Arid ecosystems occupy about two-fifths of the global land surface, and fluctuations in their productivity play a pivotal role in global carbon sequestration and ecosystem service provision. However, the global-scale effect of desertification expansion on the annual maximum photosynthetic peak has not yet been systematically quantified. In this study, 30-m high-resolution desert cover data (GLCLUC) and multi-source remote-sensing photosynthetic indicators were integrated, using a space-for-time substitution framework to establish a global desertification scenario classification system. We quantitatively evaluated the influence of diverse desert expansion and contraction scenarios on the ecosystem photosynthetic peak (GPPmax). Results indicate that the average GPPmax in high-intensity expansion regions (HIEs) is 8.23 g C m−2 8d−1, whereas medium- to low-intensity expansion regions (MIEs) show a value of 8.95 g C m−2 8d−1. By contrast, medium- to low-intensity contraction regions (MIRs) and high-intensity contraction regions (HIRs) demonstrate markedly higher GPPmax values of 10.64 g C m−2 8d−1 and 17.64 g C m−2 8d−1, respectively. Regarding the photosynthetic peak difference (ΔGPPmax), expansion scenarios (HIEs, MIEs) significantly decrease ecosystem photosynthetic potential, with average ΔGPPmax reductions of 1.19–3.95 g C m−2 8d−1 relative to contraction scenarios (HIRs, MIRs). The most pronounced losses occur in South America, North America, and Eurasia, with South America exhibiting reductions exceeding 6 g C m−2 8d−1. Additionally, ecosystems with initially higher photosynthetic potential experience greater GPPmax declines under intense desert expansion. This study provides the first global-scale evidence revealing how different desertification pathways modify ecosystem photosynthetic peaks and their regional disparities, offering critical scientific support for ecological restoration, carbon sequestration strategies, and land management across arid landscapes.
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