Explore the vast range of titles available.

Global photosynthesis is increasing with elevated atmospheric CO₂ concentrations, a response known as the CO₂ fertilization effect (CFE), but the key processes of CFE are not constrained and therefore remain uncertain. Here, we quantify CFE by combining observations from a globally distributed network of eddy covariance measurements with an analytical framework based on three well-established photosynthetic optimization theories. We report a strong enhancement of photosynthesis across the observational network (9.1 gC m−2 year−2) and show that the CFE is responsible for 44% of the gross primary production (GPP) enhancement since the 2000s, with additional contributions primarily from warming (28%). Soil moisture and specific humidity are the two largest contributors to GPP interannual variation through their influences on plant hydraulics. Applying our framework to satellite observations and meteorological reanalysis data, we diagnose a global CO₂- induced GPP trend of 4.4 gC m−2 year−2, which is at least one-third stronger than the median trends of 13 dynamic global vegetation models and eight satellite-derived GPP products, mainly because of their differences in the magnitude of CFE in evergreen broadleaf forests. These results highlight the critical role that CFE has played in the global carbon cycle in recent decades.

Rising atmospheric dryness [vapor pressure deficit (VPD)] can limit photosynthesis and thus reduce vegetation productivity. Meanwhile, plants can benefit from global warming and the fertilization effect of carbon dioxide (CO2). There are growing interests to study climate change impacts on terrestrial vegetation. However, global vegetation productivity responses to recent climate and CO2 trends remain to be fully understood. Here, we provide a comprehensive evaluation of the relative impacts of VPD, temperature, and atmospheric CO2 concentration on global vegetation productivity over the last two decades using a robust ensemble of solar‐induced chlorophyll fluorescence (SIF) and gross primary productivity (GPP) data. We document a significant increase in global vegetation productivity with rising VPD, temperature, and atmospheric CO2 concentration over this period. For global SIF (or GPP), the decrease due to rising VPD was comparable to the increase due to warming but far less than the increase due to elevated CO2 concentration. We found that rising VPD counteracted only a small proportion (approximately 8.1%–15.0%) of the warming and CO2‐induced increase in global SIF (or GPP). Despite the sharp rise in atmospheric dryness imposing a negative impact on plants, the warming and CO2 fertilization effects contributed to a persistent and widespread increase in vegetation productivity over the majority (approximately 66.5%–72.2%) of the globally vegetated areas. Overall, our findings provide a quantitative and comprehensive attribution of rising atmospheric dryness on global vegetation productivity under concurrent climate warming and CO2 increasing. Plain Language Summary Earth is undergoing a sharp rise in atmospheric dryness [vapor pressure deficit (VPD)], temperature, and carbon dioxide (CO2) concentration. Rising VPD can limit photosynthesis and thus reduce vegetation productivity. However, climate warming and CO2 increasing can benefit vegetation productivity to some extent. Therefore, global vegetation responses to a changing climate is much more complex than expected. Here, a robust ensemble of solar‐induced chlorophyll fluorescence and gross primary productivity data was used to evaluate the relative impacts of VPD, temperature, and atmospheric CO2 concentration on global vegetation productivity over the last two decades. Our multiple lines of evidence indicated that global vegetation productivity has increased under rising VPD, temperature, and atmospheric CO2 concentration during this period. Furthermore, we found that the negative impact of rising VPD on global vegetation productivity was comparable to the warming‐induced increase but much smaller than the CO2‐induced increase. That is, rising VPD counteracted only a small proportion of the warming and CO2‐induced increase. Overall, our findings provide a quantitative and comprehensive attribution of rising atmospheric dryness on global vegetation productivity under concurrent climate warming and CO2 increasing. Key Points Multiple lines of evidence showed that global vegetation productivity has increased significantly over the last two decades We quantified the relative impacts of vapor pressure deficit (VPD), temperature, and atmospheric CO2 concentration on solar‐induced chlorophyll fluorescence (SIF) or gross primary productivity (GPP) Rising VPD counteracted a small proportion of the increase in SIF (or GPP) under concurrent climate warming and CO2 increasing

The terrestrial carbon sink is a critical buffer in the climate system, yet its persistence under rising atmospheric CO2 remains a major uncertainty in Earth system projections. Using an ensemble of 20 dynamic global vegetation models from the TRENDY v12 project, we decompose the CO2 sensitivity of the land carbon sink, represented by net biome production (NBP), to diagnose long-term changes in intrinsic efficiency. We identify a robust, emergent turning point in the simulated intrinsic CO2 sensitivity of NBP, shifting from a significant multi-decadal increase to a sustained decline around 1980. This reversal is reproduced in both carbon-only and coupled carbon–nitrogen model classes and is consistent with a progressive decoupling between CO2 sensitivities of carbon inputs and losses (net primary production, NPP versus heterotrophic respiration, Rh). In contrast, the turning point is not readily detectable in the total apparent sensitivity, reflecting both the dominance of high-frequency climate and land-use variability and interacting environmental effects that may partially offset intrinsic CO2 responses. Together, these results point to a weakening intrinsic efficiency of the terrestrial carbon sink, implying diminishing marginal land uptake per unit CO2 increase and a potentially more constrained resilience of future land carbon sequestration than suggested by raw sink magnitudes alone.

Drylands, encompassing over 40% of the conterminous United States (CONUS), are crucial to the global carbon cycle and highly susceptible to climate change. However, Earth system models offer conflicting projections of future drought and vegetation activity in North America, and in-depth analyses of the long-term changes in greenness and its relationship with underlying climate drivers, considering both spatial and temporal variations at the ecosystem scale, are lacking. This study analyzes 20 year (2001–2020) MODIS normalized difference vegetation index (NDVI) observations to assess greenness trends in CONUS drylands and their relationship with climate drivers at 1 km spatial resolution. Results indicate a large scale and systematic greening trend, particularly in the northern Great Plains (NGP) region. Using an empirical linear attribution approach and empirical orthogonal function analysis, we uncover varied relationships between greenness trends and climate drivers, particularly highlighting the dominant role of increased precipitation in driving the observed greening. Trend analysis reveals that while rain use efficiency (RUE) remains stable in most areas, increases in the NGP region suggest potential CO2 fertilization effects, while decreases in southern states correlate with rising temperatures. We also develop an efficiency-based model featuring RUE which successfully reproduces historical NDVI, re-confirming the dominant influence of precipitation in local greenness interannual variability. However, CMIP6 projections for 2021–2040 under the ‘Regional Rivalry’ scenario (SSP370) paint a worrying picture, with projected browning in the NGP region and states near the 42°N latitude, contrasting recent greening trends. This potential reversal underscores the vulnerability of these ecosystems to future climate change, highlighting the need to consider both historical trends and future climate projections when assessing the resilience of drylands ecosystems. Overall, our work re-emphasizes the significance of water availability to drylands vegetation growth and contributes to a more comprehensive understanding of carbon-water cycling in arid and semi-arid regions.

Forest gross primary production (GPP) is influenced by the interplay between climate conditions and atmospheric CO2 levels, which interact in complex ways, generating both compensating and amplifying effects. In this study, eddy covariance flux measurements from 50 forest ecosystems were integrated with simulations from 14 terrestrial biosphere models to investigate how climate conditions and atmospheric CO2 concentrations regulate forest GPP. This approach bridges site-level observations with biome-scale model estimates to develop a global understanding. Our findings suggest that in boreal and cold temperate regions, temperature primarily constrains the enhancement of the CO2 fertilization on forest GPP; however, warming and higher atmospheric CO2 levels are projected to alleviate these limitations. In tropical forests, CO2 fertilization strongly enhances GPP, but this benefit will be counterbalanced by the adverse impacts of projected climate warming. Consequently, the interplay between climate and atmospheric CO2 in affecting forest GPP is dynamic and subject to continual change.

The investigation of the spatiotemporal variation trend of the atmospheric CO 2 fertilization effect ( $\\beta $ β ) has emerged as a prominent topic of interest on a global scale in recent times. Nevertheless, the spatiotemporal patterns of $\\beta $ β remain unclear. Herein, we selected the mid-latitude forests of China as the designated study region. Accordingly, remote sensing Gross Primary Productivity (GPP) products were used along with model-based GPP simulation results and tree-ring data in this study. This was combined with the random forest algorithm and a moving window approach to assess the spatiotemporal patterns of vegetation productivity and tree growth responses to atmospheric CO 2 variations between 1982 and 2015. Our findings suggest that from 1982 to 2015, the estimated $\\beta $ β derived from the two remote sensing GPP products demonstrated a declining trend. In particular, the EC-LUE GPP exhibited a decrease rate of −0.46%.100 ppm −1 yr −1 , while the NIRv GPP showed a decrease rate of −0.04%.100ppm −1 yr −1 . Similarly, the findings from the estimation based on models also indicated a decline in $\\beta $ β , with an average decrease rate of −0.08%.100 ppm −1 yr −1 across a total of 18 models. Based on the analysis of tree rings from 16 sites, it was observed that the radial growth response of vegetation to atmospheric CO 2 exhibited a decline with an average decrease rate of −0.81%.100 ppm −1 yr −1 . We speculated that the observed trend in β is primarily driven by LAI and forest age.

Terrestrial and oceanic carbon sinks together sequester >50% of the anthropogenic emissions, and the major uncertainty in the global carbon budget is related to the terrestrial carbon cycle. Hence, it is important to understand the major drivers of the land carbon uptake to make informed decisions on climate change mitigation policies. In this paper, we assess the major drivers of the land carbon uptake-CO2 fertilization, nitrogen deposition, climate change, and land use/land cover changes (LULCC)-from existing literature for the historical period and future scenarios, focusing on the results from fifth Coupled Models Intercomparison Project (CMIP5). The existing literature shows that the LULCC fluxes have led to a decline in the terrestrial carbon stocks during the historical period, despite positive contributions from CO2 fertilization and nitrogen deposition. However, several studies find increases in the land carbon sink in recent decades and suggest that CO2 fertilization is the primary driver (up to 85%) of this increase followed by nitrogen deposition (∼10%-20%). For the 21st century, terrestrial carbon stocks are projected to increase in the majority of CMIP5 simulations under the representative concentration pathway 2.6 (RCP2.6), RCP4.5, and RCP8.5 scenarios, mainly due to CO2 fertilization. These projections indicate that the effects of nitrogen deposition in future scenarios are small (∼2%-10%), and climate warming would lead to a loss of land carbon. The vast majority of the studies consider the effects of only one or two of the drivers, impairing comprehensive assessments of the relative contributions of the drivers. Further, the broad range in magnitudes and scenario/model dependence of the sensitivity factors pose challenges in unambiguous projections of land carbon uptake. Improved representation of processes such as LULCC, fires, nutrient limitation and permafrost thawing in the models are necessary to constrain the present-day carbon cycle and for more accurate future projections.

AIM: Forest responses to global‐change drivers such as rising atmospheric CO₂ concentrations (Cₐ), warming temperatures and increased aridification will depend on tree species and site characteristics. We aim to determine if rising Cₐ enhances growth of coexisting pine species along broad ecological gradients in a drought‐prone area. LOCATION: Iberian Range, Spain. METHODS: We sampled 557 trees of five pine species encompassing a wide climatic gradient and measured their radial growth. We used nonlinear flexible statistics (generalized additive mixed models) to characterize growth trends and relate them to Cₐ, temperature and water balance. RESULTS: The sites most responsive to the growing‐season water balance were dominated by Pinus pinaster and Pinus nigra at low elevations, whereas those most responsive to temperatures were high‐elevation Pinus sylvestris and Pinus uncinata stands. From 1950 onwards, most sites and species showed decreasing radial growth trends. Growth trends were coherent with a CO₂‐related fertilization effect only in one P. sylvestris site. MAIN CONCLUSIONS: We found little evidence of growth stimulation of Iberian pine forests due to rising Cₐ. The results indicated that any positive effect of a Cₐ‐induced growth increase was unlikely to reverse or cancel out the drought‐driven trends of reduced growth in most Mediterranean pine forests. Further assessments of CO₂‐fertilization effects on forest growth should be carried out in sites where climatic stressors such as drought do not override the effects of rising Cₐ on forest growth.

Elevated atmospheric CO 2 concentrations ([eCO 2 ]) and soil water deficits significantly influence gas exchange in plant leaves, affecting the carbon-water cycle in terrestrial ecosystems. However, it remains unclear how the soil water deficit modulates the plant CO 2 fertilization effect, especially for gas exchange and leaf-level water use efficiency (WUE). Here, we synthesized a comprehensive dataset including 554 observations from 54 individual studies and quantified the responses for leaf gas exchange induced by e[CO 2 ] under water deficit. Moreover, we investigated the contribution of plant net photosynthesis rate ( P n ) and transpiration rates ( T r ) toward WUE in water deficit conditions and e[CO 2 ] using graphical vector analysis (GVA). In summary, e[CO 2 ] significantly increased P n and WUE by 11.9 and 29.3% under well-watered conditions, respectively, whereas the interaction of water deficit and e[CO 2 ] slightly decreased P n by 8.3%. Plants grown under light in an open environment were stimulated to a greater degree compared with plants grown under a lamp in a closed environment. Meanwhile, water deficit reduced P n by 40.5 and 37.8%, while increasing WUE by 24.5 and 21.5% under ambient CO 2 concentration (a[CO 2 ]) and e[CO 2 ], respectively. The e[CO 2 ]-induced stimulation of WUE was attributed to the common effect of P n and T r , whereas a water deficit induced increase in WUE was linked to the decrease in T r . These results suggested that water deficit lowered the stimulation of e[CO 2 ] induced in plants. Therefore, fumigation conditions that closely mimic field conditions and multi-factorial experiments such as water availability are needed to predict the response of plants to future climate change.

Soil health underpins the productivity and ecosystem functioning of rice paddies, yet its response to elevated atmospheric CO2 (eCO2) remains poorly understood. Here, soil health responses to eCO2 are evaluated using the two longest‐running rice free‐air CO2 enrichment experiments, spanning 12 and 15 years. The results show that long‐term eCO2 significantly improves soil health, strengthening its capacity to support crop production, water purification, and climate change mitigation. Integration of global observations further indicates that these improvements are widespread and cumulative over time, with paddy soils benefiting more than other terrestrial ecosystems. Consequently, long‐term eCO2 exposure tends to enhance rice yield gains, in contrast to the productivity plateau observed in natural ecosystems. These findings provide novel and comprehensive evidence that long‐term eCO2 enhances paddy soil health, improving soil multifunctionality and reinforcing the rice CO2 fertilization effect. Combining the two longest‐running rice free‐air CO2 enrichment experiments with a global data synthesis, this study demonstrates that long‐term elevated CO2 consistently enhances soil health. In rice paddies, this improvement sustains the CO2 fertilization effect over decades. Proactive measures to avert potential phosphorus deficiency and soil acidification are essential, allowing healthier soils to further reinforce future food security.