Aims <p>Ultraviolet (UV) radiation is increasingly recognized as a key driver of litter decomposition and nutrient cycling, particularly in arid and semi-arid ecosystems. However, its role in shaping microbial communities and litter decomposition in valley-type savannas with extreme environmental conditions remains poorly understood.</p> Methods <p>A 15-month field experiment was conducted in a dry-hot valley, using UV-transparent and UV-blocking treatments to assess litter decomposition rates, chemical changes, microbial diversity, and functional pathways. High-throughput sequencing and functional predictions were employed to analyze microbial responses.</p> Results <p>UV radiation accelerated litter decomposition, increasing mass loss by 48.11% and decomposition rate constants by 60%. It promoted the breakdown of recalcitrant compounds, such as lignin and cellulose, enhancing the release of key nutrients like carbon and nitrogen. Microbial community composition shifted under UV exposure, favoring stress-tolerant taxa such as Sordariomycetes and Alphaproteobacteria. Functional predictions revealed upregulation of pathways related to oxidative stress response, DNA repair, and aromatic compound degradation. Strong positive correlations were observed between microbial diversity, stress-tolerant microbial phenotypes, such as aerobic and facultatively anaerobic bacteria, and increased decomposition rates, suggesting that microbial community diversity and function mediate UV-driven decomposition processes.</p> Conclusions <p>Our findings highlight the dual role of UV radiation as both a driver of photodegradation and a modulator of microbial community dynamics, emphasizing its importance in shaping nutrient cycling processes. This study provides critical insights into abiotic and biotic interactions in litter decomposition and underscores the need to incorporate UV radiation effects into ecological management strategies for valley-type savannas.</p>