Cumulative Soil Organic Carbon Mineralization Research Articles

Effects of Incubation Temperature and Sludge Addition on Soil Organic Carbon and Nitrogen Mineralization Characteristics in Degraded Grassland Soil

Elucidating the characteristics and underlying mechanisms of soil organic carbon (SOC) and nitrogen mineralization in the context of sludge addition is vital for enhancing soil quality and augmenting the carbon sink capacity of soil. This study examined the chemical properties, enzyme dynamics, and organic carbon and nitrogen mineralization processes of soil from degraded grasslands on the Loess Plateau at various incubation temperatures (5, 15, 25, and 35 °C) and sludge addition rates (0%, 5.0%, 10.0%, and 20.0%) through a laboratory incubation experiment. The results showed that incubation temperature, sludge addition, and their interactive effects significantly altered the soil enzyme C:N, C:P, and N:P stoichiometries. The cumulative mineralization rates of SOC and nitrogen increased significantly with increasing incubation temperature and sludge addition rate. Principal component analysis revealed a significant linear correlation between cumulative SOC and nitrogen mineralization. Random forest analysis indicated that β-1,4-Glucosidase (BG), β-1,4-N-acetyglucosaminidase (NAG), cellobiohydrolase (CBH), ammonium nitrogen (NO3−), enzyme C:P ratio, alkaline phosphatase (ALP), and incubation temperature were crucial determinants of cumulative SOC mineralization. Structural equation modeling demonstrated that sludge addition, NO3−, NAG, ALP, and enzyme C:P positively impacted SOC mineralization, whereas dissolved organic carbon and BG had negative impacts. Conversely, incubation temperature negatively affected soil nitrogen mineralization, whereas NO3−, available phosphorus, and ALP contributed positively. Sludge addition and temperature indirectly modulated soil net nitrogen mineralization by altering soil chemical properties and enzyme activities. These findings underscore the role of SOC and nitrogen mineralization as indicators for evaluating soil nutrient retention capabilities.

Linking soil organic carbon mineralization to soil physicochemical properties and bacterial alpha diversity at different depths following land use changes

BackgroundAnthropogenic land use changes (LUCs) impart intensifying impacts on soil organic carbon (SOC) turnover, leading to uncertainty concerning SOC mineralization patterns and determining whether soils act as “source” or “sink” in the global carbon budget. Therefore, understanding the SOC mineralization characteristics of different LUC patterns and their potential influencing factors is crucial. An indoor incubation experiment was conducted to study the SOC mineralization patterns and their relevance to soil physicochemical properties, soil enzyme activity, SOC fractions, and bacterial alpha diversity. The soils were collected from two layers of five typical LUC patterns in Yellow Sea Forest Park, including four that were converted from wheat–corn rotation systems [a gingko plantation (G), a metasequoia plantation (M), a gingko–wheat–corn agroforestry system (GW), and a gingko–metasequoia system (GM)] and a traditional wheat–corn system (W).ResultsLUCs had significant and diverse impacts on the SOC content and SOC fraction contents and on soil enzyme activity. The cumulative SOC mineralization was significantly higher in the M systen than in the W and GW systems at 0–20 cm depth and higher in the G system than in the GW system at 20–40 cm depth after 60-day incubation. The mineralization ratio was highest in the W system and lowest in the GW system. The soil pH and bulk density had a significant negative correlation with the cumulative SOC mineralization, while the soil bacterial Shannon index had a significant positive correlation with cumulative SOC mineralization. Multiple stepwise linear regression analysis showed that the SOC mineralization potential was dominantly explained by the bacterial Shannon index and operational taxonomic units (OTUs). The GW system had lower potentially mineralizable SOC and higher SOC stability. Additionally, the incubation time and cumulative SOC mineralization were well fitted by the first-order kinetic equation.ConclusionsLUCs significantly changed SOC mineralization characteristics and the results highlighted the important roles of the bacterial community in soil carbon cycling, which contributes to the fundamental understanding of SOC turnover regulation.

Effects of tillage management on cbbL-carrying bacteria and soil organic carbon dynamics across aggregate size classes in the farmland of North China Plain

Calvin-Benson-Bassham cycle (cbbL)-carrying bacteria in soil are essential to renew and circulate organic matter. However, the relation between cbbL-carrying bacteria and soil carbon dynamics under tillage managements, especially across the aggregate size remains unclear. Thus, in our study, soil organic carbon (SOC) storages, mineralization, and the cbbL-carrying bacterial community across five soil aggregate sizes were thoroughly investigated under four tillage treatments: conventional rotary tillage (CT), deep plowing (DP), subsoiling (SS), no-tillage (NT). We found macroaggregates (>2 mm) contributed most with regard to SOC stocks, whereas microaggregates (<0.25 mm) contributed the least among all the tillage managements (NT, DP, SS and CT). Macroaggregates (>1 mm) with the highest cumulative SOC mineralization were found in subsoiling, whereas microaggregates had the lowest cumulative mineralization under no-tillage. By physically protecting, no-tillage specifically inhibited carbon dioxide (CO2) emissions in macroaggregates (>1 mm), whereas increased SOC levels and encouraged CO2 releases across microaggregates. Shifts in the co-occurrence network demonstrated that subsoiling promoted the joint symbiotic function between cbbL-carrying bacteria, the efficiency of matter and energy, and information transfer. And the keystone species, the enhanced cooperation and stochastic processes of autotrophic microorganisms under subsoiling lead to increased carbon fixation and reduced CO2 emissions in microaggregates with limited oxygen and nutrients. Overall, our work verified physical protection of large aggregates under no-tillage and improvement of microbial interaction efficiency under subsoiling. This may offer a theoretical foundation for the choice of tillage practices in fluvo-aquic soil regions.

Linking between soil properties, bacterial communities, enzyme activities, and soil organic carbon mineralization under ecological restoration in an alpine degraded grassland.

Soil organic carbon (SOC) mineralization is affected by ecological restoration and plays an important role in the soil C cycle. However, the mechanism of ecological restoration on SOC mineralization remains unclear. Here, we collected soils from the degraded grassland that have undergone 14 years of ecological restoration by planting shrubs with Salix cupularis alone (SA) and, planting shrubs with Salix cupularis plus planting mixed grasses (SG), with the extremely degraded grassland underwent natural restoration as control (CK). We aimed to investigate the effect of ecological restoration on SOC mineralization at different soil depths, and to address the relative importance of biotic and abiotic drivers of SOC mineralization. Our results documented the statistically significant impacts of restoration mode and its interaction with soil depth on SOC mineralization. Compared with CK, the SA and SG increased the cumulative SOC mineralization but decreased C mineralization efficiency at the 0-20 and 20-40 cm soil depths. Random Forest analyses showed that soil depth, microbial biomass C (MBC), hot-water extractable organic C (HWEOC), and bacterial community composition were important indicators that predicted SOC mineralization. Structural equal modeling indicated that MBC, SOC, and C-cycling enzymes had positive effects on SOC mineralization. Bacterial community composition regulated SOC mineralization via controlling microbial biomass production and C-cycling enzyme activities. Overall, our study provides insights into soil biotic and abiotic factors in association with SOC mineralization, and contributes to understanding the effect and mechanism of ecological restoration on SOC mineralization in a degraded grassland in an alpine region.

Dynamics of soil organic carbon mineralization and enzyme activities after two months and six years of biochar addition

Applying biochar to agricultural soils has been proposed as a means of sequestering carbon while simultaneously enhancing soil health and agricultural sustainability. While, our understanding of the long-term effects of biochar on soil organic carbon mineralization and enzyme activities under field conditions is limited. In our study, soil samples, which were improved by biochar after two months and six years, were collected from biochar-amended treatments with seven biochar application rates (0, 2.5, 5, 10, 20, 30, and 40 t ha−1, respectively) in upland red soil. The results showed that the soil chemical properties (available P, pH, soil organic carbon, total nitrogen, and C/N ratio) after two months of biochar addition increased more significantly than those after six years of biochar addition. The cumulative soil organic carbon mineralization (Cm) was increased rapidly at first and then decreased gradually and finally flattened out in the late incubation. The Cm/SOC ratios were significantly lower in C1 to C6 treatments than in C0 treatment. High application rates (40 t ha−1) of biochar inhibited the carbon mineralization, while the effects diminished after six years of biochar addition. The multiple linear model and correlation analysis suggested that the effects of invertase activity and total nitrogen on Cm were more significant than other indexes.

Effects of tillage management on soil carbon decomposition and its relationship with soil chemistry properties in rice paddy fields

Decreasing the soil organic carbon (SOC) decomposition is critical to improve the quality of the soil and mitigate atmospheric CO2 emissions. To improve the ability to protect the SOC by optimizing tillage management, this study investigated the laboratory-based SOC mineralization (decomposition) and soil chemical properties under different tillage practices, including no tillage with straw mulch (NTS), rotary tillage with straw incorporated (RTS), moldboard plow tillage with straw incorporated (CTS) and moldboard plow tillage with straw removal (CT). Soil samples of six sampling dates from April 2017 to October 2018 were incubated at 25 °C and 70% water holding capacity for 60 d. Repeated Variance Analyses were conducted to compare the means of different treatments. The results showed that the average cumulative SOC mineralization (Cm) at the 0–5 cm soil depth was 7.09 g CO2 kg−1 soil under NTS, which was higher (P < 0.05) than that of the other treatments. However, the C mineralizability at both the 0–5 and 5–10 cm soil depths were lower (P < 0.05) under the NTS (0.16 and 0.15 g CO2 g−1 SOC) compared with the CTS and CT. Non-microbial CO2 emissions (CO2 emissions in sterilized soil) contributed to the lower C mineralizability under NTS, due to the lower mineralizability (0.041–0.089 g CO2 g−1 SOC) of sterilized soil under this treatment. Furthermore, some of the abiotic factors (e.g., C/N ratio and SOC content) significantly correlated with the Cm and C mineralizability. These factors might be critical for the ability to protect SOC under NTS. In summary, conservation tillage is an optimal management due to its protection on SOC, and part of this protection appeared to have been contributed by the soil abiotic factors, which were formed by long-term tillage management.

Temperature induces soil organic carbon mineralization in urban park green spaces, Chengdu, southwestern China: Effects of planting years and vegetation types

Green spaces in urban parks are an essential part of urban planning, not only meeting the environmental demands of urban dwellers but also absorbing greenhouse gases generated in urban regions. Mineralization of soil organic carbon (SOC) is one of the most important processes of C cycling, and links C sequestration and emission. However, few studies have been focused on SOC mineralization in urban parks, especially in scenarios involving rising temperature. Here, soils from different ages of deciduous forest (DT), evergreen forest (ET) and lawn (LN) were collected from the urban parks of Chengdu megacity. A soil incubation study (35 days) was conducted to examine SOC mineralization in three temperature regimes (15, 25, and 35 ℃), three vegetation types (DT, ET, and LN) and three vegetation ages (5, 10, and 15yr), making 27 treatments in total. Results demonstrate that increases in temperature stimulated the daily SOC mineralization rate, cumulative SOC mineralization, and mineralization intensity in the soils from urban green spaces, especially in soils under the 5-year-old plantings. Furthermore, results from principal component analysis (PCA) showed that the soil labile organic carbon (LOC) fraction, especially readily oxidizable carbon (ROC), soil enzyme activity and soil pH are the major factors influencing SOC mineralization. During the incubation, the average temperature sensitivity (Q10) of the SOC mineralization rate at 25−35 °C was higher than at 15−25 °C (P < 0.05), indicating that more C would release from urban green spaces under a warmer climate. However, over all planting ages, the average Q10 of SOC mineralization rate in lawn soils reduced by 1.87 %–4.04 % and 4.16 %–5.84 % relative to deciduous and evergreen forest soils, respectively. Overall, the SOC mineralization rate was ranked LN > ET > DT, while the Q10 of the SOC mineralization rate was ranked DT > ET > LN with increasing temperatures. Moreover, the older vegetation showed lower SOC mineralization rates and higher Q10 values. These findings imply that SOC stored in the soils under grass and young plantations are less susceptible to climate warming, although the mineralization rates are higher. By contrast, SOC in soils under trees is more susceptible to climate warming, but the mineralization rates are lower. Overall, the temperature change is more important for the SOC mineralization in forest soils and older plantation soils in urban green spaces.

Characteristics of soil organic carbon mineralization in low altitude and high altitude forests in Wuyi Mountains, southeastern China

Examining the variations of soil organic carbon mineralization at different altitudes is crucial for better understanding of soil organic carbon (SOC) dynamics. We selected the low altitude and high altitude broad-leaved forest soils in Wuyi Mountains as the research object, and incubated them under particular annual average temperature (17 and 9 ℃, respectively) in laboratory to investigate the difference of SOC mineralization characteristics. The results showed that the cumulative SOC mineralization had no significant difference between forest soils at low and high altitude in a 126-day incubation period under ambient temperature. Soil organic carbon content of high altitude soil was significantly higher than that from low altitude. The dynamics of SOC mineralization could fitted by the first-order kinetics. Both mineralization potential (CP) and mineralization rate constant (K) values of two soils had no significant difference, but CP/SOC value and mineralization ratio were significantly higher at low altitude, indicating that the carbon sequestration capacity of low altitude soil was relatively lower than that of high altitude under ambient temperature. Soil microbial biomass carbon and microbial quotients were significantly higher than that of low altitude with the increase of incubation time, indicating that the ability of microbial carbon assimilation was greater at high altitude. On the other hand, the activities of β-1,4-glucosidase and cellobiohydrolase in high altitude soil were higher, suggesting that more labile carbon would be decomposed by soil microbes. The carbon sequestration capacity and microbial carbon utilization efficiency in high altitude soil would be reduced and thus result in a decline of soil organic carbon storage under the scenarios of climate warming.

Persistent effects of biochar on soil organic carbon mineralization and resistant carbon pool in upland red soil, China

Biochar as a soil ameliorant has generated great interest for scientists in improving soil quality and carbon sequestration. The objective of this study was to investigate the persistent effects of biochar application on soil organic carbon (SOC) mineralization and soil-resistant carbon (Cr) in upland red soil. This experiment was conducted from September 2011 to May 2016. Biochar was applied only once in September 2011 at rates of 0, 2.5, 5, 10, 20, 30 and 40 t/ha in the field experiment, designated as treatments B0, B1, B2, B3, B4, B5 and B6. The chemical properties, dynamics of SOC mineralization and soil-resistant carbon (Cr) were measured at the 1st and 6th year after biochar application. The results were as follows: biochar application at rates of 30 and 40 t/ha (B5 and B6 treatments) distinctly increased soil pH value and available P relative to B0 in 2011. The pH value, available P, SOC, total N and C/N ratio in B4, B5 and B6 treatments were significantly higher compared with the B0 treatment, where the B6 treatment increased the pH value by 0.80 and C/N ratio by 3.88 while increasing available P, SOC and total N by 24.18, 76.29 and 19.78%, respectively, compared with the B0 treatment in 2016. The cumulative SOC mineralization (Cm) occupied around 4.62–6.91% of total organic carbon (Ct), which showed a declining trend in 2016 as compared to 2011. The Cm/Ct ratio also showed a declining trend with biochar amendment at both samplings. The Cr occupied around 26–46% of SOC and showed obviously increasing trends both in 2011 and 2016. We further found that Cm/Ct showed highly significant (p < 0.01) negative correlations with the rates of biochar application both in 2011 and 2016. The Cr, however, showed very significant (p < 0.01) positive correlations with the rates of biochar application both in 2011 and 2016. This study suggested that biochar application to upland red soil persistently improved soil properties and resistant carbon. Cumulative SOC mineralization was clearly restrained by biochar amendment. This study can provide scientific support for improving soil fertility and enhancing carbon sequestration by application of large amount of biochar (40 t/ha) in upland red soil.

Temperature sensitivity of soil organic carbon decomposition as affected by long-term fertilization under a soybean based cropping system in a sub-tropical Alfisol

Understanding temperature sensitivity of soil organic carbon (SOC) decomposition from bulk soils and aggregates of long-term fertilized plots is imperative to forecast soil C dynamics. We evaluated the impacts of 43 years of fertilization under a soybean (Glycine max) based cropping system on temperature sensitivity of SOC decomposition (Q10) in an Alfisol. Treatments were: no mineral fertilizer or manure (control), 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), NPK+lime at 0.4Mgha−1 (NPK+L), 150% recommended NPK (150% NPK), and NPK+farmyard manure (FYM) at 10Mgha−1 (NPK+FYM). Bulk soils as well as macro- and micro-aggregates were incubated for 24days at 25°C and 35°C. Cumulative SOC mineralization (Ct) in the 0–15cm soil layer of bulk soils with NPK+FYM and NPK treated plots were similar but significantly higher than unfertilized control plots. However, both Ct and Q10 values in the NPK+FYM plots were higher than NPK in the 15–30cm soil layer. In the 0–15cm soil layer, NPK+FYM plots had ∼10 and 26% greater Q10 values of macro- and microaggregates than NPK. Activation energies required for bulk soils C mineralization was ∼2 and 3 times higher in NPK+FYM and NPK+L plots, respectively, compared with unfertilized control plots in that layer. Lime along with NPK application increased the activation energy of SOC decomposition. Thus, long-term NPK+FYM and NPK+L applications have great potential for less proportional SOC decomposition than NPK or unfertilized control plots under a temperature rise in these acid soils. However, NPK+FYM management practice is recommended as it has highest SOC accumulation and can have less SOC losses under a temperature rise.

Effects of biochar on carbon mineralization of coastal wetland soils in the Yellow River Delta, China

Biochar (BC) application for improving soil quality and carbon sequestration has generated great interest for scientists and policy makers. BC can influence soil organic carbon (SOC) mineralization through priming effects. Positive, negative or no priming effects on C mineralization has been observed following BC additions to soils. However, uncertainty still remains about the influence of biochar on SOC mineralization in the coastal wetland soils of the Yellow River Delta, China. Therefore, a five months of incubation experiment using the coastal wetland soil was conducted to investigate the effects of adding BC produced from peanut shell at 350°C on SOC mineralization at the rates of 0% (0%BC), 0.1% (0.1%BC), 1% (1%BC) and 3% (3%BC) (w/w). BC addition increased the cumulative CO2 emissions, indicating that the cumulative SOC mineralization was enhanced in the coastal soil by BC application. However, the increased C mineralized only accounted for 1.71%, 0.32% and 0.17% of the BC-C added in the 0.1%BC, 1%BC and 3%BC treatments, respectively. Moreover, the experimental values of SOC mineralization was much lower than that of the theoretical values in both 1%BC and 3%BC treatments, indicating that a negative priming effect occurred. This may be explained by two reasons: (1) the conversion process of SOC to dissolved inorganic C (DIC) was accelerated by BC addition, which was confirmed by SEM image; (2) the amounts of available C substrate and microorganisms decreased via the sorption of labile organic C (LOC) and microorganisms onto BC. These results suggest that BC application will enhance soil C storage in the salinized wetland soils.

Soil Organic Carbon Mineralization as Affected by Cyclical Temperature Fluctuations in a Karst Region of Southwestern China

The diurnal fluctuation in soil temperature may influence soil organic carbon (SOC) mineralization, but there is no consensus on SOC mineralization response to the cyclical fluctuation in soil temperature. A 56-d incubation experiment was conducted to investigate the effects of constant and variable temperatures on SOC mineralization. Three soils were collected from the karst region in western Guizhou Province, southwestern China, including a limestone soil under forest, a limestone soil under crops and a yellow soil under crops. According to the World Reference Base (WRB) classification, the two limestone soils were classified as Haplic Luvisols and the yellow soil as a Dystric Luvisol. These soils were incubated at three constant temperatures (15, 20 and 25 0C) and cyclically fluctuating temperatures (diurnal cycle between 15 and 25 0C). The results showed that the 56-d cumulative SOC mineralized (C56) at the fluctuating temperatures was between those at constant 15 and 25 0C, suggesting that the cumulative SOC mineralization was restricted by temperature range. The SOC mineralization responses to the fluctuating temperatures were different among the three soils, especially in contrast to those at constant 20 0C. Compared with constant 20 0C, significant (P < 0.05) decreases and increases in C56 value were found in the limestone soil under forest and yellow soil under crops at the fluctuating temperatures, respectively. At the fluctuating temperatures, the forest soil with lower temperature coefficient Q10 (the relative change in SOC mineralization rate as a result of increasing the temperature by 10 0C) had a significantly (P < 0.05) lower SOC mineralization intensity than the two cropland soils. These indicated that differences in temperature pattern (constant or fluctuating) could significantly influence SOC mineralization, and SOC mineralization responses to the fluctuating temperatures might be affected by soil characteristics. Moreover, the warmer temperatures might improve the ability of soil microbes to decompose the recalcitrant SOC fraction, and cyclical fluctuations in temperature could influence SOC mineralization through changing the labile SOC pool size and the mineralization rate of the recalcitrant SOC in soils.

Soil moisture influence on the interannual variation in temperature sensitivity of soil organic carbon mineralization in the Loess Plateau

Abstract. Temperature sensitivity of soil organic carbon (SOC) mineralization (i.e., Q10) determines how strong the feedback from global warming may be on the atmospheric CO2 concentration; thus, understanding the factors influencing the interannual variation in Q10 is important for accurately estimating local soil carbon cycle. In situ SOC mineralization rate was measured using an automated CO2 flux system (Li-8100) in long-term bare fallow soil in the Loess Plateau (35°12' N, 107°40' E) in Changwu, Shaanxi, China from 2008 to 2013. The results showed that the annual cumulative SOC mineralization ranged from 226 to 298 g C m−2 yr−1, with a mean of 253 g C m−2 yr−1 and a coefficient of variation (CV) of 13%, annual Q10 ranged from 1.48 to 1.94, with a mean of 1.70 and a CV of 10%, and annual soil moisture content ranged from 38.6 to 50.7% soil water-filled pore space (WFPS), with a mean of 43.8% WFPS and a CV of 11%, which were mainly affected by the frequency and distribution of precipitation. Annual Q10 showed a quadratic correlation with annual mean soil moisture content. In conclusion, understanding of the relationships between interannual variation in Q10, soil moisture, and precipitation are important to accurately estimate the local carbon cycle, especially under the changing climate.