{"id":2555,"date":"2025-08-04T07:04:15","date_gmt":"2025-08-04T06:04:15","guid":{"rendered":"https:\/\/research.reading.ac.uk\/lemontree\/?p=2555"},"modified":"2025-08-04T07:04:15","modified_gmt":"2025-08-04T06:04:15","slug":"what-rain-pulses-reveal-about-carbon-losses-in-dryland-ecosystems","status":"publish","type":"post","link":"https:\/\/research.reading.ac.uk\/lemontree\/what-rain-pulses-reveal-about-carbon-losses-in-dryland-ecosystems\/","title":{"rendered":"What rain pulses reveal about carbon losses in dryland ecosystems"},"content":{"rendered":"

Drylands are sprawling regions that cover one-third of the Earth\u2019s land surface. In these regions, rain is infrequent, but when it comes, it doesn\u2019t just nourish plants, it also sparks a sudden, invisible rush of carbon dioxide into the atmosphere. This phenomenon, long known in soil science as the Birch effect, occurs when dry soils are rapidly rewetted, triggering microbial activity and soil respiration.<\/p>\n

A new study led by LEMONTREE\u2019s Ngoc B. Nguyen (a Ph.D. student from the University of California, Berkeley) published in Nature Geoscience<\/em>, shows that these brief but intense bursts of CO\u2082 emissions are widely underestimated in ecosystem models and carbon accounting methods. Using a combination of machine learning, eddy covariance data, and a new bias-correction tool called FluxPulse<\/a>, the team found that rain-induced carbon losses play a far greater role in dryland carbon balance than previously recognized.<\/p>\n

Rain pulses: small in time, large in impact<\/h2>\n

Across 34 dryland ecosystems worldwide, Nguyen and colleagues identified more than 1800 rewetting events using high-frequency data from eddy covariance towers. They found that on average, 17% of annual ecosystem respiration (Reco<\/sub>) and nearly 10% of net ecosystem productivity (NEP) occurs during these short-lived rain pulses, most of which last just a few days.<\/p>\n

Yet current models miss a large portion of this carbon flow. Traditional methods show significant underestimations of up to 30% of ecosystem respiration and photosynthesis during rain-pulse events, with rain-pulse events accounting for 16.9\u00b1 2.8% of annual ecosystem respiration and 9.6\u00b1 2.2% of net ecosystem productivity.<\/p>\n

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Figure 1\u00a0 (a) Contributions of ecosystem respiration (Reco) and net ecosystem productivity (NEP) during pulse events to annual Reco and NEP. (b) Performance of partitioning methods on estimating ecosystem respiration (Reco) and gross primary product during pulse events. (c) Half-hourly time series visualization of NEE, ecosystem respiration estimated by the FluxPulse bias-corrected algorithm (FluxPulse Reco) and by the NT method Reco at the Albuera site, Spain (ES-Abr) in 2017.<\/figcaption><\/figure>\n

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This underestimation occurs because most models assume a gradual relationship between CO\u2082 fluxes and environmental drivers like temperature and light. But rain pulses are non-steady-state events, and the sharp increases in CO\u2082 immediately following rewetting don\u2019t conform to these assumptions.<\/p>\n

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\u201cThese CO\u2082 bursts are short-lived but disproportionately important. By not capturing them, we\u2019ve been missing a major part of the carbon story in drylands\u201d says Ngoc Nguyen.<\/em><\/p>\n

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Understanding the carbon pulses: causes and drivers<\/h2>\n

The pulse itself has both biotic and abiotic origins. Microbes, long dormant in dry conditions, quickly revive and metabolise newly available organic matter after rainfall. This microbial activity releases CO\u2082, a biological response known as the Birch effect. Abiotic processes, like the displacement of CO\u2082 from soil pores, also play a role but are secondary.<\/p>\n

Crucially, the team found that these CO\u2082 pulses decay in a consistent and predictable pattern, following a universal exponential decay curve across different ecosystems. The average decay rate was 0.16 per day, meaning most of the carbon is emitted within the first few days of a rain event.<\/p>\n

\u201cWe found that when you normalize the pulse by intensity, all sites converge on the same decay function,\u201d Nguyen explains. \u201cThat consistency suggests a shared microbial or soil water dynamic at play.\u201d<\/p>\n

What controls the strength of the pulse?<\/h2>\n

While rainfall triggers these events, precipitation itself is not the best predictor of pulse size or intensity. Instead, the team identified several more important factors:<\/p>\n