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We established two field decomposition experiment s using Leymus chinensis and Stipa grandis litter, to quantify the effect of different decomposition drivers (including microbial decomposition, abiotic photodegradation and photoacceleration) on the decomposition of different litter types (surface litter and standing dead) and age (young and old). In experiment … , the presence of photodegradation greatly enhanced the effect of microorganisms. For surface litter, microbial decomposition, abiotic photodegradation and photoacceleration reduced mass 64. 4%, 18. 9% and 16.7% respectively. For standing dead, microbial decomposition, abiotic photodegradation and photoacceleration reduced mass by 51.6%, 21. 5% and 26.9% respectively. Solar radiation affected the decomposition of carbon only; it had no effect on nitrogen. Cellulose was less susceptible to the effect of solar radiation than lignin and hemicellulose. In experiment …¡, we assessed the effects of prior solar radiation on the subsequent decomposition of plant litter, and found that microbial decomposition and abiotic photodegradation decreased the mass of young litter more than that of old litter, while photoacceleration decreased the mass of young litter less than that of old litter. In conclusion, our results indicated that the impact of abiotic photodegradation tended to decrease over time, and that photoacceleration contributed more to the mass loss than the direct photo-mineralization. Our results suggest that although young and dead standing plant biomass can accelerate decomposition process, which potentially increases the carbon loss of ecosystem and decreas es the accumulation of organic carbon ; this may indicate a new challenge for grassland sustainability.