The effect of warming on grassland evapotranspiration partitioning using laser-based isotope monitoring techniques

Author's manuscript made available in accordance with the publisher's policy.The proportion of transpiration (T) in total evapotranspiration (ET) is an important parameter that provides insight into the degree of biological influence on the hydrological cycles. Studies addressing the effects of climatic warming on the ecosystem total water balance are scarce, and measured warming effects on the T/ET ratio in field experiments have not been seen in the literature. In this study, we quantified T/ET ratios under ambient and warming treatments in a grassland ecosystem using a stable isotope approach. The measurements were made at a long-term grassland warming site in Oklahoma during the May–June peak growing season of 2011. Chamber-based methods were used to estimate the δ2H isotopic composition of evaporation (δE), transpiration (δT) and the aggregated evapotranspiration (δET). A modified commercial conifer leaf chamber was used for δT, a modified commercial soil chamber was used for δE and a custom built chamber was used for δET. The δE, δET and δT were quantified using both the Keeling plot approach and a mass balance method, with the Craig–Gordon model approach also used to calculate δE. Multiple methods demonstrated no significant difference between control and warming plots for both δET and δT. Though the chamber-based estimates and the Craig–Gordon results diverged by about 12‰, all methods showed that δE was more depleted in the warming plots. This decrease in δE indicates that the evaporation flux as a percentage of total water flux necessarily decreased for δET to remain constant, which was confirmed by field observations. The T/ET ratio in the control treatment was 0.65 or 0.77 and the ratio found in the warming treatment was 0.83 or 0.86, based on the chamber method and the Craig–Gordon approach. Sensitivity analysis of the Craig–Gordon model demonstrates that the warming-induced decrease in soil liquid water isotopic composition is the major factor responsible for the observed δE depletion and the temperature dependent equilibrium effects are minor. Multiple lines of evidence indicate that the increased T/ET ratio under warming is caused mainly by reduced evaporation

Differential responses of carbon-degrading enzyme activities to warming: implications for soil respiration

Extracellular enzymes catalyze rate‐limiting steps in soil organic matter decomposi-tion, and their activities (EEAs) play a key role in determining soil respiration (SR).Both EEAs and SR are highly sensitive to temperature, but their responses to cli-mate warming remain poorly understood. Here, we present a meta‐analysis on theresponse of soil cellulase and ligninase activities and SR to warming, synthesizingdata from 56 studies. We found that warming significantly enhanced ligninase activ-ity by 21.4% but had no effect on cellulase activity. Increases in ligninase activitywere positively correlated with changes in SR, while no such relationship was foundfor cellulase. The warming response of ligninase activity was more closely related tothe responses of SR than a wide range of environmental and experimental method-ological factors. Furthermore, warming effects on ligninase activity increased withexperiment duration. These results suggest that soil microorganisms sustain long‐term increases in SR with warming by gradually increasing the degradation of therecalcitrant carbon pool

Smoking patterns and sociodemographic factors associated with tobacco use among Chinese rural male residents: a descriptive analysis

<p>Abstract</p> <p>Background</p> <p>Although evidence has shown high prevalence rates of tobacco use in the general urban populations in China, relatively little is known in its rural population. The purposes of this study were to examine smoking patterns and sociodemographic correlates of smoking in a sample of rural Chinese male residents.</p> <p>Methods</p> <p>The study employed a cross-sectional, multi-stage sampling design. Residents (N = 4,414; aged 15 years and older) were recruited from four geographic regions in China. Information on participants' tobacco use (of all forms), including their daily use, and sociodemographic characteristics were collected via survey questionnaires and the resultant data were analyzed using chi-square tests and logistic regression procedures.</p> <p>Results</p> <p>The overall smoking prevalence in the study sample was 66.8% (n = 2,950). Of these, the average use of tobacco products per day was 12.70 (SD = 7.99) and over 60% reported daily smoking of more than 10 cigarettes. Geographic regions of the study areas, age of the participants, marital status, ethnicity, education, occupation, and average personal annual income were found to be significantly associated with an increased likelihood of smoking among rural Chinese male residents.</p> <p>Conclusion</p> <p>There is a high smoking prevalence in the Chinese rural population and smoking behaviors are associated with important sociodemographic factors. Findings suggest the need for tobacco control and intervention policies aimed at reducing tobacco use in Chinese rural smoking populations.</p

Direct and indirect effects of climatic variations on the interannual variability in net ecosystem exchange across terrestrial ecosystems

Climatic variables not only directly affect the interannual variability (IAV) in net ecosystem exchange of CO2 (NEE) but also indirectly drive it by changing the physiological parameters. Identifying these direct and indirect paths can reveal the underlying mechanisms of carbon (C) dynamics. In this study, we applied a path analysis using flux data from 65 sites to quantify the direct and indirect climatic effects on IAV in NEE and to evaluate the potential relationships among the climatic variables and physiological parameters that represent physiology and phenology of ecosystems. We found that the maximum photosynthetic rate was the most important factor for the IAV in gross primary productivity (GPP), which was mainly induced by the variation in vapour pressure deficit. For ecosystem respiration (RE), the most important drivers were GPP and the reference respiratory rate. The biome type regulated the direct and indirect paths, with distinctive differences between forests and non-forests, evergreen needleleaf forests and deciduous broadleaf forests, and between grasslands and croplands. Different paths were also found among wet, moist and dry ecosystems. However, the climatic variables can only partly explain the IAV in physiological parameters, suggesting that the latter may also result from other biotic and disturbance factors. In addition, the climatic variables related to NEE were not necessarily the same as those related to GPP and RE, indicating the emerging difficulty encountered when studying the IAV in NEE. Overall, our results highlight the contribution of certain physiological parameters to the IAV in C fluxes and the importance of biome type and multi-year water conditions, which should receive more attention in future experimental and modelling research

Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms

It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystemclimate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models.This is the publisher’s final pdf. The published article is copyrighted by New Phytologist Trust and can be found at: http://www.newphytologist.org/Keywords: Climate change, Temperature acclimation, Optimum temperature, Thermal optimality, Temperature adaptatio

Research on Thermodynamic Characteristics of Hydraulic Power Take-Off System in Wave Energy Converter

Hydraulic power-take-off (PTO) systems which utilize high-pressure oil circuits to transmit energy are widely applied in wave energy generation. The properties of hydraulic oil are significantly influenced by environmental conditions, and its dynamic viscosity is sensitive to temperature, especially in relatively low-temperature cases. This paper studies the characteristics of the hydraulic PTO when started in different temperature conditions via numerical analysis and experimental verification. An improved numerical model of the hydraulic PTO system is proposed, in which the effects of temperature on the hydraulic oil viscosity and hydraulic motor efficiency are quantitatively investigated, and consequently, the thermal-hydraulic characteristics can be sufficiently considered. The performances of the hydraulic PTO in start-up processes with different initial temperatures and in long term operation are assessed. The results show that the presented model can reasonably describe the hydraulic PTO characteristics. The efficiency of hydraulic PTO degrades when it starts at low temperatures. The efficiency increases in relatively high temperature, while larger fluctuations of the flow rate and output power are observed. This study can provide guidance for enhancing the efficiency and consistency of hydraulic PTO operating in actual sea conditions

Differential responses of ecosystem respiration components to experimental warming in a meadow grassland on the Tibetan Plateau

Global warming is anticipated to have profound effects on terrestrial carbon fluxes and thus feed backs to future climate change. Ecosystem respiration (R-eco) is one of the dominant components of biosphere CO2 fluxes, but the effects of warming on Reco are still unclear. A field warming experiment using open top chambers (OTCs) was conducted in a meadow grassland on the Tibetan Plateau to study the effects of warming on the components of Reco. Warming significantly enhanced above-ground plant respiration (R-agb) and total autotrophic plant respiration (R-plant 1 by 28.7% and 19.9%, respectively, but reduced heterotrophic respiration (R-h) by 10.4%. These different responses resulted in the insensitive responses of Reco and soil respiration (R-s) to the experimental warming. The warming treatment also increased R-plant/R-eco and R-agb/R-eco. by 8.4% and 17.3%, respectively, while decreasing R-h/R-eco, by 19.0%, suggesting that warming could eventually cause R-eco to be dominated by R-plant. Enhancements in Roam and R-agb were related to the warming-induced increases in aboveground biomass (AGB) while reduced R-h was closely coupled with warming-induced decrease of microbial biomass carbon. Our results highlight that the differential responses of the components of R-eco to different environmental physics under warming scenarios should be taken into consideration to project the future carbon-climate feed backs. (C) 2016 Elsevier B.V. All rights reserved