Authors:

Mengyang You , Diankun Guo , Hongai Shi , Peng He , Martin Burger , LuJun 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.

Methods

Forest 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.

Results

Increasing 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.

Conclusion

Soil 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.

Original link

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.

 

Original link

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.

Original link

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.

Original link

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. Original link

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.

Original link

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.

Original link

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.

Original link

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. Original link

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. Original link

Authors：Vivien Brenckmann, Irène Ventrillard, Daniele Romanini, Kévin Jaulin, Pascale Calabrèse & Raphaël Briot

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. Original link

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 (R_s) 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. Original link

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 (R_h) might lead to global warming. However, issues remain on how R_h responds to changing temperatures, especially with respect to the hysteresis loop in the relationship between R_h and temperature at the daily scale, along with elucidating the underlying mechanisms.
Method We investigated hysteresis loop by measuring R_h 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 R_h was strongly dependent on temperature, with a clockwise hysteresis loop of R_h 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 R_h 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.
Original link

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. Original link

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. Original link

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

Abstract:Understanding the temperature sensitivity (Q 10) of soil organic matter (SOM) decomposition is important for predicting soil carbon (C) sequestration in terrestrial ecosystems under warming scenarios. Whether Q 10 varies predictably with ecosystem succession and the ways in which the stoichiometry of input SOM influences Q 10 remain largely unknown. We investigate these issues using a grassland succession series from free-grazing to 31-year grazing-exclusion grasslands in Inner Mongolia, and an incubation experiment performed at six temperatures (0, 5, 10, 15, 20, and 25°C) and with four substrates: control (CK), glucose (GLU), mixed grass leaf (GRA), and Medicago falcata leaf (MED). The results showed that basal soil respiration (20°C) and microbial biomass C (MBC) logarithmically decreased with grassland succession. Q 10 decreased logarithmically from 1.43 in free-grazing grasslands to 1.22 in 31-year grazing-exclusion grasslands. Q 10 increased significantly with the addition of substrates, and the Q 10 levels increased with increase in N:C ratios of substrate. Moreover, accumulated C mineralization was controlled by the N:C ratio of newly input SOM and by incubation temperature. Changes in Q 10 with grassland ecosystem succession are controlled by the stoichiometry of newly input SOM, MBC, and SOM quality, and the combined effects of which could partially explain the mechanisms underlying soil C sequestration in the long-term grazing-exclusion grasslands in Inner Mongolia, China. The findings highlight the effect of substrate stoichiometry on Q 10 which requires further study. Original link

Authors:Wang Qing,He Nianpeng,Liu Yuan,Li Meiling,Xu li

Abstract:Precipitation is a critical factor triggering soil biogeochemical processes in arid and semi-arid regions. In this study, we selected soils from two temperate forests—a mature natural forest and a degraded secondary forest—in a semi-arid region. We investigated the pulse effects of simulated precipitation (to reach 55% soil water-holding capacity) on the soil microbial respiration rate (RS). We performed high-intensity measurements (at 5-min intervals for 48 h) to determine the maximum value of RS (RS-max), the time to reach RS-max (TRS-max), and the duration of the pulse effect (from the start to the end of ½RS-max). The responses of RS to simulated precipitation were rapid and strong. RS-max was significantly higher in degraded secondary forest (18.69 µg C g soil–1 h–1) than in mature natural forest (7.9 4 µg C g soil–1 h–1). In contrast, the duration of the pulse effect and TRS-max were significantly lower in degraded secondary forest than in mature natural forest. Furthermore, the accumulative microbial respiration per gram of soil (ARS-soil) did not differ significantly between degraded secondary forest and mature natural forest, but the accumulative microbial respiration per gram of soil organic C (ARS-soc) was significantly higher in degraded secondary forest than in mature natural forest. Soil microbial biomass, soil nutrient, and litter nitrogen content were strongly correlated with the duration of the pulse effect and TRS-max. Soil physical structure, pH, and litter nitrogen content were strongly correlated with RS-max and ARS-soc. Our results indicate that the responses of soil microbial respiration to simulated precipitation are rapid and strong and that microbial respiration rate per gram C is able assess precisely the precipitation pulse of different soil samples as well as the effects of changing precipitation patterns on soil C content under various scenarios of global climate change. Original link

Authors: YUAN LIU,NIANPENG HE,JIANXING ZHU,LI XU,GUIRUI YU,SHULI NIU,XIAOMIN SUN and XUEFA WEN

Abstract:How to assess the temperature sensitivity (Q₁₀ ) of soil organic matter (SOM) decomposition and its regional variation with high accuracy is one of the largest uncertainties in determining the intensity and direction of the global carbon (C) cycle in response to climate change. In this study, we collected a series of soils from 22 forest sites and 30 grassland sites across China to explore regional variation in Q₁₀ and its underlying mechanisms. We conducted a novel incubation experiment with periodically changing temperature (5-30 °C), while continuously measuring soil microbial respiration rates. The results showed that Q₁₀ varied significantly across different ecosystems, ranging from 1.16 to 3.19 (mean 1.63). Q₁₀ was ordered as follows: alpine grasslands (2.01) > temperate grasslands (1.81) > tropical forests (1.59) > temperate forests (1.55) > subtropical forests (1.52). The Q₁₀ of grasslands (1.90) was significantly higher than that of forests (1.54). Furthermore, Q₁₀ significantly increased with increasing altitude and decreased with increasing longitude. Environmental variables and substrate properties together explained 52% of total variation in Q₁₀ across all sites. Overall, pH and soil electrical conductivity primarily explained spatial variation in Q₁₀ . The general negative relationships between Q₁₀ and substrate quality among all ecosystem types supported the C quality temperature (CQT) hypothesis at a large scale, which indicated that soils with low quality should have higher temperature sensitivity. Furthermore, alpine grasslands, which had the highest Q₁₀ , were predicted to be more sensitive to climate change under the scenario of global warming. Original link

Authors: :Liu, Yuan   He, Nianpeng   Wen, Xuefa   Xu, Li   Sun, Xiaomin   Yu, Guirui   Liang, Liyin   Schipper, Louis A.

Abstract:The temperature response of soil microbial respiration (Rh) is of significance, with the optimum temperature ofRhbeing the key parameter for accurately modeling how it responds to temperature change under climatewarming scenarios. However, knowledge about Toptin natural ecosystems remains limited, especially at largescales, which increases the uncertainty of climate projections. Here, we collected 25 soils from tropical to cold-temperate forests in the northern hemisphere to quantify regional variation in Toptand the controls underlyingthis variation. Rhwas measured at high frequency using a novel system under the mode, with temperaturegradually increasing from 5 to 50 °C. The results showed that Toptranged from 38.5 to 46.0 °C (mean: 42.4 °C). Ofnote, this study is the first to demonstrate that Toptis far higher than the assumed value used in models (35 °C),varying greatly across different climatic zones and increasing with latitude from tropical to cold-temperate forestsoils. To some extent, our results supported the substrate supply hypothesis, and contrast with the climateadaption hypothesis. In addition, climate, nutrient, and soil microorganisms jointly regulate regional variation inTopt, together explaining 53% of variation in Topt. The higher Toptin northern regions indicated that theseregions have a greater potential to release more CO2from soil, which might lead to a positive feedback to globalwarming. In conclusion, process-based models should incorporate the high variability of Toptacross regions toimprove predictions of the carbon dynamics of terrestrial ecosystems under climate warming scenarios. Original link