Cumulative CO2 Production Research Articles

Biotic relationships to aggregation in a Vertisol under long-term no-till, stubble retention and nitrogen fertilisation

Soil aggregation is critical for high-clay Vertisols to facilitate water movement, aeration, nutrient cycling, microbial activity, and hence soil productivity. Both abiotic and biotic factors affect aggregation, although the effect of biotic factors on aggregation remains unclear in subtropical Vertisols managed under no-till (NT), stubble retained (SR) and N fertilisation practice. Using a 54-years old cereal cropped NT experiment in subtropical semi-arid region, we examined the biotic effects on soil aggregate-size distribution in a smectitic Vertisol (65 % clay) at 0–0.1 m depth. The experiment consisted of NT versus conventional till (CT), SR versus stubble burned (SB), and N fertiliser rates (0, 30, and 90 kg N ha−1; N0, N30, and N90, respectively) arranged in a randomised complete block design, with four replications (48 plots). NT generally had no significant effect on biotic factors and aggregate mean weight diameter (MWD). SR had significantly higher microbial activity (as assessed by cumulative CO2 production over 140 days), C-acquiring and N-acquiring enzyme activities (β-glucosidase, cellobiohydrolase, N-acetyl-β-D-glucosaminidase), easily extractable and total glomalin-related proteins, microbial biomass C, large- (>2 mm) and medium aggregates (1–2 mm), and MWD (1.23 ± 0.06 mm in SR and 1.02 ± 0.07 mm in SB (P < 0.02)). In addition, N fertiliser rates had significantly higher soil organic C and mineral associated organic N but lower C:N ratio. Thus, soil organic C and N, microbial biomass C, glomalin, and microbial and enzyme activities enhanced by SR, and lower C:N ratio of the organic matter following N fertilisation improved MWD in this subtropical Vertisol.

Carbon Stocks and Potential Greenhouse Gas Production of Permafrost‐Affected Active Floodplains in the Lena River Delta

AbstractArctic warming increases the degradation of permafrost soils but little is known about floodplain soils in the permafrost region. This study quantifies soil organic carbon (SOC) and soil nitrogen stocks, and the potential CH4 and CO2 production from seven cores in the active floodplains in the Lena River Delta, Russia. The soils were sandy but highly heterogeneous, containing deep, organic rich deposits with &gt;60% SOC stored below 30 cm. The mean SOC stocks in the top 1 m were 12.9 ± 6.0 kg C m−2. Grain size analysis and radiocarbon ages indicated highly dynamic environments with sediment re‐working. Potential CH4 and CO2 production from active floodplains was assessed using a 1‐year incubation at 20°C under aerobic and anaerobic conditions. Cumulative aerobic CO2 production mineralized a mean 4.6 ± 2.8% of initial SOC. The mean cumulative aerobic:anaerobic C production ratio was 2.3 ± 0.9. Anaerobic CH4 production comprised 50 ± 9% of anaerobic C mineralization; rates were comparable or exceeded those for permafrost region organic soils. Potential C production from the incubations was correlated with total organic carbon and varied strongly over space (among cores) and depth (active layer vs. permafrost). This study provides valuable information on the carbon cycle dynamics from active floodplains in the Lena River Delta and highlights the key spatial variability, both among sites and with depth, and the need to include these dynamic permafrost environments in future estimates of the permafrost carbon‐climate feedback.

Calcium promotes persistent soil organic matter by altering microbial transformation of plant litter

Calcium (Ca) can contribute to soil organic carbon (SOC) persistence by mediating physico-chemical interactions between organic compounds and minerals. Yet, Ca is also crucial for microbial adhesion, potentially affecting colonization of plant and mineral surfaces. The importance of Ca as a mediator of microbe-mineral-organic matter interactions and resulting SOC transformation has been largely overlooked. We incubated 44Ca labeled soils with 13C15N labeled leaf litter to study how Ca affects microbial transformation of litter and formation of mineral associated organic matter. Here we show that Ca additions promote hyphae-forming bacteria, which often specialize in colonizing surfaces, and increase incorporation of litter into microbial biomass and carbon use efficiency by approximately 45% each. Ca additions reduce cumulative CO2 production by 4%, while promoting associations between minerals and microbial byproducts of plant litter. These findings expand the role of Ca in SOC persistence from solely a driver of physico-chemical reactions to a mediator of coupled abiotic-biotic cycling of SOC.

Residue‐ and nitrogen‐induced carbon mineralization varies with soil fertility status

AbstractBy increasing the input of corn (Zea mays L.) residues, synthetic nitrogen (N) fertilization is often assumed to enhance soil storage of organic carbon (C), which could be especially beneficial for improving the fertility of depleted soils. To ascertain whether such a strategy can be effective, C mineralization was compared for two soils with different indigenous N contents by conducting a 60‐day laboratory incubation experiment that involved continuous monitoring of CO2 emissions with periodic sampling for atmospheric δ13C analysis and for determination of soil microbial biomass and cellulolytic enzyme activities. The addition of exogenous N had a stimulatory effect on cumulative CO2 production that was greater for the low than high N supplying soil and more prominent in the first than in the second month of incubation. During residue decomposition, microbial activities were maximized by incubating the low N soil with exogenous N, whereas cellulolytic enzyme activities were greater for the high N soil. Although intensive N fertilization can substantially increase the productivity of low‐fertility soils, the additional residue inputs thereby generated are more effective for promoting C mineralization than sequestration.

Manganese effects on plant residue decomposition and carbon distribution in soil fractions depend on soil nitrogen availability

Recent studies have highlighted the critical role of manganese (Mn) in plant litter decomposition and soil organic carbon (C) cycling in forest ecosystems. Long term nitrogen (N) deposition and N fertilization can increase soil acidity and mobilize bioavailable Mn (Mn2+) in soil. However, no studies have examined the interactive effect of N and Mn fertilization on litter decomposition and carbon distribution in agricultural soils, despite agroecosystems being subject to both N and Mn management. We hypothesized that increased soil N and Mn availability would accelerate plant residue decomposition and transfer of its C to mineral-associated organic matter (MAOM), and that the combined effect of Mn and N enrichment would be greater than the individual effect. We conducted a laboratory incubation experiment by adding 13C-labeled residue of perennial grass Glyceria striata (Lam.) to agricultural soils that had received 225 kg N ha−1 yr−1 for 27 years (N1) and comparable soils that received no N (N0). Before the experiment, these soils also received three levels of dissolved Mn2+, designated M0 (no additional Mn), M1 (50 mg kg−1), or M2 (250 mg kg−1). We measured total CO2 production as well as distribution of 13C from the residue into CO2, particulate organic matter (POM), MAOM, and dissolved organic carbon (DOC) over a 1-year period. Manganese amendments significantly increased CO2 production from residue decomposition in the N1 soil, but no such effect was observed in the N0 soil. Manganese also accelerated the loss of residue-derived C from POM and DOC, but increased its recovery in MAOM. However, the positive effect of added Mn in decomposition and recovery in MAOM in the presence of N fertilization occurred only during the initial 30-day decomposition period, where M2 showed a 12% increase in cumulative CO2 production from residue, 8% increase in POM loss, and 43% increase in recovery of residue C in MAOM compared to M0. For M1, only CO2 emission from residue was significantly higher than Mo during this period. At 365 days M2 showed 8% increase in CO2 production, 1% increase in POM loss, and 16% increase in recovery of residue C in MAOM compared to M0, but none of these were statistically significant (p < 0.05). This study adds to the growing evidence that increasing Mn availability enhances plant litter decomposition. However, the occurrence and magnitude of Mn-induced stimulation of decomposition is context specific. Further investigation with greater temporal resolution, involving a multitude of litter and soil types and including microbial compositional and functional characterization, is recommended to fully elucidate the interactive role of Mn and N on C cycling.

Long-term partial substitution of chemical nitrogen fertilizer with organic fertilizers increased SOC stability by mediating soil C mineralization and enzyme activities in a rubber plantation of Hainan Island, China

The partial substitution of chemical nitrogen (N) fertilizer with organic fertilizers is widely used to maintain soil fertility and enhance crop yield, although its effects on soil organic carbon (SOC) composition, mineralization and stability are not fully understood. For this study, a 12-year field experiment was conducted in a rubber plantation field of Hainan Island, China. Three fertilizer treatments included no fertilizer application as control (CK), chemical fertilizer application (NPK), and half of the chemical N fertilizer plus manure application equivalent to half of chemical N fertilizer (NPKM). We determined the soil physicochemical properties, four labile SOC compositions (microbial biomass carbon (MBC), light fraction organic carbon (LFOC), dissolved organic carbon, dissolved organic carbon extracted by hot water (HOC), particulate organic carbon (POC)), four C-associated soil enzymes (β-1, 4-glucosidase (BG), polyphenol oxidase (POX), catalase (CAT) and cellulase), and SOC mineralization (from a 46-day aerobic incubation experiment) in two soil layers (topsoil layer (0–10 cm) and subsoil layer (10–20 cm)). Compared with NPK, NPKM significantly increased soil pH, total nitrogen, total phosphorus, available phosphorus and potassium, NH4+-N, and NO3−-N contents, and SOC, LFOC, POC, HOC, and MBC concentrations. NPKM had higher cumulative CO2 production but lower SOC mineralization potential (Cp) than NPK, although the difference was not significant. In both soil layers, NPKM significantly increased POX activity, but decreased BG and CAT activities. Soil pH can regulate enzyme activities and synthesis in acidic soil in a tropical region with a significantly positive correlation with POX activity. Compared with NPK, the relatively lower Cp/SOC and higher carbon quality index (CQI) indicated higher SOC stability (Cp/SOC) in NPKM. The redundancy analysis results revealed that the dominant factors affecting SOC stability were NH4+-N, pH, POC and MBC in NPK, and available phosphorus, BG, and pH in NPKM. In the three fertilization treatments, the POX was the dominant factor affecting the CQI. Conclusively, half of the chemical N fertilizer plus half of the manure application could facilitate SOC stability by mediating soil C mineralization and enzyme activities in the rubber plantation of Hainan Island, China.

Combined effects of biochar addition with varied particle size and temperature on the decomposition of soil organic carbon in a temperate forest, China

ABSTRACT The particle size of biochar is a vital parameter adjusting the soil CO2 production, whereas the effect of biochar addition with different particle sizeon soil CO2 production is still largely unclear. Furthermore, combined effects of biochar addition and temperature on CO2 production are still unknown. To address this gap, a series of incubation experiments were conducted to examine the single and interactive effects of biochar addition with three particle sizes (1–0.5 mm, 0.5–0.1 mm, and <0.1 mm) and temperature on CO2 production in a temperate forest, China. The soil samples were collected from a poplar (Populus nigra) forest in the sandy area of the ancient Yellow River in western Shandong Province, China. Cumulative CO2 production of fine-grained biochar addition (<0.1 mm) was 88.13–92.67% of that of coarse-grained biochar (1–0.5 mm). The addition of fine-grained biochar decreased CO2 production by reducing soil nitrogen availability (i.e., nitrate and ammonium) and increasing soil pH compared to the coarse-grained biochar. Biochar addition promoted the temperature sensitivity (Q 10) of CO2 production by increasing the relative abundance of recalcitrant carbon fractions. Interactive effects of biochar addition and increasing temperature was synergistic due to the raising Q 10 value of CO2 production. Our results highlight the importance of particle size of biochar on CO2 production, less particle size of biochar, the less CO2 production. We suggest that the simultaneous effect of biochar addition and temperature on CO2 production may be underestimated basing on their single effects. Our results suggest that <0.1 mm is a threshold value of biochar particle size that is helpful to soil carbon sequestration.

Initial leaf litter traits affect soil microbial CO2 production: A laboratory experiment using the leaf litter of 41 temperate deciduous tree species

Considering the important role of litter quality in soil processes, litter species diversity may be a key determinant of many ecosystem functions, including carbon (C) sequestration. The traits of litter that affect soil microbial CO2 production can be studied under laboratory incubation to identify specific factors through the homogenization of other conditions. However, laboratory incubation studies are often conducted using fewer plant species than in field incubation studies that involve litter bags. Thus, to test whether initial leaf litter traits were associated with soil microbial CO2 production rates, we conducted a 100-day laboratory incubation in homogenized soil using the leaf litter of 41 deciduous tree species collected in a temperate deciduous forest in Japan. Our results showed that litter effects on soil CO2 production differed over time among plant species. Leaf litter with lower C and lignin concentrations, lower lignin:nitrogen (N) and lignin:C ratios, and a lower leaf mass per area increased soil CO2 production in the early stage of the incubation (0–28 days) whereas litter with higher initial C:N and lignin:N ratios increased soil CO2 production in the later stage (43–70 days). Differences in species-specific litter effects on soil CO2 production were greatest during the early stage and declined over the course of the incubation. Cumulative CO2 production during the 100-day incubation was significantly correlated with initial leaf N content per area, leaf mass per area, C and lignin concentrations, and lignin:N and lignin:C ratios. Those parameters have been reported to be included in leaf economics spectrum. Our results indicate slower soil CO2 production by tree species at the conservative end of the spectrum. They also highlight the importance of using trait-based approaches and diverse plant species to investigate biosphere-atmosphere carbon fluxes.

“Fertile island” of Tamarix Chinensis accelerated the carbon decomposition in the coastal wetlands of the Yellow River Delta, China

Fertile island of shrub in the grass-dominated ecosystems would change the spatial distribution of soil organic carbon (SOC) and its fractions, adjusting the SOC dynamics and its response to global warming. However, the effects of fertile island on SOC decomposition and its temperature responses were still less known. An incubation experiment was conducted to investigate how the fertile island of Tamarix Chinensis affects SOC decomposition and its temperature sensitivity (Q10) in the coastal wetlands of the Yellow River Delta, China. Soil samples were collected from two areas, Tamarix Chinensis growing on bare land (SB) and the mixed-growing area of Tamarix Chinensis and herbage (SH). In each area, soil samples were collected from three sites, under the canopy of Tamarix Chinensis (CM), at the edge of the canopy (CP), and outside the canopy (OL). Results showed that the cumulative CO2 production increased from OL to CM due to the following reasons. Fertile island enriched SOC, labile fractions (i.e., O-alkyl and di- O-alkyl C), ammonium under the canopy in both sample areas and increased the relative abundance of labile SOC fractions (i.e., O-alkyl C) in SB, supplying more substrates for microbial decomposition. Subsequently, fertile island stimulated β-glucosidase and invertase activities, accelerating SOC decomposition. Moreover, fertile island decreased the Q10 value in the SB area because of the increased relative abundance of O-alkyl C. This study highlights the importance of O-alkyl C on SOC decomposition and its temperature sensitivity in the coastal wetlands of the Yellow River Delta.

Short-Term Effect of Nitrogen Fertilization on Carbon Mineralization during Corn Residue Decomposition in Soil

The effect of N fertilization on residue decomposition has been studied extensively; however, contrasting results reflect differences in residue quality, the form of N applied, and the type of soil studied. A 60 d laboratory incubation experiment was conducted to ascertain the effect of synthetic N addition on the decomposition of two corn (Zea mays L.) stover mixtures differing in C:N ratio by continuous monitoring of CO2 emissions and periodic measurement of microbial biomass and enzyme activities involved in C and N cycling. Cumulative CO2 production was greater for the high than low N residue treatment, and was significantly increased by the addition of exogenous N. The latter effect was prominent during the first month of incubation, whereas N-treated soils produced less CO2 in the second month, as would be expected due to more rapid substrate depletion from microbial C utilization previously enhanced by greater N availability. The stimulatory effect of exogenous N was verified with respect to active biomass, microbial biomass C and N, and cellulase and protease activities, all of which were significantly correlated with cumulative CO2 production. Intensive N fertilization in modern corn production increases the input of residues but is not conducive to soil C sequestration.

Wetland microtopography alters response of potential net CO2 and CH4 production to temperature and moisture: Evidence from a laboratory experiment

Coastal wetlands store significant amounts of carbon (C) belowground, which may be altered through effects of rising temperature and changing hydrology on CO2 and CH4 fluxes and related microbial activities. Wetland microtopography (hummock-hollow) also plays a critical role in mediating plant growth, microbial activity, and thus cycling of C and nutrients and may interact with rising seas to influence coastal wetland C dynamics. Recent evidence suggests that CH4 production in oxygenated surface soils of freshwater wetlands may contribute substantially to global CH4 production, but comprehensive studies linking potential CH4 production to environmental and microbial variables in temperate freshwater forested wetlands are lacking. This study investigated effects of temperature, moisture, and microtopography on potential net CO2 and CH4 production and extracellular enzyme activity (β-glucosidase, xylosidase, phenol oxidase, and peroxidase) in peat soils collected from a freshwater forested wetland in coastal North Carolina, USA. Soils were retrieved from three microsites (hummock, hollow, and subsurface peat soils (approximately 20–40 cm below surface)) and incubated at two temperatures (27 °C and 32 °C) and soil water contents (65% and 100% water holding capacity (WHC)). Hummocks had the highest cumulative potential net CO2 (13.7 ± 0.90 mg CO2-C g soil−1) and CH4 (1.8 ± 0.42 mg CH4-C g soil−1) production and enzyme activity, followed by hollows (8.7 ± 0.91 mg CO2-C g soil−1 and 0.5 ± 0.12 mg CH4-C g soil−1) and then subsurface soils (5.7 ± 0.70 mg CO2-C g soil−1 and 0.04 ± 0.019 mg CH4-C g soil−1). Fully saturated soils had lower potential net CO2 production (50–80%) and substantially higher potential net CH4 production compared to non-saturated soils (those incubated at 65% WHC). Soils incubated at 32 °C increased potential net CO2 (24–34%) and CH4 (56–404%) production under both soil moisture levels compared to those incubated at 27 °C. The Q10 values for potential net CO2 and CH4 production ranged from 1.5 to 2.3 and 3.3–8.8, respectively, and did not differ between any microsites or soil water content. Enrichment of δ13CO2-C was found in saturated soils from all microsites (−24.4 to − 29.7 ‰) compared to non-saturated soils (−31.1 to − 32.4 ‰), while δ13CH4-C ranged from −62 to −55‰ in saturated soils. Together, the CO2 and CH4 δ13C data suggest that acetoclastic methanogenesis is an important pathway for CH4 production in these wetlands. A positive relationship (Adj. R2 = 0.40) between peroxidase activity and CH4 production was also found, indicating that peroxidase activity may be important in providing fermented C substrates to acetoclastic methanogenic communities and contribute to anaerobic C mineralization. These results suggest that changes in temperature and hydrology could stimulate CO2 and CH4 emissions from surface hummock soils, and to a lesser extent from hollow soils, and provide preliminary evidence that hummocks may be a spatially important and unrecognized hotspot for CH4 production.

Estimation of komatsuna freshness using visible and near-infrared spectroscopy based on the interpretation of NMR metabolomics analysis

The objective of this study was to explore the potentiality and mechanism of visible and near-infrared (Vis-NIR) spectroscopy in estimating the freshness of komatsuna. We monitored the cumulative CO2 production of komatsuna stored under different conditions as a freshness indicator and measured the Vis-NIR spectra of komatsuna as the predictor. Using the informative wavelengths (IW) selected using the stepwise selectivity ratio method, we constructed an accurate freshness prediction model through PLSR analysis. The IW in the visible region were attributed to pigments such as chlorophyll. In the NIR region, ten amino acids were identified as directly or indirectly contributing to the IW and were highly related to freshness. They were confirmed on the basis of the strong correlations between the informative NIR signals and NMR signals, which were determined using statistical heterospectroscopy. The results demonstrate the feasibility of Vis-NIR spectroscopy in estimating the freshness of komatsuna using the IW.

Integrated use of chemical and geophysical monitoring to study the diesel oil biodegradation in microcosms with different operative conditions

This study aimed to monitor the aerobic bioremediation of diesel oil-contaminated soil by measuring: a) the CO2 production; 2) the fluorescein production; 3) the residual diesel oil concentration. Moreover, the complex dielectric permittivity was monitored through an open-ended coaxial cable. Several microcosms were prepared, changing the water content (u% = 8–15% by weight), the carbon to nitrogen ratio (C/N = 20–450), and the soil amount (200 and 800 g of dry soil). The cumulative CO2 and fluorescein production showed similar trends, but different values since these two parameters reflect different features of the biological process occurring within each microcosm. The diesel oil removal efficiency depended on the microcosm characteristics. After 84 days, in the microcosms with 200 g of dry soil, the highest removal efficiency was achieved with a water content of 8% by weight and C/N = 120, while in the microcosms with 800 g of dry soil the best result was achieved with the water content equal to 12% by weight and C/N = 100. In the tested soil, the bioremediation process is efficient if the water content is in the range 8–12% by weight, and C/N is in the range 100–180; under these operative conditions, the diesel oil removal efficiency was about 65–70% after 84 days. The dielectric permittivity was monitored in microcosms with 200 g of dry soil. The open-ended coaxial cable detected significant variations of both the real and the imaginary component of the dielectric permittivity during the bioremediation process, due to the physical and chemical changes that occurred within the microcosms.

Priming effect of stable C pool in soil and its temperature sensitivity

It is important to understand the effects of exogenous carbon (C) additions on the mineralization of native soil C in agricultural soils under changing global temperatures. The slowly mineralizable C pools represent the major component of soil carbon. Once the labile fraction of soil C is depleted through mineralization, additions of exogenous labile C may enhance decomposition of slowly mineralizable soil C through the so-called priming effect (PE). The effect of exogenous C on mineralization of slowly mineralizable C in soils that have undergone extended substrate depletion is not well understood. The aim of this study was to assess the effects of exogenous C addition on the PE and its temperature sensitivity (Q10) in two substrate depleted soils. The Mollisols with two levels of C 6.8% and 2.9% were pre-incubated at 15 and 25 ℃ for 864 days, followed by 42-day incubations with and without 13C-enriched corn (Zea mays) leaf addition at 15 and 25 ℃. Soil organic carbon (SOC) decreased by 7%−9% in low and 1%−3% in high C soil after the long-term pre-incubation, respectively. In the 42-day incubation following the long-term pre-incubation, the incubation at the higher temperature (25 ℃) significantly increased cumulative CO2 production compared to that at the lower temperature (15 °C) for both high and low C soils with or without exogenous C addition. Furthermore, corn leaves addition stimulated CO2 production derived from resistant OC in both soils, resulting in a positive PE. Higher incubation temperature resulted in a greater PE in both soils independent of pre-incubation temperature. The temperature sensitivity (Q10) of the PE in the low C soil pre-incubated at 25 °C was greater than that pre-incubated at 15 °C, but in the high C soil, the Q10 of PE was lower after pre-incubation at 25 °C. The results confirmed that exogenous C addition and a higher temperature accelerate native SOC mineralization and suggested that the temperature sensitivity of the PE depended on the soil C content and the long-term temperature regime a soil is subjected to.

Residue decomposition and priming of soil organic carbon following different NPK fertilizer histories

AbstractThe effect of mineral fertilizer practices on increasing crop yield has been well studied, but few studies have examined the influence of various long‐term subtractive fertilization designs on the decomposition of crop residues or the influence on soil organic carbon (SOC) levels. To assess the combined effects of the long‐term (27‐yr) subtractive fertilizer inputs on SOC mineralization rates, we studied the change in added 13C‐labeled corn (Zea mays L.) stem and leaf residue decomposition and the magnitude of priming effect (PE) on SOC in a 56‐d lab incubation. The long‐term history of nitrogen (N), phosphorus (P), and potassium (K) combinations showed that coupling N and P fertilization had a strong effect on SOC content which increased by 6% relative to the unfertilized treatment. Soil organic C mineralization rates with no residue added were highest in soils that received N, P, and K. Cumulative CO2 production in soils amended with residue was significantly affected by residue type and was 9–19% higher for leaves than stems across treatments with varied fertilization histories. After a 56‐d incubation 14–16% of leaf C and 18–19% of stem C was mineralized. The cumulative PE was significantly higher in the unfertilized soil with leaf addition but was not affected by residue type in other treatments. Our data showed that crop residue decomposition and SOC is affected by historical N, P, and K fertilization, with long‐term complete NPK application resulting in greater SOC content and slower SOC mineralization rates with corn leaf addition.

Phosphorus Availability Promotes Bacterial DOC-Mineralization, but Not Cumulative CO2-Production.

The current trend of increasing input of terrestrially derived dissolved organic carbon (DOC) to boreal freshwater systems is causing increased levels of carbon dioxide (CO2) supersaturation and degassing. Phosphorus (P) is often the most limiting nutrient for bacterial growth and would thus be expected to increase overall mineralization rates and CO2 production. However, high carbon (C) to P ratios of terrestrially derived DOC could also cause elevated cell-specific respiration of the excess C in heterotrophic bacteria. Using data from a survey of 75 Scandinavian lakes along an ecosystem gradient of DOC, we estimated in situ CO2 production rates. These rates showed a unimodal response with DOC-specific CO2 production negatively related to DOC:total phosphorus (TP) ratio, and a turning point at 5 mg C L−1, indicating higher DOC turnover rates in productive than in unproductive lakes. To further assess the dependency of bacterial respiration (BR) on DOC and P, we monitored CO2 production in incubations of water with a gradient of DOC crossed with two levels of inorganic P. Finally, we crossed DOC and P with a temperature gradient to test the temperature dependency of respiration rates [as oxygen (O2) consumption]. While total CO2 production seemed to be unaffected by P additions, respiration rates, and growth yields, as estimated by ribosomal gene copy numbers, suggest increased bacterial growth and decreased cell-specific respiration under non-limited P conditions. Respiration rates showed a sigmoid response to increasing DOC availability reaching a plateau at about 20 mg C L−1 of initial DOC concentrations. In addition to these P and DOC level effects, respiration rates responded in a non-monotonic fashion to temperature with an increase in respiration rates by a factor of 2.6 (±0.2) from 15 to 25°C and a decrease above 30°C. The combined results from the survey and experiments highlight DOC as the major determinant of CO2 production in boreal lakes, with P and temperature as significant modulators of respiration kinetics.

Shelf life prediction model for strawberry based on respiration and transpiration processes

Abstract The physiological behaviour of fresh horticultural produce such as respiration and transpiration affects its quality and shelf life. Several studies have reported the models for shelf life prediction of packaged and non-packaged fruits and vegetables; however, while including a single quality parameter. Fluctuations in storage conditions add further complexity to the physiological processes. In this study, an integrated mathematical modelling for shelf life prediction of strawberry based on respiration and transpiration was developed and validated under realistic supply chain conditions. The model simultaneously considered three indices: microbial deterioration, mass loss and cumulative CO2 production after harvest as a guide to predict shelf-life of packaged and non-packaged strawberries. The model was found to be useful to simulate the shelf life of strawberries under modified atmosphere packaging and open tray conditions under varying temperature and humidity as normally observed in the supply chain. Deterioration based shelf life for strawberry was 10.8 d under MAP condition as compared to 9.5 d in open tray. Mass loss based shelf life for strawberry was 8.0 d for MAP condition as compared to 2.3 d in open tray. The cumulative CO2 produced up to the keeping quality was varying in a narrow range of 6.09 ± 0.21 g kg−1, in spite of different perforation diameters and storage temperatures. The proposed model will enable optimization of supply chain and making advices to all role players, including growers, traders and consumers.

Examining CO2 and N2O pollution and reduction from forestry application of pure and mixture forest

Greenhouse gases (GHGs) carbon dioxide (CO2) and nitrous oxide (N2O), contribute significantly to global warming, and they have increased substantially over the years. Reforestation is considered as an important forestry application for carbon sequestration and GHGs emission reduction, however, it remains unknown whether reforestation may instead produce too much CO2 and N2O contibuting to GHGs pollution. This study was performed to characterize and examine the CO2 and N2O emissions and their controlling factors in different species and types of pure and mixture forest used for reforestation. Five soil layers from pure forest Platycladus orientalis (PO), Robinia pseudoacacia (RP), and their mixed forest P-R in the Taihang mountains of central China were sampled and incubated aerobically for 11 days. The P-R soil showed lower CO2 and N2O production potentials than those of the PO soils (P < 0.01). The average reduction rate of cumulative CO2 and N2O was 31.63% and 14.07%, respectively. If the mixed planting pattern is implemented for reforestation, the annual CO2 reduction amounts of China’s plantation can be achieved at 8.79 million tonnes. With the increase of soil depths, cumulative CO2 production in PO and RP soils decreased, whereas CO2 and N2O production in P-R soil did not show similar pattern. Soil particle size fraction was the main factor influencing GHGs emissions, and the clay fraction showed negative correlation with cumulative CO2 and N2O production. In summary, compared with PO pure artificial forests, the mixture plantation mode can not only reduce GHGs pollution but also improve soil fertility, which is conducive to sustainable management of artificial forests.

Evaluating the potential of different carbon sources to promote denitrification

AbstractOrganic carbon (C) plays an essential role in the denitrification process as it supplies energy for N2O, N2 and CO2 producing reactions. The objectives of this study were to: (i) rank the reactivity of different C compounds found in manures based on their availability for denitrification and (ii) explore C-quality in different C sources based on their capacity to promote denitrification. Evaluation of different C-sources in promoting denitrification was conducted based on the molar ratio of CO2 production to NO3− reduction after incubation. Results of the first experiment (a 12-day investigation) showed that glucose and glucosamine were highly reactive C compounds with all applied NO3− being exhausted by day 3, and glucosamine had significantly high amount of NH4+-N present at end of the experiment. The glucose and glucosamine treatments resulted in significantly greater cumulative CO2 production, compared to the other treatments. In the second experiment (a 9-day investigation), all NO3− had been depleted by day 6 and 9 from acetic acid and glucose, respectively, and the greatest cumulative CO2 production was from acetic acid. The CO2 appearance to NO3− molar ratios revealed that glucose and glucosamine were compounds with highly available C in the first experiment. In the second experiment, the pig slurry and acetic acid were found to be C-sources that promoted potential denitrification. The application of slurry to soil results in the promotion of denitrification and this depends on the availability of the C compounds it contains. Understanding the relationship between C availability and denitrification potential is useful for developing denitrification mitigation strategies for organic soil amendments.

Carbon dioxide production as an indicator of Aspergillus flavus colonisation and aflatoxins/cyclopiazonic acid contamination in shelled peanuts stored under different interacting abiotic factors

Aspergillus flavus is the main xerophylic species colonising stored peanuts resulting in contamination with aflatoxins (AFs) and cyclopiazonic acid (CPA). This study evaluated the relationship between storage of shelled peanuts under interacting abiotic conditions on (a) temporal respiration (R) and cumulative CO2 production, (b) dry matter losses (DMLs) and (c) aflatoxin B1 (AFB1) and CPA accumulation. Both naturally contaminated peanuts and those inoculated with A. flavus were stored for 7-days under different water activities (aw; 0.77–0.95) and temperatures (20–35°C). There was an increase in the temporal CO2 production rates in wetter and warmer conditions, with the highest respiration at 0.95 aw + A. flavus inoculum at 30°C (2474 mg CO2kg−1h−1). The DMLs were modelled to produce contour maps of the environmental conditions resulting in maximum/minimum losses. Maximum mycotoxin contamination was always at 0.95 aw although optimal temperatures were 25-30°C for AFs and 30-35°C for CPA. These results showed a correlation between CO2 production and mycotoxin accumulation. They also provide valuable information for the creation of a database focused on the development of a post-harvest decision support system to determine the relative risks of contamination with these mycotoxins in stored shelled peanuts.