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Exploring the relationship between leaf and xylem growth and nitrogen (N) deposition on tree growth helps us better understand how N deposition affects tree growth, but relevant studies are still limited. We tested if leaf and xylem growth and their relationship were affected by N deposition across multiple stages of leaf development. We studied two dominant tree species (Castanopsis chinensis and Schima superba) in a subtropical forest in South China, monitoring their leaf and xylem growth traits under canopy N addition of 0 (CK) and 50 kg N ha−1 year−1 (CAN) and compared these traits and their relationships across different treatments, periods, and species. We found that CAN significantly increased C. chinensis's leaf carbon (C) content, while the same treatment reduced leaf C content in S. superba. Specific leaf area (SLA), specific leaf weight (SLW), leaf N content, and C:N ratio showed more variation between species and within species across developmental stages than in response to different N addition treatments. Nitrogen addition also significantly increased the xylem width in both species, but the weekly xylem increment before July was notably higher in S. superba than in C. chinensis. Moreover, the leaf C content during early leaf development (ELD) following N addition was significantly and negatively correlated with the start date of xylogenesis in C. chinensis but had no significant effect on the onset of xylogenesis in S. superba. Additionally, regardless of species, SLA in ELD was negatively correlated with xylem width at the end of the early growing season (EW) under CK. However, this relationship became insignificant under CAN, suggesting that N addition alleviated the trade-off between SLA in ELD and EW. These results demonstrated that the relationship between leaf and xylem growth is influenced by both the leaf developmental stage and N availability. Traditional analyses of the leaf–xylem relationship, based solely on mature leaf traits, might oversimplify the effects of N deposition on tree growth. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition and increasing precipitation affect carbon sequestration in terrestrial ecosystems, but how these two concurrent global change variables affect xylem growth in trees (i.e. independently or interactively) remains unclear. We conducted novel experiments in central China to monitor the xylem growth in a dominant species (Quercus acutissima Caruth.) in response to N addition (CN), supplemental precipitation (CW) or both treatments (CNW), compared with untreated controls (C). Measurements were made at weekly intervals during 2014–15. We found that supplemental precipitation significantly enhanced xylem growth in the dry spring of 2015, indicating a time-varying effect of increased precipitation on intra-annual xylem growth. Elevated N had no significant effect on xylem increment, xylem growth rate, and lumen diameters and potential hydraulic conductivity (K s) of earlywood vessels, but K s with elevated N was significantly negatively related to xylem increment. The combination of additional N and supplemental precipitation suppressed the positive effect of supplemental precipitation on xylem increment in the dry spring of 2015. These findings indicated that xylem width was more responsive to supplemental precipitation than to increasing N in a dry early growing season; the positive effect of supplemental precipitation on xylem growth could be offset by elevated N resources. The negative interactive effect of N addition and supplemental precipitation also suggested that increasing N deposition and precipitation in the future might potentially affect carbon sequestration of Q. acutissima during the early growing season in central China. The effects of N addition and supplemental precipitation on tree growth are complex and might vary depending on the growth period and local climatic conditions. Therefore, future models of tree growth need to consider multiple-time scales and local climatic conditions when simulating and projecting global change. [ABSTRACT FROM AUTHOR]

Abstract: Background: Chronic obstructive pulmonary disease (COPD) is often accompanied by acute exacerbations. Patients of COPD exacerbation suffering from respiratory failure often need the support of mechanical ventilation. Helium–oxygen can be used to reduce airway resistance during mechanical ventilation. The aim of this study is to evaluate the effect of helium–oxygen‐assisted mechanical ventilation on COPD exacerbation through a meta‐analysis. Methods: A comprehensive literature search through databases of Pub Med (1966∼2016), Ovid MEDLINE (1965∼2016), Cochrane EBM (1991∼2016), EMBASE (1974∼2016) and Ovid MEDLINE was performed to identify associated studies. Randomized clinical trials met our inclusion criteria that focus on helium–oxygen‐assisted mechanical ventilation on COPD exacerbation were included. The quality of the papers was evaluated after inclusion and information was extracted for meta‐analysis. Results: Six articles and 392 patients were included in total. Meta‐analysis revealed that helium–oxygen‐assisted mechanical ventilation reduced Borg dyspnea scale and increased arterial PH compared with air–oxygen. No statistically significant difference was observed between helium–oxygen and air–oxygen as regards to WOB, PaCO2, OI, tracheal intubation rates and mortality within hospital. Conclusions: Our study suggests helium–oxygen‐assisted mechanical ventilation can help to reduce Borg dyspnea scale. In terms of the tiny change of PH, its clinical benefit is negligible. There is no conclusive evidence indicating the beneficial effect of helium–oxygen‐assisted mechanical ventilation on clinical outcomes or prognosis of COPD exacerbation. [ABSTRACT FROM AUTHOR]