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1.
Contrasting responses of leaf stomatal characteristics to climate change: a considerable challenge to predict carbon and water cycles.
Yan, W, Zhong, Y, Shangguan, Z
Global change biology. 2017;(9):3781-3793
Abstract
Stomata control the cycling of water and carbon between plants and the atmosphere; however, no consistent conclusions have been drawn regarding the response of stomatal frequency to climate change. Here, we conducted a meta-analysis of 1854 globally obtained data series to determine the response of stomatal frequency to climate change, which including four plant life forms (over 900 species), at altitudes ranging from 0 to 4500 m and over a time span of more than one hundred thousand years. Stomatal frequency decreased with increasing CO2 concentration and increased with elevated temperature and drought stress; it was also dependent on the species and experimental conditions. The response of stomatal frequency to climate change showed a trade-off between stomatal control strategies and environmental factors, such as the CO2 concentration, temperature, and soil water availability. Moreover, threshold effects of elevated CO2 and temperature on stomatal frequency were detected, indicating that the response of stomatal density to increasing CO2 concentration will decrease over the next few years. The results also suggested that the stomatal index may be more reliable than stomatal density for determination of the historic CO2 concentration. Our findings indicate that the contrasting responses of stomata to climate change bring a considerable challenge in predicting future water and carbon cycles.
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2.
Effects of Increased Nitrogen Availability on C and N Cycles in Tropical Forests: A Meta-Analysis.
Bejarano-Castillo, M, Campo, J, Roa-Fuentes, LL
PloS one. 2015;(12):e0144253
Abstract
Atmospheric N deposition is predicted to increase four times over its current status in tropical forests by 2030. Our ability to understand the effects of N enrichment on C and N cycles is being challenged by the large heterogeneity of the tropical forest biome. The specific response will depend on the forest's nutrient status; however, few studies of N addition appear to incorporate the nutrient status in tropical forests, possibly due to difficulties in explaining how this status is maintained. We used a meta-analysis to explore the consequences of the N enrichment on C and N cycles in tropical montane and lowland forests. We tracked changes in aboveground and belowground plant C and N and in mineral soil in response to N addition. We found an increasing trend of plant biomass in montane forests, but not in lowland forests, as well as a greater increase in NO emission in montane forest compared with lowland forest. The N2O and NO emission increase in both forest; however, the N2O increase in lowland forest was significantly even at first time N addition. The NO emission increase showed be greater at first term compared with long term N addition. Moreover, the increase in total soil N, ammonium, microbial N, and dissolved N concentration under N enrichment indicates a rich N status of lowland forests. The available evidence of N addition experiments shows that the lowland forest is richer in N than montane forests. Finally, the greater increase in N leaching and N gas emission highlights the importance of study the N deposition effect on the global climate change.
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3.
Quantitative assessment of maternal biomarkers related to one-carbon metabolism and neural tube defects.
Tang, KF, Li, YL, Wang, HY
Scientific reports. 2015;:8510
Abstract
Periconceptional supplementation with folic acid reduces the occurrence of neural tube defects (NTDs). The association between maternal abnormalities in homocysteine metabolism (e.g., hyperhomocysteinaemia, folate deficiency and low vitamin B12) and the risk of NTDs-affected pregnancies has been widely evaluated in recent years, although the results are conflicting. To investigate this inconsistency, we performed a meta-analysis of 32 studies, involving 1,890 NTD-affected mothers and 3,995 control mothers, to develop an understanding of the relationship between maternal biomarkers related to one-carbon metabolism and NTD. A random-effects model was used to calculate the ratio of means (RoM) between the cases and controls, along with the 95% confidence intervals (CIs). A significant increase in homocysteine levels was observed in NTD-affected mothers compared with controls (RoM: 1.16, 95% CI: 1.09-1.23, P = 1.8 × 10(-6)). The pooled analysis also revealed that NTD-affected mothers had significantly lower levels of folate (RoM: 0.93, 95% CI: 0.88-0.97, P = 0.002), vitamin B12 (RoM: 0.91, 95% CI: 0.87-0.95, P = 3.6 × 10(-5)) and red blood cell folate (RoM: 0.92, 95% CI: 0.86-0.98, P = 0.01). Therefore, altered plasma levels of biomarkers related to one-carbon metabolism are associated with NTD-affected pregnancies.
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4.
One-Carbon Metabolic Factors and Risk of Renal Cell Cancer: A Meta-Analysis.
Mao, B, Li, Y, Zhang, Z, Chen, C, Chen, Y, Ding, C, Lei, L, Li, J, Jiang, M, Wang, D, et al
PloS one. 2015;(10):e0141762
Abstract
BACKGROUND Nutrients related to one-carbon metabolism were previously shown to be significantly associated with the risk of cancer. The aim of this meta-analysis was to evaluate potential relationships between one-carbon metabolic factors and renal cell cancer (RCC) risk. METHODS PubMed, EMBASE, and Cochrane Library databases were searched through March 2015 for observational studies of quantitative RCC risk estimates in relation to one-carbon metabolic factors. The relative risks (RRs) with 95% confidence intervals (CIs) measured the relationship between one-carbon metabolic factors and RCC risk using a random-effects model. RESULTS Of the 463 citations and abstracts identified by database search, seven cohorts from five observational studies reported data on 133,995 individuals, and included 2,441 RCC cases. Comparing the highest with the lowest category, the pooled RRs of RCC were 0.72 (95%CI: 0.52-1.00; P = 0.048) for vitamin B12. In addition, an increase in folic acid supplementation of 100 μg/day was associated with a 3% lower risk of RCC (RR, 0.97; 95%CI: 0.93-1.00; P = 0.048). Similarly, an increase of 5 nmol/L of vitamin B2 was associated with a reduced risk of RCC 0.94 (95%CI: 0.89-1.00; P = 0.045). Sensitivity analyses suggested that a higher serum vitamin B6 might contribute to a reduced risk of RCC (RR, 0.83; 95%CI: 0.77-0.89; P < 0.001). CONCLUSIONS Higher levels of serum vitamin B2, B6, B12, and folic acid supplementation lowered the risk of RCC among the study participants.
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5.
Systematic review and meta-analysis of radiotherapy in various head and neck cancers: comparing photons, carbon-ions and protons.
Ramaekers, BL, Pijls-Johannesma, M, Joore, MA, van den Ende, P, Langendijk, JA, Lambin, P, Kessels, AG, Grutters, JP
Cancer treatment reviews. 2011;(3):185-201
Abstract
PURPOSE To synthesize and compare available evidence considering the effectiveness of carbon-ion, proton and photon radiotherapy for head and neck cancer. METHODS A systematic review and meta-analyses were performed to retrieve evidence on tumor control, survival and late treatment toxicity for carbon-ion, proton and the best available photon radiotherapy. RESULTS In total 86 observational studies (74 photon, 5 carbon-ion and 7 proton) and eight comparative in-silico studies were included. For mucosal malignant melanomas, 5-year survival was significantly higher after carbon-ion therapy compared to conventional photon therapy (44% versus 25%; P-value 0.007). Also, 5-year local control after proton therapy was significantly higher for paranasal and sinonasal cancer compared to intensity modulated photon therapy (88% versus 66%; P-value 0.035). No other statistically significant differences were observed. Although poorly reported, toxicity tended to be less frequent in carbon-ion and proton studies compared to photons. In-silico studies showed a lower dose to the organs at risk, independently of the tumor site. CONCLUSIONS For carbon-ion therapy, the increased survival in mucosal malignant melanomas might suggest an advantage in treating relatively radio-resistant tumors. Except for paranasal and sinonasal cancer, survival and tumor control for proton therapy were generally similar to the best available photon radiotherapy. In agreement with included in-silico studies, limited available clinical data indicates that toxicity tends to be lower for proton compared to photon radiotherapy. Since the overall quantity and quality of data regarding carbon-ion and proton therapy is poor, we recommend the construction of an international particle therapy register to facilitate definitive comparisons.
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6.
Global meta-analysis of wood decomposition rates: a role for trait variation among tree species?
Weedon, JT, Cornwell, WK, Cornelissen, JH, Zanne, AE, Wirth, C, Coomes, DA
Ecology letters. 2009;(1):45-56
Abstract
The carbon flux from woody debris, a crucial uncertainty within global carbon-climate models, is simultaneously affected by climate, site environment and species-based variation in wood quality. In the first global analysis attempting to explicitly tease out the wood quality contribution to decomposition, we found support for our hypothesis that, under a common climate, interspecific differences in wood traits affect woody debris decomposition patterns. A meta-analysis of 36 studies from all forested continents revealed that nitrogen, phosphorus, and C : N ratio correlate with decomposition rates of angiosperms. In addition, gymnosperm wood consistently decomposes slower than angiosperm wood within common sites, a pattern that correlates with clear divergence in wood traits between the two groups. New empirical studies are needed to test whether this difference is due to a direct effect of wood trait variation on decomposer activity or an indirect effect of wood traits on decomposition microsite environment. The wood trait-decomposition results point to an important role for changes in the wood traits of dominant tree species as a driver of carbon cycling, with likely feedback to atmospheric CO(2) particularly where angiosperm species replace gymnosperms regionally. Truly worldwide upscaling of our results will require further site-based multi-species wood trait and decomposition data, particularly from low-latitude ecosystems.
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7.
Altered ecosystem carbon and nitrogen cycles by plant invasion: a meta-analysis.
Liao, C, Peng, R, Luo, Y, Zhou, X, Wu, X, Fang, C, Chen, J, Li, B
The New phytologist. 2008;(3):706-714
Abstract
Plant invasion potentially alters ecosystem carbon (C) and nitrogen (N) cycles. However, the overall direction and magnitude of such alterations are poorly quantified. Here, 94 experimental studies were synthesized, using a meta-analysis approach, to quantify the changes of 20 variables associated with C and N cycles, including their pools, fluxes, and other related parameters in response to plant invasion. Pool variables showed significant changes in invaded ecosystems relative to native ecosystems, ranging from a 5% increase in root carbon stock to a 133% increase in shoot C stock. Flux variables, such as above-ground net primary production and litter decomposition, increased by 50-120% in invaded ecosystems, compared with native ones. Plant N concentration, soil NH+4 and NO-3 concentrations were 40, 30 and 17% higher in invaded than in native ecosystems, respectively. Increases in plant production and soil N availability indicate that there was positive feedback between plant invasion and C and N cycles in invaded ecosystems. Invasions by woody and N-fixing plants tended to have greater impacts on C and N cycles than those by herbaceous and nonN-fixing plants, respectively. The responses to plant invasion are not different among forests, grasslands, and wetlands. All of these changes suggest that plant invasion profoundly influences ecosystem processes.