operators trained to assess for acute appendicitis in children. For children in whom diagnostic uncertainty remains following ultrasound, magnetic resonance imaging (MRI) or low-dose computed tomography (CT) are second-line investigations.

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