Sequestration Response Research Articles

The effects of light intensity and temperature on the calcification rate of Halimeda macroloba

As a phototrophic organism the calcareous green alga Halimeda macroloba is considered an important source of primary production. These algae live in a range of environments and help sequester CO2 through photosynthesis and calcification in coastal marine ecosystems. This study examined the calcification rate of H. macroloba under various light (50, 500, 900, 1200 μmol photons m−2 s−1) and temperature (25, 30, 35 °C) conditions. The rates of calcification, photosynthetic inorganic carbon (Ci) uptake, and relative electron transport rate (rETR) were measured using alkalinity titration methods and pulse-amplitude modulated (PAM) fluorometry in an experimental setup based on observation data; additionally, a future climate change scenario was simulated. The light intensity of 500 μmol photons m−2 s−1 promoted high calcification and Ci uptake rates at all temperatures, with the highest rates at 25 °C. The very low light intensity of 50 μmol photons m−2 s−1 was not enough to stimulate plant photosynthesis and calcification. The rates of both calcification and Ci uptake were significantly lower at all temperatures when plants were subjected to a high irradiance of 1200 μmol photons m−2 s−1 than those in the other light conditions. Photosynthetic rETR seems to be dependent on light intensity, but might not reflect the high production of plants under intense light conditions. Finally, we discuss how Halimeda could contribute to CO2 sequestration in response to climate change.

Changes in Cholesterol Level Alter Integrin Sequestration in Raft-Mimicking Lipid Mixtures

The influence of cholesterol (CHOL) level on integrin sequestration in raft-mimicking lipid mixtures forming coexisting liquid-ordered (lo) and liquid-disordered (ld) lipid domains is investigated using complementary, single-molecule-sensitive, confocal detection methods. Systematic analysis of membrane protein distribution in such a model membrane environment demonstrates that variation of CHOL level has a profound influence on lo-ld sequestration of integrins, thereby exhibiting overall ld preference in the absence of ligands and lo affinity upon vitronectin addition. Accompanying photon-counting histogram analysis of integrins in the different model membrane mixtures shows that the observed changes of integrin sequestration in response to variations of membrane CHOL level are not associated with altering integrin oligomerization states. Instead, our experiments suggest that the strong CHOL dependence of integrin sequestration can be attributed to CHOL-mediated changes of lipid packing and bilayer thickness in coexisting lo and ld domains, highlighting the significance of a biophysical mechanism of CHOL-mediated regulation of integrin sequestration. We envision that this model membrane study may help clarify the influence of CHOL in integrin functionality in plasma membranes, thus providing further insight into the role of lipid heterogeneities in membrane protein distribution and function in a cellular membrane environment.

Corrigendum to: Effects of nitrogen addition on soil oxidisable organic carbon fractions in the rhizospheric and bulk soils of Chinese pines in north-western China

Increased atmospheric nitrogen (N) deposition caused by human activities has potentially important effects on ecosystem carbon (C) dynamics and different effects on C fractions with different stabilities and chemical compositions. A better understanding of the responses of different C fractions to N addition is vital for maintaining soil quality and protecting vegetation. In order to investigate the differential effects of N addition on total soil organic carbon (SOC) and four SOC fractions with increasing degrees of oxidisability in Pinus tabuliformis rhizospheric and bulk soils, a 6-year pot experiment was performed testing the effects of the addition of N at rates of 2.8, 5.6, 11.2, 22.4 and 44.8g m–2 year–1 compared with a control (CK) group (no N addition). Addition of N addition had significant (P–2 year–1. Low rates (N2.8–N5.6) of N addition considerably increased C4 and the ratio of C4 to TOC in the rhizosphere, whereas addition of high rates (N11.2–N44.8) of N decreased these parameters. The responses of C1 and C4 in the bulk soil to N addition were opposite. The SOC fraction was significantly higher in the rhizosphere than in the bulk soil, indicating large rhizospheric effects. However, increased N addition weakened these effects. These findings suggest that low rates (N2.8–N5.6) of N addition stabilise SOC against chemical and biological degradation, whereas increased rates of N addition increase the lability of SOC in the bulk soil. Thus, the rhizosphere plays a vital role in soil carbon stability and sequestration in response to N addition.

Redistribution of Different Organic Carbon Fractions in the Soil Profile of a Typical Chinese Mollisol with Land-Use Change

ABSTRACTSoil organic carbon (SOC) content depends significantly upon changes in land use and vegetation cover. This study aimed to examine the redistribution of whole soil OC, water-soluble OC (WSOC), and different density-separated OC fractions in soil profiles of 0–100 cm under different land uses and to elaborate the mechanism of C sequestration in response to the land use change. The land use types include maize plots with or without chemical fertilizer application (i.e., Maize-nitrogen, phosphorus, and potassium (NPK) and Maize-NF plots), plots with vegetation removed (No Vegetation), plots with grass (Grass), and alfalfa plant (Alfalfa). These plots used to be maize cropping system with NPK fertilizer for many years before 2003. Significant difference in SOC content generally occurred in soil layers of 0–40 cm among the different plots after 11 years of land-use change. Long-term continuous maize planting decreased SOC content; the significant SOC decrease occurred in Maize plot in the range of 9.3–23.4% for different soil layers compared with the initial soil sampled in 2003. In addition, SOC in Maize plot decreased by 3.6% and 8.5% at top two soil layers, respectively, in comparison with No Vegetation plot. The similar reduction of OC was observed in heavy OC fractions. The calculated sensitivity index for OC decreased in the order of light fraction > water-soluble fraction > the whole soil > heavy fraction. Therefore, the young and labile carbon fractions are much sensitive to land use change relative to the old and recalcitrant carbon fractions. This study indicated that land use changes led to a redistribution of SOC in soil profile, particularly at top soil layers, and conversion from arable land to natural grass cover or nitrogen-fixation plant cultivation such as alfalfa led to the enrichment of SOC at different depths of soil profile.

Effects of nitrogen addition on soil oxidisable organic carbon fractions in the rhizospheric and bulk soils of Chinese pines in north-western China

Increased atmospheric nitrogen (N) deposition caused by human activities has potentially important effects on ecosystem carbon (C) dynamics and different effects on C fractions with different stabilities and chemical compositions. A better understanding of the responses of different C fractions to N addition is vital for maintaining soil quality and protecting vegetation. In order to investigate the differential effects of N addition on total soil organic carbon (SOC) and four SOC fractions with increasing degrees of oxidisability in Pinus tabuliformis rhizospheric and bulk soils, a 6-year pot experiment was performed testing the effects of the addition of N at rates of 2.8, 5.6, 11.2, 22.4 and 44.8 g m–2 year–1 compared with a control (CK) group (no N addition). Addition of N addition had significant (P < 0.05) effects on SOC fractions of very labile C (C1) and recalcitrant C (C4), but negligible effects on total SOC (TOC) and SOC fractions of labile C (C2) and less labile C (C3). The C1 content and ratio of C1 to TOC in rhizospheres decreased following the addition of low levels (N2.8–N5.6) of N, but increased after the addition of high levels (N11.2–N44.8) of N, with minimum values obtained after the addition of 11.2 N g m–2 year–1. Low rates (N2.8–N5.6) of N addition considerably increased C4 and the ratio of C4 to TOC in the rhizosphere, whereas addition of high rates (N11.2–N44.8) of N decreased these parameters. The responses of C1 and C4 in the bulk soil to N addition were opposite. The SOC fraction was significantly higher in the rhizosphere than in the bulk soil, indicating large rhizospheric effects. However, increased N addition weakened these effects. These findings suggest that low rates (N2.8–N5.6) of N addition stabilise SOC against chemical and biological degradation, whereas increased rates of N addition increase the lability of SOC in the bulk soil. Thus, the rhizosphere plays a vital role in soil carbon stability and sequestration in response to N addition.

Carbon Sequestration Potential Promoted by Oxalate Extractable Iron Oxides through Organic Fertilization

Core Ideas Organic fertilization increased the oxalate extractable iron oxides. Oxalate extractable iron oxides contributed to soil organic carbon sequestration. Soil organic carbon from 20 to 40 cm was more labile than that from 0 to 20 cm. Oxalate extractable iron oxides preferentially preserved aromatic compounds. Carbon sequestration in paddy soils through organic fertilization is of great importance for soil quality improvement in subtropical Asia. This study explored the effect of oxalate extractable iron oxides (Feo) on soil organic carbon (SOC) sequestration in response to different fertilization treatments. Soil samples were collected from 0‐ to 10‐cm, 10‐ to 20‐cm, and 20‐ to 40‐cm depth intervals in June 2016 after a wheat (Triticum aestivum L.) harvest. This study involved five treatments: control with no fertilizer (CK), chemical fertilizer (NPK), 50% chemical fertilizer plus manure (NPKM), 100% chemical fertilizer plus straw (NPKS), and 30% chemical fertilizer plus manure organic‐inorganic compound fertilizer (NPKMOI). Organic fertilization significantly (P < 0.05) increased the SOC content and the Feo concentration compared with chemical fertilization alone. The specific C mineralization rate (SCMR, rate per unit SOC) increased with increasing soil depths, suggesting that SOC at the 20‐ to 40‐cm depth was more labile than that from 0 to 20 cm. The percentage of SOC present as microbial biomass carbon (MBC) was significantly (P < 0.001) positively correlated with SCMR, indicating that soil microorganisms influenced the potential SOC mineralization. Furthermore, the alternation of drying and wetting in paddy soils drives the biogeochemical cycles of iron and SOC, during which organic fertilization promotes the accumulation of Feo possibly by forming organo‐iron complexes as indicated by the higher Feo content in NPKM than in NPK. The Feo was significantly (P < 0.001) positively correlated with SOC and the percentage of aromatic C, indicating that Feo may play an important role in preserving SOC, especially the aromatic compounds. Therefore, the enhancement of Feo by organic fertilization, especially organic manure that is enriched in aromatic compounds, improved the SOC sequestration potential in the rice (Oryza sativa)–wheat rotation system.

Preventing Climate Change by Increasing Ocean Alkalinity

A recent paper in Reviews of Geophysics discussed increasing ocean alkalinity as an alternative method of carbon sequestration in response to climate change.

Annual climate variation modifies nitrogen induced carbon accumulation of Pinus sylvestris forests.

We report results from long-term simulated external nitrogen (N) input experiments in three northern Pinus sylvestris forests, two of moderately high and one of moderately low productivity, assessing effects on annual net primary production (NPP) of woody mass and its interannual variation in response to variability in weather conditions. Asigmoidal response of wood NPP to external N inputs was observed in the both higher and lower productivity stands, reaching a maximum of ~65% enhancement regardless of the native site productivity, saturating at an external N input of 4-5g N·m-2 ·yr-1 . The rate of increase in wood NPP and the N response efficiency (REN , increase in wood NPP per external N input) were maximized at an external N input of ~3g N·m-2 ·yr-1 , regardless of site productivity. The maximum REN was greater in the higher productivity than the lower productivity stand (~20 vs. ~14g C/gN). The N-induced enhancement of wood NPP and its REN were, however, markedly contingent on climatic variables. In both of the higher and lower productivity stands, wood NPP increased with growing season precipitation (P), but only up to ~400mm. The sensitivity of the response to P increased with increasing external N inputs. Increasing growing season temperature (T) somewhat increased the N-induced drought effect, whereas decreasing T reduced the drought effect. These responses of wood NPP infused a large temporal variation to REN , making the use of a fixed value unadvisable. Based on these results, we suggest that regional climate conditions and future climate scenarios should be considered when modeling carbon sequestration in response to N deposition in boreal P.sylvestris, and possibly other forests.

Carbon Sequestration in Response to Grassland–Shrubland–Turfgrass Conversions and a Test for Carbonate Biomineralization in Desert Soils, New Mexico, USA

Core Ideas Soil carbonate is typically viewed as a soil mineral that requires centuries to accumulate; our study indicates that it can be generated in months to years. If the source of Ca is directly from silicate minerals, soil carbonate could be managed to sequester atmospheric CO2. Carbon‐13 values can change in less than a decade for both soil organic and inorganic C. This study uses an experimental pedology approach using controls, treatments, and replications. This study uses an experimental pedology approach to examine (i) how the conversion of native C4 grassland to C3 woody shrubs then to irrigated C4 turfgrass affects both soil organic C (SOC) and soil inorganic C (SIC) and (ii) whether SIC can be enhanced by microbial biomineralization. Three sites were studied in the Chihuahuan Desert of New Mexico. At each site, SOC, SIC, and their δ13C values were measured on control soil samples and compared to samples treated with liquid growth medium and Ca(OH)2 at 10 and 40 cm. The treated samples were left to react for 1 mo in February, May, and August of 2014. Using a space‐for‐time substitution, soil organic C decreased when native grasslands converted to desert shrubs, then sharply increased after desert shrubs were converted to irrigated turfgrass. Most surprising, however, was the increase of SIC in the turfgrass site, which doubled in 6 yr. The δ13C values of both SOC and SIC reflected the change from C4 to C3 then back to C4 vegetation and showed how rapidly SOC and SIC can change their isotopic signatures. Soil inorganic C formation was slightly higher for the liquid growth medium, but no statistically significant differences were observed between the treatments and control samples. In addition, no biomineralization was observed with microscopy, perhaps because the 1‐mo reaction time was too short and the amount applied was too small. Although SIC is typically viewed as a soil mineral that requires centuries to accumulate, our study indicate that SIC can be generated in months to years if the soil environment is suitable.

Plant functional groups, grasses versus forbs, differ in their impact on soil carbon dynamics with nitrogen fertilization

Nitrogen (N) addition in N-limited grasslands often increases aboveground productivity, decreases species richness and leads to changes in species composition. In contrast to these consistant results in aboveground vegetation parameters, there is no consistant pattern in how N fertilization affects soil organic carbon (SOC) dynamics. Our objectives were to test how plant functional group changes caused by N fertilization affect soil C dynamics and determine if different plant functional groups respond similarly. We conducted a two-factorial experiment to examine soil C dynamics with N fertilization and soil inoculation with field microbial communities in a greenhouse pot experiment. We used six plant species (two grasses and four forbs) that are dominant within sub-alpine meadows on the east part of the Qinghai-Tibetan plateau. For both grasses and forbs, N fertilization and soil inoculation, alone or in combination, decreased SOC by 4–10% and increased soil microbial biomass. For grasses, N fertilization combined with inoculation caused much lower SOC content and higher soil microbial biomass carbon (MBC) as compared to inoculation alone. In contrast to forbs, grass aboveground biomass was significantly negatively correlated with SOC change and positively correlated with MBC change. Nitrogen fertilization combined with inoculation significantly increased basal respiration and cumulative C mineralization rates for both grasses and three of the four forbs as compared to inoculation alone. Grasses had higher basal respiration rates than forbs under these two treatments. Despite higher aboveground grass biomass, N-fertilization lowered the SOC pool by increasing soil MBC and basal respiration rates, thus increasing C decomposition. Overall, in these sub-alpine meadows, grasses and forbs impact on soil C dynamics differs and grasses, but not forbs, may reduce soil C sequestration in response to N fertilization.

Receptor sequestration in response to β-arrestin-2 phosphorylation by ERK1/2 governs steady-state levels of GPCR cell-surface expression

MAPKs are activated in response to G protein-coupled receptor (GPCR) stimulation and play essential roles in regulating cellular processes downstream of these receptors. However, very little is known about the reciprocal effect of MAPK activation on GPCRs. To investigate possible crosstalk between the MAPK and GPCRs, we assessed the effect of ERK1/2 on the activity of several GPCR family members. We found that ERK1/2 activation leads to a reduction in the steady-state cell-surface expression of many GPCRs because of their intracellular sequestration. This subcellular redistribution resulted in a global dampening of cell responsiveness, as illustrated by reduced ligand-mediated G-protein activation and second-messenger generation as well as blunted GPCR kinases and β-arrestin recruitment. This ERK1/2-mediated regulatory process was observed for GPCRs that can interact with β-arrestins, such as type-2 vasopressin, type-1 angiotensin, and CXC type-4 chemokine receptors, but not for the prostaglandin F receptor that cannot interact with β-arrestin, implicating this scaffolding protein in the receptor's subcellular redistribution. Complementation experiments in mouse embryonic fibroblasts lacking β-arrestins combined with in vitro kinase assays revealed that β-arrestin-2 phosphorylation on Ser14 and Thr276 is essential for the ERK1/2-promoted GPCR sequestration. This previously unidentified regulatory mechanism was observed after constitutive activation as well as after receptor tyrosine kinase- or GPCR-mediated activation of ERK1/2, suggesting that it is a central node in the tonic regulation of cell responsiveness to GPCR stimulation, acting both as an effector and a negative regulator.

Anthropogenic nitrogen deposition enhances carbon sequestration in boreal soils.

It is proposed that carbon (C) sequestration in response to reactive nitrogen (Nr ) deposition in boreal forests accounts for a large portion of the terrestrial sink for anthropogenic CO2 emissions. While studies have helped clarify the magnitude by which Nr deposition enhances C sequestration by forest vegetation, there remains a paucity of long-term experimental studies evaluating how soil C pools respond. We conducted a long-term experiment, maintained since 1996, consisting of three N addition levels (0, 12.5, and 50 kg N ha(-1) yr(-1) ) in the boreal zone of northern Sweden to understand how atmospheric Nr deposition affects soil C accumulation, soil microbial communities, and soil respiration. We hypothesized that soil C sequestration will increase, and soil microbial biomass and soil respiration will decrease, with disproportionately large changes expected compared to low levels of N addition. Our data showed that the low N addition treatment caused a non-significant increase in the organic horizon C pool of ~15% and a significant increase of ~30% in response to the high N treatment relative to the control. The relationship between C sequestration and N addition in the organic horizon was linear, with a slope of 10 kg C kg(-1) N. We also found a concomitant decrease in total microbial and fungal biomasses and a ~11% reduction in soil respiration in response to the high N treatment. Our data complement previous data from the same study system describing aboveground C sequestration, indicating a total ecosystem sequestration rate of 26 kg C kg(-1) N. These estimates are far lower than suggested by some previous modeling studies, and thus will help improve and validate current modeling efforts aimed at separating the effect of multiple global change factors on the C balance of the boreal region.

Predicting long‐term carbon sequestration in response to CO2 enrichment: How and why do current ecosystem models differ?

AbstractLarge uncertainty exists in model projections of the land carbon (C) sink response to increasing atmospheric CO2. Free‐Air CO2 Enrichment (FACE) experiments lasting a decade or more have investigated ecosystem responses to a step change in atmospheric CO2 concentration. To interpret FACE results in the context of gradual increases in atmospheric CO2 over decades to centuries, we used a suite of seven models to simulate the Duke and Oak Ridge FACE experiments extended for 300 years of CO2 enrichment. We also determine key modeling assumptions that drive divergent projections of terrestrial C uptake and evaluate whether these assumptions can be constrained by experimental evidence. All models simulated increased terrestrial C pools resulting from CO2 enrichment, though there was substantial variability in quasi‐equilibrium C sequestration and rates of change. In two of two models that assume that plant nitrogen (N) uptake is solely a function of soil N supply, the net primary production response to elevated CO2 became progressively N limited. In four of five models that assume that N uptake is a function of both soil N supply and plant N demand, elevated CO2 led to reduced ecosystem N losses and thus progressively relaxed nitrogen limitation. Many allocation assumptions resulted in increased wood allocation relative to leaves and roots which reduced the vegetation turnover rate and increased C sequestration. In addition, self‐thinning assumptions had a substantial impact on C sequestration in two models. Accurate representation of N process dynamics (in particular N uptake), allocation, and forest self‐thinning is key to minimizing uncertainty in projections of future C sequestration in response to elevated atmospheric CO2.

Terrestrial nitrogen–carbon cycle interactions at the global scale

Interactions between the terrestrial nitrogen (N) and carbon (C) cycles shape the response of ecosystems to global change. However, the global distribution of nitrogen availability and its importance in global biogeochemistry and biogeochemical interactions with the climate system remain uncertain. Based on projections of a terrestrial biosphere model scaling ecological understanding of nitrogen-carbon cycle interactions to global scales, anthropogenic nitrogen additions since 1860 are estimated to have enriched the terrestrial biosphere by 1.3 Pg N, supporting the sequestration of 11.2 Pg C. Over the same time period, CO2 fertilization has increased terrestrial carbon storage by 134.0 Pg C, increasing the terrestrial nitrogen stock by 1.2 Pg N. In 2001-2010, terrestrial ecosystems sequestered an estimated total of 27 Tg N yr(-1) (1.9 Pg C yr(-1)), of which 10 Tg N yr(-1) (0.2 Pg C yr(-1)) are due to anthropogenic nitrogen deposition. Nitrogen availability already limits terrestrial carbon sequestration in the boreal and temperate zone, and will constrain future carbon sequestration in response to CO2 fertilization (regionally by up to 70% compared with an estimate without considering nitrogen-carbon interactions). This reduced terrestrial carbon uptake will probably dominate the role of the terrestrial nitrogen cycle in the climate system, as it accelerates the accumulation of anthropogenic CO2 in the atmosphere. However, increases of N2O emissions owing to anthropogenic nitrogen and climate change (at a rate of approx. 0.5 Tg N yr(-1) per 1°C degree climate warming) will add an important long-term climate forcing.

Changes in Organic Matter Pools and Increases in Carbon Sequestration in Response to Surface Liming in an Oxisol under Long‐Term No‐Till

In a no‐till system (NTS) on naturally acidic soils, surface liming is essential to neutralize soil acidity and increases crop productivity. As a result, the soil organic matter (SOM) pools of the soil surface layers may change, reflecting increased C inputs by crop residues. The objective of this study was to quantify changes in SOM pools and the rate of C sequestration that occur in response to surface liming in a long‐term NTS experiment. The experiment was conducted in an Oxisol in southern Brazil. The treatments consisted of the application of 0 or 6 Mg ha−1 of dolomitic lime on the soil surface in 1993 and a reapplication of 0 or 3 Mg ha−1 of dolomitic lime in 2000 to plots with or without the previous lime application. Liming caused total organic C (TOC) accumulation, especially in the 0‐ to 2.5‐cm layer. The amount of TOC stored in the 20‐cm layer was 49.9, 52.9, 52.7, and 57.5 Mg ha−1 in the control, 6 + 0, 0 + 3, and 6 + 3 Mg ha−1 treatments, respectively. The levels of particulate organic C (POC) and mineral‐associated organic C (MAOC) in the SOM were also enhanced by liming. The increase in POC was directly related (R2 = 0.99, P = 0.002) to the accumulation of C from crop residues, which was greater in the plots receiving lime treatment. There were positive correlations between TOC and C extractable with hot water, total polysaccharides, and labile polysaccharides. The correlation analysis also demonstrated that TOC was more tightly correlated with POC than with MAOC, indicating a greater influence of the labile fraction on the increase in TOC with surface liming.

Amyloid-β Secretion, Generation, and Lysosomal Sequestration in Response to Proteasome Inhibition: Involvement of Autophagy

The proteasome is important for degradation of worn out and misfolded proteins. Decreased proteasome activity has been implicated in Alzheimer's disease (AD). Proteasome inhibition induces autophagy, but it is still unknown whether autophagy is beneficial or deleterious to AD neurons, as the autophagosome has been suggested as a site of amyloid-β (Aβ) generation. In this study, we investigated the effect of proteasome inhibition on Aβ accumulation and secretion, as well as the processing of amyloid-β protein precursor (AβPP) in AβPP(Swe) transfected SH-SY5Y neuroblastoma cells. We show that proteasome inhibition resulted in autophagy-dependent accumulation of Aβ in lysosomes, and increased levels of intracellular and secreted Aβ. The enhanced levels of Aβ could not be explained by increased amounts of AβPP. Instead, reduced degradation of the C-terminal fragment of AβPP (C99) by the proteasome makes C99 available for γ-secretase cleavage, leading to Aβ generation. Inhibition of autophagy after proteasome inhibition led to reduced levels of intracellular, but not secreted Aβ, and tended to further increase the C99 to AβPP ratio, supporting involvement of the autophagosome in Aβ generation. Furthermore, proteasome inhibition caused a reduction in cellular viability, which was reverted by inhibition of autophagy. Dysfunction of the proteasome could cause lysosomal accumulation of Aβ, as well as increased generation and secretion of Aβ, which is partly facilitated by autophagy. As a decrease in cellular viability was also detected, it is possible that upregulation of autophagy is an unsuccessful rescue mechanism, which instead of being protective, contributes to AD pathogenesis.

Minor stimulation of soil carbon storage by nitrogen addition: A meta-analysis

It is a well-established concept that nitrogen (N) limits plant growth and ecosystem production. However, whether N limits land carbon (C) sequestration – particularly in soil, the largest pool in the land – remains highly controversial. We conducted a meta-analysis to synthesize 257 studies published in the literature with 512 paired comparisons to quantify the changes of ecosystem C processes in response to N addition. Our results show that N addition significantly increased aboveground, belowground, and litter C pools by 35.7, 23.0, and 20.9%, respectively, across all the studies. Despite the substantial increases in C inputs from vegetation to soil system, N addition resulted in no significant change in C storage of both organic horizon and mineral soil in forests and grasslands, but a significant 3.5% increase in agricultural ecosystems, largely due to less contribution from aboveground production and increases in DOC and soil respiration. Thus, N stimulation of C storage primarily occurred in plant pools but little in soil pools. Moreover, N-induced change in soil C storage was positively related to changes in belowground production but not to those in aboveground growth. Our global synthesis also suggests that earth system models need to treat soil C inputs from aboveground and belowground sources differentially for soil C sequestration in response to N deposition and fertilization.

Soil carbon sequestration rates and associated economic costs for farming systems of south-eastern Australia

Soil organic carbon (C) sequestration rates based on the Intergovernmental Panel for Climate Change (IPCC) methodology were combined with local economic data to simulate the economic potential for C sequestration in response to conservation tillage in the six agro-ecological zones within the Southern Region of the Australian grains industry. The net C sequestration rate over 20 years for the Southern Region (which includes discounting for associated greenhouse gases) is estimated to be 3.6 or 6.3 Mg C/ha after converting to either minimum or no-tillage practices, respectively, with no-till practices estimated to return 75% more carbon on average than minimum tillage. The highest net gains in C per ha are realised when converting from conventional to no-tillage practices in the high-activity clay soils of the High Rainfall and Wimmera agro-ecological zones. On the basis of total area available for change, the Slopes agro-ecological zone offers the highest net returns, potentially sequestering an additional 7.1 Mt C under no-tillage scenario over 20 years. The economic analysis was summarised as C supply curves for each of the 6 zones expressing the total additional C accumulated over 20 years for a price per t C sequestered ranging from zero to AU$200. For a price of $50/Mg C, a total of 427 000 Mg C would be sequestered over 20 years across the Southern Region, <5% of the simulated C sequestration potential of 9.1 Mt for the region. The Wimmera and Mid-North offer the largest gains in C under minimum tillage over 20 years of all zones for all C prices. For the no-tillage scenario, for a price of $50/Mg C, 1.74 Mt C would be sequestered over 20 years across the Southern Region, <10% of the simulated C sequestration potential of 18.6 Mt for the region over 20 years. The Slopes agro-ecological zone offers the best return in C over 20 years under no-tillage for all C prices. The Mallee offers the least return for both minimum and no-tillage scenarios. At a price of $200/Mg C, the transition from conventional tillage to minimum or no-tillage practices will only realise 19% and 33%, respectively, of the total biogeochemical sequestration potential of crop and pasture systems of the Southern Region over a 20-year period.

Forest carbon sequestration changes in response to timber harvest

Forest succession contributes to the global terrestrial carbon (C) sink, but changes in C sequestration in response to varied harvest intensities have been debated. The forests of the Central Appalachian region have been aggrading over the past 100 years following widespread clear-cutting that occurred in the early 1900s and these forests are now valuable timberlands. This study compared the history of ecosystem C storage in four watersheds that have been harvested at different frequencies and intensities since 1958. We compared NPP, NEP, and component ecosystem C fluxes (g C m −2 year −1) in response to the four different harvest histories (no harvest, clear-cutting, single tree selection cutting, and 43 cm diameter-limit cutting). Clear-cutting had short-term negative effects on NEP but harvest did not significantly impact long-term average annual C sequestration rates. Average plant C (g C m −2) since 1950 was about 33% lower in response to a clear-cut event than plant C in an un-harvested forest, suggesting that the C sequestration associated with clear-cutting practices would decline over time and result in lower C storage than diameter-limit cut, selective cut, or un-harvested forests. Total C stored over a 55-year period was stimulated ∼37% with diameter-limit cutting and selective cutting relative to un-harvested forests.

Phenology of fine roots and leaves in forest and grassland

Summary 1 The phenology of temperate vegetation is advancing in association with climate warming. Most phenology data, however, comes from flowers and tree leaves. We tested the generality of results from shoot phenology by expanding data collection in two new directions. We related forest leaf phenology to root phenology, and to phenology in a second habitat, grassland. 2 We measured leaf and root phenology simultaneously in aspen forest and adjacent native grassland. Root growth accounts for 80–90% of productivity in these habitats. Seasonal variation in soil moisture and temperature were also measured. 3 Forest leaf production was greatest about 45 days before peak root production, resulting in a significant negative correlation between leaf and root production in forest. Grassland leaf production was greatest about 15 days before peak root production, and grassland leaf and root production were significantly positively correlated. The duration of root production was 40% greater than that of shoot production. 4 Forest leaf production increased significantly with increasing soil moisture, but not temperature. In contrast, the production of forest roots, grassland roots and grassland leaves increased significantly with soil temperature. 5 Synthesis. The most commonly measured aspect of phenology, forest leaves, is out of step with the majority of production in forest, as well as phenology in grassland. The invasion of grassland by woody vegetation is characterized by a decoupling of root and shoot phenology, a result that has not been reported previously. Given the global nature of woody plant encroachment, this decoupling may influence our general understanding of productivity and carbon sequestration in response to warming.