Changes In Soil Respiration Research Articles

Consecutive annual mowing reduces soil respiration and increases the proportion of autotrophic component in a meadow steppe

BcakgroundSoil respiration (Rs), as the second largest CO2 emissions of terrestrial ecosystems, is sensitive to disturbance and consequent environmental changes. Mowing is strategically implemented as an management approach and has the potential to influence carbon cycling in meadow steppes. However, it remains unclear how and why Rs and its heterotrophic (Rh) and autotrophic (Ra) components respond to consecutive mowing and associated ecological consequences. Here, we conducted a field mowing experiment in a meadow steppe in 2018 and monitored Rs, Rh, and Ra from 2019 to 2022.ResultsWe observed a significant reduction in Rs by 4.8% across four years, primarily attributed to a decrease in Rh. This decline in Rs intensified over time, indicating an accumulative effect of mowing. In addition, mowing induced an generally increasing Ra/Rs ratio over the experimental years with a simultaneous increase in the ratio of belowground to aboveground biomass (BGB/AGB). Furthermore, structural equation modeling results revealed that the decline in Rs was largely ascribed to reduced microbial biomass carbon (MBC) under mowing, while the increased Ra/Rs was primarily explained by the enhanced BGB/AGB. Partial regression analysis suggested that the biotic factor of microbial biomass dominated changes in soil respiration induced by mowing rather than abiotic soil temperature.ConclusionsOur findings showed that consecutive mowing decreased Rs and raised Ra/Rs in meadow steppe by decreasing plant biomass and altering the proportion of biomass allocation. This observed decline in Rs would help to reduce CO2 concentration in atmosphere as well as alleviate global warming. However, considering the concurrent lower microbial biomass, the potential positive impacts of mowing on climate and ecosystem function should be reevaluated in future grassland management practices.

Soil respiration and organic carbon changes along a chronosequence of Pinus nigra forest stands

Understanding the trajectory of changes in soil respiration (Rs) and soil organic carbon (SOC) with stand ages of the black pine (Pinus nigra Arnold) forest is essential for forest management and carbon budget estimates. In this research, changes of Rs and SOC were studied with respect to stand age in a chronosequence of three age classes of P. nigra plantations consisting of young (0 to 10-year-olds), middle-aged (11- to 20-year-olds), and pre-mature (35- to 45-year-olds) forest stands. Rs rates, soil temperature, and soil moisture were measured using an automated dynamic survey chamber (Li-8100A) for a year, encompassing summer, fall, winter, and spring seasons. Mean Rs significantly increased from young- to middle-aged and then stabilized, with effluxes ranging from 2.46 to 2.94 µmol CO2 m-2 s-1. Forest litter significantly increased with stand age, but not the SOC in the mineral soil layers. The Rs showed a positive correlation with soil temperature (0.77) and air temperature (0.75) but not with soil moisture (-0.43). The present results highlight the importance of stand age in assessing carbon budget and provide essential information for forest managers and stakeholders in evaluating the potential of P. nigra forests as tools for carbon sequestration and mitigating global warming impacts.

Tropical vegetation productivity and atmospheric methane over the last 40,000 years from model simulations and stalagmites in Sulawesi, Indonesia

AbstractRecent research has shown the potential of speleothem δ13C to record a range of environmental processes. Here, we report on 230Th-dated stalagmite δ13C records for southwest Sulawesi, Indonesia, over the last 40,000 yr to investigate the relationship between tropical vegetation productivity and atmospheric methane concentrations. We demonstrate that the Sulawesi stalagmite δ13C record is driven by changes in vegetation productivity and soil respiration and explore the link between soil respiration and tropical methane emissions using HadCM3 and the Sheffield Dynamic Global Vegetation Model. The model indicates that changes in soil respiration are primarily driven by changes in temperature and CO2, in line with our interpretation of stalagmite δ13C. In turn, modelled methane emissions are driven by soil respiration, providing a mechanism that links methane to stalagmite δ13C. This relationship is particularly strong during the last glaciation, indicating a key role for the tropics in controlling atmospheric methane when emissions from high-latitude boreal wetlands were suppressed. With further investigation, the link between δ13C in stalagmites and tropical methane could provide a low-latitude proxy complementary to polar ice core records to improve our understanding of the glacial–interglacial methane budget.

Simulating net ecosystem exchange under seasonal snow cover at an Arctic tundra site

Abstract. Estimates of winter (snow-covered non-growing season) CO2 fluxes across the Arctic region vary by a factor of 3.5, with considerable variation between measured and simulated fluxes. Measurements of snow properties, soil temperatures, and net ecosystem exchange (NEE) at Trail Valley Creek, NWT, Canada, allowed for the evaluation of simulated winter NEE in a tundra environment with the Community Land Model (CLM5.0). Default CLM5.0 parameterisations did not adequately simulate winter NEE in this tundra environment, with near-zero NEE (< 0.01 gCm-2d-1) simulated between November and mid-May. In contrast, measured NEE was broadly positive (indicating net CO2 release) from snow-cover onset until late April. Changes to the parameterisation of snow thermal conductivity, required to correct for a cold soil temperature bias, reduced the duration for which no NEE was simulated. Parameter sensitivity analysis revealed the critical role of the minimum soil moisture threshold of decomposition (Ψmin) in regulating winter soil respiration. The default value of this parameter (Ψmin) was too high, preventing simulation of soil respiration for the vast majority of the snow-covered season. In addition, the default rate of change of soil respiration with temperature (Q10) was too low, further contributing to poor model performance during winter. As Ψmin and Q10 had opposing effects on the magnitude of simulated winter soil respiration, larger negative values of Ψmin and larger positive values of Q10 are required to simulate wintertime NEE more adequately.

A new concept for modelling the moisture dependence of heterotrophic soil respiration

The moisture dependence of heterotrophic soil respiration is a key factor affecting the uncertainty in predicting the response of soil organic carbon (SOC) to global warming. Considering that heterotrophic respiration from unsaturated soils is primarily driven by microbial reduction of oxygen (O2), we propose a new concept to model the respiration by tracking dissolution of gaseous O2 and its subsequent diffusion and microbial reduction at hydrated microsite in the pore space of soil. Total respiration from a soil sample is calculated by summing the O2 reduced by all microbes in the soil. This allows us to separate physical processes and microbial activity occurring at microsites and incorporate pore-scale substrate heterogeneity, macropores and other factors explicitly into the model. We show that scaling up these microscopic physical processes over a soil sample makes soil moisture, temperature, and other factors inherently integrated in their influence on microbial respiration, and that a change in one of them affects the response of the respiration to the change in others. Comparison with experimental data shows the model can reproduce the diverse moisture-respiration relationships observed from various experiments and predict the change in soil respiration with temperature. It is noteworthy to point out that previous studies had attributed the variations in the moisture and temperature sensitivity of heterotrophic soil respiration to microbial adaptation; herein we demonstrate that changes in soil structure and physical processes can also give rise to such variations. Distinguishing between physical and microbial effects in data analysis and modelling is therefore crucial, as mistaking physical effects for microbial adaptation would lead to errors in predicting the response of SOC to environmental changes.

Effects of pre-commercial thinning on soil respiration and some soil properties in black pine (Pinus nigra) stands

Forestry practices may cause significant changes in soil characteristics as related to their properties and size. Although chemical attributes of the soil respond to the applications in the mid- or long-term while changes in soil respiration can react rapidly to forestry practices. Therefore, determining changes in soil attributes is needed to identify how the management practices would affect forest ecosystem function. Although there is much information on the effect of thinning practices on tree growth, there is a lack of knowledge on the impacts of pre-commercial thinning on soil properties, especially soil respiration. We aimed to determine pre-commercial thinning effects on some soil attributes in black pine sites. Four treatments with different intensities were applied to the stands studied. These practices were control (no pre-commercial thinning), 2000 (heavy), 4000 (moderate), and 6000 (light) individuals per hectare left, respectively. Measurements of soil respiration and soil temperature were carried out between 2014 and 2017 in spring, summer, autumn, and winter months. Soil characteristics, including pH, organic matter, nitrogen, and phosphor content, were measured just after and three years after the thinning. As a result, thinning increased soil respiration rate and soil temperature while decreased soil pH values. Results of the study showed that carbon balance in the ecosystem was significantly affected by thinnings, and adjusting the thinning intensity may be an efficient carbon management tool for reducing carbon emission from the soil.

Legacy of Prior Management of Cropland after Afforestation with Populus x euroamericana (Dode) Guinier: Effects on Soil Respiration

Afforestation is a good strategy for climate change mitigation through increasing carbon stocks. This study determined changes in soil respiration (SR) brought about by the afforestation of high quality agricultural land in a temperate-humid region (Galicia, NW Spain), identified the variables that explain the observed changes and determined the main factors regulating SR temporal variation. Paired plots of fertile soils (cropped vs. afforested plots) were established in two similar areas (Pontevea and Laraño) where afforestation with Populus x euroamericana (Dode) Guinier was carried out in the same year. Different management practices and crop rotations were used (maize–pasture, Laraño and maize–fallow, Pontevea). The SR was measured in situ with a CO2 static chamber every 15 days (every month in winter) for 16 months; soil temperature (Ts) and soil moisture content (W) were also measured. In both areas, significant differences (p < 0.05) in SR between paired plots were related to soil organic C content and SR was mainly influenced by Ts, except during the summer period where SR fluctuations were accompanied by W fluctuations. These findings show that growing pasture crops on high quality land can prevent the loss of soil N and C and probably improve the greenhouse gas balance in the system.

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.

Response of Bare Soil Respiration to Air and Soil Temperature Variations According to Different Models: A Case Study of an Urban Grassland

Soil respiration is an important component of the global carbon cycle and is highly responsive to disturbances in the environment. Human impacts on the terrestrial ecosystem lead to changes in the environmental conditions, and following this, changes in soil respiration. Predicting soil respiration and its changes under future climatic and land-use conditions requires a clear understanding of the processes involved. The observation of CO2 fluxes was conducted at an urban grassland, where plants were removed and respiration from bare soil was measured. Nine soil respiration models were applied to describe the temperature dependence of heterotrophic soil respiration. Modified models were suggested, including a linear relationship of the temperature sensitivity and base respiration coefficients with soil temperature at various depths. We demonstrate that modification improves the simulated soil respiration. The exponential and logistic models with linear dependences on the model parameters from the soil temperatures were the best models describing soil respiration fluxes. Variability of the apparent temperature sensitivity coefficient (Q10) was demonstrated, depending on the model used. The Q10 value can be extremely high and does not reflect the actual relationships between soil respiration and temperature. Our findings have important implications for better understanding and accurately assessing the carbon cycling characteristics of terrestrial ecosystems in response to climate change in a temporal perspective.

Canada Goldenrod Invasion Regulates the Effects of Soil Moisture on Soil Respiration

Canada goldenrod (Solidago canadensis L.) is considered one of the most deleterious and invasive species worldwide, and invasion of riparian wetlands by S. canadensis can reduce vegetation diversity and alter soil nutrient cycling. However, little is known about how S. canadensis invasion affects soil carbon cycle processes, such as soil respiration, in a riparian wetland. This study was conducted to investigate the effects of different degrees of S. canadensis invasion on soil respiration under different moisture conditions. Soil respiration rate (heterotrophic and autotrophic respiration) was measured using a closed-chamber method. S. canadensis invasion considerably reduced soil respiration under all moisture conditions. The inhibition effect on autotrophic respiration was higher than that on heterotrophic respiration. The water level gradient affects the soil autotrophic respiration, thereby affecting the soil respiration rate. The changes in soil respiration may be related to the alteration in the effective substrate of the soil substrate induced by the invasion of S. canadensis. While the effects of S. canadensis invasion were regulated by the fluctuation in moisture conditions. Our results implied that S. canadensis invasion could reduce the soil respiration, which further potentially affect the carbon sequestration in the riparian wetlands. Thus, the present study provided a reference for predicting the dynamics of carbon cycling during S. canadensis invasion and constituted a scientific basis for the sustainable development and management of riparian wetlands invaded by alien plants.

Soil Respiration Response to Simulated Precipitation Change Depends on Ecosystem Type and Study Duration

AbstractSoil respiration—the flow of biologically‐generated CO2 from the soil surface to the atmosphere—is a major component of global carbon cycling, but the long‐term response of this flux to altered precipitation regimes remains uncertain, due to different responses of soil respiration in distinct ecosystems with varying degrees of water limitation. We conducted a meta‐analysis to determine the role of soil characteristics (organic carbon stock and clay content), study duration, and ecosystem type (e.g., forest, grassland, etc) in modifying the response of soil respiration to precipitation change. In general, decreased precipitation (N = 128 effect size pairs) decreased soil respiration rates. In contrast, increased precipitation (N = 141) had a more variable and on‐average weak positive effect on this flux; significantly increasing soil respiration only in desert ecosystems. The long‐term response of ecosystems varied, with those that are less constrained by water‐availability (e.g., forests) showing acclimation over time to altered precipitation. Soil organic carbon stock strongly modified the response of soil respiration to decreased precipitation (p < 0.0001), but only weakly modified the response to increased precipitation (p < 0.01). Our results suggest that ecosystems with limited soil water‐holding capacity and strong inherent water‐limitation will show long‐term dynamic change in soil respiration regardless of the direction of precipitation change.

Straw strip mulching in a semiarid rainfed agroecosystem achieves carbon sequestration and emission reduction from winter wheat fields

Mulching practices improve soil hydrothermal conditions, which cause changes in soil respiration. Conventional straw mulching has low productivity in areas with relatively low temperatures. Meanwhile, the responses of soil respiration to mulching practices and the relationship between changes in environmental factors caused by mulching and carbon (C) components are not clear in dryland agroecosystem. In this study, we monitored seasonal changes in soil respiration flux and heterotrophic respiration flux of winter wheat fields under different mulching practices in a semiarid rainfed agroecosystem of northern China. The fields were designed for the following three treatments: straw strip mulching (SSM), plastic film mulching (PFM), and non-mulching (CK). Compared to CK, SSM decreased cumulative soil respiration and heterotrophic respiration by 11.6% and 13.3%, whereas PFM increased these values by 12.8% and 8.5%, respectively. SSM significantly decreased soil temperature but increased soil water-filled pore space (WFPS), while PFM significantly increased soil WFPS without affecting soil temperature. Respiration flux was more highly correlated with soil temperature and air temperature than with WFPS and rainfall. SSM and PFM respectively increased by 5.7–9.1% and 10.8–35.5% for grain yield, by 8.1–45.6% and 16.2–69.5% for straw yield, by 8.6–28.6% and 15.1–36.4% for net primary production, and by 23.1–80.6% and 20.3–95.2% for net ecosystem production. Furthermore, mulching practices had a great potential of soil C sequestration and SSM significantly increased soil organic carbon. Changes in ecosystem C components were primarily driven by biomass, followed by soil temperature and air temperature rather than WFPS and rainfall. Based on the sustainability of agroecosystems, SSM increased grain yield of winter wheat while reduced carbon emissions, which showed great potential for C sequestration and may create an environmentally friendly C sink system in a semiarid rainfed agroecosystem of northern China.

Effects of Functional Diversity on Soil Respiration in an Arid Desert Area

To compare the relative importance of the biomass ratio hypothesis and the niche complementarity hypothesis in explaining changes in soil respiration (Rs), and to explore whether the relationship between biodiversity and Rs was affected by both biotic and abiotic factors, dynamic plant community monitoring was conducted in the Ebinur Lake Wetland Nature Reserve. By calculating the functional diversity (FD), community-weighted mean functional traits (CWM), and soil factors, the correlation between FD and Rs was compared using a linear regression model and a structural equation model. The results showed that (1) the CWM traits could better explain the changes of Rs than the FD, indicating that the biomass ratio hypothesis was more suitable for explaining changes in Rs in arid desert areas; and (2) the correlation between biodiversity and Rs was affected by the interaction between biological factors and environmental factors. Soil water content and species richness also affected Rs. Research on the relationship between biodiversity and Rs should examine both biotic and abiotic factors and clarify and explore various factors affecting Rs, which is of great significance to evaluate the community dynamics and variation characteristics of Rs. The study of various factors affecting Rs in this region is helpful to elucidate the process of the soil carbon cycle in arid desert areas.

Changes in carbon inputs affect soil respiration and its temperature sensitivity in a broadleaved forest in central China

Soil respiration, as an important process in global carbon cycle, is drastically stimulated by warming. Changing plant carbon inputs caused by intensified human disturbances and climate change can complexly influence soil respiration and its temperature sensitivity (Q10). Although a number of experiments have been established in the world to explore the effects of changing carbon inputs, it remains a challenge to predict the direction and magnitude of changes in soil respiration and Q10 due to high spatiotemporal variability of climatic zone and ecosystem. Therefore, we conducted a field manipulative experiment to examine the impact of litter removal and root exclusion on soil respiration and Q10 in a deciduous broad-leaved forest in transition zone between subtropical and warm temperate zone. The results showed that litter removal significantly reduced soil respiration, microbial biomass carbon, soil organic carbon, total nitrogen and soil moisture. In addition, litter removal altered soil microbial community composition, expressed in increase of Gram-positive / Gram-negative bacteria ratio and percentage of actinomycetes, and enhanced microbial physiological stress index. Root exclusion significantly increased Q10 by elevating soil C/N ratio, which supporting “C quality-temperature” hypothesis. The study indicates that root exclusion may accelerate soil respiration under warming. Our study provides insights to improve carbon cycling models and accurately predict the consequences of climate change.

Effects of Warming and Increased Precipitation on Soil Respiration of Abandoned Grassland in the Loess-Hilly Regions

Clarifying the changing trends and driving factors of soil respiration in fragile habitats under the background of climate change is of great significance for understanding the regional carbon cycle and the conversion of ecosystem carbon source and sink functions. This research focused on grasslands that had been naturally abandoned and restored for 12 years in the loess hilly region of northern Shaanxi, using an open top chamber (OTC) and artificially increased natural rainfall to simulate climate warming and precipitation increase and their interaction. Furthermore, we used a combination of field monitoring and indoor analysis to explore soil water content, temperature, and nutrient characteristics and the response characteristics of soil respiration rate to warming and increased precipitation and further analyzed the key factors driving changes in soil respiration. The results showed that:① warming (W) significantly increased the 5 cm soil temperature, with an average increase of 1.34℃ throughout the sampling year, whereas the increased precipitation (P50%) treatment significantly reduced the 5 cm soil temperature, reducing the average 5 cm soil temperature during the entire sampling year by 0.88℃ and increasing the soil water content (SWC) at the same time. The SWC was 13.12% and 16.45% higher than that in the control (CK), respectively. In addition, compared with that in the CK, the treatment of warming and increased precipitation (WP50%) not only increased soil temperature but also increased SWC; in general, the increase in temperature and precipitation played an antagonistic effect on the influence of soil temperature and humidity. ② P50% significantly increased the content of soil organic carbon, dissolved organic carbon, and labile organic carbon, causing changes in the soil stoichiometric ratio and the distribution characteristics of labile-recalcitrant carbon components, whereas W did not have a significant impact on organic carbon. In addition, soil total nitrogen and phosphorus and available nitrogen and phosphorus nutrients were not significantly different between treatments. ③ P50% significantly increased the Rs rate, and the effect of W on the soil respiration rate mainly depended on the seasonal precipitation and temperature. It was demonstrated that warming in winter and seasons with abundant rainfall had a significant promotion effect on the soil respiration rate. The exponential fitting of soil respiration rate and 5 cm soil temperature found that the soil respiration temperature sensitivity (Q10) was the highest under the precipitation treatment, reaching 1.68, whereas the Q10 was the lowest under the warming treatment (1.50). ④ Linear regression analysis showed that soil organic carbon, dissolved organic carbon, and labile organic carbon were all significantly positively correlated with soil respiration rate. Variation partitioning analysis showed that soil temperature, SWC, and nutrient characteristics explained 64.43% of the variation in soil respiration rate. The soil temperature and SWC were the main controlling factors of the change in soil respiration rate, with an explanation degree of 31.16%. Correlation analysis also showed that there was a significant correlation between SWC, soil temperature and respiration rate, soil organic carbon, dissolved organic carbon, labile organic carbon, C:N, and C:P. In summary, the climate prediction of abandoned grassland tending toward warm temperatures and high humidity in the loess hilly region will significantly affect the regional hydrothermal environment and nutrient characteristics, change the distribution ratio of soil labile and recalcitrant carbon, and promote regional soil carbon emissions. The analysis results showed that the key factor driving the change in soil respiration rate of abandoned grassland in the loess hilly region was soil temperature and SWC characteristics.

Seasonal Changes in Soil Respiration with An Elevation Gradient in Abies nephrolepis (Trautv.) Maxim. Forests in North China

Soil respiration (Rs) plays an important role in regulating carbon cycle of terrestrial ecosystems and presents temporal and spatial heterogeneity. Abies nephrolepis is a tree species that prefers the cold and wet environment and is mainly distributed in Northeast Asia and East Asia. The Rs variations of Abies nephrolepis forests communities are generally environmental-sensitive and can effectively reflect the adaptive responses of forest ecosystems to climate change. In this study, the growing-seasonal variations of Rs, soil temperature, soil water content and soil properties of Abies nephrolepis forests were analyzed along an altitude gradient (2000, 2100, 2200 and 2300 m) over two years on Wutai Mountain in North China. As the main results showed, soil respiration keeps the same change trend as soil temperature and reached peaks in July at 2000 m in 2019 and 2020. During 26th July to 25th October in 2019 and 27th May to 23rd October in 2020, on the whole, the soil temperature independently explained 76.2% of Rs variations while the soil water content independently explained 26.8%. Soil temperature and soil water content jointly explained 81.8% of Rs variations. Soil properties explained 61.8% and 69.6% of Rs variation in 2019 and 2020, respectively. Soil organic carbon content and soil enzyme activity had the signifi- cant (P < 0.01) negative and positive relationships, respectively, with Rs variation. With altitudes evaluated from 2000 to 2300 m, soil respiration temperature sensitivity (Q10) and the soil organic carbon content increased by 12.4% and 10.4%, respectively, while invertase activity, cellulase activity and urease activity dropped by 41.2%, 29.45% and 38.19%, respectively. The results demonstrate that (1) soil temperature is the major factor affecting Rs variations in Abies nephrolepis forests; (2) weakened microbial carbon metabolism in high-altitude areas results in the accumulation of soil organic carbon; (3) with a higher Q1, forest ecosystems in high-altitude areas might be more easily affected by climate change; (4) climate warming might accelerate the consumption of soil organic carbon sink in forest ecosystems, especially in high-altitude areas.

Topography modifies the effect of land‐use change on soil respiration: A meta‐analysis

AbstractSoil respiration is controlled by land‐use changes associated with cropland vegetation restoration, and this can vary with topography, although the magnitude of this effect and the underlying mechanisms are still unclear. We synthesized 69 recently published papers from China to explore the influence of topography‐related changes in land use on soil respiration where croplands were converted into orchards (abbreviated as C‐O), grasslands (abbreviated as C‐G), or woodlands (abbreviated as C‐W). Our results showed that not only did land‐use change have a significant influence on soil respiration, but this varied with topography. While C‐O resulted in a decrease in soil respiration by, on average, 3.1%, both the magnitude and sign of the change varied with topography, with an 8.2% increase for flat areas and a 14.7% decrease for slopes. For the C‐G conversions, soil respiration increased, on average, by 21.4%, with a 19.5% and a 24.3% increase for flat and slope topography, respectively. For C‐W, soil respiration increased, on average, by 28.0%, with only a 1.6% increase for flat areas, but a 39.9% increase for slopes. Soil temperature, soil moisture, root biomass, soil organic carbon (SOC), soil microbial biomass carbon (MBC), soil carbon‐to‐nitrogen ratio (C:N ratio), and soil density also varied with topography, with larger changes for slopes than for flat topography. Increases in soil respiration associated with different topography were closely related to changes in soil temperature, SOC, MBC, and root biomass (P &lt; 0.05), but were not correlated with changes in soil moisture, C:N ratio, or soil density (P &gt; 0.05). The contribution of different drivers to the change in soil respiration under different topographical conditions showed a trend of SOC &gt; root biomass &gt; MBC &gt; soil temperature. Based on these results, topography‐related variations in soil respiration need to be accounted for when quantifying the impact of land‐use change on C budgets.

Stalagmite carbon isotopes suggest deglacial increase in soil respiration in western Europe driven by temperature change

Abstract. The temperate region of western Europe underwent significant climatic and environmental change during the last deglaciation. Much of what is known about the terrestrial ecosystem response to deglacial warming stems from pollen preserved in sediment sequences, providing information on vegetation composition. Other ecosystem processes, such as soil respiration, remain poorly constrained over past climatic transitions but are critical for understanding the global carbon cycle and its response to ongoing anthropogenic warming. Here we show that speleothem carbon isotope (δ13Cspel) records may retain information on soil respiration and allow its reconstruction over time. While this notion has been proposed in the past, our study is the first to rigorously test it, using a combination of multi-proxy geochemical analysis (δ13C, Ca isotopes, and radiocarbon) on three speleothems from the NW Iberian Peninsula and quantitative forward modelling of processes in soil, karst, and cave. Our study is the first to quantify and remove the effects of prior calcite precipitation (PCP, using Ca isotopes) and bedrock dissolution (using the radiocarbon reservoir effect) from the δ13Cspel signal to derive changes in respired δ13C. The coupling of soil gas pCO2 and δ13C via a mixing line describing diffusive gas transport between an atmospheric and a respired end-member allows the modelling of changes in soil respiration in response to temperature. Using this coupling and a range of other parameters describing carbonate dissolution and cave atmospheric conditions, we generate large simulation ensembles from which the results most closely matching the measured speleothem data are selected. Our results robustly show that an increase in soil gas pCO2 (and thus respiration) is needed to explain the observed deglacial trend in δ13Cspel. However, the Q10 (temperature sensitivity) derived from the model results is higher than current measurements, suggesting that part of the signal may be related to a change in the composition of the soil respired δ13C, likely from changing substrate through increasing contribution from vegetation biomass with the onset of the Holocene.

Research Progress on Spatial and Temporal Variation Characteristics of Soil Respiration

The research on soil respiration has already started as early as the 20th century, and the research in foreign countries started earlier than that in China. At present, many studies have found that soil respiration has great temporal and spatial changes. In order to understand and explore the temporal and spatial changes of soil respiration more accurately, the related articles at home and abroad were reviewed, sorted out, summed up and summarized. Temporal changes mainly included diurnal changes, seasonal changes and inter-annual changes. Spatial variability mainly included four aspects: community level, landscape level, regional scale and biotic scale. Altitude gradient also affected soil respiration.

A decreasing carbon allocation to belowground autotrophic respiration in global forest ecosystems

Belowground autotrophic respiration (RAsoil) depends on carbohydrates from photosynthesis flowing to roots and rhizospheres, and is one of the most important but least understood components in forest carbon cycling. Carbon allocation plays an important role in forest carbon cycling and reflects forest adaptation to changing environmental conditions. However, carbon allocation to RAsoil has not been fully examined at the global scale. To fill this knowledge gap, we first used a Random Forest algorithm to predict the spatio-temporal patterns of RAsoil from 1981 to 2017 based on the most updated Global Soil Respiration Database (v5) with global environmental variables; calculated carbon allocation from photosynthesis to RAsoil (CAB) as a fraction of gross primary production; and assessed its temporal and spatial patterns in global forest ecosystems. Globally, mean RAsoil from forests was 8.9 ± 0.08 Pg C yr-1 (mean ± standard deviation) from 1981 to 2017 and increased significantly at a rate of 0.006 Pg C yr-2, paralleling broader soil respiration changes and suggesting increasing carbon respired by roots. Mean CAB was 0.243 ± 0.016 and decreased over time. The temporal trend of CAB varied greatly in space, reflecting uneven responses of CAB to environmental changes. Combined with carbon use efficiency, our CAB results offer a completely independent approach to quantify global aboveground autotropic respiration spatially and temporally, and could provide crucial insights into carbon flux partitioning and global carbon cycling under climate change.