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Drylands cover roughly 40% of Earth’s land surface and play a major role in the global land-atmosphere carbon exchange. Most carbon in dryland ecosystems is stored in soils, but little is known about its stability and persistence upon climate and vegetation change. Researchers at the Max Planck Institute for Biogeochemistry now used radiocarbon to show that organic carbon in dryland topsoils is much older than previously estimated, averaging about 2,000 years. However, when dry soils are wetted, even old carbon is decomposed and respired by microbes. The results can improve predictions of soil organic carbon dynamics in global drylands under rapid climate and land use changes.
Drylands constitute the largest natural ecosystems on Earth’s surface. Their biological activity and carbon fluxes are strongly limited by water availability. Drylands are also home to nearly 40% of the global population and are experiencing rapid land-use change. Recent global assessments, including those by the Intergovernmental Panel on Climate Change (IPCC), highlight the need to understand how dryland ecosystems may evolve under future climate and land-use scenarios. Sustainable development in drylands must be built on a mechanistic understanding of the ecosystem’s biogeochemical processes. Among these, the carbon cycle is of particular concern because the large area of dryland soils holds a large store of organic carbon (C), despite generally low C concentrations. Large changes in processes regulating C uptake and loss associated with varying water supply are also a major cause of global interannual variation in land-atmosphere C exchange. However, major uncertainties remain about how soil organic carbon in drylands will respond to large fluctuations in precipitation between years and changes in land management.
Researchers at the Max Planck Institute for Biogeochemistry use radiocarbon measurements to quantify the age and turnover time of organic carbon in soils. While the unique advantage of radiocarbon has made it widely used for studying soil carbon cycling in forest and humid ecosystems, the processes responsible for carbon cycling rates in wetter systems may not hold in arid ones. “Surprisingly few radiocarbon measurements exist for drylands, limiting our ability to understand how long dryland soils store and release carbon,” says Dr. Jianbei Huang, group leader at the Max Planck Institute for Biogeochemistry and senior author of the study. “Addressing this significant gap requires combining radiocarbon measurements with soil samples collected across the broad environmental and climatic gradients of dryland ecosystems”.
To fill the gap in global understanding, Hui Wang, PhD researcher and first author of the study published in Nature Communications, analyzed radiocarbon in soil organic matter and in CO₂ released from soils. This was possible by using samples collected by an international team from 97 dryland sites across six continents. Organic carbon stored in these soils was found to be, on average, more than 2,000 years old, while carbon released as CO₂ was about 500 years old—much older than models predicted. “Organic carbon stored in and released by dryland soils is much older than previously expected,” Wang says.
To understand what controls the age of the carbon stored in and released from dryland soils, the team examined how radiocarbon ages varied with climate, plant and soil properties. The age of organic carbon and respired CO2 was strongly influenced by aridity, plant productivity, and the amount of organic carbon stored in soils. “In drylands, aridity matters more than temperature for how old soil carbon becomes, because water controls plant growth and the supply of new carbon entering soils," Wang explains.
These findings help explain how soil organic carbon and its persistence in drylands may change under future climate and land-use change. “As drylands become drier with climate change, carbon may stay longer in soils, but the soils may become less able to absorb additional carbon from the atmosphere,” says Dr. Huang. “Land management that increases vegetation C inputs, such as planting trees, can help soils store more carbon, but it may also speed up carbon cycling and reduce the ability of soils to retain additional carbon over time,” adds Prof. Trumbore, director at Max Planck Institute for Biogeochemistry in Jena.
Radiocarbon methodology proved essential for the study. The natural radioactive decay of radiocarbon allows estimation of the age of soil carbon over hundreds to thousands of years. However, over the last 6 decades, the tracing of excess radiocarbon created during atmospheric nuclear tests in the 1960s has allowed estimating of C turnover in organic matter over years to decades. “Radiocarbon provides a powerful empirical tool for studying how long carbon has been stored and how quickly it cycles between land and the atmosphere,” says Prof. Susan Trumbore.
The study was conducted within the framework of a collaborative and interdisciplinary project led by Prof. Susan Trumbore and Dr. Jianbei Huang at the Max Planck Institute for Biogeochemistry (MPI-BGC) and Prof. Bojie Fu and Prof. Nan Lu at the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (CAS-RCEES). The study greatly benefited from sample collection and laboratory analyses carried out by a large international team of researchers, coordinated by Prof. Fernando T. Maestre at King Abdullah University of Science and Technology, Saudi-Arabia. “This study highlights how international collaboration among scientists is essential for addressing the complex challenges facing drylands in a changing world,” concludes Dr. Huang.
Prof. Susan Trumbore, Ph.D.
Director
Max Planck Institute for Biogeochemistry
tel: +49 3641 57-6110
tel: +49 1609 7262795
trumbore@bgc-jena.mpg.de
Dr. Jianbei Huang
Groupleader
Max Planck Institute for Biogeochemistry
+49 3641 57-6368
hjianbei@bgc-jena.mpg.de
https://www.nature.com/articles/s41467-026-70623-9
https://doi.org/10.1038/s41467-026-70623-9
https://www.bgc-jena.mpg.de/bgp Webpage Trumbore Department
https://www.bgc-jena.mpg.de/bgp/drylands Webpage Research Group
Dryland ecosystems sampled along an aridity gradient in northern China: (a) meadow steppe, (b) typic ...
Source: Dr. Nan Lu & colleagues (CAS)
Copyright: Dr. Nan Lu, and MPI-BGC
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