Sensitivity Of Soil Respiration Research Articles

Slow post-fire carbon balance recovery despite increased net uptake rates in Alaskan tundra

Abstract Increasing wildfire occurrence and intensity have immediate effects on northern ecosystems due to combustion of aboveground vegetation and belowground soil organic matter. These immediate impacts have indirect and longer term effects, including deepening of the active layer, changes in soil decomposition rates, and shifts in plant community composition. Despite the increasing fire impacts across the tundra region, the implications of wildfire on ecosystem carbon balance are not well understood. Using paired eddy covariance towers in unburned and burned tundra, we examined the effects of a 2015 wildfire on carbon dioxide and methane fluxes in a wetland tundra ecosystem in the Yukon-Kuskokwim Delta, Alaska, from 2020 to 2022. Wildfire increased the amplitude and variability of carbon uptake and release on seasonal and annual timescales and increased the temperature sensitivity of soil respiration. Seven years post fire, there was annual net uptake in both unburned and burned tundra based on net ecosystem exchange, with the sink strength of burned tundra exceeding that of the unburned tundra by 1.18 to 1.64 times. However, when considering emissions, it would take approximately 86 years to recover the carbon lost from the wildfire itself. Soil moisture was a dominant driver of fluxes and positively associated with higher rates of carbon dioxide uptake and release and methane release. This study underscores the importance of understanding the effects of wildfire-induced shifts on tundra carbon cycling, allowing better predictions of long-term landscape-scale climate feedbacks as the climate continues to warm.

The effect of postfire regeneration pattern on soil respiration in the boreal forest of China

BackgroundAs the second largest carbon flux between the atmosphere and terrestrial ecosystems, soil respiration involves multiple components of ecosystem production. Revealing soil respiration in forests with different postfire regeneration patterns is critical for determining appropriate restoration strategies in response to increasing wildfire disturbances. Here, we examined the influence of five postfire regeneration patterns (L: Larix gmelinii monocultures, LB: L. gmelinii and Betula platyphylla mixed plantations, P: Pinus sylvestris var. mongolica monocultures, PB: P. sylvestris var. mongolica and B. platyphylla mixed plantations, N: naturally regenerated forests) on soil heterotrophic respiration (Rh) and total respiration (Rs).MethodsTrenching was implemented to monitor soil heterotrophic respiration. We used partial least squares path modeling methods to estimate the different environmental factors regulating soil respiration across forest types.ResultsThe results showed that forest type and season had significant effects on Rs and Rh. Rh was the dominant part of Rs for all forest types (68.84 ~ 90.20%). Compared to naturally regenerated forests, Rs and Rh under L, LB, and PB had higher rates (P < 0.05), while Rs and Rh under P had lower rates (P < 0.05). The temperature sensitivities of Rs under different forest types were 2.316 (L), 1.840 (LB), 1.716 (P), 1.665 (PB), and 2.096 (N).ConclusionsForests regenerated with artificial participation established their plant communities visibly faster than naturally regenerated forests. Mixed species plantation regeneration demonstrated an improvement in soil respiration compared to naturally regenerated forests but had a lower temperature sensitivity of soil respiration than their respective monocultures. Soil temperature and moisture dominated the influence factors on soil respiration throughout the broader seasonal shifts. However, for a single season, forest productivity and soil properties have a greater impact on soil respiration. This study extends our knowledge of the interaction mechanism between soil respiration and environmental variables in boreal forests and contributes to improving confidence in global carbon cycling model predictions.

Temperature sensitivity of soil respiration declines with climate warming in subalpine and alpine grassland soils

AbstractWarming as a climate change phenomenon affects soil organic matter dynamics, especially in high elevation ecosystems. However, our understanding of the controls of soil organic matter mineralization and dynamics remains limited, particularly in alpine (above treeline) and subalpine (below treeline) grassland ecosystems. Here, we investigated how downslope (warming) and upslope (cooling) translocations, in a 5-years reciprocal transplanting experiment, affects soil respiration and its temperature sensitivity (Q10), soil aggregation, and soil organic matter carbon (C) and nitrogen (N) composition (C/N ratio). Downslope translocation of the alpine (2440 m a.s.l.) and subalpine (1850 m a.s.l.) to the lowland site (350 m a.s.l.) resulted in a temperature change during the growing seasons of + 4.4K and + 3.3K, respectively. Warming of alpine soils (+ 4.4K) reduced soil organic carbon (SOC) content by 32%, which was accompanied by a significant decrease of soil macroaggregates. Macroaggregate breakdown induced an increased respiration quotient (qCO2) by 27% following warming of alpine soils. The increase in qCO2 respiration was associated with a significant decrease (from 2.84 ± 0.05 to 2.46 ± 0.05) in Q10, and a change in soil organic matter composition (lower C/N ratios). Cooling did not show the opposite patterns to warming, implying that other mechanisms, such as plant and microbial community shifts and adaptation, were involved. This study highlights the important role of SOC degradability in regulating the temperature response of soil organic matter mineralization. To predict the adverse effect of warming on soil CO2 release and, consequently, its negative feedback on climate change, a comprehensive understanding of the mechanisms of C storage and turnover is needed, especially at high elevations in the Alps that are particularly affected by rising temperatures.

Effects of simulated precipitation changes on soil respiration:Progress and prospects.

Soil respiration, the main pathway for transferring terrestrial carbon pool to atmospheric carbon pool, is profoundly affected by the intensification in global precipitation variability in the context of climate change. Nowadays, variable controlling methods and field manipulation experiments are two main methods widely used to investigate the effects of simulated precipitation changes on soil respiration. Yet, due to the heterogeneity of soil properties, vegetation types, and the magnitude of precipitation change, there is substantial inconsistency in the conclusions of simulated precipitation change effects on soil respiration. Here, we analyzed data from domestic and foreign literature, and examined the effects of simulated precipitation change on soil respiration. Firstly, we described the response pattern of soil respiration to soil moisture fluctuation and pointed out that the magnitude and direction of the response of soil respiration to simulated precipitation change depended on whether soil moisture was optimally conditioned at different precipitation treatments. Second, we summarized the response patterns of soil respiration to symmetric increase and decrease in precipitation, which mainly included symmetric and asymmetric responses (positive and negative asymmetric). Meanwhile, the adaptation of plants and soil microorganisms to drought stress and soil oxygen limitation, as well as the reduction of organic substrates, were the main mechanisms accounting for the shifts of soil respiration response patterns to simulated precipitation change from symmetric to asymmetric responses. Third, we identified a significant effect of ambient climate on soil respiration in response to precipitation treatments as increasing duration of the experimental treatments. In addition, cumulative or buffering effects of ambient climatic conditions on precipitation treatment could affect the sensitivity of soil respiration along precipitation gradient by altering hydrothermal conditions. Finally, to accurately assess the implications of precipitation changes on soil carbon balance processes, we proposed three aspects of future precipitation effects on soil respiration for attention: 1) focusing on the phenomenon of "threshold effects" in the asymmetric response of soil respiration along precipitation gradients; 2) distinguishing the intrinsic mechanisms of autotrophic and heterotrophic components in soil respiration in response to precipitation changes; and 3) focusing on the impacts of intensified precipitation variability on soil respiration in the context of future climate extremes. In conclusion, with the intensified variability in global precipitation patterns, clarifying the response mechanism of soil respiration to precipitation changes is of great significance for accurately predicting and evaluating the alterations of soil carbon cycle processes and carbon balance in the context of global changes.

Temperature sensitivity of soil respiration to elevated temperature and nitrogen availability

Plastic film mulching (PFM) and nitrogen (N) fertilization are two important agricultural management methods that are used to enhance crop yields in semi-arid dryland agriculture. However, the impacts of PFM and N fertilization on the temperature sensitivity (Q10) of soil respiration (Rt), particularly its heterotrophic (Rh) and autotrophic (Ra) components, remain unclear. To investigate this, a trenching experiment was carried out between 2019 and 2021 in a rainfed maize-cultivated cropland that had been under cultivation for 7 years. There were four treatments: no PFM and N fertilization (control), full PFM without N fertilization (PFM), 150 kg N ha–1 fertilization without PFM (Nfer), and full PFM with 150 kg N ha–1 fertilization (PFM+Nfer). PFM and N fertilization not only enhanced crop yield and root biomass but also increased soil total respiration (Rt) and its components, due to improved soil hydrothermal conditions with PFM and increased N availability with N fertilization. Soil hydrothermal conditions and root biomass were identified as the most important factors influencing Rh and Ra, respectively. The greater increase in Ra (84 %–212 %) compared to Rh (9 %–29 %) resulted in a decrease in the proportion of Rh in Rt decreasing from 81.2 % in the control to 58 % under the PFM+Nfer treatment. The Rh/Rt ratio decreased in all three treatments compared to the control (p < 0.05). The increase in Rh under PFM led to a decrease in soil organic carbon (SOC) by 17 %. Specifically, the soil labile C content (i.e. LFOC 44 %) decreased more under PFM and PFM+Nfer (p < 0.05) compared to control, but not under the Nfer treatment (p > 0.05). Plastic film mulching increased the Q10 of Rh (p < 0.05) through decrease the content of soil labile C, whereas N fertilization had no effect (p > 0.05). Both PFM and N fertilization increased the Q10 of Ra (p < 0.05) by increasing root biomass. The impact of Ra’s Q10 (0.66) on Rt’s Q10 is greater compared to Rh’s Q10 (0.31). To our knowledge, this is the first long-term field study to examine the response of Rt components and their Q10 to PFM and N fertilization. Our results highlight that soil labile C and root biomass are the determining factors for the Q10 of Rh and Ra, respectively. We emphasize the importance of accurately modeling the temperature responses of Rh and Ra when predicting Rt under climate change scenarios.

Climate Change and Soil Health: Explainable Artificial Intelligence Reveals Microbiome Response to Warming

Climate change presents an unprecedented global challenge, demanding collective action to both mitigate its effects and adapt to its consequences. Soil health and function are profoundly impacted by climate change, particularly evident in the sensitivity of soil microbial respiration to warming, known as Q10. Q10 measures the rate of microbial respiration’s increase with a temperature rise of 10 degrees Celsius, playing a pivotal role in understanding soil carbon dynamics in response to climate change. Leveraging machine learning techniques, particularly explainable artificial intelligence (XAI), offers a promising avenue to analyze complex data and identify biomarkers crucial for developing innovative climate change mitigation strategies. This research aims to evaluate the extent to which chemical, physical, and microbiological soil characteristics are associated with high or low Q10 values, utilizing XAI approaches. The Extra Trees Classifier algorithm was employed, yielding an average accuracy of 0.923±0.009, an average AUCROC of 0.964±0.004, and an average AUCPRC of 0.963±0.006. Additionally, through XAI techniques, we elucidate the significant features contributing to the prediction of Q10 classes. The XAI analysis shows that the temperature sensitivity of soil respiration increases with microbiome variables but decreases with non-microbiome variables beyond a threshold. Our findings underscore the critical role of the soil microbiome in predicting soil Q10 dynamics, providing valuable insights for developing targeted climate change mitigation strategies.

Effect of Soil Acidification on Temperature Sensitivity of Soil Respiration

Soil pH significantly impacts microbial activity and community assembly, which in turn determines the temperature sensitivity (Q10) of soil respiration. Due to the high soil acidification in China, it is necessary to understand how soil acidification impacts Q10. Here, the Q10 of soil respiration was examined in a long-term field experiment (1982–present) with different soil pH caused by fertilization management. In this experiment, we selected treatments with neutral pH: (1) no crops and fertilization (CK); (2) crops without fertilization (NF); low pH with (3) crops with chemical fertilization (NPK); and (4) crops with chemical fertilization combined with wheat straw incorporation (WS). Under natural soil temperature changes, we observed that soil acidification lowered the Q10 value of soil respiration. Considering only temperature changes, the Q10 of soil respiration was strongly associated with microbial community composition, alpha diversity, and soil ammonium nitrogen. Considering the interaction between soil pH and temperature, warming strengthened the negative effect of soil pH on the Q10 of soil respiration, and the pathway through which soil pH mediated Q10 included not only microbial community composition, alpha diversity, and biomass but also the soil’s available phosphorus. This work enhanced our insights into the relationships between Q10, temperature, and soil pH by identifying important microbial properties and key soil environmental factors.

Acid rain reduced soil carbon emissions and increased the temperature sensitivity of soil respiration: A comprehensive meta-analysis

Soil respiration the second-largest carbon flux in terrestrial ecosystems, has been extensively studied across a wide range of biomes. Surprisingly, no consensus exist on how acid rain (AR) impacts the spatiotemporal pattern of soil respiration. Therefore, we conducted a meta-analysis using 318 soil respiration and 263 soil respiration temperature sensitivity (Q10) data points obtained from 48 studies to assess the impact of AR on soil respiration components and their Q10. The results showed that AR reduced soil total respiration (Rt) and soil autotrophic respiration (Ra) by 7.41 % and 20.75 %, respectively. As the H+ input increased, the response rates of Ra to AR (RR-Ra) and soil heterotrophic respiration (Rh) to AR (RR-Rh) decreased and increased, respectively. With increased AR duration, the RR-Ra increased, whereas the RR-Rh did not change. AR increased the Q10 of Rt (Rt-Q10) and Rh (Rh-Q10) by 1.92 % and 9.47 %, respectively, and decreased the Q10 of Ra (Ra-Q10) by 2.77 %. Increased mean annual temperature, mean annual precipitation, and initial soil organic carbon increased the response rate of Ra-Q10 to AR (RR-Ra-Q10) and decreased the response rate of Rh-Q10 to AR (RR-Rh-Q10). However, as the AR frequency and initial soil pH increased, both RR-Ra-Q10 and RR-Rh-Q10 also increased. In summary, AR decreased Rt but increased Q10, likely due to soil acidification (soil pH decreased by 7.84 %), reducing plant root biomass (decreased by 5.67 %) and soil microbial biomass (decreased by 5.67 %), changing microbial communities (increased fungi to bacteria ratio of 15.91 %), and regulated by climate, vegetation, soil and AR regimes. To the best of our knowledge, this is the first study to reveal the large-scale, varied response patterns of soil respiration components and their Q10 to AR. It highlights the importance of applying the reductionism theory in soil respiration research to enhance our understanding of soil carbon cycling processes with in the context of global climate change.

Climate and vegetation collectively drive soil respiration in montane forest-grassland landscapes of the southern Western Ghats, India

Abstract CO2 release rates from soils via soil respiration play an important role in the carbon budget of terrestrial ecosystems. Though the roles of soil temperature and moisture on soil respiration are well recognised, less is known about how their effects vary across different land-cover types. This study looked at the interactive effects of land-cover change and microclimate on temporal patterns of soil respiration in a montane forest-grassland-plantation mosaic in a highly diverse but climatically sensitive ecosystem in the tropical Western Ghats of India. Across all vegetation types, soil respiration rates were highest during south-west monsoon (June–October), when root growth, litter decomposition and microbial activity are relatively high and were lowest during the summer. Among vegetation types, soil respiration rates were higher in grasslands compared to non-native pine plantations, whereas that of forest and invasive wattle (Acacia mearnsii) plantations were intermediate between grasslands and pine plantations. The decline in respiration rates following conversion from grasslands to pine plantations could be due to relatively lower microbial activity, soil temperatures and, subsequently, slower litter decomposition. In addition, the sensitivity of soil respiration to changes in temperature and moisture differed between different vegetation types. Across all vegetation types, respiration was largely insensitive to changes in soil temperature when moisture levels were low. However, when soil moisture levels were high, respiration increased with temperature in grassland and wattle patches, decreased in the case of pine plantations and remained largely unchanged in shola forests. Our results suggest that changes in aboveground vegetation type can significantly affect soil C cycling even in the absence of any underlying differences in soil type.

Long-term warming increased carbon sequestration capacity in a humid subtropical forest.

Tropical and subtropical forests play a crucial role in global carbon (C) pools, and their responses to warming can significantly impact C-climate feedback and predictions of future global warming. Despite earth system models projecting reductions in land C storage with warming, the magnitude of this response varies greatly between models, particularly in tropical and subtropical regions. Here, we conducted a field ecosystem-level warming experiment in a subtropical forest in southern China, by translocating mesocosms (ecosystem composed of soils and plants) across 600 m elevation gradients with temperature gradients of 2.1°C (moderate warming), to explore the response of ecosystem C dynamics of the subtropical forest to continuous 6-year warming. Compared with the control, the ecosystem C stock decreased by 3.8% under the first year of 2.1°C warming; but increased by 13.4% by the sixth year of 2.1°C warming. The increased ecosystem C stock by the sixth year of warming was mainly attributed to a combination of sustained increased plant C stock due to the maintenance of a high plant growth rate and unchanged soil C stock. The unchanged soil C stock was driven by compensating and offsetting thermal adaptation of soil microorganisms (unresponsive soil respiration and enzyme activity, and more stable microbial community), increased plant C input, and inhibitory C loss (decreased C leaching and inhibited temperature sensitivity of soil respiration) from soil drying. These results suggest that the humid subtropical forest C pool would not necessarily diminish consistently under future long-term warming. We highlight that differential and asynchronous responses of plant and soil C processes over relatively long-term periods should be considered when predicting the effects of climate warming on ecosystem C dynamics of subtropical forests.

Mechanisms of soil respiration and its temperature sensitivity in black soil farmland

Soil respiration is the process of decomposition of organic matter in soil and microbial metabolism to produce carbon dioxide. In the context of climate warming and degradation of agricultural soil fertility, it becomes crucial to explore the mechanisms of soil respiration to increase carbon sequestration. In this paper, five biochar applications (0, 3.79, 7.58, 11.36, 15.15 t/ha) and two tillage methods (shallow ploughing, deep ploughing) were set up to explore the mechanism of soil respiration and its temperature sensitivity by studying the effects of tillage methods and different amounts of biochar application on soil properties, soil enzyme activities, soil respiration and its temperature sensitivity during the growing season of soybeans in the black soil area. The results showed that soil respiration rate increased with biochar application in the low biochar application range; the opposite trend was observed for high biochar application beyond the threshold (11.36 t/ha). The application of 11.36 t/ha of biochar amount had the strongest promotion effect on soil respiration, reaching 2.42 μmol m−2·s−1 in the shallow ploughing treatment and increasing 0.32 μmol m−2·s−1 in the deep ploughing compared to the shallow ploughing. The application of biochar significantly increased the activity of nitrogen and phosphorus enzymes and had an inhibitory effect on carbon cycle enzymes; the increased activity of nitrogen and phosphorus cycle enzymes provided sufficient substrate for microbial respiration and thus increased soil respiration, and the decrease in the enzymatic reaction of carbon cycle enzymes led to a decrease in temperature sensitivity. The temperature sensitivity of deep ploughing (2.18–2.59) got a more substantial reduction than that of shallow ploughing (2.34–3.53), which indicates that deep ploughing treatments can better reduce the mineralization of organic carbon than shallow tillage. Meanwhile, the temperature sensitivity of soil respiration reached a minimum with the application of 7.58 t/ha of biochar, which was reduced by 16% under deep ploughing treatment compared to the control, 33% under shallow ploughing treatment compared to the control, and also reduced by 27.27% under deep ploughing compared to shallow ploughing, which suggests that the addition of biochar reduces the loss of carbon to a certain extent. This study is important for assessing the effects of tillage practices and biochar combinations on carbon sequestration in agricultural soils in black soil areas.

Plant carbon removal affects monthly temperature sensitivity of soil respiration during growing season in three typical plantations in the Loess Hilly Region, China

The temperature sensitivity of soil respiration (Q10) is primarily related to annual climate parameters and soil properties in regional models. Changes in climate and soil properties influence plant carbon (C) inputs, which in turn alter Q10 during the growing season. However, the magnitude of this influence remains uncertain. Herein, using meteorological data from small stations and field experiments across three plantations (Robinia pseudoacacia, Caragana korshinskii, and Bothriochloa ischaemum), we investigated the variations in Q10 with respect to the following four treatments: litter removal, root trenching, root trenching and litter removal, and a control group, for 6 months. We found that R. pseudoacacia had the highest relative contribution to atmospheric C release, followed by C. korshinskii, and then B. ischaemum. The Q10 components were month-dependent under C remove in three typical plantations. Litter removal significantly reduced Q10, but the effect of root trenching differed according to the plantation. The variations of Q10 with C removal were primarily controlled by interacting air temperature, air pressure, potential hydrogen, root C, root biomass, soil organic C, and relative humidity, explaining the variations of 81.29–99.33 % (R. pseudoacacia plantation), 89.1–99.76 % (C. korshinskii plantation), and 99.34–99.74 % (B. ischaemum) of the variation in Q10; among them, the cumulative contribution of climate (soil temperature, air pressure, and relative humidity), plants (root C and root biomass), and soil properties (potential hydrogen and soil organic C) accounted for 34.84 %–61.93 %, 12.15 %–32.75 %, and 8.07 %–32.11 %, respectively. These findings demonstrate that C removal variations influenced the Q10, whereas Q10 was also month-dependent. Overall, we recommend that the role of Q10 in the growing season should carefully consider C removal into the soil to improve the biosphere–atmosphere C exchange model in the context of climate change.

Temperature Sensitivity of Soil Respiration in Grasslands in Temperate Continental Climate Zone: Analysis of 25-Year-Long Monitoring Data

Field observations of soil respiration (SR) in different types of terrestrial ecosystems are very relevant because of high temporal and spatial variations of SR rate. The intra-annual dynamics of SR is mainly determined by the changes in hydrothermal conditions during the year and is often described with temperature sensitivity coefficient (Q10), which usually has a fixed value in many of the used models. This study is focused on the assessment of seasonal and interannual dynamics of SR temperature sensitivity in two grasslands in the southern Moscow oblast (temperate continental climate) based on continuous 25-year-long all-year-round measurements of CO2 emission from soils. The grasslands have been formed on two different soil types: sandy soddy-podbur (Entic Podzol (Arenic)) and gray loamy soil (Haplic Luvisol (Loamic)). The SR rate has been continuously measured from December 1997 to November 2022 with an interval of 7–10 days using the technique of closed static chambers. The temperature sensitivity of SR, estimated from the entire set of data, is higher in Haplic Luvisol as compared with Entic Podzol (3.47 vs. 2.59). The Q10 values for SR in both soils are 1.2–1.4-fold lower in dry years as compared with wet years. The interannual variation of Q10 values in grassland ecosystems amounts to 21–36% depending on the considered temperature range. A statistically significant positive correlation between the Q10 values in the temperature range ≥1°С and wetness indices is observable in both grasslands. A differentiated approach integrating different values of temperature coefficients for SR into the used models is necessary to improve the predictions of C budget in ecosystems.

Temperature Sensitivity of Soil Respiration in Grasslands under the Temperate Continental Climate Zone: Analysis of 25-Year Monitoring Data

Field observations of soil respiration (SR) in different types of terrestrial ecosystems seem to be very relevant, since the SR rate is characterized by high temporal and spatial variability. The intra-annual dynamics of SR is determined mainly by the change in hydrothermal conditions during the year and is often described using a temperature sensitivity coefficient (Q10), which usually has a fixed value in many of the models used. The aim of this study was to assess the seasonal and interannual dynamics of SR temperature sensitivity in two grasslands in the southern part of Moscow region (temperate continental climate) based on continuous 25-year year-round measurements of CO2 emissions from soils. Grasslands were formed on two different types of soils: soddy-podbur sandy soil (Entic Podzol (Arenic)) and gray loamy soil (Haplic Luvisol (Loamic)). The SR rate was measured continuously from December 1997 to November 2022 with an interval of 7–10 days using the closed static chamber method. The temperature sensitivity of SR, estimated from the entire set of data, had higher values on Haplic Luvisol compared to Entic Podzol (3.47 vs 2.59). The values of Q10 for SR in both types of soils in dry years were 1.2–1.4 times lower than in years with a normal moisture level. The interannual variability of Q10 values in grassland ecosystems was 21–36%, depending on the temperature range that was taken into account. A significant positive correlation between Q10 values in the temperature range ≥1°С and humidity indices was found in both grasslands. To obtain more accurate forecasts of the C balance in ecosystems, a differentiated approach should be applied by integrating different values of temperature coefficients for SR into the models.

Roots exert greater influence on soil respiration than aboveground litter in a subalpine Cambisol

Aboveground plant litter and roots are primary sources of soil organic carbon (SOC), profoundly affecting soil respiration and SOC dynamics. With global change, the quantities of aboveground plant litter and root inputs into soil are changing in the subalpine region; however, the impacts of these changes on soil respiration and the quantity and quality of SOC remain unclear. Here, a three-year detritus input and removal treatment (DIRT) experiment that included six treatments (namely, control, CK; double litter, DL; litter removal, NL; root exclusion, NR; root exclusion plus double litter, NRDL; and root exclusion plus litter removal, NRNL) was conducted in a subalpine Cambisol on the eastern edge of the Tibetan Plateau to assess the different effects of aboveground litter and roots on soil respiration and the quantity and quality of SOC dynamics. Among the treatments, the mean soil respiration in NL, NR and NRNL treatments significantly decreased by 21.7%, 31.9% and 40.5%, respectively, compared to the CK treatment. When with intact roots, double litter (DL) had a positive impact on soil respiration, resulting in a 13.2% increase in soil respiration compared to the CK treatment. In contrast, when with root exclusion (in the absence of roots), combined root exclusion and litter addition (NRDL) hardly influence soil respiration compared with the NR treatment, resulting in a 30.5% decrease in soil respiration. The soil respiration, labile SOC content and the abundance of soil microbes exhibited similar patterns among treatments. Roots excluded (NR, NRDL, NRNL) exerted a stronger effects on soil respiration, temperature sensitivity of soil respiration (Q10), labile SOC content and the recalcitrance index of carbon (RIC) than aboveground plant litter manipulation (CK, DL, NL). Correlation analysis and redundancy analysis revealed that soil respiration and its Q10 were regulated by the quantity and quality of SOC substrates and the abundance of soil microbes. Our results highlighted that roots exerted greater influence on the quantity and quality of SOC, the abundance of soil microbes, soil respiration and its Q10 than aboveground litter manipulation in subalpine Cambisol in response to future climate scenarios, especially the mediating effect of the presence of roots on the function of aboveground plant litter.

Temperature and soil moisture control CO2 flux and CH4 oxidation in urban ecosystems

Climate-driven shifts in soil temperature and soil moisture are crucial factors that control the ecosystem-atmosphere greenhouse gas (GHG) balance. In the present study, the relationship between CO2, CH4 fluxes and soil moisture content and temperature sensitivity was examined in three dominating types of urban ecosystems: grassland, city park and arable land. The analysis was based on the field measurements at biweekly intervals over a year using a static closed chamber method in Wroclaw urban area, Poland. The observed patterns of land-atmosphere CO2 and CH4 exchange varied across land cover types and were strongly influenced by seasonal variations in temperature and soil water content. Emission of CO2 from grassland and the city park was two times higher than from the arable land. The calculated CH4 oxidation rate was one and half times higher (p < 0.05) under grassland and the city park as compared to arable land.The estimated Q10 values ranged between 1.68 and 1.79 for CO2 and from 1.26 to 1.49 for CH4, depending on the ecosystem type. The temperature sensitivity of soil respiration decreased when the temperature was above 24.5 °C across the moisture gradient from 20 to 25 % m/v. Results suggest that despite the urban areas with agricultural land use revealed the lowest CO2 fluxes compared to grassland and city park, the former showed the lowest seasonal mean CH4 oxidation. This indicates that with ongoing warming, the higher Q10 of CO2 production vs. CH4 oxidation will further shift the carbon balance towards the source and this shift will be especially critical for arable lands in urban areas.

Response of soil respiration to hydrothermal effects of gravel–sand mulch in arid regions of the Loess Plateau, China

Gravel–sand mulching is a traditional no–tillage technique used for more than 300 years on the Loess Plateau. Applying gravel–sand mulch (mixture of gravel and sand) has an impact on the soil environment, soil microorganisms, and crop yield. However, we know surprisingly little of how respiration dynamics at the soil surface is affected by gravel–sand mulching. To study the response of soil respiration (Rs) dynamics to different in gravel–sand mulch thickness and its driving factors, we recorded Rs under a gradient of gravel–sand mulch thickness consisting of six layers (0 cm [CK], 3 cm, 5 cm, 7 cm, 9 cm, 11 cm), in situ, during the growing season by using the LI–6400–09 soil respiration measurement system on the Loess Plateau in northwest China. The trends of all six treatments in diurnal and monthly variation of soil respiration followed a single–peaked curve; the diurnal dynamics trends were consistent with soil temperature changes. With gravel–sand mulch applied, the daily peak of soil respiration decreased, and the peak in Rs under the gravel–sand mulch treatments lagged that of bare land by 2 h. Monthly changes in soil respiration were consistent with soil temperature and precipitation changes, with peaks concentrated in July and August. Compared with bare land (CK), the monthly average soil respiration is lowest at 0.67 µmol∙m–2∙s–1 under a 11–cm thick mulch layer, and reduced by 26.63–61.03% by all mulch applications. Gravel–sand mulch reduced the temperature sensitivity of soil respiration, while soil temperature and soil water content were the main factors determining soil respiration. The thickness of gravel–sand has a significant, negative exponential function relationship with the changes in monthly soil respiration. Further, compared with bare land, the presence of gravel–sand mulch reduced the positive impact of precipitation on Rs. Soil temperature (T), gravel–sand mulch thickness (M), and soil pH were all significant predictors of soil respiration (Rs) (multiple regression model: Rs = 8.561 + 0.077 T – 0.056 M – 0.989 pH), together accounting for 73% of its variation. Hence, by considering all these three factors simultaneously we can better explain the changes to soil respiration in response to gravel–sand mulch. Overall, our results show that as the thickness of the gravel–sand layer increases, soil respiration decreases.

Ambient precipitation determines the sensitivity of soil respiration to precipitation treatments in a marsh.

The effects in field manipulation experiments are strongly influenced by amplified interannual variation in ambient climate as the experimental duration increases. Soil respiration (SR), as an important part of the carbon cycle in terrestrial ecosystems, is sensitive to climate changes such as temperature and precipitation changes. A growing body of evidence has indicated that ambient climate affects the temperature sensitivity of SR, which benchmarks the strength of terrestrial soil carbon-climate feedbacks. However, whether SR sensitivity to precipitation changes is influenced by ambient climate is still not clear. In addition, the mechanism driving the above phenomenon is still poorly understood. Here, a long-term field manipulation experiment with five precipitation treatments (-60%, -40%, +0%, +40%, and +60% of annual precipitation) was conducted in a marsh in the Yellow River Delta, China, which is sensitive to soil drying-wetting cycle caused by precipitation changes. Results showed that SR increased exponentially along the experimental precipitation gradient each year and the sensitivity of SR (standardized by per 100 mm change in precipitation under precipitation treatments) exhibited significant interannual variation from 2016 to 2021. In addition, temperature, net radiation, and ambient precipitation all exhibited dramatic interannual variability; however, only ambient precipitation had a significant negative correlation with SR sensitivity. Moreover, the sensitivity of SR was significantly positively related to the sensitivity of belowground biomass (BGB) across 6 years. Structural equation modeling and regression analysis also showed that precipitation treatments significantly affected SR and its autotrophic and heterotrophic components by altering BGB. Our study demonstrated that ambient precipitation determines the sensitivity of SR to precipitation treatments in marshes. The findings underscore the importance of ambient climate in regulating ecosystem responses in long-term field manipulation experiments.

Reduction in soil CO2 efflux through alteration of hydrothermal factor in milk vetch (Astragalus sinicus L.)-rapeseed (Brassica napus L.) intercropping system.

Intercropping has a potential to reduce the CO2 emission from farmlands. Limited information is available on the underlying reasons. This study investigated the effect of milk vetch (Astragalus sinicus L.) (MV), rapeseed (Brassica napus L.) monoculture (RS) and intercropping (Intercrop) on soil CO2 emissions, moisture and temperature in a bucket experiment during 210 days from October 2015 to May 2016 on Chongqing, China. The results showed that soil CO2 efflux of MV, RS and Intercrop was 1.44, 1.55 and 2.08 μmol·m-2·s-1 during seedling and stem elongation stages and 3.08, 1.59 and 1.95 μmol·m-2·s-1 during flowering and podding stages. At seeding and stem elongation stages Intercrop had 1.4 times higher soil CO2 efflux than the mean of MV and RS. In contrast, MVhad 1.6 times higher soil CO2 efflux than Intercrop thereafter, which shows it was inhibited if milk vetch presents as Intercrop only. Decreased sensitivity of soil respiration to temperature in 1.4 times and lower soil moisture by Intercrop were found compared to MV. Intercrop decreased soil moisture, especially at the seedling and stem elongation stages, compared to the monoculture. The fluctuation on soil respiration in RS and Intercrop was slight with changes in soil moisture. Thus, milk vetch-rapeseed system has a potential to decrease CO2 emission from farmland, however soil moisture should be regulated properly.

Temperature Sensitivity of Soil Respiration Probed by Numerical Analysis of Field-Observed Data Sets

Temperature Sensitivity of Soil Respiration Probed by Numerical Analysis of Field-Observed Data Sets