Authors:
Jinyang Zheng, Xiali Mao , Kees Jan van Groenigen , Shuai Zhang , Mingming Wang , Xiaowei Guo, Wu Yu , Lun Luo , Jinfeng Chang , Zhou Shi , Zhongkui Luo
Abstract：
Soil microbes drive soil organic carbon (SOC) mineralization. Because microbial groups differ in metabolic efficiency and respond differently to temperature variation, it is reasonable to expect a close association of SOC mineralization and its temperature sensitivity (Q10 which is defined as the factor of the change of soil carbon mineralization induced by 10 °C temperature increase) with microbial community diversity and composition. However, these relations have rarely been tested. Here, we conducted an incubation experiment to assess the temperature responses of microbial α diversity and the relative abundance of microbial r- and K-strategists in soils from a wide range of ecosystems across a climate gradient in the southeast Tibet. The results indicated that the instantaneous α diversity and the relative abundance of r- and K-strategists are significantly (P < 0.05) influenced by temperature, but these microbial variables are poor predictors of SOC mineralization measured at the same time. Rather, microbial community diversity and the relative abundance of r- and K-strategists of fresh soils showed consistent and significant (P < 0.05) effects on both SOC mineralization and Q10 at different incubation stages. Importantly, path analysis indicated that microbial α diversity and r- and K-strategists exerts no independent effects on SOC mineralization and Q10 when variation in climate, SOC chemistry, physical protection, and edaphic properties are accounted for. Together, our results suggest that while soil microbial community diversity and composition are a strong proxy of SOC quality and availability, they are not a fundamental determinant of SOC mineralization and Q10.
Keywords:
Bacteria
Carbon fractions
Fungi
Microbial diversity
r/K strategists
Soil organic carbon
Temperature sensitivity (Q10)
Soil profile
原文鏈接Authors:
Jun Pan , Yuan Liu , Nianpeng He , Chao Li , Mingxu Li , Li Xu , Osbert Jianxin Sun
Abstract：
As one of the most important drivers of global climate change, land use change (LUC) has markedly altered the regional and global carbon (C) cycles. However, the geographic variations and the key drivers in the effects of LUC on temperature sensitivity (Q10) of soil microbial respiration (Rs) are still not fully elucidated, hence impeding the spatially explicit predictions of soil C cycling under climate change. Here, we used a paired-plot approach with data for 19 locations distributed from the tropical to temperate zones in eastern China, and compared the temperature responses of Rs between forest and cropland soil. Results showed that the latitudinal patterns of Q10 in forest soils were better explained by climatic variables; whereas in cropland, soil Q10 trended higher with increasing latitude, with climatic factors, pH, clay, and soil organic C (SOC) jointly modulating the spatial variations in Q10. Overall, the values of Q10 tended to converge with latitude between forests and croplands, with change in Q10 from forest to cropland, ΔQ10, significantly decreasing from the tropical region (9.23 ± 3.58 %) to the subtropical (0.58 ± 1.93 %) and temperate (−0.97 ± 1.11 %) regions. Moreover, the spatial variations of ΔQ10 were significantly affected by climatic factors, ΔpH, Δmicrobial biomass C (ΔMBC), and their interactions. Our findings highlight the potential impacts of LUC-related biogeographic variations in the temperature response of Rs, and emphasize the importance of incorporating the land-use effects on the temperature sensitivity of soil microbial respiration into terrestrial C cycle models to improve predictions of carbon-climate feedbacks in the future.
Keywords:
Carbon；Global warming；Land use change；SOM；Geographical variation；Temperature sensitivity；ORGANIC-MATTER DECOMPOSITION；LAND-USE CONVERSION；CARBON DECOMPOSITION；CLIMATE-CHANGE；CO2 EMISSIONS；Q(10) VALUES；INCUBATION；PH；MINERALIZATION；AVAILABILITY
原文鏈接Authors:
Yalong Kang , Linjun Shen , Canfeng Li , Yong Huang , Liding Chen
Abstract：
Vegetation degradation caused by intense human disturbances poses a significant challenge to the preservation and improvement of ecosystem functions and services in the karst region of southwest China. Soil microorganisms are major regulators of ecosystem multifunctionality (EMF). Currently, there is a dearth of knowledge regarding the effects of vegetation degradation on soil microbial communities and their corresponding multiple ecosystem functions in karst regions. In this study, we selected the vegetation degradation sequences of second natural forest (NF), agroforestry (AS) and cropland (CL) to investigate the diversity of bacterial, fungal and protistan communities, and their hierarchical co-occurrence network, and EMF to explore the relationships between them. Compared to the NF, the carbon cycling index, nitrogen cycling index, soil water regulation power, and the EMF were significantly decreased by 8.2%–50.6%, 48.7%–86.8%, 19.8%–24.5%, and 31.4%– 69.5% in the AS and CL, respectively. The development of EMF can be explained by the fungal, protistan and microbial hierarchical β-diversity, as well as the complexity (e.g. degree) of microbial hierarchical interactions during the process of vegetation degradation. Notably, correlations between the abundances of sensitive amplicon sequence variants (sASVs) for different karst vegetation types and EMF varied in distinct network modules, being positive in module 1 and negative in module 2. Moreover, the relative abundance of keystone taxa in fungal and protistan communities provided greater contributions to EMF than the bacterial communities. Additionally, random forest modeling showed that carbon and nitrogen sources, and soil water content, and trace elements (e.g. exchangeable magnesium, iron, manganese, and zinc) were identified as key driving factors of the EMF. Collectively, our findings demonstrate that vegetation degradation obviously alters soil microbial diversities and hierarchical interactions, emphasizing their key role in maintaining ecosystem functions and health in karst regions.
Article info:
Keywords:
Karst
Vegetation degradation
Microbial diversity
Microbial multitrophic network
Core phylotypes
Ecosystem multifunctionality
原文鏈接
Authors:
Ruiqiang Liu , Xuhui Zhou , Yanghui He , Zhenggang Du , Hongyang Chen , Yuling Fu , Liqi Guo , Guiyao Zhou , Lingyan Zhou , Jie Li , Hua Chai , Changjiang Huang , Manuel Delgado-Baquerizo
Abstract：
Ecological succession and restoration rapidly promote multiple dimensions of ecosystem functions and mitigate global climate change. However, the factors governing the limited capacity to sequester soil organic carbon (SOC) in old forests are poorly understood. Ecological theory predicts that plants and microorganisms jointly evolve into a more mutualistic relationship to accelerate detritus decomposition and nutrient regeneration in old than young forests, likely explaining the changes in C sinks across forest succession or rewilding. To test this hypothesis, we conducted a field experiment of root-mycorrhizal exclusion in successional subtropical forests to investigate plant-decomposer interactions and their effects on SOC sequestration. Our results showed that SOC accrual rate at the 0–10 cm soil layer was 1.26 mg g−1 yr−1 in early-successional arbuscular mycorrhizal (AM) forests, which was higher than that in the late-successional ectomycorrhizal (EcM) forests with non-significant change. A transition from early-successional AM to late-successional EcM forests increase fungal diversity, especially EcM fungi. In the late-successional forests, the presence of ectomycorrhizal hyphae promotes SOC decomposition and nutrient cycle by increasing soil nitrogen and phosphorus degrading enzyme activity as well as saprotrophic microbial richness. Across early- to late-successional forests, mycorrhizal priming effects on SOC decomposition explain a slow-down in the capacity of older forests to sequester soil C. Our findings suggest that a transition from AM to EcM forests supporting greater C decomposition can halt the capacity of forests to provide nature-based global climate change solutions.
原文鏈接Authors:
寧玉娜，王占義，高翠萍，呂廣一，楊昌祥，張春英，王成杰
Abstract：
在氣候變暖影響下，研究放牧對草原土壤呼吸速率(Soil respiration rate，Rs)及其溫度敏感性系數(Temperature sensitivity，Q10)的影響，對闡述草原生態系統碳收支具有重要意義。以荒漠草原為研究對象，設置無牧、輕度放牧和重度放牧3個處理，運用全自動變溫培養土壤溫室氣體在線測量系統，測定不同放牧處理區0~30 cm土壤變溫(-10~25℃)培養下的呼吸速率并計算Q10。結果表明：放牧處理9年后的Rs及其Q10值為：重度放牧Rs顯著高于無牧和輕度放牧(P<0.05)，重度放牧顯著增加0~10 cm土層Q10值；與無牧相比，輕度放牧顯著降低20~30 cm土層Q10值；主成分分析表明：放牧強度主要影響土壤pH值、粉粒含量，進而影響Rs。輕度放牧可降低土壤呼吸Q10值，從而減少荒漠草原土壤CO2排放。因此，建議實施輕度放牧管理策略以減少荒漠草原的碳排放。
關鍵詞：荒漠草原, 放牧強度, 土壤呼吸速率, 溫度敏感性
Authors:
Yuan Liu, Amit Kumar, Lisa K. Tiemann, Jie Li, Jingjing Chang, Li Xu & Nianpeng He
Abstract:
Purpose
The purpose of this study was to investigate how changes in substrate availability (stimulating root exudate input) affect the temperature response (Q10) of soil organic carbon (SOC) mineralization across different soil profiles to increase our ability to predict the response of soil organic matter dynamics to climate change.
Materials and methods
We sampled the topsoil and subsoil of two typical mineral soil profiles and one buried soil profile. Soils were incubated at 10–25 °C at 0.75 °C intervals, SOC mineralization rates were continuously measured with and without glucose addition, and Q10 was calculated.
Results and discussion
Our results showed that Q10 decreased with increasing depth in typical mineral soils, but decreased before increasing with depth in buried soil. As expected, substrate addition significantly increased Q10 across soil depths; however, the magnitude of this increase (ΔQ10) differed with soil depth and type. Unexpectedly, in typical mineral soils, ΔQ10 was higher in topsoil than in subsoils, and vice versa for buried soil. ΔQ10 was negatively correlated with initial soil substrate availability (CAI) and positively correlated with soil inorganic N.
Conclusions
Overall, our results suggested that increased substrate availability under climate change scenarios (i.e., increased root exudates with elevated CO2 concentrations) could further strengthen the temperature response of SOC mineralization, especially in soils with high inorganic N content or regions with high N deposition rates.
原文鏈接Authors:
Mengyang You , Diankun Guo , Hongai Shi , Peng He , Martin Burger , Lu Jun Li
Abstract:
Background and aim
Soil organic carbon (SOC) mineralization which relates to SOC stability and sequestration, predicating the SOC stocks under climate change, is affected by land use and exogenous carbon addition. However, how SOC chemical composition and soil enzymes regulate SOC mineralization of grassland and forest soils receiving exogenous C addition is still not well understood.
MethodsForest and grassland soils were incubated without or with two levels of 13C-enriched glucose, simulating labile C inputs, at 15 and 25 ℃ for 28 days. The priming effect, temperature sensitivity (Q10), enzyme activities and chemical composition of SOC were determined.
ResultsIncreasing labile C addition and higher temperature accelerated native SOC mineralization in forest and grassland soil. Changes of enzyme C:N and N:P ratio contributed to the differences in CO2 production in forest and grassland soil. In grassland soil, the relationship between soil-derived CO2 production and relative peak areas of SOC at 1420 cm−1 by Fourier-Transform infrared spectroscopy was significant. The temperature sensitivity of the native SOC mineralization in the forest soil amended with 0.8 g glucose-C kg−1 dry soil application was greater than that with 0.4 g glucose-C kg−1 dry soil application, but in the grassland soil, the Q10 of glucose derived CO2 emission was lower after the higher glucose application.
ConclusionSoil enzyme nutrient ratios and chemical composition of SOC together play an important role in regulating the mineralization of SOC and the Q10 value of external C addition mineralization in forest and grassland soil.
原文鏈接Authors:
Xuhui Zhou , Zhiqiang Feng , Yixian Yao , Ruiqiang Liu , Junjiong Shao , Shuxian Jia , Yining Gao , Kui Xue , Hongyang Chen , Yuling Fu , Yanghui He
Abstract:
The combination of biochar and nitrogen (N) addition has been proposed as a potential strategy to sustain crop productivity and mitigate climate change by increasing soil fertility, sequestering carbon (C), and reducing soil greenhouse gas emissions. However, our current knowledge about how biochar and N additions interactively alter mineralization of native soil organic C (SOC), which is referred to priming effects (PEs), is largely limited.To address this uncertainty, C3 biochar (pyrolyzing rice straw at 300, 550, and 800 ?C) and its combination with N fertilizer (urea) were incubated in a C4-derived soils at 25 ?C. All these 3 types of biochar with different addition rates caused positive priming of native soil organic matter decomposition (up to +58.4%). The maximum negative priming effects (up to − 25.4%) occurred in soil treated with 1% of N-bound biochar pyrolyzed at 300 ?C. In addition, a negative correlation was found between the priming intensity and soil inorganic N content across all treatments. The decrease in biochar-induced PEs was related with a shift in microbial community composition and reduction in microbial biomass determined by chloroform-fumigation. Such a reduction, however, was not confirmed by PLFA analysis. These findings advance our understanding on the microbial mechanisms mediating net soil C balance with the adequate biochar use for blending traditional mineral fertilizers.
原文鏈接
Authors:
Mengyu Liu , Yao Yu , Ying Liu , Sha Xue b, Darrell W.S. Tang , Xiaomei Yang
Abstract:
astic pollution in agricultural soils due to polyethylene plastic film mulch used, biodegradable film is being studied as a promising alternative material for sustainable agriculture. However, the impact of biodegradable and polyethylene microplastics on soil carbon remains unclear. The field experiment was conducted with Poly (butyleneadipate-co-terephthalate) debris (PBAT-D, 0.5–2 cm), low-density polyethylene debris (LDPE-D, 0.5–2 cm) and microplastic (LDPE-Mi, 500–1000 μm) contaminated soil (0% (control), 0.05%, 0.1%, 0.2%, 0.5%, 1% and 2% w:w) planted with soybean, to explore potential impacts on soil respiration (Rs), soil organic carbon (SOC) and carbon fractions (microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidizable carbon (EOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC)), and C-enzymes (β-glucosidase, β-xylosidase, cellobiohydrolase). Results showed that PBAT-D, LDPE-D and LDPE-Mi significantly inhibited Rs compared with the control during the flowering and harvesting stages (p < 0.05). SOC significantly increased in the PBAT-D treatments at both stages, and in the LDPE-Mi treatments at the harvesting stage, but decreased in the LDPE-D treatments at the flowering stage. In the PBAT-D treatments, POC increased but DOC and MAOC decreased at both stages. In the LDPE-D treatments, MBC, DOC and EOC significantly decreased but POC increased at both stages. In the LDPE-Mi treatments, MBC and DOC significantly decreased at the harvesting stage, while EOC and MAOC decreased but POC increased at the flowering stage. For C-enzymes, no significant inhibition was observed at the flowering stage, but they were significantly inhibited in all treatments at the harvesting stage. It is concluded that PBAT-D facilitates soil carbon sequestration, which may potentially alter the soil carbon pool and carbon emissions. The key significance of this study is to explore the overall effects of different forms of plastic pollution on soil carbon dynamics, and to inform future efforts to control plastic pollution in farmlands.
原文鏈接Authors:
Shenliang Zhao , Hua Chai , Yuan Liu , Xiaochun Wang , Chaolian Jiao , Cheng Liu a , Li Xu d, Jie Li , Nianpeng He
Abstract:
How and what soil fauna influence the soil organic matter (SOM) decomposition rate (Rs) and its temperature sensitivity (Q10) have been largely ignored, although this is a crucial matter, especially under the scenario of global change. In this study, a novel approach was adopted with a continuous changing-temperature incubation (daytime, from 7 °C to 22 °C; nighttime, from 22 °C to 7 °C) with rapid and continuous measurement, to examine the effect of soil macrofauna (specifically, earthworms) on Rs and Q10 with three densities (no addition, low density, and high density). According to the results, the earthworms accelerated Rs. Furthermore, Rs with earthworm addition had a symmetrical pattern during daytime and nighttime cycles, which is contrary to traditional soil incubation, with only soil microbe as asymmetrical. More importantly, earthworm addition increased Q10 markedly, ranging from 48% to 67%. Overall, the findings highlight the pivotal role of earthworms as soil macrofauna that regulating soil carbon release, and their effects should be integrated into process-based ecological models in future.
Authors:
Jinyang Zheng , Kees Jan van Groenigen d, Iain P. Hartley , Ran Xue , Mingming Wang , Shuai Zhang , Ting Sun , Wu Yu, Bin Ma, Yu Luo , Zhou Shi , Zhongkui Luo
Abstract:
Soil organic carbon (SOC) mineralization, driven by soil microbial communities, plays a crucial role in the global carbon cycle. However, the temperature sensitivity of microbial preferences for SOC substrates remains poorly understood, limiting our ability to predict SOC dynamics under climate change. Here we combined bacterial community profiling, laboratory incubations, and a pool-based carbon model to investigate the relationships between bacterial species abundances and two SOC pools with fast and slow decay rates, respectively, at different incubation temperatures. Only about half of identified bacterial species is significantly (P < 0.05) associated with the mineralization of the two pools and their temperature sensitivity (Q10). More importantly, we find that the association of the species with the two pools shifts in terms of both magnitude and direction with incubation temperature. The proportion of species associated with the Q10 of fast pool decreased, while those associated with the Q10 of slow pool increased with warming. Meanwhile, species specifically associated with the fast pool exhibit stronger temperature sensitivity compared to species specifically associated with the slow pool at lower temperatures, and vice versa at higher temperatures. These results suggest that common bacterial species associated with SOC mineralization adjust their substrate preferences in response to temperature variations, potentially impacting SOC composition and dynamics under warming. 原文鏈接Authors:
Ming Gao,Wei Hu,Meng Li,Mingming Guo,Yongsheng Yang
Abstract:
Land-use change directly impacts soil basal respiration (Br), soil microbial attributes, and soil organic matter (SOM) composition. However, the role of soil microbial attributes and SOM composition in influencing soil Br under land-use changes remains largely undetermined. We examined how interactions between soil physicochemical properties, SOM chemical structure, and microbial attributes regulate soil Br across three land-use types, cropland, forest, and grassland, in the Mollisol and Arenosol of Horqin Sandy Land. The results showed that soil Br, phospholipid fatty acid content, and the relative peak areas of aliphatic and aromatic compounds were significantly lower in cropland than in forest and grassland. Additionally, the Arenosol exhibited poorer soil properties compared to the Mollisol (p < 0.05). Soil Br in the Mollisol (3.60–5.56 mgCO2-C kg−1 h−1) was significantly higher than in the Arenosol (0.86–2.60 mgCO2-C kg−1 h−1, p < 0.05). G+/G− ratios and bacteria were identified as the main predictors of Br in the Mollisol and Arenosol, respectively. The structural equation model revealed that microbial attributes are the primary drivers of Br, influencing it indirectly through changes in SOM composition. Our findings are instrumental in understanding the role of microbial attributes in carbon turnover during land-use changes.
原文鏈接Authors:
Huiling Wang, Hang Jing , Huizhen Ma , Guoliang Wang
Abstract:
The mechanisms by which belowground plant deposits influence soil organic carbon dynamics under increasing nitrogen (N) deposition remain unclear. In this study, ingrowth cores with different mesh sizes (1?µm, 45?µm and 1?mm) were used to investigate the effects of mycelium and fine root deposits on soil dissolved organic matter (DOM) and CO2 emissions under N addition. Results indicated that mycelium did not significantly alter DOM composition or microbial community, whereas several labile (including amino sugars and carbohydrates) and recalcitrant DOM (including lignin and tannin) were enriched in the fine root and coarse root treatments, respectively. The fungal community shifted towards a K-strategy in the presence of mycelium and roots compared to the control treatment (1?µm). N addition increased the abundance of recalcitrant DOM molecules, particular in fine root treatments. Root deposit inputs increased DOM transformation and the complexity of the DOM-microbe network. The associations between microbes and labile carbon were enhanced in the mycelium and fine root treatments. The relationships between oligotrophic Basidiomycota and recalcitrant carbon were strengthened in the coarse root treatment. CO2 emissions in mycelium treatments were inhibited by N addition, primarily due to a decrease in mycorrhizal colonization. Root deposit inputs and DOM-microbe interactions dominated the CO2 emissions in the forest soil under N addition. Our findings confirm the essential role of fine root deposits, in regulating soil CO2 emissions by influencing DOM characteristics under N deposition.
原文鏈接Authors:
Zhiyun Zhou, Ni Zhang, Yijun Wang & Kelong Chen
Abstract:
Background and aims
Freeze–thaw cycles (FTC) can affect the rates of soil organic carbon (SOC) mineralization and carbon (C) and nitrogen (N) cycling in soils. However, little is known about whether this effect changes with litter inputs, especially for alpine grassland ecosystems.
Methods
Using soil and Litter from Tibetan Plateau alpine meadows, we conducted a 15-day indoor experiment under two FTC regimes (-15 to 15℃ and -10 to 10℃), constant 10℃, and litter addition.
Results
The results showed that the SOC mineralization rates under the I ± 10 and I ± 10L treatments were significantly lower than those of the control by 7.85% and 6.20%, respectively, while the C mineralization rates under the I ± 15L treatment were significantly higher than that of the control by 20.78%. The temperature sensitivity (Q10) was significantly higher under I ± 10 than under I ± 15. The C mineralization rates under the control + L treatment were 42.76% higher than those of the control and induced a significant priming effect (PE), which was significantly lower in the I ± 10L treatment compared to the control + L. Structural equation modeling suggested that FTC indirectly affected C mineralization via changes in ammonium nitrogen (NH4+-N) and microbial biomass carbon (MBC), whereas litter addition directly altered MBC to promote C release.
Conclusion
Our findings suggest that the I ± 10L treatment can reduce the rates of soil C mineralization and PE in alpine swamp meadows. However, the control + L treatment significantly enhances the availability of organic carbon for microbial decomposition, thereby accelerating C release. Therefore, the impact of the reduction in freeze–thaw events under climate warming must be re-evaluated within broader environmental and ecological contexts.
原文鏈接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. 原文鏈接
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. 原文鏈接
Abstract：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.
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. 原文鏈接
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. 原文鏈接
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. 原文鏈接
Authors: Wang Q, He NP, Yu GR, Gao Y, Wen XF, Wang RF, Koerner SE, Yu Q.
Abstract: 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.
作者：He Nianpeng, Wang Ruomeng, Gao Yang, Dai Jingzhong, Wen Xuefa, Yu Guirui
摘要：了解土壤有機質(SOM)分解的溫度敏感性(Q10)對于預測在變暖場景下的陸地生態系統中的土壤碳(C)封存是很重要的。Q10是否會隨著生態系統的演替而變化，以及輸入SOM影響Q10的化學計量方法在很大程度上仍不為人所知。我們以內蒙古草原的一個演替系列：從自由放牧到31年圍欄封育草場為研究對象，設置6個溫度(0、5、10、15、20、25°C)和四種基質:控制(CK)、葡萄糖(GLU)、混合牧草葉片(GRA)和苜蓿葉(MED)。結果表明,基底土壤呼吸(20°C)和微生物生物量C(MBC)隨草場演替呈對數降低。Q10從自由放牧草地的1.43下降到31年圍欄封育草場的1.22。隨著底物的增加，Q10顯著增加，而Q10的水平隨著N的增加而增加。此外，C礦化的積累受新輸入SOM和潛伏期溫度的控制。隨著草地生態系統的演替，Q10的變化受新輸入SOM、MBC、SOM質量的化學計量控制，其綜合作用可以部分解釋中國內蒙古長期放牧草原的土壤碳封存機制。研究結果強調了底物化學計量對Q10的影響還需要進一步研究。
摘要：土壤微生物呼吸（Rh）的溫度響應具有重要意義，Rh的最佳溫度是準確模擬氣候變暖情況下如何應對溫度變化的關鍵參數。然而，在自然生態系統中，關于溫度選擇的知識仍然有限，特別是在大范圍內，這增加了氣候預測的不確定性。在這里，我們收集了25個北半球自熱帶到冷溫帶森林的土壤，以量化溫度選擇的區域變化和這種變異的控制機理。采用一種新的系統（PRI-8800全自動變溫控制系統），溫度逐漸從5度增加到50度，在高頻率下測量Rh的溫度。結果表明，溫度的選擇范圍從38.5到46.0 ℃（平均值：42.4 ℃）。值得注意的是，這項研究首次證明了溫度的選擇遠高于模型中所使用的假設值（35 ℃），在不同的氣候帶中有很大的差異，并且隨著從熱帶到冷溫帶森林土壤的緯度的增加而增加。在一定程度上，我們的研究結果支持了底物供給假說，并與氣候適應假說形成了對比。此外，氣候、營養和土壤微生物共同調節溫度選擇的區域變異，共同解釋了溫度選擇中53%的變異。北部地區較高的溫度選擇表明，這些地區有更大的潛力從土壤中釋放更多的二氧化碳，這可能會給全球變暖帶來積極的反饋。總之，基于過程的模型應該包含不同區域的溫度具有可選性，以改善在氣候變暖情況下陸地生態系統的碳動力學的預測。 原文鏈接
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