Over the past several decades, rising atmospheric concentrations of carbon dioxide (CO₂), alongside increasing global temperatures and the escalating vapour pressure deficit (VPD), have been recognized as critical drivers influencing plant photosynthesis and terrestrial gross primary production (GPP). GPP is the total amount of carbon dioxide that vegetation captures through photosynthesis, serving as a crucial component of the global carbon cycle. However, the complex interplay between these environmental factors and their spatial variability across different climate regimes has remained elusive—until now.

Using a comprehensive dataset amalgamating globally distributed FLUXNET measurements with satellite-derived machine learning estimates of GPP spanning four decades from 1982 to 2022, the research team conducted a meticulous analysis to decipher temporal and spatial patterns in vegetation productivity. FLUXNET—a global network of eddy covariance towers—provides precise, ground-based measurements of carbon and water fluxes between ecosystems and the atmosphere, while satellite data extends this insight to a planetary scale with high temporal resolution.

Their analysis uncovered an asymmetric evolution of terrestrial carbon uptake marked by two contrasting trends. While humid regions continue to register a persistent increase in GPP, attributable largely to enhanced CO₂ fertilization effects and warming temperatures that lengthen growing seasons, dryland ecosystems show a pronounced slowdown in productivity gains. This divergence is primarily driven by a sharp increase in atmospheric aridity, reflected by surging VPD values which place severe water limitations on photosynthetic processes in these typically water-scarce environments.

The vapour pressure deficit, representing the difference between the amount of moisture in the air and the amount the air can hold when saturated, acts as a proxy for atmospheric dryness. Elevated VPD exacerbates plant water stress, causing stomatal closure to reduce water loss, but consequently restricting CO₂ uptake essential for photosynthesis. The study convincingly demonstrates that rising VPD in drylands overrides the positive influences of CO₂ and temperature, fundamentally constraining photosynthetic capacity and curtailing carbon uptake in these regions.

Interestingly, despite the mounting evidence from observational data, state-of-the-art dynamic global vegetation models (DGVMs) and Earth system models (ESMs) fail to replicate this contrasting vegetation response in both historical simulations and future projections. These models have traditionally overestimated carbon gains in drylands by underrepresenting water stress impacts and VPD dynamics, thus painting an incomplete and overly optimistic picture of the terrestrial carbon sink’s resilience to climate change.

The implications of this research are profound and multifaceted. As global atmospheric aridity continues to intensify and drylands expand—driven by climate change and land use alterations—the limitation of photosynthetic productivity in these ecosystems signals a potential cap on the land carbon sink. This cap could diminish the biosphere’s capacity to mitigate anthropogenic CO₂ emissions, thereby accelerating the rate of global warming.

Moreover, drylands, which already cover about 40% of the Earth’s terrestrial surface and support nearly 38% of the global population, are crucial for biodiversity, agriculture, and livelihoods. The study’s findings highlight the urgent need to prioritize adaptive management strategies aimed at enhancing water-use efficiency, soil conservation, and drought resistance in dryland ecosystems to sustain their ecological and socio-economic functions.

Conversely, humid regions, characterized by abundant water availability, stand to benefit substantially from the continuing increase in atmospheric CO₂ and moderate warming, which together stimulate photosynthetic activity and carbon sequestration. In these areas, nature-based solutions such as reforestation, wetland restoration, and conservation of primary forests can amplify the natural carbon sink, contributing significantly to climate mitigation efforts.

The divergence elucidated in this study underscores the necessity of region-specific approaches in climate policy and ecosystem management, eschewing one-size-fits-all strategies. Tailored interventions recognizing the water-limited constraints of drylands, alongside leveraging the growth potential of humid zones, could enhance the efficacy of global climate action.

Further research is imperative to refine Earth system models by integrating more sophisticated representations of plant physiological responses to VPD and water stress, along with incorporating fine-scale hydrological feedbacks. Augmented observational networks and high-resolution remote sensing can provide indispensable data to improve model accuracy and predictive capability at regional and global scales.

This study also prompts reconsideration of carbon budget estimates and future climate scenarios, as the diminished carbon uptake capacity in expansive drylands may necessitate recalibration of emission reduction targets and the assessment of negative emission technologies. The pronounced sensitivity of drylands to atmospheric moisture deficits exemplifies the complex interdependencies among biosphere-climate interactions, which must be comprehensively addressed to safeguard Earth’s climate stability.

In summation, the revelation that drylands dominate the recent global slowdown in vegetation carbon uptake represents a paradigm shift in our understanding of terrestrial ecosystem responses to concurrent environmental drivers. The asymmetric shift in GPP trajectories—marked by persistent growth in humid regions and deceleration in drylands—underscores the critical influence of atmospheric moisture stress, rather than temperature or CO₂ alone.

As humanity confronts escalating climate crises, this nuanced comprehension of ecosystem dynamics offers a clarion call for adaptive, scientifically informed stewardship of the planet’s diverse biomes. Recognizing drylands as both vulnerable and pivotal components of the global carbon cycle is essential to formulating effective mitigation and adaptation policies that embrace ecological heterogeneity while striving for a sustainable future.

Subject of Research: Terrestrial carbon uptake dynamics and the interaction of atmospheric CO₂, temperature, and vapour pressure deficit on global vegetation productivity.

Article Title: Dryland dominance in the slowdown of global vegetation carbon uptake.

Article References:
Li, F., Xiao, J., Chen, J. et al. Dryland dominance in the slowdown of global vegetation carbon uptake. Nat. Geosci. (2026). https://doi.org/10.1038/s41561-026-01957-8

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41561-026-01957-8

The atmospheric CO2 concentration, which hovered near 200 parts per million before the Industrial Revolution, surged past 427 parts per million in 2024 and is projected to hit approximately 600 parts per million by 2050. This unprecedented spike exerts profound physiological effects on plants, altering their growth patterns, photosynthetic dynamics, and water usage. While elevated CO2 can be beneficial by increasing photosynthetic rates, the complex interplay with heat stress, drought, and flooding frequently negates these advantages, amplifying vulnerability rather than alleviating it. Professor Long underscores how these converging stressors imperil plant development and reproductive viability, threatening global food security with potential crop failure on catastrophic scales.

Aside from carbon dioxide, the intensified heat waves expected by mid-century will challenge the intrinsic thermal tolerances of many staple crops. Photosynthesis, inherently sensitive to temperature fluctuations, often suffers from reduced enzyme activity and stability under excessive heat. This destabilization ripples through plant metabolism, curtailing net carbon assimilation and ultimately leading to yield declines. Moreover, prolonged droughts aggravate water scarcity, forcing plants to modulate leaf stomatal behavior, the microscopic pores critical for gas exchange. While partial stomatal closure conserves water, it inevitably restricts CO2 influx, creating a physiologically costly trade-off between sustaining hydration and maintaining photosynthetic carbon fixation.

In a striking advance that Professor Long highlights, researchers have identified and manipulated genetic pathways to minimize this trade-off. By increasing expression of specific sensor proteins that regulate stomatal aperture, plants can optimize water retention without compromising carbon uptake. Experiments with genetically engineered tobacco plants demonstrated a startling 15% increase in leaf-level water-use efficiency and a 30% reduction in overall water consumption. Tobacco’s rapid growth cycle and genetic malleability make it an ideal model for such pioneering work, with promising implications for transfer to crop species such as rice and wheat that feed vast populations.

Flooding presents an additional—and paradoxically elemental—threat. While excess water can drown crops like rice, certain cultivars possess innate tolerance to prolonged submergence. Through meticulous screening and evaluation, these flood-resilient varieties have been identified, raising hopes for breeding programs that can extend this resilience across diverse agroecosystems. The ability to survive two or more weeks underwater is a critical trait for regions increasingly prone to monsoon intensification and unpredictable rainfall extremes. By harnessing the genetic blueprints of flood-tolerant phenotypes, breeders can engineer cultivars capable of enduring and recovering from episodic inundations.

Professor Long also explores molecular strategies targeting rubisco, the enzyme that catalyzes the primary step in carbon fixation during photosynthesis. Rubisco notoriously exhibits suboptimal efficiency, with a tendency to catalyze wasteful oxygenation reactions under high temperature and CO2 conditions. Through genetic and biochemical modifications aimed at optimizing rubisco regulation and expression, photosynthetic performance can be enhanced even amidst elevated atmospheric CO2. This enzymatic fine-tuning holds enormous promise to bolster crop yields while optimizing resource use, further buttressing resilience in a less stable climate.

The saga of maize offers a poignant success story within this otherwise daunting landscape. Between 1980 and 2024, U.S. maize yields doubled—a testament to concentrated research efforts and substantial investments by industry leaders. Conversely, closer relatives like sorghum have witnessed a mere 12% improvement, underscoring disparities in resource allocation. Professor Long stresses the urgent need to bridge this investment gap, especially within the public domain where crops vital for direct human consumption languish without comparable support. Achieving scalable, globally impactful “future-proofing” hinges on mobilizing both public and private sectors in tandem.

Water-use efficiency is thus a core battleground in the quest for resilient crops. Enhanced drought tolerance confers not only survival advantages but also stabilizes yields across erratic seasons. Novel techniques that modulate stomatal density—effectively reducing the number of leaf pores—have achieved efficiency improvements of 15-20% without detrimental yield effects in rice and wheat. This delicate balancing act exemplifies the sophisticated, multifaceted approach necessary to overcome the myriad physiological constraints imposed by climate change.

Beyond genetics and breeding, Professor Long argues for holistic crop systems engineering that integrates mitigation strategies to abate atmospheric change itself. Agricultural practices that sequester carbon or reduce greenhouse gas emissions complement crop improvements, creating a virtuous cycle between climate regulation and food production. These integrated solutions present an ambitious blueprint for sustaining agricultural productivity while confronting environmental imperatives.

Nevertheless, the path forward is fraught with obstacles. The timeline for developing and deploying climate-resilient cultivars is lengthy, often spanning multiple growing seasons and regulatory hurdles. The financial and infrastructural demands for sustained research and implementation are substantial. Professor Long calls for a coordinated global response, emphasizing strategic investment in crop science innovation to safeguard humanity’s food supply against intensifying climatic stress.

While the challenges loom large, the review ultimately conveys a message of cautious optimism. Emerging scientific insights and technologies, when harnessed effectively, possess the transformative potential to reshape agricultural futures. By fortifying plant resilience at genetic, physiological, and system levels, researchers can help secure sustenance for a world confronting the harsh realities of environmental change.

Professor Long’s work, supported by Gates Agricultural Innovations and the Department of Energy’s Center for Advanced Bioenergy and Bioproducts Innovation, crystallizes the scientific consensus that adaptive crop development is indispensable for food security in the 21st century. As atmospheric CO2 ascends and climate variability accelerates, the imperative to innovate grows ever more urgent. The ability to “future-proof” crops may well determine the resilience of global food systems and the wellbeing of billions in the decades that lie ahead.

Subject of Research: Crop resilience to climate change; photosynthesis enhancement; water-use efficiency in plants

Article Title: Needs and opportunities to future-proof crops and the use of crop systems to mitigate atmospheric change

News Publication Date: 29-May-2025

Web References:
DOI: 10.1098/rstb.2024.0229
Stephen Long Lab at University of Illinois

Image Credits: Photo by Fred Zwicky

Keywords: Crop resilience, climate change adaptation, photosynthesis, water-use efficiency, genetic engineering, flood tolerance, stomatal regulation, rubisco optimization, maize yields, climate-smart agriculture