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A fraction of CO2 uptake by terrestrial ecosystems is exported as organic carbon (C) through the terrestrial‐aquatic continuum. This translocated C plays a significant role in the terrestrial C balance; however, obtaining global assessments remains challenging due to the predominant reliance on empirical approaches. Leaching of dissolved organic C (DOC) from soils to rivers represents an important fraction of this C export and is assumed to drive a large proportion of the net‐heterotrophy of river systems and the related CO2 emissions. Using the model JULES‐DOCM, we projected DOC leaching trends over the 21st century based on three scenarios with high (RCP 2.6), intermediate (RCP 4.5), and low (RCP 8.5) climate mitigation efforts. The RCP 8.5 scenario led to the largest DOC leaching increase of +42% to 395 Tg C yr−1 by 2100. In comparison, RCP 2.6 and RCP 4.5 led to increases of 10% and 21%, respectively. Under RCP 8.5, the sub‐tropical zone showed the highest relative increase of 50% above current levels. In the boreal and tropical zones, the simulations revealed similar increases of 48% and 41%, respectively. However, given the pre‐eminence of the tropics in DOC leaching, the absolute increment is markedly substantial from this region (+59 Tg C yr−1). The temperate zone displayed the lowest relative increase with 35%. Our analysis identified the rising atmospheric CO2 concentration and its fertilizing effect on terrestrial NPP as the main reason for the future increase in DOC leaching. Plain Language Summary: Terrestrial ecosystems absorb CO2 and some of this is transformed into dissolved organic carbon (DOC) that leaches from soils to inland waters, driving aquatic CO2 emissions. Using the JULES‐DOCM model, we analyzed future DOC leaching trends under different climate scenarios. The scenario of low climate change mitigation led to the most significant leaching increase by the end of the century. Among various regions, the sub‐tropical areas showed the greatest relative growth in DOC leaching, with the tropics also seeing a substantial rise. This increase in DOC leaching is mainly driven by rising atmospheric CO2 levels, which boosts plant growth and productivity on land. Key Points: We predict an increase of global soil dissolved organic carbon (DOC) leaching of up to 42% or 395 Tg C yr−1 by 2100The sub‐tropical zone experienced the greatest relative DOC leaching growth, while the tropics had a notable absolute increaseThe primary driver for the future surge in DOC leaching is the rising atmospheric CO2 and its fertilizing effect on terrestrial NPP [ABSTRACT FROM AUTHOR]

Abstract A fraction of CO2 uptake by terrestrial ecosystems is exported as organic carbon (C) through the terrestrial‐aquatic continuum. This translocated C plays a significant role in the terrestrial C balance; however, obtaining global assessments remains challenging due to the predominant reliance on empirical approaches. Leaching of dissolved organic C (DOC) from soils to rivers represents an important fraction of this C export and is assumed to drive a large proportion of the net‐heterotrophy of river systems and the related CO2 emissions. Using the model JULES‐DOCM, we projected DOC leaching trends over the 21st century based on three scenarios with high (RCP 2.6), intermediate (RCP 4.5), and low (RCP 8.5) climate mitigation efforts. The RCP 8.5 scenario led to the largest DOC leaching increase of +42% to 395 Tg C yr−1 by 2100. In comparison, RCP 2.6 and RCP 4.5 led to increases of 10% and 21%, respectively. Under RCP 8.5, the sub‐tropical zone showed the highest relative increase of 50% above current levels. In the boreal and tropical zones, the simulations revealed similar increases of 48% and 41%, respectively. However, given the pre‐eminence of the tropics in DOC leaching, the absolute increment is markedly substantial from this region (+59 Tg C yr−1). The temperate zone displayed the lowest relative increase with 35%. Our analysis identified the rising atmospheric CO2 concentration and its fertilizing effect on terrestrial NPP as the main reason for the future increase in DOC leaching.

Aim: Earth observation‐based estimates of land–atmosphere exchange of carbon are essential for understanding the response of the terrestrial biosphere to climatic change and other anthropogenic forcing. Temperature, soil water content and gross primary production are the main drivers of ecosystem respiration (Reco), and the main aims of this study are to develop an Reco model driven by long‐term global‐scale Earth observations and to study Reco spatiotemporal dynamics 1982–2015. Location: Global scale. Time Period: 1982–2015. Major Taxa Studied: Terrestrial ecosystems. Methods: We parameterized and applied a global Reco model for 1982–2015 using novel Earth observation‐based data. We studied the relationships between Reco measured at field sites globally and land surface temperature, gross primary production and soil water content. Trends 1982–2015 were quantified, and the contributions from terrestrial regions to the spatiotemporal variability were evaluated. Results: The Reco model (LGS‐Reco) captured the between‐site and intra‐ and interannual variability in field‐observed Reco and soil respiration well in comparison with other Earth observation‐based products. The global annual Reco was on average 105.6 ± 2.3 Pg C for 1982–2015, which is close to 105 Pg C according to residuals of the carbon exchange processes within the global carbon budgets. The trend in global terrestrial Reco 1982–2015 was 0.19 ± 0.02 Pg C y−1, with the strongest positive trends found in cropland areas, whereas negative trends were primarily observed for savannah/shrublands of Southern Africa and South America. Trends were especially strong during the eighties and nineties, but substantially smaller 1998–2015. Main Conclusions: The LGS‐Reco model revealed a substantial increase in global Reco during recent decades. However, the growth rates of global Reco were slower during 1998–2015, partially explaining the reduced growth rates of atmospheric CO2 during this period. The LGR‐Reco product may be an essential source for studying carbon sources and sinks and functioning of the Earth system. [ABSTRACT FROM AUTHOR]

The leaching of dissolved organic carbon (DOC) from soils to the river network is an overlooked component of the terrestrial soil C budget. Measurements of DOC concentrations in soil, runoff and drainage are scarce and their spatial distribution highly skewed towards industrialized countries. The contribution of terrestrial DOC leaching to the global‐scale C balance of terrestrial ecosystems thus remains poorly constrained. Here, using a process based, integrative, modelling approach to upscale from existing observations, we estimate a global terrestrial DOC leaching flux of 0.28 ± 0.07 Gt C year−1 which is conservative, as it only includes the contribution of mineral soils. Our results suggest that globally about 15% of the terrestrial Net Ecosystem Productivity (NEP, calculated as the difference between Net Primary Production and soil respiration) is exported to aquatic systems as leached DOC. In the tropical rainforest, the leached fraction of terrestrial NEP even reaches 22%. Furthermore, we simulated spatial‐temporal trends in DOC leaching from soil to the river networks from 1860 to 2010. We estimated a global increase in terrestrial DOC inputs to river network of 35 Tg C year−1 (14%) from 1860 to 2010. Despite their low global contribution to the DOC leaching flux, boreal regions have the highest relative increase (28%) while tropics have the lowest relative increase (9%) over the historical period (1860s compared to 2000s). The results from our observationally constrained model approach demonstrate that DOC leaching is a significant flux in the terrestrial C budget at regional and global scales. [ABSTRACT FROM AUTHOR]

Highlights • The 2009/2010 drought in Southwest China has damaged vegetation growth. • Ecosystem impacts by drought vary across space and vegetation types. • Precipitation deficit is the main cause of decreased vegetation growth. • Most of the drought-impacted area could recover within six months from drought. • The carbon flux responses to this drought are poorly captured by models. Abstract The 2009/2010 drought in Southwest China was a "once in a century drought" event. This drought event had strong adverse impacts, such as water scarcity, crop failure, and economic loss, on ecosystems and the human society. Explicit representations of this drought event and associated changes in vegetation dynamics and carbon cycle, however, are still largely missed in literature. Here we used the standardized anomaly of 3-month Standard Precipitation-Evapotranspiration Index (SPEI) to characterize this 2009/2010 drought event, including its onset and end months, duration and severity. We examined the drought impacts on vegetation greenness using Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI); and assessed the terrestrial carbon flux responses to drought using data from satellite-based datasets, atmospheric inversion, one data-based model, and three ecosystem models. Our analysis showed that this "autumn-winter-spring" drought mostly suppressed vegetation growth in Yunnan, North Guangxi, Guizhou and East Sichuan. In comparisons to the same months of the reference period (2000–2015), the drought caused a large reduction in carbon uptake (4.4 ± 5 gCm−2month-1) from the decrease in gross primary production (GPP, 5.7 ± 9.5 gCm−2month-1), although ecosystem respiration (TER) also decreased by a smaller extent (1.3 ± 5.1 gCm−2month-1). Nonetheless, more than 65% of the drought-impacted area recovered in both vegetation greenness and productivity within 3 months, while about 10% of the drought-affected area failed to recover even after 6 months post the drought event. Across different vegetation types, forests and shrubs had stronger capability of drought resistance and shorter post-drought recovery time than crops and grasses. Model comparison reveals that while data from different sources generally agreed on the sign of vegetation greenness and carbon flux responses to drought, they differ significantly in the extent of such responses. [ABSTRACT FROM AUTHOR]

Changes in climate and land use, caused by socio-economic changes, greenhouse gas emissions, agricultural policies and other factors, are known to affect both natural and managed ecosystems, and will likely impact on the European terrestrial carbon balance during the coming decades. This study presents a comprehensive European Union wide (EU15 plus Norway and Switzerland, EU*) assessment of potential future changes in terrestrial carbon storage considering these effects based on four illustrative IPCC-SRES storylines (A1FI, A2, B1, B2). A process-based land vegetation model (LPJ-DGVM), adapted to include a generic representation of managed ecosystems, is forced with changing fields of land-use patterns from 1901 to 2100 to assess the effect of land-use and cover changes on the terrestrial carbon balance of Europe. The uncertainty in the future carbon balance associated with the choice of a climate change scenario is assessed by forcing LPJ-DGVM with output from four different climate models (GCMs: CGCM2, CSIRO2, HadCM3, PCM2) for the same SRES storyline. Decrease in agricultural areas and afforestation leads to simulated carbon sequestration for all land-use change scenarios with an average net uptake of 17–38 Tg C/year between 1990 and 2100, corresponding to 1.9–2.9% of the EU*s CO2 emissions over the same period. Soil carbon losses resulting from climate warming reduce or even offset carbon sequestration resulting from growth enhancement induced by climate change and increasing atmospheric CO2 concentrations in the second half of the twenty-first century. Differences in future climate change projections among GCMs are the main cause for uncertainty in the cumulative European terrestrial carbon uptake of 4.4–10.1 Pg C between 1990 and 2100. [ABSTRACT FROM AUTHOR]

The leaching of dissolved organic carbon (DOC) from soils to the river network is an overlooked component of the terrestrial soil C budget. Measurements of DOC concentrations in soil, runoff and drainage are scarce and their spatial distribution highly skewed towards industrialized countries. The contribution of terrestrial DOC leaching to the global-scale C balance of terrestrial ecosystems thus remains poorly constrained. Here, using a process based, integrative, modelling approach to upscale from existing observations, we estimate a global terrestrial DOC leaching flux of 0.28 ± 0.07 Gt C year -1 which is conservative, as it only includes the contribution of mineral soils. Our results suggest that globally about 15% of the terrestrial Net Ecosystem Productivity (NEP, calculated as the difference between Net Primary Production and soil respiration) is exported to aquatic systems as leached DOC. In the tropical rainforest, the leached fraction of terrestrial NEP even reaches 22%. Furthermore, we simulated spatial-temporal trends in DOC leaching from soil to the river networks from 1860 to 2010. We estimated a global increase in terrestrial DOC inputs to river network of 35 Tg C year -1 (14%) from 1860 to 2010. Despite their low global contribution to the DOC leaching flux, boreal regions have the highest relative increase (28%) while tropics have the lowest relative increase (9%) over the historical period (1860s compared to 2000s). The results from our observationally constrained model approach demonstrate that DOC leaching is a significant flux in the terrestrial C budget at regional and global scales., (© 2020 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)