Effect of loss of plant functional group and simulated nitrogen deposition on subalpine ecosystem properties on the Tibetan Plateau

Biodiversity loss impacts on ecosystem functioning can vary greatly among ecosystems types and different ecosystem processes can respond differently. Here we conducted a plant functional group removal experiment with and without nitrogen (N) addition (5 g N m⁻² year⁻¹) to examine the effects of plant functional group types presence, nitrogen deposition and their interaction effects on plant diversity, aboveground biomass, soil nutrients, soil microbial biomass and soil enzyme activity. After 4 years, the removal of dominant grass did increase subordinates, forb richness, and decreased total aboveground biomass significantly. However, the removal of forb resulted in a rapid decline in species richness, which did not change strongly the aboveground biomass, regardless of N addition. This pattern suggests that the dominant grass can compensate for the loss of forb removal with respect to production, but cannot compensate with respect to species loss. Forb cannot compensate for grass removal with respect to production, but can compensate with respect to species loss. Nitrogen addition only has a small effect on species richness, and also not enhances aboveground biomass. In addition, the majority of soil properties did not respond to either plant functional group removal, or N addition. Only soil CO₂ efflux and soil NO₃⁻-N content significantly changed with plant functional group removal. Soil respiration rate was positively correlated with both plant species richness (R² = 0.97) and aboveground biomass (R² = 0.64). Our results show that the short-term losses of plant functional group have significant effects on plant diversity and productivity, and only minor impact on soil properties.