《Soil Biology and Biochemistry》Short-term effects of labile organic C addition on soil microbial response to temperature in a temperate steppe
Authors: Chao Li,Chunwang Xiao,Bertrand Guenet,Mingxu Li,Li Xu,Nianpeng He

Abstract: It remains unclear how soil microbes respond to labile organic carbon (LOC) inputs and how temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is affected by LOC inputs in a short-term. In this study, 13C-labeled glucose was added to a pristine grassland soil at four temperatures (10, 15, 20, and 25 °C), and the immediate utilization of LOC and native SOM by microbes was measured minutely in a short-term. We found that the LOC addition stimulated the native SOM decomposition, and elevated temperature enhanced the intensity of microbial response to LOC addition. The ratio between microbial respiration derived from LOC and native SOM increased with higher temperature, and more LOC for respiration. Additionally, LOC addition increased the Q10 of SOM decomposition, and the Q10 of LOC decomposition is higher than that of native SOM. Overall, these findings emphasize the important role of temperature and LOC inputs in soil C cycles. 原文链接
《PLOS ONE》No increasing risk of a limnic eruption at Lake Kivu: Intercomparison study reveals gas concentrations close to steady state
Authors:Fabian Bärenbold ,Bertram Boehrer,Roberto Grilli,Ange Mugisha,Wolf von Tümpling,Augusta Umutoni,Martin Schmid

Abstract:Lake Kivu, East Africa, is well known for its huge reservoir of dissolved methane (CH4) and carbon dioxide (CO2) in the stratified deep waters (below 250 m). The methane concentrations of up to ~ 20 mmol/l are sufficiently high for commercial gas extraction and power production. In view of the projected extraction capacity of up to several hundred MW in the next decades, reliable and accurate gas measurement techniques are required to closely monitor the evolution of gas concentrations. For this purpose, an intercomparison campaign for dissolved gas measurements was planned and conducted in March 2018. The applied measurement techniques included on-site mass spectrometry of continuously pumped sample water, gas chromatography of in-situ filled gas bags, an in-situ membrane inlet laser spectrometer sensor and a prototype sensor for total dissolved gas pressure (TDGP). We present the results of three datasets for CH4, two for CO2 and one for TDGP. The resulting methane profiles show a good agreement within a range of around 5–10% in the deep water. We also observe that TDGP measurements in the deep waters are systematically around 5 to 10% lower than TDGP computed from gas concentrations. Part of this difference may be attributed to the non-trivial conversion of concentration to partial pressure in gas-rich Lake Kivu. When comparing our data to past measurements, we cannot verify the previously suggested increase in methane concentrations since 1974. We therefore conclude that the methane and carbon dioxide concentrations in Lake Kivu are currently close to a steady state. 原文链接
《Scientific Reports》High inhaled oxygen concentration quadruples exhaled CO in healthy volunteers monitored by a highly sensitive laser spectrometer
Authors:Vivien Brenckmann, Irène Ventrillard, Daniele Romanini, Kévin Jaulin, Pascale Calabrèse & Raphaël Briot

Carbon monoxide (CO) monitoring in human breath is the focus of many investigations as CO could possibly be used as a marker of various diseases. Detecting CO in human breath remains a challenge because low concentrations (<ppm) must be selectively detected and short response time resolution is needed to detect the end expiratory values reflecting actual alveolar concentrations. A laser spectroscopy based instrument was developed (ProCeas) that fulfils these requirements. The aim of this study was to validate the use of a ProCeas for human breath analysis in order to measure the changes of endogenous exhaled CO (eCO) induced by different inspired fractions of oxygen (FiO2) ranging between 21% and 100%. This study was performed on healthy volunteers. 30 healthy awaked volunteers (including asymptomatic smokers) breathed spontaneously through a facial mask connected to the respiratory circuit of an anesthesiology station. FiO2 was fixed to 21%, 50% and 100% for periods of 5 minutes. CO concentrations were continuously monitored throughout the experiment with a ProCeas connected to the airway circuit. The respiratory cycles being resolved, eCO concentration is defined by the difference between the value at the end of the exhalation phase and the level during inhalation phase. Inhalation of 100% FiO2 increased eCO levels by a factor of four in every subjects (smokers and non smokers). eCO returned in a few minutes to the initial value when FiO2 was switched back to 21%. This magnification of eCO at 21% and 100% FiO2 is greater than those described in previous publications. We hypothesize that these results can be explained by the healthy status of our subjects (with low basal levels of eCO) and also by the better measurement precision of ProCeas.
《Soil Biology & Biochemistry》A new incubation and measurement approach to estimate the temperature response of soil organic matter decomposition.
Authors: Yuan Liu,Nianpeng He,Li Xu,Jing Tian,Yang Gao,Shuai Zheng,Qing Wang,Xuefa Wen,Xingliang Xu,Kuzyakov Yakov

Abstract: A reliable and precise estimate of the temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is critical to predict feedbacks between the global carbon (C) cycle and climate change. In this study, we first summarize two commonly used approaches for estimating Q10 (Approach A: constant temperature incubation and discontinuous measurements, CDM model; Approach B: varying temperature incubation and discontinuous measurements, VDM model). We then introduced a newly developed approach (Approach C, VCM model) that combines rapidly varying temperature incubations and continuous measurements of SOM decomposition rates (Rs) that may be more realistic and suitable for Q10 estimation, especially for large scale estimation. Then, we conducted a 26-day incubation experiment using three different soils to compare the performance of these three approaches for estimating Q10 using R2 and P-values as indicators. Our results demonstrate that the fitting goodness of the exponential model was consistently higher for Approach C, with higher R2 values, lower confidence intervals, and lower P-values in almost all cases compared with Approaches A and B. Furthermore,results showed that Approaches A and B underestimated the Q10 value by 9.5–13% and 2.9–5.7%, respectively,in three different soils throughout the entire incubation period. Compared with traditional commonly used methods, the newly developed Approach C (VCM model) provides a more accurate and rapid estimation of the temperature response of SOM decomposition and can be used for large-scale estimation of Q10. 原文链接
《Plant and Soil》Important interaction of chemicals, microbial biomass and dissolved substrates in the diel hysteresis loop of soil heterotrophic respiration
Authors: Qing Wang,Nianpeng He,Yuan Liu,Meiling Li,Li Xu,Xuhui Zhou 

Abstract: Background and aims Increasing the emission of carbon dioxide by heterotrophic respiration (Rh) might lead to global warming. However, issues remain on how Rh responds to changing temperatures, especially with respect to the hysteresis loop in the relationship between Rh and temperature at the daily scale, along with elucidating the underlying mechanisms.
Method We investigated hysteresis loop by measuring Rh in subtropical forest soil at the daily scale (12 h for warm-up (6–30 °C) and cool-down processes (30–6 °C), respectively) using continuous temperature variation and high resolution of measurements over a 56-day incubation period. The ratios of R20 and Q10 between warm-up and cooldown were calculated as the characteristics of diel hysteresis. We measured chemical (pH, conductivity,oxidation-reduction potential), microbial biomass and dissolved substrate (carbon and nitrogen) parameters to explain variation of diel hysteresis.
Results Rh was strongly dependent on temperature, with a clockwise hysteresis loop of Rh between the warm-up and cool-down daily processes. The average value of R20 [at a reference temperature of 20 °C] during the whole incubation period under the warm-up process was significantly higher (46.05 ± 0.96 μgC g−1 d−1) than that under the cool-down process (14.74 ± 0.03 μgC g−1 d−1). In comparison, the average value of Q10 under the cool-down process (5.27 ± 0.2) was significantly higher than that under the warm-up process (1.66 ± 0.02). Redundancy analysis showed that the interaction effects of soil chemical, microbial biomass, and dissolved substrate parameters explain most variation of diel hysteresis:98% variation in R20 and 93.5% variation in Q10.Compared with the weak effect of chemistry parameters on the diel hysteresis, the sole and interactive effects of microbial biomass and substrate were more important,especially their interaction.
Conclusions Interactions of chemical, microbial biomass,and dissolved substrate parameters dominated the variation in diel hysteresis of Rh with temperature,especially the interaction of microbial biomass and dissolved substrate. Of note, Q10 during the warm-up process might be overestimated when using the highly fitted temperature-dependent function of cool-down period.Furthermore, using a constant value of Q10 (Q10=2) in carbon cycle models might be an important source of uncertainty.     
《Science of Total Environment》Widespread asymmetric response of soil heterotrophic respiration to warming and cooling
Authors: Liu Y, Wen XF, Zhang YH, Tian J, Gao Y, Ostle NJ, Niu SL, Chen SP, Sun XM, He NP. 

Abstract: Soil is the largest organic carbon (C) pool in terrestrial ecosystems. Periodic changes in environmental temperature occur diurnally and seasonally; yet, the response of soil organic matter (SOM) decomposition to varying temperatures remains unclear. In this study, we conducted a modified incubation experiment using soils from 16 forest ecosystems in China with periodically and continuously varying incubation temperature to investigate how heterotrophic respiration (Rh) responds to different temperature patterns (both warming and cooling temperature ranging between 5 and 30°C). Our results showed a pronounced asymmetric response of Rh to temperature warming and cooling among the soils of all forest ecosystems, with Rh increasing more rapidly during the warming phase compared to the cooling phase. This asymmetric response of Rh to warming and cooling temperatures was widespread in all soils. In addition, the amplitude of this asymmetric response differed among different forest ecosystems, with subtropical and warm-temperate forest ecosystems exhibiting greater asymmetric responses. Path analyses showed that soil pH and the microbial community explained most of the variation in this asymmetric response. Furthermore, the widespread asymmetric response of Rh to warming and cooling temperatures suggests that accumulated SOM decomposition might be overestimated on average by 20% for warming alone when compared with admix warming and cooling. These findings provide new insights on the responses of Rh to natural shifts in temperature, emphasizing the need to consider this widespread asymmetric response of Rh to warming and cooling phases to predict C-climate feedback with great accuracy, especially under future non-uniform warming scenarios. 原文链接
《Journal of Geophysical Research: Biogeosciences》Soil microbial respiration rate and temperature sensitivity along a north-south forest transect in eastern China: Patterns and influencing factors

Authors: Wang Q, He NP, Yu GR, Gao Y, Wen XF, Wang RF, Koerner SE, Yu Q. 

Soil organic matter is one of the most important carbon (C) pools in terrestrial ecosystems, and future warming from climate change will likely alter soil C storage via temperature effects on microbial respiration. In this study, we collected forest soils from eight locations along a 3700km north-south transect in eastern China (NSTEC). For 8weeks these soils were incubated under a periodically changing temperature range of 6-30 degrees C while frequently measuring soil microbial respiration rate (Rs; each sample about every 20min). This experimental design allowed us to investigate Rs and the temperature sensitivity of Rs (Q(10)) along the NSTEC. Both Rs at 20 degrees C (R-20) and Q(10) significantly increased (logarithmically) with increasing latitude along the NSTEC suggesting that the sensitivity of soil microbial respiration to changing temperatures is higher in forest soils from locations with lower temperature. Our findings from an incubation experiment provide support for the hypothesis that temperature sensitivity of soil microbial respiration increases with biochemical recalcitrance (C quality-temperature hypothesis) across forest soils on a large spatial scale. Furthermore, microbial properties primarily controlled the observed patterns of R-20, whereas both substrate and microbial properties collectively controlled the observed patterns of Q(10). These findings advance our understanding of the driving factors (microbial versus substrate properties) of R-20 and Q(10) as well as the general relationships between temperature sensitivity of soil microbial respiration and environmental factors.

《Ecology & Evolution》Changes in the temperature sensitivity of SOM decomposition with grassland succession: implications for soil C sequestration

作者:He Nianpeng, Wang Ruomeng, Gao Yang, Dai Jingzhong, Wen Xuefa, Yu Guirui


《Geoderma》Strong pulse effects of precipitation events on soil microbial respiration in temperate forests
作者:Wang Qing,He Nianpeng,Liu Yuan,Li Meiling,Xu li

摘要:降水是干旱半干旱地区土壤生物地球化学过程的关键因素。在本研究中,我们选取了两个温带森林的土壤——一个成熟的天然森林和一个退化的次生森林——半干旱地区。研究了模拟降水(达到55%的土壤含水能力)对土壤微生物呼吸速率(RS)的脉冲效应。我们对以下指标进行了高强度的测量(48小时内每隔5分钟测定1次):土壤呼吸最大值(RS-max),达到最大值的时间(TRS-max)和脉冲效应的持续时间(从开始到结束的½RS-max)。RS对模拟降水的响应速度快、强度大。RS-max在退化次生林中明显高于成熟天然林(7.94 g C g soil-1h-1)。相比之下,在退化次生林中脉冲效应和TRS - max的持续时间明显低于成熟的天然林。此外,在退化次生林和成熟的天然林之间,每克土壤的累计微生物呼吸量(ARS -土壤)并无显著差异,但在退化次生林中,每克土壤有机C (ARS‐soc)的累计微生物呼吸量明显高于成熟的天然林。土壤微生物生物量、土壤养分和垃圾氮含量与脉冲效应和TRS - max的持续时间密切相关。土壤物理结构、pH值和垃圾氮含量与RS-max和ARS‐soc之间存在显著的相关性。我们的研究结果表明,土壤微生物呼吸作用对模拟降水的响应快速、强烈。每克C微生物呼吸率可以被用来精确确定全球气候变化的各种场景下不同土样的降水脉冲以及降雨模式的改变对土壤C含量的影响。
《Glob Chang Biol》Regional variation in the temperature sensitivity of soil organic matter decomposition in China's forests and grasslands
作者:Liu Yuan,He NianPeng,Zhu JianXing,Xu Li,Yu GuiRui,Niu ShuLi,Sun XiaoMin,Wen XueFa

《Soil Biology & Biochemistry》The optimum temperature of soil microbial respiration: Patterns and controls
作者:Liu, Yuan   He, Nianpeng   Wen, Xuefa   Xu, Li   Sun, Xiaomin   Yu, Guirui   Liang, Liyin   Schipper, Louis A.

摘要:土壤微生物呼吸(Rh)的温度响应具有重要意义,Rh的最佳温度是准确模拟气候变暖情况下如何应对温度变化的关键参数。然而,在自然生态系统中,关于温度选择的知识仍然有限,特别是在大范围内,这增加了气候预测的不确定性。在这里,我们收集了25个北半球自热带到冷温带森林的土壤,以量化温度选择的区域变化和这种变异的控制机理。采用一种新的系统(PRI-8800全自动变温控制系统),温度逐渐从5度增加到50度,在高频率下测量Rh的温度。结果表明,温度的选择范围从38.5到46.0 ℃(平均值:42.4 ℃)。值得注意的是,这项研究首次证明了温度的选择远高于模型中所使用的假设值(35 ℃),在不同的气候带中有很大的差异,并且随着从热带到冷温带森林土壤的纬度的增加而增加。在一定程度上,我们的研究结果支持了底物供给假说,并与气候适应假说形成了对比。此外,气候、营养和土壤微生物共同调节温度选择的区域变异,共同解释了温度选择中53%的变异。北部地区较高的温度选择表明,这些地区有更大的潜力从土壤中释放更多的二氧化碳,这可能会给全球变暖带来积极的反馈。总之,基于过程的模型应该包含不同区域的温度具有可选性,以改善在气候变暖情况下陆地生态系统的碳动力学的预测。 原文链接