Increased Soil Respiration Research Articles

Potential of biochar to restoration of microbial biomass and enzymatic activity in a highly degraded semiarid soil

Biochar is an effective material for enhancing soil ecosystem services. However, the specific impacts of biochar on microbial indicators, particularly in degraded soils, remain poorly understood. This study aimed to evaluate the effects of biochar produced from cashew residues and sewage sludge, in a highly degraded soil, on microbial indicators. We analyzed soil chemical composition and microbial biomass C and N, enzyme activity, and stoichiometry. Cashew biochar increased soil respiration, indicating a higher availability of C to microorganisms compared to sewage sludge biochar and a better adaptation of soil microbial communities to C-rich organic material obtained from a native plant. Although the biochar differentially impacted microbial biomass C, both significantly increased N in the microbial biomass. Arylsulphatase activity did not respond to biochar application, while β-glucosidase, urease, and phosphatases showed significant changes with biochar treatments. Importantly, stoichiometry and vector analysis revealed that both types of biochar increased P limitation for soil microbes. Conversely, both biochar alleviated C and N limitations for the soil microbes. Thus, biochar applications in highly degraded soils should be supplemented with external P sources to maintain soil functions, mainly for cashew residues. Our results provide evidence that biochar can restore soil biological properties and enhance the availability of C and N to microorganisms. These findings have significant implications for restoration practices in degraded lands of semiarid regions.

Integrating cover crops and organic amendments to mitigate the limitations of tillage on soil health and cotton productivity

AbstractVarious tillage systems have limitations on soil health, such as the degradation of soil structure and organic matter under conventional tillage (CT) systems, as well as short‐term soil compaction in conservation tillage systems. A 3‐year field experiment was established to evaluate the integration of cover crop (CC) and organic amendments (OAs) into CT and strip tillage (ST) systems, and their impact on soil properties and cotton (Gossypium hirsutum L.) productivity. The CC was cereal rye (Secale cereale), and the combined application of animal manure and biochar constituted the OA. In the third year, differences in soil compaction between the CT and ST systems were observed when the measurements were made after tillage. Moreover, integrating CC and OA under the CT and ST systems increased the soil depth to compaction zones. Soil compaction was observed at 27.5‐cm depth under CT, at 30‐cm depth under CT integrated with CC and OA, at 10‐cm depth under ST, and at 15‐cm depth under ST integrated with CC and OA, using 2 MPa as the threshold. In general, the integration of CC and OA tended to increase soil respiration, organic matter, and available nutrients, but the effects were not consistent across years and soil depth. Despite differences in the various soil health properties, the management systems had minimum impact on cotton productivity and fiber quality, indicating the ST was effective in preparing the seedbed. Moreover, the differences in soil properties were not at yield‐limiting levels within 3 years of the study.

Hydrogel Effects on Soil Nitrogen Transformations in pH-Contrasting Soils

ABSTRACT Superabsorbent hydrogels (HGs) are three-dimensional, polymeric networks that have been shown to increase soil water holding capacity, but little is known about their effect on nitrogen (N) transformations in soil. The objective of this study was to determine the effect of two types of HGs (polyacrylate (TS) or cellulose-based (H30)) applied as soil amendment on pH, urea hydrolysis, nitrification, NH3 volatilization, and soil respiration in two soils receiving urea or ammonium sulfate. Separate studies with each HG in each of two soils (four studies) were conducted with an acidic sandy loam collected in Georgia (USA) and a basic sandy loam collected in the Veneto region of Italy. The results showed that the addition of TS increased the pH of the acidic soil, whereas H30 did not have a major effect on soil pH in either soil. In the acidic soil receiving urea, H30 increased nitrification, whereas TS decreased initial nitrification. Neither HG affected urea hydrolysis, N immobilization and NH3 volatilization in either soil, but both HGs increased soil respiration in the basic soil, possibly due to HG degradation by microorganisms. These results show that the use of HGs together with N fertilizers may affect soil pH, nitrification, and respiration.

Additive effects of N addition and changing precipitation on soil respiration in a climate transitional forest

Global carbon (C) cycling can be greatly affected by the increasing nitrogen (N) deposition and changing precipitation regimes in terrestrial ecosystems. Nevertheless, whether N enrichment and precipitation variability interactively or additively influence soil C release during a long-term period remain largely elusive. Here, a seven-year (2016–2022) field experiment was conducted to explore the responses of soil respiration to N addition, decreased and increased precipitation in a subtropical-warm temperate forest in Central China. The results showed soil respiration was elevated by 11.0%, 12.2%, and 12.3% under N addition, decreased precipitation, and increased precipitation, respectively, primarily originating from the enhancements in plant root respiration. Increased precipitation led to a temporal increase in soil respiration over the experimental period, mostly due to the elevating understory richness and reducing soil C/N ratio. There were additive effects between N addition and changing precipitation on soil respiration observed in our study, suggesting that the impacts of concurrent global change drivers can be predicted from their respective influences. These findings indicated that global change may intensify soil C release from climate transition forests, thus helping to accurately assess the climate change–C feedback in natural ecosystems.

Green-house gas fluxes and soil microbial functional genes abundance in saturated and drained peatlands in South-West Iceland

The drainage of peatlands followed by land use conversion significantly impacts on the fluxes of green-house gases (GHGs, i.e. CO2, CH4, and N2O) to and from the atmosphere, driven by changes in soil properties and microbial communities.In this study, we compared saturated peatlands with drained ones used for sheep grazing or cultivated, which are common in South-West Iceland. These areas exhibit different degrees of soil saturation and nitrogen (N) content, reflecting the anthropic pressure gradient.We aimed at covering knowledge gaps about lack of estimates on N2O fluxes and drainage, by assessing the emissions of GHGs, and the impact of land conversion on these emissions. Moreover, we investigated soil microbial community functional diversity, and its connection with processes contributing to GHGs emission.GHGs emissions differed between saturated and drained peatlands, with increased soil respiration rates (CO2 emissions) and N mineralization (N2O), consistent with the trend of anthropogenic pressure. Drainage drastically reduced methane (CH4) emissions but increased CO2 emissions, resulting in a higher global warming potential (GWP). Cultivation, involving occasional tillage and fertilization, further increased N2O emissions, mediated by higher N availability and conditions favorable to nitrification. Functional genes mirrored the overall trend, showing a shift from prevalent methanogenic archaea (mcrA) in saturated peatlands to nitrifiers (amoA) in drained-cultivated areas.Environmental variables and nutrient content were critical factors affecting community composition in both environments, which overall affected the GHGs emissions and the relative contribution of the three gases.

Can Biochar Made from Rice Husk Affect Savanna Soils’ pH, Electrical Conductivity, and Soil Respiration?

Biochar is now gaining awareness as a sustainable tool for soil health improvement, boosting carbon (C) storage and the enhancement of nutrient cycling in agricultural soils. This study assesses the effects of biochar on soil respiration, pH, and electrical conductivity (EC) in savanna soils over a 45-day incubation trail in the laboratory. Four different biochar treatments (0, 2, 4, and 6 t/ha) were used in the study. The treatments were established at 26°C, and after 2, 5, and 10 days, the CO2 levels were recorded. After incubation for 0, 5, 10, and 45 days, the EC and pH were assessed. As the rate of application of biochar increased, the rate of CO2 evolution increased as well. During the first two days of incubation, the CO2 evolution rate rose by a value of 129 at 2 t/ha biochar, 146 at 4 t/ha biochar, and 168 ug CO2/g soil/d at 6 t/ha biochar above the 0 t/ha biochar. Following five days of incubation, the amounts of CO2 evolution that were higher than the control were 99 with 2 t/ha, 116 with 4 t/ha, and 120 ug CO2/g soil/d with 6 t/ha of biochar. The increase in CO2 evolution above the control treatment at 10 days of incubation was 61 with 2 t/ha, 79 with 4 t/ha, and 87 ug CO2/g soil/d with 6 t/ha of biochar. Analogously, rising patterns in CO2 emissions were noted. Throughout the whole incubation period, the biochar treatments' soil EC and pH were greater than those of the control treatment. After applying biochar, there were increases in the evolution of CO2, however after 10 days of incubation, the percentage of C evolved from the addition of biochar decreased as the rates of biochar increased. At two t/ha, four t/ha, and six t/ha, the percentage C developed was 1.74 %, 1.66%, and 0.82% of the applied biochar C, respectively. Although the CO2 evolved ratio to the total amount of biochar C typically reduced with increasing biochar rates, this study shows that the addition of biochar increases soil respiration, EC, and pH.

Straw application improved soil biological properties and the growth of rice plant under low water irrigation

The application of organic amendments is one way to manage low water irrigation in paddy soils. In this 60-day greenhouse pot experiment involving paddy soil undergoing drying-rewetting cycles, we examined the effects of two organic amendments: azo-compost with a low carbon to phosphorus ratio (C:P) of 40 and rice straw with a high C:P ratio of 202. Both were applied at rates of 1.5% of soil weight (w/w). The investigation focused on changes in certain soil biochemical characteristics related to C and P in the rice rhizosphere, as well as rice plant characteristics. The irrigation regimes applied in this study included constant soil moisture in a waterlogged state (130% water holding capacity (WHC)), mild drying–rewetting (from 130 to 100% WHC), and severe drying–rewetting (from 130 to 70% WHC). The results indicated that the application of amendments was effective in severe drying–rewetting irrigation regimes on soil characteristics. Drying–rewetting decreased soil respiration rate (by 60%), microbial biomass carbon (by 70%), C:P ratio (by 12%), soil organic P (by 16%), shoot P concentration (by 7%), and rice shoot biomass (by 30%). However, organic amendments increased soil respiration rate (by 8 times), soil microbial biomass C (51%), total C (TC) (53%), dissolved organic carbon (3 times), soil available P (AP) (100%), soil organic P (63%), microbial biomass P (4.5 times), and shoot P concentration (21%). The highest significant correlation was observed between dissolved organic carbon and total C (r= 0.89**). Organic amendments also increased P uptake by the rice plant in the order: azo-compost > rice straw > control treatments, respectively, and eliminated the undesirable effect of mild drying–rewetting irrigation regime on rice plant biomass. Overall, using suitable organic amendments proves promising for enhancing soil properties and rice growth under drying–rewetting conditions, highlighting the interdependence of P and C biochemical changes in the rhizosphere during the rice vegetative stage.

Pulp mill sludges as a solution for reducing the risk of mineral nitrogen leaching from agriculture

Nitrogen (N) from agricultural systems contributes to the eutrophication of waterbodies through leaching. Incorporating organic material with a high carbon-to-nitrogen (C/N) ratio, such as mixed pulp mill sludges (PMSs), into the soil in autumn could reduce the amount of leachable N. This study tested the potential of composted and lime-stabilised mixed PMSs (CPMS and LPMS) in reducing the concentration of mineral N in the soil, and thus the risk of N leaching from arable land in the boreal region using a two-year field experiment. To better understand the mechanisms of the PMSs for influencing mineral N concentration in soil, the impact of PMSs with different quality on the reactions of N in the soil was investigated in a laboratory incubation study. In the field experiment, nitrate-N (NO3--N) concentration was lower with PMSs compared to mineral fertilisation and the control during the first autumn and the following spring after PMS application. The undersowing of Italian ryegrass reduced the NO3--N concentration in the soil during the first autumn. In the incubation experiment, PMSs reduced the soil ammonium-N (NH4+-N) concentration at the beginning of the experiment and the soil NO3--N concentration throughout the experiment compared to a mineral fertiliser treatment and an organic fertiliser. Increased soil respiration in PMS-treated soils indicated increase in microbial activity, and thus immobilisation of soil NO3--N and NH4+-N due to PMSs addition. These results suggest that PMSs have the potential to reduce N leaching from agricultural soils. However, the immobilisation of N must be considered when planning the nutrient requirements of the following crops.

Warming persistently stimulates respiration from an arable soil over a decade, regardless of reduced summer precipitation

Climate change factors alter soil microbial biomass and respiration, which represent two key parameters of carbon (C) cycling in soils. While these interrelations are increasingly well described for soils in natural ecosystems, long-term studies conducted in temperate agricultural ecosystems do rarely exist. Here we used the ‘Hohenheim Climate Change Experiment (HoCC)’ to describe the response of microbial biomass and respiration to interacting effects of climate change factors. We were interested in whether effects would be season specific, and if ultimately, climate change factors would affect the total soil organic carbon (SOC) content in the arable soil. The HoCC experiment is an agroecosystem where soils were permanently warmed for one decade, and summer precipitation amount and frequency were reduced. We found that soil respiration was not affected by reduced summer precipitation, but strongly increased by warming. This increase was not season specific and persisted over the years. Further, warming continuously enhanced labile C availability, while microbial biomass did not differ between warmed and ambient temperature soils. Therefore, soil respiration stimulated by warming was independent of microbial biomass, and accordingly, we found an increase of the metabolic quotient. Despite the warming induced increase in soil respiration, no indications for a loss in SOC content of the arable soil was detected. These results suggest that in an arable soil with overall low SOC content, the persisting stimulation of respiration due to warming is driven by an agroecosystem specific labile C pool dynamic.

Promoting success in thin layer sediment placement: effects of sediment grain size and amendments on salt marsh plant growth and greenhouse gas exchange

Thin layer sediment placement (TLP) is used to build elevation in marshes, counteracting effects of subsidence and sea level rise. However, TLP success may vary due to plant stress associated with reductions in nutrient availability and hydrologic flushing or through the creation of acid sulfate soils. This study examined the influence of sediment grain size and soil amendments on plant growth, soil and porewater characteristics, and greenhouse gas exchange for three key U.S. salt marsh plants: Spartina alterniflora (synonym Sporobolus alterniflorus), Spartina patens (synonym Sporobolus pumilus), and Salicornia pacifica. We found that bioavailable nitrogen concentrations (measured as extractable NH4+‐N) and porewater pH and salinity were inversely related to grain size, while soil redox was more reducing in finer sediments. This suggests that utilizing finer sediments in TLP projects will result in a more reduced environment with higher nutrient availability, while larger grain sized sediments will be better flushed and oxygenated. We further found that grain size had a significant effect on vegetation biomass allocation and rates of gas exchange, although these effects were species‐specific. We found that soil amendments (biochar and compost) did not subsidize plant growth but were associated with increases in soil respiration and methane emissions. Biochar amendments were additionally ineffective in ameliorating acid sulfate conditions. This study uncovers complex interactions between sediment type and vegetation, emphasizing the limitations of soil amendments. The findings aid restoration project managers in making informed decisions regarding sediment type, target vegetation, and soil amendments for successful TLP projects.

The responses of CO2 emission to nitrogen application and earthworm addition in the soybean cropland.

The effects of nitrogen application or earthworms on soil respiration in the Huang-Huai-Hai Plain of China have received increasing attention. However, the response of soil carbon dioxide (CO2) emission to nitrogen application and earthworm addition is still unclear. A field experiment with nitrogen application frequency and earthworm addition was conducted in the Huang-Huai-Hai Plain. Results showed nitrogen application frequency had a significant effect on soil respiration, but neither earthworms nor their interaction with nitrogen application frequency were significant. Low-frequency nitrogen application (NL) significantly increased soil respiration by 25%, while high-frequency nitrogen application (NH), earthworm addition (E), earthworm and high-frequency nitrogen application (E*NH), and earthworm and low-frequency nitrogen application (E*NL) also increased soil respiration by 21%, 21%, 12%, and 11%, respectively. The main reason for the rise in soil respiration was alterations in the bacterial richness and keystone taxa (Myxococcales). The NH resulted in higher soil nitrogen levels compared to NL, but NL had the highest bacterial richness. The abundance of Corynebacteriales and Gammaproteobacteria were positively connected with the CO2 emissions, while Myxococcales, Thermoleophilia, and Verrucomicrobia were negatively correlated. Our findings indicate the ecological importance of bacterial communities in regulating the carbon cycle in the Huang-Huai-Hai Plain.

Tillage Depth Regulation and the Effect of Straw Return on Soil Respiration in Farmland

Straw return and tillage depth treatments are one of the most important agricultural management measures that affect farmland soil respiration, but the mechanism of their interaction affecting farmland soil respiration remains unclear. Therefore, 116 published research articles were used through Meta-analysis technology for dryland farmland ecosystems in China to explore the effects of straw return and tillage depth treatments and their interaction on farmland soil respiration and its regulatory factors, which will provide important data support and a theoretical basis for achieving "carbon neutrality" in farmland ecosystems. The results showed that no tillage reduced soil respiration by 8.3%, and the effects of shallow and deep tillage treatments on soil respiration were not significant, but the increase in soil respiration still showed a trend of deep tillage>shallow tillage>no tillage. However, both shallow and deep tillage had relatively small effects on soil respiration and soil organic carbon (SOC), whereas no tillage reduced soil respiration by 8.3% and increased SOC by 7.05%. Therefore, implementing no tillage measures is of great significance for soil carbon sequestration and emission reduction in farmland ecosystems. In addition, tillage depth significantly regulated the impact of straw return on soil respiration, and the increase in soil respiration showed a trend of deep tillage straw return>shallow tillage straw return>no tillage straw return, with an overall average increase of 14.51%. The increase in soil respiration under different tillage depth treatments after straw return was closely related to the change in soil bulk density, crop yield, SOC, soil temperature, and moisture, and the contribution to the increase in soil respiration showed a trend of soil bulk density>crop yield>soil organic carbon>soil moisture>soil temperature. However, SOC increased by 29.32%, 10.12%, and 23.94%, respectively, in the deep tillage straw return, shallow tillage straw return, and no tillage straw return treatments, whereas soil respiration increased by 29.32% and 18.92%, respectively, in the deep tillage straw return and shallow tillage straw return treatments, and it only increased by 1.2% in the no tillage straw return treatment. Therefore, no tillage straw return was also beneficial to soil carbon sequestration and emission reduction in farmland ecosystems. Thus, in the dryland farmland ecosystem of China, tillage depth treatments regulated the impact of straw return on soil respiration, which was mainly related to soil physical and chemical properties, especially being closely related to soil bulk density. Moreover, no tillage and no tillage straw return are important agricultural management measures that are conducive to soil carbon sequestration and emission reduction.

Lack of P limitation on litter decomposition: a case study from long-term addition of phosphorus and nitrogen in three subtropical forests in southern China

ABSTRACT Contrary to the widely accepted belief that elevated soil respiration after phosphorus (P) fertilization indicates P limitations for soil microorganisms in (sub)tropical forests, our previous studies have proposed that the elevated respiration results from the abiotically elevated availability of carbon (C), originating from competitive desorption from sorption sites on the surface of soil particles following P fertilization. In this study, we tested the impact of P fertilization (150 kg NaH2PO4-P ha−1 yr−1) on the decomposition of tea bags (Lipton Rooibos and Green teas) in three types of subtropical forests (primary, secondary, and planted forests) at the Dinghushan Biosphere Reserve, where previous findings reported increased soil respiration following P fertilization. If the traditional view holds true, early-stage litter decomposition should be stimulated by P fertilization, similar to the observed stimulation in soil respiration. Conversely, if this is not the case, it strongly reinforces our new hypothesis. Tea bags were employed to serve a twofold purpose: to assess the effects of P fertilization on litter decomposition within the soil, rather than on the soil surface, and to concentrate on the decomposition of early-stage litter. Our results demonstrated that P fertilization did not accelerate the decomposition of tea bags, indicating the exclusive enhancement of soil respiration without simultaneous stimulation of litter decomposition. This contradicts expectations if P were limiting microbial activity, reinforcing our hypothesis. In conclusion, our study reaffirmed the hypothesis that microbial activity in tropical forest soils is not primarily limited by P availability.

Herbivore dung deposition increases soil respiration through elevated substrate availability and microbial biomass

Soil heterotrophic respiration (Rh) is the primary pathway for terrestrial ecosystem CO2 efflux. Herbivore grazing activity is known to affect grassland soil Rh, but the effects of grazing-related dung deposition on Rh and the mechanisms involved remain unknown. Here, we explored effects of dung on Rh via altered biotic and abiotic factors in a short-term experiment with yak dung application during a growing season in a Tibetan alpine meadow. Dung application significantly decreased soil pH, but increased soil Rh, concentrations of dissolved organic carbon (C), nitrogen (N), and phosphorus (P), microbial biomass, and activities of enzymes related to C-, N-, and P-degradation. Linear regression showed that Rh was positively correlated with labile substrates, microbial biomass, and enzyme activities, and negatively correlated with soil pH, suggesting that these factors are all potential drivers of Rh. Further, using piecewise structural equation modeling, we revealed that Rh was driven directly by altered microbial biomass and enzyme activities, and indirectly by altered pH and labile substrates. Particularly labile substrates and microbial biomass had more important roles in driving Rh than pH and enzyme activities. Taken together, our work revealed some mechanisms behind short-term dung deposition effects on Rh, which can be used to develop grassland management practices and forecast C feedback in grazed ecosystems.

Integration crop-livestock system increases the sustainability of soybean cultivation through improved soil health and plant physiology

This study aimed to evaluate how different cultivation systems in integration crop-livestock regimes affect soybean growth and physiology and understand how integrated systems change soil characteristics and soil CO2 flux. We conducted a comparative analysis of the plant physiology, growth, and soil characteristics of a conventional soybean monoculture (traditional cultivation method without any plant residues on the soil surface from the previous crop) and soybean cultivated in soil containing maize residues. Moreover, we conducted experiments to assess the effect of plant residues derived from maize intercropped within or between forage grasses on the effectiveness of integrating crop-livestock systems. Our main results indicated that when soybean was cultivated in all integration crop-livestock systems tested, soybean net photosynthesis rate and leaf chlorophyll content greatly increased, resulting in increased aboveground biomass production. Moreover, the integrated system decreased soil temperature and increased soil organic carbon content, total organic carbon content, and enzymatic activity, with no concomitant increase in soil respiration. However, fewer differences were observed between the sowing methods (maize in consortium with forages within and between rows). We conclude that all tested integrated crop-livestock systems greatly improved soybean physiology by increasing the amount of carbon assimilated into the ecosystem through photosynthesis, improving carbon sink potential, soil health, and maintaining a sustainable production system.

Photodegradation modifies microplastic effects on soil properties and plant performance

Abstract Microplastics (MPs) in soil affect plant–soil systems depending on their shape and polymer type. However, previous research has not yet considered the effects of degraded plastics, which are the plastic materials actually present in the environment. We selected eight MPs representing different shapes (fibres, films and foams) and polymer types, and exposed them to UV‐C degradation. Each MP was mixed with soil at a concentration of 0.4% (w/w). The phytometer Daucus carota grew in each pot. At harvest, soil properties and plant biomass were measured. Photodegradation altered MP physical and chemical properties, impacting plant–soil systems. MP degradation effects on plant and soil were observed with fibres and foams, but there were negligible effects with films. The latter could be explained by the polymer structure of films and manufacturer's additives, potentially delaying their degradation. Degraded fibres increased soil respiration more than their non‐degraded counterparts, as photodegradation increased the positive effects of fibres on soil water retention. The emergence of oxygenated groups during degradation may have increased the hydrophilicity of fibres, enhancing their ability to retain water. Degraded foams increased soil respiration, which could be related to the possible leaching of organic substances with lower partition coefficients, which may promote soil microbial activity. In contrast, degraded foams decreased soil aggregation, likely as degradation produced larger holes increasing their permeability. Also, the increase in hydrophilic molecules could have decreased soil particle cohesiveness. Degraded fibres and foams increased shoot and root mass as a result of MP effects on soil properties. Photodegraded MPs affected root traits, which could be linked to MP effects on soil water status and plant coping strategies. Synthesis and applications. Photodegradation can intensify the effects that microplastics (MPs) have on plant–soil systems, which would have frequently been underestimated had we only worked with pristine MPs. Plastic companies, agricultural practitioners and researchers should consider that plastics are being degraded as they enter the soil. Policies should promote practices to minimize MP accumulation in soils and ensure their proper disposal.

The temporal response of soil respiration to environment differed from that on spatial scale

In the context of increasing CO2 concentrations and climate warming, there are large uncertainties regarding the regulatory mechanisms of soil respiration and its accurate assessment. As an area sensitive to global climate change, China covers a broad range of longitudes, latitudes, and altitudes, and it is of great significance to study the spatial and temporal patterns of soil respiration and its environmental response in China's terrestrial ecosystems to clarify the mechanisms of regional and global carbon balance processes. Based on the expanded annual soil respiration dataset from 1993 to 2020, we evaluated soil respiration in China's terrestrial ecosystems and its responses to environmental factors. The mean annual soil respiration in China's terrestrial ecosystems was 777.90 ± 489.43 g C m−2 yr−1 by arithmetic averaging and 595.52 g C m−2 yr−1 by area weighting, with soil respiration in wetlands being higher than that of the forest, grassland, shrubland, cropland, and desert. Soil respiration showed a significant upward trend from 2000 to 2017, which was mainly caused by a significant increase in soil respiration in grasslands due to increasing precipitation. In addition, we found differences in the environmental factors influencing the interannual and spatial variability of soil respiration. The response sensitivities of soil respiration to environmental changes differed significantly among the various ecosystem types; however, these differences were not significant when comparing interannual and spatial scales. This study provides information on soil respiration in China's terrestrial ecosystem and highlights the importance of considering the two-dimensional responses of soil respiration to environmental changes in both time and space.

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.

Effect of straw return on soil respiration in dryland agroecosystem of China: A meta-analysis

In agroecosystems, straw return is considered an important agricultural management practice influencing soil respiration. However, the impact of straw return on soil respiration is equivocal and the underlying mechanisms underpinning any responses remain unclear. To address this, we synthesized 86 recently published papers on dryland agroecosystems in China, which comprise approximately 74% of the agricultural land area, using a meta-analysis approach and explored the influence of straw return on soil respiration and the underlying mechanisms involved. Straw return resulted in a 13.5% increase in soil respiration, a 9.4% increase in soil moisture, a 10.4% increase in crop yield, a 18.9% increase in SOC (soil organic carbon), and a 2.6% decrease in soil temperature. Compared to conventional tillage without straw return treatment, the increase in soil respiration in response to straw return was closely related to modifications in soil temperature, soil moisture, SOC, and crop yield (P < 0.05). The contribution of the different drivers to increases in soil respiration in response to straw return showed a trend of crop yield > soil temperature > SOC > soil moisture. In addition, straw mulching, crop planting system, tillage method, and fertilization modified the effect of straw return on soil respiration. The increase in soil respiration was less when straw was used as a mulch (12.9%), compared to when it was incorporated into the soil (18.8%). The cropping system also influenced the effect of straw return on soil respiration and was increased by 21.1% in inter-crops, and by 17.3% and 11.0% in monocultures and rotations treatments, respectively. Our results also showed that the effect of straw return on soil respiration was larger in deep tillage treatments than in shallow tillage treatments (26.9% vs.18.7%). In addition, the effect of straw return on soil respiration was also larger in fertilized treatment compared to unfertilized one (12.7% vs. 0.5%). However, this depended on the amount of nitrogen fertilizer applied rates and was higher (14.8%) with low (<300 kg ha−1) application rates compared to high (≧300 kg ha−1) ones (2.5%). Therefore, in dryland agroecosystems in China, biological factors, especially those related to crop yield, may be a more important factor regulating the effect of straw return on soil respiration. However, straw mulching, crop planting system, tillage method, and fertilization can modify the effect of straw return on soil respiration.

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.