Loss of soil ecosystem multifunctionality during alpine grassland restoration with reseeding and organic fertilization

Abstract

The degradation of alpine grasslands threatens their capacity to provide essential ecosystem services, prompting extensive restoration efforts such as reseeding and fertilization. However, the long-term effects of these approaches on soil ecosystem multifunctionality (EMF) remain uncertain. Here, we conducted a five-year field experiment in a degraded alpine grassland on the central Qinghai-Tibet Plateau in Nagqu to assess the effect of organic fertilization, native grasses (Poa annua, Elymus nutans, and Puccinellia distans) reseeding, oat (Avena sativa L.) reseeding and their combinations. The most significant finding was that organic fertilization both alone and when combined with grass reseeding, significantly enhanced soil EMF, while all other treatments decreased it due to nutrient limitation. While most treatments increased aboveground productivity, only the combination of grass reseeding and fertilization simultaneously improved plant diversity. When combined with fertilization, grass reseeding unexpectedly resulted in higher soil nutrient contents compared to oat reseeding. Additionally, only grass reseeding combined with fertilization maintained stable soil threshold elemental ratios of C:N, suggesting a balanced nutrient cycle. Random forest analysis further confirmed that soil properties and microbial functions explained 89 % of the variation in soil EMF. We concluded that restoration strategies focused solely on aboveground productivity can result in soil EMF loss by interfering with microbial-driven nutrient cycling. Therefore, the combination of native grass reseeding with organic fertilization should be considered the optimal restoration approach for degraded alpine grasslands.