Reconciling Negative Soil CO2 Fluxes: Insights from a Large-Scale Experimental Hillslope

Soil fluxes of CO2 (Fs) have long been considered unidirectional, reflecting the predominant roles of metabolic activity by microbes and roots in ecosystem carbon cycling. Nonetheless, there is a growing body of evidence that non-biological processes in soils can outcompete biological ones, pivoting soils from a net source to sink of CO2, as evident mainly in hot and cold deserts with alkaline soils. Widespread reporting of unidirectional fluxes may lead to misrepresentation of Fs in process-based models and lead to errors in estimates of local to global carbon balances. In this study, we investigate the variability and environmental controls of Fs in a large-scale, vegetation-free, and highly instrumented hillslope located within the Biosphere 2 facility, where the main carbon sink is driven by carbonate weathering. We found that the hillslope soils were persistent sinks of CO2 comparable to natural desert shrublands, with an average rate of −0.15 ± 0.06 µmol CO2 m2 s−1 and annual sink of −56.8 ± 22.7 g C m−2 y−1. Furthermore, higher uptake rates (more negative Fs) were observed at night, coinciding with strong soil–air temperature gradients and [CO2] inversions in the soil profile, consistent with carbonate weathering. Our results confirm previous studies that reported negative values of Fs in hot and cold deserts around the globe and suggest that negative Fs are more common than previously assumed. This is particularly important as negative Fs may occur widely in arid and semiarid ecosystems, which play a dominant role in the interannual variability of the terrestrial carbon cycle. This study contributes to the growing recognition of the prevalence of negative Fs as an important yet, often overlooked component of ecosystem C cycling.

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Application of Remote Sensing to Monitor Ecosystem Carbon Source and Sink in China

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1010-1012.1254 ◽

2014 ◽

Vol 1010-1012 ◽

pp. 1254-1257

Author(s):

Jing Wang ◽

Run He Shi ◽

Lu Zhang

Keyword(s):

Remote Sensing ◽

Large Scale ◽

Carbon Sink ◽

National Development ◽

Terrestrial Ecosystem ◽

Developed Countries ◽

Related Data ◽

Ecosystem Carbon ◽

Sensing Technology ◽

Global Carbon

Kyoto Protocol states that developed countries have the responsibility to reduce the amount of greenhouse gas emissions. It, also, suggests that developed countries take measures to enhance carbon sink. Therefore, every country pays more attention on the research of global carbon cycle. China, a developing country with a fast economic increasing rate, has urgent need of related data and information so as to adjust its national development plan and negotiate with other countries. Remote sensing is one of the most important technologies and data sources for large-scale carbon-related researches including terrestrial ecosystem carbon cycling law, carbon sink/source pattern and sink enhancement technology. This paper introduces recent applications of remote sensing technology to the following aspects in China: monitoring land cover, simulating carbon flux, spatial distribution of carbon sink and carbon sink enhancement measures.

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Net ecosystem carbon exchange of a dry temperate eucalypt forest

10.5194/bg-2016-192 ◽

2016 ◽

Author(s):

Nina Hinko-Najera ◽

Stephen J Livesley ◽

Jason Beringer ◽

Peter Isaac ◽

Eva van Gorsel ◽

...

Keyword(s):

Carbon Sink ◽

Annual Rainfall ◽

Carbon Exchange ◽

Annual Variability ◽

Eucalypt Forest ◽

Ecosystem Carbon ◽

Environmental Controls ◽

Eastern Australia ◽

Net Ecosystem Carbon Exchange ◽

Ecosystem Carbon Exchange

Abstract. Forest ecosystems play a crucial role in the global carbon cycle by sequestering a considerable fraction of anthropogenic CO2 thereby contributing to climate change mitigation. However, there is a gap in our understanding about the carbon dynamics of eucalypt (broadleaf evergreen) forests in temperate climates, which might differ from temperate coniferous or deciduous forests given their fundamental differences in physiology, phenology and growth dynamics. To address this gap we undertook a three year study (2010–2012) using eddy covariance measurements in a dry temperate eucalypt forest in south-eastern Australia. We determined the annual net ecosystem carbon exchange (NEE) and investigated the temporal (seasonal and inter-annual) variability and environmental controls of NEE, gross primary productivity (GPP) and ecosystem respiration (ER). The forest was a large and constant carbon sink throughout the study period, even in winter, with an overall mean NEE of −1062 ± 53 g C m−2 yr−1. Gross CO2 ecosystem fluxes showed no significant inter-annual variability and mean annual estimate of GPP was 2521 ± 35 g C m−2 yr−1 and ER was 1458 ± 31 g C m−2 yr−1. GPP and ER had a pronounced seasonality with GPP being greatest during spring and summer and ER during summer whereas peaks of NEE occurred in early spring and again in summer. High NEE in spring was caused by a delayed increase in ER due to low temperatures. A random forest analysis showed that variability in GPP was mostly explained by incoming solar radiation whilst air temperature was the main environmental driver of ER on seasonal and inter-annual time scales. The forest experienced unusual above average annual rainfall during the first two years of this three year period so that soil moisture content remained relatively high and the forest was not water limited. Our results show the potential of temperate eucalypt forests to sequester large amounts of carbon when not water limited. Our observations can provide data on an underrepresented biome to test and parameterise ecosystem models. However, longer monitoring is needed to assess the inter-annual variability of the carbon sink strength particularly during years with drought conditions.

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The Potential of Photoelectrochemical Carbon Sinks

10.26434/chemrxiv.6231140.v2 ◽

2018 ◽

Author(s):

Matthias May ◽

Kira Rehfeld

Keyword(s):

Global Warming ◽

High Temperature ◽

Greenhouse Gas ◽

Large Scale ◽

High Efficiency ◽

Carbon Sink ◽

Solar Fuels ◽

Negative Emissions ◽

Viable Approach ◽

Low Sensitivity

Greenhouse gas emissions must be cut to limit global warming to 1.5-2C above preindustrial levels. Yet the rate of decarbonisation is currently too low to achieve this. Policy-relevant scenarios therefore rely on the permanent removal of CO2 from the atmosphere. However, none of the envisaged technologies has demonstrated scalability to the decarbonization targets for the year 2050. In this analysis, we show that artificial photosynthesis for CO2 reduction may deliver an efficient large-scale carbon sink. This technology is mainly developed towards solar fuels and its potential for negative emissions has been largely overlooked. With high efficiency and low sensitivity to high temperature and illumination conditions, it could, if developed towards a mature technology, present a viable approach to fill the gap in the negative emissions budget.

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The Potential of Photoelectrochemical Carbon Sinks

10.26434/chemrxiv.6231140 ◽

2018 ◽

Author(s):

Matthias May ◽

Kira Rehfeld

Keyword(s):

Global Warming ◽

High Temperature ◽

Greenhouse Gas ◽

Large Scale ◽

High Efficiency ◽

Carbon Sink ◽

Solar Fuels ◽

Negative Emissions ◽

Viable Approach ◽

Low Sensitivity

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Large-Scale Analysis of the Spatiotemporal Changes of Net Ecosystem Production in Hindu Kush Himalayan Region

Remote Sensing ◽

10.3390/rs13061180 ◽

2021 ◽

Vol 13 (6) ◽

pp. 1180

Author(s):

Da Guo ◽

Xiaoning Song ◽

Ronghai Hu ◽

Xinming Zhu ◽

Yazhen Jiang ◽

...

Keyword(s):

Large Scale ◽

Net Primary Production ◽

Carbon Sink ◽

Carbon Sources ◽

Spatial Dynamics ◽

Tibet Plateau ◽

Geostatistical Model ◽

Hindu Kush ◽

Temporal And Spatial ◽

The Difference

The Hindu Kush Himalayan (HKH) region is one of the most ecologically vulnerable regions in the world. Several studies have been conducted on the dynamic changes of grassland in the HKH region, but few have considered grassland net ecosystem productivity (NEP). In this study, we quantitatively analyzed the temporal and spatial changes of NEP magnitude and the influence of climate factors on the HKH region from 2001 to 2018. The NEP magnitude was obtained by calculating the difference between the net primary production (NPP) estimated by the Carnegie–Ames Stanford Approach (CASA) model and the heterotrophic respiration (Rh) estimated by the geostatistical model. The results showed that the grassland ecosystem in the HKH region exhibited weak net carbon uptake with NEP values of 42.03 gC∙m−2∙yr−1, and the total net carbon sequestration was 0.077 Pg C. The distribution of NEP gradually increased from west to east, and in the Qinghai–Tibet Plateau, it gradually increased from northwest to southeast. The grassland carbon sources and sinks differed at different altitudes. The grassland was a carbon sink at 3000–5000 m, while grasslands below 3000 m and above 5000 m were carbon sources. Grassland NEP exhibited the strongest correlation with precipitation, and it had a lagging effect on precipitation. The correlation between NEP and the precipitation of the previous year was stronger than that of the current year. NEP was negatively correlated with temperature but not with solar radiation. The study of the temporal and spatial dynamics of NEP in the HKH region can provide a theoretical basis to help herders balance grazing and forage.

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Modelling Tree Growth in Monospecific Forests from Forest Inventory Data

Forests ◽

10.3390/f12060753 ◽

2021 ◽

Vol 12 (6) ◽

pp. 753

Author(s):

Guadalupe Sáez-Cano ◽

Marcos Marvá ◽

Paloma Ruiz-Benito ◽

Miguel A. Zavala

Keyword(s):

Tree Growth ◽

Large Scale ◽

Temporal Dynamics ◽

Carbon Sink ◽

Size Variation ◽

Biotic Interactions ◽

Richards Equation ◽

Tree Level ◽

Forest Inventories ◽

Large Scale Data

The prediction of tree growth is key to further understand the carbon sink role of forests and the short-term forest capacity on climate change mitigation. In this work, we used large-scale data available from three consecutive forest inventories in a Euro-Mediterranean region and the Bertalanffy–Chapman–Richards equation to model up to a decade’s tree size variation in monospecific forests in the growing stages. We showed that a tree-level fitting with ordinary differential equations can be used to forecast tree diameter growth across time and space as function of environmental characteristics and initial size. This modelling approximation was applied at different aggregation levels to monospecific regions with forest inventories to predict trends in aboveground tree biomass stocks. Furthermore, we showed that this model accurately forecasts tree growth temporal dynamics as a function of size and environmental conditions. Further research to provide longer term prediction forest stock dynamics in a wide variety of forests should model regeneration and mortality processes and biotic interactions.

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Spatial variability and its scale dependency of observed and modeled soil moisture over different climate regions

Hydrology and Earth System Sciences ◽

10.5194/hess-17-1177-2013 ◽

2013 ◽

Vol 17 (3) ◽

pp. 1177-1188 ◽

Cited By ~ 45

Author(s):

B. Li ◽

M. Rodell

Keyword(s):

Soil Moisture ◽

Spatial Variability ◽

Land Surface ◽

Large Scale ◽

Warm Season ◽

Scale Dependency ◽

Convex Shape ◽

Spatial Moments ◽

Environmental Controls

Abstract. Past studies on soil moisture spatial variability have been mainly conducted at catchment scales where soil moisture is often sampled over a short time period; as a result, the observed soil moisture often exhibited smaller dynamic ranges, which prevented the complete revelation of soil moisture spatial variability as a function of mean soil moisture. In this study, spatial statistics (mean, spatial variability and skewness) of in situ soil moisture, modeled and satellite-retrieved soil moisture obtained in a warm season (198 days) were examined over three large climate regions in the US. The study found that spatial moments of in situ measurements strongly depend on climates, with distinct mean, spatial variability and skewness observed in each climate zone. In addition, an upward convex shape, which was revealed in several smaller scale studies, was observed for the relationship between spatial variability of in situ soil moisture and its spatial mean when statistics from dry, intermediate, and wet climates were combined. This upward convex shape was vaguely or partially observable in modeled and satellite-retrieved soil moisture estimates due to their smaller dynamic ranges. Despite different environmental controls on large-scale soil moisture spatial variability, the correlation between spatial variability and mean soil moisture remained similar to that observed at small scales, which is attributed to the boundedness of soil moisture. From the smaller support (effective area or volume represented by a measurement or estimate) to larger ones, soil moisture spatial variability decreased in each climate region. The scale dependency of spatial variability all followed the power law, but data with large supports showed stronger scale dependency than those with smaller supports. The scale dependency of soil moisture variability also varied with climates, which may be linked to the scale dependency of precipitation spatial variability. Influences of environmental controls on soil moisture spatial variability at large scales are discussed. The results of this study should be useful for diagnosing large scale soil moisture estimates and for improving the estimation of land surface processes.

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Consistent Effects of Canopy vs. Understory Nitrogen Addition on Soil Respiration and Net Ecosystem Production in Moso Bamboo Forests

Forests ◽

10.3390/f12101427 ◽

2021 ◽

Vol 12 (10) ◽

pp. 1427

Author(s):

Chunju Cai ◽

Zhihan Yang ◽

Liang Liu ◽

Yunsen Lai ◽

Junjie Lei ◽

...

Keyword(s):

Soil Respiration ◽

Carbon Cycling ◽

Forest Canopy ◽

Carbon Sink ◽

N Deposition ◽

Net Ecosystem Production ◽

Moso Bamboo ◽

Atmospheric N Deposition ◽

Ecosystem Carbon ◽

Ecosystem Production

Nitrogen (N) deposition has been well documented to cause substantial impacts on ecosystem carbon cycling. However, the majority studies of stimulating N deposition by direct N addition to forest floor have neglected some key ecological processes in forest canopy (e.g., N retention and absorption) and might not fully represent realistic atmospheric N deposition and its effects on ecosystem carbon cycling. In this study, we stimulated both canopy and understory N deposition (50 and 100 kg N ha−1 year−1) with a local atmospheric NHx:NOy ratio of 2.08:1, aiming to assess whether canopy and understory N deposition had similar effects on soil respiration (RS) and net ecosystem production (NEP) in Moso bamboo forests. Results showed that RS, soil autotrophic (RA), and heterotrophic respiration (RH) were 2971 ± 597, 1472 ± 579, and 1499 ± 56 g CO2 m−2 year−1 for sites without N deposition (CN0), respectively. Canopy and understory N deposition did not significantly affect RS, RA, and RH, and the effects of canopy and understory N deposition on these soil fluxes were similar. NEP was 1940 ± 826 g CO2 m−2 year−1 for CN0, which was a carbon sink, indicating that Moso bamboo forest the potential to play an important role alleviating global climate change. Meanwhile, the effects of canopy and understory N deposition on NEP were similar. These findings did not support the previous predictions postulating that understory N deposition would overestimate the effects of N deposition on carbon cycling. However, due to the limitation of short duration of N deposition, an increase in the duration of N deposition manipulation is urgent and essential to enhance our understanding of the role of canopy processes in ecosystem carbon fluxes in the future.

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Contrasting pH buffering patterns in neutral-alkaline soils along a 3600 km transect in northern China

Biogeosciences Discussions ◽

10.5194/bgd-12-13215-2015 ◽

2015 ◽

Vol 12 (16) ◽

pp. 13215-13240 ◽

Cited By ~ 2

Author(s):

W. Luo ◽

P. N. Nelson ◽

M.-H. Li ◽

J. Cai ◽

Y. Zhang ◽

...

Keyword(s):

Soil Ph ◽

Large Scale ◽

Aridity Index ◽

Clay Content ◽

Northern China ◽

Buffering Capacity ◽

Carbonate Content ◽

Alkaline Soils ◽

Ph Buffering ◽

Initial Ph

Abstract. Soil pH buffering capacity (pHBC) plays a crucial role in predicting acidification rates, yet its large-scale patterns and controls are poorly understood, especially for neutral-alkaline soils. Here, we evaluated the spatial patterns and drivers of pHBC along a 3600 km long transect (1900 km sub-transect with carbonate containing soils and 1700 km sub-transect with non-carbonate containing soils) across northern China. Soil pHBC was greater in the carbonate containing soils than in the non-carbonate containing soils. Acid addition decreased soil pH in the non-carbonate containing soils more markedly than in the carbonate containing soils. Within the carbonate soil sub-transect, soil pHBC was positively correlated with cation exchange capacity (CEC), carbonate content and exchangeable sodium (Na) concentration, but negatively correlated with initial pH and clay content, and not correlated with soil organic carbon (SOC) content. Within the non-carbonate sub-transect, soil pHBC was positively related to initial pH, clay content, CEC and exchangeable Na concentration, but not related to SOC content. Carbonate content was the primary determinant of pHBC in the carbonate containing soils and CEC was the main determinant of buffering capacity in the non-carbonate containing soils. Soil pHBC was positively related to aridity index and carbonate content across the carbonate containing soil sub-transect. Our results indicated that mechanisms controlling pHBC differ among neutral-alkaline soils of northern China, especially between carbonate and non-carbonate containing soils, leading to different rates, risks, and impacts of acidification. This understanding should be incorporated into the acidification risk assessment and landscape management in a changing world.

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A wavelet-based approach to detect climate change on the coherent and turbulent component of the atmospheric circulation

Earth System Dynamics ◽

10.5194/esd-7-517-2016 ◽

2016 ◽

Vol 7 (2) ◽

pp. 517-523 ◽

Cited By ~ 4

Author(s):

Davide Faranda ◽

Dimitri Defrance

Keyword(s):

Climate Change ◽

Atmospheric Circulation ◽

Coherent Structures ◽

Large Scale ◽

Dominant Role ◽

Moving Average ◽

Climate Change Signal ◽

Complex Spectrum ◽

Wind Fields ◽

Turbulent Spectra

Abstract. The modifications of atmospheric circulation induced by anthropogenic effects are difficult to capture because wind fields feature a complex spectrum where the signal of large-scale coherent structures (planetary, baroclinic waves and other long-term oscillations) is mixed up with turbulence. Our purpose is to study the effects of climate changes on these two components separately by applying a wavelet analysis to the 700 hPa wind fields obtained in climate simulations for different forcing scenarios. We study the coherent component of the signal via a correlation analysis to detect the persistence of large-scale or long-lasting structures, whereas we use the theory of autoregressive moving-average stochastic processes to measure the spectral complexity of the turbulent component. Under strong anthropogenic forcing, we detect a significant climate change signal. The analysis suggests that coherent structures will play a dominant role in future climate, whereas turbulent spectra will approach a classical Kolmogorov behaviour.

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