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Contrasting Carbon and Water Flux Dynamics in an East African Rangeland and Cropland.

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Title: Contrasting Carbon and Water Flux Dynamics in an East African Rangeland and Cropland.
Authors: Odongo, Vincent1 (AUTHOR) v.odongo@cgiar.org, Leitner, Sonja M.1 (AUTHOR), Dowling, Thomas P. F.2,3 (AUTHOR), Gluecks, Ilona4 (AUTHOR), Jackowicz‐Korczynski, Marcin5 (AUTHOR), Rinne, Janne5,6 (AUTHOR), Wooster, Martin J.2 (AUTHOR), Merbold, Lutz1,7 (AUTHOR)
Source: Journal of Geophysical Research. Biogeosciences. Oct2025, Vol. 130 Issue 10, p1-21. 21p.
Subject Terms: *Rangelands, *Carbon cycle, *Land management, *Climate change, *Farms, *Savannas, Ecological resilience, Water vapor transport
Geographic Terms: East Africa
Abstract: This study examines carbon (C) and water dynamics in two East African dryland ecosystems: a savanna rangeland grazed by livestock and wildlife, and a rainfed cropland under minimal tillage. Over 185 days, both systems were showed a similar magnitude of C emissions with differing temporal patterns. The rangeland showed fluctuating C exchange, with losses followed by increased C uptake after rainfall events. The cropland initially acted as a C sink, and when lateral C export from chickpea harvest were accounted for, the overall C balance shifted to a net source. Cropland demonstrated higher carbon use efficiency (CUE), driven by efficient C allocation for crop growth, supported by fertilizers, pesticides, and minimum tillage practices. During the peak growing period, cropland also had greater water use efficiency (WUE) likely reflecting optimized agricultural management under favorable moisture conditions. However, over the entire period, WUE was significantly higher in the rangeland than in the cropland (p > 0.05) possibly due to more consistent vegetation cover and adaptive traits that minimize water loss. The cropland showed a complex relationship between WUE and CUE, where increased productivity also simultaneously drove higher respiration rates. Our findings, particularly the shift in cropland carbon balance following harvest emphasize the importance of including lateral C fluxes and intra‐annual variations in C balance assessments for accurate budgeting. Both ecosystems were co‐limited by water and nitrogen, with plant adaptations to drought and dry spells, including efficient water use and sustained photosynthesis under moisture stress playing a critical role in maintaining ecosystem CUE. Sustainable land management strategies that account for the interactions between C and water dynamics, biodiversity, and ecosystem functioning are vital to enhancing C storage, mitigating climate change, and improving resilience in rangelands and croplands. Plain Language Summary: East Africa's drylands are vital ecosystems, but how do they balance carbon and water under the dry environmental conditions? Our study sheds light on two such ecosystems: a savanna rangeland grazed by livestock and wildlife, and a cropland managed with minimal soil disturbance. Over 6 months, we discovered that both ecosystems gained and lost about the same amount of carbon overall. However, they did so in different ways: The rangeland's carbon levels fluctuated, with losses during dry spells and gains after rain, reflecting its long‐term adaptation to semi‐arid conditions. Meanwhile, the cropland initially acted as a carbon sink, but when we factored in the carbon removed during harvest, it balanced out. The cropland was also better at using carbon and water efficiently during the growing season, thanks to farming practices like fertilizer use and pest control. Our findings highlight the delicate balance between carbon and water in these ecosystems, shaped by rainfall, nutrients, and management practices. Understanding these dynamics is crucial for improving land management strategies that protect biodiversity, enhance carbon storage, and build resilience against climate change. Key Points: Accounting for lateral carbon export from chickpea harvest adjusted the net carbon balance of cropland to near neutralRespiration in the rangeland was decoupled from increasing GPP likely due to nutrient limitations and water‐conserving plant adaptationsRangelands conserve water at the expense of biomass, reducing water use efficiency during water‐abundant periods like the growing season [ABSTRACT FROM AUTHOR]
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Abstract:This study examines carbon (C) and water dynamics in two East African dryland ecosystems: a savanna rangeland grazed by livestock and wildlife, and a rainfed cropland under minimal tillage. Over 185 days, both systems were showed a similar magnitude of C emissions with differing temporal patterns. The rangeland showed fluctuating C exchange, with losses followed by increased C uptake after rainfall events. The cropland initially acted as a C sink, and when lateral C export from chickpea harvest were accounted for, the overall C balance shifted to a net source. Cropland demonstrated higher carbon use efficiency (CUE), driven by efficient C allocation for crop growth, supported by fertilizers, pesticides, and minimum tillage practices. During the peak growing period, cropland also had greater water use efficiency (WUE) likely reflecting optimized agricultural management under favorable moisture conditions. However, over the entire period, WUE was significantly higher in the rangeland than in the cropland (p > 0.05) possibly due to more consistent vegetation cover and adaptive traits that minimize water loss. The cropland showed a complex relationship between WUE and CUE, where increased productivity also simultaneously drove higher respiration rates. Our findings, particularly the shift in cropland carbon balance following harvest emphasize the importance of including lateral C fluxes and intra‐annual variations in C balance assessments for accurate budgeting. Both ecosystems were co‐limited by water and nitrogen, with plant adaptations to drought and dry spells, including efficient water use and sustained photosynthesis under moisture stress playing a critical role in maintaining ecosystem CUE. Sustainable land management strategies that account for the interactions between C and water dynamics, biodiversity, and ecosystem functioning are vital to enhancing C storage, mitigating climate change, and improving resilience in rangelands and croplands. Plain Language Summary: East Africa's drylands are vital ecosystems, but how do they balance carbon and water under the dry environmental conditions? Our study sheds light on two such ecosystems: a savanna rangeland grazed by livestock and wildlife, and a cropland managed with minimal soil disturbance. Over 6 months, we discovered that both ecosystems gained and lost about the same amount of carbon overall. However, they did so in different ways: The rangeland's carbon levels fluctuated, with losses during dry spells and gains after rain, reflecting its long‐term adaptation to semi‐arid conditions. Meanwhile, the cropland initially acted as a carbon sink, but when we factored in the carbon removed during harvest, it balanced out. The cropland was also better at using carbon and water efficiently during the growing season, thanks to farming practices like fertilizer use and pest control. Our findings highlight the delicate balance between carbon and water in these ecosystems, shaped by rainfall, nutrients, and management practices. Understanding these dynamics is crucial for improving land management strategies that protect biodiversity, enhance carbon storage, and build resilience against climate change. Key Points: Accounting for lateral carbon export from chickpea harvest adjusted the net carbon balance of cropland to near neutralRespiration in the rangeland was decoupled from increasing GPP likely due to nutrient limitations and water‐conserving plant adaptationsRangelands conserve water at the expense of biomass, reducing water use efficiency during water‐abundant periods like the growing season [ABSTRACT FROM AUTHOR]
ISSN:21698953
DOI:10.1029/2024JG008623