Current forest carbon stocks and carbon sequestration potential in Anhui Province,China北大核心CSCD

Aims This study was conducted to investigate carbon stocks in forest ecosystems of different stand ages in Anhui Province, and to identify the carbon sequestration potential of climax forests controlled by the natural environment conditions. Methods Data were collected based on field investigations and simulations were made with the BIOME4 carbon cycle model. Important findings Currently, the total forest carbon stocks in Anhui Province amounts to 714.5 Tg C: 402.1 Tg C in vegetation and 312.4 Tg C in soil. Generally, both the total and vegetation carbon density exhibit an increasing trend with the natural growth of forest stands. Soil carbon density increases from young to near mature forests, and then gradually decreases thereafter. Young and middle-aged forests account for 75% of the total forest area in Anhui Province, with potentially an additional 125.4 Tg C to be gained after the young and middle-aged forests reach near mature stage. Results of BIOME4 simulations show that potentially an additional 245.7 Tg C, including 153.7 Tg C in vegetation and 92 Tg C in soil, could be gained if the current forests are transformed into climax forest ecosystems in Anhui Province.     

Silicon–doping in carbon nanotubes: formation energies, electronic structures, and chemical reactivity

By carrying out density functional theory (DFT) calculations, we have studied the effects of silicon (Si)-doping on the geometrical and electronic properties, as well as the chemical reactivity of carbon nanotubes (CNTs). It is found that the formation energies of these nanotubes increase with increasing tube diameters, indicating that the embedding of Si into narrower CNTs is more energetically favorable. For the given diameters, Si-doping in a (n, 0) CNT is slightly easier than that of in (n, n) CNT. Moreover, the doped CNTs with two Si atoms are easier to obtain than those with one Si atom. Due to the introduction of impurity states after Si-doping, the electronic properties of CNTs have been changed in different ways: upon Si-doping into zigzag CNTs, the band gap of nanotube is decreased, while the opening of band gap in armchair CNTs is found. To evaluate the chemical reactivity of Si-doped CNTs, the adsorption of NH₃ and H₂O on this kind of material is explored. The results show that N–H bond of NH₃ and O–H bond of H₂O can be easily split on the surface of doped CNTs. Of particular interest, the novel reactivity makes it feasible to use Si-doped CNT as a new type of splitter for NH₃ and H₂O bond, which is very important in chemical and biological processes. Future experimental studies are greatly desired to probe such interesting processes.      

Whales in the carbon cycle: can recovery remove carbon dioxide?

The great whales (baleen and sperm whales), through their massive size and wide distribution, influence ecosystem and carbon dynamics. Whales directly store carbon in their biomass and contribute to carbon export through sinking carcasses. Whale excreta may stimulate phytoplankton growth and capture atmospheric CO₂; such indirect pathways represent the greatest potential for whale-carbon sequestration but are poorly understood. We quantify the carbon values of whales while recognizing the numerous ecosystem, cultural, and moral motivations to protect them. We also propose a framework to quantify the economic value of whale carbon as populations change over time. Finally, we suggest research to address key unknowns (e.g., bioavailability of whale-derived nutrients to phytoplankton, species- and region-specific variability in whale carbon contributions).     

Is soil carbon mostly root carbon? Mechanisms for a specific stabilisation

Understanding the origin of the carbon (C) stabilised in soils is crucial in order to device management practices that will foster Caccumulation in soils. The relative contributions to soilC pools of roots vs. shoots is one aspect that has been mostly overlooked, although it appears a key factor that drives the fate of plant tissueC either as mineralized CO₂ or as stabilized soil organic matter (SOM). Available studies on the subject consistently indicate that rootC has a longer residence time in soil than shootC. From the few studies with complete datasets, we estimated that the mean residence time in soils of root-derived C is 2.4times that of shoot-derived C. Our analyses indicate that this value is biased neither by an underestimation of root contributions, as exudation was considered in the analysis, nor by a priming effect of shoot litter on SOM. Here, we discuss the main SOM stabilisation mechanisms with respect to their ability to specifically protect root-derived SOM. Comparing in situ and incubation experiments suggests that the higher chemical recalcitrance of root tissues as compared to that of shoots is responsible for only a small portion, i.e. about one fourth, of the difference in mean residence time in soils of root-derived vs. shoot-derivedC. This suggests that SOM protection mechanisms other than chemical recalcitrance are also enhanced by root activities: (1)physico-chemical protection, especially in deeper horizons, (2)micrometer-scale physical protection through myccorhiza and root-hair activities, and (3)chemical interactions with metal ions. The impact of environmental conditions within deeper soil layers on rootC stabilisation appear difficult to assess, but is likely, if anything, to further increase the ratio between the mean residence time of root vs. shootC in soils. Future advances are expected from isotopic studies conducted at the molecular level, which will help unravel the fate of individual shoot and root compounds, such as cutins and suberins, throughout soil profiles.     

Is soil carbon disappearing? The dynamics of soil organic carbon in Java

Research in the soil of the tropics mostly has demonstrated the decline of soil organic carbon (SOC) after conversion of primary forest to plantation and cultivated lands. This paper illustrates the dynamics of SOC on the island of Java, Indonesia, from 1930 to 2010. We used 2002 soil profile observations containing organic carbon (C) analysis in the topsoil, which were collected by the Indonesian Center for Agricultural Land Resources Research & Development from 1923 to 2007. Results show the obvious decline of SOC values from around 2% in 1930–1940 to 0.8% in 1960–1970. However, there has been an increase of SOC content since 1970, with a median level of 1.1% in the year 2000. Our analysis suggests that the human influence and agricultural practices on SOC in Java have been a stronger influence than the environmental factors. SOC for the top 10 cm has shown a net accumulation rate of 0.2–0.3 Mg C ha^?1 yr^?1 during the period 1990–2000. These findings give rise to optimism for increased soil C sequestration in the tropics.     

Effect of carbon monoxide,hydrogen and sulfate on thermophilic (55°C) hydrogenogenic carbon monoxide conversion in two anaerobic bioreactor sludges

The conversion routes of carbon monoxide (CO) at 55°C by full-scale grown anaerobic sludges treating paper mill and distillery wastewater were elucidated. Inhibition experiments with 2-bromoethanesulfonate (BES) and vancomycin showed that CO conversion was performed by a hydrogenogenic population and that its products, i.e. hydrogen and CO₂, were subsequently used by methanogens, homo-acetogens or sulfate reducers depending on the sludge source and inhibitors supplied. Direct methanogenic CO conversion occurred only at low CO concentrations [partial pressure of CO (P _CO) <0.5 bar (1 bar=10⁵ Pa)] with the paper mill sludge. The presence of hydrogen decreased the CO conversion rates, but did not prevent the depletion of CO to undetectable levels (<400 ppm). Both sludges showed interesting potential for hydrogen production from CO, especially since after 30 min exposure to 95°C, the production of CH₄ at 55°C was negligible. The paper mill sludge was capable of sulfate reduction with hydrogen, tolerating and using high CO concentrations (P _CO>1.6 bar), indicating that CO-rich synthesis gas can be used efficiently as an electron donor for biological sulfate reduction.     

Soil organic carbon and nutrient status in old-growth montane coniferous forest watersheds,Isla Chiloé, Chile

Montane temperate forests of the Cordillera de Piuchué Ecosystem Study, Isla Chiloé, Chile, are unaffected by air pollution, timber exploitation and agricultural clearing, and the current floristic assemblage has been relatively stable for the past 7500 years. The apparent absence of major perturbation at this location makes it an appropriate baseline site for ecosystem analysis. We measured soil bulk density, pH, soil organic C (SOC), total N, and NH₄Cl–exchangeable cations (Ca⁺², Mg⁺², K⁺, Na⁺, Al⁺³) in 0–10 and 10–40 cm depth samples from 72 soil profiles representing three vegetation zones: Fitzroya cupressoides Forest, Pilgerodendron uvifera–Tepualia stipularis Forest, and Magellanic Moorland. Fitzroya and Pilgerodendron–Tepualia Forests were indistinguishable for all measured soil characteristics (P > 0.05, Dunn's multiple comparison test on ranked data); these included very high median SOC concentrations (0–10 cm = 49.6%) and correspondingly low bulk density values (0–10 cm = 0.07). Moorland soil median values (0-10 cm) were significantly higher for bulk density (0.12) and lower for SOC (28.5%), but not for total N (Forests = 0.99%, Moorland = 0.95%), resulting in lower median C:N ratios for the moorland (Forests = 44.7; Moorland = 30.3). Across both depths and all three vegetation zones regression analysis indicated that SOC was an excellent predictor (R²; = 0.93, P < 0.001) of (exchangeable Ca⁺² + Mg⁺² + K⁺ + Na⁺). Comparison with other old growth montane environments indicates that the Fitzroya and Pilgerodendron–Tepualia soil profiles are characterized by C:N ratios typical of other relatively unpolluted conifer forest soils (33.0–49.3). Soil profiles of representative polluted montane conifer forests have lower C:N ratios (16.2–23.5). Organic horizons from representative polluted montane conifer forests also retain fewer exchangeable base cations per unit SOC than are retained by organic horizons from the Cordillera de Piuchué forests.     

Sources,bioavailability, and photoreactivity of dissolved organic carbon in the Sacramento–San Joaquin River Delta

We analyzed bioavailability, photoreactivity, fluorescence, and isotopic composition of dissolved organic carbon (DOC) collected at 13 stations in the Sacramento–San Joaquin River Delta during various seasons to estimate the persistence of DOC from diverse shallow water habitat sources. Prospective large-scale wetland restorations in the Delta may change the amount of DOC available to the food web as well as change the quality of Delta water exported for municipal use. Our study indicates that DOC contributed by Delta sources is relatively refractory and likely mostly the dissolved remnants of vascular plant material from degrading soils and tidal marshes rather than phytoplankton production. Therefore, the prospective conversion of agricultural land into submerged, phytoplankton-dominated habitats may reduce the undesired export of DOC from the Delta to municipal users. A median of 10% of Delta DOC was rapidly utilizable by bacterioplankton. A moderate dose of simulated solar radiation (286 W m⁻² for 4 h) decreased the DOC bioavailability by an average of 40%, with a larger relative decrease in samples with higher initial DOC bioavailability. Potentially, a DOC-based microbial food web could support ≤0.6 × 10⁹ g C of protist production in the Delta annually, compared to ≈17 × 10⁹ g C phytoplankton primary production. Thus, DOC utilization via the microbial food web is unlikely to play an important role in the nutrition of Delta zooplankton and fish, and the possible decrease in DOC concentration due to wetland restoration is unlikely to have a direct effect on Delta fish productivity.     

The turnover of river-transported iron,phosphorus and organic carbon in the Öre estuary,northern Sweden

The turnover of iron, phosphorus and organic carbon was followed in the Öre Estuary, northern Sweden, during the spring flood periods of 1989 and 1990. River-supplied material rapidly sediments out of the water column and is primary deposited within the estuary. The removal of iron and phosphorus is complete, with the calculated sedimentation exceeding the total amounts of particulate and dissolved iron and phosphorus supplied by the river. Aggregation of dissolved or colloidal iron-phosphate complexes due to increasing salinity and pH in combination with adsorption on rapidly sedimentating inorganic particles is suggested to explain this estuarine filter effect. Organic carbon is only affected by aggregation and sedimentation to a minor extent.     

Rangeomorphs,Thectardis (Porifera?) and dissolved organic carbon in the Ediacaran oceans

The mid-Ediacaran Mistaken Point biota of Newfoundland represents the first morphologically complex organisms in the fossil record. At the classic Mistaken Point localities the biota is dominated by the enigmatic group of "fractally" branching organisms called rangeomorphs. One of the few exceptions to the rangeomorph body plan is the fossil Thectardis avalonensis, which has been reconstructed as an upright, open cone with its apex in the sediment. No biological affinity has been suggested for this fossil, but here we show that its body plan is consistent with the hydrodynamics of the sponge water-canal system. Further, given the habitat of Thectardis beneath the photic zone, and the apparent absence of an archenteron, movement, or a fractally designed body plan, we suggest that it is a sponge. The recognition of sponges in the Mistaken Point biota provides some of the earliest body fossil evidence for this group, which must have ranged through the Ediacaran based on biomarkers, molecular clocks, and their position on the metazoan tree of life, in spite of their sparse macroscopic fossil record. Should our interpretation be correct, it would imply that the paleoecology of the Mistaken Point biota was dominated by sponges and rangeomorphs, organisms that are either known or hypothesized to feed in large part on dissolved organic carbon (DOC). The biology of these two clades gives insight into the structure of the Ediacaran ocean, and indicates that a non-uniformitarian mechanism delivered labile DOC to the Mistaken Point seafloor.     

Initial soil organic carbon stocks govern changes in soil carbon: Reality or artifact?

Changes in soil organic carbon (SOC) storage have the potential to affect global climate; hence identifying environments with a high capacity to gain or lose SOC is of broad interest. Many cross-site studies have found that SOC-poor soils tend to gain or retain carbon more readily than SOC-rich soils. While this pattern may partly reflect reality, here we argue that it can also be created by a pair of statistical artifacts. First, soils that appear SOC-poor purely due to random variation will tend to yield more moderate SOC estimates upon resampling and hence will appear to accrue or retain more SOC than SOC-rich soils. This phenomenon is an example of regression to the mean. Second, normalized metrics of SOC change—such as relative rates and response ratios—will by definition show larger changes in SOC at lower initial SOC levels, even when the absolute change in SOC does not depend on initial SOC. These two artifacts create an exaggerated impression that initial SOC stocks are a major control on SOC dynamics. To address this problem, we recommend applying statistical corrections to eliminate the effect of regression to the mean, and avoiding normalized metrics when testing relationships between SOC change and initial SOC. Careful consideration of these issues in future cross-site studies will support clearer scientific inference that can better inform environmental management.     

Ecosystem development and carbon cycle on a glacier foreland in the high Arctic, Ny-Ålesund, Svalbard

The Arctic terrestrial ecosystem is thought to be extremely susceptible to climate change. However, because of the diverse responses of ecosystem components to change, an overall response of the ecosystem carbon cycle to climate change is still hard to predict. In this review, we focus on several recent studies conducted to clarify the pattern of the carbon cycle on the deglaciated area of Ny-Ålesund, Svalbard in the high Arctic. Vegetation cover and soil carbon pools tended to increase with the progress of succession. However, even in the latter stages of succession, the size of the soil carbon pool was much smaller than those reported for the low Arctic tundra. Cryptogams contributed the major proportion of phytomass in the later stages. However, because of water limitation, their net primary production was smaller than that of the vascular plants. The compartment model that incorporated major carbon pools and flows suggested that the ecosystem of the later stages is likely to be a net sink of carbon at least for the summer season. Based on the eco-physiological characteristics of the major ecosystem components, we suggest several possible scenarios of future changes in the ecosystem carbon cycle.     

Dynamics of soil carbon,nitrogen, and phosphorus in calcareous soils after land-use abandonment – A chronosequence study

Aims

The objective of this study was to investigate changes in soil total organic C (TOC), total nitrogen (TN), phosphorus (P) fractions, and microbial community structure during secondary succession after abandonment of vineyards on calcareous soils.

Methods

Two chronosequences covering 200 years and differing in aspect and slope were established in Hungary, and the upper 10 cm of the mineral soils were studied.

Results

We found strong increases in TOC concentrations after land-use abandonment, especially at the south-exposed sites. The TOC/TN ratio increased by a factor of 1.3 in the south-west exposed chronosequence and by a factor of 1.6 in south exposed chronosequence. The concentration of labile P (NaHCO₃-extractable P) diminished during the first 50 years after land-use abandonment, leading to low P availability at the later stages of the succession. The total organic P (TOP) concentration increased during the first 40 years after abandonment. At the later stages of succession, TOP concentrations decreased again, while the ratio of TOC/TOP increased continuously over 200 years. The ratio of arbuscular-mycorrhizal-fungi-to-bacteria (AMF/bacteria) increased strongly during the first decade after abandonment of the vineyards.

Conclusions

Our study indicates that impacts of former cultivation on secondary ecosystems persisted for more than a century, and that especially P concentrations showed long lasting legacy effects.

     

Methane oxidation,biogenic carbon,and the IPCC’s emission metrics. Proposal for a consistent greenhouse-gas accounting

Purpose

The fifth assessment report by the IPCC includes methane oxidation as an additional indirect effect in the global warming potential (GWP) and global temperature potential (GTP) values for methane. An analysis of the figures provided by the IPCC reveals they lead to different outcomes measured in CO₂-eq., depending on whether or not biogenic CO₂ emissions are considered neutral. In this article, we discuss this inconsistency and propose a correction.

Methods

We propose a simple framework to account for methane oxidation in GWP and GTP in a way that is independent on the accounting rules for biogenic carbon. An equation with three components is provided to calculate metric values, and its application is tested, together with the original IPCC figures, in a hypothetical example focusing on GWP100.

Results and discussion

The hypothetical example shows that the only set of GWP100 values consistently leading to the same outcome, regardless of how we account for biogenic carbon, is the one proposed in this article. Using the methane GWP100 values from the IPCC report results in conflicting net GHG emissions, thus pointing to an inconsistency.

Conclusions

In order to consistently discriminate between biogenic and fossil methane sources, a difference of 2.75 kg CO₂-eq. is needed, which corresponds to the ratio of the molecular weights of CO₂ and methane (44/16). We propose to correct the GWP and GTP values for methane accordingly.

     

Indonesia’s blue carbon: a globally significant and vulnerable sink for seagrass and mangrove carbon

The global significance of carbon storage in Indonesia’s coastal wetlands was assessed based on published and unpublished measurements of the organic carbon content of living seagrass and mangrove biomass and soil pools. For seagrasses, median above- and below-ground biomass was 0.29 and 1.13 Mg C ha^?1 respectively; the median soil pool was 118.1 Mg C ha^?1. Combining plant biomass and soil, median carbon storage in an Indonesian seagrass meadow is 119.5 Mg C ha^?1. Extrapolated to the estimated total seagrass area of 30,000 km², the national storage value is 368.5 Tg C. For mangroves, median above- and below-ground biomass was 159.1 and 16.7 Mg C ha^?1, respectively; the median soil pool was 774.7 Mg C ha^?1. The median carbon storage in an Indonesian mangrove forest is 950.5 Mg C ha^?1. Extrapolated to the total estimated mangrove area of 31,894 km², the national storage value is 3.0 Pg C, a likely underestimate if these habitats sequester carbon at soil depths >1 m and/or sequester inorganic carbon. Together, Indonesia’s seagrasses and mangroves conservatively account for 3.4 Pg C, roughly 17 % of the world’s blue carbon reservoir. Continued degradation and destruction of these wetlands has important consequences for CO₂ emissions and dissolved carbon exchange with adjacent coastal waters. We estimate that roughly 29,040 Gg CO₂ (eq.) is returned annually to the atmosphere–ocean pool. This amount is equivalent to about 3.2 % of Indonesia’s annual emissions associated with forest and peat land conversion. These results highlight the urgent need for blue carbon and REDD+ projects as a means to stem the decline in wetland area and to mitigate the release of a significant fraction of the world’s coastal carbon stores.