Is Grass Planting Suitable for Orchard Sustainability in Xizang? Insights from the Ecosystem Services Valuation of a 4-Year Apple Orchard Grass Planting Practice

Orchard grass intercropping offers a promising strategy to mitigate forage scarcity and boost fruit yield. However, its applicability in high-altitude regions such as the Xizang Plateau remains poorly understood. During the four-year experiment, the ecosystem service values (ESV) of an apple orchard intercropped with different grass species in Linzhi, southeast Xizang, were investigated in order to assess the applicability of orchard grass planting at high altitudes and identify optimal grass species combinations. Seven treatments were established, including six artificial grass systems (annual legume, annual gramineous, annual legume + gramineous, perennial legume, perennial gramineous, perennial legume + gramineous) and a natural grass control group. Results showed that artificial grass systems, particularly perennial ones, yielded higher total ESV than the natural grass control. Perennial grasses outperformed annual grasses and natural grass in provisioning services (with higher fruit and forage yields) and regulating services (with enhanced carbon sequestration and oxygen production). However, perennial grasses also led to reduced supporting services, primarily due to decreased soil nutrient availability (especially available phosphorus and potassium) and lower plant diversity. The optimal treatments were Dactylis glomerata monoculture and Medicago sativa + D. glomerata mixed culture, which achieved the highest total ESV. Notably, the nutrient depletion observed in perennial grass treatments highlighted the need for supplemental fertilization to ensure long-term sustainability of the system. In conclusion, artificial orchard grass systems significantly enhanced total net ESV in high-altitude regions, whereas individual ecosystem services demonstrated divergent responses to different grass species. Specifically, D. glomerata monoculture and M. sativa + D. glomerata intercropping emerged as the optimal orchard grass patterns in Linzhi. To maintain long-term orchard productivity, adaptive fertilizer management strategies are recommended to counteract potential soil nutrient depletion associated with these grass cultivation systems.