High- and low-quality litter are equally important to the improvement of grassland soil multifunctionality and quality.

Grassland ecosystems, as one of the most significant ecological units on Earth, play a crucial role in the global carbon cycle and biodiversity conservation due to their extensive coverage and huge soil carbon storage. Litter, as an important component of soil ecosystems, plays a crucial role in soil nutrient cycling, organic matter dynamics, and the structure and function of grassland ecosystems. However, the mechanisms by which different quality litter and their decomposition differences affect the soil multifunctionality (SMF) and quality index (SQI) of grassland remain unclear. Through a 450-day in situ decomposition experiment in the field, we explored the mechanisms by which high-quality (low C:N ratio; Lespedeza dahurica (leaf: LL, root: LR)) and low-quality (high C:N ratio; Artemisia sacrorum (leaf: AL, root: AR)) litter decomposition affect the SMF and SQI of grassland. The results showed that the litter decomposition rate (K) was higher for high-quality litter than for low-quality litter (LL > AL, LR > AR). Moreover, K was significantly correlated with litter N, P, C:N ratio, and C:P ratio, Enzymatic stoichiometry revealed a transition from N to P limitation around 180 days, with P limitation intensifying progressively during decomposition. Despite variations in litter quality, all treatments similarly enhanced SMF and SQI, with no significant intergroup differences detected. Specifically, after 450 days of decomposition, the 0-5 cm soil layer LL, LR, AL, and AR increased SMF by 151.45 %, 128.33 %, 149.81 %, and 134.19 %, respectively; the 5-10 cm soil layer increased SMF by 163.90 %, 157.52 %, 175.94 %, and 155.32 %, respectively. Random forest and segmented regression analysis indicated that litter nutrient release rate and P limitation in the two soil layers (0-5 cm, 5-10 cm) were the key factors driving SMF and SQI, and were significantly positively correlated with SMF and SQI. Our research shows a similar capacity of contrasting-quality litters to improve SMF and SQI, revising the traditional quality-benefit paradigm. This functional equivalence challenges the traditional 'quality-benefit' paradigm, suggesting that low-quality litters could be equally effective in grassland restoration, particularly under resource-limited conditions.