Carbon Accumulation Patterns Research Articles

Global patterns of organic carbon transfer and accumulation across the land–ocean continuum constrained by radiocarbon data

Radiocarbon (Δ14C) serves as an effective tracer for identifying the origin and cycling of carbon in aquatic ecosystems. Global patterns of organic carbon (OC) Δ14C values in riverine particles and coastal sediments are essential for understanding the contemporary carbon cycle, but are poorly constrained due to under-sampling. This hinders our understanding of OC transfer and accumulation across the land–ocean continuum worldwide. Here, using machine learning approaches and >3,800 observations, we construct a high-spatial resolution global atlas of Δ14C values in river–ocean continuums and show that Δ14C values of river particles and corresponding coastal sediments can be similar or different. Specifically, four characteristic OC transfer and accumulation modes are recognized: the old–young mode for systems with low river and high coastal sediment Δ14C values; the young–old and old–old modes for coastal systems with old OC accumulation receiving riverine particles with high and low Δ14C values, respectively; and the young–young mode with young OC for both riverine and coastal deposited particles. Distinguishing these modes and their spatial patterns is critical to furthering our understanding of the global carbon system. Specifically, among coastal areas with high OC contents worldwide, old–old systems are largely neutral to slightly negative to contemporary atmospheric carbon dioxide (CO2) removal, whereas young–old and old–young systems represent CO2 sources and sinks, respectively. These spatial patterns of OC content and isotope composition constrain the local potential for blue carbon solutions.

Spatial patterns of organic matter content in the surface soil of the salt marshes of the Venice Lagoon (Italy)

Abstract. Salt marshes are crucial eco-geomorphic features of tidal environments as they provide important ecological functions and deliver a wide range of ecosystem services. Being controlled by the interplay between hydrodynamics, geomorphology, and vegetation, the contribution of both organic matter (OM) and inorganic sediments drives salt marsh vertical accretion. This allows marshes to keep pace with relative sea level rise and likewise capture and store carbon, making them valuable allies in climate mitigation strategies. Thus, soil organic matter (SOM), i.e. the organic component of the soil, plays a key role within salt marsh environments, directly contributing to soil formation and supporting carbon storage. This study aims at inspecting spatial patterns of OM in surface salt marsh soils (top 20 cm), providing further insights into the physical and biological factors driving OM dynamics that affect salt marsh survival and carbon sink potential. Our results reveal two scales of variations in SOM content in marsh environments. At the marsh scale, OM variability is influenced by the interplay between surface elevation and changes in sediment supply linked with the distance from the marsh edge. At the system scale, OM content distribution is dominated by the gradient generated by marine and fluvial influence. The observed variations in SOM are explained by the combination of inorganic and organic input, preservation conditions, and sediment grain size. Our results highlight the importance of marshes as carbon sink environments, further emphasising that environmental conditions within a tidal system may generate strongly variable and site-specific carbon accumulation patterns, enhancing blue carbon assessment complexity.

To better detect drivers of peatland carbon accumulation rates and patterns

Abstract

Effects of late-Holocene fires on the carbon sequestration capacity of peatlands in the Sanjiang Plain

Peatland fires are frequent, but the effect of fire on soil organic carbon in peatlands is still currently variable. Especially at long time scales, it has not been clarified. In order to reveal the relationship between carbon accumulation patterns in peatlands at long time scales in response to local fire changes, high-resolution peat sediments from peatlands in the Three River Plain were selected and analysed for stratified charcoal debris and organic carbon in this paper. The results showed that the stronger carbon sequestration capacity in the periods of 0.6, 0.75, 1.25, 2.3, 2.75, 2.9, 3.6 and 5 ka BP corresponded to weaker fire intensity or even no fire. Late-Holocene fires in the Sanjiang Plain reduced the rate of carbon sequestration, suggesting that fires have been an important driver of the reduction in carbon sequestration capacity over the last 6000 years.

Spatially varying peatland initiation, Holocene development, carbon accumulation patterns and radiative forcing within a subarctic fen

High latitude peatlands act as globally important carbon (C) sinks and are in constant interaction with the atmosphere. Their C storage formed during the Holocene. In the course of time, the aggregate effect of the C fluxes on radiative forcing (RF) typically changes from warming to cooling, but the timing of this shift varies among different peatlands. Here we investigated Holocene peatland development, including vegetation history, vertical peat growth and the lateral expansion of a patterned subarctic fen in northern Finland by means of multiple sampling points. We modelled the Holocene RF by combining knowledge on past vegetation communities based on plant macrofossil stratigraphies and present in situ C flux measurements. The peatland initiated at ca. 9500 calibrated years Before Present (cal yr BP), and its lateral expansion was greatest between ca. 9000 and 7000 cal yr BP. After the early expansion, vertical peat growth proceeded very differently in different parts of the peatland, regulated by internal and external factors. The pronounced surface microtopography, with high strings and wet flarks, started to form only after ca. 1000 cal yr BP. C accumulation within the peatland recorded a high degree of spatial variability throughout its history, including the recent past. We applied two flux scenarios with different interpretation of the initial peatland development phases to estimate the RF induced by C fluxes of the fen. After ca. 4000 cal yr BP, at the latest, the peatland RF has been negative (cooling), mainly driven by C uptake and biomass production, while methane emissions had a lesser role in the total RF. Interestingly, these scenarios suggest that the greatest cooling effect took place around ca. 1000 cal yr BP, after which the surface microtopography established. The study demonstrated that despite the high spatial heterogeneity and idiosyncratic behaviour of the peatland, the RF of the studied fen followed the general development pattern of more southern peatlands. Holocene climate variations and warm phases did not seem to induce any distinctive and consistent peatland-scale patterns in C accumulation, whereas our data suggests that the changes in vegetation related to autogenic succession were reflected in the C accumulation patterns and RF more clearly.

Mapping forest age and characterizing vegetation structure and species composition in tropical dry forests

Land use changes generate a mosaic of forest patches with different ages of abandonment (i.e. succession) intermingled with other land uses. Mapping the successional age of vegetation is crucial to understand carbon accumulation patterns and the recovery of vegetation structure, diversity, and composition of forests over time. The overall objective of this research was to produce maps portraying secondary vegetation age classes and to assess how successional age classes can be related to vegetation structure, diversity and composition in two types of tropical dry forests (TDF) in the Yucatan Peninsula. We used a two-stage image classification process. First, SPOT-5 imagery were segmented and then classified using a Random Forests method. Second, the classified images were post-processed to rectify any classification errors. Additionally, we evaluated the association between the different forest age classes and vegetation structure, species richness and composition using a separate Random Forests classification of field plot data. Post-processing improved the accuracy of the Random Forests classifications by 14.19% and 16.28% for the tropical semi-deciduous and semi-evergreen forests, to attain final accuracy values of 91% and 88.37%, respectively. Vegetation structure, richness and composition were all strongly associated with successional age, accounting for 77.7% and 84.7% of the total variation among forest age classes for the tropical semi-deciduous and semi-evergreen forests respectively. Therefore, the forest age maps obtained can be related to attributes of vegetation structure, diversity and composition that are useful for biodiversity conservation, forest management and climate change mitigation.

Biomass carbon accumulation patterns throughout stand development in primary uneven-aged forest driven by mixed-severity natural disturbances

Accurate estimations of changes in the forest carbon (C) pools over time are essential for predicting the future forest C balance and its part in the global C cycle. While the overall understanding of global forest C dynamics has improved, some significant forest ecosystem processes have been largely overlooked, resulting in possible biases. As an example, the effects of low and moderate severity disturbances have received disproportionately little attention. In this study, we use an extensive database of 9610 tree increment cores from 400 plots in primary uneven-aged Norway spruce (Picea abies) forests in the Carpathian Mountains, to explore the dynamics of live and dead wood C after disturbance. The data represents a chronosequence of more than 250 years since disturbance, varying highly in severity. We found that disturbance severity had a substantial impact on the post-disturbance long-term accumulation of C. Initially, live tree C accumulated at a similar rate independent of disturbance severity. However, the increase in C leveled off earlier after low disturbance severity while the most heavily disturbed forests continued to accumulate C to the latest stages of stand development. These results stress the importance of taking disturbance severity into account when predicting the long-term dynamics of C storage in forests under climate change. The results also highlight the importance of these forests as significant C pools. If harvested and turned into managed forest they would not reach their maximum C storing capacity.

Spatial distribution patterns of annual soil carbon accumulation and carbon storage in the Jiuduansha wetland of the Yangtze River estuary.

Wetlands are important carbon (C) pools for terrestrial ecosystems, and C stored in different types of wetlands accounts for about 30% of total terrestrial C. As one of the most important ecological barriers in Shanghai, with functions of climate regulation, interception, and purification, and as a C sink, the Jiuduansha wetland has received research attention. However, little research has been done on the spatial differences in amount of average annual net C accumulation and C storage of each shoal: Jiangya Nansha, Shangsha, and Zhongxiasha. In this study, plant biomass, plant organic C, soil respiration, soil organic C content, and soil bulk density of different vegetation zones in the three shoals were analyzed to determine the spatial variability of annual net C accumulation capability and soil organic C storage of the Jiuduansha wetland. The results showed that the Zhongxiasha shoal played the most important role as a C sink, and it accumulated 77,839.44 t organic C per year. Regarding the annual C accumulation capacity per unit area, the Phragmites communis zone was higher than for all other vegetation zones, indicating that P. communis had the greatest C accumulation capacity. 7835.38 t, 46,827.41 t, and 173,623.1 t of organic C were stored in the Jiangya Nansha, Shangsha, and Zhongxiasha shoals, respectively. The C storage in soil was closely related to annual C accumulation, and there were two main reasons for the difference of spatial pattern of annual C accumulation: biomass and properties of plants and the properties of tidal water.

Potential Biomass Production Estimation of Wood Energy Species in Post Mining Reclamation Area Using CO2FIX Model

One of the many potential uses of post-mining reclaimed land is for growing trees to use as a source of energy through their biomass. CO2FIX is a computer simulation model and can be used to estimate the production of biomass and carbon accumulation pattern of a wooden stand. The purpose of this research was to simulate biomass production of five wood energy species currently grown in the post-coal mining reclamation area at South Kalimantan, i.e. Paraserianthes falcataria, Senna siamea, Samanea saman, Peronema canescens, and Vitex pinnata. The CO2FIX model firstly parameterized for application on the study area. The data used for parameterization gathered through literature studies and field measurements. The result indicates that the parameterized CO2FIX model could realistically simulate the growth pattern of five wood energy species grown in post-mining reclaimed land. Next, the model was used to simulate the growth of five energy wood species in the following setting: monoculture planting, 3 x 3 m planting distance, and 20 years simulation. Total of biomass in descending order shown by the stand of Senna siamea (639.35 MgDM/ha), Paraserianthes falcataria (555.52 MgDM/ha), Samanea saman (385.77 MgDM/ha), Peronema canescens (297.71 MgDM/ha), and Vitex pinnata (219.42 MgDM/ha), respectively.

Evidence for a non-linear carbon accumulation pattern along an Alpine glacier retreat chronosequence in Northern Italy.

BackgroundThe glaciers in the Alps, as in other high mountain ranges and boreal zones, are generally retreating and leaving a wide surface of bare ground free from ice cover. This early stage soil is then colonized by microbes and vegetation in a process of primary succession. It is rarely experimentally examined whether this colonization process is linear or not at the ecosystem scale. Thus, to improve our understanding of the variables involved in the carbon accumulation in the different stages of primary succession, we conducted this research in three transects on the Matsch glacier forefield (Alps, N Italy) at an altitude between 2,350 and 2,800 m a.s.l.MethodsIn three field campaigns (July, August and September 2014) a closed transparent chamber was used to quantify the net ecosystem exchange (NEE) between the natural vegetation and the atmosphere. On the five plots established in each of the three transects, shading nets were used to determine ecosystem response function to variable light conditions. Ecosystem respiration (Reco) and gross ecosystem exchange (GEE) was partitioned from NEE. Following the final flux measurements, biometric sampling was conducted to establish soil carbon (C) and nitrogen (N) content and the biomass components for each transect.ResultsA clear difference was found between the earlier and the later successional stage. The older successional stages in the lower altitudes acted as a stronger C sink, where NEE, GEE and Reco were significantly higher than in the earlier successional stage. Of the two lower transects, the sink capacity of intermediate-succession plots exceeded that of the plots of older formation, in spite of the more developed soil. Total biomass (above- and belowground) approached its maximum value in the intermediate ecosystem, whilst the later stage of succession predominated in the corresponding belowground organic mass (biomass, N and C).OutlookWe found that the process of carbon accumulation along a glacier retreat chronosequence is not linear, and after a quite rapid increase in carbon accumulation capacity in the first 150 years, in average 9 g C m−2 year−1, it slows down, taking place mainly in the belowground biomass components. Concurrently, the photosynthetic capacity peaks in the intermediate stage of ecosystem development. If confirmed by further studies on a larger scale, this study would provide evidence for a predominant effect of plant physiology over soil physical characteristics in the green-up phase after glacier retreat, which has to be taken into account in the creation of scenarios related to climate change and future land use.

CO2 fertilization plays a minor role in long-term carbon accumulation patterns in temperate pine forests in the southwestern Pyrenees

Isolating the long-term fertilization effect of CO2 from other climate- and site-related effects on tree growth has been proven a challenging task. To isolate long-term effects of [CO2] on water use efficiency at ecosystem level, we used the FORECAST Climate forest model, calibrated for Scots pine (Pinus sylvestris L.) forests in the southwestern Pyrenees, growing at a Mediterranean montane site and at a continental subalpine site. Future climate scenarios (RCP 4.5 and RCP 8.5) were generated using a battery of six climate models to estimate daily values of temperature and precipitation in a 90-year series. A factorial experiment was designed to disentangle the importance on C pools of three growing limiting factors (nitrogen limitation, climate (temperature + precipitation) limitation and atmospheric CO2 concentration). The relative importance of each factor was quantified by comparing the scenario with the limitation of each individual factor turned on with the non-limitation scenario. Positive CO2 fertilization due to improvement in water use efficiency was detected by the model, but its quantitative impact improving tree growth was minimum: its average increase in ecosystem C pools ranged from 0.3 to 0.9%. At the site with cooler climate conditions (continental), the main limitation for tree growth was climate. Such limitation will be reduced under climate change and the ecosystem will store more carbon. At the site with milder climate conditions (Mediterranean), N availability was the main limiting factor albeit modulated by water availability. Such limitation could be reduced under climate change as N cycling could accelerate (higher litterfall production and decomposition rates) but also increase if droughts become more frequent and severe. In addition, the magnitude of the uncertainty related to climate model selection was much more important than CO2 fertilization, indicating that atmospheric processes are more important than tree physiological processes when defining how much carbon could be gained (or lost) in forests under climate change. In conclusion, due to the small changes in forest C pools caused by variation of atmospheric CO2 concentrations compared to changes caused by other growth limiting factors (nutrients, climate), reducing uncertainty related to climate projections seems a more efficient way to reduce uncertainty in tree growth projections than increasing forest model complexity.

Hydroclimatic variations reveal differences in carbon capture in two sympatric conifers in northern Mexico.

BackgroundForest ecosystems are considered among the largest terrestrial carbon sinks. The dynamics of forest carbon depend on where the carbon is stored and its responses to environmental factors, as well as the physiology of the trees. Thus, threatened forest regions with high biodiversity have great scientific importance, such as the Sierra Madre Occidental in Mexico. A comparative analysis of tree species can expand the knowledge of the carbon cycle dynamics and ecological processes in this region. Here, we examined the growth, wood density, and carbon accumulation of two threatened species (Pseudotsuga menziesii and Cupressus lusitanica) to evaluate their hydroclimatic responsiveness.MethodsThe temporal variations in the carbon accumulation patterns of two co-occurring species (P. menziesii and C. lusitanica) and their sensitivity to the local climate were studied using dendroecological techniques, X-ray densitometry, and allometric equations.ResultsThe results show that the annual carbon accumulation in C. lusitanica is positively associated with the temperature during the current fall, while the carbon accumulation in P. menziesii is correlated with the rainfall during the winter of the previous year. The climatic responses are associated with the intra-annual variations of wood density and ring widths for each species. The ring width was strongly correlated with carbon accumulation in C. lusitanica, while the mean wood density was linked to carbon accumulation in P. menziesii.DiscussionThis study has implications for the carbon accumulation rates of both species, revealing differences in the carbon capture patterns in response to climatic variations. Although the species coexist, there are variation in the hydroclimatic sensitivity of the annual carbon sequestered by trunks of trees, which would be associated with tree-ring width and/or wood density, i.e., directly by anatomical features. The results are relevant to analyze the response to the variability of climatic conditions expected in the near future of the tree communities of Sierra Madre Occidental. Therefore, this study provides a basis for modeling the long-term carbon budget projections in terrestrial ecosystems in northern Mexico.

Estimation of forest litter fractions by regression analysis in different aged stands of Pinus nigra

SUMMARY: Forest litter (FL) carbon accumulation patterns can be predicted by certain tree and stand parameters to assess how variably managed forests may accumulate carbon. The aim of our study was to use tree stand data to refine methods to predict the composition of FL fragments in temperate, semi-humid black pine forests (Pinus nigra) in western Anatolia, Turkey. Predictive models were established between FL fractions (fine fragments of 4 mm and coarse woody debris of branches 5 cm, cones and bark) and tree parameters (stand age, tree height, diameter at breast height, tree basal area, tree density, lowest tree crown height and tree crown thickness). We sampled 105 stands of ages 100 years, that were distributed at 5 altitudinal steps (500 to 1,750 m). A multi-regression analysis was used to estimate FL fraction for different-age stands. Total FL dry biomass varied from 18 to 213 Mg/ha (average: 94 Mg/ha). The fine fragment fraction (> 4 mm) represented the largest proportion of FL (36 %). Coarse woody debris amounted for 6.6-7.8 % of the FL and branches < 5 cm accounted for the highest proportion (12.4-26.4 %) of coarse woody debris. The most influential parameters predicting FL fragment proportions included dry branch thickness, thinning rate, height and age (R2: 0.11 to 0.67). The combination of long-term observation and fine and coarse litter trapping methods should improve the estimation rates of sequestered carbon in forest ecosystems.

Biomass carbon density in natural oak forests with different climate conditions and stand ages in northwest China

ABSTRACTOak forests are major communities in warm temperate forests in northern China. The dependence of biomass carbon accumulation and allocation patterns in above- and belowground on climate and stand age remains unclear. To quantitatively investigate the influence of temperature, precipitation, and stand age on the biomass carbon density (BCD) of each component in the forest and on the above/belowground allocation, field surveys were conducted at 32 plots with dimensions of 20 m × 50 m representing different ages and environmental conditions of natural oak secondary forests. Tree biomass was estimated using allometric biomass equations based on tree height and diameter at breast height (DBH). Biomass of shrubs, herbs, and litter was estimated by harvesting all the components. Carbon concentrations of all the plant components and litter were measured. Biomass carbon densities of trees and total ecosystems increased with increases in precipitation and stand age, but did not differ significantly with changes in air temperature. The ratio of above/belowground BCD showed significant positive correlation with stand age. Understory layers (shrubs and herbs) BCD showed positive relationships with precipitation, but had no obvious relations with stand age and temperature. BCD in litter layer decreased with increasing precipitation and had no definite variation trend along temperature and stand age gradients. The influence of precipitation on plant growth is greater than that of temperature in the forests. These findings indicate that water availability is the dominant environmental factor across these sub-humid climate sites.

The role of hydrodynamic sorting on the accumulation and distribution of organic carbon in an impoundment: Englebright Lake, California, USA

The global proliferation of dams is one of the most significant anthropogenic impacts on the environment, resulting in the trapping of massive loads of sediment and nutrients in impoundments. Few studies, however, have examined these impounded sediments to understand patterns of organic carbon (OC) accumulation and the effects of watershed processes on carbon delivery. This study measured total organic carbon (TOC) and stable isotopes of carbon and nitrogen (δ13C and δ15N) in Englebright Lake, CA to relate changes in OC sources and TOC accumulation to natural and anthropogenic events in the watershed and to depositional processes in the lake. Englebright Lake is a representative system for impoundments in small, mountainous rivers, and anthropogenic disturbances in the watershed caused high sediment accumulation rates in the lake. Throughout its 60-year history, 0.35 Tg OC has been trapped behind Englebright Dam and δ13C signatures indicate that more than 50% of the OC in Englebright Lake was derived from terrigenous sources. TOC content ranged from 0.03 to 30.24% of dry weight, and differed across depositional regimes; TOC content in topset deposits (0.35 ± 0.58%) was less than in foreset (2.64 ± 5.95%) and bottomset (1.51 ± 1.41%) deposits (p < 0.001) and TOC accumulation associated with flood events was higher (up to 231 kgOC m−2 year−1) than during non-event periods (0.2 to 39 kgOC m−2 year−1). TOC accumulation rates in Englebright Lake were up to an order of magnitude higher than previous estimates of OC burial in California impoundments. As the number and size of dams continues to expand worldwide, the storage of TOC in impoundments will likely add to the growing number of anthropogenic modifications to the global carbon cycle.

Controls on carbon storage and weathering in volcanic soils across a high-elevation climate gradient on Mauna Kea, Hawaii.

Volcanic ash soils retain the largest and most persistent soil carbon pools of any ecosystem. However, the mechanisms governing soil carbon accumulation and weathering during initial phases of ecosystem development are not well understood. We examined soil organic matter dynamics and soil development across a high-altitude (3,560-3,030m) 20-kyr climate gradient on Mauna Kea in Hawaii. Four elevation sites were selected (~250-500mm rainfall), which range from sparsely vegetated to sites that contain a mix of shrubs and grasses. At each site, two or three pits were dug and major diagnostic horizons down to bedrock (intact lava) were sampled. Soils were analyzed for particle size, organic C and N, soil pH, exchangeable cations, base saturation, NaF pH, phosphorous sorption, and major elements. Mass loss and pedogenic metal accumulation (hydroxlamine Fe, Al, and Si extractions) were used to measure extent of weathering, leaching, changes in soil mineralogy and carbon accumulation. Reactive-phase (SRO) minerals show a general trend of increasing abundance with increasing rainfall. However carbon accumulation patterns across the climate gradient are largely decoupled from these trends. The results suggest that after 20kyr, pedogenic processes have altered the nature and composition of the volcanic ash such that it is capable of retaining soil C even where organic acid influences from plant material and leaching from rainfall are severely limited. Carbon storage comparisons with lower-elevation soils on Mauna Kea and other moist mesic (2,500mm rainfall) sites on Hawaii suggest that these soils have reached only between 1% and 15% of their capacity to retain carbon. Our results suggest that, after 20 kyr in low rainfall and a cold climate, weathering was decoupled from soil carbon accumulation patterns and the associated influence of vegetation on soil development. Overall, we conclude that the rate of carbon supply to the subsoil (driven by coupling of rainfall above ground plant production) is a governing factor of forms and amount of soil organic matter accumulation, while soil mineralogy remained relatively uniform.

Impact of Restoration and Management on Aggregation and Organic Carbon Accumulation in Urban Grasslands

Core Ideas Few studies have examined SOC accrual in restored urban grasslands. We examined SOC accrual in 14 restored and native grasslands in Chicago. Short‐term (&lt;7 yr) restoration increased microaggregate OC toward levels in native prairies. Longer‐term restoration did not improve total SOC or aggregate OC. Differences in SOC were linked to soil moisture, N, texture, and inputs of C4–C among sites. Understanding the patterns of soil organic carbon (SOC) accumulation in restored grasslands is necessary to determine their potential to sequester atmospheric CO2. Patterns of SOC accrual after grassland restorations are generally based on studies in former agricultural fields, and these studies show an increase in SOC and aggregated‐associated OC over time. In this study, we quantified SOC accrual in a series of restored grasslands situated within the matrix of the Chicago metropolitan region. Soil samples were collected from unmanaged (no restoration), short‐term (&lt;7 yr), and longer‐term restorations (&gt;10 yr) and from native prairie remnants located on Mollisols or Alfisols and analyzed using a combination of physical fractionation (aggregate size) and chemical measurements (organic C [OC], 13C/12C natural abundance). We found that (i) total SOC declined after restoration and remained significantly lower in restored than unmanaged soils, (ii) patterns of aggregate OC in longer‐term restorations were more similar to those in unmanaged than to prairie sites, and (iii) microaggregate OC levels and C4–C inputs into aggregate fractions were significantly higher in short‐ than longer‐term restorations. Thus, an increasing time under management did not enhance SOC accrual. For all sites, path models showed that SOC accrual was correlated with soil N, texture, and moisture, whereas C4–C inputs were significant model terms only in short‐term restorations and prairie sites. Taken together, these results indicate the need to consider inter‐relationships among vegetation and soil factors as influences on SOC accrual rather than simply time under management.

Potentilla fruticosa has a greater capacity to translocate phosphorus from the lower to upper soils than herbaceous grasses in an alpine meadow

Potentilla fruticosa is widely distributed in the Northern hemisphere; however, its effect on soil properties in the ecosystems is unknown. We examined the effects of P. fruticosa (a key shrub in the system) on soil organic carbon (SOC) and nutrient accumulation patterns in an alpine meadow on the Qinghai–Tibetan Plateau. In a flat area (about 1200×400m), we extensively sampled aboveground and belowground biomasses, litter accumulation and soils in P. fruticosa and herbaceous plant patches. We also intensively sampled soils down to 1m depth along a 24-m transect that crossed through alternating P. fruticosa and herbaceous plant patches. The aboveground biomass, litter accumulation and root biomass down to 0.5m depth were all significantly greater under P. fruticosa than herbaceous plants. SOC, total nitrogen (N) and phosphorus (P) across 0–0.1, 0.1–0.2 and 0.2–0.3m soil layers were 12%, 17% and 9% greater, respectively, under the P. fruticosa than herbaceous plants. Soil N and P availability in the upper layers was also greater under P. fruticosa than under the herbaceous plants. The intensive sampling revealed that the increases in SOC and total N below P. fruticosa, relative to the herbaceous plant patches, occurred down to 0.8m depth. However, the higher total P concentrations in the upper soils under P. fruticosa occurred at the expense of lower levels of P in the deeper soil layers. Along the 24-m transect, SOC, total N and inorganic N storage in the 1m soil depth increased when P. fruticosa was present; however, total and available P storage fluctuated in the opposite pattern, decreasing when P. fruticosa was present. This indicated that during the succession of the community, greater SOC and N accumulation versus a depletion in P in the top 1-m soil layer occurred under P. fruticosa, compared to under the herbaceous plants. We concluded that there was heterogeneity in the soil nutrient resources that was associated with P. fruticosa patches in the alpine meadows. P. fruticosa had a greater capacity to translocate P from the lower to the upper soils than the herbaceous plants.

Carbon dynamics of peatlands in China during the Holocene

Understanding the responses of the carbon-rich peatland ecosystems to past climate change is crucial for predicting peat carbon fate in the future. Here we presented a data synthesis of peatland initiation ages, area changes, and peat carbon (C) accumulation rate variations in China since the Holocene, along with total C pool estimates. The data showed different controls of peatland expansion and C accumulation in different regions. The peat C accumulation rates were 32.3 (ranging from 20.7 to 50.2) g C m−2 yr−1 in the Qinghai-Tibetan Plateau (QTP) and 14.7 (ranging from 7.4 to 36.5) g C m−2 yr−1 in the Northeast China (NEC). The peaks of peatland expansion and C accumulation in the QTP occurred in the early Holocene in response to high summer insolation and strong summer-winter climate seasonality. The rapid peatland expansion and maximum C accumulation rate in the NEC occurred in the middle-late Holocene. Peatlands scattered in the coastal and lakeside regions of China expanded rapidly at the onset of the Holocene due to large transgression, consistent with the stronger summer insolation and monsoon, and during the middle and late Holocene, as a response to the high and stable sea level and the strong summer monsoon. The carbon storage of peatlands in China was estimated as 2.17 (ranging from 1.16 to 3.18) Pg, among which 1.49 (ranging from 0.58 to 2.40) Pg was contributed by peatlands in the QTP, 0.21 (ranging from 0.11 to 0.31) Pg by those in the NEC, and 0.47 Pg by those scattered in other regions of China. Our comparison of peatlands dynamics among regions in China showed that climate and monsoon are the essential factors in determining the expansion and carbon accumulation patterns of peatlands, although their effects on peatland formation and C accumulation is complex owing to land availability in peatland basins and regional moisture conditions.

Continental fens in western Canada as effective carbon sinks during the Holocene

Here, we present results of Holocene carbon accumulation from seven new peat cores at four fen sites from Alberta, western Canada. Along with two other published fen records in the same region, we provide a regional synthesis of carbon accumulation patterns, as well as peat property data in this continental climate. On the basis of &gt;3000 peat sample measurements at 1-cm intervals, organic matter content in peat samples is on average at 91.0% (±9.3% in SD) and ash-free bulk density at 0.141 g/cm3 (±0.045 g/cm3 in SD) with a range of 0.018–0.381 g/cm3. On the basis of 109 radiocarbon age determinations from these cores, the overall mean carbon accumulation rate at these fens since 9 kyr (1 kyr = 1000 cal. yr BP) is 32.5 g C/m2/yr, which is much higher than the northern peatland average of 18.6–22.9 g C/m2/yr from large-scale syntheses. The ‘instantaneous’ apparent carbon accumulation rates from all these individual measurements at mostly 1-cm intervals are highly variable throughout the Holocene, ranging from 6 to 504 g C/m2/yr. The carbon accumulation rates appear to show peak values at 8.3, 6.8, 5.3, 3.8, 2.7, and 1.1 kyr, suggesting a ~1500-year periodicity in carbon accumulation, possibly in response to Holocene climate change. Furthermore, carbon accumulation shows a gradual declining trend from 7 to 2 kyr, reaching a minimum at 2 kyr, likely in response to neoglacial climate cooling during the later part of the Holocene in the high-latitude regions. Overall, these fens accumulated and store on average 264 kg C/m2 during the Holocene, among the highest soil carbon storage reported from terrestrial ecosystems. Our results, along with previous global and regional syntheses, suggest that in contrast to conventional wisdom, fens in continental climates accumulate peat at similar or greater rates than do bogs in oceanic climates.