Divergent Roles of UV Exposure and Microclimatic Conditions in the Decomposition of Standing and Soil Surface Litter in a Semi‐Arid Steppe

• Published in: Journal of geophysical research. Biogeosciences 2024-07, Vol.129 (7), p.n/a
• Main Authors: Yang, Sen, Wang, Jing, Su, Jiao, Peng, Ziyang, Guo, Lulu, Wu, Yuntao, Chang, Pengfei, Wang, Yi, Huang, Junsheng, Liu, Lingli
• Format: Article
• Language: English
• Subjects: Air temperature; Arid lands; Arid zones; Aridity; Carbon; Climatic conditions; Decomposers; Decomposition; Degradability; Dissolved organic carbon; Exposure; Fluctuations; Grasslands; Humidity; lignin; Litter; litter decomposition; Microclimate; microclimatic fluctuation; Organic soils; Phenols; Photodegradation; Plant cover; Senescence; Sensitivity enhancement; Soil; Soil degradation; Soil surfaces; Soil temperature; Soils; Steppes; Substrates; Ultraviolet radiation; UV radiation; Vegetation cover
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2023JG007934

Recent studies have highlighted the crucial role of abiotic processes, such as photodegradation and microclimatic fluctuation, in accelerating dryland litter decomposition. In grasslands, substantial amounts of dead plant material persist upright above the soil surface after senescence, experiencing distinct microclimatic conditions compared to surface litter. However, our understanding of how ultraviolet (UV) exposure and microclimatic conditions influence their decomposition is limited. To address this knowledge gap, we conducted a field experiment manipulating UV radiation for both soil surface litter and standing litter and monitored their microclimatic conditions in a semi‐arid grassland. Our findings indicate that UV exposure enhanced the decomposition of soil surface litter by alleviating the constraint of lignin on litter decomposition, while having no significant influence on standing litter. Although the mean levels of thermal‐hydric conditions were lower, more intense fluctuation of temperature and air humidity was detected in standing litter. These higher‐level microclimatic fluctuations facilitated the release of dissolved organic carbon, potentially increasing the availability of labile substrates to microbes. Meanwhile, standing litter released more photo‐sensitive phenols, leading to decreased sensitivity to UV exposure. Consequently, while UV exposure initially increased standing litter decomposition during the early stage, its influence eventually diminished. These findings underscore the critical yet differing roles of microclimatic conditions and UV exposure in the decomposition of standing and surface litter. Relying solely on knowledges derived from surface litter decomposition and microclimate conditions may not accurately capture the patterns of grassland litter degradation. Plain Language Summary The limited precipitation in drylands is widely believed to restrict litter decomposition. However, the observed litter decomposition rates in these regions often exceed model predictions based on climatic conditions. In arid and semi‐arid steppes, the sparse vegetation cover results in intense ultraviolet (UV) radiation reaching soil surface, thereby triggering photodegradation of the recalcitrant compounds in litter. Additionally, substantial dead plant materials persist standing for months to years, and undergoes more intense warm‐cold and wet‐dry cycles. However, there have been limited studies assessing the intricate interplay between