Response Of Soil Respiration Research Articles

Rates of soil respiration components in response to inorganic and organic fertilizers in an intensively-managed Moso bamboo forest

Fertilization is a common practice to increase forest productivity; however, the responses of soil respiration (RS) components to the application of inorganic and organic fertilizers and the associated mechanisms are not clear in subtropical forest ecosystems. In this field trial conducted within an intensively-managed Moso bamboo (Phyllostachys edulis) forest, we aimed to compare the effects of inorganic and organic fertilizers, and their combination on seasonal variations in RS components, i.e., heterotrophic (RH) and autotrophic (RA) respiration, and to establish the relations of RS components with soil properties. Fertilizer additions increased RH (P < 0.05), with the increase being greater with organic than with inorganic fertilizer. Fertilization also increased RA, but the effect was greater with inorganic fertilizer. Furthermore, fertilizer additions increased (P < 0.05) the concentrations of water-soluble organic C (WSOC) and microbial biomass C, invertase and β-glucosidase activities, as well as the biomass and N concentration of fine roots. Irrespective of fertilizer treatment, strong seasonal patterns were observed in both RS and RH, and an exponential relation (P < 0.01) was found between RS components (RH and RA) and soil temperature. Additionally, the Q10 for RH was higher (P < 0.05) in the inorganic than the organic fertilizer treatment. Although RS and RH showed no correlation with soil moisture content in any treatment, each of them was positively correlated with WSOC concentration and activities of invertase and β-glucosidase (P < 0.05). In the fertilized treatments, RA was positively related to β-glucosidase activities (P < 0.05) but not to the concentrations of WSOC or microbial biomass C. In conclusion, soil RA and RH in the subtropical Moso bamboo forest responded differently to the application of inorganic and organic fertilizers, indicating that separation of total RS into soil RH and RA is critically necessary to predict RS in subtropical forests under different fertilizer regimes.

Temperature Increases Soil Respiration Across Ecosystem Types and Soil Development, But Soil Properties Determine the Magnitude of This Effect

Soil carbon losses to the atmosphere, via soil heterotrophic respiration, are expected to increase in response to global warming, resulting in a positive carbon-climate feedback. Despite the well-known suite of abiotic and biotic factors controlling soil respiration, much less is known about how the magnitude of soil respiration responses to temperature changes over soil development and across contrasting soil properties. Here we investigated the role of soil development stage and soil properties in driving the responses of soil heterotrophic respiration to temperature. We incubated soils from eight chronosequences ranging in soil age from hundreds to million years, and encompassing a wide range of vegetation types, climatic conditions and chronosequences origins, at three assay temperatures (5 °C, 15 °C and 25 °C). We found a consistent positive effect of assay temperature on soil respiration rates across the eight chronosequences evaluated. However, chronosequences parent materials (sedimentary/sand dunes or volcanic) and soil properties (pH, phosphorus content and microbial biomass) determined the magnitude of this temperature effect. Finally, we observed a positive effect of soil development stage on soil respiration across chronosequences that did not alter the magnitude of assay temperature effects. Our work reveals that key soil properties alter the magnitude of the positive effect of temperature on soil respiration found across ecosystem types and soil development stages. This information is essential to better understand the magnitude of the carbon-climate feedback and thus to establish accurate greenhouse gas emission targets.

Separating the temperature response of soil respiration derived from soil organic matter and added labile carbon compounds

Broadly, soil organic C can be characterised as either labile (highly available and soluble) or stable (physiochemically protected) carbon. Previous studies have attributed differences in the temperature response of these C pools to overall availability or chemical complexity. Here, we estimated the decomposition of the labile pool as the difference of CO2 from soils with added highly available C substrates (arginine, glucose, glutamine, lysine, and maltose) and yeast extract, and CO2 from soil without added C. We also measured the temperature response of the decomposition of soil organic matter (SOM), which encompasses both labile and stable C (no added C). Soil was incubated for five hours using a temperature gradient block consisting of 18 discrete temperatures (~8–52 °C). We also tested to see if temperature responses differed between three contrasting soils (allophanic, gley, and organic/degraded peat). We applied macromolecular rate theory (MMRT) to the RS data to calculate the temperature optimum (Topt) and the inflection temperature (Tinf).The decomposition of SOM had an exponential, Arrhenius-like behaviour. In contrast, respiration of the five labile C compounds had a clear and similar Topt of around 37 °C and Tinf of 22 °C. The temperature response of the more labile C and of the SOM pools did not significantly vary between the three very different soils, suggesting that these responses might be independent of soil properties.Our findings provide support for the hypothesis that the overall temperature dependence of soil respiration is reliant on sorption/desorption and diffusion to microbes – a process that exhibits Arrhenius behaviour, and the biological decomposition of C by these soil microbes that exhibits MMRT behaviour. The overall response to temperature is governed by substrate availability as biological processes dominate when substrate is non-limiting, and physiochemical processes dominate when substrate availability is limiting.

Impacts of land use conversion on the response of soil respiration to precipitation in drylands: A case study with four-yearlong observations

Soil respiration (Rs) in drylands is strongly influenced by precipitation. However, there is a lack of long-term studies on how land-use conversion impact the Rs's responds to precipitation variations. In situ Rs, soil moisture and soil temperature were monitored in cropland, and cropland converted jujube orchard, grassland and shrubland in the semiarid Loess Plateau, China for four years with significant interannual precipitation variation. Q10-soil moisture relationships were quantified by selecting observations within limited range of soil moisture. As soil moisture increased, Rs was found to be markedly suppressed in cropland and jujube orchard with great disturbance, with volumetric water content exceeding 0.15 and 0.16, respectively, but increased in grassland and shrubland with few disturbances. Q10 became saturated as soil moisture increased in cropland, and was linearly correlated with soil moisture in jujube orchard, grassland and shrubland. Q10 was least sensitive to soil moisture variation in shrubland, which was characterized by a nitrogen-fixing shrub. The interannual variation in mean growing season Rs (MGR) was positively correlated with mean soil moisture. The difference in MGR between land-use types was significant except during the extreme drought year: converting cropland to jujube orchard saw a reduction in MGR by 5–18%, while converting cropland to grassland and shrubland saw an increase in MGR by 16–53% and 67–126%, respectively. This corresponded with a greater sensitivity of MGR to soil moisture in grassland and shrubland. These results suggest a greater response of soil carbon emission in the land-use applied with afforestation or restoration to the enhanced soil moisture as precipitation intensify, compared to agricultural land-use.

Forest soil respiration response to increasing nitrogen deposition along an urban–rural gradient

Forest soil respiration is an important part of the terrestrial ecosystem carbon (C) cycle and controlled by multiple factors, especially atmospheric nitrogen (N) deposition and environmental change. However, it remains unclear how soil respiration responds to N deposition in forests along an urban–rural gradient, as most studies have only been conducted in single environmental areas, especially in natural forests. Here, in order to explore how N deposition influences soil respiration, a field experiment with different levels of N deposition (50 and 100 kg N·ha−1·yr−1) was conducted in forests along an urban–rural gradient of Hefei (31°52′N, 117°17′ E). Soil temperature (T), soil water content (SW), soil physiochemical properties, and soil microbes were simultaneously measured to investigate the underlying mechanisms of N deposition effects on soil respiration. The results showed that the soil respiration and cumulative emission flux of CO2 (RCUM) were increased by N deposition in all forests. Nitrogen addition treatments significantly enhanced the mean RCUM by approximately 6.04%, 11.02%, and 3.62%, respectively, in urban, suburban, and rural forests. The positive effects of N deposition on soil respiration had different temporal variations in different forests, and the strongest positive effects occurred with the shortest time was found in the urban forest. Temperature sensitivities of soil (Q10) were significantly different in the three forests, showing higher Q10 values in forests more near to the urban. In all forests, the total interpretation rates of climate factors, soil physicochemical properties and soil microbes to soil respiration were over 80%. Climate factors were the primary factor for explaining the variation of soil respiration under N deposition. The interpretations of the climate factors, soil physiochemical properties, and soil microbes to soil respiration were changed by N deposition, and the combined effects of these factors were much higher than those of the individual factors. Our findings provide novel insights for studying the response of soil respiration to N deposition under different environmental factors.

Varying soil respiration under long-term warming and clipping due to shifting carbon allocation toward below-ground

Global warming and land-use change have profound impacts on soil respiration (Rs), with consequent changes in carbon exchange between terrestrial ecosystem and atmosphere and its feedback to climate change. However, it is not clear how soil respiration and its components (heterotrophic respiration, Rh; and autotrophic respiration, Ra) respond to long-term warming and clipping in alpine meadow, and what are the controlling factors for the responses of soil respiration. To answer these questions, we conducted a field experiment of warming and clipping in an alpine meadow on the Qinghai-Tibet Plateau from 2014 to 2019. Infrared heaters were used to simulate climate warming and plots were clipped once a year to mimic hay or biofuel harvest. The results showed that warming decreased Rh by 5.06% but stimulated Ra by 10.08% across years, while clipping enhanced Rs, Rh and Ra by 12.31%, 18.65% and 1.29%, respectively, and marginally interacted with warming in impacting Ra across the years. Furthermore, the warming effect on soil respiration and its components varied largely over years, which was mostly attributable to the changes in the ratio of above-ground to below-ground net primary productivity (ANPP/BNPP, A/B) and soil temperature. Increased allocation of photosynthate toward below-ground caused the gradual increase in Ra and Rs under long-term warming. While soil temperature changes explained the variation of warming effects on Rh across years. The results demonstrated that soil respiration and its components in the alpine meadow are highly sensitive to climate warming and hay harvest but with large interannual variations in their responses. We highlight that plant carbon allocation is an emerging property in determining soil respiration under climate warming.

Impact of simulated acid rain on the composition of soil microbial communities and soil respiration in typical subtropical forests in Southwest China

The relationship between soil respiration (SR) and microbial community structure (MCS) is relevant to changes in forest soil ecosystem stability and chemical cycling under acid rain. Simulated acid rain treatments of pH 4.5 (control), 4.0, 3.25 and 2.5 were applied to two forest stands in the Three Gorges Reservoir Area of Jinyun Mountain, Chongqing. We used phospholipid fatty acid (PLFA) analysis to observe the MCS in the 0–10 cm soil layer and measured SR in situ from January 2016 to December 2017. Additionally, we determined the effects of soil properties on the MCS and SR. Acid rain simulation significantly increased the fungal PLFA abundance and decreased the bacterial PLFA abundance in the mixed coniferous and broad-leaved forest (CF). However, in the evergreen broad-leaved forest (BF), the abundance of bacterial and fungal PLFAs did not differ significantly among treatments. Redundancy analysis (RDA) showed that significant changes in the MSC were mainly due to the C/N ratio, hydrolysable N content, content, fine root biomass and sucrase activity. Acid rain simulation in the CF and BF significantly inhibited SR, but the SR sensitivity to simulated acid rain differed among forests. In 2017, the annual mean SR in the CF under the pH 4.0, 3.25 and 2.5 treatments decreased significantly by 6.1%, 19.2% and 28.9%, but in the BF, SR decreased significantly by 25.6% only under pH 2.5. The structural equation model showed that the relationship between the MCS and the variation in SR was closer and more direct than that with soil nutrients. The microbial community structure was an important factor driving the response of soil respiration to acid rain.

Changes in above‐/below‐ground biodiversity and plant functional composition mediate soil respiration response to nitrogen input

Abstract Biodiversity loss and changes in plant community composition induced by anthropogenic nitrogen (N) deposition exert profound effects on ecosystem functions. However, limited studies have considered the joint effects of plant community composition, plant species richness, plant functional diversity and soil biodiversity on the dynamics of soil autotrophic and heterotrophic respiration under extra N input. We addressed this issue by conducting a multilevel N‐manipulation experiment in a Tibetan alpine steppe. Based on soil respiration observations as well as biotic and abiotic measurements under this N addition experiment, we quantified the relative and interactive effects of above‐/below‐ground biodiversity, plant community composition and other explanatory variables (environmental factors, plant and microbial properties) on autotrophic and heterotrophic respiration. Our results showed that the effects of N enrichment via plant productivity, root amount, the proportion of sedge biomass and plant functional diversity explained 71% of the N‐induced variations in autotrophic respiration. With regard to heterotrophic respiration, the combination of N addition, soil pH, plant functional diversity and soil biota diversity accounted for 78% of its variations along the N addition gradient. Further analyses showed that above‐/below‐ground diversity loss and changes in plant community composition explained similar variation to that contributed by other factors in both autotrophic and heterotrophic respiration. The declined plant functional diversity and the increased proportion of sedge biomass promoted autotrophic respiration. Conversely, the loss of soil biodiversity together with the decreased plant functional diversity led to the decline of heterotrophic respiration along the experimental N gradient. Our results highlight that the indirect regulation of N input on ecosystem function through changes in plant community composition and above‐/below‐ground biodiversity loss should be considered for better understanding the responses of terrestrial ecosystems to atmospheric N deposition. A free Plain Language Summary can be found within the Supporting Information of this article.

Diverse soil respiration responses to extreme precipitation patterns in arid and semiarid ecosystems

Projected increases in the frequency and magnitude of extreme precipitation profoundly impact terrestrial ecosystems. However, the response of soil respiration to changing precipitation patterns has not been systematically investigated, especially in arid and semi-arid areas. Precipitation amounts of 300 and 600 mm (T300 and T600) were set to simulate normal and extremely wet summers, respectively, and were individually conducted by wetting soils in a series of sub-events—10 or 100 mm (P10, P100)—over equal time intervals. Maize straw (1300 kg ha−1) and N fertilization (200 kg N ha−1) were applied in parallel to extend our simulation to natural cropland conditions. Soil respiration pulses were observed after T300-P100, and inhibited effects occasionally occurred 1 day after T600-P100, primarily because frequent and harsh storms in T600-P100 induced saturation stress on soil respiration. Cumulative soil respiration in T600 was greater than that in T300, owing to prolonged suitable water conditions for soil respiration. Similarly, for the same total precipitation amount, P100 produced 40–44% more soil respiration than P10. Applying N and maize straw did not change response trends but produced different magnitudes of response to changing precipitation patterns. Maize straw significantly stimulated soil respiration, and this effect became more evident in P100 with improved water conditions, producing a 122–185% increase in cumulative soil respiration. Nitrogen slightly inhibited soil respiration; this effect was enhanced when maize straw was also added but was insignificant. Cumulative soil respiration was significantly correlated with β-d-glucosidase and soil microbial biomass carbon content. Such soil respiration responses highlight the need to accurately account for soil respiration contributions when projecting global carbon cycling in future climate scenarios.

Dynamics of the soil respiration response to soil reclamation in a coastal wetland

The soil carbon (C) pools in coastal wetlands are known as “blue C” and have been damaged extensively owing to climate change and land reclamation. Because soil respiration (RS) is the primary mechanism through which soil carbon is released into the atmosphere at a global scale, investigating the dynamic characteristics of the soil respiration rate in reclaimed coastal wetlands is necessary to understand its important role in maintaining the global C cycle. In the present study, seasonal and diurnal changes in soil respiration were monitored in one bare wetland (CK) and two reclaimed wetlands (CT, a cotton monoculture pattern, and WM, a wheat–maize continuous cropping pattern) in the Yellow River Delta. At the diurnal scale, the RS at the three study sites displayed single-peak curves, with the lowest values occurring at midnight (00:00 a.m.) and the highest values occurring at midday (12:00 a.m.). At the seasonal scale, the mean diurnal RS of the CK, CT and WM in April was 0.24, 0.26 and 0.79 μmol CO2 m−2 s−1, and it increased to a peak in August for these areas. Bare wetland conversion to croplands significantly elevated the soil organic carbon (SOC) pool. The magnitude of the RS was significantly different at the three sites, and the yearly total amounts of CO2 efflux were 375, 513 and 944 g CO2·m−2 for the CK, CT and WM, respectively. At the three study sites, the surface soil temperature had a significant and positive relationship to the RS at both the diurnal and seasonal scales, and it accounted for 20–52% of the seasonal variation in the daytime RS. The soil water content showed a significant but negative relationship to the RS on diurnal scale only at the CK site, while it significantly increased with the RS on seasonal scale at all study sites. Although the RS showed a noticeable relationship to the combination of soil temperature and water content, the synergic effects of these two environment factors were not much higher than the individual effects. In addition, the correlation analysis showed that the RS was also influenced by the soil physico-chemical properties and that the soil total nitrogen had a closer positive relationship to the RS than the other nutrients, indicating that the soil nitrogen content plays a more important role in promoting carbon loss.

Experimental warming increases ecosystem respiration by increasing above-ground respiration in alpine meadows of Western Himalaya

Alpine ecosystems in the Himalaya, despite low primary productivity, store considerable amount of organic carbon. However, these ecosystems are highly vulnerable to climate warming which may stimulate ecosystem carbon efflux leading to carbon-loss and positive feedback. We used open-top chambers to understand warming responses of ecosystem respiration (ER) and soil respiration (SR) in two types of alpine meadows viz., herbaceous meadow (HM) and sedge meadow (SM), in the Western Himalaya. Experimental warming increased ER by 33% and 28% at HM and SM, respectively. No significant effect on SR was observed under warming, suggesting that the increase in ER was primarily due to an increase in above-ground respiration. This was supported by the warming-induced increase in above-ground biomass and decrease in SR/ER ratio. Soil temperature was the dominant controlling factor of respiration rates and temperature sensitivity of both ER and SR increased under warming, indicating an increase in contribution from plant respiration. The findings of the study suggest that climate warming by 1.5–2 °C would promote ER via increase in above-ground respiration during the growing season. Moreover, net C uptake in the alpine meadows may increase due to enhanced plant growth and relatively resistant SR under warming.

Long-term tillage effect on with-in season variations in soil conditions and respiration from dryland winter wheat and soybean cropping systems

Soil respiration from agricultural soils is a major anthropogenic source of CO2 to the atmosphere. With-in season emission of soil CO2 from croplands are affected by changes in weather, tillage, plant row spacing, and plant growth stage. Tillage involves physical turning of soils which accelerate residue decomposition and CO2 emission. No-tillage lacks soil disturbance and residues undergo slower decomposition at the surface. In this study, we compared with-in season soil conditions (temperature and moisture) and soil respiration from two major crops (soybean and winter wheat) by making high temporal frequency measurements using automated chambers at half-hourly intervals. The experiment lasted for 179 days. Total number of measurements made from conventional and no-tillage soybean and winter wheat plots were 6480 and 4456, respectively. Average flux after the winter-dormancy period of wheat was 37% higher in tilled soil compared to no-till soil. However, average flux during the soybean growing season was 8% lower in conventional till compared to no-till soil. This differential response of soil respiration in wheat and soybean was primarily due to tillage-induced changes in surface characteristics (residue cover) and soil environmental conditions (soil temperature and soil moisture). Results from this study can help elucidate relationships for modeling and assessment of field-scale soil CO2 emissions from dryland wheat and soybean crops grown in sub-tropics.

Linkages between soil respiration and microbial communities following afforestation of alpine grasslands in the northeastern Tibetan Plateau

Knowledge gaps exist in our current understanding of the linkages among soil respiration, microbial communities, and carbon sequestration following grassland afforestation. Here, we investigated the effects of forest planting on soil respiration, microbial communities, and associated soil properties in alpine grasslands of the northeastern Tibetan Plateau, and explored microbial mechanisms of the soil respiration response to afforestation. Generally, afforestation increased the richness and diversity of soil microbial communities. Redundancy analysis indicated that the variability in bacterial and fungal communities was mainly explained by soil organic carbon (SOC, R2bacteria = 0.85, R2fungi = 0.89), nitrate nitrogen (NO3−-N, R2bacteria = 0.64, R2fungi = 0.82), available phosphorus (R2bacteria = 0.91, R2fungi = 0.91), and soil pH (R2bacteria = 0.66, R2fungi = 0.90). Afforestation also favored a significant increase in mean soil respiration rates during the growing season, and high correlations were detected between soil respiration and microbial community abundances and diversity, SOC, NO3−-N, and soil pH. Because afforestation did not affect fine root biomass, increased soil respiration can be attributed to accelerated microbial respiration and elevated substrate availability. In addition, bacterial communities transitioned from Actinobacteria (oligotrophs)-dominant to Alphaproteobacteria (copiotrophs)-dominant communities. Copiotrophs are generally expected to have higher respiration rates than oligotrophs. Thus, the shift from Actinobacteria-dominant to Alphaproteobacteria-dominant bacterial communities may have also contributed to the increase in soil respiration following afforestation.

Effects of Adding Straw and Biochar with Equal Carbon Content on Soil Respiration and Microbial Biomass Carbon and Nitrogen

In order to investigate the response of soil respiration, soil microbial biomass carbon and nitrogen, and hydrothermal factors to the addition of biochar and straw, we used an LI-8100 soil carbon flux meter (LI-COR, Lincoln, USA) to study changes in soil respiration and microbial biomass under four treatments:conventional fertilization (CK), conventional fertilization +2.25t·hm-2 biochar-C (T1), conventional fertilizer +2.25t·hm-2 straw-C (T2), and conventional fertilizer +2.25t·hm-2 (biochar-C+straw-C), biochar-C:straw-C=1:1 (T3). The results showed that:① the addition of biochar and straw significantly increased the soil respiration rate and total CO2 emissions, with the largest increase in T3 and the smallest increase in T1. The effect of T1 on soil respiration was promoted in the early stage and later inhibited. ② The microbial biomass carbon and nitrogen and the number of functional bacterial colonies increased significantly with biochar and straw amendments. T1 had a significant promotion effect on nitrogen-fixing bacteria, while T2 had no significant effect on the number of fungi, and T3 showed a positive interaction effect. Soil respiration rates were significantly and positively related to soil microbial biomass carbon and nitrogen as well as to the number of bacteria and actinomycetes. ③ The 5 cm soil temperature of T3 significantly increased by 4.53%. The soil respiration rate and soil temperature showed a significant exponential correlation. To sum up, adding straw and biochar with equal carbon content can significantly increase the soil respiration rate and microbial biomass, and the interaction effect between biochar and straw is positive. Compared with that of the straw treatments, the application of biochar can reduce carbon mineralization to a certain extent, and the effect of carbon sequestration is better.

Plant productivity is a key driver of soil respiration response to climate change in a nutrient-limited soil.

Despite knowledge of the interaction between climate change factors significant uncertainty exists concerning the individual and interactive effects of elevated carbon dioxide (eCO2) and elevated temperature (eT) on the soil microbiome and function. Here we examine the individual and interactive effects of eCO2 and eT on tree growth, soil respiration (Rsoil), biomass, structural and functional composition of microbial community, nitrogen (N) mineralisation and N availability in a whole tree chamber experiment. Eucalyptus globulus plants were grown from seedling to ca. 10 m tall for 15 months in a nutrient-poor sandy soil under ambient and elevated (+ 240 ppm) atmospheric CO2 concentrations combined with ambient or elevated temperatures (+ 3 °C) in a full factorial design. Plant growth was strongly stimulated under eCO2, but eT had little impact on any measured plant property. In contrast, Rsoil was not consistently affected by eCO2 or eT, but correlated strongly with root and leaf biomass. The response of N-mineralisation and nutrient availability to eCO2 and eT varied across time, and available N correlated strongly with plant height. Further, the C:N ratio of the microbial biomass and leaves were both higher under eCeT treatment. However, these functional measures were not significantly linked to either structural or functional diversity of the soil microbiome. Taken together, these results suggest that in this low-nutrient soil, belowground processes are principally driven by aboveground productivity. Our work provides novel insight into mechanisms underlying above- and belowground response to climate change, and the potential to sequester C in a low-nutrient status soil under future climatic conditions may be limited .

Shallow groundwater inhibits soil respiration and favors carbon uptake in a wet alpine meadow ecosystem

Wet alpine meadows generally act as a significant carbon sink, since their low rate of soil decomposition determines a much smaller ecosystem respiration (Re) than photosynthesis. However, it remains unclear whether the low soil decomposition rate is determined by low temperatures or by nearly-saturated soil moisture. We explored this issue by using five years of measurements from two eddy-covariance sites with low temperature and significantly different soil water conditions. The results showed that both sites were carbon sinks. However, despite a smaller annual gross primary productivity, the wet site with a shallow groundwater showed a much higher carbon use efficiency and larger carbon sink than the dry site (which had a deeper water table) due to its much lower Re. Our analyses showed that Re of the wet site was significantly decreased under the nearly-saturated soil condition during the unfrozen seasons. This effect of nearly-saturated soil water on Re increased with soil depths. In contrast, at the dry site the high soil water content favored Re. The corresponding soil temperature at both sites expectedly showed large and positive effects on Re. These results demonstrated that the high carbon sink of the wet alpine meadow was mainly caused by the inhibiting effects of the nearly-saturated soil condition on soil respiration rather than by the low temperatures. Therefore, we argue that a warming-induced shrinking cryosphere may affect the carbon dynamics of wet and cold ecosystems through changes in soil hydrology and its impact on soil respiration. In addition, our study highlights the different responses of soil respiration to warming across soil depths. The thawing of frozen soil may cause larger CO2 emission in the top soil, while it may also partially contribute to slowing down soil carbon decomposition in the deep soil through decreasing metabolic activity of aerobic organisms.

Impacts of land-use changes on soil respiration in the semi-arid region of Brazil

ABSTRACT Soil respiration represents the largest flux of CO2 emission from terrestrial ecosystems, being affected by land-use changes and soil properties. There are few studies investigating the response of soil respiration to land-use changes in the Caatinga biome. This study aimed to measure soil respiration from Caatinga vegetation and degraded pasture, to verify the effect of land-use changes on soil respiration. Measurements of soil respiration were performed using the infrared gas analyzer method over nine months (in rainy and dry seasons), in Caatinga and degraded pasture in the semi-arid region of Pernambuco. The soil moisture, soil temperature, soil organic carbon (SOC), Normalized Difference Vegetation Index (NDVI), and climatic variables were also measured. Soil organic carbon and NDVI were higher in Caatinga than in degraded pasture, while the inverse occurred with soil temperature. The soil respiration showed a clear seasonal variation, with the highest values occurring in the wet season, being positively correlated with soil moisture and negatively with soil temperature. Soil respiration was significantly higher in the Caatinga (8.0 ton ha-1 yr-1 of C) than in degraded pasture (3.7 ton ha-1 yr-1 of C). These higher values of soil respiration in Caatinga were due to lower soil temperature and higher SOC, and can be seen as indicators of good environmental quality.

Nonlinear decoupling of autotrophic and heterotrophic soil respiration in response to drought duration and N addition in a meadow steppe

Soil respiration (SRTOT) and its main components, soil heterotrophic (SRH) and autotrophic respiration (SRA), were monitored in response to within-season drought events of increasing duration and soil N enrichment in a semiarid meadow steppe. The experiment consisted of the combination of five drought periods (0 days, 15 days, 30 days, 45 days, and 60 days) and two N addition levels (0 and 10 g N m−2 year−1 applied as urea). Soil respiration decreased after 30 days of drought, with the response being driven by soil heterotrophs. Moreover, N addition increased the sensitivity of soil respiration to soil water content, which we attributed to greater plant C inputs and soil microbial C and N content in the N addition treatment. Our results highlight the role of SRH as a key regulator of C fluxes in nutrient-poor semiarid meadow steppe in response to extreme within-season drought and the role of soil N availability in modulating this response.

Response of soil respiration to nitrogen fertilization: Evidence from a 6-year field study of croplands

Agroecosystems receive large amounts of nitrogen (N), which can have a profound impact on soil respiration (Rs). Although Rs is the largest carbon dioxide (CO2) flux from terrestrial ecosystems to the atmosphere, the potential effects of N fertilization on Rs and its components (heterotrophic respiration (Rh) and autotrophic respiration (Ra)) remain controversial, and information on the impacts of N fertilization on C emission from long-term experiments is lacking. In this study, we conducted a field experiment during 6 growing seasons (2012–2018) in which we applied N fertilizer at three rates (0, 180 and 360 kg N ha−1, referred to as N0, N180 and N360, respectively) to two wheat varieties (Changhan No. 58 (CH) and Zhengmai No. 9023 (ZM)) and investigated the effects of N fertilization on Rs and its components by continuous half-hourly observations. We found that over the 6 growing seasons, N180 and N360 increased the mean growing season soil C emission by 29.7% and 11.6%, respectively, due to the increased C emission through Ra under fertilization, which was related to an increased leaf area index (LAI) and canopy photosynthesis (Pn). Significant seasonal variations in the Rs rate were observed; both Rh and Ra contributed to these variations, and the variations were significantly correlated with both soil and air temperature and plant-related traits (LAI and canopy Pn). In addition, the C emission through Rs during the growing season increased throughout the experiment, mainly because of an increase in C emissions through Rh that was caused by increasing temperature during the observation period due to climate change at the experimental site. However, C emission through Rs increased relatively rapidly under the N180 treatment due to the increased Rh throughout the experiment. Furthermore, interaction effects of soil moisture and temperature on the Rs rate and its components were also observed. Overall, our findings highlight the significance of N fertilization in term of soil C emission and its feedback under global warming in agroecosystems.

Effect of soil microorganisms and labile C availability on soil respiration in response to litter inputs in forest ecosystems: A meta-analysis.

Litter inputs can influence soil respiration directly through labile C availability and, indirectly, through the activity of soil microorganisms and modifications in soil microclimate; however, their relative contributions and the magnitude of any effect remain poorly understood. We synthesized 66 recently published papers on forest ecosystems using a meta‐analysis approach to investigate the effect of litter inputs on soil respiration and the underlying mechanisms involved. Our results showed that litter inputs had a strong positive impact on soil respiration, labile C availability, and the abundance of soil microorganisms, with less of an impact related to soil moisture and temperature. Overall, soil respiration was increased by 36% and 55%, respectively, in response to natural and doubled litter inputs. The increase in soil respiration induced by litter inputs showed a tendency for coniferous forests (50.7%)> broad‐leaved forests (41.3%)> mixed forests (31.9%). This stimulation effect also depended on stand age with 30‐ to 100‐year‐old forests (53.3%) and ≥100‐year‐old forests (50.2%) both 1.5 times larger than ≤30‐year‐old forests (34.5%). Soil microbial biomass carbon and soil dissolved organic carbon increased by 21.0%‐33.6% and 60.3%‐87.7%, respectively, in response to natural and doubled litter inputs, while soil respiration increased linearly with corresponding increases in soil microbial biomass carbon and soil dissolved organic carbon. Natural and doubled litter inputs increased the total phospholipid fatty acid (PLFA) content by 6.6% and 19.7%, respectively, but decreased the fungal/bacterial PLFA ratio by 26.9% and 18.7%, respectively. Soil respiration also increased linearly with increases in total PLFA and decreased linearly with decreases in the fungal/bacterial PLFA ratio. The contribution of litter inputs to an increase in soil respiration showed a trend of total PLFA > fungal/bacterial PLFA ratio > soil dissolved organic carbon > soil microbial biomass carbon. Therefore, in addition to forest type and stand age, labile C availability and soil microorganisms are also important factors that influence soil respiration in response to litter inputs, with soil microorganisms being more important than labile C availability.