Carbon Balance Of Terrestrial Ecosystems Research Articles

Quantitative Assessment of the Impact of the Three-North Shelter Forest Program on Vegetation Net Primary Productivity over the Past Two Decades and Its Environmental Benefits in China

Vegetation net primary productivity (NPP) is a crucial indicator for assessing the carbon balance in terrestrial ecosystems. Qualitative and comparative research on the NPP influenced by human activities, climate change, and their interactions remains insufficient. The Three-North Shelter Forest Program (TNSFP), initiated in 1978, provides a valuable reference for such investigations. This study employs an improved residual trend method to analyze the spatiotemporal patterns, trends, and driving factors of vegetation NPP during the second phase of the Three-North Shelter Forest Program (2001–2020), as well as TNSFP’s contribution to vegetation NPP. The results indicate that (1) from 2001 to 2020, overall vegetation NPP exhibited a significant fluctuating upward trend at a rate of 3.69 g C/m−2 annually; and (2) precipitation, accounting for 1.527 g C/m−2, had a more significant impact on vegetation net productivity compared to temperature (0.002 g C/m−2). Climate factors (76%) significantly influenced vegetation NPP in the Three-North Shelter Forest region more than human activities (24%). In the last decade (2011–2020), the climate contribution rate decreased to 67%, while the human activity contribution rate increased by seven percentage points compared to the previous decade (2001–2010); (3) during 2001–2020, TNSFP contributed 10.9% to the total human activity contribution to vegetation net primary productivity, approximately 2.6% of the overall contribution; (4) After the second phase of TNSFP was enacted, PM2.5 levels decreased by an average of −0.57 μg/m−3/a−1. Concurrently, soil conservation improved from 6.57 t/km2 in 2001 to 14.37 t/km2 in 2020.

The influence of the hydrometeorological factors on the CO2 fluxes from the oligotrophic bog surface.

The influence of the hydrometeorological factors on the CO2 fluxes from the oligotrophic bog surface.

Research on carbon balance in Japan

The article presents an overview of scientific publications on the subject of the study «carbon balance in terrestrial ecosystems», made for the territory of Japan and indexed in the Scopus database for the period 2017-2021. Within this theme, the areas with the highest number of articles are highlighted: carbon fluxes in soils, carbon stocks in above ground phytomass (mainly studies of the ecosystems of Hokkaido), features of carbon dioxide sequestration by various plant species typical for Japan, as well as the carbon balance dynamics associated with deforestation, reforestation and natural phenomena such as typhoons. The most active in publishing activity scientific and academic institutions were identified (Forestry and Forest Products Research Institute; National Agriculture and Food Research Organization; Hokkaido University).

Attribution of vegetation fluorescence changes in China based on a decision tree stratification strategy

Vegetation photosynthesis plays a key role in maintaining carbon balance in terrestrial ecosystems. Solar-Induced chlorophyll Fluorescence (SIF) was utilized as a proxy for vegetation photosynthesis in this study, and the Theil-Sen and Mann-Kendall methods were used to examine trends of vegetation change in China. The impacts of climate conditions on vegetation photosynthesis were examined with the correlation analysis and recursive feature elimination (RFE) method. To distinguish the contributions of climate change and human activities on vegetation photosynthesis, land use data and SIF change trends were employed as inputs to a decision tree model. The results revealed that 81.5% of the areas in China exhibited an improving trend of vegetation photosynthesis. Vegetation degradation areas were mainly located in Northern arid and semi-arid region (NASR), Qinghai Tibet Plateau (QTP) and Huang-Huai-Hai Plain (HHHP). Precipitation dominated the effect of vegetation photosynthesis in these regions. The increase of vegetation photosynthesis in the southern regions was positively impacted by solar radiation. The growth of agricultural technology obviously benefited the improvement of vegetation photosynthesis in the Middle-lower Yangtze Plain (MLYP) and Northeast China Plain (NCP). Furthermore, the establishment of ecological conservation programs has helped to restore vegetation in arid and semi-arid areas. The detrimental effects of human activities included overgrazing disturbance and coal mining activities, which resulted in vegetation deterioration in areas of QTP and HHHP. The methodologies and findings of this study can help to comprehend changes in vegetation dynamics and give a theoretical foundation for evaluating regional ecological conservation initiatives.

Spatio-Temporal Variation of Carbon Sources and Sinks in the Loess Plateau under Different Climatic Conditions and Land Use Types

The carbon balance of terrestrial ecosystems is intertwined with climate and changes in land use. Over the past 30 years, the Loess Plateau (LP) has experienced temperature increases and an expansion of forest and grassland. The net ecosystem productivity (NEP) underlying these changes is worth investigating. Using three periods (i.e., 1990–2000, 2000–2010, and 2010–2019) of annual average NEP and climatic, topographic, and land use data, we analyzed changes in the spatial distribution of carbon sources and sinks of the LP. Using an optimal parameter-based geographical detector model to discuss the driving factors of carbon sources and sinks, we found that: (1) The area of carbon sinks has been increasing continuously, and that the distributions of both of these elements are zonal. The carbon sinks show a downward trend from south to north, which is mainly driven by climate and land use type. (2) Carbon sources are mainly concentrated in the middle temperate zone, and they are mainly linked to impervious land, unused land, and grassland. The carbon sinks are mainly concentrated in the south temperate zone and plateau climatic zone, and they are mainly linked to forest, grassland, and cultivated land. Additionally, the southern temperate zone has been the most green, due to its superior hydrothermal conditions that sustain carbon sinks. (3) It is not uncommon for some forests, grasslands, and cultivated land to transition between being carbon sources and carbon sinks, especially when affected by human intervention and inadequate management measures. (4) NEP was primarily influenced by CO2 concentration, temperature, and precipitation, and the interaction of these factors greatly influenced the dynamics of carbon sources and sinks, while terrain exerted insignificant impacts on the NEP. This study highlights the importance of the carbon balance in terrestrial ecosystems and can be used to guide the creation of vegetation-based carbon sequestration policies.

Forest Soil Carbon Efflux Evaluation Across China: A New Estimate With Machine Learning

AbstractForest soil respiration (Rs) plays an important role in the carbon balance of terrestrial ecosystems. China's forest occupies a large part of the world's forest. However, due to the lack of integrated observation data and appropriate upscaling methodologies, substantial uncertainties exist in the Rs evaluation, which limits our understanding of the carbon balance. Here, we re‐evaluated the total soil carbon effluxes across China by combining field observations from 634 published annual Rs with a machine learning technique (i.e., Random Forest (RF)). Our results revealed that the combination of systematic measurements with the RF model allowed a definite estimate. The average annual Rs was 776.9 g C m−2 yr−1, ranging from 411.5 to 1,770.7 g C m−2 yr−1. Total forest soil carbon effluxes amounted to 1.17 Pg C yr−1 in China. Geographically, annual Rs showed a clear spatially increasing trend from northeast to southwest. Forest type is an important factor in determining the soil respiration rate. Bamboo and Evergreen broadleaf forests were higher than other types of forests. These results provide a unique insight into the magnitudes and mechanisms of soil CO2 emissions in China's forest ecosystems.

Water use efficiency and climate legacies dominate beech growth at its rear edge

Abstract Rear‐edge tree populations are experiencing a combination of higher temperatures and more intense droughts that might push individuals beyond their tolerance limits. This trend towards rising atmospheric [CO2] is concurrent with an increase in intrinsic water use efficiency (iWUE), which theoretically enhances photosynthesis and decrease evapotranspiration rates, consequently improving tree resistance to drought. However, it remains unclear whether iWUE is favouring tree growth under current climate conditions, particularly when climate and iWUE legacy effects are simultaneously considered. We evaluated this question with an extensive sampling along Iberian rear‐edge (dry) populations comprising four mountain ranges and two distinct altitudes. We simultaneously examined the effects of climate and iWUE on secondary growth using annually resolved basal area increments (BAIs) for the period 1901–2017. We used linear mixed models including second‐order autocorrelation and 1‐year legacy effects of iWUE and summer drought. BAI and iWUE increased across the studied period. iWUE increase was driven by changes in atmospheric CO2 concentration and water availability during the growing season. Climate and iWUE exerted direct and lagged effects on beech growth. Water availability during growing season was the main driver of tree growth, combining direct and indirect effects through its impact on iWUE. Legacy effects of water availability and iWUE were more important than growing season conditions. The net effect of iWUE shifted when lagged effects were considered, resulting in a net negative impact on tree growth. Synthesis: Our results reveal that climate and iWUE legacy effects must be considered to assess the net iWUE effect on secondary growth. Considering lagged effects, the current increase in iWUE is constraining tree growth. Modelling efforts of tree growth response to climate warming should include climate and iWUE legacy effects to adequately assess terrestrial ecosystem carbon balance.

Increasing temperature regulates the advance of peak photosynthesis timing in the boreal ecosystem

The shift in vegetation phenology is an essential indicator of global climate change. Numerous researches based on reflectance-based vegetation index data have explored the changes in the start (SOS) and end (EOS) of vegetation life events at long time scales, while a huge discrepancy existed between the phenological metrics of vegetation structure and function. The peak photosynthesis timing (PPT), which is crucial in regulating terrestrial ecosystem carbon balance, has not received much attention. Using two global reconstructed solar-induced chlorophyll fluorescence data (CSIF and GOSIF) directly associated with vegetation photosynthesis, the spatio-temporal dynamics in PPT as well as the key environmental controls across the boreal ecosystem during 2001–2019 were systematically explored. Multi-year mean pattern showed that PPT mainly appeared in the first half of July. Compared to the northern Eurasia, later PPT appeared in the northern North America continent for about 4–5 days. Meanwhile, spatial trend in PPT exhibited an advanced trend during the last two decades. Especially, shrubland and grassland were obvious among all biomes. Spatial partial correlation analysis revealed that preseason temperature was the dominant environmental driver of PPT trends, occupying 81.32% and 78.04% of the total pixels of PPTCSIF and PPTGOSIF, respectively. Attribution analysis by ridge regression again emphasized the largest contribution of temperature to PPT dynamics in the boreal ecosystem by 52.22% (PPTCSIF) and 46.59% (PPTGOSIF), followed by radiation (PPTCSIF: 24.44%; PPTGOSIF: 28.66%) and precipitation (PPTCSIF: 23.34%; PPTGOSIF: 24.75%). These results have significant implications for deepening our understanding between vegetation photosynthetic phenology and carbon cycling with respect to future climate change in the boreal ecosystem.

China’s terrestrial ecosystem carbon balance during the 20th century: an analysis with a process-based biogeochemistry model

BackgroundChina’s terrestrial ecosystems play a pronounced role in the global carbon cycle. Here we combine spatially-explicit information on vegetation, soil, topography, climate and land use change with a process-based biogeochemistry model to quantify the responses of terrestrial carbon cycle in China during the 20th century.ResultsAt a century scale, China’s terrestrial ecosystems have acted as a carbon sink averaging at 96 Tg C yr− 1, with large inter-annual and decadal variabilities. The regional sink has been enhanced due to the rising temperature and CO2 concentration, with a slight increase trend in carbon sink strength along with the enhanced net primary production in the century. The areas characterized by C source are simulated to extend in the west and north of the Hu Huanyong line, while the eastern and southern regions increase their area and intensity of C sink, particularly in the late 20th century. Forest ecosystems dominate the C sink in China and are responsible for about 64% of the total sink. On the century scale, the increase in carbon sinks in China’s terrestrial ecosystems is mainly contributed by rising CO2. Afforestation and reforestation promote an increase in terrestrial carbon uptake in China from 1950s. Although climate change has generally contributed to the increase of carbon sinks in terrestrial ecosystems in China, the positive effect of climate change has been diminishing in the last decades of the 20th century.ConclusionThis study focuses on the impacts of climate, CO2 and land use change on the carbon cycle, and presents the potential trends of terrestrial ecosystem carbon balance in China at a century scale. While a slight increase in carbon sink strength benefits from the enhanced vegetation carbon uptake in China’s terrestrial ecosystems during the 20th century, the increase trend may diminish or even change to a decrease trend under future climate change.

Uncertainty analysis of multiple terrestrial gross primary productivity products

AbstractAimGross primary productivity (GPP) of vegetation is an important component of the carbon balance of terrestrial ecosystems. With the development of science and technology, there has been a proliferation of multiple GPP products, yet large uncertainties exist in the global GPP estimated by different GPP products. The objectives of this study were to assess the uncertainty of 45 GPP products in 4 different categories (machine learning, Fluxnet, light use efficiency, land surface model) and to perform an attribution analysis.LocationGlobal.Time period2003–2010.Major taxa studiedTerrestrial ecosystems.MethodsThe three‐cornered hat (TCH) method was used to assess GPP uncertainty because it does not require a priori knowledge of the true GPP values. We also used generalized additive models to explore the contribution of different factors to GPP uncertainty.ResultsThe results show that the magnitude of absolute uncertainty (AU) is generally higher in the GPP high‐value region and also indicate large spatial variability of relative uncertainty (RU) among products. Deciduous broadleaf forest (20.2 g C/m2/year) and deciduous needleleaf forest (27.2 g C/m2/ year) have lower uncertainty compared to that of woody savanna (128.4 g C/m2/ year) and savanna (128.7 g C/m2/year). The RU in machine learning (ML) products overall is low (average value = 14.3%), with ORCHIDEE‐CNP (weight = 4.19%), being more recognized by GPP products are more consistent in the magnitude of spatial variability (similar in the standard deviations) and more uncertain in spatial distribution patterns. Excluding the combined effects of other factors, soil moisture (15.2%) and precipitation (8.3%) are the two factors that contribute most to GPP uncertainty, indicating that focusing on water constraints is a guarantee of GPP product quality.Main conclusionsThe TCH approach quantifies the uncertainty of GPP products well and the spatial distribution pattern variability contributes more uncertainty compared to the magnitude of spatial variability. Future GPP estimates could consider combining the advantages of different GPP products to limit uncertainty.

The Relationship between Soil Respiration and Plant Community Functional Traits in Ebinur Lake Basin

Soil respiration (Rs) plays an important role in the carbon cycle of terrestrial ecosystems. Understanding the impacts of plant community functional traits on Rs is a key prerequisite for accurate prediction of the future carbon balance of terrestrial ecosystems under climate change. This study examined the relationship of Rs with plants in the Ebinur Lake Basin in the arid desert region. Traditional statistical methods and geostatistical methods were used to study the spatial variation characteristics of Rs and to analyze the effects of plant community functional traits and environmental factors on the spatial heterogeneity of Rs. The variation in Rs in the arid desert area of the Ebinur Lake Basin showed a strong spatial dependence (C0/(C + C0) = 0.11) and a medium variation (α = 25.50, CV = 86.21%). Principal component analysis revealed that morphological traits of plants and soil water content had great contributions to PC1, soil nutrient had great contributions to PC2, and physiological traits of plants and soil temperature had large contributions to PC3. Multiple regression analysis showed that PC1, PC2, and PC3 can explain 83% of the spatial heterogeneity of Rs (F = 157.41, p < 0.01). In conclusion, maximum height, leaf width, leaf dry matter content, leaf thickness, and soil water content were the principal driving elements of soil respiration heterogeneity.

自然增温对南亚热带森林土壤微生物群落与有机碳代谢功能基因的影响

基于海拔高度下降气温上升的关系，将模拟的生态系统（含植物和土壤）从高海拔整体移位至低海拔地区，实现自然增温的效果。通过对自然增温条件下土壤环境因子及其相关理化性质的动态监测，结合磷脂脂肪酸分析与宏基因组学方法，测定土壤微生物群落结构以及与土壤有机碳分解相关基因丰度，探究自然增温对鼎湖山南亚热带山地常绿阔叶林土壤有机碳代谢的影响及其微生物学机制。结果表明：（1）增温处理显著改变了0-10 cm土壤温度与湿度：2016-2018年间土壤温度显著上升2.48℃，湿度显著下降23.93%。（2）增温处理下，干季土壤有机碳含量与湿季土壤硝态氮含量显著降低，其他土壤理化因子无显著变化。（3）增温处理下，干季和湿季土壤微生物群落结构发生改变，且湿季变化显著。土壤湿度是影响干季和湿季土壤微生物群落结构变化的主要因子，解释了干季50.2%的变异度与湿季79.2%的变异度。（4）宏基因组结果表示：增温抑制了干季山地常绿阔叶林土壤有机碳代谢基因丰度，增强了湿季山地常绿阔叶林土壤有机碳代谢基因丰度。以上结果表明，增温通过改变土壤微生物生物量和群落结构以及有机碳代谢相关功能基因的丰度，最终影响南亚热带山地常绿阔叶林土壤有机碳代谢过程。;Global warming is one of the environmental problems that cannot be ignored in the world today, which has significant impacts on soil carbon dynamics and soil microorganisms. Soil microorganisms affect the soil nutrient cycling process and play a leading role in the net carbon balance of terrestrial ecosystems. Further exploration of microbial responses to climate warming is important for predicting the feedback and carbon budget of terrestrial ecosystems in warmer climates. In this study, soil organic carbon content and microorganisms were investigated in a natural warming experiment using a whole ecosystem transplanting approach. Plots of plants and soil in a subtropical mountain evergreen broadleaf forest at high altitude (600 m asl) were moved to low altitude (30 m asl) in Dinghu Mountain to experience natural warming treatment. Plots with similar plants and soil at the high altitude were used as the control. To explore the effect of natural warming on soil organic carbon metabolism and its microbiological mechanism, soil physical and chemical properties, soil organic carbon, and soil microbial community structure were measured for the control and warmed plots. Meta-genomic method was used for soil microbial community structure and abundance of genes involved in soil organic carbon decomposition. Results showed that:(1) warming treatment significantly changed soil temperature and moisture of the 0-10 cm soil layer. From 2016 to 2018, the soil temperature was significantly increased by 2.48℃, and the soil moisture was significantly decreased by 23.93% (relative change). (2) Warming treatment significantly reduced soil organic carbon content in the dry season and the soil nitrate nitrogen content in the wet season, while other soil physical and chemical factors had no significant changes under warming treatment. (3) Warming treatment changed the soil microbial community structure in both dry and wet seasons, and the change was significant in wet season. The results of principal component analysis showed that soil moisture was the main factor affecting the variation of soil microbial community structure in dry season and wet season, which explained the variation degree of 50.2% in dry season and 79.2% in wet season. (4) The metagenomic analysis showed that increasing temperature inhibited the abundance of soil organic carbon metabolism genes of mountain evergreen broadleaf forest in the dry season, and enhanced them in the wet season. Our results showed that although warming treatment did not significantly change soil microbial biomass in the subtropical mountain evergreen broadleaf forest, it reduced soil organic carbon by changing soil microbial community structure and abundance, and significantly affected soil organic carbon metabolic processes and ecosystem carbon cycling.

Dominant influence of non-thawing periods on annual CO2 emissions from Zoige peatlands: Five-year eddy covariance analysis

Changes in freeze–thaw processes as a result of climate change significantly affect the carbon balance of terrestrial ecosystems, especially peatlands. The Qinghai-Tibetan Plateau contains substantial permafrost and seasonal frozen soils and its peatlands feature a huge carbon stock highly sensitive to global change. In this paper, we used an eddy covariance flux tower to monitor carbon fluxes on the Zoige peatlands with seasonal frozen soils on the eastern Qinghai-Tibetan Plateau from 2013 to 2017. Total net emissions (g C m−2 yr−1) over the monitoring period were 64.1, 106.7, 126.5 and 103.2 in the frozen, frozen-thawing, thawing and thawing-freezing periods; the corresponding weighted mean emission rates (g C m−2 d−1) were 0.36, 0.44, 0.64 and 0.38. Although net CO2 emissions were highest in the thawing period, emissions during the other periods accounted for approximately 68.4% of annual emissions. In fact, emissions during the two freeze–thaw periods were 1.7 times those during the thawing period despite the freeze–thaw periods lasting fewer days. CO2 emission correlated significantly with volumetric water content and soil temperature in the frozen period, with soil temperature and precipitation in the frozen-thawing period, and with precipitation in the thawing and thawing-freezing periods. Annual net CO2 emissions during each of the years were 57.2 g C m−2 yr−1 (2013), 108.3 g C m−2 yr−1 (2014), 41 g C m−2 yr−1 (2015), 62.9 g C m−2 yr−1 (2016) and 131.1 g C m−2 yr−1 (2017), and hydrological conditions were the primary determinant of interannual variations. Long-term continuous monitoring of carbon is essential to understand how freeze–thaw processes affect the ability of alpine peatland ecosystems to act as carbon sources and sinks.

Reexamine China’s terrestrial ecosystem carbon balance under land use-type and climate change

Land use and climate change can strongly affect the terrestrial ecosystem carbon balance. However, there is a lack of clarity for existing studies that investigate total carbon balance for China’s terrestrial carbon balance (carbon storage and Net Ecosystem Productivity (NEP)). In this study, based on large data and the improved NEP model, we examined land use and climate change during 2000–2015 in China, calculated terrestrial ecosystem carbon storage change caused by land use change, and carbon sink/source variation under climate change; we found that during 2000–2015, 3.05 % of China’s land area had land use type changes and caused 32.97 Tg of carbon storage loss, consisting of 10.4 Tg from vegetation carbon storage and 22.57 Tg from soil organic carbon (SOC) loss. Built-up land occupying ecological land was the most obvious land transfer type, especially for grassland degeneration. Both temperature and precipitation showed decreasing trends throughout China. Mean annual NEP showed a carbon sink value of 41.73 g C.m−2.yr−1, and the NEPs of carbon sinks were mostly distributed in South and Midland China and partly in Northeast China. There were obvious regional differences and the carbon balance showed that North China and Northwest China were regions of net carbon sources. The other four regions were net carbon sinks. Land use changes caused carbon storage loss in all regions, NEPs in North China and Northwest China were carbon sources, while in the other regions were carbon sinks. All NEPs exhibited an increasing trend during 2000–2015, except for Mid-South China. Finally, according to regional carbon balance characters, different policy implications were drawn which can serve for the formulation of territorial spatial planning. Land exploitation should be limited and environmental conservation is needed in North and Northwest China. The temperature in Southwest China has been increasing continuously and merits attention. The control of built-up land expansion in other regions should be strengthened.

Nitrogen deposition and increased precipitation interact to affect fine root production and biomass in a temperate forest: Implications for carbon cycling

Fine roots connect belowground and aboveground systems and help regulate the carbon balance of terrestrial ecosystems by providing nutrients and water for plants. To evaluate the effects of atmospheric nitrogen (N) deposition and increased precipitation on fine root production and standing biomass in a temperate deciduous forest in central China, we conducted a 6-year experiment. From 2013 to 2018, we applied N (25 kg N ha−1 yr−1) and water (336 mm, 30% of the ambient annual precipitation) above the forest canopy, and we quantified fine root production and biomass in 2017 and 2018. At 0–10 cm soil depth, the statistical interaction between addition of N and water was not significant in terms of fine root production or biomass. At 0–10 cm soil depth, N addition significantly increased fine root production by 18.1%, but did not affect fine root biomass. Water addition significantly increased fine root production and biomass by 13.6 and 17.0%, respectively. Both N and water addition had significant direct positive effects on fine root production, and water addition had indirect positive effects on fine root biomass through decreasing soil NO3− concentration. At 10–30 cm soil depth, the statistical interaction between N addition and water addition was significant in terms of both fine root production and biomass, i.e., the positive effect of N addition was reduced by water addition, and vice versa. These findings indicate that fine roots and therefore belowground carbon storage may have complex responses to increases in atmospheric N deposition and changes in precipitation predicted for the future. The findings also suggest that results obtained from experiments that consider only one independent variable (e.g., N input or water input) and only one soil depth should be interpreted with caution.

Estimation of C-CO2 balance of natural steppe ecosystems: Khakassia and Tuva (Eastern Siberia, Russia) case studies

The study of carbon balance of terrestrial ecosystems is considerable important for the forecasts of climate and environmental changes. Using a geoinformation-analytical method and a climate-driven regression model, we have calculated the C-CO2 balance of natural steppe ecosystems of Khakassia and Tuva. Our research has shown that natural steppes of the region under study are a significant sink of carbon dioxide from the atmosphere. The intensity of this carbon flux in the region can be estimate as 184±41 gCm−2 yr −1. The annual absorption of carbon dioxide in the natural steppe ecosystems of Tuva and Khakassia is evaluated as 6.9±2.2 Mt C-CO2.

Photoperiod Explains the Asynchronization Between Vegetation Carbon Phenology and Vegetation Greenness Phenology

AbstractVegetation carbon phenology is a key indicator of vegetation actual photosynthesis activity and regulates terrestrial ecosystem carbon balance. A comprehensive understanding of the structural difference of carbon phenology and greenness phenology is still lacking. This study evaluated the structural difference of vegetation greenness phenology and carbon phenology on 95 eddy covariance flux sites (637 site‐years). Vegetation greenness phenology is extracted from remote sensing vegetation indices (i.e., enhanced vegetation index [EVI] and normalized difference vegetation index [NDVI]) of Moderate Resolution Imaging Spectroradiometer satellites; carbon phenology is extracted from daily gross primary production estimates at flux sites. We found that there exists remarkable asynchronization between vegetation greenness phenology and carbon phenology on the 95 flux sites. Generally, the asynchronization is more prevalent in the withering season, with the bias about 18.7 ± 13.0 days for EVI and about 29.8 ± 14.4 days for NDVI. In comparison, in the green‐up season, the bias is only about −1.6 ± 12.9 days for EVI and −6.0 ± 13.8 days for NDVI. We found that photoperiod is the dominant factor controlling the asynchronization and the decrease of photosynthetic capacity in the withering season, other than photosynthetically active radiation or temperature. Our study also reveals that EVI × PC and NDVI × PC are good proxies of vegetation carbon phenology, where PC is the photoperiod constraint and is quantified as . Using PC in the withering season reduces the bias of EVI from 18.7 ± 13.0 days to −2.4 ± 11.2 days and the bias of NDVI from 29.8 ± 14.4 days to −1.1 ± 12.7 days.

Soil carbon release responses to long-term versus short-term climatic warming in an arid ecosystem

Abstract. Climate change severely impacts the grassland carbon cycling by altering rates of litter decomposition and soil respiration (Rs), especially in arid areas. However, little is known about the Rs responses to different warming magnitudes and watering pulses in situ in desert steppes. To examine their effects on Rs, we conducted long-term moderate warming (4 years, ∼3 ∘C), short-term acute warming (1 year, ∼4 ∘C) and watering field experiments in a desert grassland of northern China. While experimental warming significantly reduced average Rs by 32.5 % and 40.8 % under long-term moderate and short-term acute warming regimes, respectively, watering pulses (fully irrigating the soil to field capacity) stimulated it substantially. This indicates that climatic warming constrains soil carbon release, which is controlled mainly by decreased soil moisture, consequently influencing soil carbon dynamics. Warming did not change the exponential relationship between Rs and soil temperature, whereas the relationship between Rs and soil moisture was better fitted to a sigmoid function. The belowground biomass, soil nutrition, and microbial biomass were not significantly affected by either long-term or short-term warming regimes, respectively. The results of this study highlight the great dependence of soil carbon emission on warming regimes of different durations and the important role of precipitation pulses during the growing season in assessing the terrestrial ecosystem carbon balance and cycle.

On what scales can GOSAT flux inversions constrain anomalies in terrestrial ecosystems?

Abstract. Interannual variations in temperature and precipitation impact the carbon balance of terrestrial ecosystems, leaving an imprint in atmospheric CO2. Quantifying the impact of climate anomalies on the net ecosystem exchange (NEE) of terrestrial ecosystems can provide a constraint to evaluate terrestrial biosphere models against and may provide an emergent constraint on the response of terrestrial ecosystems to climate change. We investigate the spatial scales over which interannual variability in NEE can be constrained using atmospheric CO2 observations from the Greenhouse Gases Observing Satellite (GOSAT). NEE anomalies are calculated by performing a series of inversion analyses using the GEOS-Chem adjoint model to assimilate GOSAT observations. Monthly NEE anomalies are compared to “proxies”, variables that are associated with anomalies in the terrestrial carbon cycle, and to upscaled NEE estimates from FLUXCOM. Statistically significant correlations (P<0.05) are obtained between posterior NEE anomalies and anomalies in soil temperature and FLUXCOM NEE on continental and larger scales in the tropics, as well as in the northern extratropics on subcontinental scales during the summer (R2≥0.49), suggesting that GOSAT measurements provide a constraint on NEE interannual variability (IAV) on these spatial scales. Furthermore, we show that GOSAT flux inversions are generally better correlated with the environmental proxies and FLUXCOM NEE than NEE anomalies produced by a set of terrestrial biosphere models (TBMs), suggesting that GOSAT flux inversions could be used to evaluate TBM NEE fluxes.

Effects of 21st-century climate, land use, and disturbances on ecosystem carbon balance in California.

Terrestrial ecosystems are an important sink for atmospheric carbon dioxide (CO2), sequestering ~30% of annual anthropogenic emissions and slowing the rise of atmospheric CO2. However, the future direction and magnitude of the land sink is highly uncertain. We examined how historical and projected changes in climate, land use, and ecosystem disturbances affect the carbon balance of terrestrial ecosystems in California over the period 2001–2100. We modeled 32 unique scenarios, spanning 4 land use and 2 radiative forcing scenarios as simulated by four global climate models. Between 2001 and 2015, carbon storage in California's terrestrial ecosystems declined by −188.4 Tg C, with a mean annual flux ranging from a source of −89.8 Tg C/year to a sink of 60.1 Tg C/year. The large variability in the magnitude of the state's carbon source/sink was primarily attributable to interannual variability in weather and climate, which affected the rate of carbon uptake in vegetation and the rate of ecosystem respiration. Under nearly all future scenarios, carbon storage in terrestrial ecosystems was projected to decline, with an average loss of −9.4% (−432.3 Tg C) by the year 2100 from current stocks. However, uncertainty in the magnitude of carbon loss was high, with individual scenario projections ranging from −916.2 to 121.2 Tg C and was largely driven by differences in future climate conditions projected by climate models. Moving from a high to a low radiative forcing scenario reduced net ecosystem carbon loss by 21% and when combined with reductions in land‐use change (i.e., moving from a high to a low land‐use scenario), net carbon losses were reduced by 55% on average. However, reconciling large uncertainties associated with the effect of increasing atmospheric CO2 is needed to better constrain models used to establish baseline conditions from which ecosystem‐based climate mitigation strategies can be evaluated.