Lowland-ecotype switchgrass (Panicum virgatum L.) with moderate nitrogen enhances long-term productivity and ecosystem multifunctionality in acidic soils: A six-year field experiment

Switchgrass ( Panicum virgatum L.) is a promising bioenergy crop owing to high biomass production and ecological adaptability, but long-term evaluations of different ecotypes and nitrogen (N) rates on productivity and soil ecosystem functions are limited. In this six-year field experiment, we assessed the impacts of switchgrass ecotypes (upland and lowland) and N addition levels (0, 60, and 120 kg N ha −1 ) on soil physicochemical properties, nutrient stoichiometry, microbial enzyme activities, nutrient use efficiency, biomass yield, and ecosystem multifunctionality (EMF). Our results indicated that N addition significantly affected soil properties, including soil pH, soil organic carbon (SOC), and dissolved organic carbon (DOC). The lowland ecotype under moderate N (L_60N) produced biomass yields 1.89–2.32 times greater than the upland ecotype, with the maximum yield reaching 31.33 Mg ha⁻¹. Moderate N addition enhanced microbial enzyme activities involved in C and N acquisition, particularly in lowland switchgrass, thereby increasing microbial carbon and N use efficiency and directly promoting biomass production. Biomass yield showed significant positive correlations ( p < 0.05) with SOC, DOC, total N, and enzyme activities. Furthermore, moderate N addition notably enhanced EMF, with the lowland ecotype exhibiting a 16.8-fold increase compared to the upland ecotype, largely due to improved nutrient cycling. Overall, selecting lowland ecotype with moderate N addition can substantially enhance switchgrass productivity, soil carbon sequestration, and ecosystem multifunctionality in acidic soils, providing critical insights for balancing agricultural productivity with ecological sustainability. • Lowland switchgrass with moderate N optimized yield driven by enzyme activities. • Lowland rather than upland ecotype maximized ecosystem multifunctionality. • Long-term moderate N addition enhances soil microbial C and N use efficiency. • Microbial enzyme activities peaked at moderate N, shifting nutrient limitation.