Long-term Carbon Sequestration Research Articles

Woody biomass production lags stem-girth increase by over one month in coniferous forests.

Wood is the main terrestrial biotic reservoir for long-term carbon sequestration(1), and its formation in trees consumes around 15% of anthropogenic carbon dioxide emissions each year(2). However, the seasonal dynamics of woody biomass production cannot be quantified from eddy covariance or satellite observations. As such, our understanding of this key carbon cycle component, and its sensitivity to climate, remains limited. Here, we present high-resolution cellular based measurements of wood formation dynamics in three coniferous forest sites in northeastern France, performed over a period of 3 years. We show that stem woody biomass production lags behind stem-girth increase by over 1 month. We also analyse more general phenological observations of xylem tissue formation in Northern Hemisphere forests and find similar time lags in boreal, temperate, subalpine and Mediterranean forests. These time lags question the extension of the equivalence between stem size increase and woody biomass production to intra-annual time scales(3, 4, 5, 6). They also suggest that these two growth processes exhibit differential sensitivities to local environmental conditions. Indeed, in the well-watered French sites the seasonal dynamics of stem-girth increase matched the photoperiod cycle, whereas those of woody biomass production closely followed the seasonal course of temperature. We suggest that forecasted changes in the annual cycle of climatic factors(7) may shift the phase timing of stem size increase and woody biomass production in the future.

Effect of pyrolysis temperatures on stability and priming effects of C3 and C4 biochars applied to two different soils

Biochar (BC) is a recalcitrant soil amendment that is being used for long-term carbon sequestration while also enhancing soil fertility. In an effort to better understand the interaction of soil type and biochar type, Mollisol (Minnesota) and Ultisol (Georgia) were incubated with biochars prepared from C3 (rice hull and wheat straw) and C4 (maize stover and switch grass) crop residues at 400°C and 600°C and the stability of biochar was studied by CO2 evolution measurements for 60 days. The C3 and C4 biochars were applied to the Ultisol and Mollisol samples which had a long term history of cropping with C4 and C3 crops, respectively. Overall the total and fixed C content of biochar increased, while the N content decreased with increase in pyrolysis temperature from 400°C to 600°C, thus increasing the C:N of the biochar. The volatile matter component of biochar decreased significantly at the higher pyrolysis temperature. In the Mollisol, the wheat straw biochar prepared (WSBC) at 600°C was more stable than the rice hull biochar (RHBC). However, in the Ultisol, RHBC was more stable than the WSBC. Corn stover biochar (CSBC) prepared at 600°C showed greater stability in both the Mollisol and Ultisol. The WSBC and CSBC prepared at 600°C which showed negative priming of native soil organic matter (SOM) had greater potential for long term carbon sequestration in soil. The δ13C signatures of the CO2 evolved on the 2nd day matched δ13C signatures of biochar confirming the contribution of biochar. On days 9 and 20 the δ13C signatures matched that of control soil indicating very little or no contribution of biochar to CO2 evolution. In spite of significant changes in pH and EC of soil biochar mixtures, these parameters had no effect on C mineralization. Nonlinear regression model confirms that the decomposition rate constant was higher in the 400°C biochar than in the 600°C biochar. Corn biochar prepared at 600°C could be useful for enhancing carbon storage in both the Mollisol and Ultisol. Soil organic matter level might have controlled the direction and magnitude of priming effect.

Carbon flux assessment in cow-calf grazing systems.

Greenhouse gas (GHG) fluxes and soil organic carbon (SOC) accumulation in grassland ecosystems are intimately linked to grazing management. This study assessed the carbon equivalent flux (Ceq) from 1) an irrigated, heavily stocked, low-density grazing system, 2) a nonirrigated, lightly stocked, high-density grazing system, and 3) a grazing-exclusion pasture site on the basis of the GHG emissions from pasture soils and enteric methane emissions from cows grazing different pasture treatments. Soil organic carbon and total soil nitrogen stocks were measured but not included in Ceq determination because of study duration and time needed to observe a change in soil composition. Light- and heavy-stocking systems had 36% and 43% greater Ceq than nongrazed pasture sites, respectively ( < 0.01). The largest contributor to increased Ceq from grazing systems was enteric CH emissions, which represented 15% and 32% of the overall emissions for lightly and heavily stocked grazing systems, respectively. Across years, grazing systems also had increased nitrous oxide (N2O; < 0.01) and CH emissions from pasture soils ( < 0.01) compared with nongrazed pasture sites but, overall, minimally contributed to total emissions. Results indicate no clear difference in Ceqflux between the grazing systems studied when SOC change is not incorporated ( = 0.11). A greater stocking rate potentially increased total SOC stock ( = 0.02), the addition of SOC deeper into the soil horizon ( = 0.01), and soil OM content to 30 cm ( < 0.01). The incorporation of long-term annual carbon sequestration into the determination of Ceq could change results and possibly differentiate the grazing systems studied.

Differences in fertilization impacts on organic carbon content and stability in a paddy and an upland soil in subtropical China

The stability of soil organic carbon (SOC) is of great importance in controlling long-term carbon (C) sequestration and feedbacks of soil C pools to climate change. It has been well documented that rice cropping and organic amendments could enhance SOC stocks, while the stability of the sequestered C has not been well understood yet. The objective of this study was to examine the difference in SOC content and stability between a paddy and an upland field under long-term fertilization and to explore the potential link between SOC chemical and biological stability. Soils were collected from two adjacent long-term paddy (annually double-rice cropping) and upland (annually double-corn cropping) experiments with the same soil parent material, where different fertilization regimes were initiated in 1981 and 1986, respectively. The chemical and biological stability of SOC were measured by acid hydrolysis and aerobic incubations, respectively. The C concentration was significantly higher in the paddy soil than in the upland soil, regardless of fertilization regimes. As compared to the initial level, long-term rice cropping without any fertilization (CK) significantly enhanced SOC concentration, whereas corn cropping led to a slight decline. Manure amendments combined with inorganic NPK fertilizers (NPKM) significantly increased SOC content relative to the inorganic NPK application alone treatment (NPK) in both the upland and paddy fields. The paddy soil had significantly greater cumulative C released per gram of soil C (i.e., the biological stability of SOC) than the upland soil. Cumulative C released per gram of soil C was significantly higher in NPKM than in NPK in both the paddy and upland soils, whereas no significant difference was observed between the CK and NPK treatments. Acid hydrolysis could reveal the difference in C stability between the paddy and upland soils, but could not characterize the effect of fertilization. Rice cropping facilitates SOC accumulation relative to upland cropping, whereas the inherent SOC stability is lower under the former than the latter in the site. The lower SOC turnover in the paddy than in the upland is mainly due to anaerobic conditions. Organic amendments significantly enhance SOC, but reduce its stability in both the paddy and upland fields. The sensitivity of acid hydrolysis is relatively low in determining SOC stability.

An individual-based model of long-term forest growth and carbon sequestration in planted mangroves under salinity and inundation stresses

We developed a spatially explicit individual-based model of forest development trajectories of monospecific Rhizophora mucronata plantations. The model incorporates stochastic initial seedling spacing, propagule dispersal, recruitment, and mortality. We simulated and compared the growth, development and accumulation of carbon stocks of restored mangroves between optimal and sub-optimal settings. Salinity is considered as a stressor, while flooding effects are described as an inundation stress factor. In the optimal setting, the simulated mangrove population accumulated large aboveground carbon stocks (of around 140 T/ ha) after 100 years. Under sub-optimal conditions, we observed delayed maturity by at least 10 years near the salinity threshold and the carbon stock decreased through time towards much lower values (25 T/ha). More importantly, the continuous presence of stressors may lead to forest population collapse (at 50 yrs post-planting) probably as a result of the accumulated effects of physiological stresses. Thus, restored mangrove populations that are located in highly saline and frequently inundated sites, may eventually collapse even though they may appear to be healthy in the early stages of forest development. Our results imply that current and future restoration practices should carefully consider site selection in order to ensure viable long-term forest development and to have an optimum contribution to carbon sequestration. Keywords—mangroves, individual-based model, growth, forest development, restoration trajectory, salinity, inundation, carbon sequestration

Soil organic carbon associated in size-fractions as affected by different land uses in karst region of Guizhou, Southwest China

Land use change has a significant effect on soil organic carbon (SOC), especially on labile organic carbon (LOC) due to its rapid response to soil changes and carbon supply. The objective of the study was to assess the effects of different land uses on soil fraction size distribution, SOC and LOC concentrations and their stocks in karst region of Guizhou Province, Southwest China. Studies were based on soil sampling in paddy, dryland, abandoned cultivated land for 3-years (AC-3), and abandoned cultivated land for 15-years (AC-15) in the 0–10, 10–20, and 20–30 cm depths in karst mountain area of Guizhou Province. Three fraction-size classes [macro (250–2000 μm), micro (53–250 μm), silt + clay (<53 μm)] were fractioned, and SOC and LOC concentrations in whole soil (non-fractionated) and different fraction sizes were also determined. The results showed that paddy contained the highest SOC and LOC concentrations in whole soil and different size-fractions as compared with other land uses down to 30 cm depth. However, the proportions of LOC to SOC were higher in AC-3 than the other land uses, especially pronounced in whole soil, which ranged from 17.5 to 26.3 % in different soil depths. Paddy also contained 23.7 % (100.9 Mg ha−1) more SOC and 17.6 % (19.7 Mg ha−1) more LOC stocks than dryland, whereas the SOC and LOC stocks in AC-15 and dryland were very close to each other in each soil depth. In paddy field, we found that macro-sized fractions contributed the greatest quantities of SOC to whole soil. In addition, paddy had significantly higher SOC stock values in macro-sized fractions than the other land uses in the both 0–10 and 10–20 cm depths. In the present study, there were no obvious increases of SOC and LOC pools among whole soil and different soil size-fractions after 15 years of land abandonment. These results suggest that natural recovery of SOC may take a long time after land abandonment, and paddy could serve as an important land use type for long-term carbon sequestration in karst region of Southwest China.

Rice (Oryza sativa L) plantation affects the stability of biochar in paddy soil.

Conversion of rice straw into biochar for soil amendment appears to be a promising method to increase long-term carbon sequestration and reduce greenhouse gas (GHG) emissions. The stability of biochar in paddy soil, which is the major determining factor of carbon sequestration effect, depends mainly on soil properties and plant functions. However, the influence of plants on biochar stability in paddy soil remains unclear. In this study, bulk and surface characteristics of the biochars incubated without rice plants were compared with those incubated with rice plants using a suite of analytical techniques. Results showed that although rice plants had no significant influence on the bulk characteristics and decomposition rates of the biochar, the surface oxidation of biochar particles was enhanced by rice plants. Using 13C labeling we observed that rice plants could significantly increase carbon incorporation from biochar into soil microbial biomass. About 0.047% of the carbon in biochar was incorporated into the rice plants during the whole rice growing cycle. These results inferred that root exudates and transportation of biochar particles into rice plants might decrease the stability of biochar in paddy soil. Impact of plants should be considered when predicting carbon sequestration potential of biochar in soil systems.

How organic carbon derived from multiple sources contributes to carbon sequestration processes in a shallow coastal system?

Carbon captured by marine organisms helps sequester atmospheric CO2, especially in shallow coastal ecosystems, where rates of primary production and burial of organic carbon (OC) from multiple sources are high. However, linkages between the dynamics of OC derived from multiple sources and carbon sequestration are poorly understood. We investigated the origin (terrestrial, phytobenthos derived, and phytoplankton derived) of particulate OC (POC) and dissolved OC (DOC) in the water column and sedimentary OC using elemental, isotopic, and optical signatures in Furen Lagoon, Japan. Based on these data analysis, we explored how OC from multiple sources contributes to sequestration via storage in sediments, water column sequestration, and air–sea CO2 exchanges, and analyzed how the contributions vary with salinity in a shallow seagrass meadow as well. The relative contribution of terrestrial POC in the water column decreased with increasing salinity, whereas autochthonous POC increased in the salinity range 10–30. Phytoplankton-derived POC dominated the water column POC (65–95%) within this salinity range; however, it was minor in the sediments (3–29%). In contrast, terrestrial and phytobenthos-derived POC were relatively minor contributors in the water column but were major contributors in the sediments (49–78% and 19–36%, respectively), indicating that terrestrial and phytobenthos-derived POC were selectively stored in the sediments. Autochthonous DOC, part of which can contribute to long-term carbon sequestration in the water column, accounted for >25% of the total water column DOC pool in the salinity range 15–30. Autochthonous OC production decreased the concentration of dissolved inorganic carbon in the water column and thereby contributed to atmospheric CO2 uptake, except in the low-salinity zone. Our results indicate that shallow coastal ecosystems function not only as transition zones between land and ocean but also as carbon sequestration filters. They function at different timescales, depending on the salinity, and OC sources.

Enhancing phytolith carbon sequestration in rice ecosystems through basalt powder amendment

Global warming as a result of rapid increase in atmospheric CO2 emission is significantly influencing world’s economy and human activities. Carbon sequestration in phytoliths is regarded as a highly stable carbon sink mechanism in terrestrial ecosystems to mitigate climate change. However, the response of plant phytolith-occluded carbon (PhytOC) to external silicon amendments remains unclear. In this study, we investigated the effects of basalt powder (BP) amendment on phytolith carbon sequestration in rice (Oryza sativa), a high-PhytOC accumulator. The results showed that the contents of phytolith and PhytOC in rice increased with BP amendment. The PhytOC production flux in different rice plant parts varied considerably (0.005–0.041Mg CO2 ha−1 a−1), with the highest flux in the sheath. BP amendment can significantly enhance flux of phytolith carbon sequestration in croplands by 150%. If the global rice cultivation of 1.55 × 108ha had a similar flux of PhytOC production in this study, 0.61 × 107 to 1.54 × 107Mg CO2 would be occluded annually within global rice phytoliths. These findings highlight that external silicon amendment such as BP amendment represents an effective potential management tool to increase long-term biogeochemical carbon sequestration in crops such as rice and may also be an efficient way to mitigate the global warming indirectly.

Pyrolysis of urban waste streams: Their potential use as horticultural media

Biochar produced from mixture of biodegradable urban resources such as biosolids and greenwaste was slowly pyrolysed at 650°C and characterised for its chemical and physical properties. The biochar was then compared to published values for growing media. It was found that this biochar has high surface area, inherent nutrient content, high porosity, high stability, desirable water holding capacity, air filled pore space and bulk density. Comparing the results of characterisation of this biochar with ideal potting substrate showed the highly porous and nutrient rich biochar were desirable however the high salt content was problematic. Fourier transform infrared analysis shows that carboxyl/carbonyl bands were very weak in biochar spectra due to loss of carboxyl groups in the decomposition of carbohydrates in high temperature pyrolysis which also contributed to low cation exchange capacity. The pyrolysis process has multiple advantages such as waste management, energy generation in the form of syngas and long term sequestration of carbon in biochar.

Francis M. Martin.

Francis M. Martin.

Biochar carbon sequestration in soil - A myth or reality?

The soil carbon sequestration is the long-term storage of carbon in soil which could well be accomplished by the application of biochar as a soil amendment. Biochar (BC) is a fine grained, highly carbonaceous, pyrolysed (low temperature) product of biomass. The pyrolysis temperature strongly influences the stability of biochar in soil; the higher the pyrolysis temperature higher would be the stability. Biochar being highly stable in soil due to its aromaticity, presence of amorphous structure and turbostatic crystallites, rounded structures and reduced accessibility to decomposers has lot of potential for long-term carbon sequestration. The higher stability of biochar in soil is also due to strong interactions with mineral surfaces. Biochar interacts with native soil organic matter (SOM) in a complex way; sometimes biochar showed positive priming effect or negative priming effect or no effect on native SOM. This depends upon the feedstock type, pyrolysis temperature and organic matter level of soil. The soils richer in organic matter status provide positive priming effect of native SOM due to biochar addition and vice-versa. Biochar has high carbon sequestration potential and long-term influence on native SOM. Biochar has huge potential for reduction of greenhouse gas emission form paddy field soils. Therefore, optimisation of feedstock, pyrolysis temperature for preparation biochar and its application in a specific soil is extremely essential for stability of biochar and protection of native SOM and greenhouse gas reduction for long-term carbon sequestration. Thus biochar carbon sequestration is not a myth rather it would be a reality in near future.

Effects of mineral additives on biochar formation: carbon retention, stability, and properties.

Biochar is being recognized as a promising tool for long-term carbon sequestration, and biochar with high carbon retention and strong stability is supposed to be explored for that purpose. In this study, three minerals, including kaolin, calcite (CaCO3), and calcium dihydrogen phosphate [Ca(H2PO4)2], were added to rice straw feedstock at the ratio of 20% (w/w) for biochar formation through pyrolysis treatment, aiming to improve carbon retention and stabilization in biochar. Kaolin and CaCO3 had little effect on the carbon retention, whereas Ca(H2PO4)2 increased the carbon retention by up to 29% compared to untreated biochar. Although the carbon loss from the kaolin-modified biochar with hydrogen peroxide oxidation was enhanced, CaCO3 and Ca(H2PO4)2 modification reduced the carbon loss by 18.6 and 58.5%, respectively. Moreover, all three minerals reduced carbon loss of biochar with potassium dichromate oxidation from 0.3 to 38.8%. The microbial mineralization as CO2 emission in all three modified biochars was reduced by 22.2-88.7% under aerobic incubation and 5-61% under anaerobic incubation. Enhanced carbon retention and stability of biochar with mineral treatment might be caused by the enhanced formation of aromatic C, which was evidenced by cross-polarization magic angle spinning (13)C nuclear magnetic resonance spectra and Fourier transform infrared spectroscopy analysis. Our results indicated that the three minerals, especially Ca(H2PO4)2, were effective in increasing carbon retention and strengthening biochar stabilization, which provided a novel idea that people could explore and produce the designated biochar with high carbon sequestration capacity and stability.

The effects of long-term drainage and subsequent restoration on water table level and pore water chemistry in boreal peatlands

Degradation by drainage threatens biodiversity and globally important peatland ecosystem functions such as long-term carbon sequestration in peat. Restoration aims at safeguarding peatland values by recovering natural hydrology. Long-term effects of drainage and subsequent restoration, especially related to within-site variation of water table level and pore water chemistry, are poorly known. We studied hydrological variation at 38 boreal Sphagnum peatland sites (pristine, drained and restored) in Finland. The average water table level was significantly lower at Drained than Pristine sites especially near the ditches. We also observed large pore water chemical differences between Drained and Pristine sites, such as higher DOC concentration at the sites drained several decades earlier. Furthermore, there were large differences in water chemistry between the samples collected from ditches and from the peat strips between the ditches. For example, the ditch water had apparently higher minerogenic influence, while DOC concentrations were highest in peat strips. The water table level was, on average, at the targeted level of Pristine sites at 5 years ago restored (Res 5) and 10 years ago restored (Res 10) sites. The Res 10 sites were more similar to the Pristine sites in water chemical composition than were the Drained sites. Water chemical differences between ditches and peat strips were smaller at the Res 5 and Res 10 than at Drained sites indicating, on average, successful decrease of drainage-induced within-site variation in water chemistry. Our results suggest more pronounced water table inclination towards the old ditches at Res 10 than at Res 5 sites. While this pattern may be an early warning sign for incomplete recovery of hydrology in long-term, we found no chemical evidence supporting this assumption yet. Our study suggests that restoration can result in significant recovery of peatland hydrology within 10 years, while some deviation from pristine hydrology is still typical. Restoration appears to have potential to reduce leaching of nutrients and DOC to downstream waters in the long term, but practitioners should be prepared for temporary increase of leaching of N and P for at least 5 years after restoration of boreal Sphagnum peatlands.

Biochar can be used to capture essential nutrients from dairy wastewater and improve soil physico-chemical properties

Abstract. Recently, the potential for biochar use to recapture excess nutrients from dairy wastewater has been a focus of a growing number of studies. It is suggested that biochar produced from locally available excess biomass can be important in reducing release of excess nutrient elements from agricultural runoff, improving soil productivity, and long-term carbon (C) sequestration. Here we present a review of a new approach that is showing promise for the use of biochar for nutrient capture. Using batch sorption experiments, it has been shown that biochar can adsorb up to 20–43% of ammonium and 19–65% of the phosphate in flushed dairy manure in 24 h. These results suggest a potential of biochar for recovering essential nutrients from dairy wastewater and improving soil fertility if the enriched biochar is returned to soil. Based on the sorption capacity of 2.86 and 0.23 mg ammonium and phosphate, respectively, per gram of biochar and 10–50% utilization of available excess biomass, in the state of California (US) alone, 11 440 to 57 200 tonnes of ammonium-N and 920–4600 tonnes of phosphate can be captured from dairy waste each year while at the same time disposing up to 8–40 million tons of excess biomass.

Organic carbon and nitrogen stocks in a clay loam soil 10 years after a single compost application

Yang, X., Reynolds, W. D., Drury, C. F., Fleming, R., Tan, C. S., Denholm, K. and Yang, J. 2014. Organic carbon and nitrogen stocks in a clay loam soil 10 years after a single compost application. Can. J. Soil Sci. 94: 357–363. Household food waste compost (FWC), yard waste compost (YWC) and pig manure plus wheat straw compost (PMC) were applied once in the fall of 1998 to a Brookston clay loam soil in southwestern Ontario to determine immediate and long-term effects of organic amendments on soil quality and productivity. In this report, we describe the residual effects of these single compost applications on soil organic carbon (SOC) and total soil nitrogen (TN) stocks 10 yr after compost addition (2009). FWC was applied at 75 Mg ha−1, 150 Mg ha−1 and 300 Mg ha−1, while YWC and PMC were applied at the single rate of 75 Mg ha−1. The 75 Mg ha−1 additions of YWC, PMC and FWC increased SOC in the top 30 cm relative to a control (no compost additions) by 12.3% (9.0 Mg ha−1), 16.6% (12.2 Mg ha−1) and 0%, respectively; and they increased TN relative to the control by 8.0% (0.53 Mg ha−1), 11.7% (0.77 Mg ha−1), and 0%, respectively. The 150 and 300 Mg ha−1 additions of FWC increased SOC in the top 30 cm by 13.0 and 24.7 Mg ha−1, respectively, and they increased TN by 0.93 and 1.70 Mg ha−1, respectively. These results indicate that increases in SOC and TN stocks accruing from a single compost addition can persist for at least a decade, but the degree of increase depends strongly on compost type and addition rate. It was concluded that high compost addition rates of FWC and/or addition of composts derived from recalcitrant organic materials may be a good strategy for achieving long-term carbon and nitrogen sequestration in the cool, humid fine-textured soils of southwestern Ontario.

Impounded Marshes on Subsided Islands: Simulated Vertical Accretion, Processes, and Effects, Sacramento-San Joaquin Delta, CA USA

There is substantial interest in stopping and reversing the effects of subsidence in the Sacramento–San Joaquin Delta (Delta) where organic soils predominate. Also, the passage of California Assembly Bill 32 in 2006 created the potential to trade credits for carbon sequestered in wetlands on subsided Delta islands. The primary purpose of the work described here was to estimate future vertical accretion and understand processes that affect vertical accretion and carbon sequestration in impounded marshes on subsided Delta islands. Using a cohort-accounting model, we simulated vertical accretion from 4,700 calibrated years before present (BP) at a wetland area located within Franks Tract State Recreation Area (lat 38.059, long −121.611, hereafter, “Franks Wetland”)—a small, relatively undisturbed marsh island—and at the Twitchell Island subsidence-reversal demonstration project since 1997. We used physical and chemical data collected during the study as well as literature values for model inputs. Model results compared favorably with measured rates of vertical accretion, mass of carbon sequestered, bulk density and organic matter content. From 4,700 to model-estimated 350 years BP, the simulated rate of vertical accretion at Franks Wetland averaged about 0.12 cm yr-1, which is within the range of rates in tidal wetlands worldwide. Our model results indicate that large sediment inputs during the last 150 to 200 years resulted in a higher accretion rate of 0.3 cm yr -1. On Twitchell Island, greater organic inputs resulted in average vertical accretion rates as high as 9.2 cm yr -1. Future simulations indicate that the managed impounded marsh will accrete highly organic material at rates of about 3 cm yr -1. Model results coupled with GIS analysis indicate that large areas of the periphery of the Delta, if impounded and converted to freshwater marsh, could be restored to tidal elevations within 50 to 100 years. Most of the central Delta would require 50 to 250 years to be restored to projected mean sea level. A large portion of the western Delta could be restored to mean sea level within 50 to 150 years (large areas on Sherman, Jersey, and Bethel islands, and small areas on Bradford, Twitchell, and Brannan islands, and Webb Tract). We estimated that long-term carbon sequestration rates for impounded marshes such as the Twitchell Island demonstration ponds will range from 12 to 15 metric tons carbon ha-1 yr-1. Creation of impounded marshes on Delta islands can substantially benefit levee stability as demonstrated by cumulative force and hydraulic gradient calculations.

Disturbances, Their Interactions, and Cumulative Effects on Carbon and Charcoal Stocks in a Forested Ecosystem

Disturbances have a strong role in the carbon balance of many ecosystems, and the cycle of vegetation growth, disturbance, and recovery is very important in determining the net carbon balance of terrestrial biomes. Compound disturbances are phenomena of growing concern which can impact ecosystems in novel ways, altering disturbance intensity, severity, and recovery trajectories. This research focuses on carbon stocks in a compound disturbance environment, with special attention on black carbon (charcoal), a potential source of long-term carbon sequestration. We report on a well-studied compound disturbance event (wind, logging, and severe fire) in a Colorado, USA subalpine forest that was extensively surveyed for impacts on carbon, black carbon, and regeneration. All major pools were considered, including organic and mineral soil (10 cm depth), and contrasted with neighboring undisturbed forests as a reference. The disturbances had an additive effect on carbon loss, with increasing numbers of disturbances resulting in progressively decreasing carbon/black carbon stocks. This resulted from lower substrate availability and higher fire intensity. Surprisingly, there was no significant difference between reference and burned plots in terms of total black carbon. It appears that high-intensity fires do not significantly increase net black carbon in these forests (over the entire fire-return interval), with additional disturbances potentially resulting in a net loss. Disturbances, and their interactions, will have long-lasting legacies for carbon and black carbon.

Net uptake of atmospheric CO 2 by coastal submerged aquatic vegetation

‘Blue Carbon’, which is carbon captured by marine living organisms, has recently been highlighted as a new option for climate change mitigation initiatives. In particular, coastal ecosystems have been recognized as significant carbon stocks because of their high burial rates and long-term sequestration of carbon. However, the direct contribution of Blue Carbon to the uptake of atmospheric CO2 through air-sea gas exchange remains unclear. We performed in situ measurements of carbon flows, including air-sea CO2 fluxes, dissolved inorganic carbon changes, net ecosystem production, and carbon burial rates in the boreal (Furen), temperate (Kurihama), and subtropical (Fukido) seagrass meadows of Japan from 2010 to 2013. In particular, the air-sea CO2 flux was measured using three methods: the bulk formula method, the floating chamber method, and the eddy covariance method. Our empirical results show that submerged autotrophic vegetation in shallow coastal waters can be functionally a sink for atmospheric CO2. This finding is contrary to the conventional perception that most near-shore ecosystems are sources of atmospheric CO2. The key factor determining whether or not coastal ecosystems directly decrease the concentration of atmospheric CO2 may be net ecosystem production. This study thus identifies a new ecosystem function of coastal vegetated systems; they are direct sinks of atmospheric CO2.

Surface Display of Small Peptides on Escherichia coli for Enhanced Calcite Precipitation Rates.

Mineralization has emerged as a promising strategy for long-term carbon sequestration. These processes involve carbon dioxide hydration followed by mineral precipitation. We have explored the production of whole-cell biocatalysts engineered with carbonic anhydrase (CA) activity to accelerate the CO₂ hydration reaction. In this study, short polypeptides were displayed on the surface of E. coli cells and whole-cell biocatalysts containing periplasmically expressed CAs in an attempt to enhance calcite mineral formation. It was found that cells coexpressing recombinant periplasmic CA and surface-displayed GPA peptide (PEVPEGAFDTAI) outperformed other peptide-expressing biocatalysts evaluated in terms of the amount of precipitate formed, as well as the overall formation rate of solids. Cells expressing the Cab CA isoform (BLR-pCab) and Cam isoform (BLR-pCam) with the surface-displayed GPA peptide exhibited 36 and 59% improvements in precipitation amounts, as well as 18 and 60% improvements in overall formation rates, respectively, over similar biocatalysts without GPA expression. The biocatalyst with the best performance was BLR-pCam/GPA, which generated 0.15 g of CaCO₃, while BLR cells generated only 0.08 g of CaCO₃ under the same small batch reaction conditions. The BLR-pCam/GPA cells also exhibited the fastest formation rates, achieving the maximum change in solution turbidity after only 2.2 min, as opposed to 6.3 min for BLR cells. These results demonstrate that synthetic biology approaches can be used to create novel biocatalysts with the ability to enhance both catalysis and precipitation activities.